abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
this tutorial explains the procedure used to analyze an optical emission-line spectrum produced by a nebula ionized by massive star formation. particularly, the methodology used to derive physical properties, such as electron density and temperature, and the ionic abundances of the most representative elements whose emission lines are present in the optical spectrum is described. the main focus is on the direct method, which is based on the measurement of the electron temperature to derive the abundances, given that the ionization and thermal equilibrium of the ionized gas is dominated by the metallicity. the ionization correction factors used to obtain total abundances from the abundances of some of their ions are also given. finally, some strong-line methods to derive abundances are described. such methods are used when no estimation of the temperature can be derived, but which can be consistent with the direct method if they are empirically calibrated. | ionized gaseous nebulae abundance determination from the direct method |
iron is the only polyvalent major element, and controls reduction-oxidation (redox) reactions in a host of geologic processes and reservoirs, from the mineral- to planetary-scale, on earth and in space. mass transfer of fe is often accompanied by changes in bonding environment, meaning the resultant variation in bond-strength in crystals, liquids and gases induces stable isotope fractionation, even at high temperatures. in the absence of iron exchange, electron transfer can also affect iron's valence state and calculated oxygen fugacity (fo2), however its isotope composition remains unchanged. thus, iron isotopes are a powerful tool to investigate processes that involve mass transfer, redox reactions and changes in bonding environment in planetary systems. primitive chondritic meteorites show remarkable isotopic homogeneity, δ57 fe = - 0.01 ± 0.01 ‰ (2se), over a wide range of fe/mg vs ni/mg, a proxy for fo2 in the solar nebula. in chondrites, there are iron isotope differences between metal and silicates that become more pronounced at higher metamorphic grades. however, on a planetary scale, mars and vesta overlap with chondrites, preserving no trace of core formation or volatile depletion on these bodies. upon assessment of pristine lherzolites, the bulk silicate earth is heavier than chondrites (δ57 fe = + 0.05 ± 0.01 ‰; 2se), and similar to or slightly lighter than the moon. that the mantles of some differentiated inner solar system bodies extend to heavier compositions (+ 0.2 ‰) than chondrites may principally result from volatile depletion either at a nebular or late accretion stage. within terrestrial silicate reservoirs, iron isotopes provide insight into petrogenetic and geodynamic processes. partial melting of the upper mantle produces basalts that are heavier than their sources, scaling with degree of melting and driving the increasingly refractory peridotite to lighter compositions. mid-ocean ridge basalts (morbs) are homogeneous to δ57 fe = 0.10 ± 0.01 ‰ (2se) after correction to primary magmas, and can be produced from single stage melt extraction. conversely, iron isotopes in arc basalts are more varied (- 0.2 <δ57 fe (‰) < + 0.2) than can be produced from partial melting. their iron isotope compositions are significantly lighter, suggesting they form from mantle re-enriched in light fe and/or more depleted than depleted morb mantle (dmm). if arc sources are more oxidised, an agent other than iron is required. magmatic differentiation drives enrichment in heavy isotopes by partial melting of crustal rocks, fluid exsolution and crystallisation. iron isotope trajectories in evolving magmas depend on their initial fo2 and whether the system is closed or open to oxygen and/or mass exchange. granite end-members carry signatures diagnostic of their tectonic setting, where reduced, anorogenic a-type granites (δ57 fe = + 0.4 ‰) are heavier than more oxidised i-types (δ57 fe = + 0.2 ‰). | iron isotope systematics in planetary reservoirs |
we present the complete sample of stripped-envelope supernova (sn) spectra observed by the lick observatory supernova search (loss) collaboration over the last three decades: 888 spectra of 302 sne, 652 published here for the first time, with 384 spectra (of 92 sne) having photometrically determined phases. after correcting for redshift and milky way dust reddening and reevaluating the spectroscopic classifications for each sn, we construct mean spectra of the three major spectral subtypes (types iib, ib, and ic) binned by phase. we compare measures of line strengths and widths made from this sample to the results of previous efforts, confirming that o i λ7774 absorption is stronger and found at higher velocity in type ic sne than in types ib or iib sne in the first ∼30 days after peak brightness, though the widths of nebular emission lines are consistent across subtypes. we also highlight newly available observations for a few rare subpopulations of interest. | the berkeley sample of stripped-envelope supernovae |
even though sn 2012cg is one of the best-studied type ia supernovae to date, the nature of its progenitor system has been debated in numerous studies. specifically, it is difficult to reconcile recent claims of the detection of a ∼6 {m}⊙ms companion with recent deep, late-time {{h}}α flux limits. in this study we add three new constraints. (1) we analyze a new high-signal-to-noise, nebular-phase, large binocular telescope/mods spectrum of sn 2012cg and place an upper limit on the amount of low-velocity, solar-abundance material removed from a possible companion of < 7.8× {10}-3 {m}⊙ . (2) we use swift x-ray observations to constrain the pre-explosion mass-loss rate to be \dot{m}< {10}-6 {m}⊙{yr}}-1 for {v}{{w}}=100 {km} {{{s}}}-1. (3) we carefully reanalyze a prediscovery master image, and with published light curves of sn 2012cg we estimate the time of first light and conservatively constrain the radius of a roche-lobe overflowing companion to be < 0.24 {r}⊙ . these observations disagree with a large nearby companion, and when considered with other studies of sn 2012cg’s progenitor system, essentially rule out a non-degenerate companion. | strong evidence against a non-degenerate companion in sn 2012cg |
we present a new method to accurately describe the ionization fraction and the size distribution of polycyclic aromatic hydrocarbons (pahs) within astrophysical sources. to this purpose, we have computed the mid-infrared emission spectra of 308 pah molecules of varying sizes, symmetries, and compactness, generated in a range of radiation fields. we show that the intensity ratio of the solo ch out-of-plane bending mode in pah cations and anions (referred to as the '11.0' μm band, falling in the 11.0-11.3 μm region for cations and anions) to their 3.3 μm emission scales with pah size, similarly to the scaling of the 11.2/3.3 ratio with the number of carbon atoms (nc) for neutral molecules. among the different pah emission bands, it is the 3.3 μm band intensity that has the strongest correlation with nc, and drives the reported pah intensity ratio correlations with nc for both neutral and ionized pahs. the 6.2/7.7 intensity ratio, previously adopted to track pah size, shows no evident scaling with nc in our large sample. we define a new diagnostic grid space to probe pah charge and size, using the (11.2 + 11.0)/7.7 and (11.2 + 11.0)/3.3 pah intensity ratios, respectively. we demonstrate the application of the (11.2 + 11.0)/7.7-(11.2 + 11.0)/3.3 diagnostic grid for galaxies m82 and ngc 253, for the planetary nebula ngc 7027, and the reflection nebulae ngc 2023 and ngc 7023. finally, we provide quantitative relations for pah size determination depending on the ionization fraction of the pahs and the radiation field they are exposed to. | probing the size and charge of polycyclic aromatic hydrocarbons |
we present vlt/x-shooter and muse spectroscopy of a faint f814w = 28.60 ± 0.33 ({m}{uv}=-17.0), low-mass (≲{10}7{m}⊙ ), and compact (r eff = 62 pc) freshly star-forming galaxy at z = 3.1169 magnified (16×) by the hubble frontier fields galaxy cluster abell s1063. gravitational lensing allows for a significant jump toward low-luminosity regimes, in moderately high-resolution spectroscopy (r=λ /dλ ∼ 3000{--}7400). we measured c iv λ 1548,1550, he ii λ 1640, o iii]λ 1661,1666, c iii]λ λ 1907,1909, hβ, [o iii]λ λ 4959,5007 emission lines with {fwhm}≲ 50 km s-1 and (de-lensed) fluxes spanning the interval 1.0× {10}-19{--}2× {10}-18 erg s-1 cm-2 at signal-to-noise ratio (s/n) = 4-30. the double-peaked lyα emission with {{δ }}v({red}-{blue})=280(±7) km s-1 and de-lensed fluxes {2.4}({blue)}| {8.5}({red)}× {10}-18 erg s-1 cm-2 (s/n = {38}({blue)}| {110}({red)}) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large [o iii]λ 5007/ [o ii]λ 3727 \gt \quad 10 ratio. we detect c iv λ 1548,1550 resonant doublet in emission, each component with {fwhm}≲ 45 km s-1 and redshifted by +51(±10) km s-1 relative to the systemic redshift. we interpret this as nebular emission tracing an expanding optically thin interstellar medium. both c iv λ 1548,1550 and he ii λ 1640 suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). the ultraviolet slope is remarkably blue, β =-2.95+/- 0.20 ({f}λ ={λ }β ), consistent with a dust-free and young ≲20 myr galaxy. line ratios suggest an oxygen abundance 12 + log(o/h)\quad \lt \quad 7.8. we are witnessing an early episode of star formation in which a relatively low n h iand negligible dust attenuation might favor a leakage of ionizing radiation. this galaxy currently represents a unique low-luminosity reference object for future studies of the reionization epoch with the james webb space telescope. based on observations collected at the european southern observatory for astronomical research in the southern hemisphere under eso programs p095.a-0840, p095.a-0653, p186.a-0798. | high-resolution spectroscopy of a young, low-metallicity optically thin l = 0.02l* star-forming galaxy at z = 3.12 |
we present the rest-frame optical spectroscopic properties of 60 faint (r ab ∼ 27; l ∼ 0.1 l *) lyα-selected galaxies (laes) at z ≈ 2.56. these laes also have rest-uv spectra of their lyα emission line morphologies, which trace the effects of interstellar and circumgalactic gas on the escape of lyα photons. we find that the laes have diverse rest-optical spectra, but their average spectroscopic properties are broadly consistent with the extreme low-metallicity end of the populations of continuum-selected galaxies selected at z ≈ 2-3. in particular, the laes have extremely high [o iii] λ5008/hβ ratios (log([o iii]/hβ) ∼ 0.8) and low [n ii] λ6585/hα ratios (log([n ii]/hα) < 1.15). coupled with a detection of the [o iii] λ4364 auroral line, these measurements indicate that the star-forming regions in faint laes are characterized by high electron temperatures (te≈ 1.8 × 104 k), low oxygen abundances (12 + log(o/h) ≈ 8.04, z neb ≈ 0.22z ⊙), and high excitations with respect to their more luminous continuum-selected analogs. several of our faintest laes have line ratios consistent with even lower metallicities, including six with 12 + log(o/h) ≈ 6.9-7.4 (z neb ≈ 0.02-0.05z ⊙). we interpret these observations in light of new models of stellar evolution (including binary interactions) that have been shown to produce long-lived populations of hot, massive stars at low metallicities. we find that strong, hard ionizing continua are required to reproduce our observed line ratios, suggesting that faint galaxies are efficient producers of ionizing photons and important analogs of reionization-era galaxies. furthermore, we investigate the physical trends accompanying lyα emission across the largest current sample of combined lyα and rest-optical galaxy spectroscopy, including both the 60 kbss-lyα laes and 368 more luminous galaxies at similar redshifts. we find that the net lyα emissivity (parameterized by the lyα equivalent width) is strongly correlated with nebular excitation and ionization properties and weakly correlated with dust attenuation, suggesting that metallicity plays a strong role in determining the observed properties of these galaxies by modulating their stellar spectra, nebular excitation, and dust content. 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 rest-frame optical spectroscopic properties of lyalpha-emitters at z~2.5: the physical origins of strong lyalpha emission |
most massive stars form in dense clusters where gravitational interactions with other stars may be common. the two nearest forming massive stars, the bn object and source i, located behind the orion nebula, were ejected with velocities of ∼29 and ∼13 km s-1 about 500 years ago by such interactions. this event generated an explosion in the gas. new alma observations show in unprecedented detail, a roughly spherically symmetric distribution of over a hundred 12co j = 2-1 streamers with velocities extending from v lsr = -150 to +145 km s-1. the streamer radial velocities increase (or decrease) linearly with projected distance from the explosion center, forming a “hubble flow” confined to within 50″ of the explosion center. they point toward the high proper-motion, shock-excited h2 and [fe ii] “fingertips” and lower-velocity co in the h2 wakes comprising orion's “fingers.” in some directions, the h2 “fingers” extend more than a factor of two farther from the ejection center than the co streamers. such deviations from spherical symmetry may be caused by ejecta running into dense gas or the dynamics of the n-body interaction that ejected the stars and produced the explosion. this ∼1048 erg event may have been powered by the release of gravitational potential energy associated with the formation of a compact binary or a protostellar merger. orion may be the prototype for a new class of stellar explosiozn responsible for luminous infrared transients in nearby galaxies. | the alma view of the omc1 explosion in orion |
the morphology of bipolar planetary nebulae (pne) can be attributed to interactions between a fast wind from the central engine and the dense toroidal-shaped ejecta left over from common envelope (ce) evolution. here we use the 3d hydrodynamic adaptive mesh refinement (amr) code astrobear to study the possibility that bipolar pn outflows can emerge collimated even from an uncollimated spherical wind in the aftermath of a ce event. the output of a single ce simulation via the smoothed particle hydrodynamics (sph) code phantom serves as the initial conditions. four cases of winds, all with high enough momenta to account for observed high momenta pre-pn outflows, are injected spherically from the region of the ce binary remnant into the ejecta. we compare cases with two different momenta and cases with no radiative cooling versus application of optically thin emission via a cooling curve to the outflow. our simulations show that in all cases highly collimated bipolar outflows result from deflection of the spherical wind via the interaction with the ce ejecta. significant asymmetries between the top and bottom lobes are seen in all cases. the asymmetry is strongest for the lower momentum case with radiative cooling. while real post-ce winds may be aspherical, our models show that collimation via 'inertial confinement' will be strong enough to create jet-like outflows even beginning with maximally uncollimated drivers. our simulations reveal detailed shock structures in the shock-focused inertial confinement (sfic) model and develop a lens-shaped inner shock that is a new feature of sfic-driven bipolar lobes. | bipolar planetary nebulae from outflow collimation by common envelope evolution |
the estimate of stellar metallicities (z*) of high-z galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar mass, dust attenuation, stellar age, and metallicity. benefiting from uniquely deep far-uv spectra of > 500 star-forming galaxies at redshifts 2 < z < 5 extracted from the vandels survey and stacked in bins of stellar mass (m*) and uv continuum slope (β), we estimate their stellar metallicities z* from stellar photospheric absorption features at 1501 and 1719 å, which are calibrated with starburst99 models and are largely unaffected by stellar age, dust, imf, nebular continuum, or interstellar absorption. comparing them to photometric-based spectral slopes in the 1250-1750 å range, we find that the stellar metallicity increases by ∼0.5 dex from β ∼ -2 to β ∼ -1 (1 ≲ a1600 ≲ 3.2), and a dependence with β holds at fixed uv absolute luminosity muv and stellar mass up to ∼109.65 m⊙. as a result, metallicity is a fundamental ingredient for properly rescaling dust corrections based on muv and m*. using the same absorption features, we analyzed the mass-metallicity relation (mzr), and find it to be consistent with the previous vandels estimation based on a global fit of the fuv spectra. similarly, we do not find a significant evolution between z ∼ 2 and z ∼ 3.5. finally, the slopes of our mzr and z* - β relation are in agreement with the predictions of well-studied semi-analytic models (sam) of galaxy formation, while some tensions remain concerning the absolute metallicity normalization. the relation between the uv slope and stellar metallicity is fundamental to the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our universe. | the vandels survey: the relation between the uv continuum slope and stellar metallicity in star-forming galaxies at z ∼ 3 |
the moons instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. these properties provide the unprecedented potential of enabling, for the very first time, sdss-like surveys around cosmic noon (z ~ 1-2.5), when the star formation rate in the universe peaked. the high-quality spectra delivered by moons will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the moons surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affected galaxy evolution. in this article, we specifically focus on the main guaranteed time observation (gto) moons extragalactic survey, moonrise, by providing an overview of its scientific goals and observing strategy. | moonrise: the main moons gto extragalactic survey |
within the general framework of the core-nucleated accretion theory of giant planet formation, the conglomeration of massive gaseous envelopes is facilitated by a transient period of rapid accumulation of nebular material. while the concurrent build-up of angular momentum is expected to leave newly formed planets spinning at near-breakup velocities, jupiter and saturn, as well as super-jovian long-period extrasolar planets, are observed to rotate well below criticality. in this work, we demonstrate that the large luminosity of a young giant planet simultaneously leads to the generation of a strong planetary magnetic field, as well as thermal ionization of the circumplanetary disk. the ensuing magnetic coupling between the planetary interior and the quasi-keplerian motion of the disk results in efficient braking of planetary rotation, with hydrodynamic circulation of gas within the hill sphere playing the key role of expelling spin angular momentum to the circumstellar nebula. our results place early-stage giant planet and stellar rotation within the same evolutionary framework, and motivate further exploration of magnetohydrodynamic phenomena in the context of the final stages of giant planet formation. | on the terminal rotation rates of giant planets |
as part of the accretion discs in hα with omegacam (adhoc) survey, we imaged a region of 12 × 8 square degrees around the orion nebula cluster in r, i and hα. thanks to the high-quality photometry obtained, we discovered three well-separated pre-main sequences in the color-magnitude diagram. the populations are all concentrated towards the cluster's center. although several explanations can be invoked to explain these sequences, we are left with two competitive but intriguing scenarios: a population of unresolved binaries with an exotic mass ratio distribution, or three populations with different ages. independent high-resolution spectroscopy supports the presence of discrete episodes of star formation, each separated by about a million years. the stars from the two putative youngest populations rotate faster than the older ones, in agreement with the evolution of stellar rotation observed in pre-main sequence stars younger than 4 myr in several star forming regions. whatever the final explanation, our results prompt a revised look at the formation mode and early evolution of stars in clusters. | a tale of three cities. omegacam discovers multiple sequences in the color-magnitude diagram of the orion nebula cluster |
we present new determinations of disk surface density, independent of an assumed dust opacity, for a sample of seven bright, diverse, protoplanetary disks using measurements of disk dust lines. we develop a robust method for determining the location of dust lines by modeling disk interferometric visibilities at multiple wavelengths. the disks in our sample have newly derived masses that are 9%-27% of their host stellar mass, substantially larger than the minimum mass solar nebula. all are stable to gravitational collapse, except for one that approaches the limit of toomre-q stability. our mass estimates are 2-15 times larger than estimates from integrated optically thin dust emission. we derive depleted dust-to-gas ratios with typical values of ∼10-3 in the outer disk. using coagulation models, we derive dust surface density profiles that are consistent with millimeter dust observations. in these models, the disks formed with an initial dust mass that is a factor of ∼10 greater than is presently observed. of the three disks in our sample with resolved co line emission, the masses of hd 163296, as 209, and tw hya are roughly 3, 115, and 40 times more massive than estimates from co respectively. this range indicates that co depletion is not uniform across different disks and that dust is a more robust tracer of total disk mass. our method of determining surface density using dust lines is robust even if particles form as aggregates and is useful even in the presence of dust substructure caused by pressure traps. the low toomre-q values observed in this sample indicate that at least some disks do not accrete efficiently. | new constraints from dust lines on the surface densities of protoplanetary disks |
accurate distances are fundamental for interpreting various measured properties of galaxies. surprisingly, many of the best-studied spiral galaxies in the local volume have distance uncertainties that are much larger than can be achieved with modern observation techniques. using hubble space telescopeoptical imaging, we use the tip of the red giant branch method to measure the distances to six galaxies that are included in the spitzer infrared nearby galaxies survey program and its offspring surveys. the sample includes m63, m74, ngc 1291, ngc 4559, ngc 4625, and ngc 5398. we compare our results with distances reported to these galaxies based on a variety of methods. depending on the technique, there can be a wide range in published distances, particularly from the tully-fisher relation. in addition, differences between the planetary nebular luminosity function and surface brightness fluctuation techniques can vary between galaxies, suggesting inaccuracies that cannot be explained by systematics in the calibrations. our distances improve upon previous results, as we use a well-calibrated, stable distance indicator, precision photometry in an optimally selected field of view, and a bayesian maximum likelihood technique that reduces measurement uncertainties. 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. | accurate distances to important spiral galaxies: m63, m74, ngc 1291, ngc 4559, ngc 4625, and ngc 5398 |
theory predicts that we should find fast, ejected (runaway) stars of all masses around dense, young star-forming regions. n-body simulations show that the number and distribution of these ejected stars could be used to constrain the initial spatial and kinematic substructure of the regions. we search for runaway and slower walkaway stars within 100 pc of the orion nebula cluster (onc) using gaia dr2 astrometry and photometry. we compare our findings to predictions for the number and velocity distributions of runaway stars from simulations that we run for 4 myr with initial conditions tailored to the onc. in gaia dr2, we find 31 runaway and 54 walkaway candidates based on proper motion, but not all of these are viable candidates in three dimensions. about 40 per cent are missing radial velocities, but we can trace back nine 3d runaways and 24 3d walkaways to the onc, all of which are low/intermediate mass (<8 m⊙). our simulations show that the number of runaways within 100 pc decreases the older a region is (as they quickly travel beyond this boundary), whereas the number of walkaways increases up to 3 myr. we find fewer walkaways in gaia dr2 than the maximum suggested from our simulations, which may be due to observational incompleteness. however, the number of gaia dr2 runaways agrees with the number from our simulations during an age of ∼1.3-2.4 myr, allowing us to confirm existing age estimates for the onc (and potentially other star-forming regions) using runaway stars. | runaway and walkaway stars from the onc with gaia dr2 |
we present the results of the sloan digital sky survey apogee infrared spectroscopy of young nebulous clusters program (in-sync) survey of the orion a molecular cloud. this survey obtained high-resolution near-infrared spectroscopy of about 2700 young pre-main-sequence stars on a ∼ 6^\circ field of view. we have measured accurate stellar parameters ({t}{{eff}}, {log}g, v{sin}i) and extinctions and placed the sources in the hertzsprung-russel diagram (hrd). we have also extracted radial velocities for the kinematic characterization of the population. we compare our measurements with literature results to assess the performance and accuracy of the survey. source extinction shows evidence for dust grains that are larger than those in the diffuse interstellar medium: we estimate an average rv = 5.5 in the region. importantly, we find a clear correlation between hrd inferred ages and spectroscopic surface-gravity-inferred ages and between extinction and disk presence; this strongly suggests a real spread of ages larger than a few myr. focusing on the young population around ngc 1980/ι ori, which has previously been suggested to be a separate, foreground, older cluster, we confirm its older (∼5 myr) age and low av, but considering that its radial velocity distribution is indistinguishable from orion a’s population, we suggest that ngc 1980 is part of orion a’s star formation activity. based on their stellar parameters and kinematic properties, we identify 383 new candidate members of orion a, most of which are diskless sources in areas of the region poorly studied by previous works. | in-sync. iv. the young stellar population in the orion a molecular cloud |
we present spectra of 14 a-type supergiants in the metal-rich spiral galaxy m83. we derive stellar parameters and metallicities and measure a spectroscopic distance modulus μ =28.47+/- 0.10 (4.9 ± 0.2 mpc), in agreement with other methods. we use the stellar characteristic metallicity of m83 and other systems to discuss a version of the galaxy mass-metallicity relation that is independent of the analysis of nebular emission lines and the associated systematic uncertainties. we reproduce the radial metallicity gradient of m83, which flattens at large radii, with a chemical evolution model, constraining gas inflow and outflow processes. we carry out a comparative analysis of the metallicities we derive from the stellar spectra and published h ii region line fluxes, utilizing both the direct, {t}{{e}}-based method and different strong-line abundance diagnostics. the direct abundances are in relatively good agreement with the stellar metallicities, once we apply a modest correction to the nebular oxygen abundance due to depletion onto dust. popular empirically calibrated strong-line diagnostics tend to provide nebular abundances that underestimate the stellar metallicities above the solar value by ∼0.2 dex. this result could be related to difficulties in selecting calibration samples at high metallicity. the o3n2 method calibrated by pettini and pagel gives the best agreement with our stellar metallicities. we confirm that metal recombination lines yield nebular abundances that agree with the stellar abundances for high-metallicity systems, but find evidence that in more metal-poor environments they tend to underestimate the stellar metallicities by a significant amount, opposite to the behavior of the direct method. | young stars and ionized nebulae in m83: comparing chemical abundances at high metallicity. |
we present an analysis of the nebular spectra of 103 stripped-envelope (se) supernovae (sne) collected from the literature and observed with the subaru telescope from 2002 to 2012, focusing on [o i] λλ6300, 6363. the line profile and width of [o i] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the sn subtypes, and further with the [o i]/[ca ii] ratio, which is used as an indicator of the progenitor co core mass. based on the best-fit results of the [o i] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of sesne. there is a hint (at the ~1σ level) that the distributions of the line profile fractions are different between canonical sesne and broad-line sne ic. a correlation between [o i] width and [o i]/[ca ii] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive co core. such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. further, when [o i]/[ca ii] increases, the fraction of objects with gaussian [o i] profile increases, while those with double-peaked profile decreases. this phenomenon connects ejecta geometry and the progenitor co core mass. * this research is based (in part) on data collected at subaru telescope, which is operated by the national astronomical observatory of japan. | statistical properties of the nebular spectra of 103 stripped-envelope core-collapse supernovae |
the enhancement of α elements such as oxygen is an important phase in the chemical evolution of the early universe, with nebular material becoming enriched in these elements sooner than iron. here, we present models which incorporate stellar spectra with α-enhanced compositions, focusing on the impact on the integrated light of young stellar populations, including those with large binary star fractions using the binary populations and spectral synthesis (bpass) framework, while using solar-scaled stellar evolution models. we find that broad spectrum outputs such as production of ionizing flux, the ultraviolet spectral slope and optical colours are only weakly affected by a change in $[\alpha /\rm {fe}]$. a number of features such as ultraviolet line indices (e.g. at 1719 and 1853 å) and optical line indices (such as mgb) are sensitive to such changes in composition for a continuously star-forming population and a single starburst population respectively. we find that at ages of more than 1 gyr, α-enhanced stellar populations appear bluer than their solar-scaled counterparts, and show expected sensitivity of optical line indices to composition, in agreement with previous work. the ultraviolet stellar absorption lines are relatively insensitive to subtleties in the abundances ratios, although with sufficient measurement precision, a combination of uv line indices may enable a simultaneous measurement of total metallicity mass fraction and $[\alpha /\rm {fe}]$ in young stellar populations. the output models are designated as bpass v2.3 and made available to the community with the aim of assisting interpretation of observations of high-redshift galaxies with the james webb space telescope. | the dependence of theoretical synthetic spectra on α-enhancement in young, binary stellar populations |
the fraction of lyman-α emitters (laes) among the galaxy population has been found to increase from z 0 to z 6 and drop dramatically at z> 6. this drop has been interpreted as an effect of an increasingly neutral intergalactic medium (igm) with increasing redshift, while a lyman continuum escape fraction evolving with redshift and/or a sudden change of galaxy physical properties can also contribute to the decreasing lae fraction. we report the result of a large vlt/fors2 program aiming to confirm spectroscopically a large galaxy sample at z ≥ 6 that has been selected in several independent fields through the lyman break technique. combining those data with archival data, we create a large and homogeneous sample of z 6 galaxies (n = 127), complete in terms of lyα detection at > 95% for lyα equivalent width ew(lyα) ≥ 25 å. we use this sample to derive a new measurement of the lae fraction at z 6 and derive the physical properties of these galaxies through spectral energy distribution (sed) fitting. we find a median lae fraction at z 6 lower than in previous studies, while our sample exhibits typical properties for z 6 galaxies in terms of uv luminosity and uvβ slope. the comparison of galaxy physical properties between laes and non-laes is comparable to results at lower redshift: laes with the largest ew(lyα) exhibit bluer uv slopes, are slightly less massive and less star-forming. the main difference between laes and non-laes is that the latter are significantly dustier. using predictions of our sed fitting code accounting for nebular emission, we find an effective lyα escape fraction fesceff(lyα) = 0.23-0.17+0.36 remarkably consistent with the value derived by comparing uv luminosity function with lyα luminosity function. we conclude that the drop in the lae fraction from z 6 to z> 6 is less dramatic than previously found and the effect of an increasing igm neutral fraction is possibly observed at 5 <z< 6. the processes driving the escape of lyα photons at z 6 are similar to those at lower redshifts and based on our derived fesceff(lyα), we find that the igm has a relatively small impact on lyα photon visibility at z 6, with a lower limit for the igm transmission to lyα photons, tigm ≳ 0.20, likely due to the presence of outflows. | vlt/fors2 view at z 6: lyman-α emitter fraction and galaxy physical properties at the edge of the epoch of cosmic reionization |
using the exquisite data from the muse extremely deep field (mxdf), we report the discovery of an mg ii emission nebula with an area above a 2σ significance level of 1000 proper kpc2. this provides the first panoramic view of the spatial distribution of magnesium in the intragroup medium of a low-mass group of five star-forming galaxies at z = 1.31. the galaxy group members are separated by less than 50 physical kpc in projection and ≈120 km s−1 in velocity space. the most massive galaxy has a stellar mass of 109.35 m⊙ and shows an mg ii p-cygni line profile, indicating the presence of an outflow, which is consistent with the spatially resolved spectral analysis showing ≈+120 km s−1 shift of the mg ii emission lines with respect to the systemic redshift. the other galaxies are less massive and only show mg ii in emission. the detected mg ii nebula has a maximal projected extent of ≈70 kpc, including a low-surface-brightness (≈2 × 10−19 erg s−1 cm−2 arcsec−2) gaseous bridge between two subgroups of galaxies. the presence of absorption features in the spectrum of a background galaxy located at an impact parameter of 19 kpc from the closest galaxy of the group indicates the presence of gas enriched in magnesium even beyond the detected nebula seen in emission, which suggests that we are observing the tip of a larger intragroup medium. the observed mg ii velocity gradient suggests an overall rotation of the structure along the major axis of the most massive galaxy. our muse data also reveal extended fe ii* emission in the vicinity of the most massive galaxy, aligned with its minor axis and pointing towards a neighboring galaxy. extended [o ii] emission is found around the galaxy group members and at the location of the mg ii bridge. our results suggest that both tidal stripping effects from galaxy interactions and outflows are enriching the intragroup medium of this system. based on observations made with eso telescope at the la silla paranal observatory under the large program 1101.a-0127. | the muse extremely deep field: first panoramic view of an mg ii emitting intragroup medium |
high temperature condensates found in meteorites display uranium isotopic variations (235u/238u) that complicate dating of the formation of the solar system and whose origin remains mysterious. it is possible that these variations are due to decay of the short-lived radionuclide 247cm (t1/2=15.6 myr) into 235u but they could also be due to uranium kinetic isotopic fractionation during condensation. we report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of 235u reaching ~+6 % relative to average solar system composition, which can only be due to decay of 247cm. this allows us to constrain the 247cm/235u ratio at solar system formation to (7.0 +- 1.6) x 10-5. this value provides new clues on the universality of nucleosynthetic r-process of rapid neutron capture. | origin of uranium isotope variations in early solar nebula condensates |
we report the first gas-phase metallicity map of a distant galaxy measured with the james webb space telescope (jwst). we use the niriss slitless spectroscopy acquired by the glass early release science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at z = 3.06 behind the a2744 galaxy cluster. this galaxy (dubbed glass-zgrad1) has stellar mass ~108.6 m ⊙, instantaneous star formation rate ~8.6 m ⊙ yr-1 (both corrected for lensing magnification), and global metallicity one-fourth solar. from its emission-line maps ([o iii], hβ, hγ, [ne iii], and [o ii]), we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling bayesian inference method. the exquisite resolution and sensitivity of jwst/niriss, combined with lensing magnification, enable us to resolve this z ~ 3 dwarf galaxy in ≳50 resolution elements with sufficient signal, an analysis hitherto not possible. we find that the radial metallicity gradient of glass-zgrad1 is strongly inverted (i.e., positive): ${\rm{\delta }}\mathrm{log}({\rm{o}}/{\rm{h}})/{\rm{\delta }}r$ = 0.165 ± 0.023 dex kpc-1. this measurement is robust at $\gtrsim 4-\,\sigma $ confidence level against known systematics. this positive gradient may be due to tidal torques induced by a massive nearby (~15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of glass-zgrad1. these first results showcase the power of jwst wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation (z ≳ 2). reaching masses ≲ 109 m ⊙ at these redshifts is especially valuable to constrain the effects of galactic feedback and environment and is possible only with jwst's new capabilities. *based on observations acquired by the jwst under the ers program id 1324 (pi t. treu). | early results from glass-jwst. iv. spatially resolved metallicity in a low-mass z 3 galaxy with niriss |
context. early-type galaxies (etgs) are found to follow a wide variety of merger and accretion histories in cosmological simulations.aims: we characterize the photometric and kinematic properties of simulated etg stellar halos, and compare them to the observations.methods: we selected a sample of 1114 etgs in the tng100 simulation and 80 in the higher-resolution tng50. these etgs span a stellar mass range of 1010.3 - 1012 m⊙ and they were selected within the range of g - r colour and λ-ellipticity diagram populated by observed etgs. we determined photometric parameters, intrinsic shapes, and kinematic observables in their extended stellar halos. we compared the results with central ifu kinematics and epn.s planetary nebula velocity fields at large radii, studying the variation in kinematics from center to halo, and connecting it to a change in the intrinsic shape of the galaxies.results: we find that the simulated galaxy sample reproduces the diversity of kinematic properties observed in etg halos. simulated fast rotators (frs) divide almost evenly in one third having flat λ profiles and high halo rotational support, a third with gently decreasing profiles, and another third with low halo rotation. however, the peak of rotation occurs at larger r than in observed etg samples. slow rotators (srs) tend to have increased rotation in the outskirts, with half of them exceeding λ = 0.2. for m* > 1011.5 m⊙ halo rotation is unimportant. a similar variety of properties is found for the stellar halo intrinsic shapes. rotational support and shape are deeply related: the kinematic transition to lower rotational support is accompanied by a change towards rounder intrinsic shape. triaxiality in the halos of frs increases outwards and with stellar mass. simulated srs have relatively constant triaxiality profiles.conclusions: simulated stellar halos show a large variety of structural properties, with quantitative but no clear qualitative differences between frs and srs. at the same stellar mass, stellar halo properties show a more gradual transition and significant overlap between the two families, despite the clear bimodality in the central regions. this is in agreement with observations of extended photometry and kinematics. | the stellar halos of etgs in the illustristng simulations: the photometric and kinematic diversity of galaxies at large radii |
escaping lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts z ≳ 6. however, the lyman continuum is not directly observable at these redshifts and secondary indicators of lyman continuum escape must be used to estimate the budget of ionizing photons. observationally, at redshifts z ∼ 2-3 where the lyman continuum is observationally accessible, surveys have established that many objects that show appreciable lyman continuum escape fractions fesc also show enhanced [o iii]/[o ii] (o32) emission line ratios. here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection between fesc and o32. like the observations, we find that the largest fesc values occur at elevated o32 ∼ 3-10 and that the combination of high fesc and low o32 is extremely rare. while high fesc and o32 often are observable concurrently, the timescales of the physical origin for the processes are very different. large o32 values fluctuate on short (∼1 myr) timescales during the wolf-rayet-powered phase after the formation of star clusters, while channels of low absorption are established over tens of megayears by collections of supernovae. we find that while there is no direct causal relation between fesc and o32, high fesc most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large o32 emission. these calculations are in agreement with interpretations of observations that large fesc tends to occur when o32 is large, but large o32 does not necessarily imply efficient lyman continuum escape. | the lyman continuum escape survey: connecting time-dependent [o iii] and [o ii] line emission with lyman continuum escape fraction in simulations of galaxy formation |
we present photometric and spectroscopic observations of the unusual type ia supernova asassn-18tb, including a series of southern african large telescope spectra obtained over the course of nearly six months and the first observations of a supernova by the transiting exoplanet survey satellite. we confirm a previous observation by kollmeier et al. showing that asassn-18tb is the first relatively normal type ia supernova to exhibit clear broad (∼1000 km s-1) h α emission in its nebular-phase spectra. we find that this event is best explained as a sub-chandrasekhar mass explosion producing m_{ ni} ≈ 0.3 {m}_⊙. despite the strong h α signature at late times, we find that the early rise of the supernova shows no evidence for deviations from a single-component power-law and is best fit with a moderately shallow power law of index 1.69 ± 0.04. we find that the h α luminosity remains approximately constant after its initial detection at phase +37 d, and that the h α velocity evolution does not trace that of the fe iii λ4660 emission. these suggest that the h α emission arises from a circumstellar medium (csm) rather than swept-up material from a non-degenerate companion. however, asassn-18tb is strikingly different from other known csm-interacting type ia supernovae in a number of significant ways. those objects typically show an h α luminosity two orders of magnitude higher than what is seen in asassn-18tb, pushing them away from the empirical light-curve relations that define `normal' type ia supernovae. conversely, asassn-18tb exhibits a fairly typical light curve and luminosity for an underluminous or transitional sn ia, with mr ≈ -18.1 mag. moreover, asassn-18tb is the only sn ia showing h α from csm interaction to be discovered in an early-type galaxy. | asassn-18tb: a most unusual type ia supernova observed by tess and salt |
we review recent advances in our understanding of magnetism in the solar nebula and protoplanetary disks (ppds). we discuss the implications of theory, meteorite measurements, and astronomical observations for planetary formation and nebular evolution. paleomagnetic measurements indicate the presence of fields of 0.54 ± 0.21 g at ~1 to 3 astronomical units (au) from the sun and ≥0.06 g at 3 to 7 au until >1.22 and >2.51 million years (ma) after solar system formation, respectively. these intensities are consistent with those predicted to enable typical astronomically observed protostellar accretion rates of ~10-8 m⊙ year-1, suggesting that magnetism played a central role in mass transport in ppds. paleomagnetic studies also indicate fields <0.006 g and <0.003 g in the inner and outer solar system by 3.94 and 4.89 ma, respectively, consistent with the nebular gas having dispersed by this time. this is similar to the observed lifetimes of extrasolar protoplanetary disks.", "comments": "mainly to add the abstract, and include it to the astronomy and geophysics collection. the paper does not contain keywords, but i just added a few to make it more easily searchable if this is allowed. | history of the solar nebula from meteorite paleomagnetism |
we present the census of the local universe (clu) narrowband survey to search for emission-line (hα) galaxies. clu-hα has imaged ≈3π of the sky (26,470 deg2) with four narrowband filters that probe a distance out to 200 mpc. we have obtained spectroscopic follow-up for galaxy candidates in 14 preliminary fields (101.6 deg2) to characterize the limits and completeness of the survey. in these preliminary fields, clu can identify emission lines down to an hα flux limit of 10-14 erg s-1 cm-2 at 90% completeness, and recovers 83% (67%) of the hα flux from cataloged galaxies in our search volume at the σ = 2.5 (σ = 5) color excess levels. the contamination from galaxies with no emission lines is 61% (12%) for σ = 2.5 (σ = 5). also, in the regions of overlap between our preliminary fields and previous emission-line surveys, we recover the majority of the galaxies found in previous surveys and identify an additional ≈300 galaxies. in total, we find 90 galaxies with no previous distance information, several of which are interesting objects: 7 blue compact dwarfs, 1 green pea, and a seyfert galaxy; we also identify a known planetary nebula. these objects show that the clu-hα survey can be a discovery machine for objects in our own galaxy and extreme galaxies out to intermediate redshifts. however, the majority of the clu-hα galaxies identified in this work show properties consistent with normal star-forming galaxies. clu-hα galaxies with new redshifts will be added to existing galaxy catalogs to focus the search for the electromagnetic counterpart to gravitational wave events. | census of the local universe (clu) narrowband survey. i. galaxy catalogs from preliminary fields |
the detonation of a helium shell on a white dwarf (wd) has been proposed as a possible explosion triggering mechanism for sne ia. here, we report ztf 18aaqeasu (sn 2018byg/atlas 18pqq), a peculiar type i supernova, consistent with being a helium-shell double-detonation. with a rise time of ≈18 days from explosion, the transient reached a peak absolute magnitude of mr≈ -18.2 mag, exhibiting a light curve akin to sub-luminous sn 1991bg-like sne ia, albeit with an unusually steep increase in brightness within a week from explosion. spectra taken near peak light exhibit prominent si absorption features together with an unusually red color (g - r ≈ 2 mag) arising from nearly complete line blanketing of flux blueward of 5000 å. this behavior is unlike any previously observed thermonuclear transient. nebular phase spectra taken at and after ≈30 days from peak light reveal evidence of a thermonuclear detonation event dominated by fe-group nucleosynthesis. we show that the peculiar properties of ztf 18aaqeasu are consistent with the detonation of a massive (≈0.15 {m}⊙ ) helium shell on a sub-chandrasekhar mass (≈0.75 {m}⊙ ) wd after including mixing of ≈0.2 {m}⊙of material in the outer ejecta. these observations provide evidence of a likely rare class of thermonuclear supernovae arising from detonations of massive helium shells. | ztf 18aaqeasu (sn2018byg): a massive helium-shell double detonation on a sub-chandrasekhar-mass white dwarf |
the sensitivity and angular resolution of photometric surveys executed by the hubble space telescope (hst) enable studies of individual star clusters in galaxies out to a few tens of megaparsecs. the fitting of spectral energy distributions (seds) of star clusters is essential for measuring their physical properties and studying their evolution. we report on the use of the publicly available code investigating galaxy emission (cigale) sed fitting package to derive ages, stellar masses, and reddenings for star clusters identified in the physics at high angular resolution in nearby galaxies-hst (phangs-hst) survey. using samples of star clusters in the galaxy ngc 3351, we present results of benchmark analyses performed to validate the code and a comparison to sed fitting results from the legacy extragalactic ultraviolet survey. we consider procedures for the phangs-hst sed fitting pipeline, e.g. the choice of single stellar population models, the treatment of nebular emission and dust, and the use of fluxes versus magnitudes for the sed fitting. we report on the properties of clusters in ngc 3351 and find, on average, the clusters residing in the inner star-forming ring of ngc 3351 are young (<10 myr) and massive (105 m⊙) while clusters in the stellar bulge are significantly older. cluster mass function fits yield β values around -2, consistent with prior results with a tendency to be shallower at the youngest ages. finally, we explore a bayesian analysis with additional physically motivated priors for the distribution of ages and masses and analyse the resulting cluster distributions. | phangs-hst: star cluster spectral energy distribution fitting with cigale |
the so-called jellyfish galaxies are objects exhibiting disturbed morphology, mostly in the form of tails of gas stripped from the main body of the galaxy. several works have strongly suggested ram pressure stripping to be the mechanism driving this phenomenon. here, we focus on one of these objects, drawn from a sample of optically selected jellyfish galaxies, and use it to validate sinopsis, the spectral fitting code that will be used for the analysis of the gasp (gas stripping phenomena in galaxies with muse) survey, and study the spatial distribution and physical properties of the gas and stellar populations in this galaxy. we compare the model spectra to those obtained with gandalf, a code with similar features widely used to interpret the kinematics of stars and gas in galaxies from ifu data. we find that sinopsis can reproduce the pixel-by-pixel spectra of this galaxy at least as well as gandalf does, providing reliable estimates of the underlying stellar absorption to properly correct the nebular gas emission. using these results, we find strong evidences of a double effect of ram pressure exerted by the intracluster medium onto the gas of the galaxy. a moderate burst of star formation, dating between 20 and 500 myr ago and involving the outer parts of the galaxy more strongly than the inner regions, was likely induced by a first interaction of the galaxy with the intracluster medium. stripping by ram pressure, plus probable gas depletion due to star formation, contributed to create a truncated ionized gas disk. the presence of an extended stellar tail on only one side of the disk points instead to another kind of process, likely gravitational interaction by a fly-by or a close encounter with another galaxy in the cluster. | gasp. iii. jo36: a case of multiple environmental effects at play? |
the relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the lyman continuum (lyc) at these redshifts. it is thus important to identify low-redshift lyc-leaking galaxies that can be used as laboratories to investigate the physical processes that allow lyc photons to escape. the weakness of the [s ii] nebular emission lines relative to typical star-forming galaxies has been proposed as a lyc predictor. in this paper, we show that the [s ii] deficiency is an effective method to select lyc-leaking candidates using data from the low-redshift lyc survey, which has detected flux below the lyman edge in 35 out of 66 star-forming galaxies with the cosmic origins spectrograph on board the hubble space telescope. we show that lyc leakers tend to be more [s ii] deficient and that the fraction of their detections increases as [s ii] deficiency becomes more prominent. correlational studies suggest that [s ii] deficiency complements other lyc diagnostics (such as strong lyα emission and high [o iii]/[o ii]). our results verify an additional technique by which reionization-era galaxies could be studied. | the low-redshift lyman-continuum survey: [s ii] deficiency and the leakage of ionizing radiation |
core accretion is the conventional model for the formation of the gas giant planets. the model may also apply to the icy giant planets, uranus and neptune, except that it may take upward of 50 myr for them to form at their present orbital distances, which is beyond the maximum 5 myr lifetime of the solar nebula. a plausible alternative is formation in the region of the gas giants, followed by migration to their present locations at 20 and 30 au. another alternative is the gravitational instability model, which is much faster and does not require the formation of a core first. in either scenario, heavy elements (mass > helium) provide the critical observational constraints. additionally, helium and neon abundances in the observable troposphere are indicators of the interior processes in the megabar region. we investigate the atmospheric regions most suitable for accessing the above elements. volatiles containing some of the elements (c, n, s, o) undergo condensation on the icy giants. on the other hand, noble gases (he, ne, ar, kr, xe), which are chemically inert, non-condensible, and uniform all over the planet, can provide the best constraints to the formation and migration models of uranus and neptune. only entry probes are capable of measuring the key elements and isotopic ratios. they are accessible at 5-10 bars, except for the condensibles. data from an orbiter on gravity, magnetic field, upper atmospheric composition and the maps of ammonia and water with depth would be a valuable complement to the situ measurements. | deep atmosphere composition, structure, origin, and exploration, with particular focus on critical in situ science at the icy giants |
the increasing neutrality of the intergalactic medium at z > 6 suppresses lyα emission, and spectroscopic confirmation of galaxy redshifts requires the detection of alternative ultraviolet lines. the strong [c iii] λ1907+c iii] λ1909 doublet frequently observed in low-metallicity, actively star-forming galaxies is a promising emission feature. we present cloudy photoionization model predictions for c iii] equivalent widths (ews) and line ratios as a function of starburst age, metallicity, and ionization parameter. our models include a range of c/o abundances, dust content, and gas density. we also examine the effects of varying the nebular geometry and optical depth. only the stellar models that incorporate binary interaction effects reproduce the highest observed c iii] ews. the spectral energy distributions from the binary stellar population models also generate observable c iii] over a longer timescale relative to single-star models. we show that diagnostics using c iii] and nebular he ii λ1640 can separate star-forming regions from shock-ionized gas. we also find that density-bounded systems should exhibit weaker c iii] ews at a given ionization parameter, and c iii] ews could, therefore, select candidate lyman continuum-leaking systems. in almost all models, c iii] is the next strongest line at <2700 å after lyα, and c iii] reaches detectable levels for a wide range of conditions at low metallicity. c iii] may therefore serve as an important diagnostic for characterizing galaxies at z > 6. | photoionization models for the semi-forbidden c iii] 1909 emission in star-forming galaxies |
understanding the origin of life-essential volatiles such as nitrogen (n) in the solar system and beyond is critical to evaluate the potential habitability of rocky planets1-5. whether the inner solar system planets accreted these volatiles from their inception or had an exogenous delivery from the outer solar system is, however, not well understood. using previously published data of nucleosynthetic anomalies of nickel, molybdenum, tungsten and ruthenium in iron meteorites along with their 15n/14n ratios, here we show that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct n. while the sun and jupiter captured n from nebular gas6, concomitantly growing protoplanets in the inner and outer disk possibly sourced their n from organics and/or dust—with each reservoir having a different n isotopic composition. a distinct n isotopic signature of the inner solar system protoplanets coupled with their rapid accretion7,8 suggests that non-nebular, isotopically processed n was ubiquitous in their growth zone between 0 and ~0.3 myr after solar system formation. because the 15n/14n ratio of the bulk silicate earth falls between that of the inner and outer solar system reservoirs, we infer that n in the present-day rocky planets represents a mixture of both inner and outer solar system material. | a very early origin of isotopically distinct nitrogen in inner solar system protoplanets |
we analyse the rest-optical emission-line spectra of z ~ 2.3 star-forming galaxies in the complete mosfire deep evolution field (mosdef) survey. in investigating the origin of the well-known offset between the sequences of high-redshift and local galaxies in the [o iii]λ5008/hβ versus [n ii]λ6585/hα ('[n ii] bpt') diagram, we define two populations of z ~ 2.3 mosdef galaxies. these include the high population that is offset towards higher [o iii]λ5008/hβ and/or [n ii]λ6585/hα with respect to the local sdss sequence and the low population that overlaps the sdss sequence. these two groups are also segregated within the [o iii]λ5008/hβ versus [s ii]λλ6718,6733/hα and the [o iii]λλ4960,5008/[o ii ]λλ3727,3730 (o32) versus ([o iii]λλ4960,5008+[o ii]λλ3727,3730)/hβ (r23) diagrams, which suggests qualitatively that star-forming regions in the more offset galaxies are characterized by harder ionizing spectra at fixed nebular oxygen abundance. we also investigate many galaxy properties of the split sample and find that the high sample is on average smaller in size and less massive, but has higher specific star formation rate (sfr) and sfr surface density values and is slightly younger compared to the low population. from cloudy+bpass photoionization models, we estimate that the high population has a lower stellar metallicity (i.e. harder ionizing spectrum) but slightly higher nebular metallicity and higher ionization parameter compared to the low population. while the high population is more α-enhanced (i.e. higher α/fe) than the low population, both samples are significantly more α-enhanced compared to local star-forming galaxies with similar rest-optical line ratios. these differences must be accounted for in all high-redshift star-forming galaxies - not only those 'offset' from local excitation sequences. | the mosdef survey: a comprehensive analysis of the rest-optical emission-line properties of z ∼ 2.3 star-forming galaxies |
we study the spectroscopic evolution of superluminous supernovae (slsne) later than 100 days after maximum light. we present new data for gaia16apd and sn 2017egm and analyze these with a larger sample comprising 41 spectra of 12 events. the spectra become nebular within 2-4 e-folding times after light-curve peak, with the rate of spectroscopic evolution correlated to the light-curve timescale. emission lines are identified with well-known transitions of oxygen, calcium, magnesium, sodium, and iron. slsne are differentiated from other sne ic by a prominent o i λ7774 line and higher ionization states of oxygen. the iron-dominated region around 5000 å is more similar to broad-lined sne ic than to normal sne ic. principal component analysis shows that five “eigenspectra” capture ≳70% of the variance, while a clustering analysis shows no clear evidence for multiple slsn subclasses. line velocities are 5000-8000 km s-1 and show stratification of the ejecta. o i λ7774 likely arises in a dense inner region that also produces calcium emission, while [o i] λ6300 comes from farther out until 300-400 days. the luminosities of o i λ7774 and ca ii suggest significant clumping, in agreement with previous studies. ratios of [ca ii] λ7300/[o i] λ6300 favor progenitors with relatively massive helium cores, likely ≳6 {m}⊙ , though more modeling is required here. slsne with broad light curves show the strongest [o i] λ6300, suggesting larger ejecta masses. we show how the inferred velocity, density, and ionization structure point to a central power source. | nebular-phase spectra of superluminous supernovae: physical insights from observational and statistical properties |
while interaction with circumstellar material is known to play an important role in type iin supernovae (sne), analyses of the more common sne iip and iil have not traditionally included interaction as a significant power source. however, recent campaigns to observe sne within days of explosion have revealed narrow emission lines of high-ionization species in the earliest spectra of luminous sne ii of all subclasses. these “flash ionization” features indicate the presence of a confined shell of material around the progenitor star. here we present the first low-luminosity (ll) sn to show flash ionization features, sn 2016bkv. this sn peaked at mv= -16 mag and has hα expansion velocities under 1350 km s-1 around maximum light, placing it at the faint/slow end of the distribution of sne iip (similar to sn 2005cs). the light-curve shape of sn 2016bkv is also extreme among sne iip. a very strong initial peak could indicate additional luminosity from circumstellar interaction. a very small fall from the plateau to the nickel tail indicates unusually large production of radioactive nickel compared to other ll sne iip. a comparison between nebular spectra of sn 2016bkv and models raises the possibility that sn 2016bkv is an electron-capture supernova. | short-lived circumstellar interaction in the low-luminosity type iip sn 2016bkv |
recent developments in planet formation theory and measurements of low d/h in deep mantle material support a solar nebula source for some of earth's hydrogen. here we present a new model for the origin of earth's water that considers both chondritic water and nebular ingassing of hydrogen. the largest embryo that formed earth likely had a magma ocean while the solar nebula persisted and could have ingassed nebular gases. the model considers iron hydrogenation reactions during earth's core formation as a mechanism for both sequestering hydrogen in the core and simultaneously fractionating hydrogen isotopes. by parameterizing the isotopic fractionation factor and initial bulk d/h ratio of earth's chondritic material, we explore the combined effects of elemental dissolution and isotopic fractionation of hydrogen in iron. by fitting to the two key constraints (three oceans' worth of water in earth's mantle and on its surface; and d/h in the bulk silicate earth close to 150 × 10-6), the model searches for best solutions among 10,000 different combinations of chondritic and nebular contributions. we find that ingassing of a small amount, typically >0-0.5 oceans of nebular hydrogen, is generally demanded, supplementing seven to eight oceans from chondritic contributions. about 60% of the total hydrogen enters the core, and attendant isotopic fractionation plausibly lowers the core's d/h to 130 × 10-6. crystallized magma ocean material may have d/h ≈ 110 × 10-6. these modeling results readily explain the low d/h in core-mantle boundary material and account for earth's inventory of solar neon and helium. | origin of earth's water: chondritic inheritance plus nebular ingassing and storage of hydrogen in the core |
the source responsible for the reionization of the universe is believed to be the population of star-forming galaxies at z ∼ 6 to 12. the biggest uncertainty concerns the fraction of lyman-continuum photons that actually escape from the galaxies. in recent years, several relatively small samples of “leaky” galaxies have been discovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. in this paper we present the results of a pilot program to test a new technique for finding leaky galaxies, using the weakness of the [s ii] nebular emission lines relative to typical star-forming galaxies as evidence that the interstellar medium (ism) is optically thin to the lyman continuum. we use the cosmic origins spectrograph on the hubble space telescope to detect significant emerging flux below the lyman edge in two out of three [s ii]-weak star-forming galaxies at z ∼ 0.3. we show that these galaxies differ markedly in their properties from the class of leaky “green-pea” galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the ism. like the green peas, they have exceptionally high star formation rates per unit area. they also share some properties with the known leaky galaxies at z ∼ 3, but are significantly dustier. our results validate a new method to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the universe. | a new technique for finding galaxies leaking lyman-continuum radiation: [s ii]-deficiency |
the terrestrial planets are believed to have formed by violent collisions of tens of lunar- to mars-size protoplanets at time t < 200 myr after the protoplanetary gas disk dispersal (t0). the solar system giant planets rapidly formed during the protoplanetary disk stage and, after t0, radially migrated by interacting with outer disk planetesimals. an early (t < 100 myr) dynamical instability is thought to have occurred with jupiter having gravitational encounters with a planetary-size body, jumping inward by ∼0.2-0.5 au, and landing on its current, mildly eccentric orbit. here we investigate how the giant-planet instability affected the formation of the terrestrial planets. we study several instability cases that were previously shown to match many solar system constraints. we find that resonances with giant planets help to remove solids available for accretion near ∼1.5 au, thus stalling the growth of mars. it does not matter, however, whether the giant planets are placed on their current orbits at t0 or whether they realistically evolve in one of our instability models; the results are practically the same. the tight orbital spacing of venus and earth is difficult to reproduce in our simulations, including cases where bodies grow from a narrow annulus at 0.7-1 au, because protoplanets tend to spread radially during accretion. the best results are obtained in the narrow-annulus model when protoplanets emerging from the dispersing gas nebula are assumed to have (at least) the mass of mars. this suggests efficient accretion of the terrestrial protoplanets during the first ∼10 myr of the solar system. | the role of early giant-planet instability in terrestrial planet formation |
context. planetary nebulae (pne) are a brief but important phase of stellar evolution. the study of galactic pne has historically been hampered by uncertain distances, but the parallaxes of pn central stars (cspne) measured by gaia are improving the situation.aims: gaia's early data release 3 (edr3) offers higher astrometric precision and greater completeness compared to previous releases. taking advantage of these improvements requires that the cspne in the catalogue be accurately identified.methods: we applied our automated technique based on the likelihood ratio method to cross-match known pne with sources in gaia edr3, using an empirically derived position and colour distribution to score candidate matches.results: we present a catalogue of over 2000 sources in gaia edr3 that our method has identified as likely cspne or compact nebula detections. we show how the more precise parallaxes of these sources compare to previous pn statistical distances and introduce an approach to combining them to produce tighter distance constraints. we also discuss gaia's handling of close companions and bright nebulae.conclusions: gaia is unlocking new avenues for the study of pne. the catalogue presented here will remain valid for the upcoming gaia data release 3 (dr3) and thus provide a valuable resource for years to come. table a.1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/656/a110 | one star, two star, red star, blue star: an updated planetary nebula central star distance catalogue from gaia edr3 |
following our recent work on type ii supernovae (sne), we present a set of 1d nonlocal thermodynamic equilibrium radiative transfer calculations for nebular-phase type ibc sne starting from state-of-the-art explosion models with detailed nucleosynthesis. our grid of progenitor models is derived from he stars that were subsequently evolved under the influence of wind mass loss. these he stars, which most likely form through binary mass exchange, synthesize less oxygen than their single-star counterparts with the same zero-age main sequence (zams) mass. this reduction is greater in he-star models evolved with an enhanced mass loss rate. we obtain a wide range of spectral properties at 200 d. in models from he stars with an initial mass > 6 m⊙, the [o i] λλ 6300, 6364 is of a comparable or greater strength than [ca ii] λλ 7291, 7323 - the strength of [o i] λλ 6300, 6364 increases with the he-star initial mass. in contrast, models from lower mass he stars exhibit a weak [o i] λλ 6300, 6364, strong [ca ii] λλ 7291, 7323, and also strong n ii lines and fe ii emission below 5500 å. the ejecta density, which is modulated by the ejecta mass, the explosion energy, and clumping, has a critical impact on gas ionization, line cooling, and spectral properties. we note that fe ii dominates the emission below 5500 å and is stronger at earlier nebular epochs. it ebbs as the sn ages, while the fractional flux in [o i] λλ 6300, 6364 and [ca ii] λλ 7291, 7323 increases with a similar rate as the ejecta recombine. although the results depend on the adopted wind mass loss rate and pre-sn mass, we find that he-stars of 6-8 m⊙ initially (zams mass of 23-28 m⊙) match the properties of standard sne ibc adequately. this finding agrees with the offset in progenitor masses inferred from the environments of sne ibc relative to sne ii. our results for less massive he stars are more perplexing since the predicted spectra are not seen in nature. they may be missed by current surveys or associated with type ibn sne in which interaction power dominates over decay power. tables a.3-a.23 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/656/a61 | nebular phase properties of supernova ibc from he-star explosions |
by incorporating our major recent discoveries with re-measured and verified contents of existing catalogues we provide, for the first time, an accessible, reliable, on-line sql database for essential, up-to date information for all known galactic planetary nebulae (pne). we have attempted to: i) reliably remove pn mimics/false id's that have biased previous studies and ii) provide accurate positions, sizes, morphologies, multi-wavelength imagery and spectroscopy. we also provide a link to cds/vizier for the archival history of each object and other valuable links to external data. with the hash interface, users can sift, select, browse, collate, investigate, download and visualise the entire currently known galactic pne diversity. hash provides the community with the most complete and reliable data with which to undertake new science. | hash: the hong kong/aao/strasbourg hα planetary nebula database |
a current issue in the study of planetary nebulae with close binary central stars (css) is the extent to which the binaries affect the shaping of the nebulae. recent studies have begun to show a high coincidence rate between nebulae with large-scale axial or point symmetries and close binary stars. in addition, combined binary-star and spatiokinematic modeling of the nebulae have demonstrated that all of the systems studied to date appear to have their central binary axis aligned with the primary axis of the nebula. here we add two more systems to the list, the css and nebulae of ngc 6337 and sp 1. we show both systems to be low inclination, with their binary axis nearly aligned with our line of sight. their inclinations match published values for the inclinations of their surrounding nebulae. including these two systems with the existing sample statistically demonstrates a direct link between the central binary and the nebular morphology. in addition to the systems’ inclinations we give ranges for other orbital parameters from binary modeling, including updated orbital periods for the binary css of ngc 6337 and sp 1. | observational confirmation of a link between common envelope binary interaction and planetary nebula shaping |
η carinae is an extraordinary massive star famous for its 19th century great eruption and the surrounding homunculus nebula ejected in that event. the cause of this eruption has been the centre of a long-standing mystery. recent observations, including light-echo spectra of the eruption, suggest that it most likely resulted from a stellar merger in an unstable triple system. here we present a detailed set of theoretical calculations for this scenario; from the dynamics of unstable triple systems and the mass ejection from close binary encounters, to the mass outflow from the eruption caused by the stellar merger and the post-merger wind phase. in our model the bipolar post-merger wind is the primary agent for creating the homunculus, as it sweeps up external eruption ejecta into a thin shell. our simulations reproduce many of the key aspects of the shape and kinematics of both the homunculus nebula and its complex surrounding structure, providing strong support for the merger-in-a-triple scenario. | simulating the formation of η carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption |
nucleosynthetic isotope anomalies in bulk chondrites and differentiated meteorites reflect variable proportions of isotopically diverse presolar components in bulk planetary bodies, but the origin of these heterogeneities is not well understood. here, the ru isotope composition of a comprehensive suite of iron meteorites and bulk samples of ordinary, enstatite and carbonaceous chondrites, as well as acid leachates and an insoluble residue of the allende chondrite are examined using newly developed multi-collector inductively coupled plasma mass spectrometry techniques. except for iab iron meteorites and enstatite chondrites, all investigated meteorites show well-resolved ru isotope anomalies. of these, within-group ru isotopic variations observed for samples from a given chemical group of iron meteorites reflect secondary neutron capture induced ru isotope shifts during prolonged cosmic ray-exposure. after correction of these cosmogenic effects using pt isotopes as a neutron-dose monitor, the remaining ru isotope anomalies are nucleosynthetic in nature and are consistent with a deficit in s-process ru in iron meteorite parent bodies. similarly, ru isotope anomalies in bulk ordinary and carbonaceous chondrites also reflect a deficiency in s-process ru. the sequential dissolution of allende reveals the presence of an hf-soluble s-process carrier, which is either an unidentified presolar phase or a component that incorporated s-process ru liberated from sic grains during nebular or parent body processes. we show that varying proportions of the s-process carrier identified in allende resulted in the correlated ru isotope anomalies observed for bulk meteorites, and that all meteorites (except possibly iab irons and enstatite chondrites) are depleted in this s-process component relative to ru from the earth's mantle. bulk meteorites exhibit correlated ru and mo isotope anomalies, reflecting variable deficits of a common s-process component, but some iron meteorites and carbonaceous chondrites appear to deviate from this correlation. this may reflect unaccounted cosmic effects on mo isotopes in iron meteorites, sample heterogeneities in carbonaceous chondrites or nebular and parent body processes acting differently on presolar mo and ru components. the identification of s-deficits in ru isotopes in almost all iron meteorites and chondrites investigated so far implies that meteorites do not seem to represent the material delivered to the earth's mantle as a late veneer after cessation of core formation. however, additional analyses of a more comprehensive set of chondrites are necessary to firmly arrive at this conclusion. | ru isotope heterogeneity in the solar protoplanetary disk |
type iax supernovae (sn iax), also called sn 2002cx-like supernovae, are the largest class of "peculiar" white dwarf (thermonuclear) supernovae, with over 50 members known. sn iax have lower ejecta velocity and lower luminosities, and these parameters span a much wider range, than normal type ia supernovae (sn ia). sn iax are spectroscopically similar to some sn ia near maximum light, but are unique among all supernovae in their late-time spectra, which never become fully "nebular." sn iax overwhelmingly occur in late-type host galaxies, implying a relatively young population. the sn iax 2012z is the only white dwarf supernova for which a pre-explosion progenitor system has been detected. a variety of models have been proposed, but one leading scenario has emerged: a type iax supernova may be a pure deflagration explosion of a carbon-oxygen (or hybrid carbon-oxygen-neon) white dwarf, triggered by helium accretion to the chandrasekhar mass, that does not necessarily fully disrupt the star. | type iax supernovae |
we compute synthetic optical and ultraviolet (uv) emission-line properties of galaxies in a full cosmological framework by coupling, in post-processing, new-generation nebular-emission models with high-resolution, cosmological zoom-in simulations of massive galaxies. our self-consistent modelling accounts for nebular emission from young stars and accreting black holes (bhs). we investigate which optical- and uv-line diagnostic diagrams can best help to discern between the main ionizing sources, as traced by the ratio of bh accretion to star formation rates in model galaxies, over a wide range of redshifts. at low redshift, simulated star-forming galaxies, galaxies dominated by active galactic nuclei and composite galaxies are appropriately differentiated by standard selection criteria in the classical [o iii]λ5007/h β versus [n ii]λ6584/h α diagram. at redshifts z≳ 1, however, this optical diagram fails to discriminate between active and inactive galaxies at metallicities below 0.5z⊙. to robustly classify the ionizing radiation of such metal-poor galaxies, which dominate in the early universe, we confirm 3 previous and propose 11 novel diagnostic diagrams based on equivalent widths and luminosity ratios of uv emission lines, such as ew(o iii] λ1663) versus o iii] λ1663/he ii λ1640, c iii] λ1908/he ii λ1640 versus o iii] λ1663/he ii λ1640, and c iv λ1550/c iii] λ1908 versus c iii] λ1908/c ii] λ2326. we formulate associated uv selection criteria and discuss some caveats of our results (e.g. uncertainties in the modelling of the he ii λ1640 line). these uv diagnostic diagrams are potentially important for the interpretation of high-quality spectra of very distant galaxies to be gathered by next-generation telescopes, such as the james webb space telescope. | synthetic nebular emission from massive galaxies - ii. ultraviolet-line diagnostics of dominant ionizing sources |
we present a study of the thermal structure of the hot x-ray emitting atmospheres for a sample of 49 nearby x-ray and optically bright elliptical galaxies using chandra x-ray data. we focus on the connection between the properties of the hot x-ray emitting gas and the cooler h α+[n ii] emitting phase, and the possible role of the latter in the active galactic nuclei (agn) feedback cycle. we do not find evident correlations between the h α+[n ii] emission and global properties such as x-ray luminosity, mass of hot gas, and gas mass fraction. we find that the presence of h α+[n ii] emission is more likely in systems with higher densities, lower entropies, shorter cooling times, shallower entropy profiles, lower values of min(tcool/tff), and disturbed x-ray morphologies (linked to turbulent motions). however, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. the agn jet powers of the galaxies with x-ray cavities show hint of a possible weak positive correlation with their h α+[n ii] luminosities. this correlation and the observed trends in the thermodynamic properties may result from chaotic cold accretion (cca) powering agn jets, as seen in some high-resolution hydrodynamic simulations. | thermodynamic properties, multiphase gas, and agn feedback in a large sample of giant ellipticals |
identifying low-redshift galaxies that emit lyman continuum radiation (lyc leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. however, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift lyc leakers are truly 'analogues' of the sources that reionized the universe. here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed lyc leakers at z ∼ 3 and z ∼ 0. we find that the simulated galaxies with high lyc escape fractions (fesc) often exhibit high o32 and populate the same regions of the r23-o32 plane as z ∼ 3 lyc leakers. however, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the o32-fesc plane. based on emission line diagnostics and how they correlate with fesc, lower metallicity lyc leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. in contrast, local [s ii]-deficient galaxies do not overlap with the simulated high-redshift lyc leakers on the s ii baldwin-phillips-terlevich (bpt) diagram; however, this diagnostic may still be useful for identifying leakers. we use our simulated galaxies to develop multiple new diagnostics to identify lyc leakers using infrared and nebular emission lines. we show that our model using only [c ii]158 μm and [o iii]88 μm can identify potential leakers from non-leakers from the local dwarf galaxy survey. finally, we apply this diagnostic to known high-redshift galaxies and find that macs 1149_jd1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the universe. | new methods for identifying lyman continuum leakers and reionization-epoch analogues |
early-time radiative signals from type ia supernovae (sne ia) can provide important constraints on the explosion mechanism and the progenitor system. we present observations and analysis of sn 2019np, a nearby sn ia discovered within 1-2 days after the explosion. follow-up observations were conducted in optical, ultraviolet, and near-infrared bands, covering the phases from ~-16.7 d to ~+ 367.8 d relative to its b-band peak luminosity. the photometric and spectral evolutions of sn 2019np resemble the average behaviour of normal sne ia. the absolute b-band peak magnitude and the post-peak decline rate are mmax(b) = -19.52 ± 0.47 mag and δm15(b) = 1.04 ± 0.04 mag, respectively. no hydrogen line has been detected in the nebular-phase spectra of sn 2019np. assuming that the 56ni powering the light curve is centrally located, we find that the bolometric light curve of sn 2019np shows a flux excess up to 5.0 per cent in the early phase compared to the radiative diffusion model. such an extra radiation perhaps suggests the presence of an additional energy source beyond the radioactive decay of central nickel. comparing the observed colour evolution with that predicted by different models, such as interactions of sn ejecta with circumstellar matter (csm)/companion star, a double-detonation explosion from a sub-chandrasekhar mass white dwarf (wd) and surface 56ni mixing, we propose that the nickel mixing is more favoured for sn 2019np. | observations of the very young type ia supernova 2019np with early-excess emission |
local star-forming galaxies show properties that are thought to differ from galaxies in the early universe. among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the local universe. a sample of 1969 extreme emission-line galaxies (eelgs) at a redshift 0 ≲ z ≲ 0.49, selected from the sloan digital sky survey (sdss) to be local analogues of high-redshift galaxies, was used to analyse their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 < 12 + log(o/h) < 8.6 and -1.8 < log(n/o) < -0.8. they allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. our new relations are in agreement with others found for smaller samples of objects at higher redshifts. when compared with other relations calibrated in the local universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as o32 or ne3o2, but they do not when the main dependence is on the ionization parameter, such as s23. in the case of strong-line ratios depending on [n ii] lines, the derivation of o/h becomes very uncertain due to the very high n/o values derived in this sample, above all in the low-metallicity regime. finally, we adapt the bayesian-like code h ii-chi-mistry for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both o/h and n/o, in consistency with the direct method. | extreme emission-line galaxies in sdss - i. empirical and model-based calibrations of chemical abundances |
we present a detailed analysis of 317 2.0 ≤ z ≤ 2.7 star-forming galaxies from the keck baryonic structure survey. using complementary spectroscopic observations with keck/lris and keck/mosfire, as well as spectral energy distribution (sed) fits to broadband photometry, we examine the joint rest-uv and rest-optical properties of the same galaxies, including stellar and nebular dust attenuation, metallicity, and star formation rate (sfr). the inferred parameters of the stellar population (reddening, age, sfr, and stellar mass) are strongly dependent on the details of the assumed stellar population model and the shape of the attenuation curve. nebular reddening is generally larger than continuum reddening, but with large scatter. compared to local galaxies, high-redshift galaxies have lower gas-phase metallicities (and/or higher nebular excitation) at fixed nebular reddening, and higher nebular reddening at fixed stellar mass, consistent with gas fractions that increase with redshift. we find that continuum reddening is correlated with 12 + log(o/h)o3n2 at 3.0σ significance, whereas nebular reddening is correlated with only 1.1σ significance. this may reflect the dependence of both continuum reddening and o3n2 on the shape of the ionizing radiation field produced by the massive stars. finally, we show that hα-based and sed-based estimates of sfr exhibit significant scatter relative to one another, and on average agree only for particular combinations of spectral synthesis models and attenuation curves. we find that the smc extinction curve predicts consistent sfrs if we assume the subsolar (0.14 z ⊙) binary star models that are favored for high-redshift galaxies. | dust attenuation, star formation, and metallicity in z ∼ 2-3 galaxies from kbss-mosfire |
the discrepancy between abundances computed using optical recombination lines and collisionally excited lines is a major unresolved problem in nebular astrophysics. here, we show that the largest abundance discrepancies are reached in planetary nebulae with close binary central stars. we illustrate this using deep spectroscopy of three nebulae with a post common-envelope (ce) binary star. abell 46 and ou 5 have o2+/h+ abundance discrepancy factors larger than 50, and as high as 300 in the inner regions of abell 46. abell 63 has a smaller discrepancy factor around 10, which is still above the typical values in ionized nebulae. our spectroscopic analysis supports previous conclusions that, in addition to “standard” hot ({{t}e} ∼ 104 k) gas, there exists a colder ({{t}e} ∼ 103 k), ionized component that is highly enriched in heavy elements. these nebulae have low ionized masses, between 10-3 and 10-1 m⊙ depending on the adopted electron densities and temperatures. since the much more massive red giant envelope is expected to be entirely ejected in the ce phase, the currently observed nebulae would be produced much later, during post-ce mass loss episodes when the envelope has already dispersed. these observations add constraints to the abundance discrepancy problem. we revise possible explanations. some explanations are naturally linked to binarity such as, for instance, high-metallicity nova ejecta, but it is difficult at this stage to depict an evolutionary scenario consistent with all of the observed properties. we also introduce the hypothesis that these nebulae are the result of tidal destruction, accretion, and ejection of jupiter-like planets. | binarity and the abundance discrepancy problem in planetary nebulae |
calcium is a major element of the earth, the moon, terrestrial planets, and rocky meteorites. here we present equilibrium ca isotope fractionation factors of ca-bearing minerals using the first-principles calculations based on density functional theory (dft). the sequence of minerals from the isotopically heaviest to the lightest in ca is forsterite > orthopyroxene (opx) > grossular ∼ pigeonite > diopside > anorthite > oldhamite. overall, the equilibrium fractionation of ca isotopes is mainly controlled by the average bond lengths. although oldhamite is enriched in light ca isotopes relative to silicate minerals in equilibrium, natural oldhamite of enstatite chondrites are isotopically heavier than coexisting silicate materials. this implies that enstatite chondrites oldhamites should have been formed during solar nebular gas condensation instead than during parent body processing. following previous models for crystallization of the lunar magma ocean (lmo), we simulated ca isotopic fractionation of the lmo based on our calculated equilibrium ca isotope fractionation factors. it shows that the δ 44 / 40ca of the lunar anorthositic crust should be lower than the average of the bulk moon by 0.09-0.11‰. considering that the lunar mantle might have overturned and mixed after solidification of the lmo, we further predict that the lunar mantle should be isotopically heavier than the bulk moon by 0.17-0.26‰ if the mantle was fully overturned, or only by 0.06-0.08‰ for the case of fully mixing. therefore, we predict that the potential offset of ca isotopic composition between the anorthositic crust and the lunar mantle can be used to test lmo evolution models. | first-principles calculations of equilibrium ca isotope fractionation: implications for oldhamite formation and evolution of lunar magma ocean |
we present c and o abundances in the magellanic clouds derived from deep spectra of h ii regions. the data have been taken with the ultraviolet-visual echelle spectrograph at the 8.2-m very large telescope. the sample comprises five h ii regions in the large magellanic cloud (lmc) and four in the small magellanic cloud (smc). we measure pure recombination lines (rls) of c ii and o ii in all the objects, permitting to derive the abundance discrepancy factors (adfs) for o2+, as well as their o/h, c/h and c/o ratios. we compare the adfs with those of other h ii regions in different galaxies. the results suggest a possible metallicity dependence of the adf for the low-metallicity objects; but more uncertain for high-metallicity objects. we compare nebular and b-type stellar abundances and we find that the stellar abundances agree better with the nebular ones derived from collisionally excited lines (cels). comparing these results with other galaxies we observe that stellar abundances seem to agree better with the nebular ones derived from cels in low-metallicity environments and from rls in high-metallicity environments. the c/h, o/h and c/o ratios show almost flat radial gradients, in contrast with the spiral galaxies where such gradients are negative. we explore the chemical evolution analysing c/o versus o/h and comparing with the results of h ii regions in other galaxies. the lmc seems to show a similar chemical evolution to the external zones of small spiral galaxies and the smc behaves as a typical star-forming dwarf galaxy. | carbon and oxygen in h ii regions of the magellanic clouds: abundance discrepancy and chemical evolution |
in this work, we propose an accreting stellar binary model for understanding the active periodic fast radio bursts (frbs). the system consists of a stellar compact object (co) and a donor star (ds) companion in an eccentric orbit, where the ds fills its own roche lobe near the periastron. the co accretes the material from the ds and then drives relativistic magnetic blobs. the interaction between the magnetic blobs and the stellar wind of the ds produces a pair of shocks. we find that both the reverse shock and the forward shock are likely to produce frbs via the synchrotron maser mechanism. we show that this system can in principle sufficiently produce highly active frbs with a long lifetime, and also can naturally explain the periodicity and the duty cycle of the activity that appeared in frbs 180916 and 121102. the radio nebula excited by the long-term injection of magnetic blobs into the surrounding environment may account for the associated persistent radio source. in addiction, we discuss the possible multiwavelength counterparts of frb 180916 in the context of this model. finally, we encourage the search for frbs in ultraluminous x-ray sources. | an accreting stellar binary model for active periodic fast radio bursts |
we have investigated the global dynamical state of the integral shaped filament in the orion a cloud using new n2h+ (1-0) large-scale, iram 30 m observations. our analysis of its internal gas dynamics reveals the presence of accelerated motions towards the orion nebula cluster, showing a characteristic blue-shifted profile centred at the position of the omc-1 south region. the properties of these observed gas motions (profile, extension, and magnitude) are consistent with the expected accelerations for the gravitational collapse of the omc-1 region and explain both the physical and kinematic structure of this cloud. based on observations carried out with the iram 30 m telescope. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain). | gravitational collapse of the omc-1 region |
himiko is one of the most luminous lyα emitters at z = 6.595. it has three star-forming clumps detected in the rest-frame uv, with a total sfr = 20 m ⊙ yr-1. we report the atacama large millimeter/submillimeter array (alma) detection of the [c ii]158 μm line emission in this galaxy with a significance of 8σ. the total [c ii] luminosity (l [c ii] = 1.2 × 108 l ⊙) is fully consistent with the local l [c ii]-sfr relation. the alma high-angular resolution reveals that the [c ii] emission is made of two distinct components. the brightest [c ii] clump is extended over 4 kpc and is located on the peak of the lyα nebula, which is spatially offset by 1 kpc relative to the brightest uv clump. the second [c ii] component is spatially unresolved (size <2 kpc) and coincident with one of the three uv clumps. while the latter component is consistent with the local l [c ii]-sfr relation, the other components are scattered above and below the local relation. we shortly discuss the possible origin of the [c ii] components and their relation with the star-forming clumps traced by the uv emission. | alma detection of extended [c ii] emission in himiko at z = 6.6 |
we present 5-20 μm spectral maps of the reflection nebula ngc 2023 obtained with the infrared spectrograph sl and sh modes on board the spitzer space telescope, which reveal emission from polycyclic aromatic hydrocarbons (pahs), c60, and h2 superposed on a dust continuum. we show that several pah emission bands correlate with each other and exhibit distinct spatial distributions that reveal a spatial sequence with distance from the illuminating star. we explore the distinct morphology of the 6.2, 7.7, and 8.6 μm pah bands and find that at least two spatially distinct components contribute to the 7-9 μm pah emission in ngc 2023. we report that the pah features behave independently of the underlying plateaus. we present spectra of compact, oval pahs ranging in size from c66 to c210, determined computationally using density functional theory, and we investigate trends in the band positions and relative intensities as a function of pah size, charge, and geometry. based on the nasa ames pah database, we discuss the 7-9 μm components in terms of band assignments and relative intensities. we assign the plateau emission to very small grains with possible contributions from pah clusters and identify components in the 7-9 μm emission that likely originate in these structures. based on the assignments and the observed spatial sequence, we discuss the photochemical evolution of the interstellar pah family as the pahs are more and more exposed to the radiation field of the central star in the evaporative flows associated with the photo-dissociation regions in ngc 2023. | the pah emission characteristics of the reflection nebula ngc 2023 |
we present the results of an lyα profile analysis of 12 lyα emitters (laes) at z∼ 2.2 with high-resolution lyα spectra. we find that all 12 objects have an lyα profile with the main peak redward of the systemic redshift defined by nebular lines, and five have a weak, secondary peak blueward of the systemic redshift (blue bump). the average velocity offset of the red main peak (the blue bump, if any) with respect to the systemic redshift is {{δ }}{v}{lyα ,{{r}}}=174+/- 19 km s-1 ({{δ }}{v}{lyα ,{{b}}}=-316+/- 45 km s-1), which is smaller than (comparable to) that of lyman break galaxies (lbgs). the outflow velocities inferred from metal absorption lines in three individual and one stacked spectra are comparable to those of lbgs. the uniform expanding shell model constructed by verhamme et al. reproduces not only the lyα profiles but also other observed quantities, including the outflow velocity and the fwhm of nebular lines for the non-blue-bump objects. on the other hand, the model predicts too high fwhms of nebular lines for the blue bump objects, although this discrepancy may disappear if we introduce additional lyα photons produced by gravitational cooling. we show that the small {{δ }}{v}{lyα ,{{r}}} values of our sample can be explained by low neutral hydrogen column densities of log({n}{{h} {{i}}}) = 18.9 cm-2 on average. this value is more than one order of magnitude lower than those of lbgs but is consistent with recent findings that laes have high ionization parameters and low h i gas masses. this result suggests that low {n}{{h} {{i}}} values, giving reduced numbers of resonant scattering of lyα photons, are the key to the strong lyα emission of laes. this paper includes data gathered with the 6.5 meter magellan telescopes located at las campanas observatory, chile. | a close comparison between observed and modeled lyα lines for z ~ 2.2 lyα emitters |
we investigate whether triggering of the magnetorotational instability (mri) in protoplanetary discs can account for the wide diversity of observed accretion outbursts. we show that short-lived, relatively low accretion rate events probably result from triggering in the inner disc and can occur at low surface densities, comparable to or smaller than the minimum mass solar nebula, and thus are very unlikely to result from mri triggering by gravitational instability. we develop time-dependent accretion disc models using an α-viscosity approach and calculate light curves to compare with observations. our modelling indicates that the lag time between infrared and optical bursts seen in gaia 17bpi can be explained with an outside-in propagation with an α ~ 0.1 in the mri-active region, consistent with other estimates. while outbursts in inner discs can show time delays of a few yr between infrared and optical light curves, our models indicate that large, fu ori-like bursts can exhibit infrared precursors decades before optical bursts. detecting such precursors could enable analysis of the central star before it is overwhelmed by the rapid accreting material, as well as constraining outburst physics. our results emphasize the importance of near-infrared monitoring of young stellar objects in addition to optical surveys. in addition, our findings emphasize the need for more sophisticated, three-dimensional, non-ideal magnetohydrodynamic simulations to fully exploit observational results. | magnetically activated accretion outbursts of pre-main-sequence discs |
chondrules may have played a critical role in the earliest stages of planet formation by mediating the accumulation of dust into planetesimals. however, the origin of chondrules and their significance for planetesimal accretion remain enigmatic. here, we show that chondrules and matrix in the carbonaceous chondrite allende have complementary 183w anomalies resulting from the uneven distribution of presolar, stellar-derived dust. these data refute an origin of chondrules in protoplanetary collisions and, instead, indicate that chondrules and matrix formed together from a common reservoir of solar nebula dust. because bulk allende exhibits no 183w anomaly, chondrules and matrix must have accreted rapidly to their parent body, implying that the majority of chondrules from a given chondrite group formed in a narrow time interval. based on hf-w chronometry on allende chondrules and matrix, this event occurred ∼2 million years after formation of the first solids, about coeval to chondrule formation in ordinary chondrites. | tungsten isotopic constraints on the age and origin of chondrules |
we present results of our large-scale, optical, multi-epoch photometric survey across ∼180 square degrees in the orion ob1 association, complemented with extensive follow-up spectroscopy. our focus is mapping and characterizing the off-cloud, low-mass, pre-main-sequence (pms) populations. we report 2062 k- and m-type confirmed t tauri members; 59% are located in the ob1a subassociation, 27% in the ob1b subassociation, and the remaining 14% in the a and b molecular clouds. we characterize two new clusterings of t tauri stars, the hd 35762 and hr 1833 groups, both located in ob1a not far from the 25 ori cluster. we also identify two stellar overdensities in ob1b, containing 231 pms stars, and find that the ob1b region is composed of two populations at different distances, possibly due to the ob1a subassociation overlapping with the front of ob1b. a ∼2 deg wide halo of young stars surrounds the orion nebula cluster, corresponding in part to the low-mass populations of ngc 1977 and ngc 1980. we use the strength of hα in emission, combined with the ir excess and optical variability, to define a new type of t tauri star, the c/w class, stars we propose may be nearing the end of their accretion phase, in an evolutionary state between classical and weak-lined t tauri stars. the evolution of the ensemble-wide equivalent width of li i λ6707 indicates a li depletion timescale of ∼8.5 myr. disk accretion declines with an e-folding timescale of ∼2 myr, consistent with previous studies. based on observations obtained at the llano del hato national astronomical observatory of venezuela, operated by cida for the ministerio del poder popular para la educación universitaria, ciencia, tecnología, the fred lawrence whipple observatory of the smithsonian institution, the wiyn 3.5 m telescope, the 6.5 m magellan telescopes at las campanas observatory, and the southern astrophysical research (soar) telescope. | the cida variability survey of orion ob1. ii. demographics of the young, low-mass stellar populations |
strong high-ionization lines such as he ii of young galaxies are puzzling at high and low redshift. although recent studies suggest the existence of nonthermal sources, whether their ionizing spectra can consistently explain multiple major emission lines remains a question. here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (empgs) that show strong he ii λ4686. we parameterize the ionizing spectra composed of a blackbody and power-law radiation mimicking various stellar and nonthermal sources. we use photoionization models for nebulae and determine seven parameters of the ionizing spectra and nebulae by markov chain monte carlo methods, carefully avoiding systematics of abundance ratios. we obtain the general shapes of ionizing spectra explaining ~10 major emission lines within observational errors with smooth connections from observed x-ray and optical continua. we find that an ionizing spectrum of one empg has a blackbody-dominated shape, while the others have convex downward shapes at >13.6 ev, which indicate a diversity of the ionizing spectrum shapes. we confirm that the convex downward shapes are fundamentally different from ordinary stellar spectrum shapes, and that the spectrum shapes of these galaxies are generally explained by the combination of the stellar and ultraluminous x-ray sources. comparisons with stellar synthesis models suggest that the diversity of the spectrum shapes arises from differences in the stellar age. if galaxies at z ≳ 6 are similar to the empgs, high-energy (>54.4 ev) photons of the nonstellar sources negligibly contribute to cosmic reionization due to relatively weak radiation. | empress. vii. ionizing spectrum shapes of extremely metal-poor galaxies: uncovering the origins of strong he ii and the impact on cosmic reionization |
the remarkable discovery by the chandra x-ray observatory that the crab nebula's jet periodically changes direction provides a challenge to our understanding of astrophysical jet dynamics. it has been suggested that this phenomenon may be the consequence of magnetic fields and magnetohydrodynamic instabilities, but experimental demonstration in a controlled laboratory environment has remained elusive. here we report experiments that use high-power lasers to create a plasma jet that can be directly compared with the crab jet through well-defined physical scaling laws. the jet generates its own embedded toroidal magnetic fields; as it moves, plasma instabilities result in multiple deflections of the propagation direction, mimicking the kink behaviour of the crab jet. the experiment is modelled with three-dimensional numerical simulations that show exactly how the instability develops and results in changes of direction of the jet. | scaled laboratory experiments explain the kink behaviour of the crab nebula jet |
we discover clear doubly peaked line profiles in 3 out of ∼20 type ia supernovae (sne ia) with high-quality nebular-phase spectra. the profiles are consistently present in three separated co/fe emission features. the two peaks are respectively blueshifted and redshifted relative to the host galaxies and are separated by ∼5000 km s-1. the doubly peaked profiles directly reflect a bimodal velocity distribution of the radioactive 56ni in the ejecta that powers the emission of these sne. due to their random orientations, only a fraction of sne with intrinsically bimodal velocity distributions will appear as doubly peaked spectra. therefore, sne with intrinsic bimodality are likely common, especially among the sne in the low-luminosity part on the phillips relation (δm15(b) ≳ 1.3; ∼ 40 per cent of all sne ia). such bimodality is naturally expected from direct collisions of white dwarfs (wds) due to the detonation of both wds and is demonstrated in a 3d 0.64-0.64m⊙ wd collision simulation. in the future, with a large sample of nebular spectra and a comprehensive set of numerical simulations, the collision model can be unambiguously tested as the primary channel for sne ia, and the distribution of nebular line profiles will either be a smoking gun or rule it out. | type ia supernovae with bimodal explosions are common - possible smoking gun for direct collisions of white dwarfs. |
we report the dramatic mid-infrared brightening between 2004 and 2006 of herschel orion protostar survey (hops) 383, a deeply embedded protostar adjacent to ngc 1977 in orion. by 2008, the source became a factor of 35 brighter at 24 μm with a brightness increase also apparent at 4.5 μm. the outburst is also detected in the submillimeter by comparing apex/saboca to scuba data, and a scattered-light nebula appeared in newfirm ks imaging. the post-outburst spectral energy distribution indicates a class 0 source with a dense envelope and a luminosity between 6 and 14 {{l}⊙ }. post-outburst time-series mid- and far-infrared photometry show no long-term fading and variability at the 18% level between 2009 and 2012. hops 383 is the first outbursting class 0 object discovered, pointing to the importance of episodic accretion at early stages in the star formation process. its dramatic rise and lack of fading over a 6 year period hint that it may be similar to fu ori outbursts, although the luminosity appears to be significantly smaller than the canonical luminosities of such objects. | hops 383: an outbursting class 0 protostar in orion |
the bulk chemical compositions of planets are uncertain, even for major elements such as mg and si. this is due to the fact that the samples available for study all originate from relatively shallow depths. comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. specifically, the non-chondritic si isotope composition of the earth's mantle was interpreted to reflect the presence of si in the core, which can also explain its low density relative to pure fe-ni alloy. however, we have found that angrite meteorites display a heavy si isotope composition similar to the lunar and terrestrial mantles. because core formation in the angrite parent-body (apb) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of si in the core is ruled out as an explanation for this heavy si isotope signature. instead, we show that equilibrium isotopic fractionation between gaseous sio and solid forsterite at ∼1370 k in the solar nebula could have produced the observed si isotope variations. nebular fractionation of forsterite should be accompanied by correlated variations between the si isotopic composition and mg/si ratio following a slope of ∼1, which is observed in meteorites. consideration of this nebular process leads to a revised si concentration in the earth's core of 3.6 (+ 6.0 / - 3.6) wt% and provides estimates of mg/si ratios of bulk planetary bodies. | planetary and meteoritic mg/si and δ30 si variations inherited from solar nebula chemistry |
we investigate mass transfer and the formation of discs in binary systems using a combination of numerical simulations and theory. we consider six models distinguished by binary separation, secondary mass and outflow mechanism. each system consists of an asymptotic giant branch (agb) star and an accreting secondary. the agb star loses its mass via a wind. in one of our six models, the agb star incurs a short period of outburst. in all cases, the secondary accretes part of the ejected mass and also influences the mass-loss rate of the agb star. the ejected mass may remain gravitationally bound to the binary system and form a circumbinary disc, or contribute to an accretion disc around the secondary. in other cases, the ejecta will escape the binary system. the accretion rate on to the secondary changes non-linearly with binary separation. in our closest binary simulations, our models exemplify the wind roche lobe overflow while in our wide binary cases, the mass transfer exhibits bondi-hoyle accretion. the morphologies of the outflows in the binary systems are varied. the variety may provide clues to how the late agb phase influences planetary nebula shaping. we employ the adaptive-mesh-refinement code astrobear for our simulations and include ray tracing, radiation transfer, cooling and dust formation. to attain the highest computational efficiency and the most stable results, all simulations are run in the corotating frame. | mass transfer and disc formation in agb binary systems |
"i do not believe that even in a snowflake this ordered pattern exists at random." – johannes kepler one of the most important developments in exoplanet science in the past decade is the discovery of multi-planet systems with sub-neptune-sized planets interior to 1 au. this chapter explores the architectures of these planetary systems, which often display a remarkable degree of uniformity: the planets have nearly equal sizes, regular orbital spacing, low eccentricities, and small mutual inclinations. this uniformity stands in sharp contrast to the diverse nature of the exoplanet sample considered as a whole (as well as our inner solar system). we begin with a critical review of the observations—including possible biases—and find that these peas-in-a-pod planetary systems are apparently a common outcome of the planet formation process. modest departures from exact uniformity suggest additional patterns, such as the planet mass slowly increasing with semi-major axis. the star formation process naturally produces circumstellar disks with the properties required to produce these planetary systems, although the solid material must move inward from its initial location. we discuss primary modes of planetary assembly, the role of orbital migration, and post-nebular atmospheric loss. mature planetary systems are found to be near their minimum energy (tidal equilibrium) configurations; this finding provides a partial explanation for their observed properties and indicates that efficient energy dissipation must occur. finally, we consider population synthesis models and show that peas-in-a-pod patterns emerge with reasonable choices for the input parameters. nonetheless, interesting observational and theoretical challenges remain in order to understand how these surprisingly organized planetary systems arise from the disorder of their formation processes. | architectures of compact multi-planet systems: diversity and uniformity |
pyneb is a python package widely used to model emission lines in gaseous nebulae. we take advantage of its object-oriented architecture, class methods, and historical atomic database to structure a practical environment for atomic data assessment. our aim is to reduce the uncertainties in the parameter space (line ratio diagnostics, electron density and temperature, and ionic abundances) arising from the underlying atomic data by critically selecting the pyneb default datasets. we evaluate the questioned radiative-rate accuracy of the collisionally excited forbidden lines of the n- and p-like ions (o ii, ne iv, s ii, cl iii, and ar iv), which are used as density diagnostics. with the aid of observed line ratios in the dense ngc 7027 planetary nebula and careful data analysis, we arrive at emissivity ratio uncertainties from the radiative rates within 10%, a considerable improvement over a previously predicted 50%. we also examine the accuracy of an extensive dataset of electron-impact effective collision strengths for the carbon isoelectronic sequence recently published. by estimating the impact of the new data on the pivotal [n ii] and [o iii] temperature diagnostics and by benchmarking the collision strength with a measured resonance position, we question their usefulness in nebular modeling. we confirm that the effective-collision-strength scatter of selected datasets for these two ions does not lead to uncertainties in the temperature diagnostics larger than 10%. | atomic data assessment with pyneb |
aims: we perform an extensive characterization of the broadband emission of mrk 421, as well as its temporal evolution, during the non-flaring (low) state. the high brightness and nearby location (z = 0.031) of mrk 421 make it an excellent laboratory to study blazar emission. the goal is to learn about the physical processes responsible for the typical emission of mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study.methods: we performed a 4.5-month multi-instrument campaign on mrk 421 between january 2009 and june 2009, which included vlba, f-gamma, gasp-webt, swift, rxte, fermi-lat, magic, and whipple, among other instruments and collaborations. this extensive radio to very-high-energy (vhe; e> 100 gev) γ-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution.results: mrk421 was found in its typical (non-flaring) activity state, with a vhe flux of about half that of the crab nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the x-rays. we determined the power spectral densities (psd) at most wavelengths and found that all psds can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. we observed a harder-when-brighter behavior in the x-ray spectra and measured a positive correlation between vhe and x-ray fluxes with zero time lag. such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. we also observed an overall anti-correlation between optical/uv and x-rays extending over the duration of the campaign.conclusions: the harder-when-brighter behavior in the x-ray spectra and the measured positive x-ray/vhe correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. in particular, this observation supports leptonic scenarios as being responsible for the emission of mrk 421 during non-flaring activity. such a temporally extended x-ray/vhe correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. the highest variability is observed in the x-ray band, which, within the one-zone synchrotron self-compton scenario, indicates that the electron energy distribution is most variable at the highest energies. appendix a is available in electronic form at http://www.aanda.orgthe complete data set shown in fig. 1 is 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/qcat?j/a+a/576/a126 | the 2009 multiwavelength campaign on mrk 421: variability and correlation studies |
the large high altitude air shower observatory (lhaaso) recently reported the detection of gamma-ray emissions with energies up to 1.1pev from the crab nebula. using the absence of vacuum cherenkov effect by inverse-compton electrons, we improve previous bounds to linear-order lorentz invariance violation (lv) in the dispersion relations of electrons by 104 times. we show that the lv effect on electrons is severely constrained, compatible with certain type of lv as expected by some models of quantum gravity (qg), such as the string/d-brane inspired space-time foam. we argue that such models are supported by the crab nebula constraints from the lhaaso observations, as well as various lv phenomenologies for photons to date. | testing lorentz invariance of electrons with lhaaso observations of pev gamma-rays from the crab nebula |
placs (platy hibonite crystals) and related hibonite-rich calcium-, aluminum-rich inclusions (cais; hereafter collectively referred to as plac-like cais) have the largest nucleosynthetic isotope anomalies of all materials believed to have formed in the solar system. most plac-like cais have low inferred initial 26al/27al ratios and could have formed prior to injection or widespread distribution of 26al in the solar nebula. in this study, we report 26al-26mg systematics combined with oxygen, calcium, and titanium isotopic compositions for a large number of newly separated plac-like cais from the murchison cm2 chondrite (32 cais studied for oxygen, 26 of these also for 26al-26mg, calcium and titanium). our results confirm (1) the large range of nucleosynthetic anomalies in 50ti and 48ca (our data range from -70‰ to +170‰ and -60‰ to +80‰, respectively), (2) the substantial range of δ17o values (-28‰ to -17‰, with δ17o = δ17o - 0.52 × δ18o), and (3) general 26al-depletion in plac-like cais. the multielement approach reveals a relationship between δ17o and the degree of variability in 50ti and 48ca: plac-like cais with the highest δ17o (∼-17‰) show large positive and negative 50ti and 48ca anomalies, while those with the lowest δ17o (∼-28‰) have small to no anomalies in 50ti and 48ca. these observations could suggest a physical link between anomalous 48ca and 50ti carriers and an 16o-poor reservoir. we suggest that the solar nebula was isotopically heterogeneous shortly after collapse of the protosolar molecular cloud, and that the primordial dust reservoir, in which anomalous carrier phases were heterogeneously distributed, was 16o-poor (δ17o ⩾ -17‰) relative to the primordial gaseous (co + h2o) reservoir (δ17o < -35‰). however, other models such as co self-shielding in the protoplanetary disk are also considered to explain the link between oxygen and calcium and titanium isotopes in plac-like cais. | a link between oxygen, calcium and titanium isotopes in 26al-poor hibonite-rich cais from murchison and implications for the heterogeneity of dust reservoirs in the solar nebula |
context. in the hierarchical two-phase formation scenario, the halos of early type galaxies (etgs) are expected to have different physical properties from the galaxies' central regions.aims: the epn.s survey characterizes the kinematic properties of etg halos using planetary nebulae (pne) as tracers, overcoming the limitations of absorption line spectroscopy at low surface brightness.methods: we present two-dimensional velocity and velocity dispersion fields for 33 etgs, including fast (frs) and slow rotators (srs). the velocity fields were reconstructed from the measured pn velocities using an adaptive kernel procedure validated with simulations, and extend to a median of 5.6 effective radii (re). we complemented the pn kinematics with absorption line data from the literature, for a complete description of the kinematics from the center to the outskirts.results: etgs typically show a kinematic transition between inner regions and halo. estimated transition radii in units of re anti-correlate with stellar mass. srs have increased but still modest rotational support at large radii. most of the frs show a decrease in rotation, due to the fading of the inner disk in the outer, more slowly rotating spheroid. 30% of the frs are dominated by rotation also at large radii. most etgs have flat or slightly falling halo velocity dispersion profiles, but 15% of the sample have steeply falling profiles. all of the srs and 40% of the frs show signatures of triaxial halos such as kinematic twists or misalignments. we show with illustrative photometric models that this is consistent with the distribution of isophote twists from extended photometry.conclusions: etgs have more diverse kinematic properties in their halos than in the central regions. frs do contain inner disk components but these frequently fade in outer spheroids which are often triaxial. the observed kinematic transition to the halo and its dependence on stellar mass is consistent with λcdm simulations and supports a two-phase formation scenario. | the extended planetary nebula spectrograph (epn.s) early-type galaxy survey: the kinematic diversity of stellar halos and the relation between halo transition scale and stellar mass |
we use the light curve and spectral synthesis code jekyll to calculate a set of macroscopically mixed type iib supernova (sn) models, which are compared to both previously published and new late-phase observations of sn 2020acat. the models differ in the initial mass, the radial mixing and expansion of the radioactive material, and the properties of the hydrogen envelope. the best match to the photospheric and nebular spectra and lightcurves of sn 2020acat is found for a model with an initial mass of 17 solar masses, strong radial mixing and expansion of the radioactive material, and a 0.1 solar mass hydrogen envelope with a low hydrogen mass-fraction of 0.27. the most interesting result is that strong expansion of the clumps containing radioactive material seems to be required to fit the observations of sn 2020acat both in the diffusion phase and the nebular phase. these "ni bubbles" are expected to expand due to heating from radioactive decays, but the degree of expansion is poorly constrained. without strong expansion there is a tension between the diffusion phase and the subsequent evolution, and models that fit the nebular phase produce a diffusion peak that is too broad. the diffusion phase lightcurve is sensitive to the expansion of the "ni bubbles", as the resulting swiss-cheese-like geometry decreases the effective opacity and therefore the diffusion time. this effect has not been taken into account in previous lightcurve modelling of stripped-envelope sne, which may lead to a systematic underestimate of their ejecta masses. it should be emphasized, though, that jekyll is limited to a geometry that is spherically symmetric on average, and large-scale asymmetries may also play a role. the relatively high initial mass found for the progenitor of sn 2020acat places it at the upper end of the mass distribution of type iib sn progenitors, and a single star origin can not be excluded. | lightcurve and spectral modelling of the type iib sn 2020acat. evidence for a strong ni bubble effect on the diffusion time |
we present linear polarimetry for seven hydrogen-poor superluminous supernovae (slsne-i) of which only one has previously published polarimetric data. the best-studied event is sn 2017gci, for which we present two epochs of spectropolarimetry at +3 d and +29 d post-peak in rest frame, accompanied by four epochs of imaging polarimetry up to +108 d. the spectropolarimetry at +3 d shows increasing polarisation degree p towards the redder wavelengths and exhibits signs of axial symmetry, but at +29 d, p ∼ 0 throughout the spectrum, implying that the photosphere of sn 2017gci evolved from a slightly aspherical configuration to a more spherical one in the first month post-peak. however, an increase of p to ∼0.5% at ∼ + 55 d accompanied by a different orientation of the axial symmetry compared to +3 d implies the presence of additional sources of polarisation at this phase. the increase in polarisation is possibly caused by interaction with circumstellar matter (csm), as already suggested by a knee in the light curve and a possible detection of broad hα emission at the same phase. we also analysed the sample of all 16 slsne-i with polarimetric measurements to date. the data taken during the early spectroscopic phase show consistently low polarisation, indicating at least nearly spherical photospheres. no clear relation between the polarimetry and spectral phase was seen when the spectra resemble type ic sne during the photospheric and nebular phases. the light-curve decline rate, which spans a factor of eight, also shows no clear relation with the polarisation properties. while only slow-evolving slsne-i have shown non-zero polarisation, the fast-evolving ones have not been observed at sufficiently late times to conclude that none of them exhibit changing p. however, the four slsne-i with increasing polarisation degree also have irregular light-curve declines. for up to half of them, the photometric, spectroscopic, and polarimetric properties are affected by csm interaction. as such, csm interaction clearly plays an important role in understanding the polarimetric evolution of slsne-i. | polarimetry of hydrogen-poor superluminous supernovae |
we present observations of sn 2022joj, a peculiar type ia supernova discovered by the zwicky transient facility. sn 2022joj exhibits an unusually red g ztf - r ztf color at early times and a rapid blueward evolution afterward. around maximum brightness, sn 2022joj shows a high luminosity ( ${m}_{{g}_{\mathrm{ztf}},\max }\simeq -19.7$ mag), a blue broadband color (g ztf - r ztf ≃ -0.2 mag), and shallow si ii absorption lines, consistent with those of overluminous, sn 1991t-like events. the maximum-light spectrum also shows prominent absorption around 4200 å, which resembles the ti ii features in subluminous, sn 1991bg-like events. despite the blue optical-band colors, sn 2022joj exhibits extremely red ultraviolet minus optical colors at maximum luminosity (u - v ≃ 0.6 mag and uvw1 - v ≃ 2.5 mag), suggesting a suppression of flux at ~2500-4000 å. strong c ii lines are also detected at peak. we show that these unusual spectroscopic properties are broadly consistent with the helium-shell double detonation of a sub-chandrasekhar mass (m ≃ 1 m ⊙) carbon/oxygen white dwarf from a relatively massive helium shell (ms≃ 0.04-0.1 m ⊙), if observed along a line of sight roughly opposite to where the shell initially detonates. none of the existing models could quantitatively explain all the peculiarities observed in sn 2022joj. the low flux ratio of [ni ii] λ7378 to [fe ii] λ7155 emission in the late-time nebular spectra indicates a low yield of stable ni isotopes, favoring a sub-chandrasekhar mass progenitor. the significant blueshift measured in the [fe ii] λ7155 line is also consistent with an asymmetric chemical distribution in the ejecta, as is predicted in double-detonation models. | sn 2022joj: a peculiar type ia supernova possibly driven by an asymmetric helium-shell double detonation |
pattern formation is a ubiquitous phenomenon in nature, from the organization of stellar nebulae to the structuration of clouds or the growth of plants. a key mechanism through which order can emerge from a homogeneous system is a parametric instability, with a paradigmatic example being the formation of faraday waves at the surface of a vibrating liquid. similar phenomena can occur in quantum matter, driven by interactions. here, we demonstrate, using a bose-einstein condensate held in a shaken optical lattice, the emergence of an additional coherent crystal-like order with a periodic density pattern, whose spatial period directly depends on the modulation parameters. we systematically investigate this tunable order and study its growth dynamics, persistence, and decay. | emergence of tunable periodic density correlations in a floquet-bloch system |
new horizon's accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed. assuming differentiated rock-ice structures, we find that pluto is close to 2/3 solar-composition anhydrous rock by mass and charon 3/5 solar-composition anhydrous rock by mass. pluto and charon are closer to each other in density than to other large (≳1000-km diameter) kuiper belt bodies. despite this, we show that neither the possible presence of an ocean under pluto's water ice shell (and no ocean within charon), nor enhanced porosity at depth in charon's icy crust compared with that of pluto, are sufficient to make pluto and charon's rock mass fractions match. all four small satellites (styx, nix, kerberos, hydra) appear much icier in comparison with either pluto or charon. in terms of a giant impact origin, both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies (canup, astrophys. j. 141, 35, 2011). this is in turn consistent with dynamical conditions in the ancestral kuiper belt, but implies that the impact precursors themselves accreted relatively late and slowly (to limit 26al and accretional heating). the iciness of the small satellites is not consistent with direct formation of the pluto-charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound ;pebble piles,; a proposed formation mechanism for kuiper belt binaries (nesvorný et al., astron. j. 140, 785-793, 2010). growth of pluto-scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out, however, and may be needed to prevent the precursor bodies from fully differentiating, due to buried accretional heat, prior to the charon-forming impact. | origin of the pluto-charon system: constraints from the new horizons flyby |
we present the results of a detailed, systematic stellar evolution study of binary mergers for blue supergiant (bsg) progenitors of type ii supernovae. in particular, these are the first evolutionary models that can simultaneously reproduce nearly all observational aspects of the progenitor of sn 1987a, $\text{sk}-69\,^{\circ}202$, such as its position in the hr diagram, the enrichment of helium and nitrogen in the triple-ring nebula, and its lifetime before its explosion. the merger model, based on the one proposed by podsiadlowski 1992 et al. and podsiadlowski 2007 et al., consists of a main sequence secondary star that dissolves completely in the common envelope of the primary red supergiant at the end of their merger. we empirically explore a large initial parameter space, such as primary masses ($15\,\text{m}_{\odot}$, $16\,\text{m}_{\odot}$, and $17\,\text{m}_{\odot}$), secondary masses ($2\,\text{m}_{\odot}$, $3\,\text{m}_{\odot}$, ..., $8\,\text{m}_{\odot}$) and different depths up to which the secondary penetrates the he core of the primary during the merger. the evolution of the merged star is continued until just before iron-core collapse and the surface properties of the 84 pre-supernova models ($16\,\text{m}_{\odot}-23\,\mathrm{m}_{\odot}$) computed have been made available in this work. within the parameter space studied, the majority of the pre-supernova models are compact, hot bsgs with effective temperature $>12\,\text{kk}$ and radii of $30\,\text{r}_{\odot}-70\,\mathrm{r}_{\odot}$ of which six match nearly all the observational properties of $\text{sk}-69\,^{\circ}202$. | the quest for blue supergiants: binary merger models for the evolution of the progenitor of sn 1987a. |
in this work, bvri light curves of 55 type ii supernovae (sne ii) from the lick observatory supernova search programme obtained with the katzman automatic imaging telescope and the 1 m nickel telescope from 2006 to 2018 are presented. additionally, more than 150 spectra gathered with the 3 m shane telescope are published. we conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. in average, v-band plateau declines with a rate of 1.29 mag (100 d)-1, which is consistent with previously published samples. for each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: sne ii with steeper decline have shorter plateau duration and are brighter. a time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s-1 (h α line) and a standard dispersion of 2000 km s-1. nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16m⊙. all the data are available to the community and will help to understand sn ii diversity better, and therefore to improve their utility as cosmological distance indicators. | the berkeley sample of type ii supernovae: bvri light curves and spectroscopy of 55 sne ii |
context. the shape of the ionising spectra of galaxies is a key ingredient to reveal their physical properties and for our understanding of the ionising background radiation. a long-standing unsolved problem is the presence of he ii nebular emission in many low-metallicity star-forming galaxies. this emission requires ionising photons with an energy > 54 ev; it is important to note that these particular photons are not produced in sufficient amounts by normal stellar populations.aims: to examine if high mass x-ray binaries and ultra-luminous x-ray sources (hmxbs and ulxs) can explain the observed he ii nebular emission and how their presence alters other emission lines, we computed photoionisation models of galaxies including such sources.methods: we combined spectral energy distributions (seds) of integrated stellar populations with constrained seds of ulxs to obtain composite spectra with varying amounts of x-ray luminosity, parameterised by lx/sfr. with these, we computed photoionisation models to predict the emission line fluxes of the optical recombination lines of h and he+, as well as the main metal lines of [o iii], [o ii], [o i], and [n ii]. the predictions were then compared to a large sample of low-metallicity galaxies.results: we find that it is possible to reproduce the nebular he ii λ4686 and other line observations with our spectra and with amounts of lx/sfr compatible with the observations. our work suggests that hmbxs and ulxs could be responsible for the observed nebular he ii emission. however, the strengths of the high and low ionisation lines, such as he ii and [o i] λ6300, strongly depend on the x-ray contribution and on the assumed seds of the high energy source(s), the latter being poorly known. | can nebular he ii emission be explained by ultra-luminous x-ray sources? |
there are many mechanisms by which galaxies can transform from blue, star-forming spirals, to red, quiescent early-type galaxies, but our current census of them does not form a complete picture. recent observations of nearby case studies have identified a population of galaxies that quench “quietly.” traditional poststarburst searches seem to catch galaxies only after they have quenched and transformed, and thus miss any objects with additional ionization mechanisms exciting the remaining gas. the shocked poststarburst galaxy survey (spogs) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. utilizing the oh-sarzi-schawinski-yi (ossy) measurements on the sloan digital sky survey data release 7 catalog, we applied balmer absorption and shock boundary criteria to identify 1067 spog candidates (spogs*) within z = 0.2. spogs* represent 0.2% of the ossy sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). spogs* colors suggest that they are in an earlier phase of transition than ossy galaxies that meet an “e+a” selection. spogs* have a 13% 1.4 ghz detection rate from the faint images of the radio sky at twenty centimeters survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei (agns). spogs* also have stronger na i d absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. it appears that spogs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of spogs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. it is likely that many of the known pathways to transformation undergo a spog phase. studying this sample of spogs* further, including their morphologies, agn properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving. | shocked poststarbust galaxy survey. i. candidate post-starbust galaxies with emission line ratios consistent with shocks |
evidence for the capture of nebular gases by planetary interiors would place important constraints on models of planet formation. these constraints include accretion timescales, thermal evolution, volatile compositions and planetary redox states1-7. retention of nebular gases by planetary interiors also constrains the dynamics of outgassing and volatile loss associated with the assembly and ensuing evolution of terrestrial planets. but evidence for such gases in earth's interior remains controversial8-14. the ratio of the two primordial neon isotopes, 20ne/22ne, is significantly different for the three potential sources of earth's volatiles: nebular gas15, solar-wind-irradiated material16 and ci chondrites17. therefore, the 20ne/22ne ratio is a powerful tool for assessing the source of volatiles in earth's interior. here we present neon isotope measurements from deep mantle plumes that reveal 20ne/22ne ratios of up to 13.03 ± 0.04 (2 standard deviations). these ratios are demonstrably higher than those for solar-wind-irradiated material and ci chondrites, requiring the presence of nebular neon in the deep mantle. furthermore, we determine a 20ne/22ne ratio for the primordial plume mantle of 13.23 ± 0.22 (2 standard deviations), which is indistinguishable from the nebular ratio, providing robust evidence for a reservoir of nebular gas preserved in the deep mantle today. the acquisition of nebular gases requires planetary embryos to grow to sufficiently large mass before the dissipation of the protoplanetary disk. our observations also indicate distinct 20ne/22ne ratios between deep mantle plumes and mid-ocean-ridge basalts, which is best explained by addition of a chondritic component to the shallower mantle during the main phase of earth's accretion and by subsequent recycling of seawater-derived neon in plate tectonic processes. | capture of nebular gases during earth's accretion is preserved in deep-mantle neon |
giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen-helium envelope is applied in both formation and structure models. we show that the primordial internal structure depends on the planetary growth rate, in particular, the ratio of heavy elements accretion to gas accretion. for a wide range of likely conditions, this ratio is in one-to-one correspondence with the resulting post-accretion profile of heavy elements within the planet. this flux ratio depends sensitively on the assumed solid-surface density in the surrounding nebula. we suggest that giant planets’ cores might not be distinct from the envelope and includes some hydrogen and helium, and the deep interior can have a gradual heavy-element structure. accordingly, jupiter’s core may not be well defined. accurate measurements of jupiter’s gravitational field by juno could put constraints on jupiter’s core mass. however, as we suggest here, the definition of jupiter’s core is complex, and the core’s physical properties (mass, density) depend on the actual definition of the core and on the planet’s growth history. | the fuzziness of giant planets’ cores |
aims: we aim to characterize the multiwavelength emission from markarian 501 (mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios.methods: we organized a multiwavelength campaign to take place between march and july of 2012. excellent temporal coverage was obtained with more than 25 instruments, including the magic, fact and veritas cherenkov telescopes, the instruments on board the swift and fermi spacecraft, and the telescopes operated by the gasp-webt collaboration.results: mrk 501 showed a very high energy (vhe) gamma-ray flux above 0.2 tev of ∼0.5 times the crab nebula flux (cu) for most of the campaign. the highest activity occurred on 2012 june 9, when the vhe flux was ∼3 cu, and the peak of the high-energy spectral component was found to be at ∼2 tev. both the x-ray and vhe gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the x-ray and vhe flux. this study reports the hardest mrk 501 vhe spectra measured to date. the fractional variability was found to increase with energy, with the highest variability occurring at vhe. using the complete data set, we found correlation between the x-ray and vhe bands; however, if the june 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the x-ray and vhe bands throughout the campaign.conclusions: the unprecedentedly hard x-ray and vhe spectra measured imply that their low- and high-energy components peaked above 5 kev and 0.5 tev, respectively, during a large fraction of the observing campaign, and hence that mrk 501 behaved like an extreme high-frequency-peaked blazar (ehbl) throughout the 2012 observing season. this suggests that being an ehbl may not be a permanent characteristic of a blazar, but rather a state which may change over time. the data set acquired shows that the broadband spectral energy distribution (sed) of mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-compton (ssc) models, various emission regions for a satisfactory description. nevertheless the one-zone ssc scenario can successfully describe the segments of the sed where most energy is emitted, with a significant correlation between the electron energy density and the vhe gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. the one-zone ssc scenario used reproduces the behavior seen between the measured x-ray and vhe gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the x-rays. the multi-instrument light curves from fig. 1, and the broadband sed plots from figs. 5-7 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/qcat?j/a+a/620/a181 | extreme hbl behavior of markarian 501 during 2012 |
the lack of unambiguous detections of atomic features in the x-ray spectra of ultraluminous x-ray sources (ulxs) has proven a hindrance in diagnosing the nature of the accretion flow. the possible association of spectral residuals at soft energies with atomic features seen in absorption and/or emission and potentially broadened by velocity dispersion could therefore hold the key to understanding much about these enigmatic sources. here we show for the first time that such residuals are seen in several sources and appear extremely similar in shape, implying a common origin. via simple arguments we assert that emission from extreme colliding winds, absorption in a shell of material associated with the ulx nebula and thermal plasma emission associated with star formation are all highly unlikely to provide an origin. whilst ccd spectra lack the energy resolution necessary to directly determine the nature of the features (i.e. formed of a complex of narrow lines or intrinsically broad lines), studying the evolution of the residuals with underlying spectral shape allows for an important, indirect test for their origin. the ulx ngc 1313 x-1 provides the best opportunity to perform such a test due to the dynamic range in spectral hardness provided by archival observations. we show through highly simplified spectral modelling that the strength of the features (in either absorption or emission) appears to anticorrelate with spectral hardness, which would rule out an origin via reflection of a primary continuum and instead supports a picture of atomic transitions in a wind or nearby material associated with such an outflow. | diagnosing the accretion flow in ultraluminous x-ray sources using soft x-ray atomic features |
new integral field spectroscopy has been obtained for izw 18, the nearby lowest-metallicity galaxy considered to be our best local analog of systems forming at high redshift (z). here we report the spatially resolved spectral map of the nebular he ii λ4686 emission in izw 18, from which we derived for the first time its total he ii-ionizing flux. nebular he ii emission implies the existence of a hard radiation field. he ii-emitters are observed to be more frequent among high-z galaxies than for local objects. therefore, investigating the he ii-ionizing source(s) in izw 18 may reveal the ionization processes at high z. he ii emission in star-forming galaxies has been suggested to be mainly associated with wolf-rayet stars (wrs), but wrs cannot satisfactorily explain the he ii-ionization at all times, particularly at the lowest metallicities. shocks from supernova remnants, or x-ray binaries, have been proposed as additional potential sources of he ii-ionizing photons. our data indicate that conventional he ii-ionizing sources (wrs, shocks, x-ray binaries) are not sufficient to explain the observed nebular he iiλ4686 emission in izw 18. we find that the he ii-ionizing radiation expected from models for either low-metallicity super-massive o stars or rotating metal-free stars could account for the he ii-ionization budget measured, while only the latter models could explain the highest values of he iiλ4686/hβ observed. the presence of such peculiar stars in izw 18 is suggestive and further investigation in this regard is needed. this letter highlights that some of the clues of the early universe can be found here in our cosmic backyard. | the extended he ii λ4686-emitting region in izw 18 unveiled: clues for peculiar ionizing sources |
the mammoth-grism slitless spectroscopic survey is a hubble space telescope (hst) cycle 28 medium program, which is obtaining 45 orbits of wfc3/ir grism spectroscopy in the density peak regions of three massive galaxy protoclusters at z = 2-3 discovered using the mammoth technique. we introduce this survey by presenting the first measurement of the mass-metallicity relation (mzr) at high redshift in overdense environments via grism spectroscopy. from the completed mammoth-grism observations in the field of the boss1244 protocluster at z = 2.24 ± 0.02, we secure a sample of 36 protocluster member galaxies at z ≈ 2.24, showing strong nebular emission lines ([o iii], hβ, and [o ii]) in their g141 spectra. using the multi-wavelength broadband deep imaging from hst and ground-based telescopes, we measure their stellar masses in the range of [109, 1010.4] m ⊙, instantaneous star formation rates (sfr) from 10 to 240 m ⊙ yr-1, and global gas-phase metallicities $[\tfrac{1}{3},1]$ of solar. compared with similarly selected field-galaxy samples at the same redshift, our galaxies show, on average, increased sfrs by ~0.06 dex and ~0.18 dex at ~1010.1 m ⊙ and ~109.8 m ⊙, respectively. using the stacked spectra of our sample galaxies, we derive the mzr in the boss1244 protocluster core as $12+\mathrm{log}({\rm{o}}/{\rm{h}})=\left(0.136\pm 0.018\right)$ × $\mathrm{log}({m}_{* }/{m}_{\odot })+\left(7.082\pm 0.175\right)$ , showing a significantly shallower slope than that in the field. this shallow mzr slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. the former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal-poor than their coeval field counterparts. | the mass-metallicity relation at cosmic noon in overdense environments: first results from the mammoth-grism hst slitless spectroscopic survey |
in a companion work (paper i), we detected a large population of highly variable young stellar objects (ysos) in the vista variables in the via lactea (vvv) survey, typically with class i or flat spectrum spectral energy distributions and diverse light-curve types. here we present infrared spectra (0.9-2.5 μm) of 37 of these variables, many of them observed in a bright state. the spectra confirm that 15/18 sources with eruptive light curves have signatures of a high accretion rate, either showing exor-like emission features (δv = 2 co, brγ) and/or fuor-like features (δv = 2 co and h2o strongly in absorption). similar features were seen in some long-term periodic ysos and faders but not in dippers or short-term variables. the sample includes some dusty mira variables (typically distinguished by smooth mira-like light curves), two cataclysmic variables and a carbon star. in total, we have added 19 new objects to the broad class of eruptive variable ysos with episodic accretion. eruptive variable ysos in our sample that were observed at bright states show higher accretion luminosities than the rest of the sample. most of the eruptive variables differ from the established fuor and exor subclasses, showing intermediate outburst durations and a mixture of their spectroscopic characteristics. this is in line with a small number of other recent discoveries. since these previously atypical objects are now the majority amongst embedded members of the class, we propose a new classification for them as mnors. this term (pronounced emnor) follows v1647 ori, the illuminating star of mcneil's nebula. | infrared spectroscopy of eruptive variable protostars from vvv |
we present nebular phase optical and near-infrared spectroscopy of the type ia supernova (sn) 2017cbv. the early light curves of sn 2017cbv showed a prominent blue bump in the u, b, and g bands lasting for ∼5 days. one interpretation of the early light curve is that the excess blue light is due to shocking of the sn ejecta against a nondegenerate companion star—a signature of the single degenerate scenario. if this is the correct interpretation, the interaction between the sn ejecta and the companion star could result in significant hα (or helium) emission at late times, possibly along with other species, depending on the companion star and its orbital separation. a search for hα emission in our +302 d spectrum yields a nondetection, with a l hα< 8.0 × 1035 erg s-1 (given an assumed distance of d = 12.3 mpc), which we verified by implanting simulated hα emission into our data. we make a quantitative comparison to models of swept-up material stripped from a nondegenerate companion star and limit the mass of hydrogen that might remain undetected to m h < 1 × 10-4 m ⊙. a similar analysis of helium star related lines yields a m he < 5 × 10-4 m ⊙. taken at face value, these results argue against a nondegenerate h- or he-rich companion in roche lobe overflow as the progenitor of sn 2017cbv. alternatively, there could be weaknesses in the envelope-stripping and radiative transfer models necessary to interpret the strong h and he flux limits. | nebular spectroscopy of the “blue bump” type ia supernova 2017cbv |
we present results on the emission-line properties of 1.3 ≤ z ≤ 2.7 galaxies drawn from the complete the mosfire deep evolution field (mosdef) survey. specifically, we use observations of the emission-line diagnostic diagram of [o iii]λ 5007/hβ versus [s ii]λλ6717,6731/hα, i.e., the “[s ii] bpt diagram,” to gain insight into the physical properties of high-redshift star-forming regions. high-redshift mosdef galaxies are offset toward lower [s ii]λλ6717,6731/hα at fixed [o iii]λ5007/hβ, relative to local galaxies from the sloan digital sky survey (sdss). furthermore, at fixed [o iii]λ5007/hβ, local sdss galaxies follow a trend of decreasing [s ii]λλ6717,6731/hα as the surface density of star formation (σsfr) increases. we explain this trend in terms of the decreasing fractional contribution from diffuse ionized gas (f dig) as σsfr increases in galaxies, which causes galaxy-integrated line ratios to shift toward the locus of pure h ii-region emission. the z ∼ 0 relationship between f dig and σsfr implies that high-redshift galaxies have lower f dig values than typical local systems, given their significantly higher typical σsfr. when an appropriate low-redshift benchmark with zero or minimal f dig is used, high-redshift mosdef galaxies appear offset toward higher [s ii]λλ6717,6731/hα and/or [o iii]λ 5007/hβ. the joint shifts of high-redshift galaxies in the [s ii] and [n ii] bpt diagrams are best explained in terms of the harder spectra ionizing their star-forming regions at fixed nebular oxygen abundance (expected for chemically young galaxies), as opposed to large variations in n/o ratios or higher ionization parameters. the evolving mixture of h ii regions and diffuse ionized gas is an essential ingredient of our description of the interstellar medium over cosmic time. 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 the national aeronautics and space administration, and was made possible by the generous financial support of the w.m. keck foundation. | the mosdef survey: sulfur emission-line ratios provide new insights into evolving interstellar medium conditions at high redshift |
determining the origin of volatiles on terrestrial planets and quantifying atmospheric loss during planet formation is crucial for understanding the history and evolution of planetary atmospheres. using geochemical observations of noble gases and major volatiles we determine what the present day inventory of volatiles tells us about the sources, the accretion process and the early differentiation of the earth. we further quantify the key volatile loss mechanisms and the atmospheric loss history during earth's formation. volatiles were accreted throughout the earth's formation, but earth's early accretion history was volatile poor. although nebular ne and possible h in the deep mantle might be a fingerprint of this early accretion, most of the mantle does not remember this signature implying that volatile loss occurred during accretion. present day geochemistry of volatiles shows no evidence of hydrodynamic escape as the isotopic compositions of most volatiles are chondritic. this suggests that atmospheric loss generated by impacts played a major role during earth's formation. while many of the volatiles have chondritic isotopic ratios, their relative abundances are certainly not chondritic again suggesting volatile loss tied to impacts. geochemical evidence of atmospheric loss comes from the {}3he/{}^{22}ne, halogen ratios (e.g., f/cl) and low h/n ratios. in addition, the geochemical ratios indicate that most of the water could have been delivered prior to the moon forming impact and that the moon forming impact did not drive off the ocean. given the importance of impacts in determining the volatile budget of the earth we examine the contributions to atmospheric loss from both small and large impacts. we find that atmospheric mass loss due to impacts can be characterized into three different regimes: 1) giant impacts, that create a strong shock transversing the whole planet and that can lead to atmospheric loss globally. 2) large enough impactors (m_{cap} ≳ √{2} ρ0 (π h r)^{3/2}, r_{cap}∼25 km for the current earth), that are able to eject all the atmosphere above the tangent plane of the impact site, where h, r and ρ0 are the atmospheric scale height, radius of the target, and its atmospheric density at the ground. 3) small impactors (m_{min}>4 πρ0 h3, r_{min}∼ 1 km for the current earth), that are only able to eject a fraction of the atmospheric mass above the tangent plane. we demonstrate that per unit impactor mass, small impactors with r_{min} < r < r_{cap} are the most efficient impactors in eroding the atmosphere. in fact for the current atmospheric mass of the earth, they are more than five orders of magnitude more efficient (per unit impactor mass) than giant impacts, implying that atmospheric mass loss must have been common. the enormous atmospheric mass loss efficiency of small impactors is due to the fact that most of their impact energy and momentum is directly available for local mass loss, where as in the giant impact regime a lot of energy and momentum is 'wasted' by having to create a strong shock that can transverse the entirety of the planet such that global atmospheric loss can be achieved. in the absence of any volatile delivery and outgassing, we show that the population of late impactors inferred from the lunar cratering record containing 0.1% m_{\oplus } is able to erode the entire current earth's atmosphere implying that an interplay of erosion, outgassing and volatile delivery is likely responsible for determining the atmospheric mass and composition of the early earth. combining geochemical observations with impact models suggest an interesting synergy between small and big impacts, where giant impacts create large magma oceans and small and larger impacts drive the atmospheric loss. | atmosphere impact losses |
carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur (chnops) play key roles in the origin and proliferation of life on earth. given the universality of physics and chemistry, not least the ubiquity of water as a solvent and carbon as a backbone of complex molecules, chnops are likely crucial to most habitable worlds. to help guide and inform the search for potentially habitable and ultimately inhabited environments, we begin by summarizing the chnops budget of various reservoirs on earth, their role in shaping our biosphere, and their origins in the solar nebula. we then synthesize our current understanding of how these elements behave and are distributed in diverse astrophysical settings, tracing their journeys from synthesis in dying stars to molecular clouds, protoplanetary settings, and ultimately temperate rocky planets around main sequence stars. we end by identifying key branching points during this journey, highlighting instances where a forming planets' distribution of chnops can be altered dramatically, and speculating about the consequences for the chemical habitability of these worlds. | chemical habitability: supply and retention of life's essential elements during planet formation |
we study the broadband emission of mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, magic, fermi's large area telescope (lat), nustar, swift, gasp-webt, and the owens valley radio observatory. mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at x-rays and very-high-energy (vhe) γ-rays. a significant correlation (>3σ) between x-rays and vhe γ-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. this is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the swift x-ray telescope and fermi-lat. we additionally find correlations between high-energy γ-rays and radio, with the radio lagging by more than 100 days, placing the γ-ray emission zone upstream of the radio-bright regions in the jet. furthermore, mrk 501 showed a historically low activity in x-rays and vhe γ-rays from mid-2017 to mid-2019 with a stable vhe flux (>0.2 tev) of 5% the emission of the crab nebula. the broadband spectral energy distribution (sed) of this 2 yr long low state, the potential baseline emission of mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from icecube. we explore the time evolution of the sed toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock. | multimessenger characterization of markarian 501 during historically low x-ray and γ-ray activity |
we report on our study of the supernova (sn) 2022xxf based on observations obtained during the first four months of its evolution. the light curves (lcs) display two humps of similar maximum brightness separated by 75 days, unprecedented for a broad-lined (bl) type ic supernova (sn icbl). sn 2022xxf is the most nearby sn icbl to date (in ngc 3705, z = 0.0037, at a distance of about 20 mpc). optical and near-infrared photometry and spectroscopy were used to identify the energy source powering the lc. nearly 50 epochs of high signal-to-noise ratio spectroscopy were obtained within 130 days, comprising an unparalleled dataset for a sn icbl, and one of the best-sampled sn datasets to date. the global spectral appearance and evolution of sn 2022xxf points to typical sn ic/icbl, with broad features (up to ~14 000 km s−1) and a gradual transition from the photospheric to the nebular phase. however, narrow emission lines (corresponding to ~ 1000-2500 km s−1) are present in the spectra from the time of the second rise, suggesting slower-moving circumstellar material (csm). these lines are subtle, in comparison to the typical strong narrow lines of csm-interacting sne, for example, type iin, ibn, and icn, but some are readily noticeable at late times, such as in mg i λ5170 and [o i] λ5577. unusually, the near-infrared spectra show narrow line peaks in a number of features formed by ions of o and mg. we infer the presence of csm that is free of h and he. we propose that the radiative energy from the ejecta-csm interaction is a plausible explanation for the second lc hump. this interaction scenario is supported by the color evolution, which progresses to blue as the light curve evolves along the second hump, and by the slow second rise and subsequent rapid lc drop. sn 2022xxf may be related to an emerging number of csm-interacting sne ic, which show slow, peculiar lcs, blue colors, and subtle csm interaction lines. the progenitor stars of these sne likely experienced an episode of mass loss consisting of h/he-free material shortly prior to explosion. photometric and spectroscopic data are available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/678/a209 | the broad-lined type-ic supernova sn 2022xxf and its extraordinary two-humped light curves. i. signatures of h/he-free interaction in the first four months |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.