abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
the nebular phase of lanthanide-rich ejecta of a neutron star merger (nsm) is studied by using a one-zone model, in which the atomic properties a represented by a single species, neodymium (nd). under the assumption that β-decay of r-process nuclei is the heat and ionization source, we solve the ionization and thermal balance of the ejecta under non-local thermodynamic equilibrium. the atomic data including energy levels, radiative transition rates, collision strengths, and recombination rate coefficients are obtained by using atomic structure codes, grasp2k and hullac. we find that both permitted and forbidden lines roughly equally contribute to the cooling rate of nd ii and nd iii at the nebular temperatures. we show that the kinetic temperature and ionization degree increase with time in the early stage of the nebular phase, while these quantities become approximately independent of time after the thermalization break of the heating rate because the processes relevant to the ionization and thermalization balance are attributed to two-body collision between electrons and ions at later times. as a result, in spite of the rapid decline of the luminosity, the shape of the emergent spectrum does not change significantly with time after the break. we show that the emission-line nebular spectrum of the pure nd ejecta consists of a broad structure from $0.5$ to $20\, {\rm \mu m}$ with two distinct peaks around $1$ and $10\, {\rm \mu m}$. | nebular emission from lanthanide-rich ejecta of neutron star merger |
isotope anomalies among planetary bodies provide key constraints on planetary genetics and the solar system's dynamical evolution. however, to unlock the full potential of these anomalies for constraining the processing, mixing, and transport of material in the disk it is essential to identify the main components responsible for producing planetary-scale isotope variations, and to investigate how they relate to the isotopic heterogeneity inherited from the solar system's parental molecular cloud. to address these issues we measured the ti and sr isotopic compositions of ca,al-rich inclusions (cais) from the allende cv3 chondrite, as well as acid leachates and an insoluble residue from the murchison cm2 chondrite, and combine these results with literature data for presolar grains, hibonites, chondrules, and bulk meteorites. our analysis reveals that the internal mineral-scale nebular isotopic heterogeneity as sampled by leachates and presolar grains is largely decoupled from the planetary-scale isotope anomalies as sampled by bulk meteorites. we show that variable admixing of cai-like refractory material to an average inner solar nebula component can explain the planetary-scale ti and sr isotope anomalies and the elemental and isotopic difference between non-carbonaceous (nc) and carbonaceous (cc) nebular reservoirs for these elements. combining isotope anomaly data for a large number of elements (ti, sr, ca, cr, ni, zr, mo, ru, ba, nd, sm, hf, w, and os) reveals that the offset of the cc from the nc reservoir towards the composition of cais is a general trend and not limited to refractory elements. this implies that the cc reservoir is the product of mixing between nc material and a reservoir (called ic for inclusion-like chondritic component) whose isotopic composition is similar to that of cais, but whose chemical composition is similar to bulk chondrites. in our preferred model, the distinct isotopic compositions of these two nebular reservoirs reflect an inherited heterogeneity of the solar system's parental molecular cloud core, which therefore has never been fully homogenized during collapse. planetary-scale isotopic anomalies are thus caused by variable mixing of isotopically distinct primordial disk reservoirs, the selective processing of these reservoirs in different nebular environments, and the heterogeneous distribution of the thereby forming nebular products. | elemental and isotopic variability in solar system materials by mixing and processing of primordial disk reservoirs |
we characterize magnetically driven accretion at radii between 1 and 100 au in protoplanetary discs, using a series of local non-ideal magnetohydrodynamic (mhd) simulations. the simulations assume a minimum mass solar nebula (mmsn) disc that is threaded by a net vertical magnetic field of specified strength. confirming previous results, we find that the hall effect has only a modest impact on accretion at 30 au, and essentially none at 100 au. at 1-10 au the hall effect introduces a pronounced bimodality in the accretion process, with vertical magnetic fields aligned to the disc rotation supporting a strong laminar maxwell stress that is absent if the field is anti-aligned. in the anti-aligned case, we instead find evidence for bursts of turbulent stress at 5-10 au, which we tentatively identify with the non-axisymmetric hall-shear instability. the presence or absence of these bursts depends upon the details of the adopted chemical model, which suggests that appreciable regions of actual protoplanetary discs might lie close to the borderline between laminar and turbulent behaviour. given the number of important control parameters that have already been identified in mhd models, quantitative predictions for disc structure in terms of only radius and accretion rate appear to be difficult. instead, we identify robust qualitative tests of magnetically driven accretion. these include the presence of turbulence in the outer disc, independent of the orientation of the vertical magnetic fields, and a hall-mediated bimodality in turbulent properties extending from the region of thermal ionization to 10 au. | magnetically driven accretion in protoplanetary discs |
the detection of ethanolamine (nh 2ch 2ch 2oh) in a molecular cloud in the interstellar medium confirms that a precursor of phospholipids is efficiently formed by interstellar chemistry. hence, ethanolamine could have been transferred from the proto-solar nebula to planetesimals and minor bodies of the solar system and thereafter to our planet. the prebiotic availability of ethanolamine on early earth could have triggered the formation of efficient and permeable amphiphilic molecules such as phospholipids, thus playing a relevant role in the evolution of the first cellular membranes needed for the emergence of life. | discovery in space of ethanolamine, the simplest phospholipid head group |
h ii regions are ionized nebulae surrounding massive stars. they exhibit a wealth of emission lines that form the basis for estimation of chemical composition. heavy elements regulate the cooling of interstellar gas, and are essential to the understanding of several phenomena such as nucleosynthesis, star formation and chemical evolution1,2. for over 80 years3, however, a discrepancy exists of a factor of around two between heavy-element abundances derived from collisionally excited lines and those from the weaker recombination lines, which has thrown our absolute abundance determinations into doubt4,5. here we report observational evidence that there are temperature inhomogeneities within the gas, quantified by t2 (ref. 6). these inhomogeneities affect only highly ionized gas and cause the abundance discrepancy problem. metallicity determinations based on collisionally excited lines must be revised because these may be severely underestimated, especially in regions of lower metallicity such as those recently observed with the james webb space telescope in high-z galaxies7-9. we present new empirical relations for estimation of temperature and metallicity, critical for a robust interpretation of the chemical composition of the universe over cosmic time. | temperature inhomogeneities cause the abundance discrepancy in h ii regions |
we propose an expression for a local planetesimal formation rate proportional to the instantaneous radial pebble flux. the result—a radial planetesimal distribution—can be used as an initial condition to study the formation of planetary embryos. we follow the idea that one needs particle traps to locally enhance the dust-to-gas ratios sufficiently, such that particle gas interactions can no longer prevent planetesimal formation on small scales. the locations of these traps can emerge everywhere in the disk. their occurrence and lifetime is subject to ongoing research; thus, here they are implemented via free parameters. this enables us to study the influence of the disk properties on the formation of planetesimals, predicting their time-dependent formation rates and the location of primary pebble accretion. we show that large α-values of 0.01 (strong turbulence) prevent the formation of planetesimals in the inner part of the disk, arguing for lower values of around 0.001 (moderate turbulence), at which planetesimals form quickly at all places where they are needed for proto-planets. planetesimals form as soon as dust has grown to pebbles (mm to dm) and the pebble flux reaches a critical value, which is after a few thousand years at 2-3 au and after a few hundred thousand years at 20-30 au. planetesimal formation lasts until the pebble supply has decreased below a critical value. the final spatial planetesimal distribution is steeper compared to the initial dust and gas distribution, which helps explain the discrepancy between the minimum mass solar nebula and viscous accretion disks. | planetesimal population synthesis: pebble flux-regulated planetesimal formation |
fast neutron-rich material ejected dynamically over ≲10 ms during the merger of a binary neutron star (bns) can give rise to distinctive electromagnetic counterparts to the system's gravitational-wave emission that serve as a "smoking gun" to distinguish between a bns and an ns-black hole merger. we present novel ab initio modeling of the kilonova precursor and kilonova afterglow based on 3d general-relativistic magnetohydrodynamic simulations of bns mergers with nuclear, tabulated, finite-temperature equations of state (eoss), weak interactions, and approximate neutrino transport. we analyze dynamical mass ejection from 1.35-1.35 m ⊙ binaries, consistent with properties of the first observed bns merger gw170817, using three nuclear eoss that span the range of allowed compactness of 1.35 m ⊙-neutron stars. nuclear reaction network calculations yield a robust second-to-third-peak r-process. we find few ×10-6 m ⊙ of fast (v > 0.6c) ejecta that give rise to broadband synchrotron emission on ~years timescales, consistent with tentative evidence for excess x-ray/radio emission following gw170817. we find ≈2 × 10-5 m ⊙ of free neutrons that power a kilonova precursor on ≲ hours timescale. a boost in early uv/optical brightness by a factor of a few due to previously neglected relativistic effects, with enhancements up to ≲10 hr post-merger, is promising for future detection with uv/optical telescopes like swift or ultrasat. we find that a recently predicted opacity boost due to highly ionized lanthanides at ≳70,000 k is unlikely to affect the early kilonova based on the obtained ejecta structures. azimuthal inhomogeneities in dynamical ejecta composition for soft eoss found here ("lanthanide/actinide pockets") may have observable consequences for both early kilonova and late-time nebular emission. | grmhd simulations of neutron-star mergers with weak interactions: r-process nucleosynthesis and electromagnetic signatures of dynamical ejecta |
we present jwst near-infrared (nir) and mid-infrared (mir) spectroscopic observations of the nearby normal type ia supernova (sn) sn 2021aefx in the nebular phase at +255 days past maximum light. our near infrared spectrograph (nirspec) and mid infrared instrument observations, combined with ground-based optical data from the south african large telescope, constitute the first complete optical+nir+mir nebular sn ia spectrum covering 0.3-14 μm. this spectrum unveils the previously unobserved 2.5-5 μm region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. the data show a significant improvement in sensitivity and resolution compared to previous spitzer mir data. we identify numerous nir and mir nebular emission lines from iron-group elements as well as lines from the intermediate-mass element argon. the argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation sn ia models. we present fits to simple geometric line profiles to features beyond 1.2 μm and find that most lines are consistent with gaussian or spherical emission distributions, while the [ar iii] 8.99 μm line has a distinctively flat-topped profile indicating a thick spherical shell of emission. using our line profile fits, we investigate the emissivity structure of sn 2021aefx and measure kinematic properties. continued observations of sn 2021aefx and other sne ia with jwst will be transformative to the study of sn ia composition, ionization structure, density, and temperature, and will provide important constraints on sn ia progenitor and explosion models. | a jwst near- and mid-infrared nebular spectrum of the type ia supernova 2021aefx |
we present a new method for inferring the metallicity (z) and ionization parameter (q) of h ii regions and star-forming galaxies using strong nebular emission lines (sels). we use bayesian inference to derive the joint and marginalized posterior probability density functions for z and q given a set of observed line fluxes and an input photoionization model. our approach allows the use of arbitrary sets of sels and the inclusion of flux upper limits. the method provides a self-consistent way of determining the physical conditions of ionized nebulae that is not tied to the arbitrary choice of a particular sel diagnostic and uses all the available information. unlike theoretically calibrated sel diagnostics, the method is flexible and not tied to a particular photoionization model. we describe our algorithm, validate it against other methods, and present a tool that implements it called izi. using a sample of nearby extragalactic h ii regions, we assess the performance of commonly used sel abundance diagnostics. we also use a sample of 22 local h ii regions having both direct and recombination line (rl) oxygen abundance measurements in the literature to study discrepancies in the abundance scale between different methods. we find that oxygen abundances derived through bayesian inference using currently available photoionization models in the literature can be in good (~30%) agreement with rl abundances, although some models perform significantly better than others. we also confirm that abundances measured using the direct method are typically ~0.2 dex lower than both rl and photoionization-model-based abundances. | izi: inferring the gas phase metallicity (z) and ionization parameter (q) of ionized nebulae using bayesian statistics |
young, rapidly spinning magnetars are invoked as central engines behind a diverse set of transient astrophysical phenomena, including gamma-ray bursts, superluminous supernovae (slsne), fast radio bursts (frbs), and binary neutron star (ns) mergers. however, a barrier to direct confirmation of the magnetar hypothesis is the challenge of directly observing non-thermal emission from the central engine at early times due to the dense surrounding ejecta. we present cloudy calculations of the temperature and ionization structure of expanding supernova or merger ejecta due to photoionization by a magnetar engine, studying the escape of x-rays and radio waves (absorbed by neutral/ionized gas, respectively), and the evolution of the local dispersion measure due to photoionization. we find that ionization break-out does not occur if the engine's ionizing luminosity decays rapidly, and that x-rays typically escape the oxygen-rich ejecta of slsne only after {∼ } 3-30 yr, consistent with current non-detections. we apply these results to constrain engine-driven models for the binary ns merger gw170817 and the luminous transient asassn-15lh. in terms of radio transparency and dispersion measure constraints, the repeating frb 121102 is consistent with originating from a young, {≳ } 30-100 yr, magnetar similar to those inferred to power slsne. we further show that its high rotation measure can be produced within the same nebula proposed to power the quiescent radio source observed co-located with frb 121102. our results strengthen previous work suggesting that at least some frbs may be produced by young magnetars, and motivate further study of engine-powered transients. | unveiling the engines of fast radio bursts, superluminous supernovae, and gamma-ray bursts |
we present a tutorial on the determination of the physical conditions and chemical abundances in gaseous nebulae. we also include a brief review of recent results on the study of gaseous nebulae, their relevance for the study of stellar evolution, galactic chemical evolution, and the evolution of the universe. one of the most important problems in abundance determinations is the existence of a discrepancy between the abundances determined with collisionally excited lines and those determined by recombination lines: this is called abundance discrepancy factor (adf) problem, and we review results related to it. finally, we discuss the possible reasons for the large t 2 values observed in gaseous nebulae. | nebular spectroscopy: a guide on hii regions and planetary nebulae |
young solar-type stars are known to be strong x-ray emitters and their x-ray spectra have been widely studied. x-rays from the central star may play a crucial role in the thermodynamics and chemistry of the circumstellar material as well as in the atmospheric evolution of young planets. in this paper, we present model spectra based on spectral parameters derived from the observations of young stars in the orion nebula cluster from the chandra orion ultradeep project (coup). the spectra are then used to calculate new photoevaporation prescriptions that can be used in disc and planet population synthesis models. our models clearly show that disc wind mass loss rates are controlled by the stellar luminosity in the soft ($100\, \mathrm{ev}$ to $1\, \mathrm{kev}$) x-ray band. new analytical relations are provided for the mass loss rates and profiles of photoevaporative winds as a function of the luminosity in the soft x-ray band. the agreement between observed and predicted transition disc statistics moderately improved using the new spectra, but the observed population of strongly accreting large cavity discs can still not be reproduced by these models. furthermore, our models predict a population of non-accreting transition discs that are not observed. this highlights the importance of considering the depletion of millimetre-sized dust grains from the outer disc, which is a likely reason why such discs have not been detected yet. | the dispersal of protoplanetary discs - ii: photoevaporation models with observationally derived irradiating spectra |
the orion bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. our relative closeness to the orion nebula (about 1,350 light years away from earth) means that we can study the effects of stellar feedback on the parental cloud in detail. visible-light observations of the orion bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the earth-sun distance). static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the orion bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. in contrast to stationary model predictions, there is no appreciable offset between the peak of the h2 vibrational emission (delineating the h/h2 transition) and the edge of the observed co and hco+ emission. this implies that the h/h2 and c+/c/co transition zones are very close. we find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. the results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution. | compression and ablation of the photo-irradiated molecular cloud the orion bar |
massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. these processes have profound effects on the evolution of interstellar matter in our galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. the dominant feedback processes can be probed by observations of the photo-dissociation regions (pdrs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. pdr emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. pdr emission dominates the infrared (ir) spectra of star-forming galaxies. most of the galactic and extragalactic observations obtained with the james webb space telescope (jwst) will therefore arise in pdr emission. in this paper we present an early release science program using the miri, nirspec, and nircam instruments dedicated to the observations of an emblematic and nearby pdr: the orion bar. these early jwst observations will provide template data sets designed to identify key pdr characteristics in jwst observations. these data will serve to benchmark pdr models and extend them into the jwst era. we also present the science-enabling products that we will provide to the community. these template data sets and science-enabling products will guide the preparation of future proposals on star-forming regions in our galaxy and beyond and will facilitate data analysis and interpretation of forthcoming jwst observations. | pdrs4all: a jwst early release science program on radiative feedback from massive stars |
we use a sample of 532 star-forming galaxies at redshifts z ≃ 1.4-2.6 with deep rest-frame optical spectra from the mosfire deep evolution field (mosdef) survey to place the first constraints on the nebular attenuation curve at high redshift. based on the first five low-order balmer emission lines detected in the composite spectra of these galaxies (hα through ${\rm{h}}\epsilon $ ), we derive a nebular attenuation curve that is similar in shape to that of the galactic extinction curve, suggesting that the dust covering fraction and absorption/scattering properties along the lines of sight to massive stars at high redshift are similar to those of the average milky way sight line. the curve derived here implies nebular reddening values that are, on average, systematically larger than those derived for the stellar continuum. in the context of stellar population synthesis models that include the effects of stellar multiplicity, the difference in reddening of the nebular lines and stellar continuum may imply molecular cloud crossing timescales that are a factor of $\gtrsim 3\times $ longer than those inferred for local molecular clouds, star formation rates that are constant or increasing with time such that newly formed and dustier ob associations always dominate the ionizing flux, and/or that the dust responsible for reddening the nebular emission may be associated with nonmolecular (i.e., ionized and neutral) phases of the interstellar medium. our analysis points to a variety of investigations of the nebular attenuation curve that will be enabled with the next generation of ground- and space-based facilities. * based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa and was made possible by the generous financial support of the w.m. keck foundation. | the mosdef survey: the first direct measurements of the nebular dust attenuation curve at high redshift |
we measured gas-phase metallicity, ionisation parameter, and dust extinction for a representative sample of 1795 local star-forming galaxies using integral field spectroscopy from the sdss-iv manga survey. we self-consistently derive these quantities by comparing observed line fluxes with photoionisation models using a bayesian framework. we also present the first comprehensive study of the [s iii]λλ9069,9532 nebular lines, which have long been predicted to be ideal tracers of the ionisation parameter. however, we find that current photoionisation model predictions substantially over-predict the intensity of the [s iii] lines, while broadly reproducing other observed optical line ratios. we discuss how to nonetheless make use of the information provided by the [s iii] lines by setting a prior on the ionisation parameter. following this approach, we derive spatially resolved maps and radial profiles of metallicity and ionisation parameter. the metallicity radial profiles derived are comparable with previous works, with metallicity declining toward the outer parts and showing a flattening in the central regions. this is in agreement with infall models of galaxy formation, which predict that spiral discs build up through accretion of material, leading to an inside-out growth. on the other hand, ionisation parameter radial profiles are flat for low-mass galaxies, while their slope becomes positive as galaxy mass increases. however, the ionisation parameter maps we obtain are clumpy, especially for low-mass galaxies. the ionisation parameter is tightly correlated with the equivalent width of hα [ew(hα)], following a nearly universal relation, which we attribute to the change of the spectral shape of ionising sources due to ageing of h ii regions. we derive a positive correlation between ionisation parameter and metallicity at fixed ew(hα), in disagreement with previous theoretical work that predict an anti-correlation. | sdss iv manga: metallicity and ionisation parameter in local star-forming galaxies from bayesian fitting to photoionisation models |
context. the spatial distribution of elemental abundances in the disc of our galaxy gives insights both on its assembly process and subsequent evolution, and on the stellar nucleogenesis of the different elements. gradients can be traced using several types of objects as, for instance, (young and old) stars, open clusters, hii regions, planetary nebulae.aims: we aim to trace the radial distributions of abundances of elements produced through different nucleosynthetic channels - the α-elements o, mg, si, ca and ti, and the iron-peak elements fe, cr, ni and sc - by use of the gaia-eso idr4 results for open clusters and young-field stars.methods: from the uves spectra of member stars, we have determined the average composition of clusters with ages > 0.1 gyr. we derived statistical ages and distances of field stars. we traced the abundance gradients using the cluster and field populations and compared them with a chemo-dynamical galactic evolutionary model.results: the adopted chemo-dynamical model, with the new generation of metallicity-dependent stellar yields for massive stars, is able to reproduce the observed spatial distributions of abundance ratios, in particular the abundance ratios of [o/fe] and [mg/fe] in the inner disc (5 kpc <rgc< 7 kpc), with their differences, that were usually poorly explained by chemical evolution models.conclusions: oxygen and magnesium are often considered to be equivalent in tracing α-element abundances and in deducing, for example, the formation timescales of different galactic stellar populations. in addition, often [α/fe] is computed combining several α-elements. our results indicate, as expected, a complex and diverse nucleosynthesis of the various α-elements, in particular in the high metallicity regimes, pointing towards a different origin of these elements and highlighting the risk of considering them as a single class with common features. tables a.1-a.4 are also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/603/a2 | the gaia-eso survey: radial distribution of abundances in the galactic disc from open clusters and young-field stars |
we report the serendipitous discovery of an [o iii] λ λ4959/5007 and hα line emitter in the epoch of reionization (eor) with the james webb space telescope (jwst) commissioning data taken in the nircam wide-field slitless spectroscopy (wfss) mode. located ~55″ away from the flux calibrator p330-e, this galaxy exhibits bright [o iii] λ λ4959/5007 and hα lines detected at 3.7σ, 9.9σ, and 5.7σ, respectively, with a spectroscopic redshift of z = 6.112 ± 0.001. the total hβ+[o iii] equivalent width is 664 ± 98 å (454 ± 78 å from the [o iii] λ5007 line). this provides direct spectroscopic evidence for the presence of strong rest-frame optical lines (hβ+[o iii] and hα) in eor galaxies as inferred previously from the analyses of the spitzer/irac spectral energy distributions (seds). two spatial and velocity components are identified in this source, possibly indicating that this system is undergoing a major merger, which might have triggered the ongoing starburst with strong nebular emission lines over a timescale of ~2 myr, as our sed modeling suggests. the tentative detection of he ii λ4686 line (1.9σ), if real, may indicate the existence of very young and metal-poor star-forming regions with a hard uv radiation field. finally, this discovery demonstrates the power and readiness of the jwst/nircam wfss mode, and marks the beginning of a new era for extragalactic astronomy, in which eor galaxies can be routinely discovered via blind slitless spectroscopy through the detection of rest-frame optical emission lines. | first peek with jwst/nircam wide-field slitless spectroscopy: serendipitous discovery of a strong [o iii]/hα emitter at z = 6.11 |
with its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the james webb space telescope (jwst) is poised to revolutionize our view of the distant, high-redshift (z > 5) universe. while webb's spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant objects and providing more comprehensive samples than accessible to spectroscopy alone. in addition to identifying objects, photometric observations can also be used to infer physical properties and thus be used to constrain galaxy formation models. however, inferred physical properties from broad-band photometric observations, particularly in the absence of spectroscopic redshifts, often have large uncertainties. with the development of new tools for forward modelling simulations, it is now routinely possible to predict observational quantities, enabling a direct comparison with observations. with this in mind, in this work, we make predictions for the colour evolution of galaxies at z = 5-15 using the first light and reionisation epoch simulations (flares) cosmological hydrodynamical simulation suite. we predict a complex evolution with time, driven predominantly by strong nebular line emission passing through individual bands. these predictions are in good agreement with existing constraints from hubble and spitzer as well as some of the first results from webb. we also contrast our predictions with other models in the literature: while the general trends are similar, we find key differences, particularly in the strength of features associated with strong nebular line emission. this suggests photometric observations alone should provide useful discriminating power between different models and physical states of galaxies. | first light and reionisation epoch simulations (flares) - vi. the colour evolution of galaxies z = 5-15 |
ultraviolet (uv) observations of local star-forming galaxies have begun to establish an empirical baseline for interpreting the rest-uv spectra of reionization-era galaxies. however, existing high-ionization emission line measurements at z > 6 (w_{c riptsciv,0}{} ≳ 20 å) are uniformly stronger than observed locally (w_{c riptsciv,0}{} ≲ 2 å), likely due to the relatively high metallicities (z/z\odot > 0.1) typically probed by uv surveys of nearby galaxies. we present new hst/cos spectra of six nearby (z < 0.01) extremely metal-poor galaxies (xmps, z/z\odot ≲ 0.1) targeted to address this limitation and provide constraints on the highly uncertain ionizing spectra powered by low-metallicity massive stars. our data reveal a range of spectral features, including one of the most prominent nebular c iv doublets yet observed in local star-forming systems and strong he ii emission. using all published uv observations of local xmps to date, we find that nebular c iv emission is ubiquitous in very high specific star formation rate systems at low metallicity, but still find equivalent widths smaller than those measured in individual lensed systems at z > 6. our moderate-resolution hst/cos data allow us to conduct an analysis of the stellar winds in a local nebular c iv emitter, which suggests that some of the tension with z > 6 data may be due to existing local samples not yet probing sufficiently high α/fe abundance ratios. our results indicate that c iv emission can play a crucial role in the jwst and elt era by acting as an accessible signpost of very low metallicity (z/z\odot < 0.1) massive stars in assembling reionization-era systems. | extremely metal-poor galaxies with hst/cos: laboratories for models of low-metallicity massive stars and high-redshift galaxies |
roche lobe overflow from a donor star onto a black hole or neutron star binary companion can evolve to a phase of unstable runaway mass transfer, lasting as short as hundreds of orbits (≲102 yr for a giant donor) and eventually culminating in a common-envelope event. the highly super-eddington accretion rates achieved during this brief phase ( $\dot{m}\gtrsim {10}^{5}{\dot{m}}_{\mathrm{edd}})$ are accompanied by intense mass loss in disk winds, analogous to but even more extreme than ultraluminous x-ray (ulx) sources in the nearby universe. also in analogy with the observed ulx, this expanding outflow will inflate an energetic "bubble" of plasma into the circumbinary medium. embedded within this bubble is a nebula of relativistic electrons heated at the termination shock of the faster v ≳ 0.1c wind/jet from the inner accretion flow. we present a time-dependent, one-zone model for the synchrotron radio emission and other observable properties of such ulx "hypernebulae." if ulx jets are sources of repeating fast radio bursts (frb), as recently proposed, such hypernebulae could generate persistent radio emission and contribute large and time-variable rotation measure to the bursts, consistent with those seen from frb 20121102 and frb 20190520b. ulx hypernebulae can be discovered independently of an frb association in radio surveys, such as vlass, as off-nuclear point sources whose fluxes can evolve significantly on timescales as short as years, possibly presaging energetic transients from common-envelope mergers. | radio nebulae from hyperaccreting x-ray binaries as common-envelope precursors and persistent counterparts of fast radio bursts |
in recent years, sea spray as well as the biological material it contains has received increased attention as a source of ice-nucleating particles (inps). such inps may play a role in remote marine regions, where other sources of inps are scarce or absent. in the arctic, these inps can influence water-ice partitioning in low-level clouds and thereby the cloud lifetime, with consequences for the surface energy budget, sea ice formation and melt, and climate. marine aerosol is of a diverse nature, so identifying sources of inps is challenging. one fraction of marine bioaerosol (phytoplankton and their exudates) has been a particular focus of marine inp research. in our study we attempt to address three main questions. firstly, we compare the ice-nucleating ability of two common phytoplankton species with arctic seawater microlayer samples using the same instrumentation to see if these phytoplankton species produce ice-nucleating material with sufficient activity to account for the ice nucleation observed in arctic microlayer samples. we present the first measurements of the ice-nucleating ability of two predominant phytoplankton species: melosira arctica, a common arctic diatom species, and skeletonema marinoi, a ubiquitous diatom species across oceans worldwide. to determine the potential effect of nutrient conditions and characteristics of the algal culture, such as the amount of organic carbon associated with algal cells, on the ice nucleation activity, skeletonema marinoi was grown under different nutrient regimes. from comparison of the ice nucleation data of the algal cultures to those obtained from a range of sea surface microlayer (sml) samples obtained during three different field expeditions to the arctic (accacia, netcare, and ascos), we found that they were not as ice active as the investigated microlayer samples, although these diatoms do produce ice-nucleating material. secondly, to improve our understanding of local arctic marine sources as atmospheric inps we applied two aerosolization techniques to analyse the ice-nucleating ability of aerosolized microlayer and algal samples. the aerosols were generated either by direct nebulization of the undiluted bulk solutions or by the addition of the samples to a sea spray simulation chamber filled with artificial seawater. the latter method generates aerosol particles using a plunging jet to mimic the process of oceanic wave breaking. we observed that the aerosols produced using this approach can be ice active, indicating that the ice-nucleating material in seawater can indeed transfer to the aerosol phase. thirdly, we attempted to measure ice nucleation activity across the entire temperature range relevant for mixed-phase clouds using a suite of ice nucleation measurement techniques - an expansion cloud chamber, a continuous-flow diffusion chamber, and a cold stage. in order to compare the measurements made using the different instruments, we have normalized the data in relation to the mass of salt present in the nascent sea spray aerosol. at temperatures above 248 k some of the sml samples were very effective at nucleating ice, but there was substantial variability between the different samples. in contrast, there was much less variability between samples below 248 k. we discuss our results in the context of aerosol-cloud interactions in the arctic with a focus on furthering our understanding of which inp types may be important in the arctic atmosphere. | the ice-nucleating activity of arctic sea surface microlayer samples and marine algal cultures |
this is the second paper in a series aimed at investigating the main sources of uncertainty in measuring the observable parameters in galaxies from their spectral energy distributions (seds). in the first paper we presented a detailed account of the photometric redshift measurements and an error analysis of this process. in this paper we perform a comprehensive study of the main sources of random and systematic error in stellar mass estimates for galaxies, and their relative contributions to the associated error budget. since there is no prior knowledge of the stellar mass of galaxies (unlike their photometric redshifts), we use mock galaxy catalogs with simulated multi-waveband photometry and known redshift, stellar mass, age and extinction for individual galaxies. the multi-waveband photometry for the simulated galaxies were generated in 13 filters spanning from u-band to mid-infrared wavelengths. given different parameters affecting stellar mass measurement (photometric signal-to-noise ratios (s/n), sed fitting errors and systematic effects), the inherent degeneracies and correlated errors, we formulated different simulated galaxy catalogs to quantify these effects individually. for comparison, we also generated catalogs based on observed photometric data of real galaxies in the great observatories origins deep survey-south field, spanning the same passbands. the simulated and observed catalogs were provided to a number of teams within the cosmic assembly near-infrared deep extragalactic legacy survey collaboration to estimate the stellar masses for individual galaxies. a total of 11 teams participated, with different combinations of stellar mass measurement codes/methods, population synthesis models, star formation histories, extinction and age. for each simulated galaxy, the differences between the input stellar masses, minput, and those estimated by each team, mest, is defined as {{δ }}{log}(m)\equiv {log}({m}{estimated})-{log}({m}{input}), and used to identify the most fundamental parameters affecting stellar mass estimate in galaxies, with the following results. (1) no significant bias in δ log(m) was found among different codes, with all having comparable scatter (σ ({{δ }}{log}(m))=0.136 dex). the estimated stellar mass values are seriously affected by low photometric s/n, with the rms scatter increasing for galaxies with {h}{ab}\gt 26 mag; (2) a source of error contributing to the scatter in δ log(m) is found to be due to photometric uncertainties (0.136 dex) and low resolution in age and extinction grids when generating the sed templates; (3) the median of stellar masses among different methods provides a stable measure of the mass associated with any given galaxy (σ ({{δ }}{log}(m))=0.142 dex); (4) the δ log(m) values are strongly correlated with deviations in age (defined as the difference between the estimated and expected values), with a weaker correlation with extinction; (5) the rms scatter in the estimated stellar masses due to free parameters (after fixing redshifts and initial mass function) are quantified and found to be σ ({{δ }}{log}(m))=0.110 dex; (6) using the observed data, we studied the sensitivity of stellar masses to both the population synthesis codes and inclusion of nebular emission lines and found them to affect the stellar mass by 0.2 and 0.3 dex respectively. | a critical assessment of stellar mass measurement methods |
we investigate line formation processes in type iib supernovae (sne) from 100 to 500 days post-explosion using spectral synthesis calculations. the modelling identifies the nuclear burning layers and physical mechanisms that produce the major emission lines, and the diagnostic potential of these. we compare the model calculations with data on the three best observed type iib sne to-date - sn 1993j, sn 2008ax, and sn 2011dh. oxygen nucleosynthesis depends sensitively on the main-sequence mass of the star and modelling of the [o i] λλ6300, 6364 lines constrains the progenitors of these three sne to the mzams = 12-16 m⊙ range (ejected oxygen masses 0.3-0.9 m⊙), with sn 2011dh towards the lower end and sn 1993j towards the upper end of the range. the high ejecta masses from mzams ≳ 17 m⊙ progenitors give rise to brighter nebular phase emission lines than observed. nucleosynthesis analysis thus supports a scenario of low-to-moderate mass progenitors for type iib sne, and by implication an origin in binary systems. we demonstrate how oxygen and magnesium recombination lines may be combined to diagnose the magnesium mass in the sn ejecta. for sn 2011dh, a magnesium mass of 0.02-0.14 m⊙ is derived, which gives a mg/o production ratio consistent with the solar value. nitrogen left in the he envelope from cno burning gives strong [n ii] λλ6548, 6583 emission lines that dominate over hα emission in our models. the hydrogen envelopes of type iib sne are too small and dilute to produce any noticeable hα emission or absorption after ~150 days, and nebular phase emission seen around 6550 å is in many cases likely caused by [n ii] λλ6548, 6583. finally, the influence of radiative transport on the emergent line profiles is investigated. significant line blocking in the metal core remains for several hundred days, which affects the emergent spectrum. these radiative transfer effects lead to early-time blueshifts of the emission line peaks, which gradually disappear as the optical depths decrease with time. the modelled evolution of this effect matches the observed evolution in sn 2011dh. appendices are available in electronic form at http://www.aanda.org | late-time spectral line formation in type iib supernovae, with application to sn 1993j, sn 2008ax, and sn 2011dh |
we use non-local thermal equilibrium radiative transport modeling to examine observational signatures of sub-chandrasekhar mass double detonation explosions in the nebular phase. results range from spectra that look like typical and subluminous type ia supernovae (sne) for higher mass progenitors to spectra that look like ca-rich transients for lower mass progenitors. this ignition mechanism produces an inherent relationship between emission features and the progenitor mass as the ratio of the nebular [ca ii]/[fe iii] emission lines increases with decreasing white dwarf mass. examining the [ca ii]/[fe iii] nebular line ratio in a sample of observed sne we find further evidence for the two distinct classes of sne ia identified in polin et al. by their relationship between si ii velocity and b-band magnitude, both at time of peak brightness. this suggests that sne ia arise from more than one progenitor channel, and provides an empirical method for classifying events based on their physical origin. furthermore, we provide insight to the mysterious origin of ca-rich transients. low-mass double detonation models with only a small mass fraction of ca (1%) produce nebular spectra that cool primarily through forbidden [ca ii] emission. | nebular models of sub-chandrasekhar mass type ia supernovae: clues to the origin of ca-rich transients |
the explosion of a supernova releases almost instantaneously about 10^{51} ergs of mechanic energy, changing irreversibly the physical and chemical properties of large regions in the galaxies. the stellar ejecta, the nebula resulting from the powerful shock waves, and sometimes a compact stellar remnant, constitute a supernova remnant (snr). they can radiate their energy across the whole electromagnetic spectrum, but the great majority are radio sources. almost 70 years after the first detection of radio emission coming from an snr, great progress has been achieved in the comprehension of their physical characteristics and evolution. we review the present knowledge of different aspects of radio remnants, focusing on sources of the milky way and the magellanic clouds, where the snrs can be spatially resolved. we present a brief overview of theoretical background, analyze morphology and polarization properties, and review and critically discuss different methods applied to determine the radio spectrum and distances. the consequences of the interaction between the snr shocks and the surrounding medium are examined, including the question of whether snrs can trigger the formation of new stars. cases of multispectral comparison are presented. a section is devoted to reviewing recent results of radio snrs in the magellanic clouds, with particular emphasis on the radio properties of sn 1987a, an ideal laboratory to investigate dynamical evolution of an snr in near real time. the review concludes with a summary of issues on radio snrs that deserve further study, and analysis of the prospects for future research with the latest-generation radio telescopes. | radio emission from supernova remnants |
we use deep spectroscopy from the hubble space telescope wide-field-camera 3 ir grisms combined with broadband photometry to study the stellar populations, gas ionization and chemical abundances in star-forming galaxies at z ~ 1.1-2.3. the data stem from the candels lyα emission at reionization (clear) survey. at these redshifts, the grism spectroscopy measure the [o ii] λ λ3727, 3729, [o iii]λ λ4959, 5008, and hβ strong emission features, which constrain the ionization parameter and oxygen abundance of the nebular gas. we compare the line-flux measurements to predictions from updated photoionization models (mappings v; kewley et al.), which include an updated treatment of nebular gas pressure, $\mathrm{log}p/k={n}_{e}{t}_{e}$ . compared to low-redshift samples (z ~ 0.2) at fixed stellar mass, $\mathrm{log}{m}_{* }/{m}_{\odot }\,=$ 9.4-9.8, the clear galaxies at z = 1.35 (1.90) have lower gas-phase metallicity, ${\rm{\delta }}(\mathrm{log}z)$ = 0.25 (0.35) dex, and higher ionization parameters, ${\rm{\delta }}(\mathrm{log}q)$ = 0.25 (0.35) dex, where u ≡ q/c. we provide updated analytic calibrations between the [o iii], [o ii], and hβ emission-line ratios, metallicity, and ionization parameter. the clear galaxies show that at fixed stellar mass, the gas ionization parameter is correlated with the galaxy specific star formation rates, where ${\rm{\delta }}\mathrm{log}q\simeq 0.4\times {\rm{\delta }}(\mathrm{log}\,\mathrm{ssfr})$ , derived from changes in the strength of galaxy hβ equivalent width. we interpret this as a consequence of higher gas densities, lower gas covering fractions, combined with a higher escape fraction of h-ionizing photons. we discuss both tests to confirm these assertions and implications this has for future observations of galaxies at higher redshifts. | clear: the ionization and chemical-enrichment properties of galaxies at 1.1 < z < 2.3 |
we report new polarimetric and photometric maps of the massive star-forming region omc-1 using the hawc+ instrument on the stratospheric observatory for infrared astronomy. we present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 μm at angular resolutions of 5″, 8″, 14″, and 19″ for the four bands, respectively. the photometric maps enable the computation of improved spectral energy distributions for the region. we find that at the longer wavelengths, the inferred magnetic field configuration matches the “hourglass” configuration seen in previous studies, indicating magnetically regulated star formation. the field morphology differs at the shorter wavelengths. the magnetic field inferred at these wavelengths traces the bipolar structure of the explosive becklin-neugebauer/kleinman-low outflow emerging from omc-1 behind the orion nebula. using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. the correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions. | hawc+/sofia multiwavelength polarimetric observations of omc-1 |
measurement of the mass of particles in the mega- to gigadalton range is challenging with conventional mass spectrometry. although this mass range appears optimal for nanomechanical resonators, nanomechanical mass spectrometers often suffer from prohibitive sample loss, extended analysis time, or inadequate resolution. we report on a system architecture combining nebulization of the analytes from solution, their efficient transfer and focusing without relying on electromagnetic fields, and the mass measurements of individual particles using nanomechanical resonator arrays. this system determined the mass distribution of ~30-megadalton polystyrene nanoparticles with high detection efficiency and effectively performed molecular mass measurements of empty or dna-filled bacteriophage t5 capsids with masses up to 105 megadaltons using less than 1 picomole of sample and with an instrument resolution above 100. | neutral mass spectrometry of virus capsids above 100 megadaltons with nanomechanical resonators |
recent observations have revealed that the remnants of stellar-coalescence transients are bipolar. this raises the questions of how these bipolar morphologies arise and what they teach us about the mechanisms of mass ejection during stellar mergers and common-envelope phases. in this paper, we analyze hydrodynamic simulations of the lead-in to binary coalescence, a phase of unstable roche lobe overflow that takes the binary from the roche limit separation to the engulfment of the more compact accretor within the envelope of the extended donor. as mass transfer runs away at increasing rates, gas trails away from the binary. contrary to previous expectations, early mass loss from the system remains bound to the binary and forms a circumbinary torus. later ejecta, generated as the accretor grazes the surface of the donor, have very different morphologies and are unbound. these two components of mass loss from the binary interact as later, higher-velocity ejecta collide with the circumbinary torus formed by earlier mass loss. unbound ejecta are redirected toward the poles, and escaping material creates a bipolar outflow. our findings show that the transition from bound to unbound ejecta from coalescing binaries can explain the bipolar nature of their remnants, with implications for our understanding of the origin of bipolar remnants of stellar-coalescence transients and, perhaps, some preplanetary nebulae. | bound outflows, unbound ejecta, and the shaping of bipolar remnants during stellar coalescence |
we present a search for helium in the upper atmospheres of three sub-neptune-sized planets to investigate the origins of these ubiquitous objects. the detection of helium for a low-density planet would be strong evidence for the presence of a primary atmosphere accreted from the protoplanetary nebula because large amounts of helium are not expected in the secondary atmospheres of rocky planets. we used keck+nirspec to obtain high-resolution transit spectroscopy of the planets gj 1214b, gj 9827d, and hd 97658b around the 10833 å he triplet feature. we did not detect helium absorption for any of the planets despite achieving a high level of sensitivity. we used the nondetections to set limits on the planets' thermosphere temperatures and atmospheric loss rates by comparing grids of 1d models to the data. we also performed coupled interior structure and atmospheric loss calculations, which suggest that the bulk atmospheres (winds) of the planets would be at most modestly enhanced (depleted) in helium relative to their primordial composition. our lack of detections of the helium triplet for gj 1214b and gj 9827d is highly inconsistent with the predictions of models for the present-day mass loss on these planets. higher signal-to-noise data would be needed to detect the helium feature predicted for hd 97658b. we identify uncertainties in the extreme-ultraviolet fluxes of the host stars and the lack of detailed mass-loss models specifically for cool and metal-enhanced atmospheres as the main limitations to the interpretation of our results. ultimately, our results suggest that the upper atmospheres of sub-neptune planets are fundamentally different from those of gas giant planets. | nondetection of helium in the upper atmospheres of three sub-neptune exoplanets |
we present results on the star formation rate (sfr) versus stellar mass (m*) relation (i.e., the “main sequence”) among star-forming galaxies at 1.37 ≤ z ≤ 2.61 using the mosfire deep evolution field (mosdef) survey. based on a sample of 261 galaxies with hα and hβ spectroscopy, we have estimated robust dust-corrected instantaneous sfrs over a large range in m* (∼109.5-1011.5 m⊙). we find a correlation between log(sfr(hα)) and log(m*) with a slope of 0.65 ± 0.08 (0.58 ± 0.10) at 1.4 < z < 2.6 (2.1 < z < 2.6). we find that different assumptions for the dust correction, such as using the color excess of the stellar continuum to correct the nebular lines, sample selection biases against red star-forming galaxies, and not accounting for balmer absorption, can yield steeper slopes of the log(sfr)-log(m*) relation. our sample is immune from these biases as it is rest-frame optically selected, hα and hβ are corrected for balmer absorption, and the hα luminosity is dust corrected using the nebular color excess computed from the balmer decrement. the scatter of the log(sfr(hα))-log(m*) relation, after accounting for the measurement uncertainties, is 0.31 dex at 2.1 < z < 2.6, which is 0.05 dex larger than the scatter in log(sfr(uv))-log(m*). based on comparisons to a simulated sfr-m* relation with some intrinsic scatter, we argue that in the absence of direct measurements of galaxy-to-galaxy variations in the attenuation/extinction curves and the initial mass function, one cannot use the difference in the scatter of the sfr(hα)- and sfr(uv)-m* relations to constrain the stochasticity of star formation in high-redshift galaxies. | the mosdef survey: dissecting the star formation rate versus stellar mass relation using hα and hβ emission lines at z ∼ 2 |
the progenitor systems and explosion mechanism of type ia supernovae are still unknown. currently favoured progenitors include double-degenerate systems consisting of two carbon-oxygen white dwarfs with thin helium shells. in the double-detonation scenario, violent accretion leads to a helium detonation on the more massive primary white dwarf that turns into a carbon detonation in its core and explodes it. we investigate the fate of the secondary white dwarf, focusing on changes of the ejecta and observables of the explosion if the secondary explodes as well rather than survives. we simulate a binary system of a $1.05\, \mathrm{m_\odot }$ and a $0.7\, \mathrm{m_\odot }$ carbon-oxygen white dwarf with $0.03\, \mathrm{m_\odot }$ helium shells each. we follow the system self-consistently from inspiral to ignition, through the explosion, to synthetic observables. we confirm that the primary white dwarf explodes self-consistently. the helium detonation around the secondary white dwarf, however, fails to ignite a carbon detonation. we restart the simulation igniting the carbon detonation in the secondary white dwarf by hand and compare the ejecta and observables of both explosions. we find that the outer ejecta at $v~\gt ~15\, 000$ km s-1 are indistinguishable. light curves and spectra are very similar until $\sim ~40 \ \mathrm{d}$ after explosion and the ejecta are much more spherical than violent merger models. the inner ejecta differ significantly slowing down the decline rate of the bolometric light curve after maximum of the model with a secondary explosion by ~20 per cent. we expect future synthetic 3d nebular spectra to confirm or rule out either model. | on the fate of the secondary white dwarf in double-degenerate double-detonation type ia supernovae |
accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. in particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. this includes x-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole v404 cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. here we report observations of a sustained outer accretion disk wind in v404 cyg, which is unlike any seen hitherto. we find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. the large expelled mass (>10-8 solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. the luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes. | regulation of black-hole accretion by a disk wind during a violent outburst of v404 cygni |
constraints on the composition of mars principally derive from chemical analyses of a set of martian meteorites that rely either on determinations of their refractory element abundances or isotopic compositions. both approaches, however, lead to models of mars that are unable to self-consistently explain major element chemistry and match its observed geophysical properties, unless ad hoc adjustments to key parameters, namely, bulk fe/si ratio, core composition, and/or core size are made. here, we combine geophysical observations, including high-quality seismic data acquired with the insight mission, with a cosmochemical model to constrain the composition of mars. we find that the feo content of mars' mantle is 13.7±0.4 wt%, corresponding to a mg# of 0.81±0.01. because of the lower feo content of the mantle, compared with previous estimates, we obtain a higher mean core density of 6150±46 kg/m3 than predicted by recent seismic observations, yet our estimate for the core radius remains consistent around 1840±10 km, corresponding to a core mass fraction of 0.250±0.005. relying on cosmochemical constraints, volatile element behaviour, and planetary building blocks that match geophysical and isotopic signatures of martian meteorites, we find that the liquid core is made up of 88.4±3.9 wt% fe-ni-co with light elements making up the rest. to match the mean core density constraint, we predict, based on experimentally-determined thermodynamic solution models, a light element abundance in the range of ≈9 wt% s, ⩾3 wt% c, ⩽2.5 wt% o, and ⩽0.5 wt% h, supporting the notion of a volatile-rich mars. to accumulate sufficient amounts of these volatile elements, mars must have formed before the nebular gas dispersed and/or, relative to earth, accreted a higher proportion of planetesimals from the outer protoplanetary disk where volatiles condensed more readily. | geophysical and cosmochemical evidence for a volatile-rich mars |
asymmetric shapes and evidence for binary central stars suggest a common-envelope origin for many bipolar planetary nebulae. the bipolar components of the nebulae are observed to expand faster than the rest, and the more slowly expanding material has been associated with the bulk of the envelope ejected during the common-envelope phase of a stellar binary system. common-envelope evolution in general remains one of the biggest uncertainties in binary star evolution, and the origin of the fast outflow has not been explained satisfactorily. we perform three-dimensional magnetohydrodynamic simulations of common-envelope interaction with the moving-mesh code arepo. starting from the plunge-in of the companion into the envelope of an asymptotic-giant-branch star and covering hundreds of orbits of the binary star system, we are able to follow the evolution to complete envelope ejection. we find that magnetic fields are strongly amplified in two consecutive episodes: first, when the companion spirals in the envelope and, second, when it forms a contact binary with the core of the former giant star. in the second episode, a magnetically driven, high-velocity outflow of gas is launched self-consistently in our simulations. the outflow is bipolar, and the gas is additionally collimated by the ejected common envelope. the resulting structure reproduces typical morphologies and velocities observed in young planetary nebulae. we propose that the magnetic driving mechanism is a universal consequence of common-envelope interaction that is responsible for a substantial fraction of observed planetary nebulae. such a mechanism likely also exists in the common-envelope phase of other binary stars that lead to the formation of type ia supernovae, x-ray binaries, and gravitational-wave merger events. movies associated with figs. a.1-a.3 are available at https://www.aanda.org | bipolar planetary nebulae from common-envelope evolution of binary stars |
the abundance of refractory elements in giant planets can provide key insights into their formation histories1. owing to the low temperatures of the solar system giants, refractory elements condense below the cloud deck, limiting sensing capabilities to only highly volatile elements2. recently, ultra-hot giant exoplanets have allowed for some refractory elements to be measured, showing abundances broadly consistent with the solar nebula with titanium probably condensed out of the photosphere3,4. here we report precise abundance constraints of 14 major refractory elements on the ultra-hot giant planet wasp-76b that show distinct deviations from proto-solar and a sharp onset in condensation temperature. in particular, we find nickel to be enriched, a possible sign of the accretion of the core of a differentiated object during the evolution of the planet. elements with condensation temperatures below 1,550 k otherwise closely match those of the sun5 before sharply transitioning to being strongly depleted above 1,550 k, which is well explained by nightside cold-trapping. we further unambiguously detect vanadium oxide on wasp-76b, a molecule long suggested to drive atmospheric thermal inversions6, and also observe a global east-west asymmetry7 in its absorption signals. overall, our findings indicate that giant planets have a mostly stellar-like refractory elemental content and suggest that temperature sequences of hot jupiter spectra can show abrupt transitions wherein a mineral species is either present or completely absent if a cold trap exists below its condensation temperature8. | vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet |
using a large sample of spectroscopically confirmed z∼ 3 galaxies, we establish an empirical relationship between reddening (e(b-v)), neutral gas covering fraction ({f}{{cov}}({{h}} {{i}})), and the escape of ionizing (lyman continuum, lyc) photons. our sample includes 933 galaxies at z∼ 3,121 of which have deep spectroscopic observations (≳ 7 hr) at 850≲ {λ }{{rest}}≲ 1300 å with the low resolution imaging spectrograph on keck. the high covering fraction of outflowing optically thick {{h}} {{i}} indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of lyc photons. by modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by {{h}} {{i}} and reddened by a line-of-sight extinction, we derive an empirical relationship between e(b-v) and {f}{{cov}}({{h}} {{i}}). galaxies with redder uv continua have larger covering fractions of {{h}} {{i}} characterized by higher line-of-sight extinctions. we develop a model which connects the ionizing escape fraction with e(b-v), and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic lyc-to-uv flux density ratio to be < s(900 \mathring{{a}} )/s(1500 \mathring{{a}} ){> }{{int}}≳ 0.20, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from high-redshift galaxies. based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w.m. keck foundation. | the connection between reddening, gas covering fraction, and the escape of ionizing radiation at high redshift |
we present powderday (available at https://github.com/dnarayanan/powderday), a flexible, fast, open-source dust radiative transfer package designed to interface with both idealized and cosmological galaxy formation simulations. powderday builds on fsps stellar population synthesis models, and hyperion dust radiative transfer, and employs yt to interface between different software packages. we include our stellar population synthesis modeling on the fly, allowing significant flexibility in the assumed stellar physics and nebular line emission. the dust content follows either simple observationally motivated prescriptions (i.e., constant dust-to-metals ratios, or dust-to-gas ratios that vary with metallicity), direct modeling from galaxy formation simulations that include dust physics, as well as a novel approach that includes the dust content via learning-based algorithms from the simba cosmological galaxy formation simulation. active galactic nuclei (agns) can additionally be included via a range of prescriptions. the output of these models are broadband (912 å-1 mm) spectral energy distributions (seds), as well as filter-convolved monochromatic images. powderday is designed to eliminate last-mile efforts by researchers that employ different hydrodynamic galaxy formation models and seamlessly interfaces with gizmo, arepo, gasoline, changa, and enzo. we demonstrate the capabilities of the code via three applications: a model for the star formation rate-infrared luminosity relation in galaxies (including the impact of agns), the impact of circumstellar dust around agb stars on the mid-infrared emission from galaxy seds, and the impact of galaxy inclination angle on dust attenuation laws. | powderday: dust radiative transfer for galaxy simulations |
eruptive mass loss of massive stars prior to supernova (sn) explosion is key to understanding their evolution and end fate. an observational signature of pre-sn mass loss is the detection of an early, short-lived peak prior to the radioactive-powered peak in the lightcurve of the sn. this is usually attributed to the sn shock passing through an extended envelope or circumstellar medium (csm). such an early peak is common for double-peaked type iib sne with an extended hydrogen envelope but is uncommon for normal type ibc sne with very compact progenitors. in this paper, we systematically study a sample of 14 double-peaked type ibc sne out of 475 type ibc sne detected by the zwicky transient facility. the rate of these events is ~ 3-9 % of type ibc sne. a strong correlation is seen between the peak brightness of the first and the second peak. we perform a holistic analysis of this sample's photometric and spectroscopic properties. we find that six sne have ejecta mass less than 1.5 msun. based on the nebular spectra and lightcurve properties, we estimate that the progenitor masses for these are less than ~ 12 msun. the rest have an ejecta mass > 2.4 msun and a higher progenitor mass. this sample suggests that the sne with low progenitor masses undergo late-time binary mass transfer. meanwhile, the sne with higher progenitor masses are consistent with wave-driven mass loss or pulsation-pair instability-driven mass loss simulations. | probing pre-supernova mass loss in double-peaked type ibc supernovae from the zwicky transient facility |
current trends to pre-train capable large language models (llms) mostly focus on scaling of model and dataset size. however, the quality of pre-training data is an important factor for training powerful llms, yet it is a nebulous concept that has not been fully characterized. therefore, we use the recently proposed task2vec diversity coefficient to ground and understand formal aspects of data quality, to go beyond scale alone. specifically, we measure the diversity coefficient of publicly available pre-training datasets to demonstrate that their formal diversity is high when compared to theoretical lower and upper bounds. in addition, to build confidence in the diversity coefficient, we conduct interpretability experiments and find that the coefficient aligns with intuitive properties of diversity, e.g., it increases as the number of latent concepts increases. we conclude the diversity coefficient is reliable, show it's high for publicly available llm datasets, and conjecture it can be used to build useful diverse datasets for llms. | beyond scale: the diversity coefficient as a data quality metric demonstrates llms are pre-trained on formally diverse data |
the chemical enrichment of the universe; the mass spectrum of planetary nebulae, white dwarfs and gravitational wave progenitors; the frequency distribution of type i and ii supernovae; the fate of exoplanets ... a multitude of phenomena which is highly regulated by the amounts of mass that stars expel through a powerful wind. for more than half a century, these winds of cool ageing stars have been interpreted within the common interpretive framework of 1-dimensional (1d) models. i here discuss how that framework now appears to be highly problematic. * current 1d mass-loss rate formulae differ by orders of magnitude, rendering contemporary stellar evolution predictions highly uncertain. these stellar winds harbour 3d complexities which bridge 23 orders of magnitude in scale, ranging from the nanometer up to thousands of astronomical units. we need to embrace and understand these 3d spatial realities if we aim to quantify mass loss and assess its effect on stellar evolution. we therefore need to gauge * the 3d life of molecules and solid-state aggregates: the gas-phase clusters that form the first dust seeds are not yet identified. this limits our ability to predict mass-loss rates using a self-consistent approach. * the emergence of 3d clumps: they contribute in a non-negligible way to the mass loss, although they seem of limited importance for the wind-driving mechanism. * the 3d lasting impact of a (hidden) companion: unrecognised binary interaction has biased previous mass-loss rate estimates towards values that are too large. only then will it be possible to drastically improve our predictive power of the evolutionary path in 4d (classical) spacetime of any star. | evolution and mass loss of cool ageing stars: a daedalean story |
the aggregation of inorganic particles with high mass ratio will form a heterogeneous electric field in the solid polymer electrolytes (spes), which is difficult to be compatible with lithium anode, leading to inadequate ionic conductivity. herein, a facile spray drying method is adopted to increase the mass ratio of inorganic particles and solve the aggregation problems of fillers simultaneously. the polyvinylidene fluoride (pvdf) with lithium bis(trifluoromethanesulfonyl)imide (litfsi) covers the surface of each li6.4la3zr1.4ta0.6o12 (llzto) granules during the nebulization process, then forming flat solid electrolytes via layer-by-layer deposition. characterized by the atomic force microscope, the obtained solid electrolytes achieve a homogenous dispersion of young's modulus and surface electric field. as a result, the as-prepared spes present high tensile strength of 7.1 mpa, high ionic conductivity of 1.86 × 10−4 s.cm−1 at room temperature, and wide electrochemical window up to 5.0 v, demonstrating increased mechanical strength and uniform lithium-ion migration channels for spes. thanks to the as-prepared spes, the lithium-symmetrical cells show a highly stable li plating/stripping cycling for over 1,000 h at 0.1 ma.cm−2. the corresponding li/lcoo2 batteries also present good rate capability and excellent cyclic performance with capacity retention of 80% after 100 cycles at room temperature. | a homogenous solid polymer electrolyte prepared by facile spray drying method is used for room-temperature solid lithium metal batteries |
the fornax cluster provides a uniquely compact laboratory in which to study the detailed history of early-type galaxies and the role played by the environment in driving their evolution and their transformation from late-type galaxies. using the superb capabilities of the multi unit spectroscopic explorer on the very large telescope, high-quality integral-field spectroscopic data were obtained for the inner regions of all the bright (mb ≤ 15) galaxies within the virial radius of fornax. the stellar haloes of early-type galaxies are also covered out to about four effective radii. state-of-the-art stellar dynamical and population modelling allows characterising the disc components of fast-rotating early-type galaxies, constraining radial variations in the stellar initial-mass functions and measuring the stellar age, metallicity, and α-element abundance of stellar haloes in cluster galaxies. this paper describes the sample selection, observations, and overall goals of the survey, and provides initial results based on the spectroscopic data, including the detailed characterisation of stellar kinematics and populations to large radii; decomposition of galaxy components directly via their orbital structure; the ability to identify globular clusters and planetary nebulae, and derivation of high-quality emission-line diagnostics in the presence of complex ionised gas. | fornax3d project: overall goals, galaxy sample, muse data analysis, and initial results |
we present keck/mosfire spectra of the diagnostic nebular emission lines [o iii]λ λ 5007,4959, [o ii]λ 3727, and hβ for a sample of 15 redshift z≃ 3.1{--}3.7 lyα emitters (laes) and lyman break galaxies (lbgs). in conjunction with spectra from other surveys, we confirm earlier indications that laes have a much higher [o iii]/[o ii] line ratio than is seen in similar redshift lbgs. by comparing their distributions on a [o iii]/[o ii] versus r23 diagram, we demonstrate that this difference cannot arise solely because of their lower metallicities but most likely is due to a harder ionizing spectrum. using measures of hβ and recombination theory, we demonstrate, for a subset of our laes, that {ξ }{ion}—the number of lyman continuum photons per uv luminosity—is indeed 0.2-0.5 dex larger than for typical lbgs at similar redshifts. using photoionization models, we estimate the effect this would have on both [o iii]/[o ii] and r23 and conclude such a hard spectrum can only partially explain such intense line emission. the additional possibility is that such a large [o iii]/[o ii] ratio is in part due to density rather than ionization bound nebular regions, which would imply a high escape fraction of ionizing photons. we discuss how further observations could confirm this possibility. clearly laes with intense [o iii] emission represent a promising analog of those z\gt 7 sources with similarly strong lines that are thought to be an important contributor to cosmic reionization. | a hard ionizing spectrum in z = 3-4 lyα emitters with intense [o iii] emission: analogs of galaxies in the reionization era? |
using high-resolution data from the galactic arecibo l-band feed array hi (galfa-hi) survey, we show that linear structure in galactic neutral hydrogen (hi) correlates with the magnetic field orientation implied by planck 353 ghz polarized dust emission. the structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. at high galactic latitudes, where the planck data are noise dominated, the hi data provide an independent constraint on the galactic magnetic field orientation, and hence the local dust polarization angle. we detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either hi-derived angles, starlight polarization angles, or planck 353 ghz angles. the hi data thus provide a new tool in the search for inflationary gravitational wave b -mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination. | neutral hydrogen structures trace dust polarization angle: implications for cosmic microwave background foregrounds |
we present high-cadence optical and ultraviolet light curves of the normal type ia supernova (sn) 2021aefx, which shows an early bump during the first two days of observation. this bump may be a signature of interaction between the exploding white dwarf and a nondegenerate binary companion, or it may be intrinsic to the white dwarf explosion mechanism. in the case of the former, the short duration of the bump implies a relatively compact main-sequence companion star, although this conclusion is viewing-angle dependent. our best-fit companion-shocking and double-detonation models both overpredict the uv luminosity during the bump, and existing nickel-shell models do not match the strength and timescale of the bump. we also present nebular spectra of sn 2021aefx, which do not show the hydrogen or helium emission expected from a nondegenerate companion, as well as a radio nondetection that rules out all symbiotic progenitor systems and most accretion disk winds. our analysis places strong but conflicting constraints on the progenitor of sn 2021aefx; no current model can explain all of our observations. | constraining the progenitor system of the type ia supernova 2021aefx |
in many applications where small, similar-sized droplets are needed, ultrasonic nebulizers are employed. little is known about the mechanism of nebulization, for example about what determines the median droplet size. even less understood, is the droplet size distribution, which is often simply fitted with a log-normal distribution or assumed to be very narrow. we perform the first systematic study of droplet size distributions for different nebulizer technologies, showing that these distributions can be very well fitted with distributions found for sprays, where the size distribution is completely determined by the corrugation of ligaments and the distribution of ligament sizes. in our case, breakup is believed to be due to pinch-off of faraday instabilities. the droplet size distribution is then set by the distribution of wavelengths of the standing capillary waves and the roughness of the pinch-off ligaments. we show that different nebulizer technologies produce different size distributions, which we relate to (variation in) wavelengths of the waves that contribute to the droplet formation. we further show that the median droplet size scales with the capillary wavelength, with a proportionality constant that depends only slightly on the type of nebulizer, despite order-of-magnitude differences in other parameters. | size distributions of droplets produced by ultrasonic nebulizers |
recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of a large-scale meridional flow of gas inside the planetary hill sphere. this circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. here, we investigate the formation of natural satellites of jupiter and saturn within the framework of this newly outlined picture. we begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where s• ∼ 0.1-10 mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. this process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid subdisk into ${ \mathcal r }\sim 100$ km satellitesimals. subsequently, satellite conglomeration ensues via pair-wise collisions but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. the resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photoevaporation of the parent nebula. numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the jovian and saturnian moons. | formation of giant planet satellites |
chondrules are the millimetre-scale, previously molten, spherules found in most meteorites. before chondrules formed, large differentiating planetesimals had already accreted. volatile-rich olivine reveals that chondrules formed in extremely solid-rich environments, more like impact plumes than the solar nebula. the unique chondrules in cb chondrites probably formed in a vapour-melt plume produced by a hypervelocity impact with an impact velocity greater than 10 kilometres per second. an acceptable formation model for the overwhelming majority of chondrules, however, has not been established. here we report that impacts can produce enough chondrules during the first five million years of planetary accretion to explain their observed abundance. building on a previous study of impact jetting, we simulate protoplanetary impacts, finding that material is melted and ejected at high speed when the impact velocity exceeds 2.5 kilometres per second. using a monte carlo accretion code, we estimate the location, timing, sizes, and velocities of chondrule-forming impacts. ejecta size estimates indicate that jetted melt will form millimetre-scale droplets. our radiative transfer models show that these droplets experience the expected cooling rates of ten to a thousand kelvin per hour,. an impact origin for chondrules implies that meteorites are a byproduct of planet formation rather than leftover building material. | impact jetting as the origin of chondrules |
a noise-based non-parametric technique for detecting nebulous objects, for example, irregular or clumpy galaxies, and their structure in noise is introduced. “noise-based” and “non-parametric” imply that this technique imposes negligible constraints on the properties of the targets and that it employs no regression analysis or fittings. the sub-sky detection threshold is defined and initial detections are found independently of the sky value. false detections are then estimated and removed using the ambient noise as a reference. this results in a purity level of 0.88 for the final detections as compared to 0.29 for sextractor when a completeness of 1 is desired for a sample of extremely faint and diffuse mock galaxy profiles. the difference in the mean of the undetected pixels with the known background of mock images is decreased by 4.6 times depending on the diffuseness of the test profiles, quantifying the success in their detection. a non-parametric approach to defining substructure over a detected region is also introduced. noisechisel is our software implementation of this new technique. contrary to the existing signal-based approach to detection, in its various implementations, signal-related parameters such as the image point-spread function or known object shapes and models are irrelevant here. such features make this technique very useful in astrophysical applications such as detection, photometry, or morphological analysis of nebulous objects buried in noise, for example, galaxies that do not generically have a known shape when imaged. | noise-based detection and segmentation of nebulous objects |
deep observations are revealing a growing number of young galaxies in the first billion years of cosmic time1. compared to typical galaxies at later times, they show more extreme emission-line properties2, higher star formation rates3, lower masses4, and smaller sizes5. however, their faintness precludes studies of their chemical abundances and ionization conditions, strongly limiting our understanding of the physics driving early galaxy build-up and metal enrichment. here we study a rare population of ultraviolet-selected, low-luminosity galaxies at redshift 2.4 < z < 3.5 that exhibit all the rest-frame properties expected from primeval galaxies. these low-mass, highly compact systems are rapidly forming galaxies able to double their stellar mass in only a few tens of millions of years. they are characterized by very blue ultraviolet spectra with weak absorption features and bright nebular emission lines, which imply hard radiation fields from young hot massive stars6,7. their highly ionized gas phase has strongly sub-solar carbon and oxygen abundances, with metallicities more than a factor of two lower than that found in typical galaxies of similar mass and star formation rate at z≤2.58. these young galaxies reveal an early and short stage in the assembly of their galactic structures and their chemical evolution, a vigorous phase that is likely to be dominated by the effects of gas-rich mergers, accretion of metal-poor gas and strong outflows. | analogues of primeval galaxies two billion years after the big bang |
we present alma observations of co isotopes and 1.3 mm continuum emission toward the n159e-papillon nebula in the large magellanic cloud (lmc). the spatial resolution is 0.″25-0.″28 (0.06-0.07 pc), which is a factor of 3 higher than previous alma observations in this region. the high resolution allowed us to resolve highly filamentary co distributions with typical widths of ∼0.1 pc (full width half maximum) and line masses of a few 100 m ⊙ pc-1. the filaments (more than ten in number) show an outstanding hub-filament structure emanating from the nebular center toward the north. we identified for the first time two massive protostellar outflows of ∼104 yr dynamical age along one of the most massive filaments. the observations also revealed several pillar-like co features around the nebula. the h ii region and the pillars have a complementary spatial distribution and the column density of the pillars is an order of magnitude higher than that of the pillars in the eagle nebula (m16) in the galaxy, suggesting an early stage of pillar formation with an age younger than ∼105 yr. we suggest that a cloud-cloud collision triggered the formation of the filaments and protostar within the last ∼2 myr. it is possible that the collision is more recent, as part of the kpc-scale h i flows come from the tidal interaction resulting from the close encounter between the lmc and smc ∼200 myr ago as suggested for r136 by fukui et al. | an alma view of molecular filaments in the large magellanic cloud. i. the formation of high-mass stars and pillars in the n159e-papillon nebula triggered by a cloud-cloud collision |
we use medium-resolution jwst/nirspec observations from the cosmic evolution early release science survey to place the first constraints on dust attenuation and star formation based on paschen lines for a sizable sample of 63 galaxies at redshifts z = 1.0-3.1. our analysis indicates strong correlations between the balmer decrement, hα/hβ, and line ratios that include paschen lines (i.e., paα/hβ, paβ/hβ, and the paschen decrement, paα/paβ), suggesting that the former is sensitive to the overall dust obscuration toward h ii regions in high-redshift galaxies. the line ratios are used to derive nebular reddening, e(b - v)neb, and star formation rates (sfrs). there is marginal evidence that the sfrs deduced from paschen lines may exceed by ≈25% those derived from balmer lines alone, suggesting the presence of star formation that is optically thick in balmer lines, though deeper observations are needed to confirm this result. using the paschen-line constraints on the bolometric sfrs, we reevaluate the relationship between dust obscuration and uv spectral slope, and find a reddening of the uv continuum that, on average, follows the smc extinction curve. this analysis highlights the need for deeper spectroscopy of more representative samples to evaluate nebular dust attenuation and bolometric sfrs in high-redshift galaxies, and their relationship to the reddening of the uv continuum. | paschen-line constraints on dust attenuation and star formation at z 1-3 with jwst/nirspec |
selecting the first galaxies at z > 7 - 10 from jwst surveys is complicated by z < 6 contaminants with degenerate photometry. for example, strong optical nebular emission lines at z < 6 may mimic jwst/nircam photometry of z > 7-10 lyman-break galaxies (lbgs). dust-obscured 3 < z < 6 galaxies in particular are potentially important contaminants, and their faint rest-optical spectra have been historically difficult to observe. a lack of optical emission line and continuum measures for 3 < z < 6 dusty galaxies now makes it difficult to test their expected jwst/nircam photometry for degenerate solutions with nircam dropouts. toward this end, we quantify the contribution by strong emission lines to nircam photometry in a physically motivated manner by stacking 21 keck ii/nires spectra of hot, dust-obscured, massive ( $\mathrm{log}{m}_{* }/{m}_{\odot }\gtrsim 10\mbox{--}11$ ) and infrared (ir) luminous galaxies at z ~ 1-4. we derive an average spectrum and measure strong narrow (broad) [o iii]5007 and hα features with equivalent widths of 130 ± 20 å (150 ± 50 å) and 220 ± 30 å (540 ± 80 å), respectively. these features can increase broadband nircam fluxes by factors of 1.2 - 1.7 (0.2-0.6 mag). due to significant dust attenuation (av~ 6), we find hα+[n ii] to be significantly brighter than [o iii]+hβ and therefore find that emission-line dominated contaminants of high -z galaxy searches can only reproduce moderately blue perceived uv continua of sλ∝ λβwith β > - 1.5 and z > 4. while there are some redshifts (z ~ 3.75) where our stack is more degenerate with the photometry of z > 10 lbgs at λ rest ~ 0.3-0.8 μm , redder filter coverage beyond λ obs > 3.5 μm and far-ir/submillimeter follow-up may be useful for breaking the degeneracy and making a crucial separation between two fairly unconstrained populations, dust-obscured galaxies at z ~ 3-6 and lbgs at z > 10. | broad emission lines in optical spectra of hot, dust-obscured galaxies can contribute significantly to jwst/nircam photometry |
we place statistical constraints on type ia supernova (sn ia) progenitors using 227 nebular-phase spectra of 111 sne ia. we find no evidence of stripped companion emission in any of the nebular-phase spectra. upper limits are placed on the amount of mass that could go undetected in each spectrum using recent hydrodynamic simulations. with these null detections, we place an observational 3σ upper limit on the fraction of sne ia that are produced through the classical h-rich non-degenerate companion scenario of < 5.5 per cent. additionally, we set a tentative 3σ upper limit otan he star progenitor scenarios of < 6.4 per cent, although further theoretical modelling is required. these limits refer to our most representative sample including normal, 91bg-like, 91t-like, and `super-chandrasekhar' sne ia but excluding sne iax and sne ia-csm. as part of our analysis, we also derive a nebular phase phillips relation, which approximates the brightness of an sn ia from 150 to 500 d after maximum using the peak magnitude and decline rate parameter δm15(b). | nebular spectra of 111 type ia supernovae disfavour single-degenerate progenitors |
binary neutron star mergers are thought to be one of the dominant sites of production for rapid neutron capture elements, including platinum and gold. since the discovery of the binary neutron star merger gw170817, and its associated kilonova at2017gfo, numerous works have attempted to determine the composition of its outflowing material, but they have been hampered by the lack of complete atomic data. here, we demonstrate how inclusion of new atomic data in synthetic spectra calculations can provide insights and constraints on the production of the heaviest elements. we employ theoretical atomic data (obtained using $\small {\rm grasp}^{0}$) for neutral, singly and doubly ionized platinum and gold, to generate photospheric and simple nebular phase model spectra for kilonova-like ejecta properties. we make predictions for the locations of strong transitions, which could feasibly appear in the spectra of kilonovae that are rich in these species. we identify low-lying electric quadrupole and magnetic dipole transitions that may give rise to forbidden lines when the ejecta becomes optically thin. the strongest lines lie beyond 8000 å, motivating high quality near-infrared spectroscopic follow-up of kilonova candidates. we compare our model spectra to the observed spectra of at2017gfo, and conclude that no platinum or gold signatures are prominent in the ejecta. from our nebular phase modelling, we place tentative upper limits on the platinum and gold mass of ≲ a few 10-3 m⊙, and ≲ 10-2 m⊙, respectively. this work demonstrates how new atomic data of heavy elements can be included in radiative transfer calculations, and motivates future searches for elemental signatures. | constraints on the presence of platinum and gold in the spectra of the kilonova at2017gfo |
in the last few years, prominent high-ionization nebular emission lines (i.e., o iii], c iii], c iv, and he ii) have been observed in the deep uv spectra of z ∼ 5-7 galaxies, indicating that extreme radiation fields characterize reionization-era systems. these lines have been linked to the leakage of lyman continuum photons (necessary for reionization) both theoretically and observationally. consequently, high-ionization uv emission lines present our best probe to detect and characterize the most distant galaxies that we will observe in the coming years, and are key to understanding the sources of reionization, yet the physics governing their production is poorly understood. here we present recent high-resolution hubble space telescope spectra of two nearby extreme uv emission-line galaxies, j104457 and j141851. we report the first observations of intense nebular he ii and double-peaked, resonantly scattered c iv emission, a combination that suggests these galaxies both produce and transmit a significant number of very high-energy ionizing photons (e > 47.89 ev) through relatively low column densities of high-ionization gas. this suggests that, in addition to photons at the h-ionizing edge, the very hard ionizing photons that escape from these galaxies may provide a secondary source of ionization that is currently unconstrained observationally. simultaneous radiative transfer models of lyα and c iv are needed to understand how ionizing radiation is transmitted through both low- and high-ionization gas. future rest-frame far-uv observations of galaxies within the epoch of reionization using the james webb space telescope or extremely large telescopes (elts) will allow us to constrain the escape of helium-ionizing photons and provide an estimate for their contribution to the reionization budget. 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. | intense c iv and he ii emission in z ∼ 0 galaxies: probing high-energy ionizing photons |
we have simulated a common envelope interaction between a 0.88 m⊙, 90 r⊙, red giant branch star, and a 0.6 m⊙, compact companion with the smoothed particle hydrodynamics code, phantom, from the beginning of the roche lobe overflow phase to the beginning of the self-regulated inspiral, at three different resolutions. the duration of the roche lobe overflow phase is resolution dependent and would lengthen with increased resolution beyond the ∼20 yr observed, while the inspiral phase and the post-common envelope separation are largely independent of (average) resolution. mass transfer rates through the lagrangian points drive the orbital evolution during the roche lobe overflow phase, as predicted analytically. the absolute mass transfer rate is resolution dependent, but always within a factor of two of the analytical value. similarly, the gravitational drag in the simulations is close to the analytical approximation. this verifies simulations and shows that these analytical approximations are reasonable. the l2 and l3 outflows observed during roche lobe overflow remain bound, forming a circumbinary disc that is largely disrupted by the common envelope ejection. however, a longer phase of roche lobe overflow and weaker common envelope ejection typical of a more stable roche lobe phase may result in a surviving circumbinary disc. finally, we examine the density distribution resulting from the interaction for simulations that include or omit the phase of roche lobe overflow. we conclude that the degree of stability of the roche lobe phase modulates the shape of the subsequent planetary nebula, explaining the wide range of post-common envelope planetary nebula shapes observed. | extending common envelope simulations from roche lobe overflow to the nebular phase |
the physical properties of epoch of reionization (eor) galaxies are still poorly constrained by observations. to better understand the ionizing properties of galaxies in the eor, we investigate deep, rest-frame ultraviolet (uv) spectra of ≃500 star-forming galaxies at 3 ≤ z ≤ 5 selected from the public eso-vandels spectroscopic survey. the absolute ionizing photon escape fraction ($f_{\rm esc}^{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the uv attenuation. the ionizing production efficiency (ξion, i.e. the number of ionizing photons produced per non-ionizing uv luminosity) is calculated by fitting the far-uv (fuv) stellar continuum of the vandels galaxies. we find that the $f_{\rm esc}^{\rm abs}$ and ξion parameters increase towards low-mass, blue uv-continuum slopes and strong ly α emitting galaxies, and both are slightly higher-than-average for the uv-faintest galaxies in the sample. potential lyman continuum emitters (lces, $f_{\rm esc}^{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected lyman alpha emitters (laes, wlyα ≤ -20 å) show systematically higher ξion (log ξion(hz erg-1) ≈ 25.38, 25.41) than non-lces and non-laes (log ξion(hz erg-1) ≈ 25.18, 25.14) at similar uv magnitudes. this indicates very young underlying stellar populations (≈10 myr) at relatively low metallicities (≈0.2 z⊙). the fuv non-ionizing spectra of potential lces is characterized by blue uv slopes (≤-2), enhanced ly α emission (≤-25 å), strong uv nebular lines (e.g. high ${\rm c\, \small {iv}}$1550/${\rm c\, \small {iii}}$1908 ≥0.75 ratios), and weak absorption lines (≤1 å). the latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. by comparing our vandels results against other surveys in the literature, our findings imply that the ionizing budget in the eor was likely dominated by uv-faint, low-mass, and dustless galaxies. | the vandels survey: the ionizing properties of star-forming galaxies at 3 ≤ z ≤ 5 using deep rest-frame ultraviolet spectroscopy |
we utilize theoretical models of population iii stellar + nebular spectra to investigate the prospects of observing and accurately identifying population iii galaxies with jwst using both deep imaging and spectroscopy. we investigate a series of different colour cuts, finding that a combination of nircam and miri photometry through the f444w-f560w, f560w-f770w colours offers the most robust identifier of potential z = 8 pop iii candidates. we calculate that nircam will have to reach ~28.5-30.0 ab mag depths (1-20 h), and miri f560w must reach ~27.5-29.0 ab mag depths (10-100 h) to achieve 5σ continuum detections of m* = 106 m⊙ pop iii galaxies at z = 8. we also discuss the prospects of identifying pop iii candidates through slitless and nirspec spectroscopic surveys that target lyα, hβ, and/or he ii λ1640. we find small differences in the hβ rest-frame equivalent width (ew) between pop iii and non-pop iii galaxies, rendering this diagnostic likely impractical. instead, we find that the detection of high ew he ii λ1640 emission will serve as the definitive pop iii identifier, requiring (ultra-)deep integrations (5-150 h) with nirspec/g140m for m* = 106 m⊙ pop iii galaxies at z = 8. however, miri f770w detections of pop iii galaxies will require substantial gravitational lensing (μ = 10) and/or fortuitous imaging of exceptionally massive (m* = 107 m⊙) pop iii galaxies. thus, nircam medium-band imaging surveys that can search for high ew he ii λ1640 emitters in photometry may perhaps be a viable alternative for finding pop iii candidates. | on the observability and identification of population iii galaxies with jwst |
the majority of discovered exoplanetary systems harbour a new class of planets, bodies that are typically several times more massive than the earth but that orbit their host stars well inside the orbit of mercury. the origin of these close-in super-earths and mini-neptunes is one of the major unanswered questions in planet formation. unlike the earth, whose atmosphere contains less than 10-6 of its total mass, a large fraction of close-in planets have significant gaseous envelopes, containing 1-10 per cent or more of their total mass. it has been proposed that close-in super-earths and mini-neptunes formed in situ either by delivery of 50-100 m⊕ of rocky material to the inner regions of the protoplanetary disc or in a disc enhanced relative to the minimum mass solar nebula. in both cases, the final assembly of the planets occurs via giant impacts. here we test the viability of these scenarios. we show that atmospheres that can be accreted by isolation masses are small (typically 10-3-10-2 of the core mass) and that the atmospheric mass-loss during giant impacts is significant, resulting in typical post-giant impact atmospheres that are 8 × 10- 4 of the core mass. such values are consistent with terrestrial planet atmospheres but more than an order of magnitude below atmospheric masses of 1-10 per cent inferred for many close-in exoplanets. in the most optimistic scenario in which there is no core luminosity from giant impacts and/or planetesimal accretion, we find that post-giant impact envelope accretion from a depleted gas disc can yield atmospheric masses that are several per cent the core mass. if the gravitational potential energy resulting from the last mass doubling of the planet by giant impacts is released over the disc dissipation time-scale as core luminosity, then the accreted envelope masses are reduced by about an order of magnitude. finally we show that, even in the absence of type i migration, radial drift time-scales due to gas drag for many isolation masses are shorter than typical disc lifetimes for standard gas-to-dust ratios. given these challenges, we conclude that most of the observed close-in planets with envelopes larger than several per cent of their total mass likely formed at larger separations from their host stars. | the formation of super-earths and mini-neptunes with giant impacts |
stellar population synthesis techniques for predicting the observable light emitted by a stellar population have extensive applications in numerous areas of astronomy. however, accurate predictions for small populations of young stars, such as those found in individual star clusters, star-forming dwarf galaxies, and small segments of spiral galaxies, require that the population be treated stochastically. conversely, accurate deductions of the properties of such objects also require consideration of stochasticity. here we describe a comprehensive suite of modular, open-source software tools for tackling these related problems. these include the following: a greatly-enhanced version of the slug code introduced by da silva et al., which computes spectra and photometry for stochastically or deterministically sampled stellar populations with nearly arbitrary star formation histories, clustering properties, and initial mass functions; cloudy_slug, a tool that automatically couples slug-computed spectra with the cloudy radiative transfer code in order to predict stochastic nebular emission; bayesphot, a general-purpose tool for performing bayesian inference on the physical properties of stellar systems based on unresolved photometry; and cluster_slug and sfr_slug, a pair of tools that use bayesphot on a library of slug models to compute the mass, age, and extinction of mono-age star clusters, and the star formation rate of galaxies, respectively. the latter two tools make use of an extensive library of pre-computed stellar population models, which are included in the software. the complete package is available at http://www.slugsps.com. | slug - stochastically lighting up galaxies - iii. a suite of tools for simulated photometry, spectroscopy, and bayesian inference with stochastic stellar populations |
deep spectroscopy of galaxies in the reionization era has revealed intense c iii] and c iv line emission (equivalent width, ew >15-20 å). in order to interpret the nebular emission emerging at z > 6, we have begun targeting rest-frame ultraviolet (uv) emission lines in galaxies with large specific star formation rates (ssfrs) at 1.3 < z < 3.7. we find that c iii] reaches the ews seen at z > 6 only in large ssfr galaxies with [o iii]+hβ ew >1500 å. in contrast to previous studies, we find that many galaxies with intense [o iii] have weak c iii] emission (ew = 5-8 å), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong c iii]. photoionization models demonstrate that the spread in c iii] among systems with large ssfrs ([o iii]+hβ ew >1500 å) is driven by variations in metallicity, a result of the extreme sensitivity of c iii] to electron temperature. we find that the strong c iii] emission seen at z > 6 (ew >15 å) requires metal-poor gas (≃ 0.1 z⊙), whereas the weaker c iii] emission in our sample tends to be found at moderate metallicities (≃ 0.3 z⊙). the luminosity distribution of the c iii] emitters in our z ≃ 1-3 sample presents a consistent picture, with stronger emission generally linked to low-luminosity systems (muv > -19.5) where low metallicities are more likely. we quantify the fraction of strong c iii] and c iv emitters at z ≃ 1-3, providing a baseline for comparison against z > 6 samples. we suggest that the first uv line detections at z > 6 can be explained if a significant fraction of the early galaxy population is found at large ssfr (>200 gyr-1) and low metallicity (< 0.1 z⊙). | rest-frame uv spectroscopy of extreme [o iii] emitters at 1.3 < z < 3.7: toward a high-redshift uv reference sample for jwst |
renazzo-type carbonaceous (cr) chondrites are distinct from most other chondrites in having younger chondrule 26al-26mg ages, but the significance of these ages and whether they reflect true formation times or spatial variations of the 26al/27al ratio within the solar protoplanetary disk are a matter of debate. to address these issues and to determine the timescales of metal-silicate fractionation and chondrule formation in cr chondrites, we applied the short-lived 182hf-182w chronometer to metal, silicate, and chondrule separates from four cr chondrites. we also obtained mo isotope data for the same samples to assess potential genetic links among the components of cr chondrites, and between these components and bulk chondrites. all investigated samples plot on a single hf-w isochron and constrain the time of metal-silicate fractionation in cr chondrites to 3.6 ± 0.6 million years (ma) after the formation of ca-al-rich inclusions (cais). this age is indistinguishable from a ∼3.7 ma al-mg age for cr chondrules, suggesting not only that metal-silicate fractionation and chondrule formation were coeval, but also that these two processes were linked to each other. the good agreement of the hf-w and al-mg ages, combined with concordant hf-w and al-mg ages for angrites and cv chondrules, provides strong evidence for a disk-wide, homogeneous distribution of 26al in the early solar system. as such, the young al-mg ages for cr chondrules do not reflect spatial 26al/27al heterogeneities but indicate that cr chondrules formed ∼1-2 ma later than chondrules from most other chondrite groups. metal and silicate in cr chondrites exhibit distinct nucleosynthetic mo and w isotope anomalies, which are caused by the heterogeneous distribution of the same presolar s-process carrier. these data suggest that the major components of cr chondrites are genetically linked and therefore formed from a single reservoir of nebular dust, most likely by localized melting events within the solar protoplanetary disk. taken together, the chemical, isotopic, and chronological data for components of cr chondrites imply a close temporal link between chondrule formation and chondrite accretion, indicating that the cr chondrite parent body is one of the youngest meteorite parent bodies. the relatively late accretion of the cr parent body is consistent with its isotopic composition (for instance the elevated 15n/14n) that suggests a formation at a larger heliocentric distance, probably beyond the orbit of jupiter. as such, the accretion age of the cr chondrite parent body of ∼3.6 ma after cai formation provides the earliest possible time at which jupiter's growth could have led to scattering of carbonaceous meteorite parent bodies from beyond its orbit into the inner solar system. | hf-w chronology of cr chondrites: implications for the timescales of chondrule formation and the distribution of 26al in the solar nebula |
the detailed velocity structure of the diffuse x-ray emitting intra-cluster medium (icm) remains one of the last missing key ingredients in understanding the microphysical properties of these hot baryons and constraining our models of the growth and evolution of structure on the largest scales in the universe. direct measurements of the gas velocities from the widths and shifts of x-ray emission lines were recently provided for the central region of the perseus cluster of galaxies by hitomi, and upcoming high-resolution x-ray microcalorimeters onboard xrism and athena are expected to extend these studies to many more systems. in the mean time, several other direct and indirect methods have been proposed for estimating the velocity structure in the icm, ranging from resonant scattering to x-ray surface brightness fluctuation analysis, the kinematic sunyaev-zeldovich effect, or using optical line emitting nebulae in the brightest cluster galaxies as tracers of the motions of the ambient plasma. here, we review and compare the existing estimates of the velocities of the hot baryons, as well as the various overlapping physical processes that drive motions in the icm, and discuss the implications of these measurements for constraining the viscosity and identifying the source of turbulence in clusters of galaxies. | constraining gas motions in the intra-cluster medium |
we derive hα fluxes for a large spectroscopic and photometric-redshift-selected sample of sources over goods-north and south in the redshift range z = 3.8-5.0 with deep hubble space telescope (hst), spitzer/irac, and ground-based observations. the hα flux is inferred based on the offset between the irac 3.6 μm flux and that predicted from the best-fit spectral energy distribution (sed). we demonstrate that the hα flux correlates well with dust-corrected uv star formation rate (sfr) and therefore can serve as an independent sfr indicator. however, we also find a systematic offset in the {{sfr}}{{h}α }/{{sfr}}{uv+β } ratios for z ∼ 4-5 galaxies relative to local relations (assuming the same dust corrections for nebular regions and stellar light). we show that we can resolve the modest tension in the inferred sfrs by assuming bluer intrinsic uv slopes (increasing the dust correction), a rising star formation history, or assuming a low-metallicity stellar population with a hard ionizing spectrum (increasing the {l}{{h}α }/{sfr} ratio). using hα as an sfr indicator, we find a normalization of the star formation main sequence in good agreement with recent sed-based determinations and also derive the sfr functions at z∼ 4{--}8. in addition, we assess for the first time the burstiness of star formation in z∼ 4 galaxies on <100 myr timescales by comparing uv and hα-based ssfrs; their one-to-one relationship argues against significantly bursty star formation histories. | inferred h⍺ flux as a star formation rate indicator at z ~ 4-5: implications for dust properties, burstiness, and the z = 4-8 star formation rate functions |
the 30 doradus (30 dor) nebula in the large magellanic cloud (lmc) is the brightest hii region in the local group and a prototype starburst similar to those found in high redshift galaxies. it is thus a stepping stone to understand the complex formation processes of stars in starburst regions across the universe. here, we have studied the formation history of massive stars in 30 dor using masses and ages derived for 452 mainly ob stars from the spectroscopic vlt-flames tarantula survey (vfts). we find that stars of all ages and masses are scattered throughout 30 dor. this is remarkable because it implies that massive stars either moved large distances or formed independently over the whole field of view in relative isolation. we find that both channels contribute to the 30 dor massive star population. massive star formation rapidly accelerated about 8 myr ago, first forming stars in the field before giving birth to the stellar populations in ngc 2060 and ngc 2070. the r136 star cluster in ngc 2070 formed last and, since then, about 1 myr ago, star formation seems to be diminished with some continuing in the surroundings of r136. massive stars within a projected distance of 8 pc of r136 are not coeval but show an age range of up to 6 myr. our mass distributions are well populated up to 200 m⊙. the inferred imf is shallower than a salpeter-like imf and appears to be the same across 30 dor. by comparing our sample of stars to stellar models in the hertzsprung-russell diagram, we find evidence for missing physics in the models above log l/l⊙ = 6 that is likely connected to enhanced wind mass loss for stars approaching the eddington limit. our work highlights the key information about the formation, evolution and final fates of massive stars encapsulated in the stellar content of 30 dor, and sets a new benchmark for theories of massive star formation in giant molecular clouds. based on observations collected at the european southern observatory under programme id 182.d-0222. | the vlt-flames tarantula survey. xxix. massive star formation in the local 30 doradus starburst |
we present observations of sn 2020fqv, a virgo-cluster type ii core-collapse supernova (ccsn) with a high temporal resolution light curve from the transiting exoplanet survey satellite (tess) covering the time of explosion; ultraviolet (uv) spectroscopy from the hubble space telescope (hst) starting 3.3 d post-explosion; ground-based spectroscopic observations starting 1.1 d post-explosion; along with extensive photometric observations. massive stars have complicated mass-loss histories leading up to their death as ccsne, creating circumstellar medium (csm) with which the sne interact. observations during the first few days post-explosion can provide important information about the mass-loss rate during the late stages of stellar evolution. model fits to the quasi-bolometric light curve of sn 2020fqv reveal 0.23 m⊙ of csm confined within 1450 r⊙ (1014 cm) from its progenitor star. early spectra (<4 d post-explosion), both from hst and ground-based observatories, show emission features from high-ionization metal species from the outer, optically thin part of this csm. we find that the csm is consistent with an eruption caused by the injection of ~5 × 1046 erg into the stellar envelope ~300 d pre-explosion, potentially from a nuclear burning instability at the onset of oxygen burning. light-curve fitting, nebular spectroscopy, and pre-explosion hst imaging consistently point to a red supergiant (rsg) progenitor with $m_{\rm zams}\approx 13.5\!-\!15 \, \mathrm{m}_{\odot }$, typical for sn ii progenitor stars. this finding demonstrates that a typical rsg, like the progenitor of sn 2020fqv, has a complicated mass-loss history immediately before core collapse. | progenitor and close-in circumstellar medium of type ii supernova 2020fqv from high-cadence photometry and ultra-rapid uv spectroscopy |
the radioactively powered transient following a binary neutron star merger, known as a kilonova (kn), is expected to enter the steady-state nebular phase a few days after merger. steady-state holds until thermal reprocessing time-scales become long, at which point the temperature and ionization states need to be evolved time-dependently. we study the onset and significance of time-dependent effects using the non-local thermodynamic equilibrium spectral synthesis code sumo. we employ a simple single-zone model with an elemental composition of te, ce, pt, and th, scaled to their respective solar abundances. the atomic data are generated using the flexible atomic code (fac), and consist of energy levels and radiative transitions, including highly forbidden lines. we explore the kn evolution from 5 to 100 d after merger, varying ejecta mass and velocity. we also consider variations in the degree of electron magnetic field trapping, as well as radioactive power generation for alpha and beta decay (but omitting fission products). we find that the transition time, and magnitude of steady-state deviations are highly sensitive to these parameters. for typical kn ejecta, the deviations are minor within the time-frame studied. however, low density ejecta with low energy deposition show significant differences from ~10 d. important deviation of the ionization structure solution impacts the temperature by altering the overall line cooling. adiabatic cooling becomes important at t ≥ 60 d which, in addition to the temperature and ionization effects, lead to the bolometric light-curve deviating from the instantaneous radioactive power deposited. | on the validity of steady-state for nebular phase kilonovae |
distant luminous lyman-α emitters (laes) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (eor). we present deep high-resolution (r = 5000) vlt/x-shooter observations, along with an extensive collection of photometric data of cola1, a proposed double peaked lae at z = 6.6. we rule out the possibility that cola1's emission line is an [oii] doublet at z = 1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=0.31 ± 0.03) and ii) an unphysical [oii]/hα ratio ([oii]/hα > 22). we show that cola1's observed b-band flux is explained by a faint extended foreground lae, for which we detect lyα and [oiii] at z = 2.142. we thus conclude that cola1 is a real double-peaked lae at z = 6.593, the first discovered at z > 6. cola1 is uv luminous (m1500 = -21.6 ± 0.3), has a high equivalent width (ew0,lyα = 120-40+50 å) and very compact lyα emission (r50,lyα = 0.33-0.04+0.07 kpc). relatively weak inferred hβ+[oiii] line-emission from spitzer/irac indicates an extremely low metallicity of z < 1/20 z⊙ or reduced strength of nebular lines due to high escape of ionising photons. the small lyα peak separation of 220 ± 20 km s-1 implies a low hi column density and an ionising photon escape fraction of ≈15 - 30%, providing the first direct evidence that such galaxies contribute actively to the reionisation of the universe at z > 6. based on simple estimates, we find that cola1 could have provided just enough photons to reionise its own ≈0.3 pmpc (2.3 cmpc) bubble, allowing the blue lyα line to be observed. however, we also discuss alternative scenarios explaining the detected double peaked nature of cola1. our results show that future high-resolution observations of statistical samples of double peaked laes at z > 5 are a promising probe of the occurrence of ionised regions around galaxies in the eor. based on observations obtained with the very large telescope, programs: 294.a-5039, 099.a-0254 and 100.a-0213.reduced 1d x-shooter spectrum is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?j/a+a/619/a136 | confirmation of double peaked lyα emission at z = 6.593. witnessing a galaxy directly contributing to the reionisation of the universe |
ngc 1052-df2, an ultra-diffuse galaxy (udg), has been the subject of intense debate. its alleged absence of dark matter, and the brightness and number excess of its globular clusters (gcs) at an initially assumed distance of 20 mpc suggest a new formation channel for udgs. we present the first systematic spectroscopic analysis of the stellar body and the gcs in this galaxy (six previously known and one newly confirmed member) using muse at the vlt. even though ngc 1052-df2 does not show any spatially extended emission lines, we report the discovery of three planetary nebulae (pne). we conduct full spectral fitting on the udg and the stacked spectra of all the gcs. the udg's stellar population is old, 8.9 ± 1.5 gyr; metal poor, [m/h] = -1.07 ± 0.12; and with little or no α-enrichment. the stacked spectrum of all gcs indicates a similar age of 8.9 ± 1.8 gyr, but a lower metallicity of [m/h] = -1.63 ± 0.09 and a similarly low α-enrichment. there is no evidence for a variation in age and metallicity in the gc population with the available spectra. the significantly more metal-rich stellar body with respect to its associated gcs, the age of the population, its metallicity, and its α-enrichment are all in line with other dwarf galaxies. ngc 1052-df2 thus falls on the same empirical mass-metallicity relation as other dwarfs for the full distance range assumed in the literature. we find that both debated distance estimates (13 and 20 mpc) are similarly likely, given the three discovered pne. based on observations collected at the european southern observatory under eso programs 2101.b-5008(a) and 2101.b-5053(a). | the ultra-diffuse galaxy ngc 1052-df2 with muse. ii. the population of df2: stars, clusters, and planetary nebulae |
as deep spectroscopic campaigns extend to higher redshifts and lower stellar masses, the interpretation of galaxy spectra depends increasingly upon models for very young stellar populations. here we present new hst/cos ultraviolet spectroscopy of seven nearby (<120 mpc) star-forming regions hosting very young stellar populations (~4-20 myr) with optical wolf-rayet stellar wind signatures, ideal laboratories in which to benchmark these stellar models. we detect nebular c iii] in all seven, but at equivalent widths uniformly <10 å. this suggests that even for very young stellar populations, the highest equivalent width c iii] emission at ≥15 å is reserved for inefficiently cooled gas at metallicities at or below that of the smc. the spectra also reveal strong c iv p-cygni profiles and broad he ii emission formed in the winds of massive stars, including some of the most prominent he ii stellar wind lines ever detected in integrated spectra. we find that the latest stellar population synthesis prescriptions with improved treatment of massive stars nearly reproduce the entire range of stellar he ii wind strengths observed here. however, we find that these models cannot simultaneously match the strongest wind features alongside the optical nebular line constraints. this discrepancy can be naturally explained by an overabundance of very massive stars produced by a high incidence of binary mass transfer and mergers occurring on short ≲10 myr time-scales, suggesting these processes may be crucial for understanding systems dominated by young stars both nearby and in the early universe. | ultraviolet spectra of extreme nearby star-forming regions: evidence for an overabundance of very massive stars |
winds from young massive stars contribute a large amount of energy to their host molecular clouds. this has consequences for the dynamics and observable structure of star-forming clouds. in this paper, we present radiative magnetohydrodynamic simulations of turbulent molecular clouds that form individual stars of 30, 60, and 120 solar masses emitting winds and ultraviolet radiation following realistic stellar evolution tracks. we find that winds contribute to the total radial momentum carried by the expanding nebula around the star at 10 per cent of the level of photoionization feedback, and have only a small effect on the radial expansion of the nebula. radiation pressure is largely negligible in the systems studied here. the 3d geometry and evolution of wind bubbles is highly aspherical and chaotic, characterized by fast-moving 'chimneys' and thermally driven 'plumes'. these plumes can sometimes become disconnected from the stellar source due to dense gas flows in the cloud. our results compare favourably with the findings of relevant simulations, analytic models and observations in the literature while demonstrating the need for full 3d simulations including stellar winds. however, more targeted simulations are needed to better understand results from observational studies. | the geometry and dynamical role of stellar wind bubbles in photoionized h ii regions |
the streaming instability is a popular candidate for planetesimal formation by concentrating dust particles to trigger gravitational collapse. however, its robustness against the physical conditions expected in protoplanetary disks is unclear. in particular, particle stirring by turbulence may impede the instability. to quantify this effect, we develop the linear theory of the streaming instability with external turbulence modeled by gas viscosity and particle diffusion. we find the streaming instability is sensitive to turbulence, with growth rates becoming negligible for alpha viscosity parameters α ≳ st1.5, where st is the particle stokes number. we explore the effect of nonlinear drag laws, which may be applicable to porous dust particles, and find growth rates are modestly reduced. we also find that gas compressibility increases growth rates by reducing the effect of diffusion. we then apply the linear theory to global models of viscous protoplanetary disks. for minimum-mass solar nebula disk models, we find the streaming instability only grows within disk lifetimes beyond tens of astronomical units, even for centimeter-sized particles and weak turbulence (α ∼ 10-4). our results suggest it is rather difficult to trigger the streaming instability in nonlaminar protoplanetary disks, especially for small particles. | how efficient is the streaming instability in viscous protoplanetary disks? |
despite significant progress both observationally and theoretically, the origin of high-ionization nebular he ii emission in galaxies dominated by stellar photoionization remains unclear. accretion-powered radiation from high-mass x-ray binaries (hmxbs) is still one of the leading proposed explanations for the missing he+-ionizing photons, but this scenario has yet to be conclusively tested. in this paper, we present nebular line predictions from a grid of photoionization models with input spectral energy distributions containing the joint contribution of both stellar atmospheres and a multicolour disc model for hmxbs. this grid demonstrates that hmxbs are inefficient producers of the photons necessary to power he ii, and can only boost this line substantially in galaxies with hmxb populations large enough to power x-ray luminosities of 1042 erg s-1 per unit star formation rate (sfr). to test this, we assemble a sample of 11 low-redshift star-forming galaxies with high-quality constraints on both x-ray emission from chandra and he ii emission from deep optical spectra, including new observations with the mmt. these data reveal that the hmxb populations of these nearby systems are insufficient to account for the observed he ii strengths, with typical x-ray luminosities or upper limits thereon of only 1040-1041 erg s-1 per sfr. this indicates that hmxbs are not the dominant source of he+ ionization in these metal-poor star-forming galaxies. we suggest that the solution may instead reside in revisions to stellar wind predictions, softer x-ray sources, or very hot products of binary evolution at low metallicity. | high-mass x-ray binaries in nearby metal-poor galaxies: on the contribution to nebular he ii emission |
data suggest that most rocky exoplanets with orbital period p < 100 days ("hot" rocky exoplanets) formed as gas-rich sub-neptunes that subsequently lost most of their envelopes, but whether these rocky exoplanets still have atmospheres is unknown. we identify a pathway by which 1-1.7 r⊕ (1-10 m⊕) rocky exoplanets with orbital periods of 10-100 days can acquire long-lived 10-2000 bar atmospheres that are h2o-dominated, with mean molecular weight >10. these atmospheres form during the planets' evolution from sub-neptunes into rocky exoplanets. h2o that is made by reduction of iron oxides in the silicate magma is highly soluble in the magma, forming a dissolved reservoir that is protected from loss so long as the h2-dominated atmosphere persists. the large size of the dissolved reservoir buffers the h2o atmosphere against loss after the h2 has dispersed. within our model, a long-lived, water-dominated atmosphere is a common outcome for efficient interaction between a nebula-derived atmosphere (peak atmosphere mass fraction 0.1-0.6 wt%) and oxidized magma (>5 wt% feo), followed by atmospheric loss. this idea predicts that most rocky planets that have orbital periods of 10-100 days and that have radii within 0.1-0.2 r⊕ of the lower edge of the radius valley still retain h2o atmospheres. this prediction is imminently testable with james webb space telescope and has implications for the interpretation of data for transiting super-earths. | water on hot rocky exoplanets |
we investigate the relation between the optical extinction (av) and the hydrogen column density (nh) determined from x-ray observations of a large sample of galactic sightlines towards 35 supernova remnants, 6 planetary nebulae and 70 x-ray binaries for which nh was determined in the literature with solar abundances. we derive an average ratio of 〈nh/av〉 = (2.08 ± 0.02) × 1021 h cm-2 mag-1 for the whole galaxy. we find no correlation between 〈nh/av〉 and the number density of hydrogen, the distance away from the galactic centre and the distance above or below the galactic plane. the 〈nh/av〉 ratio is generally invariant across the galaxy, with 〈nh/av〉 = (2.04 ± 0.05) × 1021 h cm-2 mag-1 for the first and fourth galactic quadrants and 〈nh/av〉 = (2.09 ± 0.03) × 1021 h cm-2 mag-1 for the second and third galactic quadrants. we also explore the distribution of hydrogen in the galaxy by enlarging our sample with additional 74 supernova remnants for which both nh and distances are known. we find that, between the galactic radius of 2 and 10 kpc, the vertical distribution of hydrogen can be roughly described by a gaussian function with a scaleheight of h = 75.5 ± 12.4 pc and a mid-plane density of nh(0) = 1.11 ± 0.15 cm-3, corresponding to a total gas surface density of ∑gas ∼ 7.0 m⊙ pc-2. we also compile nh from 19 supernova remnants and 29 x-ray binaries for which nh was determined with subsolar abundances. we obtain 〈nh/av〉 = (2.47 ± 0.04) × 1021 h cm-2 mag-1 which exceeds that derived with solar abundances by ∼20 per cent. we suggest that in future studies one may simply scale nh derived from subsolar abundances by a factor of ∼1.2 when converting to nh of solar abundances. | the gas-to-extinction ratio and the gas distribution in the galaxy |
galaxies occupy different regions of the [o iii]λ5007/h β-versus-[n ii]λ6584/h α emission-line ratio diagram in the distant and local universe. we investigate the origin of this intriguing result by modelling self-consistently, for the first time, nebular emission from young stars, accreting black holes (bhs) and older, post-asymptotic giant branch (post-agb) stellar populations in galaxy formation simulations in a full cosmological context. in post-processing, we couple new-generation nebular-emission models with high-resolution, cosmological zoom-in simulations of massive galaxies to explore which galaxy physical properties drive the redshift evolution of the optical-line ratios [o iii]λ5007/h β, [n ii]λ6584/h α, [s ii]λλ6717, 6731/h α and [o i]λ6300/h α. the line ratios of simulated galaxies agree well with observations of both star-forming and active local sloan digital sky survey galaxies. towards higher redshifts, at fixed galaxy stellar mass, the average [o iii]/h β is predicted to increase and [n ii]/h α, [s ii]/h α and [o i]/h α to decrease - widely consistent with observations. at fixed stellar mass, we identify star formation history, which controls nebular emission from young stars via the ionization parameter, as the primary driver of the cosmic evolution of [o iii]/h β and [n ii]/h α. for [s ii]/h α and [o i]/h α, this applies only to redshifts greater than z = 1.5, the evolution at lower redshift being driven in roughly equal parts by nebular emission from active galactic nuclei and post-agb stellar populations. instead, changes in the hardness of ionizing radiation, ionized-gas density, the prevalence of bh accretion relative to star formation and the dust-to-metal mass ratio (whose impact on the gas-phase n/o ratio we model at fixed o/h) play at most a minor role in the cosmic evolution of simulated galaxy line ratios. | synthetic nebular emission from massive galaxies - i: origin of the cosmic evolution of optical emission-line ratios |
we hypothesize that differences in the temperatures at which the rocky material condensed out of the nebula gas can lead to differences in the composition of key rocky species (e.g. fe, mg, si, ca, al, na) and thus planet bulk density. such differences in the observed bulk density of planets may occur as a function of radial location and time of planet formation. in this work, we show that the predicted differences are on the cusp of being detectable with current instrumentation. in fact, for hd 219134, the 10 per cent lower bulk density of planet b compared to planet c could be explained by enhancements in ca-, al-rich minerals. however, we also show that the 11 per cent uncertainties on the individual bulk densities are not sufficiently accurate to exclude the absence of a density difference as well as differences in volatile layers. besides hd 219134 b, we demonstrate that 55 cnc e and wasp-47 e are similar candidates of a new super-earth class that have no core and are rich in ca and al minerals that are among the first solids that condense from a cooling proto-planetary disc. planets of this class have densities 10-20 per cent lower than earth-like compositions and may have very different interior dynamics, outgassing histories, and magnetic fields compared to the majority of super-earths. | a new class of super-earths formed from high-temperature condensates: hd219134 b, 55 cnc e, wasp-47 e |
it has recently been noted that there seems to be a strong correlation between planetary nebulae with close binary central stars and highly enhanced recombination line abundances. we present new deep spectra of seven objects known to have close binary central stars, and find that the heavy element abundances derived from recombination lines exceed those from collisionally excited lines by factors of 5-95, placing several of these nebulae among the most extreme known abundance discrepancies. this study nearly doubles the number of nebulae known to have a binary central star and an extreme abundance discrepancy. a statistical analysis of all nebulae with measured recombination line abundances reveals no link between central star surface chemistry and nebular abundance discrepancy, but a clear link between binarity and the abundance discrepancy, as well as an anticorrelation between abundance discrepancies and nebular electron densities: all nebulae with a binary central star with a period of less than 1.15 d have an abundance discrepancy factor exceeding 10, and an electron density less than ∼1000 cm-3; those with longer period binaries have abundance discrepancy factors less than 10 and much higher electron densities. we find that [o ii] density diagnostic lines can be strongly enhanced by recombination excitation, while [s ii] lines are not. these findings give weight to the idea that extreme abundance discrepancies are caused by a nova-like eruption from the central star system, occuring soon after the common-envelope phase, which ejects material depleted in hydrogen, and enhanced in cnone but not in third-row elements. | confirmation of the link between central star binarity and extreme abundance discrepancy factors in planetary nebulae |
superluminous supernovae (slsne) of type ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. ptf12dam is one of the closest and best-studied superluminous explosions that has a broad and slowly fading light curve similar to sn 2007bi. here we present new photometry and spectroscopy for ptf12dam from 200-500 d (rest frame) after peak and a detailed analysis of the host galaxy (sdss j142446.21+461348.6 at z = 0.107). using deep templates and image subtraction we show that the light curve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. the full bolometric light curve from -53 to +399 d (with respect to peak) cannot be fit satisfactorily with the pair-instability models. an alternative model of interaction with a dense circumstellar material (csm) produces a good fit to the data although this requires a very large mass (∼13 m⊙) of hydrogen-free csm. the host galaxy is a compact dwarf (physical size ∼1.9 kpc) and with mg = -19.33 ± 0.10, it is the brightest nearby slsn ic host discovered so far. the host is a low-mass system (2.8 × 108 m⊙) with a star formation rate (5.0 m⊙ yr-1), which implies a very high specific star formation rate (17.9 gyr-1). the remarkably strong nebular emission provide detections of the [o iii] λ4363 and [o ii] λλ7320, 7330auroral lines and an accurate oxygen abundance of 12 + log (o/h) = 8.05 ± 0.09. we show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar sne. | the host galaxy and late-time evolution of the superluminous supernova ptf12dam |
we analyze the x-ray spectra of the ~8000 sources detected in the cygnus ob2 chandra legacy survey (this focus issue), with the goals of characterizing the coronal plasma of the young low-mass stars in the region and estimating their intrinsic x-ray luminosities. we adopt two different strategies for x-ray sources for which more or less than 20 photons were detected. for the brighter sample we fit the spectra with absorbed isothermal models. in order to limit uncertainties, for most of the fainter cygnus ob2 members in this sample we constrain the spectral parameters to characteristic ranges defined from the brightest stars. for x-ray sources with <20 net photons we adopt a conversion factor from detected photon flux to intrinsic flux. this was defined, building on the results for the previous sample, as a function of the 20% quantile of the detected photon energy distributions, which we prove to also correlate well with extinction. we then use the x-ray extinction from the spectral fits to constrain the ratio between optical and x-ray extinction toward cyg ob2, finding it consistent with standard "galactic" values, when properly accounting for systematics. finally, we exploit the large number of sources to constrain the average coronal abundances of several elements, through two different ensemble analyses of the x-ray spectra of low-mass cyg ob2 members. we find the pattern of abundances to be largely consistent with that derived for the young stellar coronae in the orion nebula cluster. | x-ray spectral characterization of the young cygnus ob2 population |
we have studied porphyritic olivine-rich chondrules of the carbonaceous chondrite kaba (cv3) by combined high-resolution x-ray mapping, quantitative electron microprobe analyses, and oxygen isotopic analyses via secondary ion mass spectrometry. these chondrules contain smaller inner-chondrule olivine grains characterized by low refractory element (ca, al, ti) contents, and larger outer-chondrule olivine crystals that are enriched in refractory elements and show complex ti and al oscillatory zonings. our o isotopic survey revealed that many of the inner-chondrule olivines are 16o-richer than the relatively isotopically uniform outer-chondrule olivines. inner-chondrule olivine crystals-only a minority of which may be derived from earlier generations of chondrules-are likely mostly inherited from nebular condensates similar to aoas, as they share similar isotopic and chemical features and are thus interpreted as relict grains. still, being 16o-poorer than most aoas, they may have experienced significant exchange with a 16o-poor reservoir prior to chondrule formation (even if to a lesser degree than relicts in cm2 and ungrouped c2 chondrites). subsequent incomplete melting of the relict grains produced ca-al-ti-rich melts that engulfed the remaining relict olivine grains. the complex ti and al zoning patterns in outer chondrule (host) olivines, in particular the systematic dilution near the margin, seem to reflect gas-melt interactions (with e.g. sio (g), mg (g)) which also buffered the o isotopic composition of chondrule hosts. together, these results demonstrate that important episodes of recycling of nebular condensates occurred in the solar protoplanetary disk. | formation of cv chondrules by recycling of amoeboid olivine aggregate-like precursors |
we present constraints on the massive star and ionized gas properties for a sample of 62 star-forming galaxies at z ~ 2.3. using bpass stellar population models, we fit the rest-uv spectra of galaxies in our sample to estimate age and stellar metallicity which, in turn, determine the ionizing spectrum. in addition to the median properties of well-defined subsets of our sample, we derive the ages and stellar metallicities for 30 high-snr individual galaxies - the largest sample of individual galaxies at high redshift with such measurements. most galaxies in this high-snr subsample have stellar metallicities of 0.001 < z* < 0.004. we then use cloudy + bpass photoionization models to match observed rest-optical line ratios and infer nebular properties. our high-snr subsample is characterized by a median ionization parameter and oxygen abundance, respectively, of log (u)med = -2.98 ± 0.25 and 12 + log (o/h)med = 8.48 ± 0.11. accordingly, we find that all galaxies in our sample show evidence for α-enhancement. in addition, based on inferred log (u) and 12 + log (o/h) values, we find that the local relationship between ionization parameter and metallicity applies at z ~ 2. finally, we find that the high-redshift galaxies most offset from the local excitation sequence in the bpt diagram are the most α-enhanced. this trend suggests that α-enhancement resulting in a harder ionizing spectrum at fixed oxygen abundance is a significant driver of the high-redshift galaxy offset on the bpt diagram relative to local systems. the ubiquity of α-enhancement among z ~ 2.3 star-forming galaxies indicates important differences between high-redshift and local galaxies that must be accounted for in order to derive physical properties at high redshift. | the mosdef-lris survey: the connection between massive stars and ionized gas in individual galaxies at z ∼ 2 |
ionized nebulae are key to understanding the chemical composition and evolution of the universe. among these nebulae, h~{\sc ii} regions and planetary nebulae are particularly important as they provide insights into the present and past chemical composition of the interstellar medium, along with the nucleosynthetic processes involved in the chemical evolution of the gas. however, the heavy-element abundances derived from collisional excited lines (cels) and recombination lines (rls) do not align. this longstanding abundance-discrepancy problem calls into question our absolute abundance determinations. which of the lines (if any) provides the correct heavy-element abundances? recently, it has been shown that there are temperature inhomogeneities concentrated within the highly ionized gas of the h~{\sc ii} regions, causing the reported discrepancy. however, planetary nebulae do not exhibit the same trends as the h~{\sc ii} regions, suggesting a different origin for the abundance discrepancy. in this proceedings, we briefly discuss the state-of-the-art of the abundance discrepancy problem in both h~{\sc ii} regions and planetary nebulae. | the abundance discrepancy in ionized nebulae: which are the correct abundances? |
context. the region around the h2o ice line, due to its higher surface density, seems to be the ideal location to form planets. the core of jupiter, as well as the cores of close-in gas giants are therefore thought to form in this region of the disk. nevertheless, constraining the formation location of individual planets has proven to be difficult.aims: we aim to use the nitrogen abundance in jupiter, which is around four times solar, in combination with juno constraints on the total mass of heavy elements in jupiter to narrow down its formation scenario.methods: different pathways of enrichment of the atmosphere of jupiter are considered, such as the accretion of enriched gas, pebbles, and planetesimals, and their implications for the oxygen abundance of jupiter are discussed.results: the super-solar nitrogen abundance in jupiter necessitates the accretion of extra n2 from the proto-solar nebula. the only location of the disk where this can happen is outside or just inside the n2 ice line. these constraints favor a pebble accretion origin of jupiter, from the perspective of composition and planet formation. we predict that jupiter's oxygen abundance is between 3.6 and 4.5 times solar. | jupiter formed as a pebble pile around the n2 ice line |
we present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova (slsn) sn 2015bn, at redshift z = 0.1136, spanning +250-400 days after maximum light. the light curve exhibits a steepening in the decline rate from 1.4 mag (100 days)-1 to 1.7 mag (100 days)-1, suggestive of a significant decrease in the opacity. this change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium, and magnesium. there are no obvious signatures of circumstellar interaction or large 56ni mass. we show that the spectrum at +400 days is virtually identical to a number of energetic sne ic such as sn 1997dq, sn 2012au, and sn 1998bw, indicating similar core conditions and strengthening the link between “hypernovae”/long gamma-ray bursts and slsne. a single explosion mechanism may unify these events that span absolute magnitudes of -22 < mb< -17. both the light curve and spectrum of sn 2015bn are consistent with an engine-driven explosion ejecting 7-30 m ⊙ of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). a strong and relatively narrow o i λ7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine. | superluminous supernova sn 2015bn in the nebular phase: evidence for the engine-powered explosion of a stripped massive star |
convergent disk migration has long been suspected to be responsible for forming planetary systems with a chain of mean-motion resonances (mmrs). dynamical evolution over time could disrupt the delicate resonant configuration. we present toi-1136, a 700 ± 150 myr old g star hosting at least six transiting planets between ~2 and 5 r ⊕. the orbital period ratios deviate from exact commensurability by only 10-4, smaller than the ~10-2 deviations seen in typical kepler near-resonant systems. a transit-timing analysis measured the masses of the planets (3-8m ⊕) and demonstrated that the planets in toi-1136 are in true resonances with librating resonant angles. based on a rossiter-mclaughlin measurement of planet d, the star's rotation appears to be aligned with the planetary orbital planes. the well-aligned planetary system and the lack of a detected binary companion together suggest that toi-1136's resonant chain formed in an isolated, quiescent disk with no stellar flyby, disk warp, or significant axial asymmetry. with period ratios near 3:2, 2:1, 3:2, 7:5, and 3:2, toi-1136 is the first known resonant chain involving a second-order mmr (7:5) between two first-order mmrs. the formation of the delicate 7:5 resonance places strong constraints on the system's migration history. short-scale (starting from ~0.1 au) type-i migration with an inner disk edge is most consistent with the formation of toi-1136. a low disk surface density (σ1 au ≲ 103g cm-2; lower than the minimum-mass solar nebula) and the resultant slower migration rate likely facilitated the formation of the 7:5 second-order mmr. | toi-1136 is a young, coplanar, aligned planetary system in a pristine resonant chain |
the nature of fast radio bursts (frb) has been extensively debated. here we investigate frb121102, detected at arecibo telescope and remarkable for its unusually large spectral index. after extensive study we conclude that the spectral index is caused by a nebula with free-free absorption. we find that putative nebula must lie beyond the milky way. we conclude that frbs are of extra-galactic origin and that they arise in dense star-forming regions. the challenge with extra-galactic models is the the high volumetric rate of frbs. this high rate allows us to eliminate all models of catastrophic stellar deaths. hyper-giant flares from young magnetars emerge as the most likely progenitors. some of the consequences are: (i) intergalactic frb models can be safely ignored. (ii) the rich ism environment of young magnetars can result in significant contribution to dm, rotation measure (rm) and in some cases to significant free-free optical depth. (iii) the star-forming regions in the host galaxies can contribute significantly to the dm. including this contribution reduces the inferred distances to frbs and correspondingly increases the volumetric rate of frbs (and, in turn, may require that giant flares can also produce frbs). (iv) frbs are likely to be suppressed at lower frequencies. conversely, searching for frbs at higher frequencies (2-5 ghz) would be attractive. (v) the blast wave which produces the radio emission can undergo rapid deceleration if the circum-burst medium is dense (as maybe the case for frb121102), leading to x-ray, radio and possibly gamma-ray emission. (vi) galaxies with high star formation rate host will have a higher frb rate. however, such frbs will have differing dms owing to differing local contributions. (vi) the dm and rm of frbs will prove to be noisy probes of the intergalactic medium (density, magnetic field) and cosmography. | the arecibo fast radio burst: dense circum-burst medium |
we present a new basis for scaling abundances with total metallicity in nebular photoionization models, based on extensive milky way stellar abundance data, to replace the uniform scaling normally used in the analysis of h ii regions. our goal is to provide a single scaling method and local abundance reference standard for use in nebular modelling and its key inputs, the stellar atmosphere and evolutionary track models. we introduce a parametric enrichment factor, ζ, to describe how atomic abundances scale with total abundance, which allows for a simple conversion between scales based on different reference elements (usually oxygen or iron). the models and parametric description provide a more physically realistic approach than simple uniform abundance scaling. with appropriate parameters, the methods described here may be applied to h ii regions in the milky way, large and dwarf galaxies in the local universe, active galactic nuclei, and to star-forming regions at high redshift. | abundance scaling in stars, nebulae and galaxies |
we analyze the optical continuum of star-forming galaxies in the sloan digital sky survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. we fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass-star formation rate and the stellar mass-gas-phase metallicity relations, respectively. we also fit linear combinations of single-burst models with a range of metallicities and ages. star formation and chemical evolution histories are unconstrained for these models. the stellar mass-stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. these relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. we measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. however, stellar continuum attenuation is smaller than nebular emission line attenuation. the continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies. | stellar absorption line analysis of local star-forming galaxies: the relation between stellar mass, metallicity, dust attenuation, and star formation rate |
fast radio bursts (frbs) are observed to be highly polarized. most have high linear polarization but a small fraction shows significant circular polarization. we systematically investigate a variety of polarization mechanisms of frbs within the magnetar theoretical framework considering two emission sites inside and outside the magnetosphere. for each site, we discuss both intrinsic radiation mechanisms and propagation effects. inside the magnetosphere, we investigate the polarization properties of both coherent curvature radiation and inverse compton scattering by charged bunches and conclude that both mechanisms produce 100 per cent linear polarization at an on-axis geometry but can produce circular polarization if the viewing angle is off axis. the lack of circular polarization for the majority of bursts requires that the bunches have a large transverse dimension size. resonant cyclotron absorption within magnetosphere may produce high circular polarization if electrons and positrons have an asymmetric lorentz factor distribution. outside the magnetosphere, the synchrotron maser emission mechanism in general produces highly linearly polarized emission. circular polarization would appear at off-beam angles but the flux is greatly degraded and such bursts are not detectable at cosmological distances. synchrotron absorption in a nebula with ordered magnetic field may reduce the circular polarization degree. cyclotron absorption in a strongly magnetized medium may generate significant circular polarization. faraday conversion in a medium with field reversal can convert one polarization mode to another. the two absorption processes require stringent physical conditions. significant faraday conversion may be realized in a magnetized dense environment involving binary systems or supernova remnants. | polarization of fast radio bursts: radiation mechanisms and propagation effects |
sbs 0335 - 052e, one of the most metal-poor (z ∼ 3-4{{ per cent}} z⊙) he ii-emitter starbursts known in the nearby universe, is studied using optical vlt/muse spectroscopic and chandra x-ray observations. we spatially resolved the spectral map of the nebular he ii λ4686 emission from which we derived for the first time the total he ii-ionizing energy budget of sbs 0335 - 052e. the nebular he ii line is indicative of a quite hard ionizing spectrum with photon energies > 4 ryd, and is observed to be more common at high-z than locally. our study rules out a significant contribution from x-ray sources and shocks to the he ii photoionization budget, indicating that the he+ excitation is mainly due to hot stellar continua. we discovered a new wr knot, but we also discard single wolf-rayet stars as the main responsible for the he ii ionization. by comparing observations with current models, we found that the he ii-ionization budget of sbs 0335 - 052e can only be produced by either single, rotating metal-free stars or a binary population with z ∼ 10-5 and a `top-heavy' initial mass function. this discrepancy between the metallicity of such stars and that of the h ii regions in sbs 0335 - 052e is similar to results obtained by kehrig et al. for the very metal-deficient he ii-emitting galaxy izw18. these results suggest that the he ii ionization is still beyond the capabilities of state-of-the-art models. extremely metal-poor, high-ionizing starbursts in the local universe, like sbs 0335 - 052e, provide unique laboratories for exploring in detail the extreme conditions likely prevailing in the reionization era. | the extended he ii λ4686 emission in the extremely metal-poor galaxy sbs 0335 - 052e seen with muse |
we present muse deep integral-field unit spectroscopy of three planetary nebulae (pne) with high-abundance discrepancy factors (adf > 20): ngc 6778, m 1-42, and hf 2-2. we have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (te), electron density (ne), and ionic abundances maps of a number of ionic species. the effects of the contribution of recombination to the auroral [n ii] and [o ii] lines on te and the abundance maps of low-ionization species are evaluated using recombination diagnostics. as a result, low te values and a downward gradient of te are found toward the inner zones of each pn. spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of pne, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with 'normal' metal content. we have simultaneously constructed, for the first time, the adf maps of o+ and o2+ and found that they centrally peak for all three pne under study. we show that the main issue when trying to compute realistic abundances from either orls or cels is to estimate the relative contribution of each gas component to the h i emission, and we present a method to evaluate it. it is also found that, for the studied high-adf pne, the amount of oxygen in the cold and warm regions is of the same order. | muse spectroscopy of planetary nebulae with high abundance discrepancies |
metal-poor nearby galaxies hosting massive stars have a fundamental role to play in our understanding of both high-redshift galaxies and low-metallicity stellar populations. but while much attention has been focused on their bright nebular gas emission, the massive stars that power it remain challenging to constrain. here we present exceptionally deep hubble space telescope ultraviolet spectra targeting six local (z < 0.02) galaxies that power strong nebular c iv emission approaching that encountered at z > 6. we find that the strength and spectral profile of the nebular c iv in these new spectra follow a sequence evocative of resonant scattering models, indicating that the hot circumgalactic medium likely plays a key role in regulating c iv escape locally. we constrain the metallicity of the massive stars in each galaxy by fitting the forest of photospheric absorption lines, reporting measurements driven by iron that lie uniformly below 10% solar. comparison with the gas-phase oxygen abundances reveals evidence for enhancement in o/fe 2-4 times above solar across the sample, robust to assumptions about the absolute gas-phase metallicity scale. this supports the idea that these local systems are more chemically similar to their primordial high-redshift counterparts than to the bulk of nearby galaxies. finally, we find significant tension between the strong stellar wind profiles observed and our population synthesis models constrained by the photospheric forest in our highest-quality spectra. this reinforces the need for caution in interpreting wind lines in isolation at high redshift, but also suggests a unique path toward validating fundamental massive star physics at extremely low metallicity with integrated ultraviolet spectra. | direct constraints on the extremely metal-poor massive stars underlying nebular c iv emission from ultra-deep hst/cos ultraviolet spectroscopy |
finding reliable indicators of lyman continuum (ly c) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionization, where direct measurements of ly c flux are impossible. to this end, here we investigate whether strong c iv λλ1548, 1550 emission in the rest-frame uv spectra of galaxies traces conditions ripe for ample production and escape of ly c photons. we compile a sample of 19 star-forming galaxies in the redshift range $z$ = 3.1-4.6 from the vandels survey that exhibit strong c iv emission, producing a stacked spectrum where all major rest-uv emission lines are clearly detected. best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($z=0.1--0.2\, z_\odot$), young stellar ages ($\log (\rm {age\,yr^{-1}}) = 6.1--6.5$), a high ionization parameter (log u = -2) and little to no dust attenuation (e(b - v) = 0.00-0.01). however, these models are unable to fully reproduce the observed c iv and he ii line strengths. we find that the ly α line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant ly c photon leakage along the line of sight. the covering fractions of low-ionization interstellar absorption lines are also low, implying ly c escape fraction in the range ≈0.05-0.30, with signatures of outflowing gas. finally, c iv/c iii] ratios of >0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant ly c leakage. overall, we report that multiple spectroscopic indicators of ly c leakage are present in the stacked spectrum of strong c iv emitting galaxies, potentially making c iv an important tracer of ly c photon escape at $z$ > 6. | strong c iv emission from star-forming galaxies: a case for high lyman continuum photon escape |
fullerenes have recently been detected in various circumstellar and interstellar environments, raising the question of their formation pathway. it has been proposed that they can form at the low densities found in the interstellar medium by the photo-chemical processing of large polycyclic aromatic hydrocarbons (pahs). following our previous work on the evolution of pahs in the ngc 7023 reflection nebula, we evaluate, using photochemical modelling, the possibility that the pah c66h20 (i.e. circumovalene) can lead to the formation of the c60 fullerene upon irradiation by ultraviolet photons. the chemical pathway involves full dehydrogenation of c66h20, folding into a floppy closed cage and shrinking of the cage by loss of c2 units until it reaches the symmetric c60 molecule. at 10'' from the illuminating star and with realistic molecular parameters, the model predicts that 100% of c66h20 is converted into c60 in ~105 yr, a timescale comparable to the age of the nebula. shrinking appears to be the kinetically limiting step of the whole process. hence, pahs larger than c66h20 are unlikely to contribute significantly to the formation of c60, while pahs containing between 60 and 66 c atoms should contribute to the formation of c60 with shorter timescales, and pahs containing fewer than 60 c atoms will be destroyed. assuming a classical size distribution for the pah precursors, our model predicts that absolute abundances of c60 are up to several 10-4 of the elemental carbon, that is, less than a percent of the typical interstellar pah abundance, which is consistent with observational studies. according to our model, once formed, c60 can survive much longer (> 107 yr for radiation fields below g0 = 104) than other fullerenes because of the remarkable stability of the c60 molecule at high internal energies. hence, a natural consequence is that c60 is more abundant than other fullerenes in highly irradiated environments. | top-down formation of fullerenes in the interstellar medium |
understanding high-mass star formation is one of the top-priority issues in astrophysics. recent observational studies have revealed that cloud-cloud collisions may play a role in high-mass star formation in several places in the milky way and the large magellanic cloud. the trifid nebula m20 is a well-known galactic h ii region ionized by a single o7.5 star. in 2011, based on the co observations with nanten2, we reported that the o star was formed by the collision between two molecular clouds ∼0.3 myr ago. those observations identified two molecular clouds toward m20, traveling at a relative velocity of 7.5 {km} {{{s}}}-1. this velocity separation implies that the clouds cannot be gravitationally bound to m20, but since the clouds show signs of heating by the stars there they must be spatially coincident with it. a collision is therefore highly possible. in this paper we present the new co j = 1-0 and j = 3-2 observations of the colliding clouds in m20 performed with the mopra and aste telescopes. the high-resolution observations revealed that the two molecular clouds have peculiar spatial and velocity structures, i.e., a spatially complementary distribution between the two clouds and a bridge feature that connects the two clouds in velocity space. based on a new comparison with numerical models, we find that this complementary distribution is an expected outcome of cloud-cloud collisions, and that the bridge feature can be interpreted as the turbulent gas excited at the interface of the collision. our results reinforce the cloud-cloud collision scenario in m20. | triggered o star formation in m20 via cloud-cloud collision: comparisons between high-resolution co observations and simulations |
context. for up to a few millions of years, pebbles must provide a quasi-steady inflow of solids from the outer parts of protoplanetary disks to their inner regions.aims: we wish to understand how a significant fraction of the pebbles grows into planetesimals instead of being lost to the host star.methods: we examined analytically how the inward flow of pebbles is affected by the snow line and under which conditions dust-rich (rocky) planetesimals form. when calculating the inward drift of solids that is due to gas drag, we included the back-reaction of the gas to the motion of the solids.results: we show that in low-viscosity protoplanetary disks (with a monotonous surface density similar to that of the minimum-mass solar nebula), the flow of pebbles does not usually reach the required surface density to form planetesimals by streaming instability. we show, however, that if the pebble-to-gas-mass flux exceeds a critical value, no steady solution can be found for the solid-to-gas ratio. this is particularly important for low-viscosity disks (α< 10-3) where we show that inside of the snow line, silicate-dust grains ejected from sublimating pebbles can accumulate, eventually leading to the formation of dust-rich planetesimals directly by gravitational instability.conclusions: this formation of dust-rich planetesimals may occur for extended periods of time, while the snow line sweeps from several au to inside of 1 au. the rock-to-ice ratio may thus be globally significantly higher in planetesimals and planets than in the central star. | formation of dust-rich planetesimals from sublimated pebbles inside of the snow line |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.