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we investigate the mass-metallicity relationship of star-forming galaxies by analyzing the absorption line spectra of ~200,000 galaxies in the sloan digital sky survey. the galaxy spectra are stacked in bins of stellar mass, and a population synthesis technique is applied yielding the metallicities, ages, and star formation history of the young and old stellar population together with interstellar reddening and extinction. we adopt different lengths of the initial starbursts and different initial mass functions for the calculation of model spectra of the single stellar populations contributing to the total integrated spectrum. we also allow for deviations of the ratio of extinction to reddening rvfrom 3.1 and determine the value from the spectral fit. we find that burst length and rvhave a significant influence on the determination of metallicities, whereas the effect of the initial mass function is small. the rvvalues are larger than 3.1. the metallicities of the young stellar population agree with extragalactic spectroscopic studies of individual massive supergiant stars and are significantly higher than those of the older stellar population. this confirms galaxy evolution models where metallicity depends on the ratio of gas to stellar mass and where this ratio decreases with time. star formation history is found to depend on galaxy stellar mass. massive galaxies are dominated by stars formed at early times. | mass-metallicity relationship of sdss star-forming galaxies: population synthesis analysis and effects of star burst length, extinction law, initial mass function, and star formation rate |
we present analytical reconstructions of sn ia delay time distributions (dtds) by way of two independent methods: by a markov chain monte carlo best-fit technique comparing the volumetric sn ia rate history to today's compendium cosmic star formation history, and second through a maximum likelihood analysis of the star formation rate histories of individual galaxies in the goods/candels field, in comparison to their resultant sn ia yields. we adopt a flexible skew-normal dtd model, which could match a wide range of physically motivated dtd forms. we find a family of solutions that are essentially exponential dtds, similar in shape to the β ≈ -1 power-law dtds, but with more delayed events (>1 gyr in age) than prompt events (<1 gyr). comparing these solutions to delay time measures separately derived from field galaxies and galaxy clusters, we find the skew-normal solutions can accommodate both without requiring a different dtd form in different environments. these model fits are generally inconsistent with results from single-degenerate binary population synthesis models, and are seemingly supportive of double-degenerate progenitors for most sn ia events. | delay time distributions of type ia supernovae from galaxy and cosmic star formation histories |
using stellar population synthesis models to infer star formation histories (sfhs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of sunyaev-zel'dovich (sz)-selected galaxy clusters across a wide range of redshifts. we calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the python-based prospector framework, from 61 clusters in the spt-gmos spectroscopic survey (0.3 < z < 0.9) and three clusters in the spt hi-z cluster sample (1.25 < z < 1.4). we analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. we find that quiescent galaxies in our data set sample a diversity of sfhs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t 50) of z = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. we also report median age-stellar mass relations for the full sample (age of the universe at t 50 (gyr) = 2.52 (±0.04)-1.66 (±0.12) log10(m/1011 m ⊙)) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ~0.75 gyr earlier than lower-mass galaxies. we also find marginally steeper age-mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass. | synthesizing stellar populations in south pole telescope galaxy clusters. i. ages of quiescent member galaxies at 0.3 < z < 1.4 |
stellar population synthesis (sps) models are invaluable to study star clusters and galaxies. they provide means to extract stellar masses, stellar ages, star formation histories, chemical enrichment, and dust content of galaxies from their integrated spectral energy distributions, colours, or spectra. as most models, they contain uncertainties that can hamper our ability to model and interpret observed spectra. this work aims at studying a specific source of model uncertainty: the choice of an empirical versus a synthetic stellar spectral library. empirical libraries suffer from limited coverage of parameter space, while synthetic libraries suffer from modelling inaccuracies. given our current inability to have both ideal stellar-parameter coverage with ideal stellar spectra, what should one favour: better coverage of the parameters (synthetic library) or better spectra on a star-by-star basis (empirical library)? to study this question, we build a synthetic stellar library mimicking the coverage of an empirical library, and sps models with different choices of stellar library tailored to these investigations. through the comparison of model predictions and the spectral fitting of a sample of nearby galaxies, we learned that predicted colours are more affected by the coverage effect than the choice of a synthetic versus empirical library; the effects on predicted spectral indices are multiple and defy simple conclusions; derived galaxy ages are virtually unaffected by the choice of the library, but are underestimated when sps models with limited parameter coverage are used; metallicities are robust against limited hrd coverage, but are underestimated when using synthetic libraries. | to use or not to use synthetic stellar spectra in population synthesis models? |
the presence of massive quiescent galaxies at high redshifts is still a challenge for most models of galaxy formation. the aim of this work is to compare the observed number density and properties of these galaxies with the predictions of state-of-the-art models. the sample of massive quiescent galaxies has been selected from the cosmos2015 photometric catalog with z phot ≥ 2.5, {log}({m}* /{m}⊙ )≥slant 10.5, and a specific star formation rate (ssfr) of {log}({ssfr} [{yr}}-1])≤slant -11. the photometric spectral energy distributions (seds) of the selected galaxies have been thoroughly analyzed based on different stellar population synthesis models. the final sample includes only those galaxies qualified as quiescent in all sed fitting runs. the observed properties have been compared to theoretical models: the number density of quiescent galaxies with 10.5≤slant {log}({m}* /{m}⊙ )< 10.8 is reproduced by some models, although there is a large scatter in their predictions. instead, very massive {log}({m}* /{m}⊙ )≥slant 10.8 are underpredicted by most of the current models of galaxy formation: some of them, built on the carnage simulation, are consistent with data up to z ∼ 4, while at higher redshifts the volume of the considered simulation is too small to find such rare objects. simulated galaxies that match the observed properties in the ssfr-m * plane at z ∼ 3 have been analyzed by reconstructing their evolutionary paths: their merger trees suggest that agn feedback could be the key process allowing for a rapid quenching of the star formation at z ≳ 4 and that its treatment should be improved in models. | quiescent galaxies at z ≳ 2.5: observations versus models |
we present the results of a new study of dust attenuation at redshifts 3 < z < 4 based on a sample of 236 star-forming galaxies from the vandels spectroscopic survey. motivated by results from the first billion years (fiby) simulation project, we argue that the intrinsic spectral energy distributions (seds) of star-forming galaxies at these redshifts have a self-similar shape across the mass range 8.2 ≤ log (m⋆/m⊙) ≤ 10.6 probed by our sample. using fiby data, we construct a set of intrinsic sed templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (sps) model assumptions. with this set of intrinsic seds, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. we find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at z ≃ 3.5 is similar in shape to the commonly adopted calzetti starburst law, with an average total-to-selective attenuation ratio of rv = 4.18 ± 0.29. in contrast, we find that an average attenuation curve as steep as the smc extinction law is strongly disfavoured. we show that the optical attenuation (av) versus stellar mass (m⋆) relation predicted using our method is consistent with recent alma observations of galaxies at 2 < z < 3 in the hubble ultra deep field (hudf), as well as empirical av - m⋆ relations predicted by a calzetti-like law. in fact, our results, combined with other literature data, suggest that the av-m⋆ relation does not evolve over the redshift range 0 < z < 5, at least for galaxies with log(m⋆/m⊙) ≳ 9.5. finally, we present tentative evidence which suggests that the attenuation curve may become steeper at lower masses log(m⋆/m⊙) ≲ 9.0. | the vandels survey: dust attenuation in star-forming galaxies at z = 3-4 |
the recent discovery of a neutron star accretor in the ultra-luminous x-ray (ulx) source m82 x-2 challenges our understanding of high-mass x-ray binary formation and evolution. by combining binary population synthesis and detailed mass-transfer models, however, we show that the binary parameters of m82 x-2 are not surprising provided non-conservative mass transfer is allowed. specifically, the donor-mass lower limit and orbital period measured for m82 x-2 lie near the most probable values predicted by population synthesis models, and systems such as m82 x-2 should exist in approximately 13% of the galaxies with a star formation history similar to m82. we conclude that the binary system that formed m82 x-2 is most likely less than 50 myr old and contains a donor star which had an initial mass of approximately 8-10 m ⊙ , while the ns’s progenitor star had an initial mass in the 8-25 m ⊙range. the donor star still currently resides on the main sequence, and is capable of continued mt on the thermal timescale, while in the ulx regime, for as long as 400,000 yr. | on the formation of ultraluminous x-ray sources with neutron star accretors: the case of m82 x-2 |
systematic variations of the initial mass function (imf) in early-type galaxies, and their connection with possible drivers such as velocity dispersion or metallicity, have been much debated in recent years. strong lensing over galaxy scales combined with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the imf. we combine photometric and spectroscopic constraints from the latest set of population synthesis models of charlot & bruzual, including a varying imf, with a non-parametric analysis of the lens masses of 18 etgs from the slacs survey, with velocity dispersions in the range 200-300 km s-1. we find that very bottom-heavy imfs are excluded. however, the upper limit to the bimodal imf slope (μ ≲ 2.2, accounting for a dark matter fraction of 20-30 per cent, where μ = 1.3 corresponds to a kroupa-like imf) is compatible at the 1σ level with constraints imposed by gravity-sensitive line strengths. a two-segment power-law parametrization of the imf (salpeter-like for high masses) is more constrained (γ ≲ 1.5, where γ is the power index at low masses) but requires a dark matter contribution of ≳25 per cent to reconcile the results with a salpeter imf. for a standard milky way-like imf to be applicable, a significant dark matter contribution is required within 1re. our results reveal a large range of allowed imf slopes, which, when interpreted as intrinsic scatter in the imf properties of etgs, could explain the recent results of smith et al., who find milky way-like imf normalizations in a few massive lensing etgs. | strong gravitational lensing and the stellar imf of early-type galaxies |
stellar population synthesis (sps) models are used to infer many galactic properties including star formation histories, metallicities, and stellar and dust masses. however, most sps models neglect the effect of circumstellar dust shells around evolved stars and it is unclear to what extent they impact the analysis of spectral energy distributions (seds). to overcome this shortcoming we have created a new set of circumstellar dust models, using the radiative transfer code dusty, for asymptotic giant branch (agb) stars and incorporated them into the flexible stellar population synthesis code. the circumstellar dust models provide a good fit to individual agb stars as well as the ir color-magnitude diagrams of the large and small magellanic clouds. ir luminosity functions from the large and small magellanic clouds are not well-fit by the 2008 padova isochrones when coupled to our circumstellar dust models and so we adjusted the lifetimes of agb stars in the models to provide a match to the data. we show, in agreement with previous work, that circumstellar dust from agb stars can make a significant contribution to the ir (≳ 4 μ m) emission from galaxies that contain relatively little diffuse dust, including low-metallicity and/or non-star-forming galaxies. our models provide a good fit to the mid-ir spectra of early-type galaxies. circumstellar dust around agb stars appears to have a small effect on the ir seds of metal-rich star-forming galaxies (i.e., when av ≳ 0.1). stellar population models that include circumstellar dust will be needed to accurately interpret data from the james webb space telescope and other ir facilities. | circumstellar dust around agb stars and implications for infrared emission from galaxies |
the delay time distribution (dtd) of type-ia supernovae (sne ia) is important for understanding chemical evolution, sn ia progenitors, and sn ia physics. past estimates of the dtd in galaxy clusters have been deduced from sn ia rates measured in cluster samples observed at various redshifts, corresponding to different time intervals after a presumed initial brief burst of star formation. a recent analysis of a cluster sample at z = 1.13-1.75 confirmed indications from previous studies of lower redshift clusters, that the dtd has a power-law form, dtd(t) = r1(t/gyr)α, with amplitude r1, at delay $t=1\,\rm gyr$ , several times higher than measured in field-galaxy environments. this implied that sne ia are somehow produced in larger numbers by the stellar populations in clusters. this conclusion, however, could have been affected by the implicit assumption that the stars were formed in a single brief starburst at high z. here, we re-derive the dtd from the cluster sn ia data, but relax the single-burst assumption. instead, we allow for a range of star-formation histories and dust extinctions for each cluster. via mcmc modelling, we simultaneously fit, using stellar population synthesis models and dtd models, the integrated galaxy-light photometry in several bands, and the sn ia numbers discovered in each cluster. with these more-realistic assumptions, we find a best-fitting dtd with power-law index $\alpha =-1.09_{-0.12}^{+0.15}$ , and amplitude $r_1=0.41_{-0.10}^{+0.12}\times 10^{-12}\,{\rm yr}^{-1}\, {\rm m}_\odot ^{-1}$ . we confirm a cluster-environment dtd with a larger amplitude than the field-galaxy dtd, by a factor ∼2-3 (at 3.8σ). cluster and field dtds have consistent slopes of α ≈ -1.1. | the delay time distribution of type-ia supernovae in galaxy clusters: the impact of extended star-formation histories |
this work presents an in-depth analysis of four gravitationally lensed red galaxies at z = 1.6-3.2. the sources are magnified by factors of 2.7-30 by foreground clusters, enabling spectral and morphological measurements that are otherwise challenging. our sample extends below the characteristic mass of the stellar mass function and is thus more representative of the quiescent galaxy population at z > 1 than previous spectroscopic studies. we analyze deep vlt/x-shooter spectra and multiband hubble space telescope photometry that cover the rest-frame uv-to-optical regime. the entire sample resembles stellar disks as inferred from lensing-reconstructed images. through stellar population synthesis analysis, we infer that the targets are young (median age = 0.1-1.2 gyr) and formed 80% of their stellar masses within 0.07-0.47 gyr. mg ii λλ 2796, 2803 absorption is detected across the sample. blueshifted absorption and/or redshifted emission of mg ii are found in the two youngest sources, indicative of a galactic-scale outflow of warm (t ~ 104 k) gas. the [o iii] λ5007 luminosity is higher for the two young sources (median age less than 0.4 gyr) than the two older ones, perhaps suggesting a decline in nuclear activity as quenching proceeds. despite high-velocity (v ≈ 1500 km s-1) galactic-scale outflows seen in the most recently quenched galaxies, warm gas is still present to some extent long after quenching. altogether, our results indicate that star formation quenching at high redshift must have been a rapid process (<1 gyr) that does not synchronize with bulge formation or complete gas removal. substantial bulge growth is required if they are to evolve into the metal-rich cores of present-day slow rotators. | an exquisitely deep view of quenching galaxies through the gravitational lens: stellar population, morphology, and ionized gas |
this work focuses on the gas chemical composition of cgcg007-025. this compact dwarf is undergoing a galaxy wide star-forming burst, whose spatial behaviour has been observed by vlt/muse. we present a new line measurement library to treat almost 7800 voxels. the direct method chemical analysis is limited to 484 voxels with good detection of the $[\mathrm{s}\, {\small iii}]6312\, \mathring{\rm a}$ temperature diagnostic line. the recombination fluxes are corrected for stellar absorption via a population synthesis. additionally, we discuss a new algorithm to fit photoionization models via neural networks. the eight ionic abundances analysed show a spatial normal distribution with a $\sigma \sim 0.1\, {\rm dex}$, where only half this value can be explained by the uncertainty in the measurements. the oxygen abundance distribution is 12 + log(o/h) = 7.88 ± 0.11. the ${\it t}_{e}[\mathrm{s}\, {\small iii}]$ and ne[s ii] are also normally distributed. however, in the central and brightest region, the ne[s ii] is almost thrice the mean galaxy value. this is also reflected in the extinction measurements. the ionization parameter has a distribution of ${\rm log}(u) = -2.52^{0.17}_{0.19}$. the parameter spatial behaviour agrees with the s2+/s+ map. finally, the discrepancies between the direct method and the photoionization model fitting are discussed. in the latter technique, we find that mixing lines with uneven uncertainty magnitudes can impact the accuracy of the results. in these fittings, we recommend overestimating the minimum flux uncertainty one order below the maximum line flux uncertainty. this provides a better match with the direct method. | the resolved chemical composition of the starburst dwarf galaxy cgcg007-025: direct method versus photoionization model fitting |
we study the evolution in the number density of galaxies at the highest stellar masses over the past ≈9 gyr (0.4< z< 1.5) using the spitzer/hetdex exploratory large-area survey (shela). shela includes complete imaging in eight photometric bands spanning 0.3-4.5 μm over 17.5 deg2 within the sdss stripe 82 field. the size of shela produces the lowest counting uncertainties and cosmic variance yet for massive galaxies at z ∼ 1.0. we study the evolution in the intrinsic stellar mass function (smf) for galaxies with log(m*/m⊙) > 10.3 using a forward-modeling method that takes into full account the statistical and systematic uncertainties on stellar mass. from z = 0.4 to 1.5, the evolution in the massive end of the intrinsic smf shows minimal change in its shape: the characteristic mass (m*) evolves by less than 0.1 dex (±0.05 dex); furthermore, the number density of galaxies with log m*/m⊙ > 11 stays roughly constant at log (n/mpc-3)≃ -3.4 (±0.05) from z = 1 to z = 0.4, consistent with no evolution, then declines to log n/mpc-3 = -3.7 (±0.05) at z = 1.5. we discuss the uncertainties in the derived smf, which are dominated by assumptions in the star formation history and details of stellar population synthesis models for stellar mass estimations. we also study the evolution in the smf for samples of star-forming and quiescent galaxies selected by their specific star formation rate. for quiescent galaxies, the data are consistent with no (or slight) evolution (≲0.1 dex) in either the characteristic mass or number density from z ∼ 1.5 to the present even after accounting for the systematic uncertainty and the random error in the stellar mass measurement. the lack of number density evolution in the quiescent massive galaxy population means that any mass growth (presumably through "dry" mergers) must balance the rate of stellar mass losses owing to processes of late-stage stellar evolution and the formation of newly quiescent galaxies from the star-forming population. we provide an upper limit on this mass growth from z = 1.0 to 0.4 of δm*/m* = 45% (i.e., ≃0.16 dex) for quiescent galaxies more massive than 1011 m⊙. | on the (lack of) evolution of the stellar mass function of massive galaxies from z = 1.5 to 0.4 |
the probability number distribution function of binary black hole mergers observed by ligo/virgo o3a has double peaks as a function of chirp mass mchirp, total mass mtotal, primary black hole mass m1, and secondary one m2, respectively. the larger chirp mass peak is at mchirp≅ 30 m⊙. the distribution of m2 versus m1 follows the relation of m2≅ 0.7m1. for initial mass functions of population iii stars in the form of f(m) ∝ m-α, population synthesis numerical simulations with 0 ≤ α ≤ 1.5 are consistent with o3a data for mchirp ≳ 20 m⊙. the distribution of m2 versus m1 for simulation data also agrees with m2 ≅ 0.7m1 relation of o3a data. | gravitational waves from population iii binary black holes are consistent with ligo/virgo o3a data for the chirp mass larger than ∼20 m⊙ |
contact. strong lenses are a biased subset of the general population of galaxies.aims: the goal of this work is to quantify how lens galaxies and lensed sources differ from their parent distribution, namely the strong lensing bias.methods: we first studied how the strong lensing cross-section varies as a function of lens and source properties. then, we simulated strong lensing surveys with data similar to that expected for euclid and measured the strong lensing bias in different scenarios. we focused particularly on two quantities: the stellar population synthesis mismatch parameter, αsps, defined as the ratio between the true stellar mass of a galaxy and the stellar mass obtained from photometry, and the central dark matter mass at fixed stellar mass and size.results: strong lens galaxies are biased towards higher stellar masses, smaller half-mass radii, and higher dark matter masses. the amplitude of the bias depends on the intrinsic scatter in the mass-related parameters of the galaxy population and on the completeness in einstein radius of the lens sample. for values of the scatter that are consistent with observed scaling relations and a minimum detectable einstein radius of 0.5″, the strong lensing bias in αsps is 10%, while that in the central dark matter mass is 5%. the bias has little dependence on the properties of the source population: samples of galaxy-galaxy lenses and galaxy-quasar lenses that probe the same einstein radius distribution are biased in a very similar way.conclusions: given current uncertainties, strong lensing observations can be used directly to improve our current knowledge of the inner structure of galaxies, without the need to correct for selection effects. time-delay measurements of h0 from lensed quasars can take advantage of prior information obtained from galaxy-galaxy lenses with similar einstein radii. | strong lensing selection effects |
context. current research has established magnetised disc winds as a promising way of driving accretion in protoplanetary discs.aims: we investigate the evolution of large protoplanetary disc populations under the influence of magnetically driven disc winds as well as internal and external photoevaporation. we aim to constrain magnetic disc wind models through comparisons with observations.methods: we ran 1d vertically integrated evolutionary simulations for low-viscosity discs, including magnetic braking and various outflows. the initial conditions were varied and chosen to produce populations that are representative of actual disc populations inferred from observations. we then compared the observables from the simulations (e.g. stellar accretion rate, disc mass evolution, disc lifetime, etc.) with observational data.results: our simulations show that to reach stellar accretion rates comparable to those found by observations (~10−8 m⊙ yr−1), it is necessary to have access not only to strong magnetic torques, but weak magnetic winds as well. the presence of a strong magnetic disc wind, in combination with internal photoevaporation, leads to the rapid opening of an inner cavity early on, allowing the stellar accretion rate to drop while the disc is still massive. furthermore, our model supports the notion that external photoevaporation via the ambient far-ultraviolet radiation of surrounding stars is a driving force in disc evolution and could potentially exert a strong influence on planetary formation.conclusions: our disc population syntheses show that for a subset of magnetohydrodynamic wind models (weak disc wind, strong torque), it is possible to reproduce important statistical observational constraints. the magnetic disc wind paradigm thus represents a novel and appealing alternative to the classical α-viscosity scenario. | population study on mhd wind-driven disc evolution. confronting theory and observation |
we present gemini/gnirs cross-dispersed near-infrared spectra of 12 nearby early-type galaxies, with the aim of testing commonly used stellar population synthesis models. we select a subset of galaxies from the atlas3d sample which span a wide range of ages (single stellar population equivalent ages of 1-15 gyr) at approximately solar metallicity. we derive star formation histories using four different stellar population synthesis models, namely those of bruzual & charlot, conroy, gunn & white, maraston & strömbäck and vazdekis et al. we compare star formation histories derived from near-infrared spectra with those derived from optical spectra using the same models. we find that while all models agree in the optical, the derived star formation histories vary dramatically from model to model in the near-infrared. we find that this variation is largely driven by the choice of stellar spectral library, such that models including high-quality spectral libraries provide the best fits to the data, and are the most self-consistent when comparing optically derived properties with near-infrared ones. we also find the impact of age variation in the near-infrared to be subtle, and largely encoded in the shape of the continuum, meaning that the common approach of removing continuum information with a high-order polynomial greatly reduces our ability to constrain ages in the near-infrared. | comparison of stellar population model predictions using optical and infrared spectroscopy |
our proximity and external vantage point make m31 an ideal testbed for understanding the structure of spiral galaxies. the andromeda optical and infrared disk survey (androids) has mapped m31's bulge and disk out to r=40 kpc in ugrijks bands with cfht using a careful sky calibration. we use bayesian modelling of the optical-infrared spectral energy distribution (sed) to estimate profiles of m31's stellar populations and mass along the major axis. this analysis provides evidence for inside-out disk formation and a declining metallicity gradient. m31's i-band mass-to-light ratio (m/li *) decreases from 0.5 dex in the bulge to ~ 0.2 dex at 40 kpc. the best-constrained stellar population models use the full ugrijks sed but are also consistent with optical-only fits. therefore, while nir data can be successfully modelled with modern stellar population synthesis, nir data do not provide additional constraints in this application. fits to the gi-sed alone yield m/li * that are systematically lower than the full sed fit by 0.1 dex. this is still smaller than the 0.3 dex scatter amongst different relations for m/li via g - i colour found in the literature. we advocate a stellar mass of m *(30 kpc) = 10.3+2.3 -1.7 × 1010 m⊙ for the m31 bulge and disk. | the stellar mass of m31 as inferred by the andromeda optical & infrared disk survey |
the predicted and observed space density of cataclysmic variables (cvs) has been for a long time discrepant by at least an order of magnitude. the standard model of cv evolution predicts that the vast majority of cvs should be period bouncers, whose space density has been recently measured to be ρ ≲ 2 × 10-5 pc-3. we performed population synthesis of cvs using an updated version of the binary stellar evolution (bse) code for single and binary star evolution. we find that the recently suggested empirical prescription of consequential angular momentum loss (caml) brings into agreement predicted and observed space densities of cvs and period bouncers. to progress with our understanding of cv evolution it is crucial to understand the physical mechanism behind empirical caml. our changes to the bse code are also provided in details, which will allow the community to accurately model mass transfer in interacting binaries in which degenerate objects accrete from low-mass main-sequence donor stars. | no cataclysmic variables missing: higher merger rate brings into agreement observed and predicted space densities |
the chemical compositions of stars encode those of the gas from which they formed, providing important clues regarding the formation histories of galaxies. a powerful diagnostic is the abundance of α elements (o, mg, si, s, ca and ti) relative to iron, [α/fe]. the α elements are synthesized and injected into the interstellar medium by type ii supernovae, which occur about ten million years after their originating stars form; by contrast, iron is returned to the interstellar medium by type ia supernovae, which occur after a much longer timescale of roughly one billion years1. periods of rapid star formation therefore tend to produce high-[α/fe] stellar populations (because only type ii supernovae have time to contribute to interstellar-medium enrichment as the stellar population forms), whereas low-[α/fe] stars require periods of star formation that last more than a few billion years (over which timescales type ia supernovae begin to affect the elemental composition of the interstellar medium more strongly than type ii supernovae). the existence of two distinct groups of stars in the solar neighbourhood2-7, one with high [α/fe] and the other with low [α/fe], therefore suggests two different origins, but the mechanism by which this bimodal distribution arose remains unknown. here we use a model of disk-galaxy evolution to show that the two episodes of star formation8 predicted by the `cold flow' theory of galactic gas accretion9,10 also explain the observed chemical bimodality. in this scenario, the high-[α/fe] stars form early, during an initial phase of accretion that involves infalling streams of cold primordial gas. there is then a hiatus of around two billion years until the shock-heated gas in the galactic dark-matter halo has cooled as a result of radiation and can itself commence accretion. the low-[α/fe] stars form during this second phase. the peaks in these two star-formation episodes are separated by around five billion years. in addition, the large-scale variation in the abundance patterns of these two stellar populations that has been observed for the milky way5,7 is partially explained by the spatial variation in this gas-accretion history. | the formation of solar-neighbourhood stars in two generations separated by 5 billion years |
population synthesis studies constitute a powerful method to reconstruct the birth distribution of periods and magnetic fields of the pulsar population. when this method is applied to populations in different wavelengths, it can break the degeneracy in the inferred properties of initial distributions that arises from single-band studies. in this context, we extend previous works to include x-ray thermal emitting pulsars within the same evolutionary model as radio-pulsars. we find that the cumulative distribution of the number of x-ray pulsars can be well reproduced by several models that, simultaneously, reproduce the characteristics of the radio-pulsar distribution. however, even considering the most favourable magneto-thermal evolution models with fast field decay, lognormal distributions of the initial magnetic field overpredict the number of visible sources with periods longer than 12 s. we then show that the problem can be solved with different distributions of magnetic field, such as a truncated lognormal distribution, or a binormal distribution with two distinct populations. we use the observational lack of isolated neutron stars (nss) with spin periods p > 12 s to establish an upper limit to the fraction of magnetars born with b > 1015 g (less than 1 per cent). as future detections keep increasing the magnetar and high-b pulsar statistics, our approach can be used to establish a severe constraint on the maximum magnetic field at birth of nss. | population synthesis of isolated neutron stars with magneto-rotational evolution - ii. from radio-pulsars to magnetars |
we present the first single-burst stellar population models in the infrared wavelength range between 2.5 and 5 μm which are exclusively based on empirical stellar spectra. our models take as input 180 spectra from the stellar irtf (infrared telescope facility) library. our final single-burst stellar population models are calculated based on two different sets of isochrones and various types of initial mass functions of different slopes, ages larger than 1 gyr and metallicities between [fe/h] = -0.70 and 0.26. they are made available online to the scientific community on the miles web page. we analyse the behaviour of the spitzer [3.6]-[4.5] colour calculated from our single stellar population models and find only slight dependences on both metallicity and age. when comparing to the colours of observed early-type galaxies, we find a good agreement for older, more massive galaxies that resemble a single-burst population. younger, less massive and more metal-poor galaxies show redder colours with respect to our models. this mismatch can be explained by a more extended star formation history of these galaxies which includes a metal-poor or/and young population. moreover, the colours derived from our models agree very well with most other models available in this wavelength range. we confirm that the mass-to-light ratio determined in the spitzer [3.6] μm band changes much less as a function of both age and metallicity than in the optical bands. | stellar population synthesis models between 2.5 and 5 μm based on the empirical irtf stellar library |
we present the results of an analysis of pan-starrs1 medium deep survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. we use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. we characterize the structure and stellar content of the galaxy disks out to radii of about twice petrosian r 90, beyond which the halo light becomes significant. we measure normalized radial profiles for sub-samples of galaxies in three bins each of stellar mass and concentration. we also fit radial profiles to each galaxy. the majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r 90. however, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. we find that the mass/light ratio and stellar age radial profiles have a characteristic "u" shape. there is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the m/l ratio in the outer disk. as we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in m/l both decrease. our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk. | the structure and stellar content of the outer disks of galaxies: a new view from the pan-starrs1 medium deep survey |
the inverse problem of extracting the stellar population content of galaxy spectra is analysed here from a basic standpoint based on information theory. by interpreting spectra as probability distribution functions, we find that galaxy spectra have high entropy, thus leading to a rather low effective information content. the highest variation in entropy is unsurprisingly found in regions that have been well studied for decades with the conventional approach. we target a set of six spectral regions that show the highest variation in entropy - the 4000 å break being the most informative one. as a test case with real data, we measure the entropy of a set of high-quality spectra from the sloan digital sky survey, and contrast entropy-based results with the traditional method based on line strengths. the data are classified into star-forming (sf), quiescent (q), and active galactic nucleus (agn) galaxies, and show - independently of any physical model - that agn spectra can be interpreted as a transition between sf and q galaxies, with sf galaxies featuring a more diverse variation in entropy. the high level of entanglement complicates the determination of population parameters in a robust, unbiased way, and affects traditional methods that compare models with observations, as well as machine learning (especially deep learning) algorithms that rely on the statistical properties of the data to assess the variations among spectra. entropy provides a new avenue to improve population synthesis models so that they give a more faithful representation of real galaxy spectra. | the entropy of galaxy spectra: how much information is encoded? |
large surveys of star-forming regions have unveiled power-law correlations between the stellar mass and the disc parameters, such as the disc mass $m_{\mathrm{d}} \!-\! {m_{\star }}$ and the accretion rate $\dot{m} \!-\! {m_{\star }}$. the observed slopes appear to be increasing with time, but the reason behind the establishment of these correlations and their subsequent evolution is still uncertain. we conduct a theoretical analysis of the impact of viscous evolution on power-law initial conditions for a population of protoplanetary discs. we find that, for evolved populations, viscous evolution enforces the two correlations to have the same slope, λm = λacc, and that this limit is uniquely determined by the initial slopes λm, 0 and λacc, 0. we recover the increasing trend claimed from the observations when the difference in the initial values, δ0 = λm, 0-λacc, 0, is larger than 1/2; moreover, we find that this increasing trend is a consequence of a positive correlation between the viscous time-scale and the stellar mass. we also present the results of disc population synthesis numerical simulations, that allow us to introduce a spread and analyse the effect of sampling, which show a good agreement with our analytical predictions. finally, we perform a preliminary comparison of our numerical results with observational data, which allows us to constrain the parameter space of the initial conditions to λm, 0 ∈ [1.2, 2.1], λacc, 0 ∈ [0.7, 1.5]. | on the time evolution of the md-m⋆ and ṁ-m⋆ correlations for protoplanetary discs: the viscous time-scale increases with stellar mass |
we estimate the stellar mass for a sample of low surface brightness galaxies (lsbgs) by fitting their multiband spectral energy distributions (seds) to the stellar population synthesis model. the derived stellar masses (log m*/m⊙) span from 7.1 to 11.1, with a mean of log m*/m⊙ = 8.5, which is lower than that for normal galaxies. the stellar mass-to-light ratio (γ*) in each band varies little with the absolute magnitude but increases with higher m*. this trend of γ* with m* is even stronger in bluer bands. in addition, the γ* for our lsbgs slightly declines from the r band to the longer-wavelength bands. the log ${\gamma }_{* }^{j} (j = g, r, i, and z) have relatively tight relations with optical colors of g - r and g - i. compared with several representative γ*-color relations (mlcrs) from the literature, our mlcrs based on lsbg data are consistently among those literature mlcrs previously defined on diverse galaxy samples, and the existing minor differences between the mlcrs are caused by the differences in the sed model ingredients (including initial mass function, star formation history, and stellar population model), line fitting techniques, galaxy samples, and photometric zero-point, rather than the galaxy surface brightness itself, which distinguishes lsbgs from high surface brightness galaxies. our lsbgs would be very likely to follow those representative mlcrs previously defined in diverse galaxy populations, if those main ingredients were taken into account. | stellar mass and stellar mass-to-light ratio-color relations for low surface brightness galaxies |
we present a study of the stellar populations within the central regions of four nearby barred galaxies, and use a novel technique to constrain the duration of bar activity. we focus on the star formation `desert', a region within each of these galaxies where star formation appears to have been suppressed by the bar. new hβ spectroscopic data are presented, and used to produce spectroscopic line indices which are compared with theoretical predictions from population synthesis models for simple stellar populations and temporally truncated star formation histories. this analysis shows that the dearth of star formation activity in these regions appears to have been continuing for at least 1 gyr, with time-scales of several gyr indicated for two of the galaxies. this favours models in which strong bars can be long-lived features of galaxies, but our results also indicate a significant diversity in stellar population ages, and hence in the implied histories of bar activity in these four galaxies. | stellar population constraints on the ages of galactic bars |
the observed line-of-sight velocity dispersion σ los of the ultra-diffuse galaxy dragonfly 44 (df44) requires a newtonian dynamical mass-to-light ratio of {m}dyn}/{l}i={26}-6+7 solar units. this is well outside the acceptable limits of our stellar population synthesis (sps) models, which we construct using the integrated galactic initial mass function (igimf) theory. assuming df44 is in isolation and using jeans analysis, we calculate σ los profiles of df44 in milgromian dynamics (mond) and modified gravity (mog) theories without invoking dark matter. comparing with the observed kinematics, the best-fitting mond model has {m}dyn}/{l}i={3.6}-1.2+1.6 and a constant orbital anisotropy of β =-{0.5}-1.6+0.4. in mog, we first fix its two theoretical parameters α and μ based on previous fits to the observed rotation curve data of the hi nearby galaxy survey (things). the df44 σ los profile is best fit with {m}dyn}/{l}i={7.4}-1.4+1.5, larger than plausible sps values. mog produces a σ los profile for df44 with acceptable m dyn/liand isotropic orbits if α and μ are allowed to vary. mond with the canonical a 0 can explain df44 at the 2.40σ confidence level (1.66%) if considering both its observed kinematics and typical star formation histories in an igimf context. however, mog is ruled out at 5.49σ (p-value of 4.07 × 10-8) if its free parameters are fixed at the highest values consistent with things data. | the star formation history and dynamics of the ultra-diffuse galaxy dragonfly 44 in mond and mog |
we present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. the mock spectra are produced from the illustristng tng100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). we compare the simulated dn4000 and ew(hδ) of galaxies with $10.5\leqslant \mathrm{log}({m}_{* }/{m}_{\odot })\leqslant 11.5$ at 0.6 ≤ z ≤ 1.0 to the observed distributions from the lega-c survey. tng100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in tng100 is generally realistic. yet there are small but significant differences. for old galaxies, tng100 shows small dn4000 when compared to lega-c, while lega-c galaxies have larger ew(hδ) at fixed dn4000 . there are several possible explanations: (1) lega-c galaxies have overall older ages combined with small contributions (a few percent in mass) from younger (<1 gyr) stars, while tng100 galaxies may not have such young subpopulations; (2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. in conclusion, the latest cosmological galaxy-formation simulations broadly reproduce the global age distribution of galaxies at z ~ 1 and, at the same time, the high quality of the latest observed and simulated data sets help constrain stellar population synthesis models as well as the physical models underlying the simulations. | toward precise galaxy evolution: a comparison between spectral indices of z1 galaxies in the illustristng simulation and the lega-c survey |
using the oxford short wavelength integral field spectrograph, we trace radial variations of initial mass function (imf)-sensitive absorption features of three galaxies in the coma cluster. we obtain resolved spectroscopy of the central 5 kpc for the two central brightest cluster galaxies (bcgs) ngc4889, ngc4874, and the bcg in the south-west group ngc4839, as well as unresolved data for ngc4873 as a low-σ* control. we present radial measurements of the imf-sensitive features: sodium na isdss, calcium triplet cat, and iron-hydride feh0.99, along with the magnesium mg i0.88 and titanium oxide tio0.89 features. we employ two separate methods for both telluric correction and sky subtraction around the faint feh feature to verify our analysis. within ngc4889 we find strong gradients of na isdss and cat but a flat feh profile, which, from comparing to stellar population synthesis models, suggests an old, α-enhanced population with a chabrier, or even bottom-light imf. the age and abundance are in line with previous studies but the normal imf is in contrast to recent results suggesting an increased imf slope with increased velocity dispersion. we measure flat na isdss and feh profiles within ngc4874, and determine an old, possibly slightly α-enhanced and chabrier imf population. we find an α-enhanced, chabrier imf population in ngc4873. within ngc4839 we measure both strong na isdss and strong feh, although with a large systematic uncertainty, suggesting a possible heavier imf. the imfs we infer for these galaxies are supported by published dynamical modelling. we stress that imf constraints should be corroborated by further spectral coverage and independent methods on a galaxy-by-galaxy basis. | radial gradients in initial mass function sensitive absorption features in the coma brightest cluster galaxies |
we present an extended version of the spectral synthesis code starlight designed to incorporate both λ-by-λ spectra and photometric fluxes in the estimation of stellar population properties of galaxies. the code is tested with simulations and data for 260 galaxies culled from the calar alto legacy integral field area (califa) survey, spatially matching the 3700-7000 å optical data cubes to galaxy evolution explorer (galex) near-ultraviolet (nuv) and far-ultraviolet (fuv) images. the sample spans e-sd galaxies with masses from 109 to 1012 m⊙ and stellar populations all the way from star-forming to old, passive systems. comparing results derived from purely optical fits with those which also consider the nuv and fuv data we find that the following. (1) the new code is capable of matching the input ultraviolet (uv) data within the errors while keeping the quality of the optical fit essentially unchanged. (2) despite being unreliable predictors of the uv fluxes, purely optical fits yield stellar population properties which agree well with those obtained in optical+uv fits for nearly 90 per cent of our sample. (3) the addition of uv constraints has little impact on properties such as stellar mass and dust optical depth. mean stellar ages and metallicities also remain nearly the same for most galaxies, the exception being low-mass, late-type galaxies, which become older and less enriched due to rearrangements of their youngest populations. (4) the revised ages are better correlated with observables such as the 4000 å break index, and the nuv - r and u - r colours, an empirical indication that the addition of uv constraints helps mitigating the effects of age-metallicity-extinction degeneracies. | simultaneous spectroscopic and photometric analysis of galaxies with starlight: califa+galex |
we propose a fresh look at the main galaxy sample of the sloan digital sky survey by packing the galaxies in stellar mass and redshift bins. we show how important it is to consider the emission-line equivalent widths, in addition to the commonly used emission-line ratios, to properly identify retired galaxies (i.e. galaxies that have stopped forming stars and are ionized by their old stellar populations) and not mistake them for galaxies with low-level nuclear activity. we find that the proportion of star-forming galaxies decreases with decreasing redshift in each mass bin, while that of retired galaxies increases. galaxies with m⋆ > 1011.5 m⊙ have formed all their stars at redshift larger than 0.4. the population of agn hosts is never dominant for galaxy masses larger than 1010 m⊙. we warn about the effects of stacking galaxy spectra to discuss galaxy properties. we estimate the lifetimes of active galactic nuclei (agn) relying entirely on demographic arguments - i.e. without any assumption on the agn radiative properties. we find upper-limit lifetimes of about 1-5 gyr for detectable agn in galaxies with masses between 1010-1012 m⊙. the lifetimes of the agn-dominated phases are a few 108 yr. finally, we compare the star formation histories of star-forming, agn and retired galaxies as obtained by the spectral synthesis code starlight. once the agn is turned on, it inhibits star formation for the next ∼0.1 gyr in galaxies with masses around 1010 m⊙, ∼ 1 gyr in galaxies with masses around 1011 m⊙. | retired galaxies: not to be forgotten in the quest of the star formation - agn connection |
the milky way disk consists of two prominent components—a thick, alpha-rich, low-metallicity component and a thin, metal-rich, low-alpha component. external galaxies have been shown to contain thin- and thick-disk components, but whether distinct components in the [α/fe]-[z/h] plane exist in other milky way-like galaxies is not yet known. we present very large telescope (vlt)—multi unit spectroscopic explorer (muse) observations of ugc 10738, a nearby, edge-on milky way-like galaxy. we demonstrate through stellar population synthesis model fitting that ugc 10738 contains alpha-rich and alpha-poor stellar populations with similar spatial distributions to the same components in the milky way. we discuss how the finding that external galaxies also contain chemically distinct disk components may act as a significant constraint on the formation of the milky way's own thin and thick disk. | identification of an [α/fe]—enhanced thick disk component in an edge-on milky way analog |
long-duration gamma-ray bursts (grbs) allow us to pinpoint and study star-forming galaxies in the early universe, thanks to their orders of magnitude brighter peak luminosities compared to other astrophysical sources, and their association with the deaths of massive stars. we present hubble space telescope wide field camera 3 detections of three swift grb host galaxies lying at redshifts z = 5.913 (grb 130606a), z = 6.295 (grb 050904), and z = 6.327 (grb 140515a) in the f140w (wide-jh band, {λ }{{obs}}∼ 1.4 μ {{m}}) filter. the hosts have magnitudes (corrected for galactic extinction) of {m}{λ {obs},{ab}}={26.34}-0.16+0.14,{27.56}-0.22+0.18, and {28.30}-0.33+0.25, respectively. in all three cases, the probability of chance coincidence of lower redshift galaxies is ≲ 2 % , indicating that the detected galaxies are most likely the grb hosts. these are the first detections of high-redshift (z\gt 5) grb host galaxies in emission. the galaxies have luminosities in the range 0.1-0.6 {l}z=6*(with {m}1600* =-20.95+/- 0.12) and half-light radii in the range 0.6-0.9 {{kpc}}. both their half-light radii and luminosities are consistent with existing samples of lyman-break galaxies at z∼ 6. spectroscopic analysis of the grb afterglows indicate low metallicities ([{{m/h}}]≲ -1) and low dust extinction ({a}{{v}}≲ 0.1) along the line of sight. using stellar population synthesis models, we explore the implications of each galaxy’s luminosity for its possible star-formation history and consider the potential for emission line metallicity determination with the upcoming james webb space telescope. | detection of three gamma-ray burst host galaxies at z ∼ 6 |
most ultraluminous x-ray sources (ulxs) are believed to be x-ray binary systems, but previous observational and theoretical studies tend to prefer a black hole rather than a neutron star (ns) accretor. the recent discovery of 1.37 s pulsations from the ulx m82 x-2 has established its nature as a magnetized ns. in this work we model the formation history of ns ulxs in an m82- or milky way (mw)-like galaxy, by use of both binary population synthesis and detailed binary evolution calculations. we find that the birth rate is around 10-4 yr-1 for the incipient x-ray binaries in both cases. we demonstrate the distribution of the ulx population in the donor mass-orbital period plane. our results suggest that, compared with black hole x-ray binaries, ns x-ray binaries may significantly contribute to the ulx population, and high-mass and intermediate-mass x-ray binaries dominate the ns ulx population in m82- and mw-like galaxies, respectively. | a population of ultraluminous x-ray sources with an accreting neutron star |
aims: in this paper, we aim to measure the strength of the surface magnetic fields for a sample of five intermediate mass t tauri stars and one low mass t tauri star from late-f to mid-k spectral types. while magnetic fields of t tauri stars at the low mass range have been extensively characterized, our work complements previous studies towards the intermediate mass range; this complementary study is key to evaluate how magnetic fields evolve during the transition from a convective to a radiative core.methods: we studied the zeeman broadening of magnetically sensitive spectral lines in the h-band spectra obtained with the crires high-resolution near-infrared spectrometer. these data are modelled using magnetic spectral synthesis and model atmospheres. additional constraints on non-magnetic line broadening mechanisms are obtained from modelling molecular lines in the k band or atomic lines in the optical wavelength region.results: we detect and measure mean surface magnetic fields for five of the six stars in our sample: chxr 28, coup 107, v2062 oph, v1149 sco, and par 2441. magnetic field strengths inferred from the most magnetically sensitive diagnostic line range from 0.8 to 1.8 kg. we also estimate a magnetic field strength of 1.9 kg for coup 107 from an alternative diagnostic. the magnetic field on ylw 19 is the weakest in our sample and is marginally detected, with a strength of 0.8 kg.conclusions: we populate an uncharted area of the pre-main-sequence hr diagram with mean magnetic field measurements from high-resolution near-infrared spectra. our sample of intermediate mass t tauri stars in general exhibits weaker magnetic fields than their lower mass counterparts. our measurements will be used in combination with other spectropolarimetric studies of intermediate mass and lower mass t tauri stars to provide input into pre-main-sequence stellar evolutionary models. | magnetic fields of intermediate mass t tauri stars |
population synthesis studies of binary black hole mergers often lack robust black hole spin estimates as they cannot accurately follow tidal spin-up during the late black hole-wolf-rayet evolutionary phase. we provide an analytical approximation of the dimensionless second-born black hole spin given the binary orbital period and wolf-rayet stellar mass at helium depletion or carbon depletion. these approximations are obtained from fitting a sample of around 105 detailed mesa simulations that follow the evolution and spin up of close black hole-wolf-rayet systems with metallicities in the range $[{10}^{-4},1.5\ {z}_{\odot }]$ . following the potential spin up of the wolf-rayet progenitor, the second-born black hole spin is calculated using up-to-date core collapse prescriptions that account for any potential disk formation in the collapsing wolf-rayet star. the fits for second-born black hole spin provided in this work can be readily applied to any astrophysical modeling that relies on rapid population synthesis, and will be useful for the interpretation of gravitational-wave sources using such models. | approximations of the spin of close black hole-wolf-rayet binaries |
the search for chemically unevolved galaxies remains prevalent in the nearby universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. the most promising candidates are extremely metal-poor galaxies (xmps), i.e. galaxies with <1/10 solar metallicity. however, due to the bright emission-line-based search criteria traditionally used to find xmps, we may not be sampling the full xmp population. in 2014, we reoriented this search using only morphological properties and uncovered a population of ∼150 'blue diffuse dwarf (bdd) galaxies', and published a sub-sample of 12 bdd spectra. here, we present optical spectroscopic observations of a larger sample of 51 bdds, along with their sloan digital sky survey (sdss) photometric properties. with our improved statistics, we use direct-method abundances to confirm that bdds are chemically unevolved (7.43 < 12 + log(o/h) < 8.01), with ∼20 per cent of our sample classified as being xmp galaxies, and find that they are actively forming stars at rates of ∼1-33 × 10-2 m⊙ yr-1 in h ii regions randomly embedded in a blue, low-surface-brightness continuum. stellar masses are calculated from population synthesis models and estimated to be in the range log (m*/m⊙) ≃ 5-9. unlike other low-metallicity star-forming galaxies, bdds are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. bdd galaxies appear to be a population of actively star-forming dwarf irregular (dirr) galaxies which fall within the class of low-surface-brightness dirr galaxies. their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early universe. | blue diffuse dwarf galaxies: a clearer picture |
we have performed population synthesis calculation on the formation of binaries containing a black hole (bh) and a neutron star (ns) in the galactic disc. some of important input parameters, especially for the treatment of common envelope evolution, are updated in the calculation. we have discussed the uncertainties from the star formation rate of the galaxy and the velocity distribution of ns kicks on the birthrate (∼ 0.6-13 m yr^{-1}) of bh/ns binaries. from incident bh/ns binaries, by modelling the orbital evolution due to gravitational wave radiation and the ns evolution as radio pulsars, we obtain the distributions of the observable parameters such as the orbital period, eccentricity, and pulse period of the bh/pulsar binaries. we estimate that there may be ∼3-80 bh/pulsar binaries in the galactic disc and around 10 per cent of them could be detected by the five-hundred-metre aperture spherical radio telescope. | black hole/pulsar binaries in the galaxy |
we present the stellar mass-stellar metallicity relationship (mzr) in the galaxy cluster cl0024+1654 at z ∼ 0.4 using full-spectrum stellar population synthesis modeling of individual quiescent galaxies. the lower limit of our stellar mass range is m * = 109.7 m ⊙, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. we report a detection of an evolution of the stellar mzr with observed redshift at 0.037 ± 0.007 dex per gyr, consistent with the predictions from hydrodynamical simulations. additionally, we find that the evolution of the stellar mzr with observed redshift can be explained by an evolution of the stellar mzr with the formation time of galaxies, i.e., when the single stellar population (ssp)-equivalent ages of galaxies are taken into account. this behavior is consistent with stars forming out of gas that also has an mzr with a normalization that decreases with redshift. lastly, we find that over the observed mass range, the mzr can be described by a linear function with a shallow slope ([{fe}/{{h}}]\propto (0.16+/- 0.03){log}{m}* ). the slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range. | evolution of the stellar mass-metallicity relation. i. galaxies in the z ∼ 0.4 cluster cl0024 |
we performed population synthesis simulations of population iii binary stars with maxwellian kick velocity distribution when mgcos (mass gap compact objects, with mass $2$ - $5\,m_{\odot}$ ) are formed. we found that for eight kick velocity dispersion models of $\sigma_{\rm k}=0$ - $500$ km $ s $^{-1}$ , the mean mass of black hole (bh)-mgco binary is $\sim (30 \,m_\odot,\,2.6 \,m_\odot)$ . in numerical data of our simulations, we found the existence of a bh-mgco binary with mass $(22.9 \,m_\odot,\,2.5 \,m_\odot)$ which looks like gw190814. | formation of mass gap compact object and black hole binary from population iii stars |
the fastest-spinning neutron stars in low-mass x-ray binaries, despite having undergone millions of years of accretion, have been observed to spin well below the keplerian break-up frequency. we simulate the spin evolution of synthetic populations of accreting neutron stars in order to assess whether gravitational waves can explain this behaviour and provide the distribution of spins that is observed. we model both persistent and transient accretion and consider two gravitational-wave-production mechanisms that could be present in these systems: thermal mountains and unstable rmodes. we consider the case of no gravitational-wave emission and observe that this does not match well with observation. we find evidence for gravitational waves being able to provide the observed spin distribution; the most promising mechanisms being a permanent quadrupole, thermal mountains, and unstable r modes. however, based on the resultant distributions alone, it is difficult to distinguish between the competing mechanisms. | population synthesis of accreting neutron stars emitting gravitational waves |
we combine data from the sloan digital sky survey (sdss) and the galaxy evolution explorer (galex) to simultaneously analyse optical spectra and ultraviolet photometry of 231 643 galaxies with the starlight spectral synthesis code using state-of-the-art stellar population models. we present a new method to estimate galex photometry in the sdss spectroscopic aperture, which proves quite reliable if applied to large samples. in agreement with previous experiments with califa, we find that adding uv constraints leads to a moderate increase on the fraction of ∼107-108 yr populations and a concomitant decrease of younger and older components, yielding slightly older luminosity-weighted mean stellar ages. these changes are most relevant in the low-mass end of the blue cloud. an increase in dust attenuation is observed for galaxies dominated by young stars. we investigate the contribution of different stellar populations to the fraction of light in galex and sdss bands across the uv optical colour-magnitude diagram. as an example application, we use this λ dependence to highlight differences between retired galaxies with and without emission lines. in agreement with an independent study by herpich et al., we find that the former shows an excess of intermediate-age populations when compared to the later. finally, we test the suitability of two different prescription for dust, finding that our data set is best-fitting using the attenuation law of starburst galaxies. however, results for the milky way extinction curve improve with decreasing τv, especially for edge-on galaxies. | simultaneous analysis of sdss spectra and galex photometry with starlight: method and early results |
a model of a population of ultraluminous x-ray sources with magnetized neutron stars (nulxs) in a spiral galaxy with a star formation history as in the thin disk of the milky way is constructed by the hybrid population synthesis method. first, based on analytical approximations (bse code), we compute a set of close binary systems (cbss), potential precursors of nulxs, and, then, the evolution with mass accretion onto magnetized neutron stars (nss) is computed by the mesa evolutionary code. the accretion rate onto nss and the x-ray luminosity of sources are calculated for the models of sub- or supercritical disks and disks with advection. during accretion onto magnetized nss, super-eddington luminosities $l_{\textrm{x}}>10^{38}$ erg s${}^{-1}$ are reached already at the subcritical stage, when the energy release at the inner boundary of the disk defined by the ns magnetosphere is sub-eddington one. our calculations show that the standard evolution of cbss, given the peculiarities of accretion onto magnetized nss, allows the observed properties of nulxs (x-ray luminosities, ns spin periods, cbs orbital periods, and optical component masses) to be quantitatively explained without requiring additional model assumptions about the collimation of x-ray emission from nss with a high observed super-eddington luminosity. in a model galaxy with a star formation rate ${∼}5m_{\odot}$ yr${}^{-1}$ there can be several nulxs. the detection of a powerful wind from nulxs with $l_{\textrm{x}}∼ 10^{41}$ erg s${}^{-1}$ may suggest supercritical accretion onto magnetized nss. | population synthesis of ultraluminous x-ray sources with magnetized neutron stars |
the fermi-lat galactic centre excess and the 511 kev positron-annihilation signal from the inner galaxy bear a striking morphological similarity. we propose that both can be explained through a scenario in which millisecond pulsars produce the galactic centre excess and their progenitors, low-mass x-ray binaries, the 511 kev signal. as a proof of principle, we study a specific population synthesis scenario from the literature involving so-called ultracompact x-ray binaries. moreover, for the first time, we quantitatively show that neutron star, rather than black hole, low-mass x-ray binaries can be responsible for the majority of the positrons. in this particular scenario, binary millisecond pulsars can be both the source of the fermi-lat γ-ray excess and the bulge positrons. future avenues to test this scenario are discussed. | galactic binaries can explain the fermi galactic centre excess and 511 kev emission |
we report on advances to interpret current and future gravitational-wave events in light of astrophysical simulations. a machine-learning emulator is trained on numerical population-synthesis predictions and inserted into a bayesian hierarchical framework. in this case study, a modest but state-of-the-art suite of simulations of isolated binary stars is interpolated across two event parameters and one population parameter. the validation process of our pipelines highlights how omitting some of the event parameters might cause errors in estimating selection effects, which propagates as systematics to the final population inference. using ligo/virgo data from o1 and o2 we infer that black holes in binaries are most likely to receive natal kicks with one-dimensional velocity dispersion σ =10 5-29+44 km /s . our results showcase potential applications of machine-learning tools in conjunction with population-synthesis simulations and gravitational-wave data. | machine-learning interpolation of population-synthesis simulations to interpret gravitational-wave observations: a case study |
our knowledge about the photometric and structural properties of bulges in late-type galaxies (ltgs) is founded upon image decomposition into a sérsic model for the central luminosity excess of the bulge and an exponential model for the more extended underlying disk. we argue that the standard practice of adopting an exponential model for the disk all the way to its center is inadequate because it implicitly neglects the fact of star formation (sf) quenching in the centers of ltgs. extrapolating the fit to the observable star-forming zone of the disk (outside the bulge) inwardly overestimates the true surface brightness of the disk in its sf-quenched central zone (beneath the bulge). we refer to this effect as δio. using predictions from evolutionary synthesis models and by applying to integral field spectroscopy data removeyoung, a tool that allows the suppression of stellar populations younger than an adjustable age cutoff we estimate the δio in the centers of massive sf-quenched ltgs to be up to ∼2.5 (0.7) b (k) mag. the primary consequence of the neglect of δio in bulge-disk decomposition studies is the oversubtraction of the disk underneath the bulge, leading to a systematic underestimation of the true luminosity of the latter. secondary biases impact the structural characterization (e.g., sérsic exponent η and effective radius) and color gradients of bulges, and might include the erroneous classification of ltgs with a moderately faint bulge as bulgeless disks. framed in the picture of galaxy downsizing and inside-out sf quenching, δio is expected to differentially impact galaxies across redshift and stellar mass ℳ⋆, thus leading to systematic and complex biases in the scatter and slope of various galaxy scaling relations. we conjecture that correction for the δio effect will lead to a down-bending of the bulge versus supermassive black hole relation for galaxies below log(ℳ⋆/m⊙) ∼ 10.7. a decreasing ℳ∙/ℳ⋆ ratio with decreasing ℳ⋆ would help to consistently explain the scarcity and weakness of accretion-powered nuclear activity in low-mass spiral galaxies. finally, it is pointed out that a well-detectable δio (> 2 r mag) can emerge early on through inward migration of star-forming clumps from the disk in combination with a strong contrast of emission-line equivalent widths between the quenched protobulge and its star-forming periphery. spatially resolved studies of δio with the james webb space telescope, the extremely large telescope, and euclid could therefore offer key insights into the chronology and physical drivers of sf-quenching in the early phase of galaxy assembly. | inside-out star formation quenching and the need for a revision of bulge-disk decomposition concepts for spiral galaxies |
context. the proximity to the eddington luminosity has been attributed as the cause of several observed effects in massive stars. computationally, if the luminosity carried through radiation exceeds the local eddington luminosity in the low-density envelopes of massive stars, it can result in numerical difficulties, inhibiting further computation of stellar models. this problem is exacerbated by the fact that very few massive stars are observed beyond the humphreys-davidson limit, the same region in the hertzsprung-russell diagram where the aforementioned numerical issues relating to the eddington luminosity occur in stellar models.aims: one-dimensional stellar evolution codes have to use pragmatic solutions to evolve massive stars through this computationally difficult phase. in this work, we quantify the impact of these solutions on the evolutionary properties of massive stars.methods: we used the stellar evolution code mesa with commonly used input parameters for massive stellar models to compute the evolution of stars in the initial mass range of 10-110 m⊙ at one-tenth of solar metallicity.results: we find that numerical difficulties in stellar models with initial masses greater than or equal to 30 m⊙ cause these models to fail before the end of core helium burning. recomputing these models using the same physical inputs but three different pragmatic solutions to treat the numerical instability, we find that the maximum radial expansion achieved by stars can vary by up to 2000 r⊙, while the remnant mass of the stars can vary by up to 14 m⊙ between the sets. these differences can have implications on studies such as binary population synthesis. | a systematic study of super-eddington layers in the envelopes of massive stars |
we investigate the properties of the host galaxies of compact binary mergers across cosmic time. to this end, we combine population synthesis simulations together with galaxy catalogues from the hydrodynamical cosmological simulation eagle to derive the properties of the host galaxies of binary neutron star (bns), black hole-neutron star (bhns), and binary black hole (bbh) mergers. within this framework, we derive the host galaxy probability, i.e. the probability that a galaxy hosts a compact binary coalescence as a function of its stellar mass, star formation rate, ks magnitude, and b magnitude. this quantity is particularly important for low-latency searches of gravitational wave (gw) sources as it provides a way to rank galaxies lying inside the credible region in the sky of a given gw detection, hence reducing the number of viable host candidates. furthermore, even if no electromagnetic counterpart is detected, the proposed ranking criterion can still be used to classify the galaxies contained in the error box. our results show that massive galaxies (or equivalently galaxies with a high luminosity in ks band) have a higher probability of hosting bns, bhns, and bbh mergers. we provide the probabilities in a suitable format to be implemented in future low-latency searches. | an astrophysically motivated ranking criterion for low-latency electromagnetic follow-up of gravitational wave events |
within a galaxy the stellar mass-to-light ratio ϒ* is not constant. recent studies of spatially resolved kinematics of nearby early-type galaxies suggest that allowing for a variable initial mass function (imf) returns significantly larger ϒ* gradients than if the imf is held fixed. we show that ignoring such imf-driven ϒ* gradients can have dramatic effect on dynamical (m_*^dyn), though stellar population (m_*^sp) based estimates of early-type galaxy stellar masses are also affected. this is because m_*^dyn is usually calibrated using the velocity dispersion measured in the central regions (e.g. re/8) where stars are expected to dominate the mass (i.e. the dark matter fraction is small). on the other hand, m_*^sp is often computed from larger apertures (e.g. using a mean ϒ* estimated from colours). if ϒ* is greater in the central regions, then ignoring the gradient can overestimate m_*^dyn by as much as a factor of two for the most massive galaxies. large ϒ*-gradients have four main consequences: first, m_*^dyn cannot be estimated independently of stellar population synthesis models. secondly, if there is a lower limit to ϒ* and gradients are unknown, then requiring m_*^dyn=m_*^sp constrains them. thirdly, if gradients are stronger in more massive galaxies, then accounting for this reduces the slope of the correlation between m_*^dyn/m_*^sp of a galaxy with its velocity dispersion. in particular, imf-driven gradients bring m_*^dyn and m_*^sp into agreement, not by shifting m_*^sp upwards by invoking constant bottom-heavy imfs, as advocated by a number of recent studies, but by revising m_*^dyn estimates in the literature downwards. fourthly, accounting for ϒ* gradients changes the high-mass slope of the stellar mass function φ (m_*^dyn), and reduces the associated stellar mass density. these conclusions potentially impact estimates of the need for feedback and adiabatic contraction, so our results highlight the importance of measuring ϒ* gradients in larger samples. | m*/l gradients driven by imf variation: large impact on dynamical stellar mass estimates |
context. accurate star formation histories (sfhs) of galaxies are fundamental for understanding the build-up of their stellar content. however, the most accurate sfhs - those obtained from colour-magnitude diagrams (cmds) of resolved stars reaching the oldest main-sequence turnoffs (omsto) - are presently limited to a few systems in the local group. it is therefore crucial to determine the reliability and range of applicability of sfhs derived from integrated light spectroscopy, as this affects our understanding of unresolved galaxies from low to high redshift.aims: we evaluate the reliability of current full spectral fitting techniques in deriving sfhs from integrated light spectroscopy by comparing sfhs from integrated spectra to those obtained from deep cmds of resolved stars.methods: we have obtained a high signal-to-noise (s/n ~ 36.3 per å) integrated spectrum of a field in the bar of the large magellanic cloud (lmc) using efosc2 at the 3.6-metre telescope at la silla observatory. for this same field, resolved stellar data reaching the omsto are available. we have compared the star formation rate (sfr) as a function of time and the age-metallicity relation (amr) obtained from the integrated spectrum using steckmap, and the cmd using the iac-star/minniac/iac-pop set of routines. for the sake of completeness we also use and discuss other synthesis codes (starlight and ulyss) to derive the sfr and amr from the integrated lmc spectrum.results: we find very good agreement (average differences ~4.1%) between the sfr (t) and the amr obtained using steckmap on the integrated light spectrum, and the cmd analysis. steckmap minimizes the impact of the age-metallicity degeneracy and has the advantage of preferring smooth solutions to recover complex sfhs by means of a penalized χ2. we find that the use of single stellar populations (ssps) to recover the stellar content, using for instance starlight or ulyss codes, hampers the reconstruction of the sfr (t) and amr shapes, yielding larger discrepancies with respect to the cmd results. these discrepancies can be reduced if spectral templates based on known and complex sfhs are employed rather than ssps. based on observations obtained at the 3.6 m eso telescope on la silla (chile) and with the hubble space telescope, operated by nasa.appendices are available in electronic form at http://www.aanda.org | recovering star formation histories: integrated-light analyses vs. stellar colour-magnitude diagrams |
we present low-resolution near-infrared stacked spectra from the 3d-hst survey up to z = 2.0 and fit them with commonly used stellar population synthesis models: bc03, fsps10 (flexible stellar population synthesis), and fsps-c3k. the accuracy of the grism redshifts allows the unambiguous detection of many emission and absorption features and thus a first systematic exploration of the rest-frame optical spectra of galaxies up to z = 2. we select massive galaxies ({log}({m}*/{m}⊙ )\gt 10.8), we divide them into quiescent and star-forming via a rest-frame color-color technique, and we median-stack the samples in three redshift bins between z = 0.5 and z = 2.0. we find that stellar population models fit the observations well at wavelengths below the 6500 å rest frame, but show systematic residuals at redder wavelengths. the fsps-c3k model generally provides the best fits (evaluated with χ 2 red statistics) for quiescent galaxies, while bc03 performs the best for star-forming galaxies. the stellar ages of quiescent galaxies implied by the models, assuming solar metallicity, vary from 4 gyr at z ∼ 0.75 to 1.5 gyr at z ∼ 1.75, with an uncertainty of a factor of two caused by the unknown metallicity. on average, the stellar ages are half the age of the universe at these redshifts. we show that the inferred evolution of ages of quiescent galaxies is in agreement with fundamental plane measurements, assuming an 8 gyr age for local galaxies. for star-forming galaxies, the inferred ages depend strongly on the stellar population model and the shape of the assumed star-formation history. | ages of massive galaxies at 0.5 > z > 2.0 from 3d-hst rest-frame optical spectroscopy |
background: stellar carbon synthesis occurs exclusively via the 3 α process, in which three α particles fuse to form 12c in the excited hoyle state, followed by electromagnetic decay to the ground state. the hoyle state is above the α threshold, and the rate of stellar carbon production depends on the radiative width of this state. the radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. one of these quantities is the e 0 decay branching ratio of the hoyle state, and the current 10 % uncertainty on the radiative width stems mainly from the uncertainty on this ratio. the rate of the 3 α process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models. purpose: to deduce a new, more precise value for the e 0 decay branching ratio of the hoyle state. method: the e 0 branching ratio was deduced from a series of pair conversion measurements of the e 0 and e 2 transitions depopulating the 02+ hoyle state and 21+ state in 12c, respectively. the excited states were populated by the 12c(p ,p') reaction at 10.5 mev beam energy, and the pairs were detected with the electron-positron pair spectrometer, super-e, at the australian national university. the deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the 21+ state in the reaction. for this purpose, proton scattering and γ -ray angular distribution experiments were also performed. results: an e 0 branching ratio of γπe 0/γ =8.2 (5 ) ×10-6 was deduced in the current work, and an adopted value of γπe 0/γ =7.6 (4 ) ×10-6 is recommended based on a weighted average of previous literature values and the new result. conclusions: the new recommended value for the e 0 branching ratio is about 14% larger than the previous adopted value of γπe 0/γ =6.7 (6 ) ×10-6 , while the uncertainty has been reduced from 9% to 5%. the new result reduces the radiative width, and hence 3 α reaction rate, by 11% relative to the adopted value, and the uncertainty to 6.1%. this reduction in width and increased precision is likely to constrain possible outcomes of astrophysical calculations. | improved precision on the experimental e 0 decay branching ratio of the hoyle state |
in this chapter we discuss the population and spectral synthesis of stellar populations. we describe the method required to achieve such synthesis and discuss examples where inclusion of interacting binaries are vital to reproducing the properties of observed stellar systems. these examples include the hertzsprung-russell diagram, massive star number counts, core-collapse supernovae and the ionising radiation from stellar populations that power both nearby hii regions and the epoch of reionization. we finally offer some speculations on the future paths of research in spectral synthesis. | population and spectral synthesis: it doesn't work without binaries |
it is well established that magnetars are neutron stars with extreme magnetic fields and young ages, but the evolutionary pathways to their creation are still uncertain. since most massive stars are in binaries, if magnetars are a frequent result of core-collapse supernovae, some fractions are expected to have a bound companion at the time of observation. in this paper, we utilize literature constraints, including deep hubble space telescope imaging, to search for bound stellar companions to magnetars. the magnitude and colour measurements are interpreted in the context of binary population synthesis predictions. we find two candidates for stellar companions associated with cxou j171405.7-381031 and sgr 0755-2933, based on their j-h colours and h-band absolute magnitudes. overall, the proportion of the galactic magnetar population with a plausibly stellar near-infrared (nir) counterpart candidate, based on their magnitudes and colours, is between 5 and 10 per cent. this is consistent with a population synthesis prediction of 5 per cent, for the fraction of core-collapse neutron stars arising from primaries that remain bound to their companion after the supernova. these results are therefore consistent with magnetars being drawn in an unbiased way from the natal core-collapse neutron star population, but some contribution from alternative progenitor channels cannot be ruled out. | where are the magnetar binary companions? candidates from a comparison with binary population synthesis predictions |
we construct empirical models of star-forming galaxy evolution assuming that individual galaxies evolve along well-known scaling relations between stellar mass, gas mass, and star formation rate following a simple description of chemical evolution. we test these models by a comparison with observations and detailed magneticum high-resolution hydrodynamic cosmological simulations. galaxy star formation rates, stellar masses, gas masses, ages, interstellar medium, and stellar metallicities are compared. it is found that these simple look-back models capture many of the crucial aspects of galaxy evolution reasonably well. their key assumption of a redshift-dependent power-law relationship between galaxy interstellar medium gas mass and stellar mass is in agreement with the outcome of the complex magneticum simulations. star formation rates decline toward lower redshift not because galaxies are running out of gas, but because the fraction of the cold interstellar medium gas, which is capable of producing stars, becomes significantly smaller. gas accretion rates in both model approaches are of the same order of magnitude. metallicity in the magneticum simulations increases with the ratio of stellar mass to gas mass as predicted by the look-back models. the mass-metallicity relationships agree, and the star formation rate dependence of these relationships is also reproduced. we conclude that these simple models provide a powerful tool for constraining and interpreting more complex models based on cosmological simulations and for population synthesis studies analyzing the integrated spectra of stellar populations. | galaxy look-back evolution models: a comparison with magneticum cosmological simulations and observations |
we present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmological simulations and show how the catalogues can be used to test and interpret observational data. the catalogues are constructed from a combination of methods. a semi-analytic galaxy formation model is used to calculate the star formation history in haloes in an n-body simulation and dark matter particles are tagged with this stellar mass. the tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original n-body simulation is maintained. a set of catalogues based on the λ cold dark matter aquarius simulations of milky way mass haloes have been created and made publicly available on a website. two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. we show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. we also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stellar populations, allow streams to be easily identified. | creating mock catalogues of stellar haloes from cosmological simulations |
we present the first results from the deep and wide 5 ghz radio observations of the great observatories origins deep survey (goods)-north (σ = 3.5 μjy beam-1, synthesized beam size θ = 1.″47 × 1.″42, and 52 sources over 109 arcmin2) and goods-south (σ = 3.0 μjy beam-1, θ = 0.″98 × 0.″45, and 88 sources over 190 arcmin2) fields using the karl g. jansky very large array. we derive radio spectral indices α between 1.4 and 5 ghz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. we also find a clustering of faint radio sources around α = 0.8, but only within s 5 ghz < 150 μjy. we demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radio-fir correlation, and adopting a single value of α = 0.8 leads to a significant scatter and a strong bias in the analysis of the radio-fir correlation, resulting from the broad and asymmetric spectral index distribution. when characterized by specific star formation rates, the starburst population (58%) dominates the 5 ghz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio-fir correlation. lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and agn activity using radio continuum as a probe. | nature of faint radio sources in goods-north and goods-south fields. i. spectral index and radio-fir correlation |
the relation between nuclear (≲50 pc) star formation and nuclear galactic activity is still elusive; theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (agns) should appear at the same time, before, or after nuclear star formation activity. we present a study of this relation in a complete, volume-limited sample of nine of the most luminous (log l14 − 195 kev > 1042.5 erg s−1) local agns (the llama sample), including a sample of 18 inactive control galaxies (six star-forming; 12 passive) that are matched by hubble type, stellar mass (9.5 ≲ log m⋆/m⊙ ≲ 10.5), inclination, and distance. this allows us to calibrate our methods on the control sample and perform a differential analysis between the agn and control samples. we performed stellar population synthesis on vlt/x-shooter spectra in an aperture corresponding to a physical radius of ≈150 pc. we find young (≲30 myr) stellar populations in seven out of nine agns and in four out of six star-forming control galaxies. in the non-star-forming control population, in contrast, only two out of 12 galaxies show such a population. we further show that these young populations are not indicative of ongoing star formation, providing evidence for models that see agn activity as a consequence of nuclear star formation. based on the similar nuclear star formation histories of agns and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. under this assumption, and making use of the volume completeness of our sample, we infer that the agn phase lasts for about 5% of the nuclear starburst phase. spectra are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/654/a132 | llama: stellar populations in the nuclei of ultra-hard x-ray-selected agn and matched inactive galaxies |
we study and compare different examples of stellar evolutionary synthesis input parameters used to produce photoionization model grids using the mappings v modeling code. the aim of this study is to (a) explore the systematic effects of various stellar evolutionary synthesis model parameters on the interpretation of emission lines in optical strong-line diagnostic diagrams, (b) characterize the combination of parameters able to reproduce the spread of local galaxies located in the star-forming region in the sloan digital sky survey, and (c) investigate the emission from extremely metal-poor galaxies using photoionization models. we explore and compare the stellar input ionizing spectrum (stellar population synthesis code [starburst99, slug, bpass], stellar evolutionary tracks, stellar atmospheres, star formation history, sampling of the initial mass function), as well as parameters intrinsic to the h ii region (metallicity, ionization parameter, pressure, h ii region boundedness). we also perform a comparison of the photoionization codes mappings and cloudy. on the variations in the ionizing spectrum model parameters, we find that the differences in strong emission-line ratios between varying models for a given input model parameter are small, on average ∼0.1 dex. an average difference of ∼0.1 dex in emission-line ratio is also found between models produced with mappings and cloudy. large differences between the emission-line ratios are found when comparing intrinsic h ii region parameters. we find that low-metallicity galaxies are better explained by a density-bounded h ii region and higher pressures better encompass the spread of galaxies at high redshift. | comparison of theoretical starburst photoionization models for optical diagnostics |
we analyze the oxygen abundances of a stellar sample representative of the two major galactic populations: the thin and thick disks. the aim is to investigate the differences between members of the galactic disks and contribute to the understanding of the origin of oxygen chemical enrichment in the galaxy. the analysis is based on the [o i] = 6300.30 å oxygen line in high-resolution spectra (r ∼ 52,500) obtained from the gaia-eso public spectroscopic survey (ges). by comparing the observed spectra with a theoretical data set computed in lte with the spectrum synthesis and atlas12 codes, we derive the oxygen abundances of 516 fgk dwarfs for which we have previously measured carbon abundances. based on kinematic, chemical, and dynamical considerations, we identify 20 thin and 365 thick disk members. we study the potential trends of both subsamples in terms of their chemistry ([o/h], [o/fe], [o/mg], and [c/o] versus [fe/h] and [mg/h]), age, and position in the galaxy. the main results are that (a) [o/h] and [o/fe] ratios versus [fe/h] show systematic differences between thin and thick disk stars with an enhanced o abundance of thick disk stars with respect to thin disk members and a monotonic decrement of [o/fe] with increasing metallicity, even at metal-rich regime; (b) there is a smooth correlation of [o/mg] with age in both populations, suggesting that this abundance ratio can be a good proxy of stellar ages within the milky way; and (c) thin disk members with [fe/h] ≃ 0 display a [c/o] ratio smaller than the solar value, suggesting a possibly outward migration of the sun from lower galactocentric radii. * based on observations collected with the flames instrument at the vlt/ut2 telescope (paranal observatory, eso, chile) for the gaia-eso large public spectroscopic survey (188.b-3002, 193.b-0936). | the gaia-eso survey: oxygen abundance in the galactic thin and thick disks |
in their most recent observing run, the ligo-virgo-kagra collaboration observed gravitational waves from compact binary mergers with highly asymmetric mass ratios, including both binary black holes (bbhs) and neutron star-black holes (nsbhs). it appears that nsbhs with mass ratios q ≃ 0.2 are more common than equally asymmetric bbhs, but the reason for this remains unclear. we use the binary population synthesis code cosmic to investigate the evolutionary pathways leading to the formation and merger of asymmetric compact binaries. we find that within the context of isolated binary stellar evolution, most asymmetric mergers start off as asymmetric stellar binaries. because of the initial asymmetry, these systems tend to first undergo a dynamically unstable mass transfer phase. however, after the first star collapses into a compact object, the mass ratio is close to unity and the second phase of mass transfer is usually stable. according to our simulations, this stable mass transfer fails to shrink the orbit enough on its own for the system to merge. instead, the natal kick received by the second-born compact object during its collapse is key in determining how many of these systems can merge. for the most asymmetric systems with mass ratios of q ≤ 0.1, the merging systems in our models receive an average kick magnitude of 255 km s-1 during the second collapse, while the average kick for non-merging systems is 59 km s-1. because lower mass compact objects, like neutron stars, are expected to receive larger natal kicks than higher mass bhs, this may explain why asymmetric nsbh systems merge more frequently than asymmetric bbh systems. | the role of natal kicks in forming asymmetric compact binary mergers |
stellar population studies of early-type galaxies (etgs) based on their optical stellar continuum suggest that these are quiescent systems. however, emission lines and ultraviolet photometry reveal a diverse population. we use a new version of the starlight spectral synthesis code and state-of-the-art stellar population models to simultaneously fit sloan digital sky survey spectra and galaxy evolution explorer photometry for a sample of 3453 galaxies at z < 0.1 with near ultraviolet (nuv) - r > 5 that are classified as elliptical by galaxy zoo. we reproduce far ultraviolet (fuv) magnitudes for 80 per cent of uv upturn galaxies selected using criteria from the literature, suggesting that additional stellar population ingredients such as binaries and extreme horizontal branch stars may have a limited contribution to the uv upturn. the addition of ultraviolet data leads to a broadening of the distributions of mean stellar ages, metallicities, and attenuation. stellar populations younger than $1\,$ gyr are required to reproduce the ultraviolet emission in 17 per cent of our sample. these systems represent 43 per cent of the sample at 5 < nuv - r < 5.5 and span the same stellar mass range as other etgs in our sample. etgs with young stellar components have larger h α equivalent widths (wh α) and larger dust attenuation. emission line ratios and wh α indicate that the ionizing source in these systems is a mixture of young and old stellar populations. their young stellar populations are metal-poor, especially for high-mass galaxies, indicating recent star formation associated with rejuvenation events triggered by external processes, such as minor mergers. | clues on the history of early-type galaxies from sdss spectra and galex photometry |
high-resolution numerical simulations including feedback and aimed at calculating the escape fraction (fesc) of hydrogen-ionizing photons often assume stellar radiation based on single-stellar population synthesis models. however, strong evidence suggests the binary fraction of massive stars is ≳70%. moreover, simulations so far have yielded values of fesc falling only on the lower end of the ∼10%-20% range, the amount presumed necessary to reionize the universe. analyzing a high-resolution (4 pc) cosmological radiation-hydrodynamic simulation, we study how fesc changes when we include two different products of binary stellar evolution—stars stripped of their hydrogen envelopes and massive blue stragglers. both produce significant amounts of ionizing photons 10-200 myr after each starburst. we find the relative importance of these photons to be amplified with respect to escaped ionizing photons, because peaks in star formation rates (sfrs) and fesc are often out of phase by this 10-200 myr. additionally, low-mass, bursty galaxies emit lyman continuum radiation primarily from binary products when sfrs are low. observations of these galaxies by the james webb space telescope could provide crucial information on the evolution of binary stars as a function of redshift. overall, including stripped stars and massive blue stragglers increases our photon-weighted mean escape fraction ( $\langle {f}_{\mathrm{esc}}\rangle $ ) by ∼13% and ∼10%, respectively, resulting in $\langle {f}_{\mathrm{esc}}\rangle =17 \% $ . our results emphasize that using updated stellar population synthesis models with binary stellar evolution provides a more sound physical basis for stellar reionization. | delayed photons from binary evolution help reionize the universe |
we present cool j1323+0343, an early-type galaxy at z = 1.0153 ± 0.0006, strongly lensed by a cluster of galaxies at z = 0.353 ± 0.001. this object was originally imaged by decals and noted as a gravitational lens by cool-lamps, a collaboration initiated to find strong-lensing systems in recent public optical imaging data, and confirmed with follow-up data. with ground-based grzh imaging and optical spectroscopy from the las campanas observatory and the nordic optical telescope, we derive a stellar mass, metallicity, and star formation history from stellar-population synthesis modeling. the lens modeling implies a total magnification, summed over the three images in the arc, of μ ~ 113. the stellar mass in the source plane is m * ~ 10.64 m ⊙ and the 1σ upper limit on the star formation rate (sfr) in the source plane is sfr ~ 3.75 × 10-2 m ⊙ yr-1 (log ssfr = -12.1 yr-1) in the youngest two age bins (0-100 myr), closest to the epoch of observation. our measurements place cool j1323+0343 below the characteristic mass of the stellar mass function, making it an especially compelling target that could help clarify how intermediate-mass quiescent galaxies evolve. we reconstruct cool j1323+0343 in the source plane and fit its light profile. this object is below the expected size evolution of an early-type galaxy at this mass with an effective radius r e~ 0.5 kpc. this extraordinarily magnified and bright lensed early-type galaxy offers an exciting opportunity to study the morphology and star formation history of an intermediate-mass early-type galaxy in detail at z ~ 1. | cool-lamps. ii. characterizing the size and star formation history of a bright strongly lensed early-type galaxy at redshift 1.02 |
by employing monte carlo random sampling, traditional binary population synthesis (bps) offers a substantial improvement in efficiency over brute force, grid-based studies. even so, bps models typically require a large number of simulation realizations, a computationally expensive endeavor, to generate statistically robust results. recent advances in statistical methods have led us to revisit the traditional approach to bps. in this work we describe our publicly available code dart_board, which combines rapid binary evolution codes, typically used in traditional bps, with modern markov chain monte carlo methods. dart_board takes a novel approach that treats the initial binary parameters and the supernova kick vector as model parameters. this formulation has several advantages, including the ability to model either populations of systems or individual binaries, the natural inclusion of observational uncertainties, and the flexible addition of new constraints, which are problematic to include using traditional bps. after testing our code with mock systems, we demonstrate the flexibility of dart_board by applying it to three examples: (i) a generic population of high-mass x-ray binaries (hmxbs); (ii) the population of hmxbs in the large magellanic cloud (lmc), in which the spatially resolved star formation history is used as a prior; and (iii) one particular hmxb in the lmc, swift j0513.4-6547, in which we include observations of the system’s component masses and orbital period. although this work focuses on hmxbs, dart_board can be applied to a variety of stellar binaries, including the recent detections by gravitational wave observatories of merging compact object binaries. | dart_board: binary population synthesis with markov chain monte carlo |
we present a semi-analytical population synthesis model of protoplanetary clumps formed by disk instability at radial distances of 80-120 au. various clump density profiles, initial mass functions, protoplanetary disk models, stellar masses, and gap opening criteria are considered. when we use more realistic gap opening criteria, we find that gaps open only rarely, which strongly affects clump survival rates and their physical properties (mass, radius, and radial distance). the inferred surviving population is then shifted toward less massive clumps at smaller radial distances. we also find that populations of surviving clumps are very sensitive to the model assumptions and used parameters. depending on the chosen parameters, the protoplanets occupy a mass range between 0.01 and 16 m j and may either orbit close to the central star or as far out as 75 au, with a sweet spot at 10-30 au for the massive ones. however, in all of the cases we consider, we find that massive giant planets at very large radial distances are rare, in qualitative agreement with current direct imaging surveys. we conclude that caution should be taken in deriving population synthesis models as well as when comparing the models’ results with observations. | on the diversity in mass and orbital radius of giant planets formed via disk instability |
aims: i aim to explain the mass discrepancy between the observed double neutron-star binary population by radio pulsar observations and gravitational-wave observation.methods: i performed binary population synthesis calculations and compared their results with the radio and the gravitational-wave observations simultaneously.results: simulations of binary evolution were used to link different observations of double neutron star binaries with each other. i investigated the progenitor of gw190425 in more detail. a distribution of masses and merger times of the possible progenitors is presented.conclusions: a mass discrepancy between the radio pulsars in the milky way with another neutron star companion and the inferred masses from gravitational-wave observations of those kind of merging systems is naturally found in binary evolution. | masses of double neutron star mergers |
the inclusion of aligned-spin effects in gravitational-wave search pipelines for neutron-star-black-hole binary coalescence has been shown to increase the astrophysical reach with respect to search methods where spins are neglected completely, under astrophysically reasonable assumptions about black-hole spins. however, theoretical considerations and population synthesis models suggest that many of these binaries may have a significant misalignment between the black-hole spin and the orbital angular momentum, which could lead to precession of the orbital plane during the inspiral and a consequent loss in detection efficiency if precession is ignored. this work explores the effect of spin misalignment on a search pipeline that completely neglects spin effects and on a recently developed pipeline that only includes aligned-spin effects. using synthetic but realistic data, which could reasonably represent the first scientific runs of advanced-ligo detectors, the relative sensitivities of both pipelines are shown for different assumptions about black-hole spin magnitude and alignment with the orbital angular momentum. despite the inclusion of aligned-spin effects, the loss in signal-to-noise ratio due to precession can be as large as 40%, but this has a limited impact on the overall detection rate: even if precession is a predominant feature of neutron-star-black-hole binaries, an aligned-spin search pipeline can still detect at least half of the signals compared to an idealized generic precessing search pipeline. | impact of precession on aligned-spin searches for neutron-star-black-hole binaries |
one of the key observations regarding the stellar initial mass function (imf) is its near-universality in the milky way (mw), which provides a powerful way to constrain different star formation models that predict the imf. however, those models are almost universally 'cloud-scale' or smaller - they take as input or simulate single molecular clouds (gmcs), clumps or cores, and predict the resulting imf as a function of the cloud properties. without a model for the progenitor properties of all clouds that formed the stars at different locations in the mw (including ancient stellar populations formed in high redshift, likely gas-rich dwarf progenitor galaxies that looked little like the galaxy today), the predictions cannot be fully explored nor safely applied to 'live' cosmological calculations of the imf in different galaxies at different cosmological times. we therefore combine a suite of high-resolution cosmological simulations (from the feedback in realistic environments project), which form mw-like galaxies with reasonable star formation properties and explicitly resolve massive gmcs, with various proposed cloud-scale imf models. we apply the models independently to every star particle formed in the simulations to synthesize the predicted imf in the present-day galaxy. we explore models where the imf depends on jeans mass, sonic or 'turbulent bonnor-ebert' mass, fragmentation with a polytropic equation of state, or where it is self-regulated by protostellar feedback. we show that all of these models, except the feedback-regulated ones, predict far more variation (∼0.6-1 dex 1σ scatter in the imf turnover mass) in the simulations than is observed in the mw. | comparing models for imf variation across cosmological time in milky way-like galaxies |
we present a new technique for empirically calibrating how the x-ray luminosity function (xlf) of x-ray binary (xrb) populations evolves following a star formation event. we first utilize detailed stellar population synthesis modeling of far-uv-to-far-ir photometry of the nearby face-on spiral galaxy m51 to construct maps of the star formation histories (sfhs) on subgalactic (≈400 pc) scales. next, we use the ≈850 ks cumulative chandra exposure of m51 to identify and isolate 2-7 kev detected point sources within the galaxy, and we use our sfh maps to recover the local properties of the stellar populations in which each x-ray source is located. we then divide the galaxy into various subregions based on their sfh properties (e.g., star formation rate (sfr) per stellar mass ({m}\star ) and mass-weighted stellar age) and group the x-ray point sources according to the characteristics of the regions in which they are found. finally, we construct and fit a parameterized xlf model that quantifies how the xlf shape and normalization evolves as a function of the xrb population age our best-fit model indicates that the xrb xlf per unit stellar mass declines in normalization, by ∼3-3.5 dex, and steepens in slope from ≈10 myr to ≈10 gyr. we find that our technique recovers results from past studies of how xrb xlfs and xrb luminosity scaling relations vary with age and provides a self-consistent picture for how xrb xlfs evolve with age. | on the spatially resolved star formation history in m51. ii. x-ray binary population evolution |
context. most of our knowledge of the stellar component of galaxies is based on the analysis of distant systems and comes from integrated light data. it is important to test whether the results of the star formation histories (sfh) obtained with standard full-spectrum fitting methods are in agreement with those obtained through colour-magnitude diagram (cmd) fitting (usually considered the most reliable approach).aims: we compare sfhs recovered from the two techniques in leo a, a local group dwarf galaxy most of whose stars formed during the last 8 gyrs. this complements our previous findings in a field in the large magellanic cloud bar, where star formation has been in progress since early epochs at varying rates.methods: we have used gtc/osiris in long-slit mode to obtain a high-quality integrated light spectrum by scanning a selected region within leo a, for which a cmd reaching the old main sequence turn-off (omsto) is available from hst. we compared the sfh obtained from the two datasets, using state-of-art methods of integrated light (steckmap) and resolved stellar population analysis. in the case of the cmd, we computed the sfh both from a deep cmd (observed with hst/acs) and from a shallower cmd (archival data from hst/wfpc2).results: the agreement between the sfhs recovered from the omsto cmd and from full spectrum fitting is remarkable, particularly regarding the time evolution of the star formation rate. the overall extremely low metallicity of leo a is recovered up to the last 2 gyrs when some discrepancies appear. a relatively high metallicity found for the youngest stars from the integrated data is a recurring feature that might indicate that the current models or synthesis codes should be revised, but that can be significantly mitigated using a more restrictive metallicity range. we thoroughly inspect the robustness of both approaches separately, finding that the subtle differences between them are inherent to the methods themselves. the sfh recovered from the shallow cmd also presents differences with the other two.conclusions: modern full-spectral fitting codes are able to recover both average constant sfhs (lmc case) and sfhs with a dominant fraction of young stellar populations. the analysis of high s/n spectra seems to provide more reliable sfh estimates than that of cmds not reaching the omsto. the comparison presented in this paper needs to be repeated for predominantly old systems, thus assessing the performance of full-spectrum fitting for a full range of sfhs. | integrated-light analyses vs. colour-magnitude diagrams. ii. leo a: an extremely young dwarf in the local group |
"changing-look" active galactic nuclei (cl-agns) are a newly discovered class of agns that show the appearance (or disappearance) of broad emission lines within short timescales (months to years), and are often associated with dramatic changes in their continuum emissions. they provide us with an unprecedented chance to directly investigate the host galaxy properties with minimal contamination from the luminous central engine during the turn-off state, which is difficult for normal luminous agns. in this work, for the first time, we systematically characterize the stellar populations and star formation histories of host galaxies for 26 turn-off cl-agns using the stellar population synthesis code starlight. we find that the stellar populations of cl-agns are similar to those of normal agns, except that the intermediate stellar populations contribute more fractions. we estimate their stellar velocity dispersions (σ ⋆) and black hole masses (m bh,vir), and find that cl-agns also follow the overall m bh-σ ⋆ relationship. we also confirm the previous claims that cl-agns tend to be biased toward lower eddington ratios, and that their extreme variabilities are more likely due to the intrinsic changes of the accretion rates. in addition, cl-agns with recent star formations tend to have higher eddington ratios. compared with previous studies, our analysis suggests that there may be a correlation between cl-agn host galaxy properties and their cl phenomena. | a systematic analysis of stellar populations in the host galaxies of changing-look agns |
context. large spectroscopic galactic surveys imply a selection function in the way they performed their target selection.aims: we investigate here the effect of the selection function on the metallicity distribution function (mdf) and on the vertical metallicity gradient by studying similar lines of sight using four different spectroscopic surveys (apogee, lamost, rave, and gaia-eso), which have different targeting strategies and therefore different selection functions.methods: we use common fields between the spectroscopic surveys of apogee, lamost, rave (alr) and apogee, rave, gaia-eso (agr) and use two stellar population synthesis models, galaxia and trilegal, to create mock fields for each survey. we apply the selection function in the form of colour and magnitude cuts of the respective survey to the mock fields to replicate the observed source sample. we make a basic comparison between the models to check which best reproduces the observed sample distribution. we carry out a quantitative comparison between the synthetic mdf from the mock catalogues using both models to understand the effect of the selection function on the mdf and on the vertical metallicity gradient.results: using both models, we find a negligible effect of the selection function on the mdf for apogee, lamost, and rave. we find a negligible selection function effect on the vertical metallicity gradients as well, though galaxia and trilegal have steeper and shallower slopes, respectively, than the observed gradient. after applying correction terms on the metallicities of rave and lamost with respect to our reference apogee sample, our observed vertical metallicity gradients between the four surveys are consistent within 1σ. we also find consistent gradient for the combined sample of all surveys in alr and agr. we estimated a mean vertical metallicity gradient of - 0.241 ± 0.028 dex kpc-1. there is a significant scatter in the estimated gradients in the literature, but our estimates are within their ranges.conclusions: we have shown that there is a negligible selection function effect on the mdf and the vertical metallicity gradients for apogee, rave, and lamost using two stellar population synthesis models. therefore, it is indeed possible to combine common fields of different surveys in studies using mdf and metallicity gradients provided their metallicities are brought to the same scale. | effects of the selection function on metallicity trends in spectroscopic surveys of the milky way |
intermediate-richness galaxy groups are an important testing ground for modified newtonian dynamics (mond). first, they constitute a distinct type of galactic systems, with their own evolution histories and underlying physical processes; second, they probe little-chartered regions of parameter space, as they have baryonic masses similar to massive galaxies, and similar velocity dispersions, but much larger sizes—similar to cluster cores (or even to clusters), but much lower dispersions. importantly in the context of mond, they have the lowest internal accelerations reachable inside galactic systems. following my recent analysis of mond in galaxy groups, i came across a much superior sample, which i analyze here. this extensive catalog permits strict quality cuts that still leave a large sample of 56 medium-richness groups, better suited for dynamical analysis—e.g., in having a large number (≥15 ) of members with measured velocities. i find that these groups obey the deep-mond relation between baryonic mass, mm, and velocity dispersion, σ : mmg a0=(81 /4 )σ4 , with individual, mond, mass-to-light ratios, mm/lk of order 1 m⊙/lk ,⊙ , and a sample median value of (mm/lk)med=0.7 m⊙/lk ,⊙ . these compare well with stellar values deduced for single galaxies, and with values deduced from population-synthesis analyses. in contrast, the dynamical, newtonian md/lk values are much larger—several tens solar units, and (md/lk)med=37 m⊙/lk ,⊙ . the same mond relation describes (isolated) dwarf spheroidals—two-three orders smaller in size, and seven-eight orders lower in mass. the groups conformation to the mond relation is equivalent to their lying on the deep-mond branch of the "mass-discrepancy-acceleration relation," g ≈(gna0)1 /2 , for g as low as a few percents of a0 (gn is the newtonian, baryonic, gravitational acceleration, and g the actual one). this argues against systematic departure from mond at extremely low accelerations (as has been suggested). this conformation also argues against the hypothesis that the remaining mond conundrum in cluster cores bespeaks a breakdown of mond on large-distance scales; our groups are as large as cluster cores, but do not show obvious disagreement with mond. i also discuss the possible presence of the idiosyncratic, mond external-field effect. | mond in galaxy groups: a superior sample |
we present the first results from an integral field unit (ifu) spectroscopic survey of a ∼75 kpc region around three brightest cluster galaxies (bcgs), combining over 100 ifu fibres to study the intracluster light (icl). we fit population synthesis models to estimate age and metallicity. for abell 85 and abell 2457, the icl is best-fit with a fraction of old, metal-rich stars like in the bcg, but requires 30-50 per cent young and metal-poor stars, a component not found in the bcgs. this is consistent with the icl having been formed by a combination of interactions with less massive, younger, more metal-poor cluster members in addition to stars that form the bcg. we find that the three galaxies are in different stages of evolution and may be the result of different formation mechanisms. the bcg in abell 85 is near a relatively young, metal-poor galaxy, but the dynamical friction time-scale is long and the two are unlikely to be undergoing a merger. the outer regions of abell 2457 show a higher relative fraction of metal-poor stars, and we find one companion, with a higher fraction of young, metal-poor stars than the bcg, which is likely to merge within a gigayear. several luminous red galaxies are found at the centre of the cluster iizw108, with short merger time-scales, suggesting that the system is about to embark on a series of major mergers to build up a dominant bcg. the young, metal-poor component found in the icl is not found in the merging galaxies. | stellar populations of bcgs, close companions and intracluster light in abell 85, abell 2457 and iizw108 |
properties of the to-date observed binary black hole (bbh) merger events suggest a preference toward spin-orbit aligned mergers. naturally, this has caused widespread interest and speculations regarding implications on various merger formation channels. here we show that (i) not only the bbh merger population from isolated binaries but also (ii) bbh population formed in young massive clusters (ymcs) would possess an asymmetry in favor of aligned mergers, in the distribution of the events' effective spin parameter (χ eff). in our analysis, we utilize bbh merger outcomes from state-of-the-art n-body evolutionary models of ymcs and isolated binary population synthesis. we incorporate, for the first time in such an analysis, misalignments due to both natal kicks and dynamical encounters. the ymc χ eff distribution has a mean (an antialigned merger fraction) of <χ eff> ≤ 0.04 (fx- ≈ 40%), which is smaller (larger) than but consistent with the observed asymmetry of <χ eff> ≈ 0.06 (fx- ≈ 28%) as obtained from the population analysis by the ligo-virgo-kagra collaboration. in contrast, isolated binaries alone tend to produce a much stronger asymmetry; for the tested physical models, <χ eff> ≈ 0.25 and fx- ≲ 7%. although the ymc χ eff distribution is more similar to the observed counterpart, none of the channels correctly reproduce the observed distribution. our results suggest that further extensive model explorations for both isolated binary and dynamical channels as well as better observational constraints are necessary to understand the physics of "the symmetry breaking" of the bbh merger population. | symmetry breaking in merging binary black holes from young massive clusters and isolated binaries |
in this paper, we use an rxte library of spectral models from 10 black hole and 9 pulsar x-ray binaries, as well as model spectra available in the literature from 13 extra-galactic ultra-luminous x-ray sources (ulxs). we compute average bolometric corrections (bc = lband/lbol) for our sample as a function of different accretion rates. we notice the same behaviour between black hole and pulsar bcs only when ulx pulsars are included. these measurements provide a picture of the energetics of the accretion flow for an x-ray binary based solely on its observed luminosity in a given band. moreover, it can be a powerful tool in x-ray binary population synthesis models. furthermore, we calculate the x-ray (2-10 kev) to optical (v band) flux ratios originating from the disc/corona at different eddington ratios for the black hole x-ray binaries in our sample. this provides a metric of the maximum contribution of the disc to the optical emission of a binary system and better constraints on its nature (donor type, etc.). we find that the optical to x-ray flux ratio shows very little variation as a function of accretion rate, but testing for different disc geometry scenarios we find that the optical contribution of the disc increases as the p value decreases [t(r) ~ r-p]. moreover, observational data are in agreement with a thicker disc scenario (p < 0.65), which could also possibly explain the lack of observed high-inclination systems. | average bolometric corrections and optical to x-ray flux measurements as a function of accretion rate for x-ray binaries |
the binding energy parameter λ plays a vital role in common envelope evolution. though it is well known that λ takes different values for stars with different masses and varies during stellar evolution, it has been erroneously adopted as a constant in most population synthesis calculations. we have systematically calculated the values of λ for stars of masses 1 - 60 m ⊙ by use of an updated stellar evolution code, taking into account the contribution from both gravitational energy and internal energy to the binding energy of the envelope. we adopt the criterion for the core-envelope boundary advocated by ivanova. a new kind of λ with an enthalpy prescription is also investigated. we present fitting formulae for the calculated values of various kinds of λ, which can be used in future population synthesis studies. | the binding energy parameter for common envelope evolution |
populations of massive stars are directly reflective of the physics of stellar evolution. counts of subtypes of massive stars and ratios of massive stars in different evolutionary states have been used ubiquitously as diagnostics of age and metallicity effects. while the binary fraction of massive stars is significant, inferences are often based upon models incorporating only single-star evolution. in this work, we utilize custom synthetic stellar populations from the binary population and stellar synthesis code to determine the effect of stellar binaries on number count ratios of different evolutionary stages in both young massive clusters and galaxies with massive stellar populations. we find that many ratios are degenerate in metallicity, age, and/or binary fraction. we develop diagnostic plots using these stellar count ratios to help break this degeneracy, and use these plots to compare our predictions to observed data in the milky way and the local group. these data suggest a possible correlation between the massive star binary fraction and metallicity. we also examine the robustness of our predictions in samples with varying levels of completeness. we find including binaries and imposing a completeness limit can both introduce ≳0.1 dex changes in inferred ages. our results highlight the impact that binary evolution channels can have on the massive star population. | stellar population diagnostics of the massive star binary fraction |
a galaxy’s stellar mass is one of its most fundamental properties, but it remains challenging to measure reliably. with the advent of very large optical spectroscopic surveys, efficient methods that can make use of low signal-to-noise spectra are needed. with this in mind, we created a new software package for estimating effective stellar mass-to-light ratios {{{\upsilon }}}*that uses a principal component analysis (pca) basis set to optimize the comparison between observed spectra and a large library of stellar population synthesis models. in paper i, we showed that with a set of six pca basis vectors we could faithfully represent most optical spectra from the mapping nearby galaxies at apo (manga) survey, and we tested the accuracy of our m/l estimates using synthetic spectra. here, we explore sources of systematic error in our mass measurements by comparing our new measurements to data from the literature. we compare our stellar mass surface density estimates to kinematics-derived dynamical mass surface density measurements from the diskmass survey and find some tension between the two that could be resolved if the disk scale heights used in the kinematic analysis were overestimated by a factor of ∼1.5. we formulate an aperture-corrected stellar mass catalog for the manga survey, and compare to previous stellar mass estimates based on multiband optical photometry, finding typical discrepancies of 0.1 dex. using the spatially resolved manga data, we evaluate the impact of estimating total stellar masses from spatially unresolved spectra, and we explore how the biases that result from unresolved spectra depend upon the galaxy’s dust extinction and star formation rate. finally, we describe an sdss value-added catalog that will include both spatially resolved and total (aperture-corrected) stellar masses for manga galaxies. | resolved and integrated stellar masses in the sdss-iv/manga survey. ii. applications of pca-based stellar mass estimates |
the distribution of inner orbital periods of solar-type main-sequence (ms) triple star systems is known to be peaked at a few days, and this has been attributed to tidal evolution combined with eccentricity excitation due to lidov-kozai oscillations. solar-type ms quadruple star systems also show peaks in their inner orbital period distributions at a few days. here, we investigate the natural question whether tidal evolution combined with secular evolution can explain the observed inner orbital period distributions in quadruple stars. we carry out population synthesis simulations of solar-type ms quadruple star systems in both the 2+2 (two binaries orbiting each other's barycentre) and 3+1 (triple orbited by a fourth star) configurations. we take into account secular gravitational and tidal evolution and the effects of passing stars. we assume that no short-period systems are formed initially, and truncate the initial orbital period distributions below 10 d accordingly. we find that, due to secular and tidal evolution, the inner orbital period distributions develop tails at short periods. although qualitatively consistent with the observations, we find that our simulated orbital period distributions only quantitatively agree with the observations for the 3+1 systems. the observed 2+2 systems, on the other hand, show an enhancement of systems around 10 d, which is not reproduced in the simulations. this suggests that the inner orbital periods of 2+2 systems are not predominantly shaped by tidal and secular evolution, but by other processes, most likely occurring during the stellar formation and early evolution. | shrinking orbits in hierarchical quadruple star systems |
galactic binary neutron stars (bnss) are a unique laboratory to probe the evolution of bnss and their progenitors. here, we use a new version of the population synthesis code sevn to evolve the population of galactic bnss, by modelling the spin up and down of pulsars self-consistently. we analyse the merger rate $\mathcal {r}_{\rm mw}$, orbital period porb, eccentricity e, spin period p, and spin period derivative $\dot{p}$ of the bns population. values of the common envelope parameter α = 1-3 and an accurate model of the milky way star formation history best reproduce the bns merger rate in our galaxy ($\mathcal {r}_{\rm mw}\approx {}30$ myr-1). we apply radio-selection effects to our simulated bnss and compare them to the observed population. using a dirichlet process gaussian mixture method, we evaluate the four-dimensional likelihood in the $(p_{\rm orb}, e, p, \dot{p})$ space, by comparing our radio-selected simulated pulsars against galactic bnss. our analysis favours an uniform initial distribution for both the magnetic field (1010-13 g) and the spin period (10-100 ms). the implementation of radio selection effects is critical to match not only the spin period and period derivative, but also the orbital period and eccentricity of galactic bnss. according to our fiducial model, the square kilometre array will detect ~20 new bnss in the milky way. | binary neutron star populations in the milky way |
there are important but unresolved processes in the standard formation scenarios of double compact star binaries (dcbs; black hole-black hole (bh-bh), bh-neutron star (bh-ns), ns-ns systems), such as mass transfer and the common envelope (ce) phase. we analyze the effects of different assumptions on key physical processes and binary initial conditions on massive star binary evolution with binary population synthesis (bps), including a survey of proposed prescriptions for the mass transfer (q cr) and the binding energy parameter (λ) in the ce phase. we find that q cr clearly affects the properties of ns-ns systems while λ has an influence on the mass distributions of bh-bh systems. the merger rates of dcbs are increased by efficient ce ejection, which in our prescription is related to the binding energy parameter, including all the possible budgets to the energy content. it has been suggested that the difference in the properties of gw150914 and gw151226 may reflect different metallicity. we reproduce their properties with our bps calculations and find that the property of bh-bh systems at low metallicity is sensitive to λ the efficient ce ejection leads to a top-heavy mass distribution both for the primary and secondary bhs, which is favored to explain the nature of gw150914. the efficient ce ejection also leads to enhancement of both the bh-bh and ns-ns merger rates to the level consistent with the observational constraints from the detected gravitational-wave sources, including gw170817. | monte carlo population synthesis on massive star binaries: astrophysical implications for gravitational-wave sources |
context. recent studies on stellar evolution have shown that the properties of compact objects strongly depend on the metallicity of the environment in which they were formed.aims: using some very simple assumptions on the metallicity of the stellar populations, we explore how this property affects the unresolved gravitational-wave background from extragalactic compact binaries.methods: we obtained a suit of models using population synthesis code, estimated the gravitational-wave background they produce, and discuss its detectability with second- (advanced ligo, advanced virgo) and third- (einstein telescope) generation detectors.results: our results show that the background is dominated by binary black holes for all considered models in the frequency range of terrestrial detectors, and that it could be detected in most cases by advanced ligo/virgo, and with einstein telescope with a very high signal-to-noise ratio. the observed peak in a gravitational-wave spectrum depends on the metallicity of the stellar population. | effect of metallicity on the gravitational-wave signal from the cosmological population of compact binary coalescences |
the chemical enrichments detected in carbon- and s-element-enhanced metal-poor (cemp-s) stars are believed to be the consequence of a past episode of mass transfer from a now extinct asymptotic-giant-branch primary star. this hypothesis is borne out by the evidence that most cemp-s stars exhibit radial-velocity variations suggesting that they belong to binary systems in which the companion is not directly visible. we used the orbital-period distribution of an unbiased sample of observed cemp-s stars to investigate the constraints it imposes on our models of binary evolution and on the properties of the metal-poor binary population in the galactic halo. we generated synthetic populations of metal-poor binary stars using different assumptions about the initial period distribution and about the physics of the mass-transfer process, and we compared the predicted period distributions of our synthetic cemp-s stars with the observed one. with a set of default assumptions often made in binary population-synthesis studies, the observed period distribution cannot be reproduced. the percentage of observed cemp-s systems with periods shorter than about 2000 days is underestimated by almost a factor of three, and by about a factor of two between 3000 and 10 000 days. conversely, about 40% of the simulated systems have periods longer than 104 days, which is approximately the longest measured period among cemp-s stars. variations in the assumed stability criterion for roche-lobe overflow and the efficiency of wind mass transfer do not alter the period distribution enough to overcome this discrepancy. to reconcile the results of the models with the orbital properties of observed cemp-s stars, one or both of the following conditions are necessary: (i) the specific angular momentum carried away by the material that escapes the binary system is approximately two to five times higher than currently predicted by analytical models and hydrodynamical simulations of wind mass transfer, and (ii) the initial period distribution of very metal-poor binary stars is significantly different from that observed in the solar vicinity and weighted towards periods shorter than about ten thousand days. our simulations show that some, perhaps all, of the observed cemp-s stars with apparently constant radial velocity could be undetected binaries with periods longer than 104 days, but the same simulations also predict that twenty to thirty percent of detectable binaries should have periods above this threshold, much more than are currently observed. | understanding the orbital periods of cemp-s stars |
the copper abundances of 29 metal-poor stars are determined based on the high-resolution, high-signal-to-noise ratio spectra from the uves spectrograph at the eso vlt telescope. our sample consists of the stars of the galactic halo, thick- and thin-disk, with [fe/h] ranging from ∼-3.2 to ∼0.0 dex. the non-local thermodynamic equilibrium (nlte) effects of cu i lines are investigated, and line formation calculations are presented for an atomic model of copper including 97 terms and 1089 line transitions. we adopted the recently calculated photoionization cross sections of cu i, and investigated the hydrogen collision by comparing the theoretical and observed line profiles of our sample stars. the copper abundances are derived for both local thermodynamic equilibrium (lte) and nlte based on the spectrum synthesis methods. our results show that the nlte effects for cu i lines are important for metal-poor stars, in particular for very metal-poor stars, and these effects depend on the metallicity. for very metal-poor stars, the nlte abundance correction reaches as large as ∼+0.5 dex compared to standard lte calculations. our results indicate that [cu/fe] is under-abundant for metal-poor stars (∼-0.5 dex) when the nlte effects are included. based on data obtained from eso science archive and the subaru telescope. | nlte analysis of copper lines in different stellar populations |
we present analysis of the integrated spectral energy distribution (sed) from the ultraviolet (uv) to the far-infrared and hα of a sample of 29 local systems and individual galaxies with infrared (ir) luminosities between 1011l⊙ and 1011.8l⊙. we combined new narrow-band hα + [n ii] and broad-band g, r optical imaging taken with the nordic optical telescope (not), with archival galex, 2mass, spitzer, and herschel data. their seds(photometry and integrated hα flux) were fitted simultaneously with a modified version of the magphys code using stellar population synthesis models for the uv-near-ir range and thermal emission models for the ir emission taking the energy balance between the absorbed and re-emitted radiation into account. from the sed fits, we derive the star-formation histories (sfh) of these galaxies. for nearly half of them, the star-formation rate appears to be approximately constant during the last few gyr. in the other half, the current star-formation rate seems to be enhanced by a factor of 3-20 with respect to what occurred ~1 gyr ago. objects with constant sfh tend to be more massive than starbursts, and they are compatible with the expected properties of a main-sequence (m-s) galaxy. likewise, the derived sfhs show that all our objects were m-s galaxies ~1 gyr ago with stellar masses between 1010.1 and 1011.5 m⊙. we also derived the average extinction (av = 0.6-3 mag) and the polycyclic aromatic hydrocarbon luminosity to lir ratio (0.03-0.16) from our fits. we combined the av with the total ir and hα luminosities into a diagramthat can be used to identify objects with rapidly changing (increasing or decreasing) sfr during the past 100 myr. appendices are available in electronic form at http://www.aanda.orgfits files for all the reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/577/a78 | star-formation histories of local luminous infrared galaxies |
recently, the possible coexistence of a first family composed of “normal” neutron stars (nss) with a second family of strange quark stars (qss) has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. in this paper, we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and nss in different subpopulations. we incorporate the strange qs formation model provided by the two-families scenario, and we perform a large-scale population synthesis study in order to obtain the population characteristics. according to our results, the main channel for strange qs formation in binary systems is accretion from a secondary companion on an ns. therefore, a rather large number of strange qss form by accretion in low-mass x-ray binaries and this opens the possibility of having explosive grb-like phenomena not related to supernovae and not due to the merger of two nss. the number of double strange qs systems is rather small, with only a tiny fraction that merge within a hubble time. this drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from earth and lunar experiments. moreover, this value of the flux rules out at least one relevant channel for the transformation of all nss into strange qss by strangelets’ absorption. | strange quark stars in binaries: formation rates, mergers, and explosive phenomena |
photoevaporation from high-energy stellar radiation has been thought to drive the dispersal of protoplanetary discs. different theoretical models have been proposed, but their predictions diverge in terms of the rate and modality at which discs lose their mass, with significant implications for the formation and evolution of planets. in this paper, we use disc population synthesis models to interpret recent observations of the lowest accreting protoplanetary discs, comparing predictions from euv-driven, fuv-driven, and x-ray-driven photoevaporation models. we show that the recent observational data of stars with low accretion rates (low accretors) point to x-ray photoevaporation as the preferred mechanism driving the final stages of protoplanetary disc dispersal. we also show that the distribution of accretion rates predicted by the x-ray photoevaporation model is consistent with observations, while other dispersal models tested here are clearly ruled out. | lowest accreting protoplanetary discs consistent with x-ray photoevaporation driving their final dispersal |
we study the atomic neutral hydrogen (h i) content of ~1600 galaxies up to z ~ 0.1 using stacking techniques. the observations were carried out with the westerbork synthesis radio telescope (wsrt) in the area of the sdss south galactic cap (ssgc), where we selected a galaxy sample from the sdss spectroscopic catalog. multi-wavelength information is provided by sdss, nvss, galex, and wise. we use the collected information to study h i trends with color, star-forming, and active galactic nuclei (agn) properties. using near-uv (nuv) -r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies. as expected based on previous observations, we detect h i in green valley objects with lower amounts of h i than blue galaxies, while stacking only produces a 3σ upper limit for red galaxies with mhi< (5 ± 1.5) × 108 m⊙ and mhi/lr< 0.02 ± 0.006 m⊙/l⊙ (averaged over four redshift bins up to z ~ 0.1). we find that the h i content is more dependent on nuv -r color, and less on ionization properties, in the sense that regardless of the presence of an optical agn (based on optical ionization line diagnostics), green-valley galaxies always show h i, whereas red galaxies only produce an upper limit. this suggests that feedback from optical agn is not the (main) reason for depleting large-scale gas reservoirs. low-level radio continuum emission in our galaxies can stem either from star formation, or from agn. we use the wise color-color plot to separate these phenomena by dividing the sample into ir late-type and ir early-type galaxies. we find that the radio emission in ir late-type galaxies stems from enhanced star formation, and this group is detected in h i. however, ir early-type galaxies lack any sign of h i gas and star formation activity, suggesting that radio agn are likely to be the source of radio emission in this population. future h i surveys will allow for extending our studies to higher redshift, and for testing any possible evolution of the h i content in relation to star-forming and agn properties up to cosmologically significant distances. such surveys will provide enough data to test the effect of radio/optical agn feedback on the h i content at lower, currently rather unexplored h i detection limit (mhi < 107 m⊙). the final stacked spectra of the galaxies are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/580/a43 | from star-forming galaxies to agn: the global hi content from a stacking experiment |
the extragalactic background light (ebl) consists of integrated light from all sources of emission throughout the history of the universe. at near-infrared wavelengths, the ebl is dominated by stellar emission across cosmic time; however, the spectral and redshift information of the emitting sources is entangled and cannot be directly measured by absolute photometry or fluctuation measurements. cross-correlating near-infrared maps with tracers of known redshift enables ebl redshift tomography, as ebl emission will only correlate with external tracers from the same redshift. here, we forecast the sensitivity of probing the ebl spectral energy distribution as a function of redshift by cross-correlating the upcoming near-infrared spectro-imaging survey, spherex, with several current and future galaxy redshift surveys. using a model galaxy luminosity function, we estimate the cross power spectrum clustering amplitude on large scales, and forecast that the near-infrared ebl spectrum can be detected tomographically out to z ~ 6. we also predict a high-significance measurement (~102-104 σ) of the small-scale cross power spectrum out to z ~ 10. the amplitudes of the large-scale cross power spectra can constrain the cosmic evolution of the stellar synthesis process through both continuum and the line emission, while on the nonlinear and poisson noise scales, the high-sensitivity measurements can probe the mean spectra associated with the tracer population across redshift. | cosmic near-infrared background tomography with spherex using galaxy cross-correlations |
planets open deep gaps in protoplanetary discs when their mass exceeds a gap opening mass, mgap. we use one- and two-dimensional simulations to study planet gap opening in discs with angular momentum transport powered by mhd disc winds. we parametrize the efficiency of the mhd disc wind angular momentum transport through a dimensionless parameter αdw, which is an analogue to the turbulent viscosity αv. we find that magnetized winds are much less efficient in counteracting planet tidal torques than turbulence is. for discs with astrophysically realistic values of αdw, mgap is always determined by the residual disc turbulence, and is a factor of a few to ten smaller than usually obtained for viscous discs. we introduce a gap opening criterion applicable for any values of αv and αdw that may be useful for planet formation population synthesis. we show that in discs powered by magnetized winds growing planets detach from the disc at planet masses below $\sim 0.1{\, {\rm m}_{\rm j}}$ inside 10 au. this promotes formation of super-earth planets rather than gas giants in this region, in particular precluding formation of hot jupiters in situ. on larger scales, alma gap opening planet candidates may be less massive than currently believed. future high-resolution observations with instruments such as the extended alma, ngvla, and ska are likely to show abundant narrow annular features at r < 10 au due to ubiquitous super-earth planets. | gap opening by planets in discs with magnetized winds |
binary neutron star mergers are one of the ultimate events of massive binary star evolution, and our understanding of their parent systems is still in its infancy. upcoming gravitational wave detections, coupled with multi-wavelength follow-up observations, will allow us to study an increasing number of these events by characterizing their neighbouring stellar populations and searching for their progenitors. stellar evolution simulations are essential to this work, but they are also based on numerous assumptions. additionally, the models used to study the host galaxies differ from those used to characterize the progenitors and are typically based on single-star populations. here we introduce a framework to perform an end-to-end analysis and deploy it to the first detected binary neutron star merger event, gw170817. with the binary population and spectral synthesis codes we are able to retrieve the physical properties of the host galaxy ngc 4993 as well as infer progenitor candidates. in our simulations, there is a >98% chance that gw170817 originated from a stellar population with metallicity z = 0.010, born between 5 and 12.5 gyr ago. by carefully weighing the stellar genealogies, we find that gw170817 most likely came from a binary system born with a 13-24 m⊙ primary and 10-12 m⊙ secondary that underwent 2 or 3 common envelope events over their lifetime. | end-to-end study of the host galaxy and genealogy of the first binary neutron star merger |
context. spectral population synthesis (ps) is a fundamental tool in extragalactic research that aims to decipher the assembly history of galaxies from their spectral energy distribution (sed). whereas this technique has led to key insights into galaxy evolution in recent decades, star formation histories (sfhs) inferred therefrom have been plagued by considerable uncertainties stemming from inherent degeneracies and the fact that until recently all ps codes were restricted to purely stellar fits, neglecting the essential contribution of nebular emission (ne). with the advent of fado (fitting analysis using differential evolution optimisation), the now possible self-consistent modelling of stellar and ne opens new routes to the exploration of galaxy sfhs.aims: the main goal of this study is to quantitatively explore the accuracy to which fado can recover physical and evolutionary properties of galaxies and compare its output with that from purely stellar ps codes.methods: fado and starlight were applied to synthetic seds that track the spectral evolution of stars and gas in extinction-free mock galaxies of solar metallicity that form their stellar mass (m⋆) according to different parametric sfhs. spectral fits were computed for two different set-ups that approximate the spectral range of sdss and califa (v500) data, using up to seven libraries of simple stellar population spectra in the 0.005-2.5 z⊙ metallicity range.results: our analysis indicates that fado can recover the key physical and evolutionary properties of galaxies, such as m⋆ and mass- and light-weighted mean age and metallicity, with an accuracy better than 0.2 dex. this is the case even in phases of strongly elevated specific star formation rate (ssfr) and thus with considerable ne contamination (ew(hα) > 103 å). likewise, population vectors from fado adequately recover the mass fraction of stars younger than 10 myr and older than 1 gyr (m⋆<10myr/m⋆total and m⋆>1gyr/m⋆total, respectively) and reproduce with a high fidelity the observed hα luminosity. as for starlight, our analysis documents a moderately good agreement with theoretical values only for evolutionary phases for which ne drops to low levels (ew(hα) ≤ 60 å) which, depending on the assumed sfh, correspond to an age between ∼0.1 gyr and 2-4 gyr. however, fits with starlight during phases of high ssfr severely overestimate both m⋆ and the mass-weighted stellar age, whereas strongly underestimate the light-weighted age and metallicity. furthermore, our analysis suggests a subtle tendency of starlight to favour a bi-modal sfh, as well a slightly overestimated m⋆<10myr/m⋆total, regardless of galaxy age. whereas the amplitude of these biases can be reduced, depending on the specifics of the fitting procedure (e.g. accuracy and completeness of flagging emission lines, omission of the balmer and paschen jump from the fit), they persist even in the idealised case of a line-free sed comprising only stellar and nebular continuum emission.conclusions: the insights from this study suggest that the neglect of nebular continuum emission in starlight and similar purely stellar ps codes could systematically impact m⋆ and sfh estimates for star-forming galaxies. we argue that these biases can be relevant in the study of a range of topics in extragalactic research, including the redshift-dependent slope of the star formation (sf) main sequence, the sf frosting hypothesis, and the regulatory role of supermassive black holes on the global sfh of galaxies. | self-consistent population spectral synthesis with fado. i. the importance of nebular emission in modelling star-forming galaxies |
kilonovae produced by mergers of binary neutron stars (bnss) are important transient events to be detected by time domain surveys with the alerts from the ground-based gravitational wave detectors. the observational properties of these kilonovae depend on the physical processes involved in the merging processes and the equation of state (eos) of neutron stars (nss). in this paper, we investigate the dependence of kilonova luminosities on the parameters of bns mergers, and estimate the distribution functions of kilonova peak luminosities (klfs) at the u, g, r, i, y, and z bands as well as its dependence on the ns eos, by adopting a comprehensive semi-analytical model for kilonovae (calibrated by the observations of gw170817), a population synthesis model for the cosmic bnss, and the ejecta properties of bns mergers predicted by numerical simulations. we find that the kilonova light curves depend on both the bns properties and the ns eos, and the klfs at the considered bands are bimodal with the bright components mostly contributed by bns mergers with total mass $\lesssim 3.2\, \mathrm{m}_\odot$/$2.8\, \mathrm{m}_\odot$ and fainter components mostly contributed by bns mergers with total mass $\gtrsim 3.2\, \mathrm{m}_\odot$/$2.8\, \mathrm{m}_\odot$ by assuming a stiff/soft (dd2/sly) eos. the emission of the kilonovae in the klf bright components is mostly due to the radiation from the wind ejecta by the remnant discs of bns mergers, while the emission of the kilonovae in the klf faint components is mostly due to the radiation from the dynamical ejecta by the bns mergers. | the luminosity functions of kilonovae from binary neutron star mergers under different equation of states |
we map the gas excitation and kinematics, and the stellar population properties of the seyfert 1 galaxy ngc 5548 using gemini near infrared integral field spectrograph in the j and k bands at a spatial and velocity resolution of 105 pc and 45 km s-1, respectively. emission-line flux distributions in ionized and molecular gas extend up to ≈400 pc from the nucleus, where they are found to peak. the mass of h ii is 4.8±0.6 × 106 m⊙ and the mass of warm h2 is 1.1±0.2 × 103 m⊙, while the mass of cold h2 is estimated as 5.8±1.2 × 108 m⊙. the pa β emission shows two kinematic components: one in blueshift, with velocity reaching ≈-300 km s-1 and another showing a velocity field characteristic of rotation in the galaxy plane. the blueshifted component is also observed in the coronal line [s ix]λ1.2523 μm, while the rotational component is also observed in the molecular gas. we interpret this velocity field as due to gas rotating in the galaxy plane plus an outflow, and estimate a mass outflow rate of 6.8±0.75 m⊙ yr-1. spectral synthesis of the continuum shows nuclear emission dominated by a featureless agn continuum combined with hot dust emission attributed to a dusty torus. the stellar population is dominated by an old (2 gyr < t ≤ 15 gyr) component between 160 and 300 pc, while closer to the nucleus, an intermediate age (50 myr < t ≤ 2 gyr) component contributes at levels ranging from ≈40 per cent to ≈100 per cent to the flux at 2.12 μm. | feeding versus feedback in active galactic nuclei from near-infrared integral field spectroscopy - xii. ngc 5548 |
context. the study of old, metal-poor stars deepens our knowledge on the early stages of the universe. in particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their emission of ionising photons.aims: we present a detailed chemical analysis and determination of the kinematic and orbital properties of a sample of 11 dwarf stars. these are metal-poor stars, and a few of them present a low lithium content. we inspected whether the other elements also present anomalies.methods: we analysed the high-resolution uves spectra of a few metal-poor stars using the turbospectrum code to synthesise spectral lines profiles. this allowed us to derive a detailed chemical analysis of fe, c, li, na, mg, al, si, cai, caii, scii, tiii, cr, mn, co, ni, sr, and ba.results: we find excellent coherence with the reference metal-poor first stars sample. the lithium-poor stars do not present any anomaly of the abundance of the elements other than lithium. among the li-poor stars, we show that cs 22882-027 is very probably a blue-straggler. the star cs 30302-145, which has a li abundance compatible with the plateau, has a very low si abundance and a high mn abundance. in many aspects, it is similar to the α-poor star he 1424-0241, but it is less extreme. it could have been formed in a satellite galaxy and later been accreted by our galaxy. this hypothesis is also supported by its kinematics. the table with equivalent widths discussed in this paper is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/654/a170 based on observations collected at the european organisation for astronomical research in the southern hemisphere (programmes 076.a-0463 pi(lopez), 077.d-0299 pi(bonifacio)), 086.d-0871(a) (pi meléndez). | the metal-poor end of the spite plateau. ii. chemical and dynamical investigation |
we have modelled the stellar and nebular continua and emission-line intensity ratios of massive stellar populations in the antennae galaxy using high resolution and self-consistent libraries of model h ii regions around central clusters of ageing stars. the model libraries are constructed using the stellar population synthesis code, starburst99, and photoionization model, and cloudy. the geneva and parsec stellar evolutionary models are plugged into starburst99 to allow comparison between the two models. using a spectrum-fitting methodology that allows the spectral features in the stellar and nebular continua [e.g. wolf-rayet (wr) features, paschen jump], and emission-line diagnostics to constrain the models, we apply the libraries to the high-resolution multi-unit spectroscopic explorer spectra of the starbursting regions in the antennae galaxy. through this approach, we were able to model the continuum emission from wr stars and extract stellar and gas metallicities, ages, electron temperatures, and densities of starbursts by exploiting the full spectrum. from the application to the antennae galaxy, we find that (1) the starbursts in the antennae galaxy are characterized by stellar and gas metallicities of around solar, (2) the star-forming gas in starbursts in the western loop of ngc 4038 appears to be more enriched, albeit slightly, than the rest of galaxy, (3) the youngest starbursts are found across the overlap region and over parts of the western-loop, though in comparison, the regions in the western-loop appear to be at a slightly later stage in star formation than the overlap region, and (4) the results obtained from fitting the geneva and parsec models are largely consistent. | stellar populations and physical properties of starbursts in the antennae galaxy from self-consistent modelling of muse spectra |
low-mass star formation regions are unlikely to fully populate their initial mass functions (imfs), leading to a deficit of massive stars. in binary stellar populations, the full range of binary separations and mass ratios will also be underpopulated. to explore the effects of stochastic sampling in the integrated light of stellar clusters, we calculate models at a broad range of cluster masses, from 102 to 107 m⊙, using a binary stellar population synthesis code. for clusters with stellar masses less than 105 m⊙, observable quantities show substantial scatter and their mean properties reflect the expected deficit of massive stars. in common with previous work, we find that purely stochastic sampling of the imf appears to underestimate the mass of the most massive star in known clusters. however, even with this constraint, the majority of clusters likely inject sufficient kinetic energy to clear their birth clusters of gas. for quantities that directly measure the impact of the most massive stars, such as nion, ξion, and βuv, uncertainties due to stochastic sampling dominate over those from the imf shape or distribution of binary parameters, while stochastic sampling has a negligible effect on the stellar continuum luminosity density. | exploring the impact of imf and binary parameter stochasticity with a binary population synthesis code |
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