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context. the form and evolution of the galaxy stellar mass function (gsmf) at high redshifts provide crucial information on star formation history and mass assembly in the young universe, close or even prior to the epoch of reionization.aims: we used the unique combination of deep optical/near-infrared/mid-infrared imaging provided by hst, spitzer, and the vlt in the candels-uds, goods-south, and hudf fields to determine the gsmf over the redshift range 3.5 ≤ z ≤ 7.5.methods: we used the hst wfc3/ir near-infrared imaging from candels and hudf09, reaching h ≃ 27 - 28.5 over a total area of 369 arcmin2, in combination with associated deep hst acs optical data, deep spitzer irac imaging from the seds programme, and deep y and k-band vlt hawk-i images from the hugs programme, to select a galaxy sample with high-quality photometric redshifts. these have been calibrated with more than 150 spectroscopic redshifts in the range 3.5 ≤ z ≤ 7.5, resulting in an overall precision of σz/ (1 + z) ~ 0.037. with this database we have determined the low-mass end of the high-redshift gsmf with unprecedented precision, reaching down to masses as low as m∗ ~ 109 m⊙ at z = 4 and ~6 × 109 m⊙ at z = 7.results: we find that the gsmf at 3.5 ≤ z ≤ 7.5 depends only slightly on the recipes adopted to measure the stellar masses, namely the photometric redshifts, the star formation histories, the nebular contribution, or the presence of agn in the parent sample. the low-mass end of the gsmf is steeper than has been found at lower redshifts, but appears to be unchanged over the redshift range probed here. meanwhile the high-mass end of the gsmf appears to evolve primarily in density, although there is also some evidence of evolution in characteristic mass. our results are very different from previous mass function estimates based on converting uv galaxy luminosity functions into mass functions via tight mass-to-light relations. integrating our evolving gsmf over mass, we find that the growth of stellar mass density is barely consistent with the time-integral of the star formation rate density over cosmic time at z> 4.conclusions: these results confirm the unique synergy of the candels+hudf, hugs, and seds surveys for the discovery and study of moderate/low-mass galaxies at high redshifts, and reaffirm the importance of space-based infrared selection for the unbiased measurement of the evolving gsmf in the young universe. appendices are available in electronic form at http://www.aanda.org | the galaxy stellar mass function at 3.5 ≤z ≤ 7.5 in the candels/uds, goods-south, and hudf fields |
we present an analysis of the star formation rates (sfrs) and dust attenuation properties of star-forming galaxies at 2.7 ≤ z < 6.5 drawn from the cosmic evolution early release science survey. our analysis is based on jwst/nirspec micro-shutter assembly r ~ 1000 spectroscopic observations covering approximately 1-5 μm. our primary rest-frame optical spectroscopic measurements are hα/hβ balmer decrements, which we use as an indicator of nebular dust attenuation. in turn, we use balmer decrements to obtain dust-corrected hα-based sfrs (i.e., sfr(hα)). we construct the relationship between sfr(hα) and stellar mass (m *) in three bins of redshift (2.7 ≤ z < 4.0, 4.0 ≤ z < 5.0, and 5.0 ≤ z < 6.5), which represents the first time the star-forming main sequence has been traced at these redshifts using direct spectroscopic measurements of balmer emission as a proxy for sfr. in tracing the relationship between sfr(hα) and m * back to such early times (z > 3), it is essential to use a conversion factor between hα and sfr that accounts for the subsolar metallicity prevalent among distant galaxies. we also use measured balmer decrements to investigate the relationship between dust attenuation and stellar mass out to z ~ 6. the lack of significant redshift evolution in attenuation at fixed stellar mass, previously confirmed using balmer decrements out to z ~ 2.3, appears to hold out to z ~ 6.5. given the rapidly evolving gas, dust, and metal content of star-forming galaxies at fixed mass, this lack of significant evolution in attenuation provides an ongoing challenge to explain. | jwst/nirspec balmer-line measurements of star formation and dust attenuation at z 3-6 |
far-ultraviolet (fuv; ~1200-2000 å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. the launch of the james webb space telescope will soon usher in a new era, pushing the uv spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed uv spectral features. this requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any fuv spectral database. we present the cosmic origins spectrograph legacy spectroscopic survey (classy) treasury and its first high-level science product, the classy atlas. classy builds on the hubble space telescope (hst) archive to construct the first high-quality (s/n1500 å ≳ 5/resel), high-resolution (r ~ 15,000) fuv spectral database of 45 nearby (0.002 < z < 0.182) star-forming galaxies. the classy atlas, available to the public via the classy website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of hst observations. the classy sample covers a broad range of properties including stellar mass (6.2 < log m ⋆(m ⊙) < 10.1), star formation rate (-2.0 < log sfr (m ⊙ yr-1) < +1.6), direct gas-phase metallicity (7.0 < 12+log(o/h) < 8.8), ionization (0.5 < o32 < 38.0), reddening (0.02 < e(b - v) < 0.67), and nebular density (10 < ne(cm-3) < 1120). classy is biased to uv-bright star-forming galaxies, resulting in a sample that is consistent with the z ~ 0 mass-metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to z ≳ 2 galaxies. this unique set of properties makes the classy atlas the benchmark training set for star-forming galaxies across cosmic time. ∗ based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | the cos legacy archive spectroscopy survey (classy) treasury atlas |
while x-ray spectroscopy, timing, and imaging have improved much since 1962 when the first astronomical nonsolar source was discovered, especially wi the launch of the newton/x-ray multi-mirror mission, rossi/x-ray timing explorer, and chandra/advanced x-ray astrophysics facility, the progress of x-ray polarimetry has been meager. this is in part due to the lack of sensitive polarization detectors, which in turn is a result of the fate of approved missions and because celestial x-ray sources appear less polarized than expected. only one positive measurement has been available until now: the orbiting solar observatory measured the polarization of the crab nebula in the 1970s. the advent of microelectronics techniques has allowed for designing a detector based on the photoelectric effect of gas in an energy range where the optics are efficient at focusing in x-rays. here we describe the instrument, which is the major contribution of the italian collaboration to the small explorer mission called ixpe, the imaging x-ray polarimetry explorer, which will launch in late 2021. the instrument is composed of three detector units based on this technique and a detector service unit. three mirror modules provided by marshall space flight center focus x-rays onto the detectors. we show the technological choices, their scientific motivation, and results from the calibration of the instrument. ixpe will perform imaging, timing, and energy-resolved polarimetry in the 2-8 kev energy band opening this window of x-ray astronomy to tens of celestial sources of almost all classes. | the instrument of the imaging x-ray polarimetry explorer |
current estimates of the budget and distribution of water in the earth have large uncertainties, most of which are due to the lack of information about the deep earth. recent studies suggest that the earth could have gained a considerable amount of water during the early stages of its evolution from the hydrogen-rich solar nebula, and that a large amount of the water in the earth may have partitioned into the core. here we calculate the partitioning of water between iron and silicate melts at 20-135 gpa and 2,800-5,000 k, using ab initio molecular dynamics and thermodynamic integration techniques. our results indicate a siderophile nature of water at core-mantle differentiation and core-mantle boundary conditions, which weakens with increasing temperature; nevertheless, we found that water always partitions strongly into the iron liquid under core-formation conditions for both reducing and oxidizing scenarios. the siderophile nature of water was also verified by an empirical-counting method that calculates the distribution of hydrogen in an equilibrated iron and silicate melt. we therefore conclude that the earth's core may act as a large reservoir that contains most of the earth's water. in addition to constraining the accretion models of volatile delivery, the findings may partially account for the low density of the earth's core implied by measured seismic velocities. | the earth's core as a reservoir of water |
we present the public release of the stellar mass catalogs for the goods-s and uds fields obtained using some of the deepest near-ir images available, achieved as part of the cosmic assembly near-infrared deep extragalactic legacy survey project. we combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. each team adopted their preferred fitting code, assumptions, priors, and parameter grid. the combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. the choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). on the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. the inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ~80% of the sample). nevertheless, the stellar mass for the subsample of young galaxies (age <100 myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 myr sources) if nebular contribution is ignored. | stellar masses from the candels survey: the goods-south and uds fields |
ionized nebulae provide critical insights into the conditions of the interstellar medium (ism). their bright emission lines enable the measurement of physical properties, such as the gas-phase metallicity, across galaxy discs and in distant galaxies. the phangs-muse survey has produced optical spectroscopic coverage of the central star-forming discs of 19 nearby main-sequence galaxies. here, we use the $\rm {h}\,\alpha$ morphology from this data to identify 30 790 distinct nebulae, finding thousands of nebulae per galaxy. for each nebula, we extract emission line fluxes and, using diagnostic line ratios, identify the dominant excitation mechanism. a total of 23 244 nebulae (75 per cent) are classified as h ii regions. the dust attenuation of every nebulae is characterized via the balmer decrement and we use existing environmental masks to identify their large-scale galactic environment (centre, bar, arm, interarm, and disc). using strong-line prescriptions, we measure the gas-phase oxygen abundances (metallicity) and ionization parameter for all h ii regions. with this new catalogue, we measure the radial metallicity gradients and explore second-order metallicity variations within each galaxy. by quantifying the global scatter in metallicity per galaxy, we find a weak negative correlation with global star formation rate and stronger negative correlation with global gas velocity dispersion (in both ionized and molecular gas). with this paper we release the full catalogue of strong line fluxes and derived properties, providing a rich data base for a broad variety of ism studies. | the phangs-muse nebular catalogue |
the final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. many massive stars are stripped of their outer hydrogen envelopes as they evolve. such wolf-rayet stars1 emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. a fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types wc/wo). evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types ib/ic) cannot result from massive wc/wo stars2,3, leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion4. here we report observations of sn 2019hgp, beginning about a day after the explosion. its short rise time and rapid decline place it among an emerging population of rapidly evolving transients5-8. spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. our observations are consistent with an explosion of a massive wc/wo star, and suggest that massive wolf-rayet stars may be the progenitors of some rapidly evolving transients. | a wc/wo star exploding within an expanding carbon-oxygen-neon nebula |
we discuss the galactic foreground emission between 20 and 100 ghz based on observations by planck and wmap. the total intensity in this part of the spectrum is dominated by free-free and spinning dust emission, whereas the polarized intensity is dominated by synchrotron emission. the commander component-separation tool has been used to separate the various astrophysical processes in total intensity. comparison with radio recombination line templates verifies the recovery of the free-free emission along the galactic plane. comparison of the high-latitude hα emission with our free-free map shows residuals that correlate with dust optical depth, consistent with a fraction (≈30%) of hα having been scattered by high-latitude dust. we highlight a number of diffuse spinning dust morphological features at high latitude. there is substantial spatial variation in the spinning dust spectrum, with the emission peak (in iν) ranging from below 20 ghz to more than 50 ghz. there is a strong tendency for the spinning dust component near many prominent h ii regions to have a higher peak frequency, suggesting that this increase in peak frequency is associated with dust in the photo-dissociation regions around the nebulae. the emissivity of spinning dust in these diffuse regions is of the same order as previous detections in the literature. over the entire sky, the commander solution finds more anomalous microwave emission (ame) than the wmap component maps, at the expense of synchrotron and free-free emission. this can be explained by the difficulty in separating multiple broadband components with a limited number of frequency maps. future surveys, particularly at 5-20 ghz, will greatly improve the separation by constraining the synchrotron spectrum. we combine planck and wmap data to make the highest signal-to-noise ratio maps yet of the intensity of the all-sky polarized synchrotron emission at frequencies above a few ghz. most of the high-latitude polarized emission is associated with distinct large-scale loops and spurs, and we re-discuss their structure. we argue that nearly all the emission at 40deg > l > -90deg is part of the loop i structure, and show that the emission extends much further in to the southern galactic hemisphere than previously recognised, giving loop i an ovoid rather than circular outline. however, it does not continue as far as the "fermi bubble/microwave haze", making it less probable that these are part of the same structure. we identify a number of new faint features in the polarized sky, including a dearth of polarized synchrotron emission directly correlated with a narrow, roughly 20deg long filament seen in hα at high galactic latitude. finally, we look for evidence of polarized ame, however many ame regions are significantly contaminated by polarized synchrotron emission, and we find a 2σ upper limit of 1.6% in the perseus region. | planck 2015 results. xxv. diffuse low-frequency galactic foregrounds |
we present keck/mosfire observations of uv metal emission lines in four bright (h = 23.9-25.4) gravitationally lensed z ≃ 6-8 galaxies behind the cluster abell 1703. the spectrum of a1703-zd6, a highly magnified star-forming galaxy with a lyα redshift of z = 7.045, reveals a confident detection of the nebular c iv λ1548 emission line (unresolved with full width at half-maximum<125 km s-1). uv metal emission lines are not detected in the three other galaxies. at z ≃ 2-3, nebular c iv emission is observed in just 1 per cent of uv-selected galaxies. the presence of strong c iv emission in one of the small sample of galaxies targeted in this paper may indicate that hard ionizing spectra are more common at z ≃ 7. the total estimated rest-frame equivalent width of the c iv doublet and c iv/lyα flux ratio are comparable to measurements of narrow-lined agns. photoionization models show that the nebular c iv line can also be reproduced by a young stellar population, with very hot metal-poor stars dominating the photon flux responsible for triply ionizing carbon. regardless of the origin of the c iv, we show that the ionizing spectrum of a1703-zd6 is different from that of typical galaxies at z ≃ 2, producing more h ionizing photons per unit 1500 å luminosity (log(ξion/erg- 1 hz) = 25.68) and a larger flux density at 30-50 ev. if such extreme radiation fields are typical in uv-selected systems at z ≳ 7, it would indicate that reionization-era galaxies are more efficient ionizing agents than previously thought. alternatively, we suggest that the small sample of lyα emitters at z ≳ 7 may trace a rare population with intense radiation fields capable of ionizing their surrounding hydrogen distribution. additional constraints on high-ionization emission lines in galaxies with and without lyα detections will help clarify whether hard ionizing spectra are common in the reionization era. | spectroscopic detection of c iv λ1548 in a galaxy at z = 7.045: implications for the ionizing spectra of reionization-era galaxies |
we present a search for spatial extension in high-latitude (| b| > 5^\circ ) sources in recent fermi point source catalogs. the result is the fermi high-latitude extended sources catalog, which provides source extensions (or upper limits thereof) and likelihood profiles for a suite of tested source morphologies. we find 24 extended sources, 19 of which were not previously characterized as extended. these include sources that are potentially associated with supernova remnants and star-forming regions. we also found extended γ-ray emission in the vicinity of the cen a radio lobes and—at gev energies for the first time—spatially coincident with the radio emission of the snr cta 1, as well as from the crab nebula. we also searched for halos around active galactic nuclei, which are predicted from electromagnetic cascades induced by the e + e - pairs that are deflected in intergalactic magnetic fields. these pairs are produced when γ-rays interact with background radiation fields. we do not find evidence for extension in individual sources or in stacked source samples. this enables us to place limits on the flux of the extended source components, which are then used to constrain the intergalactic magnetic field to be stronger than 3 × 10-16 g for a coherence length λ ≳ 10 kpc, even when conservative assumptions on the source duty cycle are made. this improves previous limits by several orders of magnitude. | the search for spatial extension in high-latitude sources detected by the fermi large area telescope |
when a star passes within the tidal radius of a supermassive black hole, it will be torn apart1. for a star with the mass of the sun (m ⊙) and a non-spinning black hole with a mass <108 m ⊙, the tidal radius lies outside the black hole event horizon2 and the disruption results in a luminous flare3-6. here we report observations over a period of ten months of a transient, hitherto interpreted7 as a superluminous supernova8. our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution6, the presence of highly ionized cno gas in the line of sight9 and our improved localization of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely10,11. while the supermassive black hole has a mass >108 m ⊙ 12,13, a star with the same mass as the sun could be disrupted outside the event horizon if the black hole were spinning rapidly14. the rapid spin and high black hole mass can explain the high luminosity of this event. | the superluminous transient asassn-15lh as a tidal disruption event from a kerr black hole |
a sub-array of the large high altitude air shower observatory (lhaaso), km2a is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 tev. even though the detector construction is still underway, half of the km2a array has been operating stably since the end of 2019. in this paper, we present the km2a data analysis pipeline and the first observation of the crab nebula, a standard candle in very high energy γ-ray astronomy. we detect γ-ray signals from the crab nebula in both energy ranges of 10 $ - $ 100 tev and $ \gt $ 100 tev with high significance, by analyzing the km2a data of 136 live days between december 2019 and may 2020. with the observations, we test the detector performance, including angular resolution, pointing accuracy and cosmic-ray background rejection power. the energy spectrum of the crab nebula in the energy range 10-250 tev fits well with a single power-law function dn/de = (1.13 $ \pm $ 0.05 $ _{\rm stat} $ $ \pm $ 0.08 $ _{\rm sys} $ ) $ \times $ 10 $ ^{-14} $ $ \cdot $ (e/20 tev) $ ^{-3.09\pm0.06_{\rm stat}\pm0.02_{\rm sys}} $ cm $ ^{-2} $ s $ ^{-1} $ tev $ ^{-1} $ . it is consistent with previous measurements by other experiments. this opens a new window of γ-ray astronomy above 0.1 pev through which new ultrahigh-energy γ-ray phenomena, such as cosmic pevatrons, might be discovered. * supported in china by national key r&d program of china under the grants (2018yfa0404201, 2018yfa0404202, 2018yfa0404203), by nsfc (12022502, 11905227, 11635011, 11761141001, u1931112, 11775131, u1931201, 11905043, u1931108), by nsfspc (zr2019ma014), and in thailand by rta6280002 from thailand science research and innovation | observation of the crab nebula with lhaaso-km2a - a performance study |
we report the detection of weak pulsations from the archetypal ultraluminous x-ray source (ulx) ngc 1313 x-2. acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of ∼1.5 s and a pulsed fraction of ∼ 5 per cent. we use monte carlo simulations to demonstrate that the individual detections are unlikely to originate in false poisson noise detections given their very close frequencies; their strong similarity to other pulsations detected from ulxs also argues they are real. the presence of a large bubble nebula surrounding ngc 1313 x-2 implies an age of order 1 myr for the accreting phase of the ulx, which implies that the neutron star's (ns) magnetic field has not been suppressed over time by accreted material, nor has the ns collapsed into a black hole, despite an average energy output into the nebula two orders of magnitude above eddington. this argues that most of the accreted material has been expelled over the lifetime of the ulx, favouring physical models including strong winds and/or jets for ns ulxs. | the discovery of weak coherent pulsations in the ultraluminous x-ray source ngc 1313 x-2 |
a surprising finding of recent studies is the large number of active galactic nuclei (agn) associated with moderately massive black holes ($\rm \log(m_\bullet/m_\odot)\sim 6-8$), in the first billion years after the big bang ($z>5$). in this context, a relevant finding has been the large fraction of candidate dual agn, both at large separations (several kpc) and in close pairs (less than a kpc), likely in the process of merging. frequent black hole merging may be a route for black hole growth in the early universe; however, previous findings are still tentative and indirect. we present jwst/nirspec-ifu observations of a galaxy at $z=7.15$ in which we find evidence for a $\rm \log(m_\bullet/m_\odot)\sim7.7$ accreting black hole, as traced by a broad component of h$\beta$ emission, associated with the broad line region (blr) around the black hole. this blr is offset by 620 pc in projection from the centroid of strong rest-frame optical emission, with a velocity offset of $\sim$40 km/s. the latter region is also characterized by (narrow) nebular emission features typical of agn, hence also likely hosting another accreting black hole, although obscured (type 2, narrow-line agn). we exclude that the offset blr is associated with supernovae or massive stars, and we interpret these results as two black holes in the process of merging. this finding may be relevant for estimates of the rate and properties of gravitational wave signals from the early universe that will be detected by future observatories like lisa. | ga-nifs: jwst discovers an offset agn 740 million years after the big bang |
we present the star-formation-rate -- stellar-mass (sfr-m$_\ast$) relation for galaxies in the ceers survey at $4.5\leq z\leq 12$. we model the \jwst\ and \hst\ rest-uv and rest-optical photometry of galaxies with flexible star-formation histories (sfhs) using \bagpipes. we consider sfrs averaged from the sfhs over 10~myr (\sfrten) and 100~myr (\sfrcen), where the photometry probes sfrs on these timescales, effectively tracing nebular emission lines in the rest-optical (on $\sim10$~myr timescales) and the uv/optical continuum (on $\sim100$ myr timescales). we measure the slope, normalization and intrinsic scatter of the sfr-m$_\ast$ relation, taking into account the uncertainty and the covariance of galaxy sfrs and $m_\ast$. from $z\sim 5-9$ there is larger scatter in the $\sfrten-m_\ast$ relation, with $\sigma(\log \sfrcen)=0.4$~dex, compared to the $\sfrcen-m_\ast$ relation, with $\sigma(\log \sfrten)=0.1$~dex. this scatter increases with redshift and increasing stellar mass, at least out to $z\sim 7$. these results can be explained if galaxies at higher redshift experience an increase in star-formation variability and form primarily in short, active periods, followed by a lull in star formation (i.e. ``napping'' phases). we see a significant trend in the ratio $r_\mathrm{sfr}=\log(\sfrten/\sfrcen)$ in which, on average, $r_\mathrm{sfr}$ decreases with increasing stellar mass and increasing redshift. this yields a star-formation ``duty cycle'' of $\sim40\%$ for galaxies with $\log m_\ast/m_\odot\geq 9.3$, at $z\sim5$, declining to $\sim20\%$ at $z\sim9$. galaxies also experience longer lulls in star formation at higher redshift and at higher stellar mass, such that galaxies transition from periods of higher sfr variability at $z\gtrsim~6$ to smoother sfr evolution at $z\lesssim~4.5$. | ceers: increasing scatter along the star-forming main sequence indicates early galaxies form in bursts |
we present new [${\rm o\, {\small iii}}$] 88-$\mu \mathrm{{m}}$ observations of five bright z ~ 7 lyman-break galaxies spectroscopically confirmed by alma through [${\rm c\, {\small ii}}$] 158 $\mu \mathrm{{m}}$, unlike recent [${\rm o\, {\small iii}}$] detections where lyman α was used. this nearly doubles the sample of epoch of reionization galaxies with robust (5σ) [${\rm c\, {\small ii}}$] and [${\rm o\, {\small iii}}$] detections. we perform a multiwavelength comparison with new deep hst images of the rest-frame uv, whose compact morphology aligns well with [${\rm o\, {\small iii}}$] tracing ionized gas. in contrast, we find more spatially extended [${\rm c\, {\small ii}}$] emission likely produced in neutral gas, as indicated by an [${\rm n\, {\small ii}}$] 205-$\mu \mathrm{{m}}$ non-detection in one source. we find a correlation between the optical ${[{\rm o\, {\small iii}}]}+ {\mathrm{h\,\beta }}$ equivalent width and [${\rm o\, {\small iii}}$]/[${\rm c\, {\small ii}}$], as seen in local metal-poor dwarf galaxies. cloudy models of a nebula of typical density harbouring a young stellar population with a high-ionization parameter adequately reproduce the observed lines. surprisingly, however, our models fail to reproduce the strength of [${\rm o\, {\small iii}}$] 88-$\mu \mathrm{{m}}$, unless we assume an α/fe enhancement and near-solar nebular oxygen abundance. on spatially resolved scales, we find [${\rm o\, {\small iii}}$]/[${\rm c\, {\small ii}}$] shows a tentative anticorrelation with infrared excess, lir/luv, also seen on global scales in the local universe. finally, we introduce the far-infrared spectral energy distribution fitting code mercurius to show that dust-continuum measurements of one source appear to favour a low dust temperature and correspondingly high dust mass. this implies a high stellar metallicity yield and may point towards the need of dust production or grain-growth mechanisms beyond supernovae. | dual constraints with alma: new [o iii] 88-μm and dust-continuum observations reveal the ism conditions of luminous lbgs at z 7 |
multi-phase filamentary structures around brightest cluster galaxies (bcg) are likely a key step of agn-feedback. we observed molecular gas in three cool cluster cores, namely centaurus, abell s1101, and rxj1539.5, and gathered alma (atacama large millimeter/submillimeter array) and muse (multi unit spectroscopic explorer) data for 12 other clusters. those observations show clumpy, massive, and long (3-25 kpc) molecular filaments, preferentially located around the radio bubbles inflated by the agn. two objects show nuclear molecular disks. the optical nebula is certainly tracing the warm envelopes of cold molecular filaments. surprisingly, the radial profile of the hα/co flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 and 6 times more cold gas could be present and (ii) local processes must be responsible for the excitation. projected velocities are between 100 and 400 km s-1, with disturbed kinematics and sometimes coherent gradients. this is likely due to the mixing in projection of several thin (and as yet) unresolved filaments. the velocity fields may be stirred by turbulence induced by bubbles, jets, or merger-induced sloshing. velocity and dispersions are low, below the escape velocity. cold clouds should eventually fall back and fuel the agn. we compare the radial extent of the filaments, rfil, with the region where the x-ray gas can become thermally unstable. the filaments are always inside the low-entropy and short-cooling-time region, where tcool/tff < 20 (9 of 13 sources). the range of tcool/tff of 8-23 at rfil, is likely due to (i) a more complex gravitational potential affecting the free-fall time tff (sloshing, mergers, etc.) and (ii) the presence of inhomogeneities or uplifted gas in the icm, affecting the cooling time tcool. for some of the sources, rfil lies where the ratio of the cooling time to the eddy-turnover time, tcool/teddy, is approximately unity. | ubiquitous cold and massive filaments in cool core clusters |
we derive a uv-optical stellar dust attenuation curve of galaxies at z = 1.4-2.6 as a function of gas-phase metallicity. we use a sample of 218 star-forming galaxies, excluding those with very young or heavily obscured star formation, from the mosfire deep evolution field survey with hα, hβ, and [n ii]λ 6585 spectroscopic measurements. we constrain the shape of the attenuation curve by comparing the average flux densities of galaxies sorted into bins of dust obscuration using balmer decrements, i.e., hα-to-hβ luminosities. the average attenuation curve for the high-metallicity sample ( $12+\mathrm{log}({\rm{o}}/{\rm{h}})\gt 8.5$ , corresponding to ${m}_{* }\gtrsim {10}^{10.4}$ ${m}_{\odot }$ ) has a shallow slope, identical to that of the calzetti local starburst curve, and a significant uv 2175 å extinction bump that is ∼0.5× the strength of the milky way bump. on the other hand, the average attenuation curve of the low-metallicity sample ( $12+\mathrm{log}({\rm{o}}/{\rm{h}})\sim 8.2-8.5$ ) has a steeper slope similar to that of the smc curve, only consistent with the calzetti slope at the 3σ level. the uv bump is not detected in the low-metallicity curve, indicating the relative lack of the small dust grains causing the bump at low metallicities. furthermore, we find that on average the nebular reddening (e(b - v)) is a factor of 2 times larger than that of the stellar continuum for galaxies with low metallicities, while the nebular and stellar reddening are similar for galaxies with higher metallicities. the latter is likely due to a high surface density of dusty clouds embedding the star-forming regions but also reddening the continuum in the high-metallicity galaxies. | the mosdef survey: the variation of the dust attenuation curve with metallicity |
the james webb space telescope will allow to spectroscopically study an unprecedented number of galaxies deep into the reionization era, notably by detecting [o iii]λλ4959, 5007, and h β nebular emission lines. to efficiently prepare such observations, we photometrically select a large sample of galaxies at z ∼ 8 and study their rest-frame optical emission lines. combining data from the goods re-ionization era wide-area treasury from spitzer (greats) survey and from hst we perform spectral energy distribution (sed) fitting, using synthetic seds from a large grid of photoionization models. the deep spitzer/irac data combined with our models exploring a large parameter space enables to constrain the [o iii] + h β fluxes and equivalent widths for our sample, as well as the average physical properties of z ∼ 8 galaxies, such as the ionizing photon production efficiency with \log (ξ _ion/erg^{-1}hz)\ge 25.77. we find a relatively tight correlation between the [o iii] + h β and uv luminosity, which we use to derive for the first time the [o iii]λλ4959, 5007 + h β luminosity function (lf) at z ∼ 8. the z ∼ 8 [o iii] + h β lf is higher at all luminosities compared to lower redshift, as opposed to the uv lf, due to an increase of the [o iii] + h β luminosity at a given uv luminosity from z ∼ 3 to z ∼ 8. finally, using the [o iii] + h β lf, we make predictions for jwst/nirspec number counts of z ∼ 8 galaxies. we find that the current wide-area extragalactic legacy fields are too shallow to use jwst at maximal efficiency for z ∼ 8 spectroscopy even at 1 h depth and jwst pre-imaging to ≳30 mag will be required. | the greats h β + [o iii] luminosity function and galaxy properties at z ∼ 8: walking the way of jwst |
nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below z⊙/2. such tests are particularly important for interpreting the surprising high-ionization ultraviolet (uv) line emission detected at z > 6 in recent years. we present hst/cos uv spectra of 10 nearby metal-poor star-forming galaxies selected to show he ii emission in sdss optical spectra. the targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + log o/h < 8.5) and present uniformly large specific star formation rates (ssfr ∼102 gyr-1). the uv spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization uv lines, reaching c iii] equivalent widths comparable to those seen in systems at z ∼ 6-7. our data reveal a marked transition in uv spectral properties with decreasing metallicity, with systems below 12 + log o/h ≲ 8.0 (z/z⊙ ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in he ii and c iv. this is consistent with nearly an order of magnitude increase in ionizing photon production beyond the he+-ionizing edge relative to h-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive o-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. consequently, nebular emission in c iv and he ii powered by these stars may provide useful metallicity constraints in the reionization era. | ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for jwst |
we present new measurements of the evolution of the galaxy stellar mass functions (gsmfs) and ultraviolet luminosity functions (uv lfs) for galaxies from z = 6-9 within the frontier field cluster macsj0416.1-2403 and its parallel field. to obtain these results, we derive the stellar masses of our sample by fitting synthetic stellar population models to their observed spectral energy distribution with the inclusion of nebular emission lines. this is the deepest and farthest in distance mass function measured to date and probes down to a level of m* = 106.8 m⊙. the main result of this study is that the low-mass end of our gsmf to these limits and redshifts appears to become steeper from -1.98_{-0.07}^{+0.07} at z = 6 to -2.38_{-0.88}^{+0.72} at z = 9, steeper than previously observed mass functions at slightly lower redshifts, and we find no evidence of turnover in the mass range probed. we furthermore demonstrate that the uv lf for these systems also appears to show a steepening at the highest redshifts, without any evidence of turnover in the luminosity range probed. our muv-m* relation exhibit shallower slopes than previously observed and are in accordance with a constant mass-to-light ratio. integrating our gsmf, we find that the stellar mass density increases by a factor of {∼ }15_{-6}^{+21} from z = 9 to z = 6. we estimate the dust-corrected star formation rates (sfrs) to calculate the specific sfrs (ssfr = sfr/m*) of our sample, and find that for a fixed stellar mass of 5 × 109 m⊙, ssfr ∝ (1 + z)2.01 ± 0.16. finally, from our new measurements, we estimate the uv luminosity density (ρuv) and find that our results support a smooth decline of ρuv towards high redshifts. | evolution of the galaxy stellar mass functions and uv luminosity functions at z = 6-9 in the hubble frontier fields |
we examine lyman continuum (lyc) leakage through h ii regions regulated by turbulence and radiative feedback in a giant molecular cloud in the context of fully coupled radiation hydrodynamics (rhd). the physical relations of the lyc escape with h i covering fraction, kinematics, ionizing photon production efficiency, and emergent lyα line profiles are studied using a series of rhd turbulence simulations performed with ramses-rt. the turbulence-regulated mechanism allows ionizing photons to leak out at early times before the onset of supernova feedback. the lyc photons escape through turbulence-generated low column density channels that are evacuated efficiently by radiative feedback via photoheating-induced shocks across the d-type ionization fronts. the lyα photons funnel through the photoionized channels along the paths of lyc escape, resulting in a diverse lyα spectral morphology including narrow double-peaked profiles. the lyα peak separation is controlled by the residual h i column density of the channels, and the line asymmetry correlates with the porosity and multiphase structure of the h ii region. this mechanism through the turbulent h ii regions can naturally reproduce the observed lyα spectral characteristics of some of the lyc-leaking galaxies. this rhd turbulence origin provides an appealing hypothesis to explain high lyc leakage from very young (∼3 myr) star-forming galaxies found in the local universe without need of extreme galactic outflows or supernova feedback. we discuss the implications of the turbulent h ii regions on other nebular emission lines and a possible observational test with the magellanic system and local blue compact dwarf galaxies as analogs of reionization-era systems. | radiation hydrodynamics of turbulent h ii regions in molecular clouds: a physical origin of lyc leakage and the associated lyα spectra |
we present interferometric co observations, made with the combined array for millimeter-wave astronomy (carma) interferometer, of galaxies from the extragalactic database for galaxy evolution survey (edge). these galaxies are selected from the calar alto legacy integral field area (califa) sample, mapped with optical integral field spectroscopy. edge provides good-quality co data (3σ sensitivity {{{σ }}}{mol}∼ 11 {m}⊙{{pc}}-2 before inclination correction, resolution ∼1.4 kpc) for 126 galaxies, constituting the largest interferometric co survey of galaxies in the nearby universe. we describe the survey and data characteristics and products, then present initial science results. we find that the exponential scale lengths of the molecular, stellar, and star-forming disks are approximately equal, and galaxies that are more compact in molecular gas than in stars tend to show signs of interaction. we characterize the molecular-to-stellar ratio as a function of hubble type and stellar mass and present preliminary results on the resolved relations between the molecular gas, stars, and star-formation rate. we then discuss the dependence of the resolved molecular depletion time on stellar surface density, nebular extinction, and gas metallicity. edge provides a key data set to address outstanding topics regarding gas and its role in star formation and galaxy evolution, which will be publicly available on completion of the quality assessment. | the edge-califa survey: interferometric observations of 126 galaxies with carma |
using the zwicky transient facility alert stream, we are conducting a large spectroscopic campaign to construct a complete, volume-limited sample of transients brighter than 20 mag, and coincident within 100″ of galaxies in the census of the local universe catalog. we describe the experiment design and spectroscopic completeness from the first 16 months of operations, which have classified 754 supernovae. we present results from a systematic search for calcium-rich gap transients in the sample of 22 low-luminosity (peak absolute magnitude m > -17), hydrogen-poor events found in the experiment. we report the detection of eight new events, and constrain their volumetric rate to ≳15% ± 5% of the sn ia rate. combining this sample with 10 previously known events, we find a likely continuum of spectroscopic properties ranging from events with sn ia-like features (ca-ia objects) to those with sn ib/c-like features (ca-ib/c objects) at peak light. within the ca-ib/c events, we find two populations distinguished by their red (g - r ≈ 1.5 mag) or green ( $g-r\approx 0.5$ mag) colors at the r-band peak, wherein redder events show strong line blanketing features and slower light curves (similar to ca-ia objects), weaker he lines, and lower [ca ii]/[o i] in the nebular phase. we find that all together the spectroscopic continuum, volumetric rates, and striking old environments are consistent with the explosive burning of he shells on low-mass white dwarfs. we suggest that ca-ia and red ca-ib/c objects arise from the double detonation of he shells, while green ca-ib/c objects are consistent with low-efficiency burning scenarios like detonations in low-density shells or deflagrations. | the zwicky transient facility census of the local universe. i. systematic search for calcium-rich gap transients reveals three related spectroscopic subclasses |
rapid solidification cellular structures are known to play a crucial role in helping achieve high strength and high ductility in 316l austenitic stainless steels fabricated by laser powder-bed-fusion (l-pbf). despite this, the understanding of their intrinsic characteristics (e.g., crystallographic orientations, dislocations, precipitates, elemental segregations) and the respective impacts on the material's strength and thermal stability remains nebulous. we conduct several dedicated transmission electron microscopy (tem) studies to investigate these strengthening mechanisms and identified that cell walls follow specific crystallographic orientations. the high density of tangled dislocations inside cell walls are found to have a higher tendency to dissociate, forming wider stacking faults while oxide precipitates are confined inside cell walls. these features act as barriers to moving dislocations upon plastic deformation and contribute to the high strength. our dislocation dynamic simulations indicate that segregated particles are effective in blocking dislocations locally, helping the formation of dislocation cells and participating to the material strengthening. to study the thermal stability of l-pbf 316l ss, we perform systematic post-processing heat treatments from 400-1200°c. microstructure characterizations using electron backscatter diffraction, tem, and synchrotron x-ray diffraction coupled with dislocation dynamics and calphad simulations and tensile testing reveal three heat treatment zones where the structure-property relationship can be tuned. after annealing up to 600°c, the microstructure remains stable; but the work hardening behavior is altered with a material that retains high strength and high ductility. annealing between 600-1000°c activates elemental diffusion and gradual disappearance of cell walls, leading to a sharp drop in yield strength and a tradeoff between strength and ductility. low-angle grain boundaries remain stable up to 1000°c while the average grain size defined by high angle grain boundaries is near constant at annealing temperatures up to 800°c. annealing above 1100°c removes all l-pbf microstructure footprints and renders a conventional-like microstructure. compared to conventional materials, l-pbf 316lss displays substantially higher thermal stability and superior performance at elevated temperatures. | new insights on cellular structures strengthening mechanisms and thermal stability of an austenitic stainless steel fabricated by laser powder-bed-fusion |
we infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low redshift observed with the hubble space telescope and 19 at z ∼ 2 from the megasaura sample. we fit each stellar continuum with a linear combination of up to 50 single-age and single-metallicity starburst99 models. from these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. inferred light-weighted stellar metallicities span 0.05-1.5 z ⊙ and are similar to the measured nebular metallicities. we quantify the ionizing continua using the ratio of the ionizing flux at 900 å to the non-ionizing flux at 1500 å and demonstrate the evolution of this ratio with stellar age and metallicity using theoretical single-burst models. these single-burst models only match the inferred ionizing continua of half of the sample, while the other half are described by a mixture of stellar ages. mixed-age populations produce stronger and harder ionizing spectra than continuous star formation histories, but, contrary to previous studies that assume constant star formation, have similar stellar and nebular metallicities. stellar population age and metallicity affect the far-uv continua in different and distinguishable ways; assuming a constant star formation history diminishes the diagnostic power. finally, we provide simple prescriptions to determine the ionizing photon production efficiency (ξ ion) from the stellar population properties. the ξ ion inferred from the observed star-forming galaxies has a range of log(ξ ion) = 24.4-25.7 hz erg-1 that depends on the stellar population age, metallicity, star formation history, and contributions from binary star evolution. these stellar population properties must be observationally determined to accurately determine the number of ionizing photons generated by massive stars. based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | constraining the metallicities, ages, star formation histories, and ionizing continua of extragalactic massive star populations |
large terrestrial carnivores are an ecologically important, charismatic and highly endangered group of species. here, we assess the importance of prey depletion as a driver of large carnivore endangerment globally using lists of prey species for each large carnivore compiled from the literature. we consider spatial variation in prey endangerment, changes in endangerment over time and the causes of prey depletion, finding considerable evidence that loss of prey base is a major and wide-ranging threat among large carnivore species. in particular, the clouded leopard (neofelis nebulosa), sunda clouded leopard (neofelis diardi), tiger (panthera tigris), dhole (cuon alpinus) and ethiopian wolf (canis simensis) all have at least 40% of their prey classified as threatened on the international union for the conservation of nature (iucn) red list and, along with the leopard (panethra pardus), all of these species except the ethiopian wolf have at least 50% of their prey classified as declining. of the 494 prey species in our analysis, an average of just 6.9% of their ranges overlap protected areas. together these results show the importance of a holistic approach to conservation that involves protecting both large carnivores directly and the prey upon which they depend. | prey depletion as a threat to the world's large carnivores |
the high-precision astrometry from the second data release of the gaia mission has made it possible to greatly improve the census of members of nearby clusters and associations. i have applied the gaia data to the taurus star-forming region, refining the sample of known members and identifying candidates for undiscovered members. the resulting samples of members and candidates provide the best constraints to date on the distribution of ages and the initial mass function (imf) in taurus. several studies over the last 30 years have proposed the existence of a population of older stars (≳10 myr) that is associated with the taurus clouds. the data from gaia demonstrate that such a population does not exist. meanwhile, previous imf estimates for small fields surrounding the taurus aggregates have exhibited a surplus of k7-m0 stars (0.7-0.8 m ⊙) relative to star-forming clusters such as ic 348 and the orion nebula cluster. however, that difference disappears when the new census of the entire region is considered, which should be complete for spectral types earlier than m6-m7 at aj< 1. thus, there is little variation in the stellar imf across the 3-4 orders of magnitude in stellar density that are present in nearby star-forming regions. finally, i note that the proper motions of two previously known members, kpno 15 and 2mass j04355209 + 2255039, indicate that they may have been ejected from the same location within the l1536 cloud ∼7200 years ago. based on observations performed with the gaia mission, the two micron all sky survey, and the united kingdom infrared telescope infrared deep sky survey. | the stellar membership of the taurus star-forming region |
we present the photometric properties of galaxies in the first light and reionization epoch simulations (flares). the simulations trace the evolution of galaxies in a range of overdensities through the epoch of reionization. with a novel weighting scheme, we combine these overdensities, extending significantly the dynamic range of observed composite distribution functions compared to periodic simulation boxes. flares predicts a significantly larger number of intrinsically bright galaxies, which can be explained through a simple model linking dust attenuation to the metal content of the interstellar medium, using a line-of-sight extinction model. with this model, we present the photometric properties of the flares galaxies for z ∈ [5, 10]. we show that the ultraviolet (uv) luminosity function (lf) matches the observations at all redshifts. the function is fitted by schechter and double power-law forms, with the latter being favoured at these redshifts by the flares composite uv lf. we also present predictions for the uv-continuum slope as well as the attenuation in the uv. the impact of environment on the uv lf is also explored, with the brightest galaxies forming in the densest environments. we then present the line luminosity and equivalent widths of some prominent nebular emission lines arising from the galaxies, finding rough agreement with available observations. we also look at the relative contribution of obscured and unobscured star formation, finding comparable contributions at these redshifts. | first light and reionization epoch simulations (flares) - ii: the photometric properties of high-redshift galaxies |
moderately volatile elements (mves) are sensitive tracers of vaporisation in geological and cosmochemical processes owing to their balanced partitioning between vapour and condensed phases. differences in their volatilities allow the thermodynamic conditions, particularly temperature and oxygen fugacity (fo2), at which vaporisation occurred to be quantified. however, this exercise is hindered by a lack of experimental data relevant to the evaporation of mves from silicate melts. we report a series of experiments in which silicate liquids are evaporated in one-atmosphere (1-atm) gas-mixing furnaces under controlled fo2, from the fe-"feo" buffer (iron-wüstite, iw) to air (10-0.68 bar), bracketing the range of most magmatic rocks. time- (t) and temperature (t) series were conducted from 15 to 930 min and 1300-1550 °c, at or above the liquidus for a synthetic ferrobasalt, to which 20 elements, each at 1000 ppm, were added. refractory elements (e.g., ca, sc, v, zr, ree) are quantitatively retained in the melt under all conditions. the mves show highly redox-dependent volatilities, where the extent of element loss as a function of fo2 depends on the stoichiometry of the evaporation reaction(s), each of which has the general form mx+no(x+n)/2 (l) = mxox/2 (g) + n/4o2. where n is positive (as in most cases), the oxidation state of the element in the gas is more reduced than in the liquid, meaning lower oxygen fugacity promotes evaporation. we develop a general framework, by integrating element vaporisation stoichiometries with hertz-knudsen-langmuir (hkl) theory, to quantify evaporative loss as a function of t, t and fo2. element volatilities from silicate melts differ from those during solar nebular condensation, and can thus constrain the conditions of volatile loss in post-nebular processes. evaporation in a single event strongly discriminates between mves, producing a step-like abundance pattern in the residuum, similar to that observed in the moon or vesta. contrastingly, the gradual depletion of mves according to their volatility in the earth is inconsistent with their loss in a single evaporation event, and instead likely reflects accretion from many smaller bodies that had each experienced different degrees of volatilisation. | evaporation of moderately volatile elements from silicate melts: experiments and theory |
we investigate the strongly lensed (μ ≃ ×10 − 100) lyman continuum (lyc) galaxy, dubbed sunburst, at z = 2.37, taking advantage of a new accurate model of the lens. a characterization of the intrinsic (delensed) properties of the system yields a size of ≃3 sq. kpc, a luminosity of muv = −20.3, and a stellar mass of m ≃ 109 m⊙; 16% of the ultraviolet light is located in a 3 myr old gravitationally bound young massive star cluster (ymc), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼107 m⊙ (similar to the stellar mass) - from which lyc radiation is detected (λ < 912 å). the star formation rate and stellar mass surface densities for the ymc are log10(σsfr[m⊙ yr−1 kpc−2]) ≃ 3.7 and log10(σm[m⊙ pc−2]) ≃ 4.1, with ssfr > 330 gyr−1, consistent with the values observed in local young massive star clusters. the inferred outflowing gas velocity (> 300 km s−1) exceeds the escape velocity of the cluster. the resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6−12%, whilst it is ≳46 − 93% if inferred from the ymc multiple line of sights. at least 12 additional unresolved star-forming knots with radii spanning the interval 3 − 20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. a significant fraction (40−60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. in adopting a formation timescale of the star clusters of 20 myr, a cluster formation efficiency γ ≳ 30%. the star formation rate surface density of the sunburst galaxy (log10(σsfr) = 0.5−0.2+0.3) is consistent with the high inferred γ, as observed in local galaxies experiencing extreme gas physical conditions. overall, the presence of a bursty event (i.e., the 3 myr old ymc with large ssfr) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. without lensing magnification, the ymc would be associated to an unresolved 0.5 kpc-size star-forming clump. the delensed lyc and uv magnitude m1600 (at 1600 å) of the ymc are ≃30.6 and ≃26.9, whilst the entire galaxy has m1600 ≃ 24.8. the sunburst galaxy shows a relatively large rest-frame equivalent width of ewrest(hβ + [o iii]λλ4959, 5007) ≃ 450 å, with the ymc contributing to ∼30% (having a local ewrest ≃ 1100 å) and ∼1% of the total stellar mass. if o-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (hβ + [o iii]) observed at z > 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high γ) at reionization. future facilities, which will perform at few tens milliarcsec resolution (e.g., vlt/mavis or elt), will probe bound clusters on moderately magnified (μ < 5 − 10) galaxies across cosmic epochs up to reionization. based on observations collected at the european southern observatory for astronomical research in the southern hemisphere under eso programmes id 0103.a-0688(a), 0103.a-0688(c) (pi e. vanzella). | high star cluster formation efficiency in the strongly lensed sunburst lyman-continuum galaxy at z = 2.37 |
in the transitional mass range (~8-10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate o + ne + mg core, and electron capture onto ne and mg nuclei should initiate core collapse1-4. however, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition5-7, explosion energy, light curve and nucleosynthesis8-12. for supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. the light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. this identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range. | the electron-capture origin of supernova 2018zd |
we present the completed kmos3d survey, an integral field spectroscopic survey of 739 {log}({m}\star /{m}⊙ )> 9 galaxies at 0.6 < z < 2.7 using the k-band multi object spectrograph (kmos) at the very large telescope. the kmos3d survey provides a population-wide census of kinematics, star formation, outflows, and nebular gas conditions both on and off the star-forming galaxy main sequence through the spatially resolved and integrated properties of hα, [n ii], and [s ii] emission lines. we detect hα emission for 91% of galaxies on the main sequence of star formation and 79% overall. the depth of the survey has allowed us to detect galaxies with star formation rates below 1 m ⊙ yr-1, as well as to resolve 81% of detected galaxies with ≥3 resolution elements along the kinematic major axis. the detection fraction of hα is a strong function of both color and offset from the main sequence, with the detected and nondetected samples exhibiting different spectral energy distribution shapes. comparison of hα and uv+ir star formation rates reveal that dust attenuation corrections may be underestimated by 0.5 dex at the highest masses ({log}({m}\star /{m}⊙ )> 10.5). we confirm our first year results of a high rotation-dominated fraction (monotonic velocity gradient and v rot/{σ }0> \sqrt{3.36}) of 77% for the full kmos3d sample. the rotation-dominated fraction is a function of both stellar mass and redshift, with the strongest evolution measured over the redshift range of the survey for galaxies with {log}({m}\star /{m}⊙ )< 10.5. with this paper, we include a final data release of all 739 observed objects (http://www.mpe.mpg.de/ir/kmos3d). based on observations obtained at the very large telescope (vlt) of the european southern observatory (eso), paranal, chile (eso program ids 092a-0091, 093.a-0079, 093.a-0079, 094.a-0217, 095.a-0047, 096.a-0025, 097.a-0028, 098.a-0045, 099.a-0013, 0100.a-0039, and 0101.a-0022). | the kmos3d survey: data release and final survey paper |
we present an analysis of ground-based and jwst observations of sn 2022pul, a peculiar "03fg-like" (or "super-chandrasekhar") type ia supernova (sn ia), in the nebular phase at 338 d post explosion. our combined spectrum continuously covers 0.4-14 $\mu$m and includes the first mid-infrared spectrum of an 03fg-like sn ia. compared to normal sn ia 2021aefx, sn 2022pul exhibits a lower mean ionization state, asymmetric emission-line profiles, stronger emission from the intermediate-mass elements (imes) argon and calcium, weaker emission from iron-group elements (iges), and the first unambiguous detection of neon in a sn ia. strong, broad, centrally peaked [ne ii] at 12.81 $\mu$m was previously predicted as a hallmark of "violent merger'' sn ia models, where dynamical interaction between two sub-$m_{\text{ch}}$ white dwarfs (wds) causes disruption of the lower mass wd and detonation of the other. the violent merger scenario was already a leading hypothesis for 03fg-like sne ia; in sn 2022pul it can explain the large-scale ejecta asymmetries seen between the imes and iges and the central location of narrow oxygen and broad neon. we modify extant models to add clumping of the central ejecta to better reproduce the optical iron emission, and add mass in the innermost region ($< 2000$ km s$^{-1}$) to account for the observed narrow [o i] $\lambda\lambda6300$, 6364 emission. a violent wd-wd merger explains many of the observations of sn 2022pul, and our results favor this model interpretation for the subclass of 03fg-like sn ia. | ground-based and jwst observations of sn 2022pul: ii. evidence from nebular spectroscopy for a violent merger in a peculiar type-ia supernova |
we report the discovery by the intermediate palomar transient factory (iptf) of a candidate tidal disruption event (tde) iptf16axa at z = 0.108 and present its broadband photometric and spectroscopic evolution from three months of follow-up observations with ground-based telescopes and swift. the light curve is well fitted with a t -5/3 decay, and we constrain the rise time to peak to be <49 rest-frame days after disruption, which is roughly consistent with the fallback timescale expected for the ∼5 × 106 m ⊙ black hole inferred from the stellar velocity dispersion of the host galaxy. the uv and optical spectral energy distribution is well described by a constant blackbody temperature of t ∼ 3 × 104 k over the monitoring period, with an observed peak luminosity of 1.1 × 1044 erg s-1. the optical spectra are characterized by a strong blue continuum and broad he ii and hα lines, which are characteristic of tdes. we compare the photometric and spectroscopic signatures of iptf16axa with 11 tde candidates in the literature with well-sampled optical light curves. based on a single-temperature fit to the optical and near-uv photometry, most of these tde candidates have peak luminosities confined between log(l [erg s-1]) = 43.4-44.4, with constant temperatures of a few ×104 k during their power-law declines, implying blackbody radii on the order of 10 times the tidal disruption radius, that decrease monotonically with time. for tde candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. we find no correlation between the peak luminosity and the black hole mass, contrary to the expectations for tdes to have \dot{m}\propto {m}{bh}-1/2. | revisiting optical tidal disruption events with iptf16axa |
we analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionization (eor) within the smacs j0723.3-7327 jwst early release observations field. given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using nircam photometry alone, finding that f115w imaging is essential to distinguish between z ~ 8 galaxies with high equivalent width (ew) [o iii] λ5007 emission and z ~ 10 balmer break galaxies. we find that all four sources exhibit strong (≥0.6 mag) f356w-f444w colours, which sit at the extreme end of theoretical predictions from numerical simulations. we find that these galaxies deviate (by ≈0.5 dex) from the local correlation between [o iii] λ5007/h β and [ne iii] λ3869/[o ii], which is consistent with the predictions from simulations of high-redshift galaxies having elevated line-excitation ratios. we measure the [o iii] λ5007 rest-frame ews both directly from the spectroscopy, and indirectly as inferred from the strong f356w-f444w colours, finding large [o iii] λ5007 ews of 225-1740 å. the [o iii] λ5007 and h β ews are consistent with those seen in extreme, intensely star-forming dwarf galaxies in the local universe. our structural analysis indicates that these galaxies are resolved, exhibiting irregular shapes with bright clumps. in line with the predictions from the flares hydrodynamic simulations, such intense star formation and extreme nebular conditions are likely the norm, rather than the exception, in the eor. | seeing sharper and deeper: jwst's first glimpse of the photometric and spectroscopic properties of galaxies in the epoch of reionization |
we use photoionization models that are designed to reconcile the joint rest-uv-optical spectra of high-z star-forming galaxies to self-consistently infer the gas chemistry and nebular ionization and excitation conditions for ∼150 galaxies from the keck baryonic structure survey (kbss), using only observations of their rest-optical nebular spectra. we find that the majority of z ∼ 2-3 kbss galaxies are moderately o-rich, with an interquartile range in 12 + log(o/h) = 8.29-8.56, and have significantly sub-solar fe enrichment, with an interquartile range of [fe/h] = [-0.79, -0.53], which contributes additional evidence in favor of super-solar o/fe in high-z galaxies. the model-inferred ionization parameters and n/o are strongly correlated with common strong-line indices (such as o32 and n2o2), with the latter exhibiting similar behavior to local extragalactic h ii regions. in contrast, diagnostics commonly used for measuring gas-phase o/h (such as n2 and o3n2) show relatively large scatter with the overall amount of oxygen present in the gas and behave differently than observed at z ∼ 0. we provide a new calibration for using r23 to measure o/h in typical high-z galaxies, although it is most useful for relatively o-rich galaxies; combining o32 and r23 does not yield a more effective calibration. finally, we consider the implications for the intrinsic correlations between physical conditions across the galaxy sample and find that n/o varies with o/h in high-z galaxies in a manner that is almost identical to local h ii regions. however, we do not find a strong anti-correlation between ionization parameter and metallicity (o/h or fe/h) in high-z galaxies, which is one of the principal bases for using strong-line ratios to infer oxygen abundance. | measuring the physical conditions in high-redshift star-forming galaxies: insights from kbss-mosfire |
we present a vlt/x-shooter spectroscopy of the lyman continuum (lyc) emitting galaxy ion2 at z = 3.2121 and compare it to that of the recently discovered strongly lensed lyc emitter at z = 2.37, known as the sunburst arc. three main results emerge from the x-shooter spectrum: (a) the ly α has three distinct peaks with the central one at the systemic redshift, indicating a ionized tunnel through which both ly α and lyc radiation escape; (b) the large o32 oxygen index ([o iii] λλ4959, 5007/[o ii] λλ3727, 3729) of 9.18_{-1.32}^{+1.82} is compatible to those measured in local (z ∼0.4) lyc leakers; (c) there are narrow nebular high-ionization metal lines with σv < 20 km s-1, which confirms the presence of young hot, massive stars. the he iiλ1640 appears broad, consistent with a young stellar component including wolf-rayet stars. similarly, the sunburst lyc emitter shows a triple-peaked ly α profile and from vlt/muse spectroscopy the presence of spectral features arising from young hot and massive stars. the strong lensing magnification, (μ > 20), suggests that this exceptional object is a gravitationally bound star cluster observed at a cosmological distance, with a stellar mass m ≲ 107 m⊙ and an effective radius smaller than 20 pc. intriguingly, sources like sunburst but without lensing magnification might appear as ion2-like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. this work supports the idea that dense young star clusters can contribute to the ionization of the igm through holes created by stellar feedback. | ionizing the intergalactic medium by star clusters: the first empirical evidence |
the recent launch of jwst has ushered in a new era of high-redshift astronomy by providing detailed insights into the gas and stellar populations of galaxies in the epoch of reionization. interpreting these observations and translating them into constraints on the physics of early galaxy formation is a complex challenge that requires sophisticated models of star formation and the interstellar medium (ism) in high-redshift galaxies. to this end, we present version 1 of the sphinx$^{20}$ public data release. sphinx$^{20}$ is a full box cosmological radiation hydrodynamics simulation that simultaneously models the large-scale process of cosmic reionization and the detailed physics of a multiphase ism, providing a statistical sample of galaxies akin to those currently being observed by jwst. the data set contains $\sim14,000$ mock images and spectra of the stellar continuum, nebular continuum, and 52 nebular emission lines, including ly$\alpha$, for each galaxy in sphinx$^{20}$ with a star formation rate $\geq0.3\ {\rm m_{\odot}\ yr^{-1}}$. all galaxy emission has been processed with dust radiative transfer and/or resonant line radiative transfer, and data is provided for ten viewing angles for each galaxy. additionally, we provide a comprehensive set of intrinsic galaxy properties, including halo masses, stellar masses, star formation histories, and ism characteristics (e.g., metallicity, ism gas densities, lyc escape fractions). this paper outlines the data generation methods, presents a comparative analysis with jwst ers and cycle 1 observations, and addresses data set limitations. the sphinx$^{20}$ data release can be downloaded at the following url: https://github.com/harleykatz/sphinx-20-data | the sphinx public data release: forward modelling high-redshift jwst observations with cosmological radiation hydrodynamics simulations |
any injection of electromagnetically interacting particles during the cosmic dark ages will lead to increased ionization, heating, production of lyman-α photons and distortions to the energy spectrum of the cosmic microwave background, with potentially observable consequences. in this paper we describe numerical results for the low-energy electrons and photons produced by the cooling of particles injected at energies from kev to multi-tev scales, at arbitrary injection redshifts (but focusing on the post-recombination epoch). we use these data, combined with existing calculations modeling the cooling of these low-energy particles, to estimate the resulting contributions to ionization, excitation and heating of the gas, and production of low-energy photons below the threshold for excitation and ionization. we compute corrected deposition-efficiency curves for annihilating dark matter, and demonstrate how to compute equivalent curves for arbitrary energy-injection histories. these calculations provide the necessary inputs for the limits on dark matter annihilation presented in the accompanying paper i, but also have potential applications in the context of dark matter decay or deexcitation, decay of other metastable species, or similar energy injections from new physics. we make our full results publicly available at http://nebel.rc.fas.harvard.edu/epsilon, to facilitate further independent studies. in particular, we provide the full low-energy electron and photon spectra, to allow matching onto more detailed codes that describe the cooling of such particles at low energies. | indirect dark matter signatures in the cosmic dark ages. ii. ionization, heating, and photon production from arbitrary energy injections |
we perform joint modeling of the composite rest-frame far-uv and optical spectra of redshift 1.85 ≤ z ≤ 3.49 star-forming galaxies to deduce key properties of the massive stars, ionized interstellar medium (ism), and neutral ism, with the aim of investigating the principal factors affecting the production and escape of lyα photons. our sample consists of 136 galaxies with deep keck/lris and mosfire spectra covering, respectively, lyβ through c iii] λλ1907, 1909 and [o ii], [ne iii], hβ, [o iii], hα, [n ii], and [s ii]. spectral and photoionization modeling indicates that the galaxies are uniformly consistent with stellar population synthesis models that include the effects of stellar binarity. over the dynamic range of our sample, there is little variation in stellar and nebular abundance with lyα equivalent width, wλ (lyα), and only a marginal anticorrelation between age and wλ (lyα). the inferred range of ionizing spectral shapes is insufficient to solely account for the variation in wλ (lyα); rather, the covering fraction of optically thick h i appears to be the principal factor modulating the escape of lyα, with most of the lyα photons in down-the-barrel observations of galaxies escaping through low column density or ionized channels in the ism. our analysis shows that a high star-formation-rate surface density, σsfr, particularly when coupled with a low galaxy potential (i.e., low stellar mass), can aid in reducing the covering fraction and ease the escape of lyα photons. we conclude with a discussion of the implications of our results for the escape of ionizing radiation at high redshift. *based on data obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa and was made possible by the generous financial support of the w. m. keck foundation. | the effects of stellar population and gas covering fraction on the emergent lyα emission of high-redshift galaxies |
line intensity mapping (lim) is rapidly emerging as a powerful technique to study galaxy formation and cosmology in the high-redshift universe. we present lim estimates of select spectral lines originating from the interstellar medium (ism) of galaxies and 21 cm emission from neutral hydrogen gas in the universe using the large volume, high resolution thesan reionization simulations. a combination of subresolution photoionization modelling for h ii regions and monte carlo radiative transfer calculations is employed to estimate the dust-attenuated spectral energy distributions (seds) of high-redshift galaxies (z ≳ 5.5). we show that the derived photometric properties such as the ultraviolet (uv) luminosity function and the uv continuum slopes match observationally inferred values, demonstrating the accuracy of the sed modelling. we provide fits to the luminosity-star formation rate relation (l-sfr) for the brightest emission lines and find that important differences exist between the derived scaling relations and the widely used low-z ones because the ism of reionization era galaxies is generally less metal enriched than in their low-redshift counterparts. we use these relations to construct line intensity maps of nebular emission lines and cross-correlate with the 21 cm emission. interestingly, the wavenumber at which the correlation switches sign (ktransition) depends heavily on the reionization model and to a lesser extent on the targeted emission line, which is consistent with the picture that ktransition probes the typical sizes of ionized regions. the derived scaling relations and intensity maps represent a timely state-of-the-art framework for forecasting and interpreting results from current and upcoming lim experiments. | the thesan project: predictions for multitracer line intensity mapping in the epoch of reionization |
aims: cosmic reionization is an important process occurring in the early epochs of the universe. however, because of observational limitations due to the opacity of the intergalactic medium to lyman continuum photons, the nature of ionizing sources is still not well constrained. while high-redshift star-forming galaxies are thought to be the main contributors to the ionizing background at z> 6, it is impossible to directly detect their ionizing emission. therefore, looking at intermediate redshift analogues (z ~ 2-4) can provide useful hints about cosmic reionization.methods: we investigate the physical properties of one of the best lyman continuum emitter candidate at z = 3.212 found in the goods-s/candels field with photometric coverage from the u to the mips 24 μm band and vimos/vlt and mosfire/keck spectroscopy. these observations allow us to derive physical properties such as stellar mass, star formation rate, age of the stellar population, dust attenuation, metallicity, and ionization parameter, and to determine how these parameters are related to the lyman continuum emission.results: investigation of the uv spectrum confirms a direct spectroscopic detection of the lyman continuum emission with s/n> 5. non-zero lyα flux at the systemic redshift and high lyman-α escape fraction (fesc(lyα) ≥ 0.78) suggest a low h i column density. the weak c and si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. the subsolar abundances are consistent with a young and extreme starburst. the [o iii]λλ4959,5007+hβ equivalent width (ew) is one of the largest reported for a galaxy at z> 3 (ew( [ o iii ] λλ4959,5007 + hβ) ≃ 1600 å, rest-frame; 6700 å observed-frame) and the near-infrared spectrum shows that this is mainly due to an extremely strong [o iii] emission. the large observed [o iii]/[o ii] ratio (>10) and high ionization parameter are consistent with prediction from photoionization models in the case of a density-bounded nebula scenario. furthermore, the ew([o iii]λλ4959,5007+hβ) is comparable to recent measurements reported at z ~ 7-9, in the reionization epoch. we also investigate the possibility of an agn contribution to explain the ionizing emission but most of the agn identification diagnostics suggest that stellar emission dominates instead.conclusions: this source is currently the first high-z example of a lyman continuum emitter exhibiting indirect and direct evidences of a lyman continuum leakage and having physical properties consistent with theoretical expectation from lyman continuum emission from a density-bounded nebula. a low h i column density, low covering fraction, compact star formation activity, and a possible interaction/merging of two systems may contribute to the lyman continuum photon leakage. | an extreme [o iii] emitter at z = 3.2: a low metallicity lyman continuum source |
we present hubble space telescope (hst) and chandra imaging, combined with very large telescope muse integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star merger detected via gravitational-wave emission by ligo and virgo, gw170817. the host galaxy, ngc 4993, is an s0 galaxy at z = 0.009783. there is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. this suggests that ngc 4993 has undergone a relatively recent (≲ 1 gyr) “dry” merger. this merger may provide the fuel for a weak active nucleus seen in chandra imaging. at the location of the counterpart, hst imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. the population in the vicinity is predominantly old with ≲1% of any light arising from a population with ages < 500 {myr}. both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius ({r}e∼ 3 kpc), providing an re -normalized offset that is closer than ∼ 90 % of short grbs. for the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. we do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy. | the environment of the binary neutron star merger gw170817 |
context. we investigate two stripped-envelope supernovae (sne) discovered in the nearby galaxy ngc 5806 by the (intermediate) palomar transient factory [(i)ptf]. these sne, designated ptf12os/sn 2012p and iptf13bvn, exploded within ~520 days of one another at a similar distance from the host-galaxy center. we classify ptf12os as a type iib sn based on our spectral sequence; iptf13bvn has previously been classified as type ib having a likely progenitor with zero age main sequence (zams) mass below ~17 m⊙. because of the shared and nearby host, we are presented with a unique opportunity to compare these two sne.aims: our main objective is to constrain the explosion parameters of iptf12os and iptf13bvn, and to put constraints on the sn progenitors. we also aim to spatially map the metallicity in the host galaxy, and to investigate the presence of hydrogen in early-time spectra of both sne.methods: we present comprehensive datasets collected on ptf12os and iptf13bvn, and introduce a new automatic reference-subtraction photometry pipeline (fpipe) currently in use by the iptf. we perform a detailed study of the light curves (lcs) and spectral evolution of the sne. the bolometric lcs are modeled using the hydrodynamical code hyde. we analyze early spectra of both sne to investigate the presence of hydrogen; for iptf13bvn we also investigate the regions of the paschen lines in infrared spectra. we perform spectral line analysis of helium and iron lines to map the ejecta structure of both sne. we use nebular models and late-time spectroscopy to constrain the zams mass of the progenitors. we also perform image registration of ground-based images of ptf12os to archival hst images of ngc 5806 to identify a potential progenitor candidate.results: we find that our nebular spectroscopy of iptf13bvn remains consistent with a low-mass progenitor, likely having a zams mass of ~12m⊙. our late-time spectroscopy of ptf12os is consistent with a zams mass of ~15m⊙. we successfully identify a source in pre-explosion hst images coincident with ptf12os. the colors and absolute magnitude of this object are consistent between pre-explosion and late-time hst images, implying it is a cluster of massive stars. our hydrodynamical modeling suggests that the progenitor of ptf12os had a compact he core with a mass of 3.25+ 0.77-0.56m⊙ at the time of the explosion, which had a total kinetic energy of 0.54+ 0.41-0.25 × 1051 erg and synthesized 0.063+ 0.020-0.011m⊙ of strongly mixed 56ni. spectral comparisons to the type iib sn 2011dh indicate that the progenitor of ptf12os was surrounded by a thin hydrogen envelope with a mass lower than 0.02m⊙. we also find tentative evidence that the progenitor of iptf13bvn could have been surrounded by a small amount of hydrogen prior to the explosion. this result is supported by possible weak signals of hydrogen in both optical and infrared spectra. tables 3-6 are only, and spectra are also, available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/593/a68 | ptf12os and iptf13bvn. two stripped-envelope supernovae from low-mass progenitors in ngc 5806 |
using the space telescope imaging spectrograph, we have obtained ultraviolet spectra from ∼1200 to 2000 å of known lyman continuum (lyc) emitting galaxies at low redshift (z ∼ 0.3 − 0.4) with varying absolute lyc escape fractions (fesc ∼ 0.01 − 0.72). our observations include in particular the galaxy j1243+4646, which has the highest known lyc escape fraction at low redshift. while all galaxies are known lyman alpha emitters, we consistently detect an inventory of additional emission lines, including c iv λ1550, he ii λ1640, o iii] λ1666, and c iii] λ1909, whose origin is presumably essentially nebular. c iv λ1550 emission is detected above 4σ in six out of eight galaxies, with equivalent widths of ew(c iv) = 12 − 15 å for two galaxies, which exceeds the previously reported maximum emission in low-z star-forming galaxies. we detect c iv λ1550 emission in all lyc emitters with escape fractions fesc > 0.1 and find a tentative increase in the flux ratio c iv λ1550/c iii] λ1909 with fesc. based on the data, we propose a new criterion to select and classify strong leakers (galaxies with fesc > 0.1): c iv λ1550/c iii] λ1909 ≳ 0.75. finally, we also find he ii λ1640 emission in all the strong leakers with equivalent widths from 3 to 8 å rest frame. these are among the highest values observed in star-forming galaxies and are primarily due to a high rate of ionizing photon production. the nebular he ii λ1640 emission of the strong lyc emitters does not require harder ionizing spectra at > 54 ev compared to those of typical star-forming galaxies at similarly low metallicity. | strong lyman continuum emitting galaxies show intense c iv λ1550 emission |
we present lyα and uv-nebular emission line properties of bright lyα emitters (laes) at z = 6-7 with a luminosity of log llyα/[erg s-1] = 43-44 identified in the 21 deg2 area of the silverrush early sample developed with the subaru hyper suprime-cam survey data. our optical spectroscopy newly confirms 21 bright laes with clear lyα emission, and contributes to making a spectroscopic sample of 96 laes at z = 6-7 in silverrush. from the spectroscopic sample, we select seven remarkable laes as bright as himiko and cr7 objects, and perform deep keck/mosfire and subaru/numoircs near-infrared spectroscopy reaching the 3 σ flux limit of ∼2 × 10-18 erg s-1 for the uv-nebular emission lines of he ii λ1640, c iv λλ1548,1550, and o iii]λλ1661,1666. except for one tentative detection of c iv, we find no strong uv-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (ew0) of ∼2-4 å for c iv, he ii, and o iii] lines. we also investigate the vlt/x-shooter spectrum of cr7 whose 6 σ detection of he ii is claimed by sobral et al. although two individuals and the eso archive service carefully reanalyzed the x-shooter data that are used in the study of sobral et al., no he ii signal of cr7 is detected, supportive of weak uv-nebular lines of the bright laes even for cr7. the spectral properties of these bright laes are thus clearly different from those of faint dropouts at z ∼ 7 that have strong uv-nebular lines shown in the various studies. comparing these bright laes and the faint dropouts, we find anti-correlations between the uv-nebular line ew0 and the uv-continuum luminosity, which are similar to those found at z ∼ 2-3. | silverrush. iii. deep optical and near-infrared spectroscopy for lyα and uv-nebular lines of bright lyα emitters at z = 6-7 |
we present observations and analysis of 18 stripped-envelope supernovae observed during 2013-2018. this sample consists of five h/he-rich sne, six h-poor/he-rich sne, three narrow lined sne ic, and four broad lined sne ic. the peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive 56ni and ejecta masses (mni and mej). additionally, the temperature evolution and spectral line velocity curves of each sn are examined. analysis of the [o i] line in the nebular phase of eight sne suggests their progenitors had initial masses <20 m⊙. the bolometric light curve properties are examined in combination with those of other se events from the literature. the resulting data set gives the mej distribution for 80 se-sne, the largest such sample in the literature to date, and shows that sne ib have the lowest median mej, followed by narrow-lined sne ic, h/he-rich sne, broad-lined sne ic, and finally gamma-ray burst sne. sne ic-6/7 show the largest spread of mej ranging from ∼1.2-11 m⊙, considerably greater than any other subtype. for all se-sne <mej> = 2.8 ± 1.5 m⊙ which further strengthens the evidence that se-sne arise from low-mass progenitors which are typically <5 m⊙ at the time of explosion, again suggesting mzams <25 m⊙. the low <mej> and lack of clear bimodality in the distribution implies <30 m⊙ progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these sne. | investigating the properties of stripped-envelope supernovae; what are the implications for their progenitors? |
this book provides two state-of-the-art quantitative techniques to determine ultra-trace rare earth elements (rees) in natural carbonates using solution nebulization-inductively coupled plasma mass spectrometry (sn-icpms) and laser ablation-inductively coupled plasma mass spectrometry (la-icpms) with respective applications were presented in this dissertation. these techniques were applied to natural carbonates, including corals and stalagmites, to understand volcano eruptions and the impacts on modern biosystem and paleoclimate regimes. in the first sn-icpms protocol, direct measurements for femtogram quantity carbonate samples without chemical separation steps can offer accurate and high-precision analysis (±1.9-6.5%, 2σ) with a high sample throughput of 8-10 samples/hr routinely. application to modern porites corals collected from south china sea region, the anomalies of ree contents and al/ca ratios associated with micro-domain images, register modern coral reefs could be exacerbated by volcanic eruptions. in the second protocol, a high-sensitivity quantitative open-cell la-icpms technique has been established to allow direct sampling on stalagmite surface in the atmospheric air. this technique improved limits of detection down to sub-ng/g range and promises analyses of carbonate ree profiles at the single digit parts-per-billion (ppb) levels. application to a 15-cm stalagmite collected from east timor reveals two peaks of ree contents by at least one order of magnitude, possibly due to volcanic ash preserved in stalagmite. both improved sn-icpms and la-icpms techniques highlight the high-sensitivity and high-temporal-resolution carbonate ree analyses for corals and stalagmites, with great potential to other natural carbonates such as travertine, tufa, and flowstone, benefit our understanding of paleoclimatic and paleoenvironmental dynamics. | advanced and applied studies on ultra-trace rare earth elements (rees) in carbonates using sn-icpms and la-icpms |
we present new hubble space telescope/wide field camera 3 (hst/wfc3) imaging of 25 extremely luminous (-23.2 ≤ muv ≲ -21.2) lyman-break galaxies (lbgs) at z ≃ 7. the sample was initially selected from 1.65 deg2 of ground-based imaging in the ultravista/cosmos and uds/sxds fields, and includes the extreme lyman α emitters, 'himiko' and 'cr7'. a deconfusion analysis of the deep spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (ew0(hβ + [o iii]) > 600 å). we find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z ≃ 7 galaxies, and ubiquitous at the very bright end (muv < -22.5). the galaxies have half-light radii in the range r1/2 ∼ 0.5-3 kpc. the size measurements provide the first determination of the size-luminosity relation at z ≃ 7 that extends to muv ∼ -23. we find the relation to be steep with r1/2 ∝ l1/2. excluding clumpy, multicomponent galaxies however, we find a shallower relation that implies an increased star formation rate surface density in bright lbgs. using the new, independent, hst/wfc3 data we confirm that the rest-frame uv luminosity function at z ≃ 7 favours a power-law decline at the bright end, compared to an exponential schechter function drop-off. finally, these results have important implications for the euclid mission, which we predict will detect >1000 similarly bright galaxies at z ≃ 7. our new hst imaging suggests that the vast majority of these galaxies will be spatially resolved by euclid, mitigating concerns over dwarf star contamination. | unveiling the nature of bright z ≃ 7 galaxies with the hubble space telescope |
stellar population models produce radiation fields that ionize oxygen up to o+2, defining the limit of standard h ii region models (<54.9 ev). yet, some extreme emission-line galaxies, or eelgs, have surprisingly strong emission originating from much higher ionization potentials. we present uv hst/cos and optical lbt/mods spectra of two nearby eelgs that have very high-ionization emission lines (e.g., he ii λλ1640,4686 c iv λλ1548,1550, [fe v]λ4227, [ar iv]λλ4711,4740). we define a four-zone ionization model that is augmented by a very high-ionization zone, as characterized by he+2 (>54.4 ev). the four-zone model has little to no effect on the measured total nebular abundances, but does change the interpretation of other eelg properties: we measure steeper central ionization gradients; higher volume-averaged ionization parameters; and higher central te , ne , and log u values. traditional three-zone estimates of the ionization parameter can underestimate the average log u by up to 0.5 dex. additionally, we find a model-independent dichotomy in the abundance patterns, where the α/h abundances are consistent but n/h, c/h, and fe/h are relatively deficient, suggesting these eelgs are α/fe-enriched by more than three times. however, there still is a high-energy ionizing photon production problem (heip3). even for such α/fe enrichment and very high log u s, photoionization models cannot reproduce the very high-ionization emission lines observed in eelgs. *based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | characterizing extreme emission-line galaxies. i. a four-zone ionization model for very high-ionization emission |
the chemical abundances of spiral galaxies, as probed by h ii regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. we present large binocular telescope/multi-object double spectrographs spectra of 52 h ii regions in ngc 3184 as part of the chemical abundances of spirals (chaos) project. we explore the direct-method gas-phase abundance trends for the first four chaos galaxies, using temperature measurements from one or more auroral-line detections in 190 individual h ii regions. we find that the dispersion in ${t}_{e}-{t}_{e}$ relationships is dependent on ionization, as characterized by ${f}_{\lambda 5007}/{f}_{\lambda 3727}$ , and so we recommend ionization-based temperature priorities for abundance calculations. we confirm our previous results that [n ii] and [s iii] provide the most robust measures of electron temperature in low-ionization zones, while [o iii] provides reliable electron temperatures in high-ionization nebula. we measure relative and absolute abundances for o, n, s, ar, and ne. the four chaos galaxies marginally conform with a universal o/h gradient, as found by empirical integral field unit studies when plotted relative to effective radius. however, after adjusting for vertical offsets, we find a tight universal n/o gradient of ${\alpha }_{{\rm{n}}/{\rm{o}}}=-0.33$ dex/re with σtot. = 0.08 for rg/re < 2.0, where n is dominated by secondary production. despite this tight universal n/o gradient, the scatter in the n/o-o/h relationship is significant. interestingly, the scatter is similar when n/o is plotted relative to o/h or s/h. the observable ionic states of s probe lower ionization and excitation energies than o, which might be more appropriate for characterizing abundances in metal-rich h ii regions. | chaos iv: gas-phase abundance trends from the first four chaos galaxies |
ultraviolet nebular emission lines are important for understanding the time evolution and nucleosynthetic origins of their associated elements, but the underlying trends of their relative abundances are unclear. we present uv spectroscopy of 20 nearby low-metallicity, high-ionization dwarf galaxies obtained using the hubble space telescope. building upon previous studies, we analyze the c/o relationship for a combined sample of 40 galaxies with significant detections of the uv o+2/c+2 collisionally excited lines and direct-method oxygen abundance measurements. using new analytic carbon ionization correction factor relationships, we confirm the flat trend in c/o versus o/h observed for local metal-poor galaxies. we find an average log(c/o) = -0.71 with an intrinsic dispersion of σ = 0.17 dex. the c/n ratio also appears to be constant at log(c/n) = 0.75, plus significant scatter (σ = 0.20 dex), with the result that carbon and nitrogen show similar evolutionary trends. this large and real scatter in c/o over a large range in o/h implies that measuring the uv c and o emission lines alone does not provide a reliable indicator of the o/h abundance. by modeling the chemical evolution of c, n, and o of individual targets, we find that the c/o ratio is very sensitive to both the detailed star formation history and to supernova feedback. longer burst durations and lower star formation efficiencies correspond to low c/o ratios, while the escape of oxygen atoms in supernovae winds produces decreased effective oxygen yields and larger c/o ratios. further, a declining c/o relationship is seen with increasing baryonic mass due to increasing effective oxygen yields. based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas5-26555. these observations are associated with program no. 14628. | the chemical evolution of carbon, nitrogen, and oxygen in metal-poor dwarf galaxies |
observation shows that nebular emission, molecular gas, and young stars in giant galaxies are associated with rising x-ray bubbles inflated by radio jets launched from nuclear black holes. we propose a model where molecular clouds condense from low-entropy gas caught in the updraft of rising x-ray bubbles. the low-entropy gas becomes thermally unstable when it is lifted to an altitude where its cooling time is shorter than the time required to fall to its equilibrium location in the galaxy, i.e., {t}{{c}}/{t}{{i}}≲ 1. the infall speed of a cloud is bounded by the lesser of its free-fall and terminal speeds, so that the infall time here can exceed the free-fall time by a significant factor. this mechanism is motivated by atacama large millimeter array observations revealing molecular clouds lying in the wakes of rising x-ray bubbles with velocities well below their free-fall speeds. our mechanism would provide cold gas needed to fuel a feedback loop while stabilizing the atmosphere on larger scales. the observed cooling time threshold of ∼ 5× {10}8 {yr}—the clear-cut signature of thermal instability and the onset of nebular emission and star formation—may result from the limited ability of radio bubbles to lift low-entropy gas to altitudes where thermal instabilities can ensue. outflowing molecular clouds are unlikely to escape, but instead return to the central galaxy in a circulating flow. we contrast our mechanism to precipitation models where the minimum value of {t}{{c}}/{t}{{ff}}≲ 10 triggers thermal instability, which we find to be inconsistent with observation. | a mechanism for stimulating agn feedback by lifting gas in massive galaxies |
we have conducted a homogeneous near-infrared (near-ir) spectroscopic survey of 33 objects with varying degrees of similarity to fu orionis. common spectroscopic features that are characteristic of the three classical fuors, fu ori, v1057 cyg, and v1515 cyg, are strong co absorption, weak metal absorption, strong water bands, low gravity, strong blueshifted he i absorption, and few (if any) emission lines. based on these criteria, we classify the 33 objects as either bona fide fuors (eruption observed), fuor-like objects (eruption not observed), or peculiar objects with some fuor-like characteristics, and present a spectral atlas of 14 bona fide fuors, 10 fuor-like objects, and 9 peculiar objects. all objects that we classify as fuors or fuor-like have very similar near-ir spectra. we use this spectral similarity to determine the extinction to each source, and correlate the extinction to the depth of the 3 μm ice band. all bona fide fuors still today maintain the spectrum of a fuor, despite the eruption occurring up to 80 years ago. most fuors and fuor-like objects occupy a unique space on a plot of na+ca versus co equivalent widths, whereas the peculiar objects tend to be found mostly elsewhere. since most fuors show a reflection nebula, we also present an atlas of k-band images of each target. we found that the near-ir spectra of fuors and young brown dwarfs can be extremely similar, a distinguishing feature being the paschen β absorption in the spectra of fuors. although v1647 ori, ar 6a, and v346 normae had been previously classified as candidate fuors, we classify them as peculiar objects with some fuor-like properties since their spectra now differ significantly from bona fide fuors. we confirm two new fuor-like objects that were initially identified as candidates based on their near-ir morphology. | a near-infrared spectroscopic survey of fu orionis objects |
we have discovered a 300 kpc-wide giant lyman-α (lyα) nebula centered on the massive galaxy group ro-1001 at z = 2.91 in the cosmic evolution survey field. keck cosmic web imager observations reveal three cold gas filaments converging into the center of the potential well of its ∼4 × 1013 m⊙ dark matter halo, hosting 1200 m⊙ yr−1 of star formation as probed by atacama large millimeter array and northern extended millimeter array observations. the nebula morphological and kinematics properties and the prevalence of blueshifted components in the lyα spectra are consistent with a scenario of gas accretion. the upper limits on active galactic nuclei activity and overall energetics favor gravity as the primary lyα powering source and infall as the main source of gas flows to the system. although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift. | three lyman-α-emitting filaments converging to a massive galaxy group at z = 2.91: discussing the case for cold gas infall |
the study of carbon and oxygen abundances yields information on the time evolution and nucleosynthetic origins of these elements, yet they remain relatively unexplored. at low metallicities, (12+log(o/h) < 8.0), nebular carbon measurements are limited to rest-frame uv collisionally excited emission lines. therefore, we present the uv spectrophotometry of 12 nearby low-metallicity high-ionization h ii regions in dwarf galaxies obtained using the cosmic origins spectrograph on the hubble space telescope. we present the first analysis of the c/o ratio in local galaxies based solely on simultaneous significant detections of the uv {{{o}}}+2 and {{{c}}}+2 collisionally excited lines in seven of our targets and five objects from the literature to create a final sample of 12 significant detections. our sample is complemented by optical sdss spectra, from which we measured the nebular physical conditions and oxygen abundances using the direct method. at low metallicity, (12+log(o/h) < 8.0), no clear trend is evident in c/o versus o/h for the present sample given the large dispersion observed. when combined with recombination line observations at higher values of o/h, a general trend of increasing c/o with increasing o/h is also viable but with some significant outliers. additionally, we find the c/n ratio appears to be constant (but with significant scatter) over a large range in oxygen abundance, indicating that carbon is predominantly produced by similar nucleosynthetic mechanisms as nitrogen. if true, and our current understanding of nitrogen production is correct, this would indicate that primary production of carbon (a flat trend) dominates at low metallicity, but quasi-secondary production (an increasing trend) becomes prominent at higher metallicities. a larger sample will be needed to determine the true nature and dispersion of the relation. | carbon and oxygen abundances in low metallicity dwarf galaxies |
we present the calibration of the insight-hard x-ray modulation telescope (insight-hxmt) x-ray satellite, which can be used to perform timing and spectral studies of bright x-ray sources. insight-hxmt carries three main payloads onboard: the high energy x-ray telescope (he), the medium energy x-ray telescope (me) and the low energy x-ray telescope (le). in orbit, the radioactive sources, activated lines, the fluorescence lines and celestial sources are used to calibrate the energy scale and energy resolution of the payloads. the crab nebular is adopted as the primary effective area calibrator and empirical functions are constructed to modify the simulated effective areas of the three payloads respectively. the systematic errors of he, compared to the model of the crab nebular, are less than 2% in 28-120 kev and 2%-10% above 120 kev. the systematic errors of me are less than 1.5% in 10-35 kev. the systematic errors of le are less than 1% in 1-7 kev except the si k-edge (1.839 kev, up to 1.5%) and less than 2% in 7-10 kev. | in-flight calibration of the insight-hard x-ray modulation telescope |
supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. the nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds—a departure from the ‘hot mode’ accretion model—although unambiguous observational support for this prediction remains elusive. here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the abell 2597 brightest cluster galaxy (bcg), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy’s centre, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core. the observations show that these cold clouds also fuel black hole accretion, revealing ‘shadows’ cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it. | cold, clumpy accretion onto an active supermassive black hole |
we present a joint analysis of rest-ultraviolet (uv) and rest-optical spectra obtained using keck/lris and keck/mosfire for a sample of 62 star-forming galaxies at z ~ 2.3. we divide our sample into two bins based on their location in the [o iii]5007/hβ versus [n ii]6584/hα bpt diagram, and perform the first differential study of the rest-uv properties of massive ionizing stars as a function of rest-optical emission-line ratios. fitting binary population and spectral synthesis (bpass) stellar population synthesis models, including nebular continuum emission, to our rest-uv composite spectra, we find that high-redshift galaxies offset towards higher [o iii]λ5007/hβ and [n ii]λ6584/hα have younger ages ($\log (\rm {\,age/yr})=7.20^{+0.57}_{-0.20}$) and lower stellar metallicities ($z_*=0.0010^{+0.0011}_{-0.0003}$) resulting in a harder ionizing spectrum, compared to the galaxies in our sample that lie on the local bpt star-forming sequence ($\log (\textrm {age/yr})=8.57^{+0.88}_{-0.84}$, $z_*=0.0019^{+0.0006}_{-0.0006}$). additionally, we find that the offset galaxies have an ionization parameter of $\log (u)=-3.04^{+0.06}_{-0.11}$ and nebular metallicity of ($12+\log (\rm {\,o/h})=8.40^{+0.06}_{-0.07}$), and the non-offset galaxies have an ionization parameter of $\log (u)=-3.11^{+0.08}_{-0.08}$ and nebular metallicity of $12+\log (\rm {\,o/h})=8.30^{+0.05}_{-0.06}$. the stellar and nebular metallicities derived for our sample imply that the galaxies offset from the local bpt relation are more α-enhanced ($7.28^{+2.52}_{-2.82}\rm {\,o/fe}_{\odot }$) compared to those consistent with the local sequence ($3.04^{+0.95}_{-0.54}\rm {\,o/fe}_{\odot }$). however, even galaxies that are entirely consistent with the local nebular excitation sequence appear to be α-enhanced - in contrast with typical local systems. such differences must be considered when estimating gas-phase oxygen abundances at high redshift based on strong emission-line ratios. specifically, a similarity in the location of high-redshift and local galaxies in the bpt diagram may not be indicative of a similarity in their physical properties. | the mosdef-lris survey: the interplay between massive stars and ionized gas in high-redshift star-forming galaxies |
we present a joint analysis of the galaxy s04590 at z = 8.496 based on nirspec, nircam, and niriss observations obtained as part of the early release observations program of the james webb space telescope (jwst) and the far-infrared [c ii] 158 μm emission line detected by dedicated atacama large millimeter/submillimeter array (alma) observations. we determine the physical properties of s04590 from modeling of the spectral energy distribution (sed) and through the redshifted optical nebular emission lines detected with jwst/nirspec. the best-fit sed model reveals a low-mass (m ⋆ = 107.2-108 m ⊙) galaxy with a low oxygen abundance of $12+\mathrm{log}({\rm{o}}/{\rm{h}})={7.16}_{-0.12}^{+0.10}$ derived from the strong nebular and auroral emission lines. assuming that [c ii] effectively traces the interstellar medium, we estimate the total gas mass of the galaxy to be m gas = (8.0 ± 4.0) × 108 m ⊙ based on the luminosity and spatial extent of [c ii]. this yields an exceptionally high gas fraction, f gas = m gas/(m gas + m ⋆) ≳ 90%, though one still consistent with the range expected for low metallicity. we further derive the metal mass of the galaxy based on the gas mass and gas-phase metallicity, which we find to be consistent with the expected metal production from type ii supernovae. finally, we make the first constraints on the dust-to-gas (dtg) and dust-to-metal (dtm) ratios of galaxies in the epoch of reionization at z ≳ 6, showing overall low mass ratios of logdtg < -3.8 and logdtm < -0.5, though they are consistent with established scaling relations and in particular with those of the local metal-poor galaxy i zwicky 18. our analysis highlights the synergy between alma and jwst in characterizing the gas, metal, and stellar content of the first generation of galaxies. | the gas and stellar content of a metal-poor galaxy at z = 8.496 as revealed by jwst and alma |
the orion nebula cluster toward the h ii region m42 is the most outstanding young cluster at the smallest distance (410 pc) among the rich high-mass stellar clusters. by newly analyzing the archival molecular data of the 12co(j = 1-0) emission at 21″ resolution, we identified at least three pairs of complementary distributions between two velocity components at 8 and 13 km s-1. we present a hypothesis that the two clouds collided with each other and triggered formation of the high-mass stars, mainly toward two regions including the nearly 10 o stars in m42 and the b star, nu ori, in m43. the timescale of the collision is estimated to be ∼0.1 myr by a ratio of the cloud size and velocity corrected for projection, which is consistent with the age of the youngest cluster members less than 0.1 myr. the majority of the low-mass cluster members were formed prior to the collision in the last myr. we discuss the implications of the present hypothesis and the scenario of high-mass star formation by comparing with the other eight cases of triggered o-star formation via cloud-cloud collision. | a new look at the molecular gas in m42 and m43: possible evidence for cloud-cloud collision that triggered formation of the ob stars in the orion nebula cluster |
we use spatially resolved spectroscopy from the calar alto legacy integral field area (califa) survey to study the nature of the line emitting gas in galaxies of different hubble types, focusing on the separation of star-forming (sf) regions from those better characterized as diffuse ionized gas (dig). the diagnosis is carried out in terms of the equivalent width of h α (wh α). three nebular regimes are identified. regions where wh α < 3 å define what we call the hdig, the component of the dig where photoionization is dominated by hot, low-mass, evolved stars. regions where wh α > 14 å trace sf complexes. wh α values in the intermediate 3-14 å range reflect a mixed regime (mdig) where more than one process contributes. this three-tier scheme is inspired both by theoretical and empirical considerations. its application to califa galaxies of different types and inclinations leads to the following results: (i) the hdig component is prevalent throughout ellipticals and s0's as well as in bulges, and explains the strongly bimodal distribution of wh α both among and within galaxies. (ii) early-type spirals have some hdig in their discs, but this component becomes progressively less relevant for later hubble types. (iii) hdig emission is also present above and below galactic discs, as seen in several edge-on spirals in our sample. (iv) the sf/mdig proportion grows steadily from early- to late-type spirals, and from inner to outer radii. (v) besides circumventing basic inconsistencies in conventional dig/sf separation criteria based on the h α surface brightness, our wh α-based method produces results in agreement with a classical excitation diagram analysis. | diffuse ionized gas in galaxies across the hubble sequence at the califa resolution |
ultraluminous x-ray sources (ulxs) were identified as a separate class of objects in 2000 based on data from the chandra x-ray observatory. these are unique objects: their x-ray luminosities exceed the eddington limit for a typical stellar-mass black hole. for a long time, the nature of ulxs remained unclear. however, the gradual accumulation of data, new results of x-ray and optical spectroscopy, and the study of the structure and energy of nebulae surrounding ulxs led to the understanding that most of the ultraluminous x-ray sources must be supercritical accretion disks like ss 433. the discovery of neutron stars in a number of objects only increased the confidence of the scientific community in the conclusions obtained, since the presence of neutron stars in such systems clearly indicates a supercritical accretion regime. in this review, we systematize the main facts about the observational manifestations of ulxs and ss 433 in the x-ray and optical ranges and discuss their explanation from the point of view of the supercritical accretion theory. | ultraluminous x-ray sources |
the origin of nebular he ii emission, which is frequently observed in low-metallicity (o/h) star-forming galaxies, remains largely an unsolved question. using the observed anticorrelation of the integrated x-ray luminosity per unit of star formation rate (lx/sfr) of an x-ray binary population with metallicity and other empirical data from the well-studied galaxy i zw 18, we show that the observed he ii λ4686 intensity and its trend with metallicity is naturally reproduced if the bulk of he+ ionizing photons are emitted by the x-ray sources. we also show that a combination of x-ray binary population models with normal single and/or binary stellar models reproduces the observed i(4686)/i(hβ) intensities and its dependency on metallicity and age. we conclude that both empirical data and theoretical models suggest that high-mass x-ray binaries are the main source of nebular he ii emission in low-metallicity star-forming galaxies. | x-ray binaries as the origin of nebular he ii emission in low-metallicity star-forming galaxies |
the ubiquity of lyman alpha (lyα) emission in a sample of four bright [o iii]-strong star-forming galaxies with redshifts above seven has led to the suggestion that such luminous sources represent a distinct population compared with their fainter, more numerous counterparts. the presence of lyα emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly because of the presence of active galactic nuclei. to test this hypothesis, we secured long integration spectra with xshooter on the vlt for three z≃ 7 sources selected to have similar luminosities and prominent excess fluxes in the irac 3.6 or 4.5 μm band, usually attributed to strong [o iii] emission. we secured additional spectroscopy for one of these galaxies at z = 7.15 using mosfire at the keck telescope. for the most well-studied source in our sample with the strongest irac excess, we detect significant nebular emission from he ii and n v indicative of a non-thermal source. for the other two sources at z = 6.81 and z = 6.85, for which no previous optical/near-infrared spectroscopy was available, lyα is seen in one and c iii] emission in the other. although based on a modest sample, our results further support the hypothesis that the phenomenon of intense [o iii] emission is associated preferentially with sources lying in early ionized bubbles. however, even though one of our sources at z = 7.15 suggests the presence of non-thermal radiation, such ionized bubbles may not uniquely arise in this manner. we discuss the unique advantages of extending such challenging diagnostic studies with jwst. | a spectroscopic search for agn activity in the reionization era |
theoretical models predict that core-collapse supernovae (ccsne) can be efficient dust producers (0.1-1.0 m⊙), potentially accounting for most of the dust production in the early universe. observational evidence for this dust production efficiency is however currently limited to only a few ccsn remnants (e.g. sn 1987a, crab nebula). in this paper, we revisit the dust mass produced in cassiopeia a (cas a), a ∼330-yr old o-rich galactic supernova remnant (snr) embedded in a dense interstellar foreground and background. we present the first spatially resolved analysis of cas a based on spitzer and herschel infrared and submillimetre data at a common resolution of ∼0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. we fit the dust continuum from 17 to 500 μm with a four-component interstellar medium and supernova (sn) dust model. we find a concentration of cold dust in the unshocked ejecta of cas a and derive a mass of 0.3-0.5 m⊙ of silicate grains freshly produced in the snr, with a lower limit of ≥0.1-0.2 m⊙. for a mixture of 50 per cent of silicate-type grains and 50 per cent of carbonaceous grains, we derive a total sn dust mass between 0.4 and 0.6 m⊙. these dust mass estimates are higher than from most previous studies of cas a and support the scenario of sn-dominated dust production at high redshifts. we furthermore derive an interstellar extinction map for the field around cas a which towards cas a gives average values of av = 6-8 mag, up to a maximum of av = 15 mag. | the dust mass in cassiopeia a from a spatially resolved herschel analysis |
we analyze the spatial distribution of dusty young stellar objects (ysos) identified in the spitzer survey of the orion molecular clouds, augmenting these data with chandra x-ray observations to correct for incompleteness in dense clustered regions. we also devise a scheme to correct for spatially varying incompleteness when x-ray data are not available. the local surface densities of the ysos range from 1 pc-2 to over 10,000 pc-2, with protostars tending to be in higher density regions. this range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. by identifying clusters and groups as continuous regions with surface densities ≥10 pc-2, we find that 59% of the ysos are in the largest cluster, the orion nebula cluster (onc), while 13% of the ysos are found in a distributed population. a lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. an examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. the onc becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 myr in age. we find that the star formation efficiency (sfe) of the orion b cloud is unusually low, and that the sfes of individual groups and clusters are an order of magnitude higher than those of the clouds. finally, we discuss the relationship between the young low mass stars in the orion clouds and the orion ob 1 association, and we determine upper limits to the fraction of disks that may be affected by uv radiation from ob stars or dynamical interactions in dense, clustered regions. | the spitzer space telescope survey of the orion a and b molecular clouds. ii. the spatial distribution and demographics of dusty young stellar objects |
one of the most challenging aspects of studying galaxies in the z≳ 7 universe is the infrequent confirmation of their redshifts through spectroscopy, a phenomenon thought to occur from the increasing opacity of the intergalactic medium to lyα photons at z\gt 6.5. the resulting redshift uncertainties inhibit the efficient search for [c ii] in z∼ 7 galaxies with sub-millimeter instruments such as alma, given their limited scan speed for faint lines. one means by which to improve the precision of the inferred redshifts is to exploit the potential impact of strong nebular emission lines on the colors of z ∼ 4 - 8 galaxies as observed by spitzer/irac. at z∼ 6.8, galaxies exhibit irac colors as blue as [3.6]-[4.5]∼ -1, likely due to the contribution of [o iii]+hβ to the 3.6 μm flux combined with the absence of line contamination in the 4.5 μm band. in this paper we explore the use of extremely blue [3.6]-[4.5] colors to identify galaxies in the narrow redshift window z ∼ 6.6 - 6.9. when combined with an i-dropout criterion, we demonstrate that we can plausibly select a relatively clean sample of z∼ 6.8 galaxies. through a systematic application of this selection technique to our catalogs from all five candels fields, we identify 20 probable z ∼ 6.6 - 6.9 galaxies. we estimate that our criteria select the ∼50% strongest line emitters at z∼ 6.8 and from the irac colors we estimate a typical [o iii]+hβ rest-frame equivalent width of 1085 å for this sample. the small redshift uncertainties on our sample make it particularly well suited for follow-up studies with facilities such as alma. | high-precision photometric redshifts from spitzer/irac: extreme [3.6] - [4.5] colors identify galaxies in the redshift range z ∼ 6.6 - 6.9 |
we report new observations of sl2s j021737-051329, a lens system consisting of a bright arc at z = 1.84435, magnified ∼17× by a massive galaxy at z = 0.65. sl2s0217 is a low-mass (m < 109 m ⊙), low-metallicity (z ∼ 1/20 z ⊙) galaxy, with extreme star-forming conditions that produce strong nebular uv emission lines in the absence of any apparent outflows. here we present several notable features from rest-frame uv keck/lris spectroscopy: (1) very strong narrow emission lines are measured for c iv λλ1548, 1550, he ii λ1640, o iii] λλ1661, 1666, si iii] λλ1883, 1892, and c iii] λλ1907, 1909. (2) double-peaked lyα emission is observed with a dominant blue peak and centered near the systemic velocity. (3) the low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. the relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of he ii, which indicates that an additional ionization source is needed. we rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. therefore, sl2s0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe. | a window on the earliest star formation: extreme photoionization conditions of a high-ionization, low-metallicity lensed galaxy at z ∼ 2* |
the nebular recombination line h α is widely used as a star formation rate (sfr) indicator in the local and high-redshift universe. we present a detailed h α radiative transfer study of high-resolution isolated milky-way and large magellanic cloud simulations that include radiative transfer, non-equilibrium thermochemistry, and dust evolution. we focus on the spatial morphology and temporal variability of the h α emission, and its connection to the underlying gas and star formation properties. the h α and h β radial and vertical surface brightness profiles are in excellent agreement with observations of nearby galaxies. we find that the fraction of h α emission from collisional excitation amounts to fcol ~ 5-$10{{\ \rm per\ cent}}$, only weakly dependent on radius and vertical height, and that scattering boosts the h α luminosity by $\sim 40{{\ \rm per\ cent}}$. the dust correction via the balmer decrement works well (intrinsic h α emission recoverable within 25 per cent), though the dust attenuation law depends on the amount of attenuation itself both on spatially resolved and integrated scales. important for the understanding of the h α-sfr connection is the dust and helium absorption of ionizing radiation (lyman continuum [lyc] photons), which are about $f_{\rm abs}\approx 28{{\ \rm per\ cent}}$ and $f_{\rm he}\approx 9{{\ \rm per\ cent}}$, respectively. together with an escape fraction of $f_{\rm esc}\approx 6{{\ \rm per\ cent}}$, this reduces the available budget for hydrogen line emission by nearly half ($f_{\rm h}\approx 57{{\ \rm per\ cent}}$). we discuss the impact of the diffuse ionized gas, showing - among other things - that the extraplanar h α emission is powered by lyc photons escaping the disc. future applications of this framework to cosmological (zoom-in) simulations will assist in the interpretation of spectroscopy of high-redshift galaxies with the upcoming james webb space telescope. | h α emission in local galaxies: star formation, time variability, and the diffuse ionized gas |
we present an optical analysis of 55 members of r136, the central cluster in the tarantula nebula of the large magellanic cloud. our sample was observed with stis aboard the hubble space telescope, is complete down to about 40 m⊙, and includes seven very massive stars with masses over 100 m⊙. we performed a spectroscopic analysis to derive their physical properties. using evolutionary models, we find that the initial mass function of massive stars in r136 is suggestive of being top-heavy with a power-law exponent γ ≈ 2 ± 0.3, but steeper exponents cannot be excluded. the age of r136 lies between 1 and 2 myr with a median age of around 1.6 myr. stars more luminous than log l/l⊙ = 6.3 are helium enriched and their evolution is dominated by mass-loss, but rotational mixing or some other form of mixing could be still required to explain the helium composition at the surface. stars more massive than 40 m⊙ have larger spectroscopic than evolutionary masses. the slope of the wind-luminosity relation assuming unclumped stellar winds is 2.41 ± 0.13 which is steeper than usually obtained (∼1.8). the ionizing ( $\log q_0\, [{\rm ph/s}] = 51.4$ ) and mechanical ( $\log l_{\rm sw}\, [{\rm erg/s}] = 39.1$ ) output of r136 is dominated by the most massive stars ( $\gt 100\, \mathrm{ m}_{\odot }$ ). r136 contributes around a quarter of the ionizing flux and around a fifth of the mechanical feedback to the overall budget of the tarantula nebula. for a census of massive stars of the tarantula nebula region, we combined our results with the vlt-flames tarantula survey plus other spectroscopic studies. we observe a lack of evolved wolf-rayet stars and luminous blue and red supergiants. | the r136 star cluster dissected with hubble space telescope/stis - ii. physical properties of the most massive stars in r136 |
high-resolution x-ray spectroscopy with hitomi was expected to resolve the origin of the faint unidentified e≈ 3.5 {kev} emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the perseus cluster. we have analyzed the hitomi first-light observation of the perseus cluster. the emission line expected for perseus based on the xmm-newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the hitomi data. however, the previously reported 3.5 kev flux from perseus was anomalously high compared to the sample-based prediction. we find no unidentified line at the reported high flux level. taking into account the xmm measurement uncertainties for this region, the inconsistency with hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. we do not find anomalously high fluxes of the nearby faint k line or the ar satellite line that were proposed as explanations for the earlier 3.5 kev detections. we do find a hint of a broad excess near the energies of high-n transitions of s xvi (e≃ 3.44 {kev} rest-frame)—a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. while its energy is consistent with xmm pn detections, it is unlikely to explain the mos signal. a confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment. | hitomi constraints on the 3.5 kev line in the perseus galaxy cluster |
the radiative torque (rat) alignment of interstellar grains with ordinary paramagnetic susceptibilities has been supported by earlier studies. the alignment of such grains depends on the so-called rat parameter q max, which is determined by the grain shape. in this paper, we elaborate on our model of rat alignment for grains with enhanced magnetic susceptibility due to iron inclusions, such that rat alignment is magnetically enhanced, which we term the mrat mechanism. such grains can be aligned with high angular momentum at the so-called high-j attractor points, achieving a high degree of alignment. using our analytical model of rats, we derive the critical value of the magnetic relaxation parameter δ m to produce high-j attractor points as functions of q max and the anisotropic radiation angle relative to the magnetic field ψ. we find that if about 10% of the total iron abundance present in silicate grains is forming iron clusters, this is sufficient to produce high-j attractor points for all reasonable values of q max. to calculate the degree of grain alignment, we carry out numerical simulations of mrat alignment by including stochastic excitations from gas collisions and magnetic fluctuations. we show that large grains can achieve perfect alignment when the high-j attractor point is present, regardless of the values of q max. our obtained results pave the way for the physical modeling of polarized thermal dust emission as well as magnetic dipole emission. we also find that millimeter-sized grains in accretion disks may be aligned with the magnetic field if they are incorporated with iron nanoparticles. | a unified model of grain alignment: radiative alignment of interstellar grains with magnetic inclusions |
this paper presents a maximum-likelihood algorithm for combining sky maps with disparate sky coverage, angular resolution and spatially varying anisotropic noise into a single map of the sky. we use this to merge hundreds of individual maps covering the 2008-2018 act observing seasons, resulting in by far the deepest act maps released so far. we also combine the maps with the full planck maps, resulting in maps that have the best features of both planck and act: planck's nearly white noise on intermediate and large angular scales and act's high-resolution and sensitivity on small angular scales. the maps cover over 18 000 square degrees, nearly half the full sky, at 100, 150 and 220 ghz. they reveal 4 000 optically-confirmed clusters through the sunyaev zel'dovich effect (sz) and 18 500 point source candidates at > 5σ, the largest single collection of sz clusters and millimeter wave sources to date. the multi-frequency maps provide millimeter images of nearby galaxies and individual milky way nebulae, and even clear detections of several nearby stars. other anticipated uses of these maps include, for example, thermal sz and kinematic sz cluster stacking, cmb cluster lensing and galactic dust science. the method itself has negligible bias. however, due to the preliminary nature of some of the component data sets, we caution that these maps should not be used for precision cosmological analysis. the maps are part of act dr5, and will be made available on \href{https://lambda.gsfc.nasa.gov/}{lambda} no later than three months after the journal publication of this article, along with an interactive sky atlas. | the atacama cosmology telescope: arcminute-resolution maps of 18 000 square degrees of the microwave sky from act 2008-2018 data combined with planck |
we present lyman continuum (lyc) radiation escape fraction (fesc) measurements for 183 spectroscopically confirmed star-forming galaxies in the redshift range 3.11 < z < 3.53 in the chandra deep field south. we use ground-based imaging to measure fesc, and use ground- and space-based photometry to derive galaxy physical properties using spectral energy distribution (sed) fitting. we additionally derive [o iii] + h β equivalent widths (that fall in the observed k band) by including nebular emission in sed fitting. after removing foreground contaminants, we report the discovery of 11 new candidate lyc leakers at ≳ 2σ level, with fesc in the range 0.14-0.85. from non-detections, we place 1σ upper limits of fesc <0.12, where the lyman-break selected galaxies have fesc <0.11 and 'blindly' discovered galaxies with no prior photometric selection have fesc <0.13. we find a slightly higher 1σ limit of fesc <0.20 from extreme emission line galaxies with rest-frame [o iii] + h β equivalent widths >300 å. for candidate lyc leakers, we find a weak negative correlation between fesc and galaxy stellar masses, no correlation between fesc and specific star-formation rates (ssfrs) and a positive correlation between fesc and ew0([o iii] + h β). the weak/no correlations between stellar mass and ssfrs may be explained by misaligned viewing angles and/or non-coincident time-scales of starburst activity and periods of high fesc. alternatively, escaping radiation may predominantly occur in highly localized star-forming regions, or fesc measurements may be impacted by stochasticity of the intervening neutral medium, obscuring any global trends with galaxy properties. these hypotheses have important consequences for models of reionization. | no strong dependence of lyman continuum leakage on physical properties of star-forming galaxies at ≲ z ≲ 3.5 |
we present atacama large millimeter/submillimeter array and multi-unit spectroscopic explorer observations of the brightest cluster galaxy in abell 2597, a nearby (z = 0.0821) cool core cluster of galaxies. the data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy’s core. its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot x-ray atmosphere. the clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. the entire scenario is therefore consistent with a galaxy-spanning “fountain,” wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. all velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long lived. the data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales. | a galaxy-scale fountain of cold molecular gas pumped by a black hole |
we discuss the rest-frame optical emission line spectra of a large (∼50) sample of z ∼ 3.1 lyα emitting galaxies (laes) whose physical properties suggest such sources are promising analogs of galaxies in the reionization era. reliable lyman continuum (lyc) escape fractions have now been determined for a large sample of such laes from the lyman continuum escape survey (laces) undertaken via deep hubble space telescope imaging in the ssa22 survey area reported in fletcher et al. using new measures of [o ii] emission secured from keck mosfire spectra we re-examine, for a larger sample, earlier claims that lyc leakages may correlate with the nebular emission line ratio [o iii]/[o ii] as expected for density-bound h ii regions. we find that a large [o iii]/[o ii] line ratio is indeed a necessary condition for lyc leakage, strengthening earlier claims made using smaller samples at various redshifts. however, not all laes with large [o iii]/[o ii] line ratios are leakers and leaking radiation appears not to be associated with differences in other spectral diagnostics. this suggests the detection of leaking radiation is modulated by an additional property, possibly the viewing angle for porous h ii regions. we discuss our new results in the context of the striking bimodality of lae leakers and non-leakers found in the laces program and the implications for the sources of cosmic reionization. | the lyman continuum escape survey. ii. ionizing radiation as a function of the [o iii]/[o ii] line ratio |
prior to the launch of jwst, spitzer/irac photometry offers the only means of studying the rest-frame optical properties of z >7 galaxies. many such high-redshift galaxies display a red [3.6]-[4.5] micron colour, often referred to as the 'irac excess', which has conventionally been interpreted as arising from intense [o iii]+h β emission within the [4.5] micron bandpass. an appealing aspect of this interpretation is similarly intense line emission seen in star-forming galaxies at lower redshift as well as the redshift-dependent behaviour of the irac colours beyond z ∼ 7 modelled as the various nebular lines move through the two bandpasses. in this paper, we demonstrate that, given the photometric uncertainties, established stellar populations with balmer (4000 å rest frame) breaks, such as those inferred at z > 9 where line emission does not contaminate the irac bands, can equally well explain the redshift-dependent behaviour of the irac colours in 7 ≲ z ≲ 9 galaxies. we discuss possible ways of distinguishing between the two hypotheses using alma measures of [o iii] λ88 micron and dust continuum fluxes. prior to further studies with jwst, we show that the distinction is important in determining the assembly history of galaxies in the first 500 myr. | interpreting the spitzer/irac colours of 7 ≤ z ≤ 9 galaxies: distinguishing between line emission and starlight using alma |
we present numerical models of the nebular emission from h ii regions around young stellar populations over a range of compositions and ages. the synthetic stellar populations include both single stars and interacting binary stars. we compare these models to the observed emission lines of 254 h ii regions of 13 nearby spiral galaxies and 21 dwarf galaxies drawn from archival data. the models are created using the combination of the bpass (binary population and spectral synthesis) code with the photoionization code cloudy to study the differences caused by the inclusion of interacting binary stars in the stellar population. we obtain agreement with the observed emission line ratios from the nearby star-forming regions and discuss the effect of binary-star evolution pathways on the nebular ionization of h ii regions. we find that at population ages above 10 myr, single-star models rapidly decrease in flux and ionization strength, while binary-star models still produce strong flux and high [o iii]/h β ratios. our models can reproduce the metallicity of h ii regions from spiral galaxies, but we find higher metallicities than previously estimated for the h ii regions from dwarf galaxies. comparing the equivalent width of h β emission between models and observations, we find that accounting for ionizing photon leakage can affect age estimates for h ii regions. when it is included, the typical age derived for h ii regions is 5 myr from single-star models, and up to 10 myr with binary-star models. this is due to the existence of binary-star evolution pathways, which produce more hot wolf-rayet and helium stars at older ages. for future reference, we calculate new bpass binary maximal starburst lines as a function of metallicity, and for the total model population, and present these in appendix a. | emission-line diagnostics of nearby h ii regions including interacting binary populations |
the redshift range z = 4-6 marks a transition phase between primordial and mature galaxy formation in which galaxies considerably increase their stellar mass, metallicity, and dust content. the study of galaxies in this redshift range is therefore important to understanding early galaxy formation and the fate of galaxies at later times. here, we investigate the burstiness of the recent star formation history (sfh) of 221z ∼ 4.5 main-sequence galaxies at {log}(m/{m}⊙ )> 9.7 by comparing their ultra-violet (uv) continuum, hα luminosity, and hα equivalent-width (ew). the hα properties are derived from the spitzer [3.6 μm]-[4.5 μm] broadband color, thereby properly taking into account model and photometric uncertainties. we find a significant scatter between hα- and uv-derived luminosities and star formation rates (sfrs). about half of the galaxies show a significant excess in hα compared to expectations from a constant smooth sfh. we also find a tentative anticorrelation between hα ew and stellar mass, ranging from 1000 å at {log}(m/{m}⊙ )< 10 to below 100 å at {log}(m/{m}⊙ )> 11. consulting models suggests that most z ∼ 4.5 galaxies had a burst of star formation within the last 50 myr, increasing their sfrs by a factor of >5. the most massive galaxies on the other hand might decrease their sfrs and may be transitioning to a quiescent stage by z = 4. we identify differential dust attenuation (f) between stars and nebular regions as the main contributor to the uncertainty. with local galaxies selected by increasing hα ew (reaching values similar to high-z galaxies), we predict that f approaches unity at z > 4, consistent with the extrapolation of measurements out to z = 2. | the recent burstiness of star formation in galaxies at z ∼ 4.5 from hα measurements |
we present accurate mass and thermodynamic profiles for 57 galaxy clusters observed with the chandra x-ray observatory. we investigate the effects of local gravitational acceleration in central cluster galaxies, and explore the role of the local free-fall time ({t}{ff}) in thermally unstable cooling. we find that the radially averaged cooling time ({t}{cool}) is as effective an indicator of cold gas, traced through its nebular emission, as the ratio {t}{cool}/{t}{ff}. therefore, {t}{cool} primarily governs the onset of thermally unstable cooling in hot atmospheres. the location of the minimum {t}{cool}/{t}{ff}, a thermodynamic parameter that many simulations suggest is key in driving thermal instability, is unresolved in most systems. consequently, selection effects bias the value and reduce the observed range in measured {t}{cool}/{t}{ff} minima. the entropy profiles of cool-core clusters are characterized by broken power laws down to our resolution limit, with no indication of isentropic cores. we show, for the first time, that mass isothermality and the k\propto {r}2/3 entropy profile slope imply a floor in {t}{cool}/{t}{ff} profiles within central galaxies. no significant departures of {t}{cool}/{t}{ff} below 10 are found. this is inconsistent with models that assume thermally unstable cooling ensues from linear perturbations at or near this threshold. we find that the inner cooling times of cluster atmospheres are resilient to active galactic nucleus (agn)-driven change, suggesting gentle coupling between radio jets and atmospheric gas. our analysis is consistent with models in which nonlinear perturbations, perhaps seeded by agn-driven uplift of partially cooled material, lead to cold gas condensation. | the onset of thermally unstable cooling from the hot atmospheres of giant galaxies in clusters: constraints on feedback models |
a quantitative understanding of the elemental and isotopic fractionations recorded in the compositions of the chondritic meteorites would provide fundamental constraints for astrophysical models of early solar system evolution. here it is shown through least squares fitting that almost all features of the bulk elemental and isotopic compositions of the main carbonaceous chondrite (cc) groups, as well as the ungrouped tagish lake (c2) meteorite, can be reproduced using mixtures of the same four components. the fractionations amongst the non-ccs (ordinary, rumuruti and enstatite chondrites) are distinctly different to those in the ccs and are the subject of a separate study (alexander, 2019). the four cc components are: (1) a 'chondrule' (or chondrule precursor) component that partially lost fe,ni metal and volatiles, but is otherwise ci-like, (2) the cc-ri component that has a refractory inclusion-like bulk composition and is largely responsible for the refractory element enrichments and nucleosynthetic isotope anomalies in the bulk ccs, (3) anhydrous and reduced but otherwise ci-like matrix that accounts for almost all of the most volatile element (e.g., zn, se and c) contents of the ccs, and (4) water with relatively high δ17o and δ18o values. comparison of the inferred component compositions to additional meteoritic constraints produces some notable results. the ɛ48ca ≈ 8 and ɛ50ti ≈ 8 values for the cc-ri component are consistent with the average values for refractory inclusions. on the other hand, the ɛ54cr ≈ -10 is not, but is required by the negative correlation between ɛ50ti and ɛ54cr amongst the bulk ccs. the cc-ri component may be comprised of a more cai-like sub-component that carries the ɛ48ca and ɛ50ti anomalies, and a more ferromagnesian sub-component that carries the negative ɛ54cr anomalies. the compositions of the volatile and metal subcomponents lost from the 'chondrule' component are consistent with condensation models, suggesting that the fractionations predated chondrule formation. the isotopic compositions of chondrules from the more cc-ri-rich cc groups (e.g., cv, co and cm) seem to require the addition of some of the cc-ri component to their precursors. the assumption that matrix is ci-like is inconsistent with chondrule-matrix complementarity, but is justified by the success of the fits and the relatively uniform and ci-like abundances of organics and presolar grains in the matrices of the most primitive ccs. the inferred δ17o = 3.5‰ for the water component is consistent with most constraints from secondary phases in the ccs. the large o isotopic mass fractionation (δ18o ≈ 18-21‰) of the water is consistent with ∼89-95% condensation of ice from a vapor under rayleigh conditions at 150-170 k. the water was entirely accreted with the matrix with fairly constant (0.32 ± 0.06 by wt.) and ci-like (∼0.38 by wt.) water/matrix ratios. these water/matrix ratios are much less than the water/rock ratio of one that is often cited for a nebula of solar composition, but can be explained if much of the c in the cc formation regions was present as co and co2, and the abundance of ch4 was low. | quantitative models for the elemental and isotopic fractionations in chondrites: the carbonaceous chondrites |
we present a photometric and spectroscopic analysis of the ultraluminous and slowly evolving 03fg-like type ia sn 2021zny. our observational campaign starts from ~5.3 h after explosion (making sn 2021zny one of the earliest observed members of its class), with dense multiwavelength coverage from a variety of ground- and space-based telescopes, and is concluded with a nebular spectrum ~10 months after peak brightness. sn 2021zny displayed several characteristics of its class, such as the peak brightness (mb = -19.95 mag), the slow decline (δm15(b) = 0.62 mag), the blue early-time colours, the low ejecta velocities, and the presence of significant unburned material above the photosphere. however, a flux excess for the first ~1.5 d after explosion is observed in four photometric bands, making sn 2021zny the third 03fg-like event with this distinct behaviour, while its +313 d spectrum shows prominent [o i] lines, a very unusual characteristic of thermonuclear sne. the early flux excess can be explained as the outcome of the interaction of the ejecta with $\sim 0.04\, \mathrm{m_{\odot }}$ of h/he-poor circumstellar material at a distance of ~1012 cm, while the low ionization state of the late-time spectrum reveals low abundances of stable iron-peak elements. all our observations are in accordance with a progenitor system of two carbon/oxygen white dwarfs that undergo a merger event, with the disrupted white dwarf ejecting carbon-rich circumstellar material prior to the primary white dwarf detonation. | sn 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event |
stars stripped of their envelopes from interaction with a binary companion emit a significant fraction of their radiation as ionizing photons. they are potentially important stellar sources of ionizing radiation, however, they are still often neglected in spectral synthesis simulations or simulations of stellar feedback. in anticipating the large datasets of galaxy spectra from the upcoming james webb space telescope, we modeled the radiative contribution from stripped stars by using detailed evolutionary and spectral models. we estimated their impact on the integrated spectra and specifically on the emission rates of h i-, he i-, and he ii-ionizing photons from stellar populations. we find that stripped stars have the largest impact on the ionizing spectrum of a population in which star formation halted several myr ago. in such stellar populations, stripped stars dominate the emission of ionizing photons, mimicking a younger stellar population in which massive stars are still present. our models also suggest that stripped stars have harder ionizing spectra than massive stars. the additional ionizing radiation, with which stripped stars contribute affects observable properties that are related to the emission of ionizing photons from stellar populations. in co-eval stellar populations, the ionizing radiation from stripped stars increases the ionization parameter and the production efficiency of hydrogen ionizing photons. they also cause high values for these parameters for about ten times longer than what is predicted for massive stars. the effect on properties related to non-ionizing wavelengths is less pronounced, such as on the ultraviolet continuum slope or stellar contribution to emission lines. however, the hard ionizing radiation from stripped stars likely introduces a characteristic ionization structure of the nebula, which leads to the emission of highly ionized elements such as o2+ and c3+. we, therefore, expect that the presence of stripped stars affects the location in the bpt diagram and the diagnostic ratio of o iii to o ii nebular emission lines. our models are publicly available through cds database and on the starburst99 website. our models are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/629/a134 | the impact of stars stripped in binaries on the integrated spectra of stellar populations |
we present very faint dropout galaxies at z ∼ 6-9 with a stellar mass m⋆ down to ${m}_{\star }\sim {10}^{6}\,{m}_{\odot }$ that are found in deep optical/near-infrared (nir) images of the full data sets of the hubble frontier fields (hff) program in conjunction with deep ground-based and spitzer images and gravitational-lensing magnification effects. we investigate stellar populations of the hff dropout galaxies with the optical/nir photometry and beagle models made of self-consistent stellar population synthesis and photoionization models, carefully including strong nebular emission impacting on the photometry. we identify 453 galaxies with ${m}_{\star }\sim {10}^{6}\mbox{--}{10}^{9}\,{m}_{\odot }$ . our best-estimate ${m}_{\star }/{l}_{\mathrm{uv}}$ function is comparable to a model of star formation duration time of 100 myr that is assumed in bouwens et al. we derive the galaxy stellar mass functions (gsmfs) at z ∼ 6-9 that agree with those obtained by previous studies at ${m}_{\star }\gtrsim {10}^{8}\,{m}_{\odot }$ , and that extend to ${m}_{\star }\sim {10}^{6}\,{m}_{\odot }$ . estimating the stellar mass densities ${\rho }_{\star }$ with the gsmfs, we find a very slow evolution from z ∼ 9 to z ∼ 6-7, which is consistent with the one estimated from star formation rate density measurements. in conjunction with the estimates of the galaxy effective radii re on the source plane, we have pinpointed four objects with low stellar masses ( ${m}_{\star }\leqslant {10}^{7}\,{m}_{\odot }$ ) and very compact morphologies ( ${r}_{{\rm{e}}}\leqslant 40$ pc) that are comparable with those of globular clusters (gcs) in the milky way today. these objects are candidates of star clusters, some of which may be related to gcs today. | early low-mass galaxies and star-cluster candidates at z ∼ 6-9 identified by the gravitational-lensing technique and deep optical/near-infrared imaging |
we present spectroscopic redshifts of {\text{}}{s}870μ {{m}} ≳ 2 mjy submillimeter galaxies (smgs), which have been identified from the alma follow-up observations of 870 μm detected sources in the extended chandra deep field south (the alma-less survey). we derive spectroscopic redshifts for 52 smgs, with a median of z = 2.4 ± 0.1. however, the distribution features a high-redshift tail, with ∼23% of the smgs at z≥slant 3. spectral diagnostics suggest that the smgs are young starbursts, and the velocity offsets between the nebular emission and uv ism absorption lines suggest that many are driving winds, with velocity offsets of up to 2000 km s-1. using the spectroscopic redshifts and the extensive uv-to-radio photometry in this field, we produce optimized spectral energy distributions (seds) using magphys, and use the seds to infer a median stellar mass of {m}\star= (6 ± 1)× 1010 m {}⊙for our smgs with spectroscopic redshift. by combining these stellar masses with the star formation rates (measured from the far-infrared seds), we show that smgs (on average) lie a factor of ∼5 above the so-called “main sequence” at z∼ 2. we provide this library of 52 template fits with robust and uniquely well-sampled seds as a resource for future studies of smgs, and also release the spectroscopic catalog of ∼2000 (mostly infrared-selected) galaxies targeted as part of the spectroscopic campaign. | an alma survey of submillimeter galaxies in the extended chandradeep field south: spectroscopic redshifts |
we present the discovery and analysis of j1316+2614 at z = 3.6130, a uv-bright star-forming galaxy (muv ≃ -24.7) with large escape of lyman continuum (lyc) radiation. j1316+2614 is a young (≃10 myr) star-forming galaxy with sfr ≃ 500 m⊙ yr-1 and a starburst mass of log(m⋆/m⊙) ≃ 9.7. it shows a very steep uv continuum, βuv = -2.59 ± 0.05, consistent with residual dust obscuration, e(b - v) ≃ 0. lyc emission is detected with high significance (≃17σ) down to 830 å, for which a very high relative (absolute) lyc escape fraction $f_{\rm esc} \rm (lyc) \simeq 0.92$ (≃0.87) is inferred. the contribution of a foreground or active galactic nucleus contamination to the lyc signal is discussed, but is unlikely. j1316+2614 is the most powerful ionizing source known among the star-forming galaxy population, both in terms of production (qh ≈ 1056 s-1) and escape of ionizing photons ($f_{\rm esc} \rm (lyc) \approx 0.9$). nebular emission in ly α, h β, and other rest-frame optical lines are detected, but these are weak ($ew_{0} \rm [h\beta ] \simeq 35$ å), with their strengths reduced roughly by $\simeq 90{{\ \rm per\ cent}}$. j1316+2614 is the first case known where the effect of large escape of ionizing photons on the strength of nebular lines and continuum emission is clearly observed. gas inflows are detected in j1316+2614 from the blue-dominated peak ly α emission (with a blue-to-red peak line ratio iblue/ired ≃ 3.7) and redshifted interstellar medium absorption (≃100 km s-1). our results suggest that j1316+2614 is undergoing a gas compaction event, possibly representing a short-lived phase in the evolution of massive and compact galaxies, where strong gas inflows have triggered an extreme star formation episode and nearly 100 per cent lyc photons are escaping. | an extreme blue nugget, uv-bright starburst at z = 3.613 with 90 per cent of lyman continuum photon escape |
deep rest-optical observations are required to accurately constrain the stellar populations of z ~ 8 galaxies. due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. to revolutionize the present characterization of z ~ 8 galaxies, we exploit the ultradeep (~27 mag, 3σ) spitzer/infrared array camera (irac) 3.6 and 4.5 μm data, probing the rest-frame optical at z ~ 8, over ~200 arcmin2 of the goods fields from the recently completed goods re-ionization era wide-area treasury from spitzer program (greats), combined with observations in the cosmic assembly near-infrared deep extragalactic legacy survey (candels)/ultra deep survey (uds) and candels/cosmic evolution survey (cosmos) fields. we stacked ≳100 z ~ 8 lyman-break galaxies in four bins of uv luminosity (m uv ~ -20.7 to -18.4 mag) and study their h 160 - [3.6] and [3.6]-[4.5] colors. we find young ages (≲100 myr) for the three faintest stacks, inferred from their blue h 160 - [3.6] ~ 0 mag colors, consistent with a negative balmer break. meanwhile, the redder h 160 - [3.6] color seen in the brightest stack is suggestive of slightly older ages. we explored the existence of a correlation between the uv luminosity and age, and find either no trend or fainter galaxies being younger. the stacked seds also exhibit very red [3.6]-[4.5] ~ 0.5 mag colors, indicative of intense [o iii]+hβ nebular emission and star formation rate (sfr). the correspondingly high specific sfrs, ssfr ≳10 gyr-1, are consistent with recent determinations at similar redshifts and higher luminosities, and support the coevolution between the ssfr and the specific halo mass accretion rate. | blue rest-frame uv-optical colors in z 8 galaxies from greats: very young stellar populations at650 myr of cosmic time |
we derive stringent constraints on the persistent source associated with frb 121102: size 0.3< {r}17.5 =(r/{10}17.5 {cm})< 3, age < {10}2.5 year, energy e≈ {10}49{({\varepsilon }e/0.2{gev})}3 erg, characteristic electron energy 0.1≤slant {\varepsilon }e/1 {gev}≤slant 0.5; the radiating plasma is confined by a cold plasma of mass {m}c< {10}-1.5{r}17.54 {m}⊙ ; these properties are inconsistent with typical “magnetar wind nebulae” model predictions. the fact that {\varepsilon }e∼ {m}p{c}2 suggests that the hot plasma was created by the ejection of a mildly relativistic, m≈ e/{c}2≈ {10}-5 {m}⊙shell, which propagated into an extended ambient medium or collided with a pre-ejected shell. independent of the persistent source model, we suggest a physical mechanism for the generation of fast radio bursts (frbs): the ejection from an underlying compact object, {r}s={10}6{r}s,6 cm, of highly relativistic shells with energy {e}s={10}41{e}41 erg and lorentz factor {γ }s={10}3{e}411/8{r}s,6-3/8, into a surrounding e - p plasma with density n∼ {10}-1 {{cm}}-3 (consistent with that inferred for the persistent source). for essimilar to observed frb energies, plasma conditions appropriate for strong synchrotron maser emission at {ν }{coh.}≈ 0.5{e}411/4{r}s,6-3/4 {ghz} are formed. a significant fraction of the deposited energy is converted to an frb with duration {r}s/c, accompanied by ∼10 mev gamma-rays carrying less energy than the frb. the inferred energy and mass associated with the source suggest some type of a “weak stellar explosion,” where a neutron star is formed with relatively low mass and energy ejection. however, the current upper limit on r does not allow one to rule out {m}c∼ 1 {m}⊙ , or the ejection of a larger mass well before the ejection of the confining shell. | on the origin of fast radio bursts (frbs) |
infrared and nebular lines provide some of our best probes of the physics regulating the properties of the interstellar medium (ism) at high redshift. however, interpreting the physical conditions of high-redshift galaxies directly from emission lines remains complicated due to inhomogeneities in temperature, density, metallicity, ionization parameter, and spectral hardness. we present a new suite of cosmological, radiation-hydrodynamics simulations, each centred on a massive lyman-break galaxy that resolves such properties in an inhomogeneous ism. many of the simulated systems exhibit transient but well-defined gaseous discs that appear as velocity gradients in [c ii] 157.6 μm emission. spatial and spectral offsets between [c ii] 157.6 μm and [o iii] 88.33 μm are common, but not ubiquitous, as each line probes a different phase of the ism. these systems fall on the local [c ii]-sfr relation, consistent with newer observations that question previously observed [c ii] 157.6 μm deficits. our galaxies are consistent with the nebular line properties of observed z ∼ 2-3 galaxies and reproduce offsets on the bpt and mass-excitation diagrams compared to local galaxies due to higher star formation rate (sfr), excitation, and specific-sfr, as well as harder spectra from young, metal-poor binaries. we predict that local calibrations between h α and [o ii] 3727 å luminosity and galaxy sfr apply up to z > 10, as do the local relations between certain strong line diagnostics (r23 and [o iii] 5007 å/h β) and galaxy metallicity. our new simulations are well suited to interpret the observations of line emission from current (alma and hst) and upcoming facilities (jwst and ngvla). | probing cosmic dawn with emission lines: predicting infrared and nebular line emission for alma and jwst |
ninety per cent of baryons are located outside galaxies, either in the circumgalactic or intergalactic medium1,2. theory points to galactic winds as the primary source of the enriched and massive circumgalactic medium3-6. winds from compact starbursts have been observed to flow to distances somewhat greater than ten kiloparsecs7-10, but the circumgalactic medium typically extends beyond a hundred kiloparsecs3,4. here we report optical integral field observations of the massive but compact galaxy sdss j211824.06+001729.4. the oxygen [o uc(ii)] lines at wavelengths of 3726 and 3729 angstroms reveal an ionized outflow spanning 80 by 100 square kiloparsecs, depositing metal-enriched gas at 10,000 kelvin through an hourglass-shaped nebula that resembles an evacuated and limb-brightened bipolar bubble. we also observe neutral gas phases at temperatures of less than 10,000 kelvin reaching distances of 20 kiloparsecs and velocities of around 1,500 kilometres per second. this multi-phase outflow is probably driven by bursts of star formation, consistent with theory11,12. | a 100-kiloparsec wind feeding the circumgalactic medium of a massive compact galaxy |
context. the orion molecular cloud is the nearest massive-star forming region. massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies.aims: we aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. velocity-resolved observations of the [c ii] 158 μm fine-structure line allow us to study the kinematics of uv-illuminated gas. here, we present a square-degree-sized map of [c ii] emission from the orion nebula complex at a spatial resolution of 16'' and high spectral resolution of 0.2 km s-1, covering the entire orion nebula (m 42) plus m 43 and the nebulae ngc 1973, 1975, and 1977 to the north. we compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them.methods: we use [c ii] 158 μm line observations over an area of 1.2 deg2 in the orion nebula complex obtained by the upgreat instrument onboard sofia.results: the bubble blown by the o7v star θ1 ori c in the orion nebula expands rapidly, at 13 km s-1. simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 myr. m 43 with the b0.5v star nu ori also exhibits an expanding bubble structure, with an expansion velocity of 6 km s-1. comparison with analytical models for the pressure-driven expansion of h ii regions gives an age estimate of 0.02 myr. the bubble surrounding ngc 1973, 1975, and 1977 with the central b1v star 42 orionis expands at 1.5 km s-1, likely due to the over-pressurized ionized gas as in the case of m 43. we derive an age of 0.4 myr for this structure.conclusions: we conclude that the bubble of the orion nebula is driven by the mechanical energy input by the strong stellar wind from θ1 ori c, while the bubbles associated with m 43 and ngc 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars. | expanding bubbles in orion a: [c ii] observations of m 42, m 43, and ngc 1977 |
planets with 2 r⊕ < r < 3 r⊕ and orbital period <100 days are abundant; these sub-neptune exoplanets are not well understood. for example, kepler sub-neptunes are likely to have deep magma oceans in contact with their atmospheres, but little is known about the effect of the magma on the atmosphere. here we study this effect using a basic model, assuming that volatiles equilibrate with magma at t ∼ 3000 k. for our fe-mg-si-o-h model system, we find that chemical reactions between the magma and the atmosphere and dissolution of volatiles into the magma are both important. thus, magma matters. for h, most moles go into the magma, so the mass target for both h2 accretion and h2 loss models is weightier than is usually assumed. the known span of magma oxidation states can produce sub-neptunes that have identical radius but with total volatile masses varying by 20-fold. thus, planet radius is a proxy for atmospheric composition but not for total volatile content. this redox diversity degeneracy can be broken by measurements of atmosphere mean molecular weight. we emphasize h2 supply by nebula gas, but also consider solid-derived h2o. we find that adding h2o to fe probably cannot make enough h2 to explain sub-neptune radii because >103 km thick outgassed atmospheres have high mean molecular weight. the hypothesis of magma-atmosphere equilibration links observables such as atmosphere h2o/h2 ratio to magma feo content and planet formation processes. our model's accuracy is limited by the lack of experiments (lab and/or numerical) that are specific to sub-neptunes; we advocate for such experiments. | atmosphere origins for exoplanet sub-neptunes |
we analyze the rest-optical emission-line ratios of star-forming galaxies at 2.7 ≤ z < 6.5 drawn from the cosmic evolution early release science (ceers) survey and their relationships with stellar mass (m *). our analysis includes both line ratios based on the [n ii] λ6583 feature ([n ii] λ6583/hα, ([o iii] λ5007/hβ)/([n ii] λ6583/hα) (o3n2), and [n ii] λ6583/[o ii] λ3727) and those featuring α-elements ([o iii] λ5007/hβ, [o iii] λ5007/[o ii] λ3727 (o32), ([o iii] λλ4959, 5007 + [o ii] λ3727)/hβ (r23), and [ne iii] λ3869/[o ii] λ3727). given the typical flux levels of [n ii] λ6583 and [ne iii] λ3869, which are undetected in the majority of individual ceers galaxies at 2.7 ≤ z < 6.5, we construct composite spectra in bins of m * and redshift. using these composite spectra, we compare the relationships between emission-line ratios and m * at 2.7 ≤ z < 6.5 with those observed at lower redshift. while there is significant evolution toward higher excitation (e.g., higher [o iii] λ5007/hβ, o32, o3n2) and weaker nitrogen emission (e.g., lower [n ii] λ6583/hα and [n ii] λ6583/[o ii] λ3727) between z ~ 0 and z ~ 3, we find in most cases that there is no significant evolution in the relationship between line ratio and m * beyond z ~ 3. the [ne iii] λ3869/[o ii] λ3727 ratio is anomalous in showing evidence for significant elevation at 4.0 ≤ z < 6.5 at fixed mass, relative to z ~ 3.3. collectively, however, our empirical results suggest no significant evolution in the mass-metallicity relationship at 2.7 ≤ z < 6.5. representative galaxy samples and metallicity calibrations based on existing and upcoming jwst/nirspec observations will be required to translate these empirical scaling relations into ones tracing chemical enrichment and gas cycling and to distinguish among descriptions of feedback in galaxy formation simulations at z > 3. | jwst/nirspec measurements of the relationships between nebular emission-line ratios and stellar mass at z 3-6 |
nebular-phase observations and spectral models of type ic superluminous supernovae (slsne) are presented. lsq14an and sn 2015bn both display late-time spectra similar to galaxy-subtracted spectra of sn 2007bi, and the class shows strong similarity with broad-lined sne ic such as sn 1998bw. near-infrared observations of sn 2015bn show a strong ca ii triplet, o i 9263, o i 1.13 μm, and mg i 1.50 μm, but no distinct he, si, or s emission. the high ca ii nir/[ca ii] 7291, 7323 ratio of ∼2 indicates a high electron density of {n}e≳ {10}8 cm-3. spectral models of oxygen-zone emission are investigated to put constraints on the emitting region. models require m({{o}} - {zone})≳ 10 m⊙ to produce enough [o i] 6300, 6364 luminosity, irrespective of the powering situation and the density. the high oxygen-zone mass, supported by high estimated magnesium masses, points to explosions of massive co cores, requiring {m}{zams}≳ 40 {m}⊙ . collisions of pair-instability pulsations do not provide enough mass to account for the emission. [o ii] and [o iii] lines emerge naturally in many models, which strengthens the identification of broad [o ii] 7320, 7330, [o iii] 4363, and [o iii] 4959, 5007 in some spectra. a small filling factor f≲ 0.01 for the o/mg zone is needed to produce enough luminosity in mg i] 4571, mg i 1.504 μm, and o i recombination lines, which shows that the ejecta is clumped. we review the constraints from the nebular spectral modeling in the context of the various scenarios proposed for slsne. | long-duration superluminous supernovae at late times |
the hydrogen-isotope [deuterium/hydrogen (d/h)] ratio of earth can be used to constrain the origin of its water. however, the most accessible reservoir, earth’s oceans, may no longer represent the original (primordial) d/h ratio, owing to changes caused by water cycling between the surface and the interior. thus, a reservoir completely isolated from surface processes is required to define earth’s original d/h signature. here we present data for baffin island and icelandic lavas, which suggest that the deep mantle has a low d/h ratio (δd more negative than -218 per mil). such strongly negative values indicate the existence of a component within earth’s interior that inherited its d/h ratio directly from the protosolar nebula. | evidence for primordial water in earth’s deep mantle |
we derive new self-consistent theoretical uv, optical, and ir diagnostics for the interstellar medium (ism) pressure and electron density in the ionized nebulae of star-forming galaxies. our uv diagnostics utilize the intercombination, forbidden, and resonance lines of silicon, carbon, aluminum, neon, and nitrogen. we also calibrate the optical and ir forbidden lines of oxygen, argon, nitrogen, and sulfur. we show that line ratios used as ism pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas. in addition, the traditional electron density diagnostic [s ii] λ6731/[s ii] λ6717 is strongly dependent on the gas-phase metallicity. we show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae. the [s ii] and [o ii] ratios are produced in different zones and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant. we review the temperature and density distributions observed within h ii regions and discuss the implications of these distributions on measuring the electron density of the gas. many h ii regions contain radial variations in density. we suggest that the ism pressure is a more meaningful quantity to measure in h ii regions or galaxies. specific combinations of line ratios can cover the full range of ism pressures (4 < log(p/k) < 9). as h ii regions become resolved at increasingly high redshift through the next generation of telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day. | theoretical ism pressure and electron density diagnostics for local and high-redshift galaxies |
most galaxies comparable to or larger than the mass of the milky way host hot, x-ray emitting atmospheres, and many such galaxies are radio sources. hot atmospheres and radio jets and lobes are the ingredients of radio-mechanical active galactic nucleus (agn) feedback. while a consensus has emerged that such feedback suppresses cooling of hot cluster atmospheres, less attention has been paid to massive galaxies where similar mechanisms are at play. observation indicates that the atmospheres of elliptical and s0 galaxies were accreted externally during the process of galaxy assembly and augmented significantly by stellar mass loss. their atmospheres have entropy and cooling time profiles that are remarkably similar to those of central cluster galaxies. about half display filamentary or disky nebulae of cool and cold gas, much of which has likely cooled from the hot atmospheres. we review the observational and theoretical perspectives on thermal instabilities in galactic atmospheres and the evidence that agn heating is able to roughly balance the atmospheric cooling. such heating and cooling may be regulating star formation in all massive spheroids at late times. | hot atmospheres, cold gas, agn feedback and the evolution of early type galaxies: a topical perspective |
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