abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
it is now clear that a binary evolutionary pathway is responsible for a significant fraction of all planetary nebulae, with some authors even going so far as to claim that binarity may be a near requirement for the formation of an observable nebula. this has led to the requirement that textbooks most likely need to be rewritten. building upon the review of jones and boffin in nature astronomy (2017), this springer brief takes a first step in this direction. it offers the first expanded presentation of all the theoretical and observational support for the importance of binarity in the formation of planetary nebulae, initially focusing on common envelope evolution but also covering wider binaries. this book emphasises the wider impact of the field, highlighting the critical role binary central stars of planetary nebulae have in understanding a plethora of astrophysical phenomena, including type ia supernovae, chemically peculiar stars and circumbinary exoplanets. | the importance of binaries in the formation and evolution of planetary nebulae |
circumplanetary disks (cpds) may be essential to the formation of planets, regulating their spin and accretion evolution. we perform a series of 3d hydrodynamics simulations in both the isothermal and adiabatic limits to systematically measure the rotation rates, sizes, and masses of cpds as functions of {q}thermal}, the ratio of the planet mass to the disk thermal mass. our {q}thermal} ranges from 0.1 to 4; for our various disk temperatures, this corresponds to planet masses between one earth mass and four jupiter masses. within this parameter space, we find that isothermal cpds are disky and bound within ∼10% of the planet’s bondi radius {r}{{b}}, with the innermost ∼ 0.05 {r}{{b}} in full rotational support. adiabatic cpds are spherical (and therefore not actually “disks”), bound within ∼ 0.2 {r}{{b}}, and mainly pressure-supported, with rotation rates scaling linearly with {q}thermal}; extrapolation suggests full rotational support of adiabatic envelopes at ∼ 10 {q}thermal}. fast rotation and 3d supersonic flow render isothermal cpds significantly different in structure from—and orders of magnitude less massive than—their 1d isothermal hydrostatic counterparts. inside a minimum-mass solar nebula, even a maximally cooled, isothermal cpd around a 10 earth-mass core may have less than one earth mass, suggesting that gas giant formation may hinge on angular momentum transport processes in cpds. our cpd sizes and masses appear consistent with the regular satellites orbiting solar system giants. | circumplanetary disk dynamics in the isothermal and adiabatic limits |
we present the discovery and analysis of sn\,2022oqm, a type ic supernova (sn) detected $<1$\,day after explosion. the sn rises to a blue and short-lived (2\,days) initial peak. early-time spectral observations of sn\,2022oqm show a hot (40,000\,k) continuum with high-ionization c and o absorption features at velocities of 4000\,km\,s$^{-1}$, while its photospheric radius expands at 20,000\,\kms, indicating a pre-existing distribution of expanding c/o material. after $\sim2.5$\,days, both the spectrum and light curves evolve into those of a typical sn ic, with line velocities of $\sim10,000$\,km\,s$^{-1}$, in agreement with the photospheric radius evolution. the optical light curves reach a second peak at $t\approx15$\,days. by $t=60$\,days, the spectrum of \oqm\ becomes nearly nebular, displaying strong \ion{ca}{2} and [\ion{ca}{2}] emission with no detectable [\ion{o}{1}], marking this event as ca-rich. the early behavior can be explained by $10^{-3}$\,\msun\ of optically thin circumstellar material (csm) surrounding either (1) a massive compact progenitor such as a wolf-rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. we propose that the early-time light curve is powered by both interaction of the ejecta with the optically thin csm and shock cooling (in the massive-star scenario). the observations can be explained by csm that is optically thick to x-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered x-rays or from the shock-heated ejecta. calculations show that this scenario is self-consistent. | sn 2022oqm -- a ca-rich explosion of a compact progenitor embedded in c/o circumstellar material |
we use the sphinx20 cosmological radiation hydrodynamics simulation to study how lyman continuum (lyc) photons escape from galaxies and the observational signatures of this escape. we define two classes of lyc leaker: bursty leakers and remnant leakers, based on their star formation rates (sfrs) that are averaged over 10 myr (sfr10) or 100 myr (sfr100). both have $f_{\rm esc}\gt 20{{\ \rm per\ cent}}$ and experienced an extreme burst of star formation, but bursty leakers have sfr10 > sfr100, while remnant leakers have sfr10 < sfr100. the maximum sfrs in these bursts were typically ~100 times greater than the sfr of the galaxy prior to the burst, a rare 2σ outlier among the general high-redshift galaxy population. bursty leakers are qualitatively similar to ionization-bounded nebulae with holes, exhibiting high ionization parameters and typical h ii region gas densities. remnant leakers show properties of density-bounded nebulae, having normal ionization parameters but much lower h ii region densities. both types of leaker exhibit [c ii]158μm deficits on the [c ii]-sfr100 relation, while only bursty leakers show deficits when sfr10 is used. we predict that [c ii] luminosity and sfr indicators such as h α and m$_{\rm 1500\mathring{\rm a}}$ can be combined to identify both types of lyc leaker and the mode by which photons are escaping. these predictions can be tested with [c ii] observations of known z = 3-4 lyc leakers. finally, we show that leakers with $f_{\rm esc}\gt 20{{\ \rm per\ cent}}$ dominate the ionizing photon budget at z ≳ 7.5 but the contribution from galaxies with $f_{\rm esc}\lt 5{{\ \rm per\ cent}}$ becomes significant at the tail-end of reionization. | two modes of lyc escape from bursty star formation: implications for [c ii] deficits and the sources of reionization |
integral field units enable resolved studies of a large number of star-forming regions across entire nearby galaxies, providing insight on the conversion of gas into stars and the feedback from the emerging stellar populations over unprecedented dynamic ranges in terms of spatial scale, star-forming region properties, and environments. we use the very large telescope (vlt) muse (multi unit spectroscopic explorer) legacy data set covering the central 35 arcmin2 (~12 kpc2) of the nearby galaxy ngc 300 to quantify the effect of stellar feedback as a function of the local galactic environment. we extract spectra from emission line regions identified within dendrograms, combine emission line ratios and line widths to distinguish between ${\rm h\, \small {ii}}$ regions, planetary nebulae, and supernova remnants, and compute their ionized gas properties, gas-phase oxygen abundances, and feedback-related pressure terms. for the ${\rm h\, \small {ii}}$ regions, we find that the direct radiation pressure (pdir) and the pressure of the ionized gas ($p_{{\rm h\, \small {ii}}}$) weakly increase towards larger galactocentric radii, i.e. along the galaxy's (negative) abundance and (positive) extinction gradients. while the increase of $p_{{\rm h\, \small {ii}}}$ with galactocentric radius is likely due to higher photon fluxes from lower-metallicity stellar populations, we find that the increase of pdir is likely driven by the combination of higher photon fluxes and enhanced dust content at larger galactocentric radii. in light of the above, we investigate the effect of increased pre-supernova feedback at larger galactocentric distances (lower metallicities and increased dust mass surface density) on the ism, finding that supernovae at lower metallicities expand into lower-density environments, thereby enhancing the impact of supernova feedback. | the impact of pre-supernova feedback and its dependence on environment |
we study the evolution and final dispersal of protoplanetary discs that evolve under the action of internal and external photoevaporation, and different degrees of viscous transport. we identify five distinct dispersal pathways, which are (i) very long-lived discs ($\gt 20\,$ myr), (ii) inside-out dispersal where internal photoevaporation dominates and opens inner holes, (iii) outside-in dispersal where external photoevaporation dominates through disc truncation, and two intermediate regimes characterized by lingering material in the inner disc with the outer disc dispersed predominantly by either internal or external photoevaporation. we determine how the lifetime, relative impact of internal and external winds, and clearing pathway vary over a wide, plausible, parameter space of stellar/disc/radiation properties. there are a number of implications, for example, in high uv environments because the outer disc lifetime is shorter than the time-scale for clearing the inner disc, we do not expect transition discs to be common, which appears to be reflected in the location of transition disc populations towards the orion nebular cluster. irrespective of environment, we find that ongoing star formation is required to reproduce observed disc fractions as a function of stellar cluster age. this work demonstrates the importance of including both internal and external winds for understanding protoplanetary disc evolution. | dispersal of protoplanetary discs: how stellar properties and the local environment determine the pathway of evolution |
context. the gaia early data release 3 (edr3), published in december 2020, features improved photometry and astrometry compared to that published in the previous dr2 file and includes a substantially larger number of sources, of the order of 2000 million, making it a paradigm of big data astronomy. many of the central stars of planetary nebulae (cspne) are inherently faint and difficult to identify within the field of the nebula itself. gaia measurements may be relevant not only in identifying the ionising source of each nebula, but also in the study their physical and evolutionary properties.aims: we demonstrate how gaia data mining can effectively help to solve the issue of central star misidentification, a problem that has plagued the field since its origin. as we did for dr2, our objective is to present a catalogue of cspne with astrometric and photometric information in edr3. from that catalogue, we selected a sample of stars with high-quality astrometric parameters, on which we carried out a more accurate analysis of cspne properties. methods.gaiagbp − grp colours allow us to select the sources with sufficient temperatures to ionise the nebula. in order to estimate the real colour of a source, it is important to take into account interstellar extinction and, in the case of compact nebulae, nebular extinction when available. in addition, distances derived from edr3 parallaxes (combined with consistent literature values) can be used to obtain nebular intrinsic properties from those observed. with this information, cspne can be plotted in an hertzsprung-russell diagram. from information on the spectral classification of the cs (from the literature) and evolutionary models for post-agb stars, their evolutionary state can then be analysed. furthermore, edr3 high-quality astrometric data enable us to search for objects comoving with css in the field of each nebula by detecting sources with parallaxes and proper motions similar to those of the cs.results: we present a catalogue of 2035 pne with their corresponding cs identification from among gaia edr3 sources. we obtain the distances for those with known parallaxes in edr3 (1725 pne). in addition, for a sub-sample (405 pne) with the most accurate distances, we obtain different nebular properties such as their galactic distribution, radius, kinematic age, and morphology. furthermore, for a set of 74 cspne, we present the evolutionary state (mass and age) derived from their luminosities and effective temperatures from evolutionary models. finally, we highlight the detection of several wide binary cspne through an analysis of the edr3 astrometric parameters, and we contribute to shedding some light on the relevance of close binarity in cspne. full tables a.1 and a.2 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/a51 | planetary nebulae in gaia edr3: central star identification, properties, and binarity |
in the core-accretion formation scenario of gas giants, most of the gas accreting onto a planet is processed through an accretion shock. in this series of papers we study this shock because it is key in setting the structure of the forming planet and thus its postformation luminosity, with dramatic observational consequences. we perform one-dimensional gray radiation-hydrodynamical simulations with nonequilibrium (two-temperature) radiation transport and up-to-date opacities. we survey the parameter space of accretion rate, planet mass, and planet radius and obtain postshock temperatures, pressures, and entropies, as well as global radiation efficiencies. we find that the shock temperature tshock is usually given by the "free-streaming" limit. at low temperatures the dust opacity can make the shock hotter but not significantly so. we corroborate this with an original semianalytical derivation of tshock. we also estimate the change in luminosity between the shock and the nebula. neither tshock nor the luminosity profile depend directly on the optical depth between the shock and the nebula. rather, tshock depends on the immediate preshock opacity, and the luminosity change on the equation of state. we find quite high immediate postshock entropies (s≈ 13-20 kb mh-1), which makes it seem unlikely that the shock can cool the planet. the global radiation efficiencies are high (ηphys≳ 97%), but the remainder of the total incoming energy, which is brought into the planet, exceeds the internal luminosity of classical cold starts by orders of magnitude. overall, these findings suggest that warm or hot starts are more plausible. | the planetary accretion shock. ii. grid of postshock entropies and radiative shock efficiencies for nonequilibrium radiation transport |
we examine the clustering and kinematics of young stellar objects (ysos) in the north america/pelican nebulae, as revealed by gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular-line maps. the gaia parallaxes and proper motions allow us to significantly refine previously published lists of ysos, demonstrating that many of the objects previously thought to form a distributed population turn out to be nonmembers. the members are subdivided into at least six spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. three of the groups are expanding, with velocity gradients of 0.3-0.5 km s-1 pc-1, up to maximum velocities of ∼8 km s-1 away from the groups' centers. the two known o-type stars associated with the region, 2mass j20555125+4352246 and hd 199579, are rapidly escaping one of these groups, following the same position-velocity relation as the low-mass stars. we calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. however, on a global scale, the relative motions of the groups do not appear either divergent or convergent. the velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. most of the stellar population has ages similar to the freefall timescales for the natal clouds. thus, we suggest the nearly freefall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex. | the formation of a stellar association in the ngc 7000/ic 5070 complex: results from kinematic analysis of stars and gas |
despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. observations of the kilonova following the gravitational-wave-detected neutron star merger gw170817 established mergers as one site of the r-process, but additional sources may be needed to fully explain r-process enrichment in the universe. one intriguing possibility is that rapidly rotating massive stars undergoing core collapse launch r-process-rich outflows off the accretion disks formed from their infalling matter. in this scenario, r-process winds are one component of the supernova (sn) ejecta produced by "collapsar" explosions. we present the first systematic study of the effects of r-process enrichment on the emission from collapsar-generated sne. we semianalytically model r-process sn emission from explosion out to late times and determine its distinguishing features. the ease with which r-process sne can be identified depends on how effectively wind material mixes into the initially r-process-free outer layers of the ejecta. in many cases, enrichment produces a near-infrared (nir) excess that can be detected within ~75 days of explosion. we also discuss optimal targets and observing strategies for testing the r-process collapsar theory, and find that frequent monitoring of optical and nir emission from high-velocity sne in the first few months after explosion offers a reasonable chance of success while respecting finite observing resources. such early identification of r-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the nir and mid-infrared, for example, with the james webb space telescope. | signatures of r-process enrichment in supernovae from collapsars |
the mg ii λλ2796, 2803 doublet is often used to measure interstellar medium absorption in galaxies, thereby serving as a diagnostic for feedback and outflows. however, the interpretation of mg ii remains confusing, due to resonant trapping and re-emission of the photons, analogous to lyα. therefore, in this paper, we present new mmt blue channel spectrograph observations of mg ii for a sample of 10 green pea galaxies at z ∼ 0.2-0.3, where lyα was previously observed with the cosmic origins spectrograph on the hubble space telescope. with strong, (mostly) double-peaked lyα profiles, these galaxies allow us to observe mg ii in the limit of low h i column density. we find strong mg ii emission and little-to-no absorption. we use photoionization models to show that nebular mg ii from h ii regions is non-negligible, and the ratios of mg ii λλ2796, 2803/[o iii] λ5007 versus [o iii] λ5007/[o ii] λ3727 form a tight sequence. using this relation, we predict intrinsic mg ii flux, and show that mg ii escape fractions range from 0 to 0.9. we find that the mg ii escape fraction correlates tightly with the lyα escape fraction, and the mg ii line profiles show evidence for broader and more redshifted emission when the escape fractions are low. these trends are expected if the escape fractions and velocity profiles of lyα and mg ii are shaped by resonant scattering in the same low column density gas. as a consequence of a close relation with lyα, mg ii may serve as a useful diagnostic in the epoch of reionization, where lyα and lyman continuum photons are not easily observed. | a close relationship between lyα and mg ii in green pea galaxies |
refractory organics are the main hosts of carbon, nitrogen, and other biogenic elements in primitive solar system material. we have synthesized refractory organics by ionizing a gas mixture reminiscent of the composition of the protosolar nebula, at temperatures up to 1,000 k in a plasma. synthesized compounds share chemical and structural features with chondritic organics, and trapped noble gases reproduce well the elemental and isotopic characteristics of meteoritic noble gases. our study suggests that organosynthesis took place in the solar system, including in its warm regions, and was ubiquitous anywhere the nebular gas was subject to ionization. | synthesis of refractory organic matter in the ionized gas phase of the solar nebula |
the origin and evolution of planetary protoatmospheres in relation to the protoplanetary disk is discussed. the initial atmospheres of planets can mainly be related via two formation scenarios. if a protoplanetary core accretes mass and grows inside the gas disk, it can capture h2, he and other gases from the disk. when the gas of the disk evaporates, the core that is surrounded by the h2/he gas envelope is exposed to the high x-ray and extreme ultraviolet flux and stellar wind of the young host star. this period can be considered as the onset of atmospheric escape. it is shown that lower mass bodies accrete less gas and depending on the host stars radiation environment can therefore lose the gaseous envelope after tens or hundreds of million years. massive cores may never get rid of their captured hydrogen envelopes and remain as sub-neptunes, neptunes or gas giants for their whole life time. terrestrial planets which may have lost the captured gas envelope by thermal atmospheric escape, or which accreted after the protoplanetary nebula vanished will produce catastrophically outgassed steam atmospheres during the magma ocean solidification process. these steam atmospheres consist mainly of water and co2 that was incorporated into the protoplanet during its accretion. planets, which are formed in the habitable zone, solidify within several million years. in such cases the outgassed steam atmospheres cool fast, which leads to the condensation of water and the formation of liquid oceans. on the other hand, magma oceans are sustained for longer if planets form inside a critical distance, even if they outgassed a larger initial amount of water. in such cases the steam atmosphere could remain 100 million years or for even longer. hydrodynamic atmospheric escape will then desiccate these planets during the slow solidification process. | formation and evolution of protoatmospheres |
this review provides useful background and information on how we find, vet and compile planetary nebulae (pne) candidates and verify them. it presents a summary of the known galactic pne population and their curation in the hong kong/aao/strasbourg/hα pne catalogue, "hash". it is a simple introduction for anyone interested in working with pne, including postgraduate students entering the field and for more general interest too. | planetary nebulae and how to find them: a concise review |
the morphology of planetary nebulae emerging from the common envelope phase of binary star evolution is investigated. using initial conditions based on the numerical results of hydrodynamical simulations of the common envelope phase, it was found that the shapes and sizes of the resulting nebula are very sensitive to the effective temperature of the remnant core, the mass-loss rate at the onset of the common envelope phase, and the mass ratio of the binary system. these parameters are related to the efficiency of the mass ejection after the spiral-in phase, the stellar evolutionary phase (i.e., rg, agb, or tp-agb), and the degree of departure from spherical symmetry in the stellar wind mass-loss process itself, respectively. it was also found that the shapes are mostly bipolar in the early phase of evolution, but that they can quickly transition to elliptical and barrel-type shapes. solutions for nested lobes are found where the outer lobes are usually bipolar and the inner lobes are elliptical, bipolar, or barrel-type, a result due to the flow of the photo-evaporated gas from the equatorial region. also, the lobes can be produced without the need for two distinct mass ejection events. in all the computations, the bulk of the mass is concentrated in the orbital or equatorial plane, in the form of a large toroid, which can be either neutral (early phases) or photoionized (late phases), depending of the evolutionary state of the system. | common envelope shaping of planetary nebulae |
we present a new catalogue of h ii regions based on the integral field spectroscopy (ifs) data of the extended califa and pisco samples. the selection of h ii regions was based on two assumptions: a clumpy structure with high contrast of h α emission and an underlying stellar population comprising young stars. the catalogue provides the spectroscopic information of 26 408 individual regions corresponding to 924 galaxies, including the flux intensities and equivalent widths of 51 emission lines covering the wavelength range between 3745 and 7200 å. to our knowledge, this is the largest catalogue of spectroscopic properties of h ii regions. we explore a new approach to decontaminate the emission lines from diffuse ionized gas contribution. this diffuse gas correction was estimated to correct every emission line within the considered spectral range. with the catalogue of h ii regions corrected, new demarcation lines are proposed for the classical diagnostic diagrams. finally, we study the properties of the underlying stellar populations of the h ii regions. it was found that there is a direct relationship between the ionization conditions on the nebulae and the properties of stellar populations besides the physicals condition on the ionized regions. | h ii regions in the califa survey: i. catalogue presentation |
a series of optical and one near-infrared nebular spectra covering the first year of the type ia supernova sn 2011fe are presented and modelled. the density profile that proved best for the early optical/ultraviolet spectra, `ρ-11fe', was extended to lower velocities to include the regions that emit at nebular epochs. model ρ-11fe is intermediate between the fast deflagration model w7 and a low-energy delayed-detonation. good fits to the nebular spectra are obtained if the innermost ejecta are dominated by neutron-rich, stable fe-group species, which contribute to cooling but not to heating. the correct thermal balance can thus be reached for the strongest [fe ii] and [fe iii] lines to be reproduced with the observed ratio. the 56ni mass thus obtained is ∼0.47 ± 0.05 m⊙. the bulk of 56ni has an outermost velocity of ∼8500 km s-1. the mass of stable iron is ∼0.23 ± 0.03 m⊙. stable ni has low abundance, ∼10-2 m⊙. this is sufficient to reproduce an observed emission line near 7400 å. a sub-chandrasekhar explosion model with mass 1.02 m⊙ and no central stable fe does not reproduce the observed line ratios. a mock model where neutron-rich fe-group species are located above 56ni following recent suggestions is also shown to yield spectra that are less compatible with the observations. the densities and abundances in the inner layers obtained from the nebular analysis, combined with those of the outer layers previously obtained, are used to compute a synthetic bolometric light curve, which compares favourably with the light curve of sn 2011fe. | nebular spectra and abundance tomography of the type ia supernova sn 2011fe: a normal sn ia with a stable fe core |
sn 2018aoz is a type ia sn with a b-band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. here, we advance the constraints on the nature and origin of sn 2018aoz based on its evolution until the nebular phase. near-peak spectroscopic features show that the sn is intermediate between two subtypes of normal type ia: core normal and broad line. the excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. nebular-phase limits on hα and he i favor a white dwarf companion, consistent with the small companion size constrained by the low early sn luminosity, while the absence of [o i] and he i disfavors a violent merger of the progenitor. of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in sn 2018aoz, the asymmetric chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [fe ii] and [ni ii]. the helium-shell double-detonation explosion is compatible with the observed lack of c spectral features, but current 1d models are incompatible with the infant-phase excess emission, ${b}_{\max }\mbox{--}{v}_{\max }$ color, and weak strength of nebular-phase [ca ii]. although the explosion processes of sn 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of type ia sne that appear to be normal after ~1 day. | the origin and evolution of the normal type ia sn 2018aoz with infant-phase reddening and excess emission |
the classic single-degenerate model for the progenitors of type ia supernova (sn ia) predicts that the supernova ejecta should be enriched with solar-like abundance material stripped from the companion star. spectroscopic observations of normal sne ia at late times, however, have not resulted in definite detection of hydrogen. in this letter, we study line formation in sne ia at nebular times using non-lte spectral modeling. we present, for the first time, multidimensional radiative transfer calculations of sne ia with stripped material mixed in the ejecta core, based on hydrodynamical simulations of ejecta-companion interaction. we find that interaction models with main-sequence companions produce significant hα emission at late times, ruling out these types of binaries being viable progenitors of sne ia. we also predict significant he i line emission at optical and near-infrared wavelengths for both hydrogen-rich or helium-rich material, providing an additional observational probe of stripped ejecta. we produce models with reduced stripped masses and find a more stringent mass limit of m st ≲ 1 × 10-4 m ⊙ of stripped companion material for sn 2011fe. | multidimensional models of type ia supernova nebular spectra: strong emission lines from stripped companion gas rule out classic single-degenerate systems |
context. dust attenuation shapes the spectral energy distribution of galaxies. it is particularly true for dusty galaxies in which stars experience a heavy attenuation. the combination of uv to ir photometry with the spectroscopic measurement of the hα recombination line helps to quantify dust attenuation of the whole stellar population and its wavelength dependence.aims: we want to derive the shape of the global attenuation curve and the amount of obscuration affecting young stars or nebular emission and the bulk of the stellar emission in a representative sample of galaxies selected in ir. we will compare our results to the commonly used recipes of calzetti et al. and charlot and fall, and to predictions of radiative transfer models.methods: we selected an ir complete sample of galaxies in the cosmos 3d-hst candels field detected with the herschel satellite with a signal to noise ratio larger than five. optical to nir photometry is available as well as nir spectroscopy for each source. we reduced the sample to the redshift range 0.6 < z < 1.6 to include the hα line in the g141 grism spectra. we have used a new version of the cigale code to fit simultaneously the continuum and hα line emission of the 34 selected galaxies.results: using flexible attenuation laws with free parameters, we are able to measure the shape of the attenuation curve for each galaxy as well as the amount of attenuation of each stellar population, the former being in general steeper than the starburst law in the uv-optical with a large variation of the slope among galaxies. the attenuation of young stars or nebular continuum is found on average about twice the attenuation affecting older stars, again with a large variation. our model with power-laws, based on a modification of the charlot and fall recipe, gives results in better agreement with the radiative transfer models than the global modification of the slope of the calzetti law. | dust attenuation and hα emission in a sample of galaxies observed with herschel at 0.6 < z < 1.6 |
the ratios of strong rest-frame optical emission lines are the dominant indicator of metallicities in high-redshift galaxies. since typical strong-line based metallicity indicators are calibrated on auroral lines at $z=0$, their applicability for galaxies in the distant universe is unclear. in this paper, we make use of mock emission line data from cosmological simulations to investigate the calibration of rest-frame optical emission lines as metallicity indicators at high redshift. our model, which couples the simba cosmological galaxy formation simulation with cloudy photoionization calculations, includes contributions from hii regions, post-agb stars and diffuse ionized gas (dig). we find mild redshift evolution in the 12 indicators that we study, which implies that the dominant physical properties that evolve in our simulations do have a discernible impact on the metallicity calibrations at high redshifts. when comparing our calibrations with high redshift auroral line observations from james webb space telescope we find a slight offset between our model results and the observations and find that a higher ionization parameter at high redshifts can be one of the possible explanations. we explore the physics that drives the shapes of strong-line metallicity relationships and propose calibrations for hitherto unexplored low-metallicity regimes. finally, we study the contribution of dig to total line fluxes. we find that the contribution of dig increases with metallicity at z $\sim$ 0 for singly ionized oxygen and sulfur lines and can be as high as 70% making it crucial to include their contribution when modeling nebular emission. | theoretical strong line metallicity diagnostics for the jwst era |
context. the chemical composition of planets is an important constraint for planet formation and subsequent differentiation. while theoretical studies try to derive the compositions of planets from planet formation models in order to link the composition and formation process of planets, other studies assume that the elemental ratios in the formed planet and in the host star are the same.aims: using a chemical model combined with a planet formation model, we aim to link the composition of stars with solar mass and luminosity with the composition of the hosted planets. for this purpose, we study the three most important elemental ratios that control the internal structure of a planet: fe/si, mg/si, and c/o.methods: a set of 18 different observed stellar compositions was used to cover a wide range of these elemental ratios. the gibbs energy minimization assumption was used to derive the composition of planets, taking stellar abundances as proxies for nebular abundances, and to generate planets in a self-consistent planet formation model. we computed the elemental ratios fe/si, mg/si and c/o in three types of planets (rocky, icy, and giant planets) formed in different protoplanetary discs, and compared them to stellar abundances.results: we show that the elemental ratios mg/si and fe/si in planets are essentially identical to those in the star. some deviations are shown for planets that formed in specific regions of the disc, but the relationship remains valid within the ranges encompassed in our study. the c/o ratio shows only a very weak dependence on the stellar value. appendix a is available in electronic form at http://www.aanda.org | elemental ratios in stars vs planets |
dust grains are classically thought to form in the winds of asymptotic giant branch (agb) stars. however, there is increasing evidence today for dust formation in supernovae (sne). to establish the relative importance of these two classes of stellar sources of dust, it is important to know the fraction of freshly formed dust in sn ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. with this aim, we have developed a new code, grash_rev, that allows following the dynamics of dust grains in the shocked sn ejecta and computing the time evolution of the mass, composition, and size distribution of the grains. we considered four well-studied sne in the milky way and large magellanic cloud: sn 1987a, casa, the crab nebula, and n49. these sources have been observed with both spitzer and herschel, and the multiwavelength data allow a better assessment the mass of warm and cold dust associated with the ejecta. for each sn, we first identified the best explosion model, using the mass and metallicity of the progenitor star, the mass of 56ni, the explosion energy, and the circumstellar medium density inferred from the data. we then ran a recently developed dust formation model to compute the properties of freshly formed dust. starting from these input models, grash_rev self-consistently follows the dynamics of the grains, considering the effects of the forward and reverse shock, and allows predicting the time evolution of the dust mass, composition, and size distribution in the shocked and unshocked regions of the ejecta. all the simulated models aagree well with observations. our study suggests that sn 1987a is too young for the reverse shock to have affected the dust mass. hence the observed dust mass of 0.7-0.9 m⊙ in this source can be safely considered as indicative of the mass of freshly formed dust in sn ejecta. conversely, in the other three sne, the reverse shock has already destroyed between 10-40% of the initial dust mass. however, the largest dust mass destruction is predicted to occur between 103 and 105 yr after the explosions. since the oldest sn in the sample has an estimated age of 4800 yr, current observations can only provide an upper limit to the mass of sn dust that will enrich the interstellar medium, the so-called effective dust yields. we find that only between 1-8% of the currently observed mass will survive, resulting in an average sn effective dust yield of (1.55 ± 1.48) × 10-2m⊙. this agrees well with the values adopted in chemical evolution models that consider the effect of the sn reverse shock. we discuss the astrophysical implications of our results for dust enrichment in local galaxies and at high redshift. | dust grains from the heart of supernovae |
the wise catalog of galactic h ii regions contains ∼2000 h ii region candidates lacking ionized gas spectroscopic observations. all candidates have the characteristic h ii region mid-infrared morphology of wise 12 μ {{m}} emission surrounding 22 μ {{m}} emission, and additionally have detected radio continuum emission. we here report green bank telescope hydrogen radio recombination line and radio continuum detections in the x-band (9 ghz; 3 cm) of 302 wise h ii region candidates (out of 324 targets observed) in the zone 225^\circ ≥slant {\ell }≥slant -20^\circ , | {\text{}}b| ≤slant 6^\circ . here we extend the sky coverage of our h ii region discovery survey, which now contains nearly 800 h ii regions distributed across the entire northern sky. we provide lsr velocities for the 302 detections and kinematic distances for 131 of these. of the 302 new detections, 5 have ({\ell },{\text{}}b,v) coordinates consistent with the outer scutum-centaurus arm (osc), the most distant molecular spiral arm of the milky way. due to the galactic warp, these nebulae are found at galactic latitudes >1° in the first galactic quadrant, and therefore were missed in previous surveys of the galactic plane. one additional region has a longitude and velocity consistent with the osc but lies at a negative galactic latitude (g039.183-01.422 -54.9 {km} {{{s}}}-1). with heliocentric distances >22 kpc and galactocentric distances >16 kpc, the osc h ii regions are the most distant known in the galaxy. we detect an additional three h ii regions near {\ell }≃ 150^\circ whose lsr velocities place them at galactocentric radii >19 kpc. if their distances are correct, these nebulae may represent the limit to galactic massive star formation. | finding distant galactic hii regions |
the discovery of planetary systems beyond our solar system has posed challenges to established theories of planetary formation. planetary orbits display a variety of architectures not predicted by first principles, and free-floating planets appear ubiquitous. the recent discovery of candidate jupiter mass binary objects (jumbos) by the james webb space telescope (jwst) further expanded this enigma. here, by means of high-accuracy, direct $n$-body simulations, we evaluate the possibility that jumbos may form as a result of ejection after a close stellar flyby. we consider a system of two jupiter-like planets moving in circular orbits with velocities $v_1$ and $v_2$ at distances $a_1$ and $a_2$ around a sun-like star. the interloper is another sun-like star approaching with asymptotic velocity $v_\infty$. we find that jumbos can indeed be formed upon ejection if the two planets are nearly aligned as the interloper reaches the closest approach. the ratio of the cross-section of jumbos production to that of single ejected free-floating planets can approach $\sim 20\%$ for $v_\infty/v_2\sim 0.1 - 0.2$ and $a_1/a_2\sim 0.65-0.7$. jumbos formed via this channel are expected to have an average semi-major axis comparable to $\delta a~\sim 3(a_2-a_1)$ and high eccentricity, with a distinctive superthermal distribution which can help to observationally identify this formation channel and distinguish it from primordial formation. we determine an upper limit on the jumbo formation efficiency per planetary system. in very dense star clusters like the trapezium in the orion nebula, this efficiency can reach several tens of percent. if the ejection channel is confirmed for these or future jwst observations, these jumbos will directly inform us of the conditions where these giant planets formed in protoplanetary disks, putting stringent constraints on the giant planet formation theory. | floating binary planets from ejections during close stellar encounters |
we present a first study based on the analysis of the deep spectra of ionized regions data base (desired). this is a compilation of 190 high signal-to-noise ratio optical spectra of $\mathrm{h\, \scriptstyle ii}$ regions and other photoionized nebulae, mostly observed with 8-10 m telescopes and containing ~29 380 emission lines. we find that the electron density -ne- of the objects is underestimated when [$\mathrm{s\, \scriptstyle ii}$] λ6731/λ6716 and/or [$\mathrm{o\, \scriptstyle ii}$] λ3726/λ3729 are the only density indicators available. this is produced by the non-linear density dependence of the indicators in the presence of density inhomogeneities. the average underestimate is ~300 cm-3 in extragalactic $\mathrm{h\, \scriptstyle ii}$ regions, introducing systematic overestimates of te([$\mathrm{o\, \scriptstyle ii}$]) and te([$\mathrm{s\, \scriptstyle ii}$]) compared to te([$\mathrm{n\, \scriptstyle ii}$]). the high-sensitivity of [$\mathrm{o\, \scriptstyle ii}$] λλ7319 + 20 + 30 + 31/λλ3726 + 29 and [$\mathrm{s\, \scriptstyle ii}$] λλ4069 + 76/λλ6716 + 31 to density makes them more suitable for the diagnosis of the presence of high-density clumps. if te([$\mathrm{n\, \scriptstyle ii}$]) is adopted, the density underestimate has a small impact in the ionic abundances derived from optical spectra, being limited to up to ~0.1 dex when auroral [$\mathrm{s\, \scriptstyle ii}$] and/or [$\mathrm{o\, \scriptstyle ii}$] lines are used. however, these density effects are critical for the analysis of infrared fine structure lines, such as those observed by the jwst in local star forming regions, implying strong underestimates of the ionic abundances. we present temperature relations between te([$\mathrm{o\, \scriptstyle iii}$]), te([$\mathrm{ar\, \scriptstyle iii}$]), te([$\mathrm{s\, \scriptstyle iii}$]), and te([$\mathrm{n\, \scriptstyle ii}$]) for the extragalactic $\mathrm{h\, \scriptstyle ii}$ regions. we confirm a non-linear dependence between te([$\mathrm{o\, \scriptstyle iii}$]) and te([$\mathrm{n\, \scriptstyle ii}$]) due to a more rapid increase of te([$\mathrm{o\, \scriptstyle iii}$]) at lower metallicities. | density biases and temperature relations for desired h ii regions |
we report the first measurements with sub-kiloparsec spatial resolution of strongly inverted gas-phase metallicity gradients in two dwarf galaxies at z ∼ 2. the galaxies have stellar masses ∼109{m}⊙ , specific star formation rate ∼20 gyr-1, and global metallicity 12+{log}({{o}}/{{h}})∼ 8.1 (1/4 solar), assuming the strong-line calibrations of [o iii]/hβ and [o ii]/hβ from maiolino et al. their radial metallicity gradients are measured to be highly inverted, i.e., 0.122 ± 0.008 and 0.111 ± 0.017 dex kpc-1, which is hitherto unseen at such small masses in similar redshift ranges. from the hubble space telescope observations of the source nebular emission and stellar continuum, we present two-dimensional spatial maps of star formation rate surface density, stellar population age, and gas fraction, which show that our galaxies are currently undergoing rapid mass assembly via disk inside-out growth. more importantly, using a simple chemical evolution model, we find that the gas fractions for different metallicity regions cannot be explained by pure gas accretion. our spatially resolved analysis based on a more advanced gas regulator model results in a spatial map of net gaseous outflows, triggered by active central starbursts, that potentially play a significant role in shaping the spatial distribution of metallicity by effectively transporting stellar nucleosynthesis yields outwards. the relation between wind mass loading factors and stellar surface densities measured in different regions of our galaxies shows that a single type of wind mechanism, driven by either energy or momentum conservation, cannot explain the entire galaxy. these sources present a unique constraint on the effects of gas flows on the early phase of disk growth from the perspective of spatially resolved chemical evolution within individual systems. | discovery of strongly inverted metallicity gradients in dwarf galaxies at z ∼ 2 |
extreme, young stellar populations are considered to be the primary contributor to cosmic reionization. how the lyman continuum (lyc) escapes these galaxies remains highly elusive, and it is challenging to observe this process in actual lyc emitters without resolving the relevant physical scales. we investigate the sunburst arc, a strongly lensed lyc emitter at z = 2.37 that reveals an exceptionally small-scale (tens of parsecs) region of high lyc escape. the small (<100 pc) lyc-leaking region has extreme properties: a very blue uv slope (β = -2.9 ± 0.1), a high ionization state ([o iii] λ5007/[o ii] λ3727 = 11 ± 3 and [o iii] λ5007/hβ = 6.8 ± 0.4), strong oxygen emission (ew([o iii]) = 1095 ± 40 å), and a high lyα escape fraction (0.3 ± 0.03), none of which are found in nonleaking regions of the galaxy. the leaking region's uv slope is consistent with approximately "pure" stellar light that is minimally contaminated by the surrounding nebular continuum emission or extinguished by dust. these results suggest a highly anisotropic lyc escape process such that lyc is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster creates one or more "pencil-beam" channels in the surrounding gas through which lyc can directly escape. such anisotropic escape processes imply that random sight-line effects drive the significant scatters between measurements of galaxy properties and lyc escape fraction, and that strong lensing is a critical tool for resolving the processes that regulate the ionizing budget of galaxies for reionization. | small region, big impact: highly anisotropic lyman-continuum escape from a compact starburst region with extreme physical properties |
we use paschen-β (paβ; 1282 nm) observations from the hubble space telescope g141 grism to study the star formation and dust-attenuation properties of a sample of 29 low-redshift (z < 0.287) galaxies in the candels lyα emission at reionization survey. we first compare the nebular attenuation from paβ/hα with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) paβ to (ground-based) hα to that from (ground-based) hα/hβ. this implies there are important differences between attenuation measured from grism-based/wide-aperture paβ fluxes and the ground-based/slit-measured balmer decrement. we next compare star formation rates (sfrs) from paβ to those from dust-corrected uv. we perform a survival analysis to infer a census of paβ emission implied by both detections and nondetections. we find evidence that galaxies with lower stellar mass have more scatter in their ratio of paβ to attenuation-corrected uv sfrs. when considering our paβ detection limits, this observation supports the idea that lower-mass galaxies experience "burstier" star formation histories. together, these results show that paβ is a valuable tracer of a galaxy's sfr, probing different timescales of star formation and potentially revealing star formation that is otherwise missed by uv and optical tracers. | clear: paschen-β star formation rates and dust attenuation of low-redshift galaxies |
context. strong nebular emission is ubiquitous in galaxies that contribute to cosmic reionization at redshift z ≳ 6. high-ionization uv metal lines, such as ciii]λ1908 å, show high equivalent widths (ew) in these early galaxies, suggesting harder radiation fields at low metallicity than low-z galaxies of similar stellar mass. understanding the physical properties driving the observed uv nebular line emission at high-z requires large and very deep spectroscopic surveys, which are now only accessible out to z ∼ 4.aims: we study the mean properties of a large representative sample of 217 galaxies showing ciii] emission at 2 < z < 4, selected from a parent sample of ∼750 main-sequence star-forming galaxies in the vandels survey. these ciii] emitters have a broad range of uv luminosities, allowing for a detailed stacking analysis to characterize their stellar mass, star formation rate (sfr), and metallicity as a function of the uv emission line ratios, ews, and the carbon-to-oxygen (c/o) abundance ratio.methods: stacking provides unprecedented high signal-to-noise (s/n) spectra for ciii] emitters over more than three decades in luminosity, stellar mass, and sfr. this enables a full spectral fitting to derive stellar metallicities for each stack. moreover, we use diagnostics based on photoionization models and uv line ratios to constrain the ionization sources of the galaxies and derive the c/o abundance.results: reliable ciii] detections (s/n ≥ 3) represent ∼30% of the parent sample. however, stacked spectra of non-detections (s/n < 3) show weak (ew ≲ 2 å) ciii] emission, suggesting that this line is common in normal star-forming galaxies at z ∼ 3. on the other hand, extreme ciii] emitters (ew(ciii]) ≳ 8 å) are exceedingly rare (∼3%) in vandels. the uv line ratios of the sample suggest no ionization source other than massive stars. stacks with larger ew(ciii]) show larger ew(lyα) and lower metallicity, but not all ciii] emitters are lyα emitters. the stellar metallicities of ciii] emitters are not significantly different from that of the parent sample, increasing from ∼10% to ∼40% solar for stellar masses log(m⋆/m⊙) ∼ 9−10.5. the stellar mass-metallicity relation of the ciii] emitters is consistent with previous works, exhibiting a strong evolution from z = 0 to z ∼ 3. the c/o abundances of the sample range between 35%−150% solar, with a noticeable increase with fuv luminosity and a smooth decrease with the ciii] ew. here, we discuss the ciii] emitters in the c/o-fe/h and the c/o-o/h planes and we find that they follow stellar and nebular abundance trends consistent with those of milky way halo and thick-disk stars and local hii galaxies, respectively. a qualitative agreement is also found with chemical evolution models, which suggests that ciii] emitters at z ∼ 3 are experiencing an active phase of chemical enrichment.conclusions: our results provide new insights into the nature of uv line emitters at z ∼ 2 − 4, paving the way for future studies at higher z using the james webb space telescope. the spectra built and used for the analysis in this paper are publicly available at https://github.com/mfllerena/stacks_c3emittersvandels. | the vandels survey: global properties of ciii]λ1908 å emitting star-forming galaxies at z ∼ 3 |
feo-poor (type i) porphyritic chondrules formed by incomplete melting of solid dust precursors via a yet-elusive mechanism. two settings are generally considered for their formation: (i) a nebular setting where primordial solids were melted, e.g. by shock waves propagating through the gas and (ii) a collisional planetary setting. here we report a method combining high-current electron microprobe x-ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from chondrule precursors. we find that these olivine crystals are ca-al-ti-poor relative to host olivine crystals. their variable δ17o, even in individual chondrule, is inconsistent with derivation from planetary interiors as previously argued from 120 ° triple junctions also exhibited by the chondrules studied herein. this indicates that chondrule precursors correspond to solid nebular condensates formed under changing physical conditions. we propose that porphyritic chondrules formed during gas-assisted melting of nebular condensates comprising relict olivine grains with varying δ17o values and ca-al-ti-rich minerals such as those observed within amoeboid olivine aggregates. incomplete melting of chondrule precursors produced ca-al-ti-rich melts (cat-melts), allowing subsequent crystallization of ca-al-ti-rich host olivine crystals via epitaxial growth on relict olivine grains. incoming mgo and sio from the gas phase induced (i) the dilution of cat-melts, as attested by the positive al-ti correlation observed in chondrule olivine crystals, and (ii) buffering of the o-isotope compositions of chondrules, as recorded by the constant δ17o values of host olivine grains. the o-isotopic compositions of host olivine grains are chondrule-specific, suggesting that chondrules formed in an array of environments of the protoplanetary disk with different δ17o values, possibly due to variable solid/gas mixing ratios. | oxygen isotopic diversity of chondrule precursors and the nebular origin of chondrules |
previous studies have found that ∼1 deg2 fields surrounding the stellar aggregates in the taurus star-forming region exhibit a surplus of solar-mass stars relative to denser clusters like ic 348 and the orion nebula cluster. to test whether this difference reflects mass segregation in taurus or a variation in the initial mass function, we have performed a survey for members of taurus across a large field (∼40 deg2) that was imaged by the sloan digital sky survey (sdss). we obtained optical and near-infrared spectra of candidate members identified with those images and the two micron all sky survey, as well as miscellaneous candidates that were selected with several other diagnostics of membership. we have classified 22 of the candidates as new members of taurus, which includes one of the coolest known members (m9.75). our updated census of members within the sdss field shows a surplus of solar-mass stars relative to clusters, although it is less pronounced than in the smaller fields toward the stellar aggregates that were surveyed for previously measured mass functions in taurus. in addition to spectra of our new members, we include in our study near-ir spectra of roughly half of the known members of taurus, which are used to refine their spectral types and extinctions. we also present an updated set of near-ir standard spectra for classifying young stars and brown dwarfs at m and l types. based on observations performed with the sloan digital sky survey, hobby-eberly telescope, nasa infrared telescope facility, gemini observatory, and canada-france-hawaii telescope. | a survey for new members of the taurus star-forming region with the sloan digital sky survey |
context. establishing the origin of the water d/h ratio in the solar system is central to our understanding of the chemical trail of water during the star and planet formation process. recent modeling suggests that comparisons of the d2o/hdo and hdo/h2o ratios are a powerful way to trace the chemical evolution of water and, in particular, determine whether the d/h ratio is inherited from the molecular cloud or established locally.aims: we seek to determine the d2o column density and derive the d2o/hdo ratios in the warm region toward the low-mass class 0 sources b335 and l483. the results are compared with astrochemical models and previous observations to determine their implications for the chemical evolution of water.methods: we present alma observations of the d2o 11,0-10,1 transition at 316.8 ghz toward b335 and l483 at ≲0.''5 (≲100 au) resolution, probing the inner warm envelope gas. the column densities of d2o, hdo, and h218o are determined by synthetic spectrum modeling and direct gaussian fitting, under the assumption of a single excitation temperature and similar spatial extent for the three water isotopologs.results: d2o is detected toward both sources in the inner warm envelope. the derived d2o/hdo ratio is (1.0 ± 0.2) × 10−2 for l483 and (1.4 ± 0.1) × 10−2 for b335. these values indicate that the d2o/hdo ratio is higher than the hdo/h2o ratios by a factor of ≳2 toward both sources.conclusions: the high d2o/hdo ratios are a strong indication of chemical inheritance of water from the prestellar phase down to the inner warm envelope. this implies that the local cloud conditions in the prestellar phase, such as temperatures and timescales, determine the water chemistry at later stages and could provide a source of chemical differentiation in young systems. in addition, the observed d2o/h2o ratios support an observed dichotomy in the deuterium fractionation of water toward isolated and clustered protostars, namely, a higher d/h ratio toward isolated sources. | alma observations of doubly deuterated water: inheritance of water from the prestellar environment |
we present photometric and spectroscopic observations of the nearby type ia sn 2019yvq, from its discovery ~1 day after explosion to ~100 days after its peak brightness. this sn exhibits several unusual features, most notably an extremely bright uv excess seen within ~5 days of its explosion. as seen in swift uv data, this early excess outshines its "peak" brightness, making this object more extreme than other supernovae (sne) with early uv/blue excesses (e.g., iptf14atg and sn 2017cbv). in addition, it was underluminous mb = -18.4, relatively quickly declining (δm15(b) = 1.37), and shows red colors past its early blue bump. unusual (although not unprecedented) spectral features include extremely broad-lined and high-velocity si absorption. despite obvious differences in peak spectra, we classify sn 2019yvq as a transitional member of the 02es-like subclass due to its similarities in several respects (e.g., color, peak luminosity, peak ti, and nebular [ca ii]). we model this data set with a variety of published models, including sn ejecta-companion shock interaction and sub-chandrasekhar-mass white dwarf (wd) double-detonation models. radio constraints from the vla place an upper limit of (4.5-20) × 10-8 m⊙ yr-1 on the mass-loss rate from a symbiotic progenitor, which does not exclude a red giant or main-sequence companion. ultimately, we find that no one model can accurately replicate all aspects of the data set, and further we find that the ubiquity of early excesses in 02es-like sne ia requires a progenitor system that is capable of producing isotropic uv flux, ruling out some models for this class of objects. | a bright ultraviolet excess in the transitional 02es-like type ia supernova 2019yvq |
disk vortices have been heralded as promising routes for planet formation due to their ability to trap significant amounts of pebbles. while the gas motions and trapping properties of two-dimensional vortices have been studied in enough detail in the literature, pebble trapping in three dimensions has received less attention, due to the higher computational demand. here we use the pencil code to study 3d vortices generated by convective overstability and the trapping of solids within them. the gas is unstratified whereas the pebbles settle to the midplane due to vertical gravity. we find that for pebbles of normalized friction times of $\mathrm{st}=0.05$ and $\mathrm{st}=1$ , and dust-to-gas ratio $\varepsilon =0.01$ , the vortex column in the midplane is strongly perturbed. yet when the initial dust-to-gas ratio is decreased the vortices remain stable and function as efficient pebble traps. streaming instability is triggered even for the lowest dust-to-gas ratio ( ${\varepsilon }_{0}={10}^{-4}$ ) and smallest pebble sizes ( $\mathrm{st}=0.05$ ) we assumed, showing a path for planetesimal formation in vortex cores from even extremely subsolar metallicity. to estimate if the reached overdensities can be held together solely by their own gravity we estimate the roche density at different radii. depending on disk model and radial location of the pebble clump we do reach concentrations higher than the roche density. we infer that if self-gravity was included for the pebbles then gravitational collapse would likely occur. | pebble trapping in vortices: three-dimensional simulations |
we present a detailed spectroscopic analysis of a galaxy at z ≃ 4.88 that is, by chance, magnified ~30× by gravitational lensing. only three sources at z ≳ 5 are known with such high magnification. this particular source has been shown to exhibit widespread, high equivalent width ${{\rm c\, \small {iv}}}\ \lambda 1549\, \mathring{\rm a}$ emission, implying it is a unique example of a metal-poor galaxy with a hard radiation field, likely representing the galaxy population responsible for cosmic reionization. using ultraviolet (uv) nebular line ratio diagnostics, very large telescope (vlt)/x-shooter observations rule out strong active galactic nuclei (agn) activity, indicating a stellar origin of the hard radiation field instead. we present a new detection of ${[{\rm ne\, \small {iii}}]}\ \lambda 3870\, \mathring{\rm a}$ and use the [${\rm ne\, \small {iii}}$]/[${\rm o\, \small {ii}}$] line ratio to constrain the ionization parameter and gas-phase metallicity. closely related to the commonly used [${\rm o\, \small {iii}}$]/[${\rm o\, \small {ii}}$] ratio, our [${\rm ne\, \small {iii}}$]/[${\rm o\, \small {ii}}$] measurement shows this source is similar to local 'green pea' galaxies and lyman-continuum leakers. it furthermore suggests this galaxy is more metal poor than expected from the fundamental metallicity relation, possibly as a consequence of excess gas accretion diluting the metallicity. finally, we present the highest redshift detection of ${{\rm mg\, \small {ii}}}\ \lambda 2796\, \mathring{\rm a}$, observed at high equivalent width in emission, in contrast to more evolved systems predominantly exhibiting ${\rm mg\, \small {ii}}$ absorption. strong ${\rm mg\, \small {ii}}$ emission has been observed in most z ~ 0 lyman-continuum leakers known and has recently been proposed as an indirect tracer of escaping ionizing radiation. in conclusion, this strongly lensed galaxy, observed just $300\, \mathrm{myr}$ after reionization ends, enables testing of observational diagnostics proposed to constrain the physical properties of distant galaxies in the james webb space telescope (jwst)/extremely large telescope (elt) era. | assessing the sources of reionization: a spectroscopic case study of a 30× lensed galaxy at z 5 with lyα, c iv, mg ii, and [ne iii] |
we provide new planetary nebula luminosity function (pnlf) distances to 19 nearby spiral galaxies that were observed with vlt/muse by the phangs collaboration. emission line ratios are used to separate planetary nebulae (pne) from other bright $[\mathrm{o}\, {\small iii}]$ emitting sources like compact supernovae remnants (snrs) or h ii regions. while many studies have used narrowband imaging for this purpose, the detailed spectral line information provided by integral field unit (ifu) spectroscopy grants a more robust way of categorizing different $[\mathrm{o}\, {\small iii}]$ emitters. we investigate the effects of snr contamination on the pnlf and find that we would fail to classify all objects correctly, when limited to the same data narrowband imaging provides. however, the few misclassified objects usually do not fall on the bright end of the luminosity function, and only in three cases does the distance change by more than 1σ. we find generally good agreement with literature values from other methods. using metallicity constraints that have also been derived from the same ifu data, we revisit the pnlf zero-point calibration. over a range of 8.34 < 12 + log (o/h) < 8.59, our sample is consistent with a constant zero-point and yields a value of $m^{*} = -4.542^{+0.103}_{-0.059}\, \mathrm{mag}$, within 1σ of other literature values. muse pushes the limits of pnlf studies and makes galaxies beyond ${20}{\, \mathrm{mpc}}$ accessible for this kind of analysis. this approach to the pnlf shows great promise for leveraging existing archival ifu data on nearby galaxies. | planetary nebula luminosity function distances for 19 galaxies observed by phangs-muse |
context. the formation of gas giant planets by the accretion of 100 km diameter planetesimals is often thought to be inefficient. a diameter of this size is typical for planetesimals and results from self-gravity. many models therefore use small kilometer-sized planetesimals, or invoke the accretion of pebbles. furthermore, models based on planetesimal accretion often use the ad hoc assumption of planetesimals that are distributed radially in a minimum-mass solar-nebula way.aims: we use a dynamical model for planetesimal formation to investigate the effect of various initial radial density distributions on the resulting planet population. in doing so, we highlight the directive role of the early stages of dust evolution into pebbles and planetesimals in the circumstellar disk on the subsequent planet formation.methods: we implemented a two-population model for solid evolution and a pebble flux-regulated model for planetesimal formation in our global model for planet population synthesis. this framework was used to study the global effect of planetesimal formation on planet formation. as reference, we compared our dynamically formed planetesimal surface densities with ad hoc set distributions of different radial density slopes of planetesimals.results: even though required, it is not the total planetesimal disk mass alone, but the planetesimal surface density slope and subsequently the formation mechanism of planetesimals that enables planetary growth through planetesimal accretion. highly condensed regions of only 100 km sized planetesimals in the inner regions of circumstellar disks can lead to gas giant growth.conclusions: pebble flux-regulated planetesimal formation strongly boosts planet formation even when the planetesimals to be accreted are 100 km in size because it is a highly effective mechanism for creating a steep planetesimal density profile. we find that this leads to the formation of giant planets inside 1 au already by pure 100 km planetesimal accretion. eventually, adding pebble accretion regulated by pebble flux and planetesimal-based embryo formation as well will further complement this picture. | effect of pebble flux-regulated planetesimal formation on giant planet formation |
recently published episodic spectral (levesque and massey, 2020) and high angular resolution (montarges et al, 2020) observations of betelgeuse suggest that the deep minimum of 2019-2020 was caused by an enhanced dust abundance in the stellar atmosphere. detailed monitoring of such events may prove useful for constructing consistent physical models of mass loss by evolved stars. for such observations it is fundamentally important to employ methods resolving an inhomogeneous stellar atmosphere. we present the differential speckle polarimetric observations of betelgeuse at 2.5-m telescope of caucasian mountain observatory of sai msu covering the period of 2019-2020 minimum. the observations were secured on 17 dates at wavelengths 465, 550, 625 and 880 nm. the circumstellar reflection nebula with the angular size of $\approx0.1^{\prime\prime}$ was detected for all the dates and at all wavelengths. the morphology of the nebula changed significantly over the observational period. net polarized brightness of the envelope remained constant until february 2020, while the stellar $v$ band flux decreased 2.5 times. starting from mid-february 2020, polarized flux of the envelope rose 2.1 times, at the same time the star returned to the pre-minimum state of october 2019. basing on these data and our low resolution spectrum obtained on 2020-04-06 we confirm a conclusion that the minimum is caused by the formation of a dust cloud located on the line of sight. a quantitative characterisation of this cloud will be possible when the data on its thermal radiation are employed. | differential speckle polarimetry of betelgeuse in 2019-2020: the rise is different from the fall |
we search for passive galaxies at z > 3 in the goods-south field, using different techniques based on photometric data, and paying attention to develop methods that are sensitive to objects that have become passive shortly before the epoch of observation. we use candels hst catalogues, ultra-deep ks data and new irac photometry, performing spectral energy distribution fitting using models with abruptly quenched star formation histories. we then single out galaxies which are best fitted by a passively evolving model, and having only low probability (<5 per cent) star-forming solutions. we verify the effects of including nebular lines emission, and we consider possible solutions at different redshifts. the number of selected sources dramatically depends on the models used in the spectral energy distribution (sed) fitting. without including emission lines and with photometric redshifts fixed at the candels estimate, we single out 30 candidates; the inclusion of nebular lines emission reduces the sample to 10 objects; allowing for solutions at different redshifts, only two galaxies survive as robust candidates. most of the candidates are not far-infrared emitters, corroborating their association with passive galaxies. our results translate into an upper limit in the number density of ∼0.173 arcmin2 above the detection limit. however, we conclude that the selection of passive galaxies at z > 3 is still subject to significant uncertainties, being sensitive to assumptions in the sed modelling adopted and to the relatively low s/n of the objects. by means of dedicated simulations, we show that jwst will greatly enhance the accuracy, allowing for a much more robust classification. | chasing passive galaxies in the early universe: a critical analysis in candels goods-south |
we present nebular spectra of the type ia supernova (sn ia) sn 2019yvq, which had a bright flash of blue and ultraviolet light after exploding, followed by a rise similar to other sne ia. although sn 2019yvq displayed several other rare characteristics, such as persistent high ejecta velocity near peak brightness, it was not especially peculiar, and if the early "excess" emission were not observed, it would likely be included in cosmological samples. the excess flux can be explained by several different physical models linked to the details of the progenitor system and explosion mechanism. each has unique predictions for the optically thin emission at late times. in our nebular spectra, we detect strong [ca ii] λλ7291, 7324 and ca near-ir triplet emission, consistent with a double-detonation explosion. we do not detect h, he, or [o i] emission, predictions for some single-degenerate progenitor systems and violent white dwarf mergers. the amount of swept-up h or he is <2.8 × 10-4 and 2.4 × 10-4 m⊙, respectively. aside from strong ca emission, the sn 2019yvq nebular spectrum is similar to those of typical sne ia with the same light-curve shape. comparing to double-detonation models, we find that the ca emission is consistent with a model with a total progenitor mass of 1.15 m⊙. however, we note that a lower progenitor mass better explains the early light-curve and peak luminosity. the unique properties of sn 2019yvq suggest that thick he-shell double detonations only account for ${1.1}_{-1.1}^{+2.1} \% $ of the total "normal" sn ia rate. the sn 2019yvq is one of the best examples yet that multiple progenitor channels appear necessary to reproduce the full diversity of "normal" sne ia. | strong calcium emission indicates that the ultraviolet-flashing sn ia 2019yvq was the result of a sub-chandrasekar-mass double-detonation explosion |
the light curves of type ia supernovae (sne ia) are powered by the radioactive decay of 56ni to 56co at early times, and the decay of 56co to 56fe from ∼60 d after explosion. we examine the evolution of the [co iii] λ5893 emission complex during the nebular phase for sne ia with multiple nebular spectra and show that the line flux follows the square of the mass of 56co as a function of time. this result indicates both efficient local energy deposition from positrons produced in 56co decay and long-term stability of the ionization state of the nebula. we compile sn ia nebular spectra from the literature and present 21 new late-phase spectra of 7 sne ia, including sn 2014j. from these we measure the flux in the [co iii] λ5893 line and remove its well-behaved time dependence to infer the initial mass of 56ni (mni) produced in the explosion. we then examine 56ni yields for different sn ia ejected masses (mej - calculated using the relation between light-curve width and ejected mass) and find that the 56ni masses of sne ia fall into two regimes: for narrow light curves (low stretch s ∼ 0.7-0.9), mni is clustered near mni ≈ 0.4 m⊙ and shows a shallow increase as mej increases from ∼1 to 1.4 m⊙; at high stretch, mej clusters at the chandrasekhar mass (1.4 m⊙) while mni spans a broad range from 0.6 to 1.2 m⊙. this could constitute evidence for two distinct sn ia explosion mechanisms. | measuring nickel masses in type ia supernovae using cobalt emission in nebular phase spectra |
there is a long history of using optical emission and absorption lines to constrain the metallicity and ionization parameters of gas in galaxies. however, comparable diagnostics are less well developed for the ultraviolet (uv). here, we assess the diagnostic potential of both absorption and emission features in the uv and evaluate the diagnostics against observations of local and high-redshift galaxies. we use the flexible stellar population synthesis (fsps) nebular emission model of byler et al., extended to include emission predictions in the uv, to evaluate the metallicity sensitivity of established uv stellar absorption indices and to identify those that include a significant contribution from nebular emission. we present model uv emission-line fluxes as a function of metallicity and ionization parameter, assuming both instantaneous bursts and constant star formation rates. we identify combinations of strong emission lines that constrain metallicity and ionization parameters, including [c iii] λ1907, c iii] λ1909, o iii] λ1661,1666, si iii] λ1883,1892, c iv λ1548,1551, n ii] λ1750,1752, and mg ii λ2796, and we develop uv versions of the canonical “baldwin phillips terlevich” diagram. we quantify the relative contribution from stellar wind emission and nebular line emission to diagnostic line ratios that include the c iv λ1548,1551 lines, and we also develop an observationally motivated relationship for n and c enrichment that improves the performance of photoionization models. we summarize the best diagnostic choices and the associated redshift range for low-, mid-, and high-resolution rest-uv spectroscopy in preparation for the launch of the james webb space t elescope. | stellar and nebular diagnostics in the ultraviolet for star-forming galaxies |
the nearby sn 2017eaw is a type ii-p (“plateau”) supernova (sn) showing early-time, moderate csm interaction. we present a comprehensive study of this sn, including the analysis of high-quality optical photometry and spectroscopy covering the very early epochs up to the nebular phase, as well as near-ultraviolet and near-infrared spectra and early-time x-ray and radio data. the combined data of sne 2017eaw and 2004et allow us to get an improved distance to the host galaxy, ngc 6946, of d ∼ 6.85 ± 0.63 mpc; this fits into recent independent results on the distance of the host and disfavors the previously derived (30% shorter) distances based on sn 2004et. from modeling the nebular spectra and the quasi-bolometric light curve, we estimate the progenitor mass and some basic physical parameters for the explosion and ejecta. our results agree well with previous reports on a red supergiant progenitor star with a mass of ∼15-16 m ⊙. our estimation of the pre-explosion mass-loss rate (\dot{m}∼ 3× {10}-7{--}1× {10}-6{m}⊙yr-1) agrees well with previous results based on the opacity of the dust shell enshrouding the progenitor, but it is orders of magnitude lower than previous estimates based on general light-curve modeling of type ii-p sne. combining late-time optical and mid-infrared data, a clear excess at 4.5 μm can be seen, supporting the previous statements on the (moderate) dust formation in the vicinity of sn 2017eaw. | the type ii-p supernova 2017eaw: from explosion to the nebular phase |
in this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star mn48 disclosed via detection of a mid-infrared circular shell around it with the spitzer space telescope. follow-up optical spectroscopy of mn48 with the southern african large telescope (salt) carried out in 2011-2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (lbvs). the lbv status of mn48 was further supported by photometric monitoring which shows that in 2009-2011 this star has brightened by ≈0.9 and 1 mag in the v and ic bands, respectively, then faded by ≈1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. the detected changes in the spectrum and brightness of mn48 make this star the 18th known galactic bona fide lbv and increase the percentage of lbvs associated with circumstellar nebulae to more than 70 per cent. we discuss the possible birth place of mn48 and suggest that this star might have been ejected either from a putative star cluster embedded in the h ii region iras 16455-4531 or the young massive star cluster westerlund 1. | mn48: a new galactic bona fide luminous blue variable revealed by spitzer and salt |
spatially resolved studies of high-redshift galaxies, an essential insight into galaxy formation processes, have been mostly limited to stacking or unusually bright objects. we present here the study of a typical (l*, m⋆ = 6 × 109 m⊙) young lensed galaxy at z = 3.5, observed with multi unit spectroscopic explorer (muse), for which we obtain 2d resolved spatial information of lyα and, for the first time, of c iii] emission. the exceptional signal-to-noise ratio of the data reveals uv emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (te ∼ 15600 k, ne ∼ 300 cm-3, covering fraction fc ∼ 0.4) using multiple diagnostics. inferred stellar and gas-phase metallicities point towards a low-metallicity object (zstellar = ∼0.07 z⊙ and zism < 0.16 z⊙). the lyα emission extends over ∼10 kpc across the galaxy and presents a very uniform spectral profile, showing only a small velocity shift which is unrelated to the intrinsic kinematics of the nebular emission. the lyα extension is approximately four times larger than the continuum emission, and makes this object comparable to low-mass laes at low redshift, and more compact than the lyman-break galaxies and lyα emitters usually studied at high redshift. we model the lyα line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a good description of both observables. | a young star-forming galaxy at z = 3.5 with an extended lyman α halo seen with muse |
early observations of type ia supernovae (sne ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. we present exquisite observations of sn 2019yvq, the second observed sn ia, after iptf 14atg, to display an early flash of emission in the ultraviolet (uv) and optical. our analysis finds that sn 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an sn ia ( ${m}_{g}\approx -18.5$ mag at peak) yet featured very high absorption velocities ( $v\approx 15{\rm{,0}}00$ km s-1 for si ii λ6355 at peak). we find that many of the observational features of sn 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56ni is relatively low (we measure ${m}_{{56}_{\mathrm{ni}}}=0.31\pm 0.05\,{m}_{\odot }$ ) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. to explain both the uv/optical flash and peak properties of sn 2019yvq we consider four different models: interaction between the sn ejecta and a nondegenerate companion, extended clumps of 56ni in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match sn 2019yvq. in closing, we predict that the nebular spectra of sn 2019yvq will feature either h or he emission, if the ejecta collided with a companion, strong [ca ii] emission, if it was a double detonation, or narrow [o i] emission, if it was due to a violent merger. | the spectacular ultraviolet flash from the peculiar type ia supernova 2019yvq |
supernova (sn) 2016bdu is an unusual transient resembling sn 2009ip. sn 2009ip-like events are characterized by a long-lasting phase of erratic variability which ends with two luminous outbursts a few weeks apart. the second outburst is significantly more luminous (about 3 mag) than the first. in the case of sn 2016bdu, the first outburst (event a) reached an absolute magnitude m(r) ~ -15.3 mag, while the second one (event b) occurred over one month later and reached m(r) ~ -18 mag. by inspecting archival data, a faint source at the position of sn 2016bdu is detectable several times in the past few years. we interpret these detections as signatures of a phase of erratic variability, similar to that experienced by sn 2009ip between 2008 and mid-2012, and resembling the currently observed variability of the luminous blue variable sn 2000ch in ngc 3432. spectroscopic monitoring of sn 2016bdu during the second peak initially shows features typical of a sn iin. one month after the event b maximum, the spectra develop broad balmer lines with p cygni profiles and broad metal features. at these late phases, the spectra resemble those of a typical type ii sn. all members of this sn 2009ip-like group are remarkably similar to the type iin sn 2005gl. for this object, the claim of a terminal sn explosion is supported by the disappearance of the progenitor star. the similarity with sn 2005gl suggests that all members of this family may finally explode as genuine sne, although the unequivocal detection of nucleosynthesised elements in their nebular spectra is still missing. | supernovae 2016bdu and 2005gl, and their link with sn 2009ip-like transients: another piece of the puzzle |
we present a new multi-pixel high resolution (r ≳ 107) spectrometer for the stratospheric observatory for far-infrared astronomy (sofia). the receiver uses 2 × 7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. we present the first results for this new instrument after commissioning campaigns in may and december 2015 and after science observations performed in may 2016. the receiver is designed to ultimately cover the full 1.8-2.5 thz frequency range but in its first implementation, the observing range was limited to observations of the [cii] line at 1.9 thz in 2015 and extended to 1.83-2.07 thz in 2016. the instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. an example of large scale mapping around the horsehead nebula is presented here illustrating this improvement. the array has been added to sofia's instrument suite already for ongoing observing cycle 4. the datacube of the horsehead observations is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/595/a34 | the upgreat 1.9 thz multi-pixel high resolution spectrometer for the sofia observatory |
context. models of stellar spectra are necessary for interpreting light from individual stars, planets, integrated stellar populations, nebulae, and the interstellar medium.aims: we provide a comprehensive and homogeneous collection of synthetic spectra for a wide range of atmospheric parameters and chemical compositions.methods: we compile atomic and molecular data from the literature. we adopt the largest and most recent set of atlas9 model atmospheres, and use the radiative code assɛt.results: the resulting collection of spectra is made publicly available at medium and high-resolution (r ≡ λ/δλ = 10 000, 100 000 and 300 000) spectral grids, which include variations in effective temperature between 3500 k and 30 000 k, surface gravity (0 ≤ log g ≤ 5), and metallicity (-5 ≤ [fe/h] ≤ +0:5), spanning the wavelength interval 120-6500 nm. a second set of denser grids with additional dimensions, [α/fe] and micro-turbulence, are also provided (covering 200-2500 nm). we compare models with observations for a few representative cases. data files 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/618/a25 | a collection of model stellar spectra for spectral types b to early-m |
as part of the 100ias survey, a program aimed to obtain nebular-phase spectra for a volume-limited and homogeneous sample of type ia supernovae (sne ia), we observed asassn-18tb (sn 2018fhw) at 139 d past maximum light. asassn-18tb was a fast-declining, sub-luminous event that fits well within the observed photometric and spectroscopic distributions of the sn ia population. we detect a prominent h α emission line (lh α = 2.2 ± 0.2 × 1038 ergs s-1) with fwhm ≈ 1100 km s-1 in the nebular-phase spectrum of this sn ia. high-luminosity h α emission (lh α ≳ 1040 ergs s-1) has previously been discovered in a rare class of sne ia-like objects showing circum-stellar medium (csm) interactions (sne ia-csm). they predominantly belong to overluminous (mmax < -19 mag in optical) 1991t-like sne ia and are exclusively found in star-forming galaxies. by contrast, asassn-18tb is a sub-luminous sn ia (mb,max ∼ -17.7 mag) found in an early-type galaxy dominated by old stellar populations. we discuss possible origins for the observed hydrogen. of the 75 sne ia for which we have so far obtained nebular spectra in 100ias, no other sn shows a {∼ } 1000 {km s^{-1}} h α emission line with comparable line luminosity as asassn-18tb, emphasizing the rarity of such emission in the nebular phase. based on preliminary results from our survey, the rate for asassn-18tb-like nebular h α emission could be as high as {∼ } 10{{ per cent}} among sub-luminous sne ia. | h α emission in the nebular spectrum of the type ia supernova asassn-18tb |
we present the first determination of the galaxy luminosity function (lf) at z ∼ 4, 5, 6, and 7, in the rest-frame optical at {λ }{rest}∼ 900 {nm} (z‧ band). the rest-frame optical light traces the content in low-mass evolved stars (∼stellar mass—m *), minimizing potential measurement biases for m *. moreover, it is less affected by nebular line emission contamination and dust attenuation, is independent of stellar population models, and can be probed up to z ∼ 8 through spitzer/irac. our analysis leverages the unique full-depth spitzer/irac 3.6-8.0 μm data over the candels/goods-n, candels/goods-s, and cosmos/ultravista fields. we find that, at absolute magnitudes where {m}z\primeis fainter than ≳ -23 mag, {m}z\primelinearly correlates with {m}{uv,1600}. at brighter {m}z\prime , {m}{uv,1600} presents a turnover, suggesting that the stellar mass-to-light ratio {m}* /{l}{uv,1600} could be characterized by a very broad range of values at high stellar masses. median-stacking analyses recover an {m}* /{l}z\primeroughly independent on {m}z\primefor {m}z\prime ≳ -23 mag, but exponentially increasing at brighter magnitudes. we find that the evolution of the lf marginally prefers a pure luminosity evolution over a pure density evolution, with the characteristic luminosity decreasing by a factor of ∼ 5× between z ∼ 4 and z ∼ 7. direct application of the recovered {m}* /{l}z\primegenerates stellar mass functions consistent with average measurements from the literature. measurements of the stellar-to-halo mass ratio at fixed cumulative number density show that it is roughly constant with redshift for {m}h≳ {10}12{m}⊙ . this is also supported by the fact that the evolution of the lf at 4≲ z≲ 7 can be accounted for by a rigid displacement in luminosity, corresponding to the evolution of the halo mass from abundance matching. | the rest-frame optical (900 nm) galaxy luminosity function at z ∼ 4-7: abundance matching points to limited evolution in the m star/m halo ratio at z ≥ 4 |
we present the palomar transient factory discoveries and the photometric and spectroscopic observations of ptf11kmb and ptf12bho. we show that both transients have properties consistent with the class of calcium-rich gap transients, specifically lower peak luminosities and rapid evolution compared to ordinary supernovae, and a nebular spectrum dominated by [ca ii] emission. a striking feature of both transients is their host environments: ptf12bho is an intracluster transient in the coma cluster, while ptf11kmb is located in a loose galaxy group, at a physical offset ∼150 kpc from the most likely host galaxy. deep subaru imaging of ptf12bho rules out an underlying host system to a limit of {m}r> -8.0 {mag}, while hubble space telescope imaging of ptf11kmb reveals a marginal counterpart that, if real, could be either a background galaxy or a globular cluster. we show that the offset distribution of ca-rich gap transients is significantly more extreme than that seen for sne ia or even short-hard gamma-ray bursts (sgrbs). thus, if the offsets are caused by a kick, they require higher kick velocities and/or longer merger times than sgrbs. we also show that almost all ca-rich transients found to date are in group and cluster environments with elliptical host galaxies, indicating a very old progenitor population; the remote locations could partially be explained by these environments having the largest fraction of stars in the intragroup/intracluster light following galaxy-galaxy interactions. | two new calcium-rich gap transients in group and cluster environments |
we use a newly developed cascade model of turbulent concentration of particles in protoplanetary nebulae to calculate several properties of interest to the formation of primitive planetesimals and to the meteorite record. the model follows, and corrects, calculations of the primary initial mass function (imf) of planetesimals by cuzzi et al., in which an incorrect cascade model was used. here we use the model of hartlep et al., which has been validated against several published numerical simulations of particle concentration in turbulence. we find that, for a range of nebula and particle properties, planetesimals may be "born big," formed as sandpiles with diameters in the range 10-100 km, directly from freely floating particles. the imfs have a modal nature, with a well-defined peak rather than a power-law size dependence. predictions for the inner and outer parts of the nebula behave similarly in this regard, and observations of primitive bodies in the inner and outer nebula support such modal imfs. also, we present predictions of local particle concentrations on several lengthscales in which particles "commonly" find themselves, which have significance for meteoritical observations of the redox state and isotopic fractionation in regions of chondrule formation. an important difference between these results and those of cuzzi et al. is that particle growth by sticking must proceed to a radius range of at least one to a few centimeters for the imf and meteoritical properties to be most plausibly satisfied. that is, as far as the inner nebula goes, the predominant "particles" must be aggregates of chondrules (or chondrule-size precursors) rather than individual chondrules themselves. | cascade model for planetesimal formation by turbulent clustering |
context. this is the second paper of a series on galactic ob groups that uses astrometric and photometric data from gaia and spectral classifications from the galactic o-star spectroscopic survey (gosss) and the library of libraries of massive-star high-resolution spectra (lilimarlin). the previous paper was based on the second gaia data release (dr2). since then, the early third gaia data release (edr3) has appeared with new astrometry and photometry.aims: the two aims of this paper are to revise the results for the sample from paper i using gaia edr3 data and to expand the sample of analyzed stellar groups to 26, from villafranca o-001 to villafranca o-026.methods: we used gosss to select galactic stellar groups with o stars and an updated version of the method in paper 0 of this series, combining gaia edr3 g + gbp + grp photometry, positions, proper motions, and parallaxes to assign memberships and measure distances. we present 99 spectra from gosss and 32 from lilimarlin for stars in the analyzed groups or in their foreground.results: we derived distances to the 26 stellar groups with unprecedented precision and accuracy, with total (random plus systematic) uncertainties lower than 1% for distances within 1 kpc and of ∼3% around 3 kpc, which are values almost four times better than for gaia dr2. we provide homogeneous spectral types for 110 stars and correct a number of errors in the literature, especially for objects in villafranca o-023 (orion nebula cluster). for each group, we discuss its membership and present possible runaway and walkaway stars. at least two of the studied groups, villafranca o-o12 s in ngc 2467 and villafranca o-014 nw in the north america nebula, are orphan clusters in which the most massive stars have been ejected by dynamical interactions, leaving objects with a capped mass function. the existence of such clusters has important consequences for the study of the initial mass function (imf), the distribution of supernova explosions across the galaxy, and the population and dynamics of isolated compact objects. we fit pre-main-sequence (pms) isochrones to the color-magnitude diagrams (cmds) of four clusters to derive ages of 2.0 ± 0.5 ma for villafranca o-026 (σ orionis cluster), 4 ± 2 ma for villafranca o-016 (ngc 2264), 5.0 ± 0.5 ma for villafranca o-021 (ngc 2362), and 8 ± 2 ma for villafranca o-024 (γ velorum cluster). | the villafranca catalog of galactic ob groups. ii. from gaia dr2 to edr3 and ten new systems with o stars |
manga (mapping nearby galaxies at apache point observatory) is a 6-yr sloan digital sky survey (sdss-iv) survey that will obtain spatially resolved spectroscopy from 3600 to 10 300 å for a representative sample of over 10 000 nearby galaxies. in this paper, we present the analysis of nebular emission-line properties using observations of 14 galaxies obtained with p-manga, a prototype of the manga instrument. by using spatially resolved diagnostic diagrams, we find extended star formation in galaxies that are centrally dominated by seyfert/liner-like emission, which illustrates that galaxy characterizations based on single fibre spectra are necessarily incomplete. we observe extended low ionization nuclear emission-line regions (liner)-like emission (up to 1re) in the central regions of three galaxies. we make use of the hα equivalent width [ew(hα)] to argue that the observed emission is consistent with ionization from hot evolved stars. we derive stellar population indices and demonstrate a clear correlation between dn(4000) and ew(hδa) and the position in the ionization diagnostic diagram: resolved galactic regions which are ionized by a seyfert/liner-like radiation field are also devoid of recent star formation and host older and/or more metal-rich stellar populations. we also detect extraplanar liner-like emission in two highly inclined galaxies, and identify it with diffuse ionized gas. we investigate spatially resolved metallicities and find a positive correlation between metallicity and star formation rate surface density. we further study the relation between n/o versus o/h on resolved scales. we find that, at given n/o, regions within individual galaxies are spread towards lower metallicities, deviating from the sequence defined by galactic central regions as traced by sloan 3-arcsec fibre spectra. we suggest that the observed dispersion can be a tracer for gas flows in galaxies: infalls of pristine gas and/or the effect of a galactic fountain. | p-manga galaxies: emission-lines properties - gas ionization and chemical abundances from prototype observations |
the magnetospheric multiscale mission observes, in detail, charged particle heating and substantial nonthermal acceleration in a region of strong turbulence ( $| \delta {\boldsymbol{b}}| /| {\boldsymbol{b}}| \sim 1$ , where ${\boldsymbol{b}}$ is the magnetic field) that surrounds a magnetic reconnection x-line. magnetic reconnection enables magnetic field annihilation in a volume that far exceeds that of the diffusion region. the formidable magnetic field annihilation breaks into strong, intermittent turbulence with magnetic field energy as the driver. the strong, intermittent turbulence appears to generate the necessary conditions for nonthermal acceleration. it creates intense, localized currents ( ${\boldsymbol{j}}$ ) and unusually large-amplitude electric fields ( ${\boldsymbol{e}}$ ). the combination of turbulence-generated ${\boldsymbol{e}}$ and ${\boldsymbol{j}}$ results in a significant net positive mean of ${\boldsymbol{j}}\cdot {\boldsymbol{e}}$ , which signifies particle energization. ion and electron heating rates are such that they experience a fourfold increase from their initial temperature. importantly, the strong turbulence also generates magnetic holes or depletions in $| {\boldsymbol{b}}| $ that can trap particles. trapping considerably increases the dwell time of a subset of particles in the turbulent region, which results in significant nonthermal particle acceleration. the direct observation of strong turbulence that is enabled by magnetic reconnection with nonthermal particle acceleration has far-reaching implications, since turbulence in plasmas is pervasive and may occupy significant volumes of the interstellar medium and intergalactic space. for example, strong turbulence from magnetic field annihilation in the supernova nebulae may dominate large volumes. as such, this observed energization process could plausibly contribute to the supply and development of the cosmic-ray spectrum. | observations of particle acceleration in magnetic reconnection-driven turbulence |
noble gases have played a key role in our understanding of the origin of earth's volatiles, mantle structure, and long-term degassing of the mantle. here we synthesize new insights into these topics gained from high-precision noble gas data. our analysis reveals new constraints on the origin of the terrestrial atmosphere, the presence of nebular neon but chondritic krypton and xenon in the mantle, and a memory of multiple giant impacts during accretion. furthermore, the reservoir supplying primordial noble gases to plumes appears to be distinct from the mid-ocean ridge basalt (morb) reservoir since at least 4.45 ga. while differences between the morb mantle and plume mantle cannot be explained solely by recycling of atmospheric volatiles, injection and incorporation of atmospheric-derived noble gases into both mantle reservoirs occurred over earth history. in the morb mantle, the atmospheric-derived noble gases are observed to be heterogeneously distributed, reflecting inefficient mixing even within the vigorously convecting morb mantle. | noble gases: a record of earth's evolution and mantle dynamics |
we investigate the impact of the diffuse ionized gas (dig) on abundance determinations in star-forming (sf) galaxies. the dig is characterized using the h α equivalent width (wh α). from a set of 1 409 sf galaxies from the mapping nearby galaxies at apo (manga) survey, we calculate the fractional contribution of the dig to several emission lines using high-s/n data from sf spaxels (instead of using noisy emission-lines in dig-dominated spaxels). our method is applicable to spectra with observed wh α ≳ 10 å (which are not dominated by dig emission). since the dig contribution depends on galactocentric distance, we provide dig-correction formulae for both entire galaxies and single aperture spectra. applying those to a sample of > 90 000 sf galaxies from the sloan digital sky survey, we find the following. (1) the effect of the dig on strong-line abundances depends on the index used. it is negligible for the ([o iii]/h β)/([n ii]/h α) index, but reaches ∼0.1 dex at the high-metallicity end for [n ii]/h α. (2) this result is based on the ∼kpc manga resolution, so the real effect of the dig is likely greater. (3) we revisit the mass-metallicity-star formation rate (sfr) relation by correcting for the dig contribution in both abundances and sfr. the effect of dig removal is more prominent at higher stellar masses. using the [n ii]/hα index, o/h increases with sfr at high stellar mass, contrary to previous claims. | diffuse ionized gas and its effects on nebular metallicity estimates of star-forming galaxies |
context. the journey from dust particle to planetesimal involves physical processes acting on scales ranging from micrometers (the sticking and restructuring of aggregates) to hundreds of astronomical units (the size of the turbulent protoplanetary nebula). considering these processes simultaneously is essential when studying planetesimal formation.aims: the goal of this work is to quantify where and when planetesimal formation can occur as the result of porous coagulation of icy grains and to understand how the process is influenced by the properties of the protoplanetary disk.methods: we develop a novel, global, semi-analytical model for the evolution of the mass-dominating dust particles in a turbulent protoplanetary disk that takes into account the evolution of the dust surface density while preserving the essential characteristics of the porous coagulation process. this panoptic model is used to study the growth from sub-micron to planetesimal sizes in disks around sun-like stars.results: for highly porous ices, unaffected by collisional fragmentation and erosion, rapid growth to planetesimal sizes is possible in a zone stretching out to ~10 au for massive disks. when porous coagulation is limited by erosive collisions, the formation of planetesimals through direct coagulation is not possible, but the creation of a large population of aggregates with stokes numbers close to unity might trigger the streaming instability (si). however, we find that reaching conditions necessary for si is difficult and limited to dust-rich disks, (very) cold disks, or disks with weak turbulence.conclusions: behind the snow-line, porosity-driven aggregation of icy grains results in rapid (~104 yr) formation of planetesimals. if erosive collisions prevent this, si might be triggered for specific disk conditions. the numerical approach introduced in this work is ideally suited for studying planetesimal formation and pebble delivery simultaneously and will help build a coherent picture of the start of the planet formation process. | a panoptic model for planetesimal formation and pebble delivery |
short gamma-ray bursts (sgrbs) are among the most luminous explosions in the universe and their origin still remains uncertain. observational evidence favors the association with binary neutron star or neutron star-black hole (ns-bh) binary mergers. leading models relate sgrbs to a relativistic jet launched by the bh-torus system resulting from the merger. however, recent observations have revealed a large fraction of sgrb events accompanied by x-ray afterglows with durations ~102-105 s, suggesting continuous energy injection from a long-lived central engine, which is incompatible with the short (lsim 1 s) accretion timescale of a bh-torus system. the formation of a supramassive ns, resisting the collapse on much longer spin-down timescales, can explain these afterglow durations, but leaves serious doubts on whether a relativistic jet can be launched at the merger. here we present a novel scenario accommodating both aspects, where the sgrb is produced after the collapse of a supramassive ns. early differential rotation and subsequent spin-down emission generate an optically thick environment around the ns consisting of a photon-pair nebula and an outer shell of baryon-loaded ejecta. while the jet easily drills through this environment, spin-down radiation diffuses outward on much longer timescales and accumulates a delay that allows the sgrb to be observed before (part of) the long-lasting x-ray signal. by analyzing diffusion timescales for a wide range of physical parameters, we find delays that can generally reach ~105 s, compatible with observations. the success of this fundamental test makes this "time-reversal" scenario an attractive alternative to current sgrb models. | short gamma-ray bursts in the "time-reversal" scenario |
we present an integral field unit survey of 73 galaxy clusters and groups with the visible multi object spectrograph on the very large telescope. we exploit the data to determine the h α gas dynamics on kpc scales to study the feedback processes occurring within the dense cluster cores. we determine the kinematic state of the ionized gas and show that the majority of systems (∼2/3) have relatively ordered velocity fields on kpc scales that are similar to the kinematics of rotating discs and are decoupled from the stellar kinematics of the brightest cluster galaxy. the majority of the h α flux (>50 per cent) is typically associated with these ordered kinematics and most systems show relatively simple morphologies suggesting they have not been disturbed by a recent merger or interaction. approximately 20 per cent of the sample (13/73) have disturbed morphologies which can typically be attributed to active galactic nuclei activity disrupting the gas. only one system shows any evidence of an interaction with another cluster member. a spectral analysis of the gas suggests that the ionization of the gas within cluster cores is dominated by non-stellar processes, possibly originating from the intracluster medium itself. | optical emission line nebulae in galaxy cluster cores 1: the morphological, kinematic and spectral properties of the sample |
aims: we wish to investigate the physical properties of a sample of lyα emitting galaxies in the vandels survey, with particular focus on the role of kinematics and neutral hydrogen column density in the escape and spatial distribution of lyα photons.methods: from all the lyα emitting galaxies in the vandels data release 2 at 3.5 ≲ z ≲ 4.5, we selected a sample of 52 galaxies that also have a precise systemic redshift determination from at least one nebular emission line (heii or ciii]). for these galaxies, we derived different physical properties (stellar mass, age, dust extinction, and star formation rate) from spectral energy distribution (sed) fitting of the exquisite multiwavelength photometry available in the vandels fields, using the dedicated spectral modeling tool beagle and the uv β slope from the observed photometry. we characterized the lyα emission in terms of kinematics, equivalent width (ew), full width at half-maximum, and spatial extension and then estimated the velocity of the neutral outflowing gas. the ultra-deep vandels spectra (up to 80 h on-source integration) enable this for individual galaxies without the need to rely on stacks. we then investigated the correlations between the lyα properties and the other measured properties to study how they affect the shape and intensity of lyα emission.results: we reproduce some of the well-known correlations between lyα ew and stellar mass, dust extinction, and uv β slope, in the sense that the emission line appears brighter in galaxies with lower mass that are less dusty and bluer. we do not find any correlation with the sed-derived star formation rate, while we find that galaxies with brighter lyα tend to be more compact in both uv and in lyα. our data reveal an interesting correlation between the lyα velocity offset and the shift of the interstellar absorption lines with respect to the systemic redshift, observed for the first time at high redshifts: galaxies with higher interstellar medium (ism) outflow velocities show smaller lyα velocity shifts. we interpret this relation in the context of the shell-model scenario, where the velocity of the ism and the hi column density contribute together in determining the lyα kinematics. in support to our interpretation, we observe that galaxies with high hi column densities have much more extended lyα spatial profiles; this is a sign of increased scattering. however, we do not find any evidence that the hi column density is related to any other physical properties of the galaxies, although this might be due in part to the limited range of parameters that our sample spans. based on data obtained with the european southern observatory very large telescope, paranal, chile, under large program 194.a-2003(ek). | the vandels survey: the role of ism and galaxy physical properties in the escape of lyα emission in z ∼ 3.5 star-forming galaxies |
we investigated the ultraviolet (uv) spectral properties of faint lyman-α emitters (laes) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint universe. we used data from the muse hubble ultra deep survey to construct mean rest-frame spectra of continuum-faint (median muv of -18 and down to muv of -16), low stellar mass (median value of 108.4 m⊙ and down to 107 m⊙) laes at redshift z ≳ 3. we computed various averaged spectra of laes, subsampled on the basis of their observational (e.g., lyα strength, uv magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. we searched for uv spectral features other than lyα, such as higher ionization nebular emission lines and absorption features. we successfully observed the o iii]λ1666 and [c iii]λ1907+c iii]λ1909 collisionally excited emission lines and the he iiλ1640 recombination feature, as well as the resonant c ivλλ1548,1551 doublet either in emission or p-cygni. we compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the laes. in particular, the mean spectra of laes with larger lyα equivalent widths, fainter uv magnitudes, bluer uv spectral slopes, and lower stellar masses show the strongest nebular emission. the line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z > 2 galaxies. this suggests that weak uv features are likely ubiquitous in high z, low-mass, and faint laes. we publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the james webb space telescope and the extremely large telescope. the average spectra computed in this work are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/641/a118 based on observations made with eso telescopes at the la silla paranal observatory under programs 094.a-0289(b), 095.a-0010(a), 096.a-0045(a) and 096.a-0045(b). | the muse hubble ultra deep field survey. xv. the mean rest-uv spectra of lyα emitters at z > 3 |
we present the results from a high-cadence, multiwavelength observation campaign of at 2016jbu (aka gaia16cfr), an interacting transient. this data set complements the current literature by adding higher cadence as well as extended coverage of the light-curve evolution and late-time spectroscopic evolution. photometric coverage reveals that at 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of mv ~ -18.5 mag. this is similar to the transient sn 2009ip whose nature is still debated. spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. at 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (csm). we see slowly evolving asymmetric hydrogen line profiles, with velocities of 500 km s-1 seen in narrow emission features from a slow-moving csm, and up to 10 000 km s-1 seen in broad absorption from some high-velocity material. late-time spectra (~+1 yr) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from h, he i, and ca ii. strong asymmetric emission features, a bumpy light curve, and continually evolving spectra suggest an inhibit nebular phase. we compare the evolution of h α among sn 2009ip-like transients and find possible evidence for orientation angle effects. the light-curve evolution of at 2016jbu suggests similar, but not identical, circumstellar environments to other sn 2009ip-like transients. | photometric and spectroscopic evolution of the interacting transient at 2016jbu(gaia16cfr) |
the cos legacy archive spectroscopic survey (classy) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to those seen at high z (z > 6). the prime high-level science product of classy is accurately coadded uv spectra, ranging from ~1000 to 2000 å, derived from a combination of archival and new data obtained with hst's cosmic origins spectrograph (cos). this paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (nuv) spectra. we provide guidelines on how to successfully utilize cos observations of extended sources, despite cos being optimized for point sources, and best-practice recommendations for the coaddition of uv spectra in general. moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the classy data. in particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of nuv spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via c iii] nebular emission. despite changes in spectral resolution of up to ~25% between individual data sets (due to changes in the cos line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of s/n < 20. * based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | classy. ii. a technical overview of the cos legacy archive spectroscopic survey |
of the long-lived chronometric systems, only the dual decay of 238u and 235u to 206pb and 207pb, respectively, have appropriate half-lives to resolve the ages of meteorites and their components formed in the first 5 myr of the solar system. this paper reviews the theory and methods behind this chronometer, offers criteria to critically evaluate pb-pb ages and presents a summary of the current state and immediate future of the chronometry of the early solar system. we recognize that there is some debate over the age of the solar system, but conclude that an age of 4567.30 ± 0.16 ma based on four cais dated individually by the same method in two different laboratories is presently the best constrained published value. we further conclude that nebular chondrules dated by the pb-pb method require that they formed contemporaneously with cais and continued to form for at least ∼4 myr, a conclusion that implies heterogeneous distribution of the short-lived 26al nuclide in the protoplanetary disk. planetesimals were already forming by ∼1 myr after cai formation, consistent with their growth predominantly through the accretion of chondrules. nebular chondrule formation was completed by ∼5 myr after cai formation when the impact-generated cba chondrules formed after the disk was cleared of gas and dust. we note that the absolute age of the solar system or any single early solar system object is not fundamental to any significant scientific question and that it is important only to know the correct relative ages of objects being used to piece together the formation history of the solar system. as such, we point out the risks inherent in comparing pb-pb ages produced by different approaches in different laboratories at the level of the internal errors of individual ages. until a cross-calibration exercise using synthetic and natural standards establishes the reproducibility between laboratories, only ages from a single laboratory, or between laboratories having demonstrated concordance, can provide a reliable relative chronometric framework for the formation and evolution of the early solar system. | pb-pb chronometry and the early solar system |
we identify 709 arc-shaped mid-infrared nebula in 24 μm spitzer space telescope or 22 μm wide field infrared explorer surveys of the galactic plane as probable dusty interstellar bowshocks powered by early-type stars. about 20% are visible at 8 μm or at shorter mid-infrared wavelengths. the vast majority (660) have no previous identification in the literature. these extended infrared sources are strongly concentrated near the galactic mid-plane, with an angular scale height of ∼0.°6. all host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. these are candidate “runaway” stars potentially having high velocities in the reference frame of the local medium. among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. we discuss a population of “in situ” bowshocks (∼103 objects) that face giant h ii regions where the relative motions between the star and ism may be caused by bulk outflows from an overpressured bubble. we also identify ∼58 objects that face 8 μm bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (pef) from an eroding molecular cloud interface (i.e., “pef bowshocks”). orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as h ii regions are responsible for producing some bowshock nebulae. however, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences. | a comprehensive search for stellar bowshock nebulae in the milky way: a catalog of 709 mid-infrared selected candidates |
a code computing consistently the evolution of stars, gas and dust, as well as the energy they radiate, is required to derive reliably the history of galaxies by fitting synthetic spectral energy distributions (seds) to multiwavelength observations. the new code pégase.3 described in this paper extends to the far-infrared/submillimeter the ultraviolet-to-near-infrared modeling provided by previous versions of pégase. it first computes the properties of single stellar populations at various metallicities. it then follows the evolution of the stellar light of a galaxy and the abundances of the main metals in the interstellar medium (ism), assuming some scenario of mass assembly and star formation. it simultaneously calculates the masses of the various grain families, the optical depth of the galaxy and the attenuation of the sed through the diffuse ism in spiral and spheroidal galaxies, using grids of radiative transfer precomputed with monte carlo simulations taking scattering into account. the code determines the mean radiation field and the temperature probability distribution of stochastically heated individual grains. it then sums up their spectra to yield the overall emission by dust in the diffuse ism. the nebular emission of the galaxy is also computed, and a simple modeling of the effects of dust on the sed of star-forming regions is implemented. the main outputs are ultraviolet-to-submillimeter seds of galaxies from their birth up to 20 gyr, colors, masses of galactic components, ism abundances of metallic elements and dust species, supernova rates. the temperatures and spectra of individual grains are also available. the paper discusses several of these outputs for a scenario representative of milky way-like spirals. pégase.3 is fully documented and its fortran 95 source files are public. the code should be especially useful for cosmological simulations and to interpret future mid- and far-infrared data, whether obtained by jwst, lsst, euclid or e-elt. available at http://www.iap.fr/users/fioc/pegase/pegase.3/ and http://www.iap.fr/pegase/a copy of the code is 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/623/a143 | pégase.3: a code for modeling the uv-to-ir/submm spectral and chemical evolution of galaxies with dust |
metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. in this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, na=0.32) using deep-ultraviolet (duv) projection lithography. our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are unique to such large area metasurfaces. we demonstrate direct astronomical imaging of the sun, the moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications. | all-glass 100 mm diameter visible metalens for imaging the cosmos |
we present photoionization modeling of galaxy populations at z ∼ 0, 2, and >6 to bridge optical and far-infrared (fir) emission-line diagrams. we collect galaxies with measurements of optical and/or fir ([o iii] 88 μm and [c ii] 158 μm) emission-line fluxes and plot them on the [o iii]λ5007/hβ-[n ii]λ6585/hα (bpt) and l([o iii]88)/sfr-l([c ii]158)/sfr diagrams, where sfr is the star formation rate and l([o iii]88) and l([c ii]158) are the fir line luminosities. we aim to explain the galaxy distributions on the two diagrams with photoionization models that employ three nebular parameters: the ionization parameter u, hydrogen density nh, and gaseous metallicity zgas. our models successfully reproduce the nebular parameters of local galaxies, and then predict the distributions of the z ∼ 0, 2, and >6 galaxies in the diagrams. the predicted distributions illustrate the redshift evolution on all the diagrams; e.g., [o iii]/hβ and [o iii]88/[c ii]158 ratios continuously decrease from z > 6 to 0. specifically, the z > 6 galaxies exhibit ∼0.5 dex higher u than low-redshift galaxies at a given zgas and show predicted flat distributions on the bpt diagram at log[o iii]/hβ = 0.5-0.8. we find that some of the z > 6 galaxies exhibit high l([o iii]88)/sfr ratios. to explain these high ratios, our photoionization models require a low stellar-to-gaseous-metallicity ratio or bursty/increasing star formation history at z > 6. jwst will test the predictions and scenarios for the z > 6 galaxies proposed by our photoionization modeling. | bridging optical and far-infrared emission-line diagrams of galaxies from local to the epoch of reionization: characteristic high [o iii] 88 μm/sfr at z > 6 |
we report the first occurrence of a natural quasicrystal with decagonal symmetry. the quasicrystal, with composition al71ni24fe5, was discovered in the khatyrka meteorite, a recently described cv3 carbonaceous chondrite. icosahedrite, al63cu24fe13, the first natural quasicrystal to be identified, was found in the same meteorite. the new quasicrystal was found associated with steinhardtite (al38ni32fe30), fe-poor steinhardtite (al50ni40fe10), al-bearing trevorite (nife2o4) and al-bearing taenite (feni). laboratory studies of decagonal al71ni24fe5 have shown that it is stable over a narrow range of temperatures, 1120 k to 1200 k at standard pressure, providing support for our earlier conclusion that the khatyrka meteorite reached heterogeneous high temperatures [1100 < t(k) <= 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 gya. the occurrences of metallic al alloyed with cu, ni, and fe raises new questions regarding conditions that can be achieved in the early solar nebula. | natural quasicrystal with decagonal symmetry |
the cb chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the cba chondrite gujba are interpreted to reflect a single-stage impact origin. here, we report high-precision internal isochrons for four individual chondrules of the gujba chondrite to probe the formation history of cb chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. all four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 myr. finally, given the well-behaved pb-pb systematics of all four chondrules, a precise formation age and the concordancy of the mn-cr, hf-w, and i-xe short-lived radionuclide relative chronometers, we propose that gujba may serve as a suitable time anchor for these systems. | pb-pb dating of individual chondrules from the cba chondrite gujba: assessment of the impact plume formation model |
we present the detection of persistent soft x-ray radiation with {l}x∼ {10}41-1042 erg s-1 at the location of the extremely luminous, double-humped transient asassn-15lh as revealed by chandra and swift. we interpret this finding in the context of observations from our multiwavelength campaign, which revealed the presence of weak narrow nebular emission features from the host-galaxy nucleus and clear differences with respect to superluminous supernova optical spectra. significant uv flux variability on short timescales detected at the time of the rebrightening disfavors the shock interaction scenario as the source of energy powering the long-lived uv emission, while deep radio limits exclude the presence of relativistic jets propagating into a low-density environment. we propose a model where the extreme luminosity and double-peaked temporal structure of asassn-15lh is powered by a central source of ionizing radiation that produces a sudden change in the ejecta opacity at later times. as a result, uv radiation can more easily escape, producing the second bump in the light curve. we discuss different interpretations for the intrinsic nature of the ionizing source. we conclude that, if the x-ray source is physically associated with the optical-uv transient, then asassn-15lh most likely represents the tidal disruption of a main-sequence star by the most massive spinning black hole detected to date. in this case, asassn-15lh and similar events discovered in the future would constitute the most direct probes of very massive, dormant, spinning, supermassive black holes in galaxies. future monitoring of the x-rays may allow us to distinguish between the supernova hypothesis and the hypothesis of a tidal disruption event. | x-rays from the location of the double-humped transient asassn-15lh |
we present deep spectrophotometry of 18 h ii regions in the nearby massive spiral galaxies m 101 and m 31. we have obtained direct determinations of electron temperature in all the nebulae. we detect the c ii 4267 å line in several h ii regions, permitting to derive the radial gradient of c/h in both galaxies. we also determine the radial gradients of o/h, n/o, ne/o, s/o, cl/o, and ar/o ratios. as in other spiral galaxies, the c/h gradients are steeper than those of o/h producing negative slopes of the c/o gradient. the scatter of the abundances of o with respect to the gradient fittings do not support the presence of significant chemical inhomogeneities across the discs of the galaxies, especially in the case of m101. we find trends in the s/o, cl/o, and ar/o ratios as a function of o/h in m101 that can be reduced using te indicators different from the standard ones for calculating some ionic abundances. the distribution of the n/o ratio with respect to o/h is rather flat in m31, similarly to previous findings for the milky way. using the disc effective radius - re - as a normalization parameter for comparing gradients, we find that the latest estimates of re for the milky way provide an excess of metallicity in apparent contradiction with the mass-metallicity relation; a value about two times larger might solve the problem. finally, using different abundance ratios diagrams we find that the enrichment time-scales of c and n result to be fairly similar despite their different nucleosynthetic origin. | carbon, nitrogen, and oxygen abundance gradients in m101 and m31 |
gravitational-wave emission can lead to the coalescence of close pairs of compact objects orbiting each other1,2. in the case of neutron stars, such mergers may yield masses above the tolman-oppenheimer-volkoff limit (2 to 2.7 solar masses)3, leading to the formation of black holes4. for white dwarfs, the mass of the merger product may exceed the chandrasekhar limit, leading either to a thermonuclear explosion as a type ia supernova5,6 or to a collapse forming a neutron star7,8. the latter case is expected to result in a hydrogen- and helium-free circumstellar nebula and a hot, luminous, rapidly rotating and highly magnetized central star with a lifetime of about 10,000 years9,10. here we report observations of a hot star with a spectrum dominated by emission lines, which is located at the centre of a circular mid-infrared nebula. the widths of the emission lines imply that wind material leaves the star with an outflow velocity of 16,000 kilometres per second and that rapid stellar rotation and a strong magnetic field aid the wind acceleration. given that hydrogen and helium are probably absent from the star and nebula, we conclude that both objects formed recently from the merger of two massive white dwarfs. our stellar-atmosphere and wind models indicate a stellar surface temperature of about 200,000 kelvin and a luminosity of about 104.6 solar luminosities. the properties of the star and nebula agree with models of the post-merger evolution of super-chandrasekhar-mass white dwarfs9, which predict a bright optical and high-energy transient upon collapse of the star11 within the next few thousand years. our observations indicate that super-chandrasekhar-mass white-dwarf mergers can avoid thermonuclear explosion as type ia supernovae, and provide evidence of the generation of magnetic fields in stellar mergers. | a massive white-dwarf merger product before final collapse |
we combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ism) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ism in star-forming galaxies. we start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ism-free ultraviolet spectra of 10 large magellanic cloud clusters. in doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (∼10-100 myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. then, we proceed and develop a simple approach, based on an idealized description of the main features of the ism, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. we use this approach to explore the entangled signatures of stars, the ionized and the neutral ism in ultraviolet spectra of star-forming galaxies. we find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ism-free stellar populations are prone to significant contamination by the ism, which increases with metallicity. we also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ism. | modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies |
we present the detection of an unresolved radio source coincident with the position of the type i superluminous supernova (slsn) ptf10hgi (z = 0.098) about 7.5 yr post-explosion, with a flux density of fν (6 ghz) ≈ 47.3 μjy and a luminosity of lν (6 ghz) ≈ 1.1 × 1028 erg s-1 hz-1. this represents the first detection of radio emission coincident with an slsn on any timescale. we investigate various scenarios for the origin of the radio emission: star formation activity, an active galactic nucleus, and a non-relativistic supernova blastwave. while any of these would be quite novel if confirmed, none appear likely when considered within the context of the other properties of the host galaxy, previous radio observations of slsne, and the general population of hydrogen-poor supernovae (sne). instead, the radio emission is reminiscent of the quiescent radio source associated with the repeating frb 121102, which has been argued to be powered by a magnetar born in a slsn or long gamma-ray burst explosion several decades ago. we show that the properties of the radio source are consistent with a magnetar wind nebula or an off-axis jet, indicating the presence of a central engine. our directed search for fast radio bursts from the location of ptf10hgi using 40 minutes of very large array phased-array data reveals no detections to a limit of 22 mjy (10σ 10 ms duration). we outline several follow-up observations that can conclusively establish the origin of the radio emission. | a radio source coincident with the superluminous supernova ptf10hgi: evidence for a central engine and an analog of the repeating frb 121102? |
aims: this study aims at constraining the origin of the nearby type ia supernovae (sne), 2011fe and 2014j. the two most favoured scenarios for triggering the explosion of the white dwarf supernova progenitor is either mass loss from a non-degenerate companion or merger with another white dwarf. in the former, there could be a significant amount of leftover material from the companion at the centre of the supernova. detecting such material would therefore favour the single-degenerate scenario.methods: the left-over material from a possible non-degenerate companion can reveal itself after about one year, and in this study such material was searched for in the spectra of sn 2011fe (at 294 days after the explosion) using the large binocular telescope and for sn 2014j using the nordic optical telescope (315 days past explosion). the observations were interpreted using numerical models simulating the expected line emission from ablated material from the companion star. the spectral lines sought for are hα, [o i] λ6300, and [ca ii] λλ7291,7324, and the expected width of these lines is ~1000 km s-1, which in the case of the [ca ii] lines blend to a broader feature.results: no signs of hα, [o i] λ6300, or [ca ii] λλ7291, 7324 could be traced for in any of the two supernovae. when systematic uncertainties are included, the limits on hydrogen-rich ablated gas are 0.003 m⊙ in sn 2011fe and 0.0085 m⊙ in sn 2014j, where the limit for sn 2014j is the second lowest ever, and the limit for sn 2011fe is a revision of a previous limit. limits are also put on helium-rich ablated gas, and here limits from [o i] λ6300 provide the upper mass limits 0.002 m⊙ and 0.005 m⊙ for sne 2011fe and 2014j, respectively. these numbers are used in conjunction with other data to argue that these supernovae can stem from double-degenerate systems or from single-degenerate systems with a spun-up/spun-down super-chandrasekhar white dwarf. for sn 2011fe, other types of hydrogen-rich donors can very likely be ruled out, whereas a main-sequence donor system with large intrinsic separation is still possible for sn 2014j. helium-rich donor systems cannot be ruled out for any of the two supernovae, but the expected short delay time for such progenitors makes this possibility less likely, especially for sn 2011fe. published data for sne 1998bu, 2000cx, 2001el, 2005am, and 2005cf are used to constrain their origin. we emphasise that the results of this study depend on the sought-after lines emerging unattenuated from the central regions of the nebula. detailed radiative transfer calculations with longer line lists than are presently used are needed to confirm that this is, in fact, true. finally, the broad lines of sne 2011fe and 2014j are discussed, and it is found that the [ni ii] λ7378 emission is redshifted by ~+1300 kms-1, as opposed to the known blueshift of ~-1100 kms-1 for sn 2011fe. [fe ii] λ7155 is also redshifted in sn 2014j. sn 2014j belongs to a minority of sne ia that both have a nebular redshift of [fe ii] λ7155 and [ni ii] λ7378, and a slow decline of the si ii λ6355 absorption trough just after b-band maximum. | no trace of a single-degenerate companion in late spectra of supernovae 2011fe and 2014j |
context. evolved low-mass stars lose a significant fraction of their mass through stellar winds. while the overall morphology of the stellar wind structure during the asymptotic giant branch (agb) phase is thought to be roughly spherically symmetric, the morphology changes dramatically during the post-agb and planetary nebula phase, during which bipolar and multi-polar structures are often observed.aims: we aim to study the inner wind structure of the closest well-known agb star cw leo. different diagnostics probing different geometrical scales have implied a non-homogeneous mass-loss process for this star: dust clumps are observed at milli-arcsec scale, a bipolar structure is seen at arcsecond-scale, and multi-concentric shells are detected beyond 1''.methods: we present the first alma cycle 0 band 9 data around 650 ghz (450 μm) tracing the inner wind of cw leo. the full-resolution data have a spatial resolution of 0.̋42 × 0.̋24, allowing us to study the morpho-kinematical structure of cw leo within ~6''.results: we have detected 25 molecular emission lines in four spectral windows. the emission of all but one line is spatially resolved. the dust and molecular lines are centered around the continuum peak position, which is assumed to be dominated by stellar emission. the dust emission has an asymmetric distribution with a central peak flux density of ~2 jy. the molecular emission lines trace different regions in the wind acceleration region and imply that the wind velocity increases rapidly from about 5 r⋆, almost reaching the terminal velocity at ~11 r⋆. the images prove that vibrational lines are excited close to the stellar surface and that sio is a parent molecule. the channel maps for the brighter lines show a complex structure; specifically, for the 13co j = 6-5 line, different arcs are detected within the first few arcseconds. the curved structure in the position-velocity (pv) map of the 13co j = 6-5 line can be explained by a spiral structure in the inner wind of cw leo, probably induced by a binary companion. from modelling the alma data, we deduce that the potential orbital axis for the binary system lies at a position angle of ~10-20° to the north-east and that the spiral structure is seen almost edge-on. we infer an orbital period of 55 yr and a binary separation of 25 au (or ~8.2 r⋆). we tentatively estimate that the companion is an unevolved low-mass main-sequence star.conclusions: a scenario of a binary-induced spiral shell can explain the correlated structure seen in the alma pv images of cw leo. moreover, this scenario can also explain many other observational signatures seen at different spatial scales and in different wavelength regions, such as the bipolar structure and the almost concentric shells. alma data hence for the first time provide the crucial kinematical link between the dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen at arcsecond scale. appendix a is available in electronic form at http://www.aanda.org | alma data suggest the presence of spiral structure in the inner wind of cw leonis |
space observatories have provided unprecedented depictions of the many variability behaviors typical of low-mass, young stars. however, those studies have so far largely omitted more massive objects (~2 m⊙ to 4-5 m⊙) and were limited by the absence of simultaneous, multiwavelength information. we present a new study of young star variability in the ~1-2 myr old, massive lagoon nebula region. our sample encompasses 278 young, late b to k-type stars, monitored with kepler/k2. auxiliary u, g, r, i, hα time-series photometry, simultaneous with k2, was acquired at the paranal observatory. we employed this comprehensive data set and archival infrared photometry to determine individual stellar parameters, assess the presence of circumstellar disks, and tie the variability behaviors to inner disk dynamics. we found significant mass-dependent trends in variability properties, with b/a stars displaying substantially reduced levels of variability compared to g/k stars for any light-curve morphology. these properties suggest different magnetic field structures at the surface of early-type and later-type stars. we also detected a dearth of some disk-driven variability behaviors, particularly dippers, among stars earlier than g. this indicates that their higher surface temperatures and more chaotic magnetic fields prevent the formation and survival of inner disk dust structures corotating with the star. finally, we examined the characteristic variability timescales within each light curve and determined that the day-to-week timescales are predominant over the k2 time series. these reflect distinct processes and locations in the inner disk environment, from intense accretion triggered by instabilities in the innermost disk regions to variable accretion efficiency in the outer magnetosphere. | multicolor variability of young stars in the lagoon nebula: driving causes and intrinsic timescales |
we present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 6 ≲ z ≲ 8 galaxy candidates from the reionization lensing cluster survey (relics) and spitzer-relics surveys. we measure photometry using t-phot and perform spectral energy distribution fitting using eazy and bagpipes. of the 207 candidates for which we could successfully measure (or place limits on) spitzer fluxes, 23 were demoted to likely z < 4. among the high-z candidates, we find intrinsic stellar masses between 1 × 106m⊙ and 4 × 109m⊙, and rest-frame uv absolute magnitudes between -22.6 and -14.5 mag. while our sample is mostly comprised of ${l}_{m\mathrm{uv}}/{l}_{m\mathrm{uv}}^{* }\lt 1$ <!-- --> galaxies, it extends to ${l}_{m\mathrm{uv}}/{l}_{m\mathrm{uv}}^{* }\sim 2$ <!-- --> . our sample spans ∼4 orders of magnitude in stellar mass and star formation rates, and exhibits ages that range from maximally young to maximally old. we highlight 11 z ≥ 6.5 galaxies with detections in spitzer/irac imaging, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. among these is plckg287+32-2013, one of the brightest z ∼ 7 candidates known (ab mag 24.9 at 1.6 μm) with a spitzer 3.6 μm flux excess suggesting strong [o iii] + h-β emission (∼1000 å rest-frame equivalent width). we discuss the possible uses and limits of our sample and present a public catalog of hubble + spitzer photometry along with physical property estimates for all objects in the sample. because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with the james webb space telescope. | relics: properties of z ≥ 5.5 galaxies inferred from spitzer and hubble imaging, including a candidate z ∼ 6.8 strong [o iii] emitter |
to first order, the earth as well as other rocky planets in the solar system and rocky exoplanets orbiting other stars, are refractory pieces of the stellar nebula out of which they formed. to estimate the chemical composition of rocky exoplanets based on their stellar hosts' elemental abundances, we need a better understanding of the devolatilization that produced the earth. to quantify the chemical relationships between the earth, the sun and other bodies in the solar system, the elemental abundances of the bulk earth are required. the key to comparing earth's composition with those of other objects is to have a determination of the bulk composition with an appropriate estimate of uncertainties. here we present concordance estimates (with uncertainties) of the elemental abundances of the bulk earth, which can be used in such studies. first we compile, combine and renormalize a large set of heterogeneous literature values of the primitive mantle (pm) and of the core. we then integrate standard radial density profiles of the earth and renormalize them to the current best estimate for the mass of the earth. using estimates of the uncertainties in i) the density profiles, ii) the core-mantle boundary and iii) the inner core boundary, we employ standard error propagation to obtain a core mass fraction of 32.5 ± 0.3 wt%. our bulk earth abundances are the weighted sum of our concordance core abundances and concordance pm abundances. unlike previous efforts, the uncertainty on the core mass fraction is propagated to the uncertainties on the bulk earth elemental abundances. our concordance estimates for the abundances of mg, sn, br, b, cd and be are significantly lower than previous estimates of the bulk earth. our concordance estimates for the abundances of na, k, cl, zn, sr, f, ga, rb, nb, gd, ta, he, ar, and kr are significantly higher. the uncertainties on our elemental abundances usefully calibrate the unresolved discrepancies between standard earth models under various geochemical and geophysical assumptions. | the elemental abundances (with uncertainties) of the most earth-like planet |
the attenuation of starlight by dust in galactic environments is investigated through models of radiative transfer in a spherical, clumpy interstellar medium (ism). we show that the attenuation curves are primarily determined by the wavelength dependence of absorption rather than by the underlying extinction (absorption+scattering) curve; the observationally derived attenuation curves cannot constrain a unique extinction curve unless the absorption or scattering efficiency is specified. attenuation curves consistent with the “calzetti curve” are found by assuming the silicate-carbonaceous dust model for the milky way (mw), but with the 2175 å bump suppressed or absent. the discrepancy between our results and previous work that claimed the small magellanic cloud dust to be the origin of the calzetti curve is ascribed to the difference in adopted albedos; we use the theoretically calculated albedos, whereas the previous works adopted albedos derived empirically from observations of reflection nebulae. it is found that the attenuation curves calculated with the mw dust model are well represented by a modified calzetti curve with a varying slope and uv bump strength. the strong correlation between the slope and uv bump strength, as found in star-forming galaxies at 0.5\lt z\lt 2.0, is well reproduced when the abundance of the uv bump carriers is assumed to be 30%-40% of that of the mw dust; radiative transfer effects lead to shallower attenuation curves with weaker uv bumps as the ism is more clumpy and dustier. we also argue that some local starburst galaxies have a uv bump in their attenuation curves, albeit very weak. | radiative transfer model of dust attenuation curves in clumpy, galactic environments |
we investigate the integrated properties of massive (> 10 {m}⊙ ) rotating single-star stellar populations for a variety of initial rotation rates (v/{v}crit}=0.0, 0.2, 0.4, 0.5, and 0.6). we couple the new mesa isochrone and stellar tracks (mist) models to the flexible stellar population synthesis (fsps) package, extending the stellar population synthesis models to include the contributions from very massive stars (> 100 {m}⊙ ), which can be significant in the first ∼4 myr after a starburst. these models predict ionizing luminosities that are consistent with recent observations of young nuclear star clusters. we also construct composite stellar populations assuming a distribution of initial rotation rates. even in low-metallicity environments where rotation has a significant effect on the evolution of massive stars, we find that stellar population models require a significant contribution from fast-rotating (v/{v}crit}> 0.4) stars in order to sustain the production of ionizing photons beyond a few myr following a starburst. these results have potentially important implications for cosmic reionization by massive stars and the interpretation of nebular emission lines in high-redshift star-forming galaxies. | the evolution and properties of rotating massive star populations |
magic, a system of two imaging atmospheric cherenkov telescopes, achieves its best performance under dark conditions, i.e. in absence of moonlight or twilight. since operating the telescopes only during dark time would severely limit the duty cycle, observations are also performed when the moon is present in the sky. here we develop a dedicated moon-adapted analysis to characterize the performance of magic under moonlight. we evaluate energy threshold, angular resolution and sensitivity of magic under different background light levels, based on crab nebula observations and tuned monte carlo simulations. this study includes observations taken under non-standard hardware configurations, such as reducing the camera photomultiplier tubes gain by a factor ∼1.7 (reduced hv settings) with respect to standard settings (nominal hv) or using uv-pass filters to strongly reduce the amount of moonlight reaching the cameras of the telescopes. the crab nebula spectrum is correctly reconstructed in all the studied illumination levels, that reach up to 30 times brighter than under dark conditions. the main effect of moonlight is an increase in the analysis energy threshold and in the systematic uncertainties on the flux normalization. the sensitivity degradation is constrained to be below 10%, within 15-30% and between 60 and 80% for nominal hv, reduced hv and uv-pass filter observations, respectively. no worsening of the angular resolution was found. thanks to observations during moonlight, the maximal duty cycle of magic can be increased from ∼18%, under dark nights only, to up to ∼40% in total with only moderate performance degradation. | performance of the magic telescopes under moonlight |
tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early solar system. we report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf gaia dr2 4353607450860305024, which we ascribe to the accretion of a planetesimal. using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the solar system. we compare the measured lithium abundance with measurements in old stars and with expectations from big bang nucleosynthesis. | lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal |
we model pop iii star formation in different fuv and x-ray backgrounds, including radiation feedback from protostars. we confirm previous results that a moderate x-ray background increases the number of pop iii systems per unit cosmological volume, but masses and multiplicities of the system are reduced. the stellar mass function also agrees with previous results, and we confirm the outward migration of the stars within the protostellar discs. we find that nearly all pop iii star systems are hierarchical, i.e. binaries of binaries. typically, two equal-mass stars form near the centre of the protostellar disc and migrate outwards. around these stars, mini-discs fragment forming binaries that also migrate outwards. stars may also form at lagrange points l4/l5 of the system. afterwards, star formation becomes more stochastic due to the large multiplicity, and zero-metallicity low-mass stars can form when rapidly ejected from the disc. stars in the disc often have eccentric orbits, leading to a periodic modulation of their accretion rates and luminosities. at the pericentre, due to strong accretion, the star can enter a red-supergiant phase reaching nearly eddington luminosity in the optical bands (mab ~ 34 for a 100 m⊙ star at z = 6). during this phase, the star, rather than its nebular lines, can be observed directly by jwst, if sufficiently magnified by a gravitational lens. the ~10 000 au separations and high eccentricities of many pop iii star binaries in our simulations are favourable parameters for imbh mergers - and gravitational waves emission - through orbital excitation by field stars. | population iii star formation in an x-ray background: iii. periodic radiative feedback and luminosity induced by elliptical orbits |
we present the first jwst observations of the z = 4.11 luminous radio galaxy tn j1338-1942, obtained as part of the 'prime extragalactic areas for reionization and lensing science' ('pearls') project. our nircam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. with an estimated stellar mass of log10(m/m⊙) ~ 10.9, tn j1338-1942 is confirmed to be one of the most massive galaxies known at this epoch. our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous agn jets that is best fit by radiative shocks surrounded by extensive recent star formation. we estimate the total star-formation rate (sfr) could be as high as $\sim 1600\, \text{m}_{\odot }\, \text{yr}^{-1}$ , with the sfr that we attribute to the jet induced burst conservatively $\gtrsim 500\, \text{m}_{\odot }\, \text{yr}^{-1}$ . the mass-weighted age of the star-formation, tmass < 4 myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. the extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive agn feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with jwst. | jwst's pearls: tn j1338-1942 - i. extreme jet-triggered star formation in a z = 4.11 luminous radio galaxy |
to understand the mechanism behind high-z lyα nebulae, we simulate the scattering of lyα in a h i halo about a central lyα source. for the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total h i column densities, h i spatial concentrations, and central source galaxies (e.g., with lyα line widths corresponding to those typical of active galactic nucleus or star-forming galaxies). we compute the spatial-frequency diffusion and the polarization of the lyα photons scattered by atomic hydrogen. our scattering-only model reproduces the typical size of lyα nebulae (~100 kpc) at total column densities n h i ≥ 1020 cm-2 and predicts a range of positive, flat, and negative polarization radial gradients. we also find two general classes of lyα nebula morphologies: with and without bright cores. cores are seen when n h i is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. of all the parameters tested in our smooth or clumpy medium model, n h i dominates the trends. the radial behaviors of the lyα surface brightness, spectral line shape, and polarization in the clumpy model with covering factor fc≳ 5 approach those of the smooth model at the same n h i. a clumpy medium with high n h i and low fc≲ 2 generates lyα features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump. | radiative transfer in lyα nebulae. i. modeling a continuous or clumpy spherical halo with a central source |
the identification and localization of fast radio bursts (frbs) to their host galaxies have revealed important details about the progenitors of these mysterious, millisecond-long bursts of coherent radio emission. in this work, we study the most probable host galaxy of the apparently non-repeating chime/frb event frb 20190425a - a particularly high-luminosity, low-dispersion measure event that was demonstrated in a recent paper to be temporally and spatially coincident with the ligo-virgo-kagra binary neutron star merger gw190425, suggesting an astrophysical association (p-value 0.0052). in this paper, we remain agnostic to this result, and we confirm ugc10667 as the most probable host galaxy of frb 20190425a, demonstrating that the host galaxies of low-dispersion measure, one-off chime frbs can be plausibly identified. we then perform multiwavelength observations to characterize the galaxy and search for any afterglow emission associated with the frb and its putative gw counterpart. we find no radio or optical transient emission in our observations $2.5\, \mathrm{yr}$ post-burst. ugc10667 is a spiral galaxy at z ~ 0.03, dominated by an old stellar population. we find no evidence of a large population of young stars, with nebular emission dominated by star formation at a rate of $1\!-\!2\, ~\mathrm{m_\odot \, yr^{-1}}$. while we cannot rule out a young magnetar as the origin of frb 20190425a, our observations are consistent with an origin in a long delay-time neutron star binary merger. | the most probable host of chime frb 190425a, associated with binary neutron star merger gw190425, and a late-time transient search |
current and future cosmological surveys are targeting star-forming galaxies at z ∼ 1 with nebular emission lines. we use a state-of-the-art semi-analytical model of galaxy formation and evolution to explore the large-scale environment of star-forming emission line galaxies (elgs). model elgs are selected such that they can be compared directly with the deep2, vvds, eboss-sgc, and desi surveys. the large-scale environment of the elgs is classified using velocity-shear-tensor and tidal-tensor algorithms. half of the model elgs live in filaments and about a third in sheets. model elgs that reside in knots have the largest satellite fractions. we find that the shape of the mean halo occupation distribution of model elgs varies widely for different large-scale environments. to interpret our results, we also study fixed number density samples of elgs and galaxies selected using simpler criteria, with single cuts in stellar mass, star formation rate, and [o ii] luminosity. the fixed number density elg selection produces samples that are close to l[o ii] and sfr-selected samples for densities above 10-4.2 h3 mpc-3. elgs with an extra cut in stellar mass applied to fix their number density, present differences in sheets and knots with respect to the other samples. elgs, sfr, and l[o ii] selected samples with equal number density have similar large-scale bias but their clustering below separations of 1h-1 mpc is different. | do model emission line galaxies live in filaments at z ∼ 1? |
we present and describe the astro-photometric catalog of more than 800,000 sources found in the hubble tarantula treasury project (http). http is a hubble space telescope treasury program designed to image the entire 30 doradus region down to the sub-solar (∼0.5 m⊙) mass regime using the wide field camera 3 and the advanced camera for surveys. we observed 30 doradus in the near-ultraviolet (f275w, f336w), optical (f555w, f658n, f775w), and near-infrared (f110w, f160w) wavelengths. the stellar photometry was measured using point-spread function fitting across all bands simultaneously. the relative astrometric accuracy of the catalog is 0.4 mas. the astro-photometric catalog, results from artificial star experiments, and the mosaics for all the filters are available for download. color-magnitude diagrams are presented showing the spatial distributions and ages of stars within 30 dor as well as in the surrounding fields. http provides the first rich and statistically significant sample of intermediate- and low-mass pre-main sequence candidates and allows us to trace how star formation has been developing through the region. the depth and high spatial resolution of our analysis highlight the dual role of stellar feedback in quenching and triggering star formation on the giant h ii region scale. our results are consistent with stellar sub-clustering in a partially filled gaseous nebula that is offset toward our side of the large magellanic cloud. based on observations with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by aura inc., under nasa contract nas 5-26555. | hubble tarantula treasury project. iii. photometric catalog and resulting constraints on the progression of star formation in the 30 doradus region |
the unprecedented astrometry from gaia's second data release (dr2) provides us with an opportunity to study molecular clouds in the solar neighbourhood in detail. extracting the wealth of information in these data remains a challenge, however. we have further improved our gaussian-processes-based, three-dimensional dust mapping technique to allow us to study molecular clouds in more detail. these improvements include a significantly better scaling of the computational cost with the number of stars, and taking into account distance uncertainties to individual stars. using gaia dr2 astrometry together with the two micron all sky survey (2mass) and the wide-field infrared survey explorer (wise) photometry for 30 000 stars, we infer the distribution of dust out to 600 pc in the direction of the orion a molecular cloud. we identify a bubble-like structure in front of orion a, centred at a distance of about 350 pc from the sun. the main orion a structure is visible at slightly larger distances, and we clearly see a tail extending over 100 pc that is curved and slightly inclined to the line of sight. the location of our foreground structure coincides with 5-10 myr old stellar populations, suggesting a star formation episode that predates that of the orion nebula cluster itself. we also identify the main structure of the orion b molecular cloud, and in addition discover a background component to this at a distance of about 460 pc from the sun. finally, we associate our dust components at different distances with the plane-of-the-sky magnetic field orientation as mapped by planck. this provides valuable information for modelling the magnetic field in three dimensions around star-forming regions. | detailed 3d structure of orion a in dust with gaia dr2 |
we present an analysis of the newly identified μ tau association (muta) of young stars at ≃150 pc from the sun that is part of the large cas-tau structure, coeval and comoving with the α persei cluster. this association is also located in the vicinity of the taurus-auriga star-forming region and the pleiades association, although it is unrelated to them. we identify more than 500 candidate members of muta using gaia dr2 data and the banyan σ tool, and we determine an age of 62 ± 7 myr for its population based on an empirical comparison of its color-magnitude diagram sequence with those of other nearby young associations. the muta association is related to the theia 160 group of kounkel & covey and corresponds to the e tau group of liu et al. it is also part of the cas-tau group of blaauw. as part of this analysis, we introduce an iterative method based on spectral templates to perform an accurate correction of interstellar extinction of gaia dr2 photometry, needed because of its wide photometric bandpasses. we show that the members of muta display an expected increased rate of stellar activity and faster rotation rates compared with older stars, and that literature measurements of the lithium equivalent width of nine g0- to k3-type members are consistent with our age determination. we show that the present-day mass function of muta is consistent with other known nearby young associations. we identify wd 0340+103 as a hot, massive white dwarf remnant of a b2 member that left its planetary nebula phase only 270,000 yr ago, posing an independent age constraint of ${60}_{-6}^{+8}$ myr for muta, consistent with our isochrone age. this relatively large collection of comoving young stars near the sun indicates that more work is required to unveil the full kinematic structure of the complex of young stars surrounding α persei and cas-tau. | the μ tau association: a 60 myr old coeval group at 150 pc from the sun |
the analysis and combination of data from different gamma-ray instruments involves the use of collaboration proprietary software and case-by-case methods. the effort of defining a common data format for high-level data, namely event lists and instrument response functions (irfs), has recently started for very-high-energy gamma-ray instruments, driven by the upcoming cherenkov telescope array (cta). in this work we implemented this prototypical data format for a small set of magic, veritas, fact, and h.e.s.s. crab nebula observations, and we analyzed them with the open-source gammapy software package. by combining data from fermi-lat, and from four of the currently operating imaging atmospheric cherenkov telescopes, we produced a joint maximum likelihood fit of the crab nebula spectrum. aspects of the statistical errors and the evaluation of systematic uncertainty are also commented upon, along with the release format of spectral measurements. the results presented in this work are obtained using open-access on-line assets that allow for a long-term reproducibility of the results. | towards open and reproducible multi-instrument analysis in gamma-ray astronomy |
we model particle growth in a turbulent, viscously evolving protoplanetary nebula, incorporating sticking, bouncing, fragmentation, and mass transfer at high speeds. we treat small particles using a moments method and large particles using a traditional histogram binning, including a probability distribution function of collisional velocities. the fragmentation strength of the particles depends on their composition (icy aggregates are stronger than silicate aggregates). the particle opacity, which controls the nebula thermal structure, evolves as particles grow and mass redistributes. while growing, particles drift radially due to nebula headwind drag. particles of different compositions evaporate at “evaporation fronts” (efs) where the midplane temperature exceeds their respective evaporation temperatures. we track the vapor and solid phases of each component, accounting for advection and radial and vertical diffusion. we present characteristic results in evolutions lasting 2 × 105 years. in general, (1) mass is transferred from the outer to the inner nebula in significant amounts, creating radial concentrations of solids at efs; (2) particle sizes are limited by a combination of fragmentation, bouncing, and drift; (3) “lucky” large particles never represent a significant amount of mass; and (4) restricted radial zones just outside each ef become compositionally enriched in the associated volatiles. we point out implications for millimeter to submillimeter seds and the inference of nebula mass, radial banding, the role of opacity on new mechanisms for generating turbulence, the enrichment of meteorites in heavy oxygen isotopes, variable and nonsolar redox conditions, the primary accretion of silicate and icy planetesimals, and the makeup of jupiter’s core. | global modeling of nebulae with particle growth, drift, and evaporation fronts. i. methodology and typical results |
spatially resolved spectroscopy of the environments of explosive transients carries detailed information about the physical properties of the stellar population that gave rise to the explosion, and thus the progenitor itself. here, we present new observations of eso184-g82, the galaxy hosting the archetype of the γ-ray burst/supernova connection, grb 980425/sn 1998bw, obtained with the integral field spectrograph muse mounted at the very large telescope. these observations have yielded detailed maps of emission-line strength for various nebular lines along with physical parameters such as dust extinction, stellar age, and oxygen abundance on spatial scales of 160 pc. the immediate environment of grb 980425 is young (5-8 myr) and consistent with a mildly extinguished (av 0.1 mag) progenitor of zero-age main-sequence mass between 25 m⊙ and 40 m⊙ and an oxygen abundance 12 + log (o / h) 8.2 (z 0.3 z⊙), which is slightly lower than that of an integrated measurement of the whole galaxy (12 + log (o / h) 8.3) and a prominent nearby h ii region (12 + log (o / h) 8.4). this region is significantly younger than the explosion site, and we argue that a scenario in which the grb progenitor formed in this environment and was subsequently ejected appears very unlikely. we show that empirical strong-line methods based on [o iii] and/or [n ii] are inadequate to produce accurate maps of oxygen abundance at the level of detail of our muse observation as these methods strongly depend on the ionization state of the gas. the metallicity gradient in eso184-g82 is - 0.06 dex kpc-1, indicating that the typical offsets of at most few kpc for cosmological grbs on average have a small impact on oxygen abundance measurements at higher redshift. based on observations collected at the eso paranal observatory under eso program 095.d-0172(a) and data obtained from the eso science archive facility.the muse data cubes are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/602/a85 | hot gas around sn 1998bw: inferring the progenitor from its environment |
the heart of the large magellanic cloud, 30 doradus, is a complex region with a clear core-halo structure. feedback from the stellar cluster r136 has been shown to be the main source of energy creating multiple parsec-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. we present the morphology and strength of the magnetic fields (b-fields) of 30 doradus inferred from the far-infrared polarimetric observations by sofia/hawc+ at 89, 154, and 214 μm. the b-field morphology is complex, showing bending structures around r136. in addition, we use high spectral and angular resolution [c ii] observations from sofia/great and co(2-1) from apex. the kinematic structure of the region correlates with the b-field morphology and shows evidence of multiple expanding-shells. our b-field strength maps, estimated using the davis-chandrasekhar-fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350 μg at 89, 154, and 214 μm, respectively. we estimated that the majority of the 30 doradus clouds are subcritical and sub-alfvénic. the probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. we show that the b-field is sufficient to hold the cloud structure integrity under feedback from r136. we suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. the velocity gradient technique using [c ii] and co(2-1) is likely to confirm these suggestions. | sofia observations of 30 doradus. ii. magnetic fields and large-scale gas kinematics |
we investigate dust attenuation and its dependence on viewing angle for 308 star-forming galaxies at 1.3 ≤ z ≤ 2.6 from the mosfire deep evolution field survey. we divide galaxies with a detected hα emission line and coverage of hβ into eight groups by stellar mass, star formation rate (sfr), and inclination (i.e., axis ratio), and we then stack their spectra. from each stack, we measure the balmer decrement and gas-phase metallicity, and then we compute the median a v and uv continuum spectral slope (β). first, we find that none of the dust properties (balmer decrement, a v, or β) varies with the axis ratio. second, both stellar and nebular attenuation increase with increasing galaxy mass, showing little residual dependence on sfr or metallicity. third, nebular emission is more attenuated than stellar emission, and this difference grows even larger at higher galaxy masses and sfrs. based on these results, we propose a three-component dust model in which attenuation predominantly occurs in star-forming regions and large, dusty star-forming clumps, with minimal attenuation in the diffuse ism. in this model, nebular attenuation primarily originates in clumps, while stellar attenuation is dominated by star-forming regions. clumps become larger and more common with increasing galaxy mass, creating the above mass trends. finally, we argue that a fixed metal yield naturally leads to mass regulating dust attenuation. infall of low-metallicity gas increases the sfr and lowers the metallicity, but leaves the dust column density mostly unchanged. we quantify this idea using the kennicutt-schmidt and fundamental metallicity relations, showing that galaxy mass is indeed the primary driver of dust attenuation. | an updated dust-to-star geometry: dust attenuation does not depend on inclination in 1.3 ≤z ≤2.6 star-forming galaxies from mosdef |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.