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<sec id="asec1"><title>abstract—we describe a homogeneous catalog compilation of common proper motion stars based on gaia dr2. a preliminary list of all pairs of stars within the radius of 100 pc around the sun with a separation less than a parsec was compiled. also, a subset of comoving pairs, wide binary stars, was selected. the clusters and systems with multiplicity larger than 2 were excluded from consideration. the resulting catalog contains 10 358 pairs of stars. the catalog selectivity function was estimated by comparison with a set of randomly selected field stars and with a model sample obtained by population synthesis. the estimates of the star masses in the catalogued objects, both components of which belong to the main-sequence, show an excess of "twins", composed by stars with similar masses. this excess decreases with increasing separation between components. it is shown that such an effect cannot be a consequence of the selectivity function only and does not appear in the model where star formation of similar masses is not artificially preferred. the article is based on the talk presented at the conference "astrometry yesterday, today, tomorrow" (sternberg astronomical institute of the moscow state university, october 14-16, 2019).</sec> | binary star population with common proper motion in gaia dr2 |
in the population synthesis simulations of pop iii stars, many bh (black hole)-bh binaries with merger time less than the age of the universe (τh) are formed, while ns (neutron star)-bh binaries are not. the reason is that pop iii stars have no metal so that no mass loss is expected. then, in the final supernova explosion to ns, much mass is lost so that the semimajor axis becomes too large for pop iii ns-bh binaries to merge within τh . however it is almost established that the kick velocity of the order of 200 -500 km s-1 exists for ns from the observation of the proper motion of the pulsar. therefore, the semimajor axis of the half of ns-bh binaries can be smaller than that of the previous argument for pop iii ns-bh binaries to decrease the merging time. we perform population synthesis monte carlo simulations of pop iii ns-bh binaries including the kick of ns and find that the event rate of pop iii ns-bh merger rate is 1 gpc-3 yr-1 . this suggests that there is a good chance of detecting pop iii ns-bh mergers in o2 (observation run 2) of advanced ligo and advanced virgo from this autumn. | the possible existence of pop iii ns-bh binary and its detectability |
context. the identification and characterisation of populations of young massive stars in (giant) h ii regions provides important constraints on (i) the formation process of massive stars and their early feedback on the environment, and (ii) the initial conditions for population synthesis models predicting the evolution of ensembles of stars.aims: we identify and characterise the stellar populations of the following young giant h ii regions: m 8, g333.6-0.2, and ngc 6357.methods: we have acquired h- and k-band spectra of around 200 stars using the k-band multi object spectrograph on the eso very large telescope. the targets for m 8 and ngc 6357 were selected from the massive young star-forming complex study in infrared and x-ray (mystix), which combines x-ray observations with near-infrared (nir) and mid-infrared data. for g333.6-0.2, the sample selection is based on the nir colours combined with x-ray data. we introduce an automatic spectral classification method in order to obtain temperatures and luminosities for the observed stars. we analysed the stellar populations using their photometric, astrometric, and spectroscopic properties and compared the position of the stars in the hertzprung-russell diagram with stellar evolution models to constrain their ages and mass ranges.results: we confirm the presence of candidate ionising sources in the three regions and report new ones, including the first spectroscopically identified o stars in g333.6-0.2. in m 8 and ngc 6357, two populations are identified: (i) ob main-sequence stars (m > 5 m⊙) and (ii) pre-main sequence stars (m ≈ 0.5 - 5 m⊙). the ages of the clusters are ∼1-3 myr, < 3 myr, and ∼0.5-3 myr for m 8, g333.6-0.2, and ngc 6357, respectively. we show that mystix selected targets have > 90% probability of being members of the h ii region, whereas a selection based on nir colours leads to a membership probability of only ∼70%. full table 4 and normalized spectra are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/633/a155 based on observations collected at the european southern observatory at paranal, chile (eso program 095.c-0048). | the young stellar content of the giant h ii regions m 8, g333.6-0.2, and ngc 6357 with vlt/kmos |
context. the perseus complex in the outer disk of the galaxy hosts a number of clusters and associations of young stars. gaia is providing a detailed characterization of their kinematic structure and evolutionary properties.aims: within the spa large program at the tng, we secured harps-n and giano-b high-resolution optical and near-infrared (nir) spectra of the young red supergiant (rsg) stars in the perseus complex in order to obtain accurate radial velocities, stellar parameters, and detailed chemical abundances.methods: we used spectral synthesis to best fit hundreds of atomic and molecular lines in the spectra of the observed 27 rsgs. we obtained accurate estimates of the stellar temperature, gravity, micro- and macroturbulence velocities, and chemical abundances for 25 different elements. we also measured the 12c/13c abundance ratio.results: our combined optical and nir chemical study provides homogeneous half-solar iron with a low dispersion, about solar-scaled abundance ratios for the iron-peak, alpha-, and other light elements, and a low enhancement of na, k, and neutron-capture elements. this is consistent with the thin-disk chemistry traced by older stellar populations at a similar galactocentric distance of about 10 kpc. we inferred an enhancement of n and a depletion of c and of the 12c/13c isotopic abundance ratio that are consistent with mixing processes in the stellar interiors during the rsg evolution. tables a.1-a3 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/660/a7 based on observations made with the italian telescopio nazionale galileo (tng) operated on the island of la palma by the fundación galileo galilei of the inaf (istituto nazionale di astrofisica) at the spanish observatorio del roque de los muchachos of the instituto de astrofisica de canarias. this study is part of the large program titled spa - stellar population astrophysics: the detailed, age-resolved chemistry of the milky way disk (pi: l. origlia), granted observing time with harps-n and giano-b echelle spectrographs at the tng. | stellar population astrophysics (spa) with the tng. the chemical content of the red supergiant population in the perseus complex |
two neutron star (ns)-black hole (bh) binaries, gw200105 and gw200115 found in the ligo/virgo o3b run have smaller bh mass of 6-9 m⊙, which is consistent with population i and ii origin. our population synthesis simulations using 106 population i and ii binaries with appropriate initial parameters show consistent binary mass, event rate, no detection of radio pulsar (psr), and bh binaries in our galaxy so far. especially, we found possible progenitors of gw200105 and gw200115, which were formed at redshift z = 0.15 and z = 1.6 with binary mass of $(34\,{\mathrm{ m}}_{\odot },\, 9.2\,{\mathrm{ m}}_{\odot })$ and $(23.7\,{\mathrm{ m}}_{\odot },\, 10.6\,{\mathrm{ m}}_{\odot })$, respectively. the final masses of these binaries are $(6.85\,{\mathrm{ m}}_{\odot },\, 2.14\,{\mathrm{ m}}_{\odot })$ and $(6.04\,{\mathrm{ m}}_{\odot },\, 1.31\,{\mathrm{ m}}_{\odot })$ which look like $(9.0_{-1.7}^{+1.7}\,{\mathrm{ m}}_{\odot },\, 1.91_{-0.24}^{+0.33}\,{\mathrm{ m}}_{\odot })$ of gw200105 and $(5.9_{-2.5}^{+2.0}\,{\mathrm{ m}}_{\odot },\, 1.44_{-0.29}^{+0.85}\,{\mathrm{ m}}_{\odot })$ of gw200115, respectively. we also estimate that 2.68-19.7 psr-bh binaries in our galaxy will be observed by ska. the existence of ns-bhs in our galaxy can be confirmed in future ska era. using the gw observation of ns-bh mergers and the radio observation of psr-bhs in future, we can get more severe constraints on the ns-bh formation process. | constraints on population i/ii neutron star-black hole binary formation by gravitational wave and radio observations |
we tested whether refracted gravity, a theory of modified gravity that describes the dynamics of galaxies without the aid of dark matter, can model the dynamics of the three massive elliptical galaxies, ngc 1407, ngc 4486, and ngc 5846, out to ∼10re, where the baryonic mass component fades out and dark matter is required in newtonian gravity. we probed these outer regions with the kinematics of the globular clusters provided by the sluggs survey. refracted gravity mimics dark matter with the gravitational permittivity, a monotonic function of the local mass density depending on three parameters, ϵ0, ρc, and q, which are expected to be universal. refracted gravity satisfactorily reproduces the velocity dispersion profiles of the stars and red and blue globular clusters, with stellar mass-to-light ratios in agreement with stellar population synthesis models, and orbital anisotropy parameters consistent with previous results obtained in newtonian gravity with dark matter. the sets of the three parameters of the gravitational permittivity found for each galaxy are consistent with each other within ∼2σ. we compare the mean ϵ0,q,log10(ρc[g cm−3])} = {0.089−0.035+0.038, 0.47−0.21+0.29, −24.25−0.20+0.28 found here with the means of the parameters required to model the rotation curves and vertical velocity dispersion profiles of 30 disk galaxies from the diskmass survey (dms): ρc and q agree within 1σ with the dms values, whereas ϵ0 agrees within 3σ. this agreement suggests that ellipticals and disk galaxies allow for common values of the parameters of the permittivity and supports the universality of the permittivity function. | the dynamics of three nearby e0 galaxies in refracted gravity |
comparison with artificial galaxy models is essential for translating the incomplete and low signal-to-noise data we can obtain on astrophysical stellar populations to physical interpretations which describe their composition, physical properties, histories and internal conditions. in particular, this is true for distant galaxies, whose unresolved light embeds clues to their formations and evolutions, and their impacts on their wider environs. stellar population synthesis models are now used as the foundation of analysis at all redshifts, but are not without their problems. here we review the use of stellar population synthesis models, with a focus on applications in the distant universe. | applications of stellar population synthesis in the distant universe |
we present an analysis of the cn and ch molecular band strengths in ngc 6791 from low-resolution sloan extension for galactic understanding and exploration spectra as a means to detect chemical variations in the cluster. ngc 6791 is a heavily studied open cluster (oc) due to its unique combination of old age, high mass, and high metallicity. these characteristics place ngc 6791 between the physical properties of most globular and ocs. recent photometric and spectroscopic studies yield contradicting results, with some claiming to detect signs of multiple populations, as in globular clusters, while others do not. we do not find large spreads in the cn and ch band strength distributions that would suggest multiple populations. by pairing spectral synthesis with the measured cn values, we conclude that the maximum [n/fe] variation in the cluster is 0.2 dex. additionally, we find that the saturation of the ch band at high metallicities limits its usefulness in detecting multiple populations and determining c abundances. | limitations of cn and ch molecular band strengths at high metallicities: a case study in ngc 6791 |
although fossil galaxy systems are thought to be very old, and thus should possess above-average halo concentrations, typically fossils have unexceptional concentrations of their masses. we revisit the massive isolated elliptical galaxy/fossil group ngc 6482 for which previous x-ray studies of a modest chandra observation obtained a very uncertain, but also possibly very high, halo concentration. we present new measurements of the hot gas surface brightness, temperature, and iron abundance using the modest chandra observation and a previously unpublished suzaku observation, the latter of which allows the measurements of the gas properties to be extended out to ∼ {r}2500. by constructing hydrostatic equilibrium models of the gas with separate components for the gas, the stellar mass of the large central galaxy (bcg), and the dark matter (dm), we measure {c}200=32.2+/- 7.1 and {m}200=(4.5+/- 0.6)× {10}12 {m}⊙using a navarro-frenk-white (nfw) dm profile. for a halo of this mass, the measured concentration c200 exceeds the mean value (7.1) expected for relaxed λcdm halos by 3.5σ in terms of the observational error, and by 6σ considering the intrinsic scatter in the λcdm c-m relation, which situates ngc 6482 as the most extreme outlier known for a fossil system. we explored several variants of adiabatic contraction (ac) models and, while the ac models provide fits of the same quality as the uncontracted models, they do have the following advantages: (1) lower c200 that is less of an outlier in the λcdm c-m relation, and (2) baryon fractions ({f}{{b},200}) that agree better with the mean cosmic value. while the standard ac prescriptions yield a bcg stellar mass that is uncomfortably low compared to results from stellar population synthesis (sps) models, a weaker ac variant that artificially shuts off cooling and star formation at z = 2 yields the same stellar mass as the uncontracted models. these are probably the reasons why our x-ray analysis prefers this weaker ac variant applied to either an nfw or einasto dm halo. finally, the stellar mass we measure for the bcg from the hydrostatic analysis strongly favors results from sps models with a chabrier or kroupa initial mass function (imf) over a salpeter imf. | the unusually high halo concentration of the fossil group ngc 6482: evidence for weak adiabatic contraction |
the mass spectrum of stellar black holes (bhs) is highly uncertain. theoretical models of bh formation strongly depend on the efficiency of stellar winds of the progenitor stars and on the supernova (sn) explosion mechanism. we discuss the bh mass spectrum we obtain using sevn{}, a new public population-synthesis code that includes up-to-date stellar-wind prescriptions and several sn explosion models. our models have been used by the ligo and virgo collaboration to constrain the properties of the gravitational wave (gw) source gw150914, indicating a sub-solar metallicity environment for its progenitors. we show that our models predict substantially larger bh masses (up to ∼ 100 m⊙) than other population synthesis codes, at low metallicity. in this proceeding, we also discuss the impact of pair-instability sne on our previously published models. | shedding light on the black hole mass spectrum. |
we present a model of evolution of solitary neutron stars, including spin parameters, magnetic field decay, motion in the galactic potential and birth inside spiral arms. we use two parametrizations of the radio-luminosity law and model the radio selection effects. dispersion measure is estimated from the recent model of free electron distribution in the galaxy (ymw16). model parameters are optimized using the markov chain monte carlo technique. the preferred model has a short decay scale of the magnetic field of 4.27 +0.4 -0.38 myr. however, it has non-negligible correlation with parameters describing the pulsar radio luminosity. based on the best-fit model, we predict that the square kilometre array surveys will increase the population of known single radio pulsars by between 23 and 137 per cent. the indri code used for simulations is publicly available to facilitate future population synthesis efforts. | markov chain monte carlo population synthesis of single radio pulsars in the galaxy |
two low-mass (m < 1.4 m ⊙) neutron stars, j0737-3039b and the companion to j1756-2251, show strong evidence of being formed in an ultra-stripped supernova explosion (us-sn) with a onemg or fe progenitor. using systematically generated sets of equations of state we map out the relationship between the moment of inertia of j0737-3039a, a candidate for a moment of inertia measurement within a decade, and the binding energy of the two low-mass neutron stars. this relationship, similar to the i-love-q relations, is more robust than a previously explored correlation between the binding energy and the slope of the nuclear symmetry energy l. we find that, if either j0737-3039b or the j1756-2251 companion were formed in a us-sn, no more than 0.06 m ⊙ could have been lost from the progenitor core. furthermore, a measurement of the moment of inertia of j0737-3039a to within 10% accuracy can discriminate between formation scenarios and, given current constraints on the predicted core mass loss, potentially rule them out. advanced ligo can potentially measure the neutron star tidal polarizability to equivalent accuracy which, using the i-love-q relations, would obtain similar constraints on the formation scenarios. such information would help constrain important aspects of binary evolution used for population synthesis predictions of the rate of binary neutron star mergers and resulting electromagnetic and gravitational wave signals. further progress needs to be made in modeling the core-collapse process that leads to low-mass neutron stars, particularly in making robust predictions for the mass loss from the progenitor core. | testing the formation scenarios of binary neutron star systems with measurements of the neutron star moment of inertia |
we present the results of a pilot near-infrared spectroscopic campaign of five very massive galaxies ({log}({m}\star /{m}⊙ )> 11.45) in the range of 1.7< z< 2.7. we measure an absorption feature redshift for one galaxy at {z}{spec}=2.000+/- 0.006. for the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. we define a continuum redshift ({z}{cont} ) as one in which the redshift is estimated probabilistically from the combination of catalog photometry and the observed spectrum using eazy. we derive the uncertainties on the stellar population synthesis properties using a monte carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions. the spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. we find that three out of five galaxies are quiescent (star-formation rate of ≲ 1{m}⊙{{yr}}-1) with low levels of dust obscuration ({a}{{v}}< 1) , that one galaxy displays both high levels of star formation and dust obscuration ({sfr}≈ 300{m}⊙{{yr}}-1, {a}{{v}}≈ 1.7 mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations. | near-infrared spectroscopy of five ultra-massive galaxies at 1.7 < z < 2.7 |
observations of star-forming galaxies in the distant universe (z > 2) are starting to confirm the importance of massive stars in shaping galaxy emission and evolution. inevitably, these distant stellar populations are unresolved, and the limited data available must be interpreted in the context of stellar population synthesis models. with the imminent launch of jwst and the prospect of spectral observations of galaxies within a gigayear of the big bang, the uncertainties in modelling of massive stars are becoming increasingly important to our interpretation of the high redshift universe. in turn, these observations of distant stellar populations will provide ever stronger tests against which to gauge the success of, and flaws in, current massive star models. | what can distant galaxies teach us about massive stars? |
using a new color-color diagnostic diagram in the mid-infrared (mir) built from wise data, the mirdd, we compare narrow-emission-line galaxies (nelgs) that exhibit different activity types (star-forming galaxies (sfgs) and active galactic nuclei (agns), i.e., liners, seyfert 2 galaxies (sy2s), and transition-type objects (tos)), as determined using one standard diagnostic diagram in the optical (bpt-vo), with broad-line agns (qsos and sy1s) and bl lac objects at low redshift (z≤slant 0.25). we show that the bl lac objects occupy the same region as the liners in the mirdd, whereas the qsos and sy1s occupy an intermediate region between the liners and the sy2s. in the mirdd these galaxies trace a sequence that can be reproduced by a power law, {{f}ν }={{ν }α }, where the spectral index, α, varies from 0 to -2, which is similar to what is observed in the optical/ultraviolet part of the spectra of agns with different luminosities. for the nelgs with different activity types, we perform a stellar-population synthesis analysis, confirming that their specific positions in the mird depend on their star formation histories (sfh) and demonstrating that the w2-w3 color is tightly correlated with the level of star formation in their host galaxies. in good agreement with the sfh analysis, a comparison of their mir colors with the colors yielded by spectral energy distributions (seds) of galaxies with different activity types shows that the sed of the liners is similar to the seds of the qsos and sy1s, consistent with agn galaxies with mild star formation, whereas the seds of the sy2s and tos are consistent with agn galaxies with strong star formation components. for the bl lac objects, we show that their blue mir colors can only be fitted with an sed that has no star formation component, consistent with agns in elliptical-type galaxies. from their similarities in mir colors and seds, we infer that, in the nearby universe, the level of star formation activity most probably increases in the host galaxies of emission-line galaxies with different activity types along the sequence bl lac \to liner \to qso/sy1 \to sy2 \to to \to sfg. | comparing narrow- and broad-line agns in a new diagnostic diagram for emission-line galaxies based on wise data |
hd 49798 (a hydrogen depleted subdwarf o6 star) with its massive white dwarf (wd) companion has been suggested to be a progenitor candidate of a type ia supernova (sn ia). however, it is still uncertain whether the companion of hd 49798 is a carbon-oxygen (co) wd or an oxygen-neon (one) wd. a co wd will explode as an sn ia when its mass grows and approaches the chandrasekhar limit, but the outcome of an accreting one wd is likely to be a neutron star. we generated a series of monte carlo calculations that incorperate binary population synthesis to simulate the formation of one wd + he star systems. we found that there is almost no orbital period as large as hd 49798 with its wd companion in these one wd + he star systems based on our simulations, which means that the companion of hd 49798 might not be an one wd. we suggest that the companion of hd 49798 is most likely a co wd, which can be expected to increase its mass to the chandrasekhar limit by accreting he-rich material from hd 49798. thus, hd 49798 and its companion may produce an sn ia as a result of its future evolution. | is the x-ray pulsating companion of hd 49798 a possible type ia supernova progenitor? |
fast radio bursts (frbs) are the first cosmological radio sources that vary on millisecond time-scales, which makes them a unique probe of the universe. many proposed applications of frbs require associated redshifts. these can only be obtained by localizing frbs to their host galaxies and subsequently measuring their redshifts. upcoming frb surveys will provide arcsecond localization for many frbs, not all of which can be followed up with dedicated optical observations. we aim to estimate the fraction of frb hosts that will be catalogued with redshifts by existing and future optical surveys. we use the population synthesis code frbpoppy to simulate several frb surveys, and the semi-analytical galaxy formation code galform to simulate their host galaxies. we obtain redshift distributions for the simulated frbs and the fraction with host galaxies in a survey. depending on whether frbs follow the cosmic star formation rate or stellar mass, 20-40 per cent of chime frb hosts will be observed in an sdss-like survey, all at z < 0.5. the deeper delve survey will detect 63-85 per cent of askap frbs found in its coherent search mode. chime frbs will reach z ~ 3, ska1-mid frbs z ~ 5, but ground based follow-up is limited to z ≲ 1.5. we discuss the consequences for several frb applications. if ~1/2 of askap frbs have measured redshifts, 1000 detected frbs can be used to constrain ωbh70 to within ~10 per cent at 95 per cent credibility. we provide strategies for optimized follow-up, when building on data from existing surveys. data and codes are made available. | how limiting is optical follow-up for fast radio burst applications? forecasts for radio and optical surveys |
galaxy groups, which have hardly been looked at in modified newtonian dynamics (mond), afford probing the acceleration discrepancies in regions of system-parameter space that are not accessible in well-studied galactic systems: galaxies, galaxy clusters, and dwarf spheroidal satellites of galaxies. groups are typically the size of galaxy-cluster cores, but have masses typically only a few times that of a single galaxy. accelerations in groups get far below those in galaxies, and far below the mond acceleration, so much so that many groups might be affected by the external-field effect, which is unique to mond, due to background accelerations. here, i analyze the mond dynamics of 53 galaxy groups, recently catalogued in three lists. their newtonian, k-band, dynamical m /l ratios are a few tens to several hundreds solar units, with ⟨md/lk ⟩=(56 ,25 ,30 ) m⊙/l⊙ , respectively, for the three lists, thus evincing very large acceleration discrepancies. i find here that mond requires dynamical mm/lk values of order 1 m⊙/l⊙ , with ⟨mm/lk ⟩=(0.8 ,0.56 ,1.0 ) m⊙/l⊙ , for the three lists, which are in good agreement with population-synthesis stellar values, and with those found in individual galaxies. mond thus accounts for the observed dynamics in those groups with baryons alone, with no need for dark matter—an important extension of mond analysis from galaxies to galactic systems, which, to boot, have characteristic sizes of several hundred kpc, and accelerations much lower than probed before—only a few percent of mond's a0. the acceleration discrepancies evinced by these groups thus conform to the deep-mond prediction: g ≈(gna0)1/2, down to these very low accelerations (g is the measured, and gn the baryonic, newtonian acceleration). | mond in galaxy groups |
we present spatially resolved hubble space telescope grism spectroscopy of 15 galaxies at z ~ 0.8 drawn from the deep2 survey. we analyze hα+[n ii], [s ii], and [s iii] emission on kiloparsec scales to explore which mechanisms are powering emission lines at high redshifts, testing which processes may be responsible for the well-known offset of high-redshift galaxies from the z ~ 0 locus in the [o iii]/hβ versus [n ii]/hα baldwin-phillips-terlevich (bpt) excitation diagram. we study spatially resolved emission-line maps to examine evidence for active galactic nuclei (agn), shocks, diffuse ionized gas (dig), or escaping ionizing radiation, all of which may contribute to the bpt offsets observed in our sample. we do not find significant evidence of agn in our sample and quantify that, on average, agn would need to contribute ~25% of the hα flux in the central resolution element in order to cause the observed bpt offsets. we find weak (2σ) evidence of dig emission at low surface brightnesses, yielding an implied total dig emission fraction of ~20%, which is not significant enough to be the dominant emission line driver in our sample. in general we find that the observed emission is dominated by star-forming h ii regions. we discuss trends with demographic properties and the possible role of α-enhanced abundance patterns in the emission spectra of high-redshift galaxies. our results indicate that photoionization modeling with stellar population synthesis inputs is a valid tool to explore the specific star formation properties which may cause bpt offsets, to be explored in future work. | disentangling the physical origin of emission line ratio offsets at high redshift with spatially resolved spectroscopy |
we present the analysis of archival very large telescope (vlt) multi-unit spectroscopic explorer (muse) observations of the interacting galaxies ngc 4038/39 (a.k.a. the antennae) at a distance of 18.1 mpc. up to 38 young star-forming complexes with evident contribution from wolf-rayet (wr) stars are unveiled. we use publicly available templates of galactic wr stars in conjunction with available photometric extinction measurements to quantify and classify the wr population in each star-forming region, on the basis of its nearly solar oxygen abundance. the total estimated number of wr stars in the antennae is 4053 ± 84, of which there are 2021 ± 60 wnl and 2032 ± 59 wc-types. our analysis suggests a global wc to wn-type ratio of 1.01 ± 0.04, which is consistent with the predictions of the single star evolutionary scenario in the most recent bpass stellar population synthesis models. | wolf-rayet stars in the antennae unveiled by muse |
an all-sky sample of 1227 visual binaries based on washington double star catalogue is constructed to infer the initial mass function (imf), mass ratio, and projected distance distribution with a dedicated population synthesis model. parallaxes from gaia dr2 and hipparcos are used to verify the distance distribution. the model is validated on the single-star tycho-2 sample and successfully reproduces the observed magnitudes and angular separations. the projected separation distribution follows f(s) ∼ s-1.2 in 102-2 × 103 au range for 1-4.5 m⊙ primary stars. several algorithms are explored as pairing functions. random pairing is confidently rejected. primary-constrained pairing (pcp) and split-core pairing (scp), the scenarios adopting primary component's or total system's mass as fundamental, are considered. the preferred imf slope is α ∼ 2.8 either way. a simple power-law mass ratio distribution is unlikely, but the introduction of a twin excess provides a favourable result. pcp with f(q) ∼ q-1 is preferred with a tiny twin fraction, models with f(q) ∼ q-1.5 are acceptable when a larger twin excess is allowed. scp is similar to pcp when a larger slope of the power law is adopted: f(q) ∼ qβ + 0.7. | pairing function of visual binary stars |
we present a new two-component dust geometry model, the chocolate chip cookie model, where the clumpy nebular regions are embedded in a diffuse stellar/interstellar medium disk, like chocolate chips in a cookie. by approximating the binomial distribution of the clumpy nebular regions with a continuous gaussian distribution and omitting the dust scattering effect, our model solves the dust attenuation process for both the emission lines and stellar continua via analytical approaches. our chocolate chip cookie model successfully fits the inclination dependence of both the effective dust reddening of the stellar components derived from stellar population synthesis and that of the emission lines characterized by the balmer decrement for a large sample of milky way-like (mw-like) disk galaxies selected from the main galaxy sample of the sloan digital sky survey. our model shows that the clumpy nebular disk is about 0.55 times thinner and 1.6 times larger than the stellar disk for mw-like galaxies, whereas each clumpy region has a typical optical depth of τ cl,v~ 0.5 in the v band. after considering the aperture effect, our model prediction on the inclination dependence of dust attenuation is also consistent with observations. not only that, in our model, the dust attenuation curve of the stellar population naturally depends on the inclination, and its median case is consistent with the classical calzetti law. as the modeling constraints are from the optical wavelengths, our model is unaffected by the optically thick dust component, which however could bias the model's prediction of the infrared emissions. | the chocolate chip cookie model: dust geometry of milky way-like disk galaxies |
the recent discovery of an unambiguous quiescent black hole (bh) and main-sequence o star companion in vfts 243 opens the door to new constraints on theoretical stellar evolution and population models looking to reproduce the progenitors of bh-bh binaries. here, we show that the binary population and spectral synthesis fiducial models natively predict vfts 243-like systems: we find that vfts 243 likely originated from a binary system in an ~15 d orbit with primary mass ranging from 40 to 50 $\mathrm{\, m}_\odot$ and secondary star with initial mass of 24-25 $\mathrm{\, m}_\odot$. additionally, we find that the death of the primary star must have resulted in a low-energy explosion e < 1050 erg. with a uniform prior, we find that the kick velocity of the newborn bh was ≤10 $\, \text{km s}^{-1}$. the very low eccentricity reported for vfts 243 and the subsequent conclusion by the authors that the supernova kick must have been very small are in line with the peak in the posterior distribution between 0 and 5 $\, \text{km s}^{-1}$ found from our numerical simulations performed with a uniform prior. finally, the reduced hobbs kick distribution commonly used in bh population synthesis is strongly disfavoured. | vfts 243 as predicted by the bpass fiducial models |
the upcoming james webb space telescope (jwst) will allow observations of high-redshift galaxies at fainter detection levels than ever before, and jwst surveys targeting gravitationally lensed fields are expected to bring z ≳ 6 objects with very low star formation rate (sfr) within reach of spectroscopic studies. as galaxies at lower and lower star formation activity are brought into view, many of the standard methods used in the analysis of integrated galaxy spectra are at some point bound to break down, due to violation of the assumptions of a well-sampled stellar initial mass function (imf) and a slowly varying sfr. we argue that galaxies with sfr ∼ 0.1 m⊙ yr-1 are likely to turn up at the spectroscopic detection limit of jwst in lensed fields, and investigate to what extent star formation sampling may affect the spectral analysis of such objects. we use the slug spectral synthesis code to demonstrate that such effects are likely to have significant impacts on spectral diagnostics of, for example, the balmer emission lines. these effects are found to stem primarily from sfrs varying rapidly on short (∼myr) time-scales due to star formation in finite units (star clusters), whereas the effects of an undersampled imf is deemed insignificant in comparison. in contrast, the ratio between the he ii- and h i-ionizing flux is found to be sensitive to imf-sampling as well as icmf-sampling (sampling of the initial cluster mass function), which may affect interpretations of galaxies containing population iii stars or other sources of hard ionizing radiation. | the impact of star formation sampling effects on the spectra of lensed z > 6 galaxies detectable with jwst |
a minimum in stellar velocity dispersion is often observed in the central regions of disc galaxies. to investigate the origin of this feature, known as a σ-drop, we analyse the stellar kinematics of a high-resolution n-body + smooth particle hydrodynamical simulation, which models the secular evolution of an unbarred disc galaxy. we compared the intrinsic mass-weighted kinematics to the recovered luminosity-weighted ones. the latter were obtained by analysing synthetic spectra produced by a new code, syntra, that generates synthetic spectra by assigning a stellar population synthesis model to each star particle based on its age and metallicity. the kinematics were derived from the synthetic spectra as in real spectra to mimic the kinematic analysis of real galaxies. we found that the recovered luminosity-weighted kinematics in the centre of the simulated galaxy are biased to higher rotation velocities and lower velocity dispersions due to the presence of young stars in a thin and kinematically cool disc, and are ultimately responsible for the σ-drop. our procedure for building mock observations and thus recovering the luminosity-weighted kinematics of the stars in a galaxy simulation is a powerful tool that can be applied to a variety of scientific questions, such as multiple stellar populations in kinematically decoupled cores and counter-rotating components, and galaxies with both thick and thin disc components. | the kinematics of σ-drop bulges from spectral synthesis modelling of a hydrodynamical simulation |
we have applied stellar population synthesis to 500-pc-sized regions in a sample of 102 galaxy discs observed with the muse spectrograph. we derived the star formation history and analyse specifically the 'recent' ( $20\,\rm {myr}$ ) and 'past' ( $570\,\rm {myr}$ ) age bins. using a star formation self-regulator model, we can derive local mass-loading factors, η for specific regions, and find that this factor depends on the local stellar mass surface density, σ*, in agreement with the predictions form hydrodynamical simulations including supernova feedback. we integrate the local η-σ* relation using the stellar mass surface density profiles from the spitzer survey of stellar structure in galaxies (s4g) to derive global mass-loading factors, ηg, as a function of stellar mass, m*. the ηg-m* relation found is in very good agreement with hydrodynamical cosmological zoom-in galaxy simulations. the method developed here offers a powerful way of testing different implementations of stellar feedback, to check on how realistic are their predictions. | a quantitative demonstration that stellar feedback locally regulates galaxy growth |
in order to determine the spatial distribution, galactic model parameters and luminosity function of cataclysmic variables (cvs), a j-band magnitude limited sample of 263 cvs has been established using a newly constructed period-luminosity-colours (plcs) relation which includes j,ks and w1-band magnitudes in 2mass and wise photometries, and the orbital periods of the systems. this cv sample is assumed to be homogeneous regarding to distances as the new plcs relation is calibrated with new or re-measured trigonometric parallaxes. our analysis shows that the scaleheight of cvs is increasing towards shorter periods, although selection effects for the periods shorter than 2.25 h dramatically decrease the scaleheight: the scaleheight of the systems increases from 192 pc to 326 pc as the orbital period decreases from 12 to 2.25 h. the z-distribution of all cvs in the sample is well fitted by an exponential function with a scaleheight of 213-10+11 pc. however, we suggest that the scaleheight of cvs in the solar vicinity should be ∼300 pc and that the scaleheights derived using the sech2 function should be also considered in the population synthesis models. the space density of cvs in the solar vicinity is found 5.58(1.35)×10-6 pc-3 which is in the range of previously derived space densities and not in agreement with the predictions of the population models. the analysis based on the comparisons of the luminosity function of white dwarfs with the luminosity function of cvs in this study show that the best fits are obtained by dividing the luminosity functions of white dwarfs by a factor of 350-450. | galactic model parameters of cataclysmic variables: results from a new absolute magnitude calibration with 2mass and wise |
in this work, we characterize the properties of the object sdss j020536.84-081424.7, an extended nebular region with projected extension of 14 × 14 kpc2 in the line of sight of the etg mrk 1172, using unprecedented spectroscopic data from muse. we perform a spatially resolved stellar population synthesis and estimate the stellar mass for both mrk 1172 (1 × 1011 m⊙) and our object of study (3 × 109 m⊙). while the stellar content of mrk 1172 is dominated by an old (~10 gyr) stellar population, the extended nebular emission has its light dominated by young to intermediate age populations (from ~100 myr to ~1 gyr) and presents strong emission lines such as h β; [o iii] λλ4959, 5007 å; h α; [n ii] λλ6549, 6585 å; and [s ii] λλ6717, 6732 å. using these emission lines, we find that it is metal poor (with z ~ 1/3 z⊙, comparable to the lmc) and is actively forming stars (0.70 m⊙ yr-1), especially in a few bright clumpy knots that are readily visible in h α. the object has an ionized gas mass ≥3.8 × 105 m⊙. moreover, the motion of the gas is well described by a gas in circular orbit in the plane of a disc and is being affected by interaction wtih mrk 1172. we conclude that sdss j020536.84-081424.7 is most likely a dwarf irregular galaxy (the digal). | the metal-poor dwarf irregular galaxy candidate next to mrk 1172 |
neutron star x-ray binaries (ns xrbs) associated with supernova remnants (snrs) are youngest x-ray binaries that can provide insights into the early evolution of x-ray binaries and formation properties of neutron stars. there are an increasing number of ns xrbs that have been discovered within snrs in our own and nearby galaxies. in this work, we perform binary population synthesis calculations to simulate the population of ns xrbs associated with snrs for different types of companions, including roche-lobe-overfilling main-sequence stars, be stars, and supergiants. we estimate their birth rates and present the distributions of orbital parameters and companion mass for each type of companion. our calculations show that the majority of the companions are be x-ray binaries (bexrbs) and that a few bexrbs are expected to be associated with snrs in a milky way-type galaxy. | population synthesis of neutron star x-ray binaries associated with supernova remnants |
we present the stellar and gaseous kinematics of an sb galaxy, ngc 3223, with the aim of determining the vertical and radial stellar velocity dispersion as a function of radius, which can help to constrain disk heating theories. together with the observed nir photometry, the vertical velocity dispersion is also used to determine the stellar mass-to-light (m/l) ratio, typically one of the largest uncertainties when deriving the dark matter distribution from the observed rotation curve. we find a vertical-to-radial velocity dispersion ratio of σz/σr = 1.21 ± 0.14, significantly higher than expectations from known correlations, and a weakly-constrained ks-band stellar m/l ratio in the range 0.5-1.7, which is at the high end of (but consistent with) the predictions of stellar population synthesis models. such a weak constraint on the stellar m/l ratio, however, does not allow us to securely determine the dark matter density distribution. to achieve this, either a statistical approach or additional data (e.g. integral-field unit) are needed. based on observations collected at the european southern observatory, chile, under proposal 68.b-0588. | disk mass and disk heating in the spiral galaxy ngc 3223 |
population iii (pop iii) galaxies are predicted to exist at high redshifts and may be rendered sufficiently bright for detection with current telescopes when gravitationally lensed by a foreground galaxy cluster. pop iii galaxies that exhibit strong lyα emission should furthermore be identifiable from broadband photometry because of their unusual colors. here, we report on a search for such objects at z≳ 6 in the imaging data from the cluster lensing and supernova survey with hubble (clash), covering 25 galaxy clusters in 16 filters. our selection algorithm returns five singly imaged candidates with lyα-like color signatures, for which ground-based spectroscopy with current 8-10 m class telescopes should be able to test the predicted strength of the lyα line. none of these five objects have been included in previous clash compilations of high-redshift galaxy candidates. however, when large grids of spectral synthesis models are applied to the study of these objects, we find that only two of these candidates are significantly better fitted by pop iii models than by more mundane, low-metallicity stellar populations. | a search for population iii galaxies in clash. i. singly-imaged candidates at high redshift |
recent studies based on the integrated light of distant galaxies suggest that the initial mass function (imf) might not be universal. variations of the imf with galaxy type and/or formation time may have important consequences for our understanding of galaxy evolution. we have developed a new stellar population synthesis (sps) code specifically designed to reconstruct the imf. we implement a novel approach combining regularization with hierarchical bayesian inference. within this approach, we use a parametrized imf prior to regulate a direct inference of the imf. this direct inference gives more freedom to the imf and allows the model to deviate from parametrized models when demanded by the data. we use markov chain monte carlo sampling techniques to reconstruct the best parameters for the imf prior, the age and the metallicity of a single stellar population. we present our code and apply our model to a number of mock single stellar populations with different ages, metallicities and imfs. when systematic uncertainties are not significant, we are able to reconstruct the input parameters that were used to create the mock populations. our results show that if systematic uncertainties do play a role, this may introduce a bias on the results. therefore, it is important to objectively compare different ingredients of sps models. through its bayesian framework, our model is well suited for this. | a hierarchical bayesian approach for reconstructing the initial mass function of single stellar populations |
a new grid of detailed atmosphere model spectra for hot and moderately cool subdwarf stars is presented. high-resolution spectra and synthetic photometry are calculated in the range from 1000-10,000 å using non-lte fully line-blanketed atmosphere structures. our grid covers eight temperatures within 10,000 ≤ teff [k] ≤ 65,000, three surface gravities in the range 4.5 ≤ log g [cgs] ≤ 6.5, two helium abundances matching two extreme helium-rich and helium-poor scenarios, and two limiting metallicity boundaries regarding both solar ([fe/h] = 0) and galactic halos ([fe/h] = -1.5 and [α/fe] = +0.4). besides its application in the determination of fundamental parameters of subdwarfs in isolation and in binaries, the resulting database is also of interest for population synthesis procedures in a wide variety of stellar systems. | a grid of synthetic spectra for subdwarfs: non-lte line-blanketed atmosphere models |
an overview is provided of the scientific goals of the magellanic cloud component of the stsci directors discretionary uv initiative ullyses, together with the complementary spectroscopic survey xshootu (vlt/xshooter) and other ancillary datasets. together, ullyses and xshootu permit the first comprehensive, homogeneous study of wind densities and velocities in metal-poor massive stars, plus uv/optical spectroscopic libraries for population synthesis models and a large number of interstellar sight-lines towards the magellanic clouds. | ullyses and complementary surveys of massive stars in the magellanic clouds |
context. although oxygen is an important tracer of the early galactic evolution, its abundance trends with metallicity are still relatively poorly known at [fe/h] ≲ -2.5. this is in part due to a lack of reliable oxygen abundance indicators in the metal-poor stars, and in part due to shortcomings in 1d lte abundance analyses where different abundance indicators, such as oh lines located in the uv and ir or the forbidden [o i] line at 630 nm, frequently provide inconsistent results.aims: in this study, we determined the oxygen abundance in the metal-poor halo giant hd 122563 using a 3d hydrodynamical co5bold model atmosphere. our main goal was to understand whether a 3d lte analysis can help to improve the reliability of oxygen abundances that are determined from oh uv lines in comparison to those obtained using standard 1d lte methodology.methods: the oxygen abundance in hd 122563 was determined using 71 oh uv lines located in the wavelength range between 308-330 nm. the analysis was performed using a high-resolution vlt uves spectrum with a 1d lte spectral line synthesis performed using the synthe package and classical atlas9 model atmosphere. subsequently, a 3d hydrodynamical co5bold and 1d hydrostatic lhd model atmospheres were used to compute 3d-1d abundance corrections. for this, the microturbulence velocity used with the 1d lhd model atmosphere was derived from the hydrodynamical co5bold model atmosphere of hd 122563. the obtained abundance corrections were then applied to determine 3d lte oxygen abundances from each individual oh uv line.results: as in previous studies, we found trends in the 1d lte oxygen abundances determined from oh uv lines with line parameters, such as the line excitation potential, χ, and the line equivalent width, w. these trends become significantly less pronounced in 3d lte. using oh uv lines, we determined a 3d lte oxygen abundance in hd 122563 of a(o)3d lte = 6.23 ± 0.13 ([o/fe] = 0.07 ± 0.13). this is in fair agreement with the oxygen abundance obtained from oh ir lines, a(o)3d lte = 6.39 ± 0.11 ([o/fe] = 0.23 ± 0.11), but it is noticeably lower than that determined when using the forbidden [o i] line, a(o)3d lte = 6.53 ± 0.15 ([o/fe] = 0.37 ± 0.15). while the exact cause of this discrepancy remains unclear, it is very likely that non-lte effects may play a decisive role here. oxygen-to-iron ratios determined in hd 122563 using oh uv/ir lines and the forbidden [o i] line fall on the lower boundary of the [o/fe] distribution as observed in the galactic field stars at this metallicity and suggest a very mild oxygen overabundance with respect to iron, [o/fe] ≲ 0.4. | three-dimensional hydrodynamical co5bold model atmospheres of red giant stars. v. oxygen abundance in the metal-poor giant hd 122563 from oh uv lines |
a new model of the chemical evolution of primordial species in the recombination era, focusing on rovibrational molecular level populations and line emission, the main cooling process for low-temperature primordial gas, is presented. since molecular excitation calculations are vital in determining particle velocity distributions, internal state distributions, abundances, and ionization balance in gaseous environments, our model of the early universe considers nonthermal level populations using new state-to-state collisional excitation rate coefficients and reaction rates. this model of recombination era astrochemistry highlights the level populations of {{{h}}}2+, hd, and h2 and expands upon the current chemical networks by considering deuterated, ionized, and excited species. we furthermore couple the heat equation to the chemical network to form a complete model of thermal balance and dynamical evolution of primordial gas in the early universe. a developmental version of the spectral synthesis package cloudy was used to model the primordial gas, and a data set of {{{h}}}2+ vibrational excitation rate coefficients due to h collisions are provided. | rovibrational chemistry of {{\\rm{h}}}_{2}^{+}, hd, and h2 in the recombination era |
we present a list of galaxy-scale lens candidates including a highly probable interacting galaxy-scale lens in the hyper suprime-cam (hsc) imaging survey. we combine hsc imaging with the blended-spectra catalog from the galaxy and mass assembly (gama) survey to identify lens candidates, and use lens mass modeling to confirm the candidates. there are 45 matches between the hsc s14a_0b imaging data release and the gama catalog. we separate lens and lensed arcs using color information, and exclude those candidates with small image separations (<1.″0, estimated with the lens/source redshifts from the gama survey) that are not easily resolved with ground-based imaging. after excluding these, we find 10 probable lens systems. there is one system with an interacting galaxy pair, hsc j084928+000949, that has a valid mass model. we predict the total mass enclosed by the einstein radius of ∼0.″72 (∼1.65 kpc) for this new expected lens system to be ∼ {10}10.59 {m}⊙ . using the photometry in the grizy bands of the hsc survey and stellar population synthesis modeling with a salpeter stellar initial mass function, we estimate the stellar mass within the einstein radius to be ∼ {10}10.46 {m}⊙ . we thus find a dark matter mass fraction within the einstein radius of ∼ 25 % . further spectroscopy or high-resolution imaging would allow confirmation of the nature of these lens candidates. the particular system with the interacting galaxy pair, if confirmed, would provide an opportunity to study the interplay between dark matter and stars as galaxies build up through hierarchical mergers. | galaxy-scale gravitational lens candidates from the hyper suprime-cam imaging survey and the galaxy and mass assembly spectroscopic survey |
we developed a new semi-analytic galaxy formation model: galaxy assembly with binary evolution (gabe). for the first time, we introduce binary evolution into semi-analytic models of galaxy formation by using the yunnan-ii stellar population synthesis model, which includes various binary interactions. when implementing our galaxy formation model onto the merger trees extracted from the millennium simulation, it can reproduce a large body of observational results. we find that in the local universe, the model including binary evolution reduces the luminosity at optical and infrared wavelengths slightly, but it increases the luminosity at ultraviolet wavelengths significantly, especially in f uv band. the resulting luminosity function does not change very much over sdss optical bands and infrared band, but the predicted colors are bluer, especially when the f uv band is under consideration. the new model allows us to explore the physics of various high energy events related to the remnants of binary stars, such as type ia supernovae, short gamma-ray bursts and gravitational wave events, and their relation with host galaxies in a cosmological context. | gabe: galaxy assembly with binary evolution |
the surface brightness fluctuation (sbf) technique is one of the distance measurement methods that has been applied on the low surface brightness (lsb) galaxy ngc 1052-df2 yielding a distance of about 20 mpc implying it to be a dark matter deficient galaxy. we assume the number of giant stars above a given luminosity threshold to represent the sbf magnitude. the sbf magnitude depends on the distance, but this is degenerate with the star formation history (sfh). using a stellar population synthesis model, we calculate the number of giant stars for stellar populations with different galaxy-wide stellar initial mass functions (gwimfs), ages, metallicities, and sfhs. if the gwimf is the invariant canonical imf, the 1σ (3σ) uncertainty in colour allows a distance as low as 12 mpc (8 mpc). if instead the true underlying gwimf is the integrated galaxy-wide imf (igimf) then overestimating distances for low-mass galaxies would be a natural result, allowing ngc 1052-df2 to have a distance of 11 mpc within the 1σ colour uncertainty. finally, we show that our main conclusion on the existence of a bias in the sbf distance estimation is not much affected by changing the luminosity lower limit for counting giant stars. | imf-induced intrinsic uncertainties on measuring galaxy distances based on the number of giant stars: the case of the ultradiffuse galaxy ngc 1052-df2 |
aims: star formation rate (sfr) inferences are based on the so-called constant sfr approximation, where synthesis models are required to provide a calibration. we study the key points of such an approximation with the aim to produce accurate sfr inferences.methods: we use the intrinsic algebra of synthesis models and explore how the sfr can be inferred from the integrated light without any assumption about the underlying star formation history (sfh).results: we show that the constant sfr approximation is a simplified expression of deeper characteristics of synthesis models: it characterizes the evolution of single stellar populations (ssps), from which the ssps as a sensitivity curve over different measures of the sfh can be obtained. as results, we find that (1) the best age to calibrate sfr indices is the age of the observed system (i.e., about 13 gyr for z = 0 systems); (2) constant sfr and steady-state luminosities are not required to calibrate the sfr; (3) it is not possible to define a single sfr timescale over which the recent sfh is averaged, and we suggest to use typical sfr indices (ionizing flux, uv fluxes) together with untypical ones (optical or ir fluxes) to correct the sfr for the contribution of the old component of the sfh. we show how to use galaxy colors to quote age ranges where the recent component of the sfh is stronger or softer than the older component.conclusions: despite of sfr calibrations are unaffected by this work, the meaning of results obtained by sfr inferences does. in our framework, results such as the correlation of sfr timescales with galaxy colors, or the sensitivity of different sfr indices to variations in the sfh, fit naturally. this framework provides a theoretical guide-line to optimize the available information from data and numerical experiments to improve the accuracy of sfr inferences. | recent sfr calibrations and the constant sfr approximation |
context. massive luminous red galaxies (lrgs) are believed to be evolving passively and can be used as cosmic chronometers to estimate the hubble constant (the differential age method). however, different lrgs may be located in different environments. the environmental effects, if any, on the mean ages of lrgs, and the ages of the oldest lrgs at different redshift, may limit the use of the lrgs as cosmic chronometers.aims: we aim to investigate the environmental and mass dependence of the formation of "quiescent" lrgs, selected from the sloan digital sky survey (sdss) data release 8, and to pave the way for using lrgs as cosmic chronometers.methods: using the population synthesis software starlight, we derive the stellar populations in each lrg through the full spectrum fitting and obtain the mean age distribution and the mean star formation history (sfh) of those lrgs.results: we find that there is no apparent dependence of the mean age and the sfh of quiescent lrgs on their environment, while the ages of those quiescent lrgs depend weakly on their mass. we compare the sfhs of the sdss lrgs with those obtained from a semi-analytical galaxy formation model and find that they are roughly consistent with each other if we consider the errors in the starlight-derived ages. we find that a small fraction of later star formation in lrgs leads to a systematical overestimation (~28%) of the hubble constant by the differential age method, and the systematical errors in the starlight-derived ages may lead to an underestimation (~ 16%) of the hubble constant. however, these errors can be corrected by a detailed study of the mean sfh of those lrgs and by calibrating the starlight-derived ages with those obtained independently by other methods.conclusions: the environmental effects do not play a significant role in the age estimates of quiescent lrgs; and the quiescent lrgs as a population can be used securely as cosmic chronometers, and the hubble constant can be measured with high precision by using the differential age method. | quiescent luminous red galaxies as cosmic chronometers: on the significance of mass and environmental dependence |
the optical morphology of galaxies holds the cumulative record of their assembly history, and techniques for its quantitative characterization offer a promising avenue toward understanding galaxy formation and evolution. however, the morphology of star-forming galaxies is generally dictated by the youngest stellar component, which can readily overshine faint structural/morphological features in the older underlying stellar background (e.g., relics from recent minor mergers) that could hold important insights into the galaxy build-up process. stripping off galaxy images from the emission from stellar populations younger than an adjustable age cutoff tcut can therefore provide a valuable tool in extragalactic research. removeyoung (), a publicly available tool that is presented here, exploits the combined power of integral field spectroscopy (ifs) and spectral population synthesis (sps) toward this goal. two-dimensional (2d) post-processing of sps models to ifs data cubes with permits computation of the spectral energy, surface brightness, and stellar surface density distribution of stellar populations older than a user-defined tcut. this suggests a variety of applications of star-forming galaxies, such as interacting or merging galaxy pairs and lower mass starburst galaxies near and far; these include blue compact and tidal dwarf galaxies. | removeyoung: a tool for the removal of the young stellar component in galaxies within an adjustable age cutoff |
the recently discovered burst of gravitational waves gw150914 provides a good new chance to verify the current view on the evolution of close binary stars. modern population synthesis codes help to study this evolution from two main sequence stars up to the formation of two final remnant degenerate dwarfs, neutron stars or black holes (masevich and tutukov, 1988). to study the evolution of the gw150914 predecessor we use the ;scenario machine; code presented by lipunov et al. (1996). the scenario modeling conducted in this study allowed to describe the evolution of systems for which the final stage is a massive bh+bh merger. we find that the initial mass of the primary component can be 100÷140m⊙ and the initial separation of the components can be 50÷350r⊙. our calculations show the plausibility of modern evolutionary scenarios for binary stars and the population synthesis modeling based on it. | wolf-rayet stars, black holes and the first detected gravitational wave source |
early attempts to apply asteroseismology to study the galaxy have already shown unexpected discrepancies for the mass distribution of stars between the galactic models and the data; a result that is still unexplained. here, we revisit the analysis of the asteroseismic sample of dwarf and subgiant stars observed by kepler and investigate in detail the possible causes for the reported discrepancy. we investigate two models of the milky way based on stellar population synthesis, galaxia and trilegal. in agreement with previous results, we find that trilegal predicts more massive stars compared to galaxia, and that trilegal predicts too many blue stars compared to 2mass observations. both models fail to match the distribution of the stellar sample in ({log} g,{t}{eff}) space, pointing to inaccuracies in the models and/or the assumed selection function. when corrected for this mismatch in ({log} g,{t}{eff}) space, the mass distribution calculated by galaxia is broader and the mean is shifted toward lower masses compared to that of the observed stars. this behavior is similar to what has been reported for the kepler red giant sample. the shift between the mass distributions is equivalent to a change of 2% in νmax, which is within the current uncertainty in the νmax scaling relation. applying corrections to the δν scaling relation predicted by the stellar models makes the observed mass distribution significantly narrower, but there is no change to the mean. | stellar population synthesis-based modelling of the milky way using asteroseismology of dwarfs and subgiants from kepler |
we use gemini integral field unit observations to map the stellar population properties in the inner region (~680 × 470 pc2) of the galaxy ngc 6868. in order to understand the physical and chemical properties of the stellar content of this galaxy, we performed stellar population synthesis using the starlight code with the miles simple stellar population models. we measured the absorption line indices fe4383, mg2, mgb, fe5270, and fe5335 for the whole fov, and used them to derive fe3 and [mgfe]'. these indices were used to derive [α/fe]. this galaxy is dominated by old metal-rich populations (12.6 gyr; 1.0 and 1.6 z⊙) with a negative metallicity gradient. we also found a recent (~63 myr) metal-rich (1.6 z⊙) residual star formation in the centre of the galaxy. a dust lane with a peak extinction in the v band of 0.65 mag is seen. no signs of ordered stellar motion are found and the stellar kinematics is dispersion dominated. all indices show a spatial profile varying significantly along the fov. mg2 shows a shallow gradient, compatible with the occurrence of mergers in the past. mgb and fe3 profiles suggest different enrichment processes for these elements. we observe three distinct regions: for r< 100 pc and r > 220 pc, mg2, mgb anticorrelate with respect to fe3 and [mgfe]', and for 100 pc <r< 220 pc, they correlate, hinting at different enrichment histories. the [α/fe] profile is really complex and has a central value of ~0.2 dex. we interpret this as the result of a past merger with another galaxy with a different [α/fe] history, thus explaining the [α/fe] maps. | digging deeper into ngc 6868 i: stellar population |
recently discovered bursts of gravitational waves provide a good opportunity to verify the current view on the evolution of close binary stars. modern population synthesis computer programs help to study this evolution from two main sequence stars up to the formation of compact remnants. to calculate the evolution of predecessors of black hole (bh) mergers we used the `scenario machine' code. the scenario modelling allowed to describe the evolution of systems for which the final stage is a bh+bh merger and showed the plausibility of modern evolutionary scenarios for binary stars and population synthesis models based on it. we discuss possible values of spins in bh mergers, and give arguments in favour of different values of spins of bh components in bh mergers (low spin + low spin, low spin + high spin, high spin + high spin). we predict that $\geq 50\%$ bh mergers originated through isolated binary evolution should possess spins of both bhs close to zero (low spin + low spin). up to $\approx$10\% of bh mergers are able to consist of two bhs with spins close to one (high spin + high spin), predecessors of such binaries could be sources of two gamma ray bursts. the bh with the spin close to one could be formed as the result of the merger of two bhs formed via the collapse of a fast rotating star accompanied with a long gamma ray burst and/or a gravitational wave burst with smaller power in comparison with the merger of two bh remnants of binary components. | spin of ligo/virgo merging black holes as the result of binary evolution |
the mergers of double helium white dwarfs are believed to form isolated helium-rich hot subdwarfs. observations show that helium-rich hot subdwarfs can be divided into two subgroups based on whether the surface is carbon-rich or carbon-normal. however, it is not clear whether this distribution directly comes from binary evolution. we adopt the binary population synthesis to obtain the population of single helium-rich hot subdwarfs according to the merger channel of double helium white dwarfs. we find that the merger channel can represent the two subgroups in the teff-log g plane related to different masses of progenitor helium white dwarfs. for z = 0.02, the birth rate and local density of helium-rich hot subdwarf stars from the merger of two helium white dwarfs are $\sim 4.82 \times 10^{-3}\, \rm yr^{-1}$ and ~ 290.0 $\rm kpc^{-3}$ at 13.7 gyr in our galaxy, respectively. the proportions of carbon-rich and carbon-normal helium-rich hot subdwarfs are 32 per cent and 68 per cent, respectively. | post-merger evolution of double helium white dwarfs and distribution of helium-rich hot subdwarfs |
the smpl body model is widely used for the estimation, synthesis, and analysis of 3d human pose and shape. while popular, we show that smpl has several limitations and introduce star, which is quantitatively and qualitatively superior to smpl. first, smpl has a huge number of parameters resulting from its use of global blend shapes. these dense pose-corrective offsets relate every vertex on the mesh to all the joints in the kinematic tree, capturing spurious long-range correlations. to address this, we define per-joint pose correctives and learn the subset of mesh vertices that are influenced by each joint movement. this sparse formulation results in more realistic deformations and significantly reduces the number of model parameters to 20% of smpl. when trained on the same data as smpl, star generalizes better despite having many fewer parameters. second, smpl factors pose-dependent deformations from body shape while, in reality, people with different shapes deform differently. consequently, we learn shape-dependent pose-corrective blend shapes that depend on both body pose and bmi. third, we show that the shape space of smpl is not rich enough to capture the variation in the human population. we address this by training star with an additional 10,000 scans of male and female subjects, and show that this results in better model generalization. star is compact, generalizes better to new bodies and is a drop-in replacement for smpl. star is publicly available for research purposes at http://star.is.tue.mpg.de. | star: sparse trained articulated human body regressor |
searching in the manga ifu survey, i identify nine galaxies that have strong balmer absorption lines and weak nebular emission lines measured from the spectra integrated over the entire ifu. the spectral features measured from the bulk of the stellar light make these galaxies local analogs of high-redshift spectroscopically selected poststarburst galaxies and thus proxies to understand the mechanisms producing poststarburst galaxies at high redshifts. i present the distributions of absorption line indices and emission line strengths, as well as the stellar kinematics of these local poststarburst galaxies. almost all local poststarburst galaxies have central compact emission line regions at the central <1 kpc, mostly powered by weak star formation activities. the age-sensitive absorption line indices ew(hδ) and dn4000 indicate that the stellar populations at the outskirts are older. toy stellar population synthesis models suggest that the galaxies as a whole are experiencing a rapid decline of star formation with residual star formation activities at the centers. these features indicate that most poststarburst galaxies are the aftermath of highly dissipative processes that drive gas into centers, invoke centrally concentrated star formation, and then quench the galaxies. meanwhile, when measurable, poststarburst galaxies have the directions of maximum stellar velocity gradients aligned with photometric major axes, which suggest against major mergers being the principal driving mechanism, while gas-rich minor mergers are plausible. while directly obtaining the same quality of spatially resolved spectra of high-redshift poststarburst galaxies is very difficult, finding proper local counterparts provides an alternative to understand quenching processes in the distant universe. | searching for local counterparts of high-redshift poststarburst galaxies in integral field unit spectroscopic surveys of nearby galaxies |
we present an empirical stellar spectra library, atlas, with resolution r ~ 1800 and wavelength coverage from 3800-8700 å. these spectra are homogeneously observed by the large sky area multi-object fiber spectroscopic telescope and have been released in its dr5. atlas is separated into two groups, atlas-a and -t. the former contains 5584 spectra covering spectral types from o- to m-type and some special types such as a supergiant, blue horizontal-branch, and carbon stars. all of the spectra have absolutely calibrated fluxes at certain characteristic wavelengths corresponding to the optical passbands with accuracy better than 2.9% by comparing with panstarrs1 g-, r-, and i-band photometry. in addition, greater than 1% systematic uncertainty from the fundamental calibration should be considered separately. atlas-a contains 5342 spectra with spectral energy distribution effective temperature, surface gravity, and metallicity and 242 spectra with only the effective temperature and surface gravity. these parameters are consistent with the spectroscopic derived parameters of the same stars. compared to current empirical libraries, atlas-a contains more cool giant stars, which may play a critical role in understanding the evolution of galaxies. atlas-t, on the other hand, contains 1118 spectral templates averaging over spectra with similar stellar parameters from atlas-a. it smooths out some special features in the individual spectra and can be used as a "standard" atlas of stellar spectra. containing stellar spectra with almost all normal types, atlas may not only be a complete training data set for stellar spectra parameter determination but also an ideal legacy for stellar population synthesis. | all spectral type lamost spectra library (atlas) |
the majority of massive stars are born in binaries, and most unbind upon the first supernova. with precise proper motion surveys such as gaia, it is possible to trace back the motion of stars in the vicinity of young remnants to search for ejected companions. establishing the fraction of remnants with an ejected companion, and the photometric and kinematic properties of these stars, offers unique insight into supernova progenitor systems. in this paper, we employ binary population synthesis to produce kinematic and photometric predictions for ejected secondary stars. we demonstrate that the unbound neutron star velocity distribution from supernovae in binaries closely traces the input kicks. therefore, the observed distribution of neutron star velocities should be representative of their natal kicks. we evaluate the probability for any given filter, magnitude limit, minimum measurable proper motion (as a function of magnitude), temporal baseline, distance, and extinction that an unbound companion can be associated with a remnant. we compare our predictions with results from previous companion searches, and demonstrate that the current sample of stars ejected by the supernova of their companion can be increased by a factor of ~5-10 with gaia data release 3. further progress in this area is achievable by leveraging the absolute astrometric precision of gaia, and by obtaining multiple epochs of deep, high resolution near-infrared imaging with the hubble space telescope, jwst and next-generation wide-field near-infrared observatories such as euclid or the nancy grace roman space telescope. | searching for ejected supernova companions in the era of precise proper motion and radial velocity measurements |
upcoming spectroscopic redshift surveys use emission line galaxies (elgs) to trace the three-dimensional matter distributions with wider area coverage in the deeper universe. since the halos hosting elgs are young and undergo infall towards more massive halos along filamentary structures, contrary to a widely employed luminous red galaxy sample, the dynamics specific to elgs should be taken into account to refine the theoretical modelling at non-linear scales. in this paper, we scrutinize the halo occupation distribution (hod) and clustering properties of elgs by utilizing illustristng galaxy formation hydrodynamical simulations. leveraging stellar population synthesis technique coupled with the photo-ionization model, we compute line intensities of simulated galaxies and construct mock h α and [o ii] elg catalogues. the line luminosity functions and the relation between the star formation rate and line intensity are well consistent with observational estimates. next, we measure the hod and demonstrate that there is a distinct population for the central hod, which corresponds to low-mass infalling halos. we then perform the statistical inference of hod parameters from the projected correlation function. our analysis indicates that the inferred hods significantly deviate from the hod measured directly from simulations although the best-fitting model yields a good fit to the projected correlation function. it implies that the information content of the projected correlation function is not adequate to constrain hod models correctly and thus, it is important to employ mock elg catalogues to calibrate the functional form of hod models and add prior information on hod parameters to robustly determine the hod. | clustering of emission line galaxies with illustristng - i. fundamental properties and halo occupation distribution |
an empirical stellar spectral library with large coverage of stellar parameters is essential for stellar population synthesis and studies of stellar evolution. in this work, we present stellar spectra factory (ssf), a tool to generate empirical-based stellar spectra from arbitrary stellar atmospheric parameters. the relative flux-calibrated empirical spectra can be predicted by ssf given arbitrary effective temperature, surface gravity, and metallicity. ssf constructs the interpolation approach based on the stellar label machine, using atlas-a library, which contains spectra covering from o type to m type, as the training data set. ssf is composed of four data-driven sub-models to predict empirical stellar spectra. sub-model ssf-n can generate spectra from a to k type and some m giant stars, covering 3700 < t eff < 8700 k, 0 < $\mathrm{log}g$ < dex, and -1.5 < [m/h] < 0.5 dex. sub-model ssf-gm is mainly used to predict m giant spectra with 3520 < t eff < 4000 k and -1.5 < [m/h] < 0.4 dex. sub-model ssf-dm is for generating m dwarf spectra with 3295 < t eff < 4040 k, -1.0 < [m/h] < 0.1 dex. sub-model ssf-b can predict b-type spectra with 9000 < t eff < 24,000 k and -5.2 < mg< 1.5 mag. the accuracy of the predicted spectra is validated by comparing the flux of predicted spectra to those with same stellar parameters selected from the known spectral libraries, miles and mastar. the averaged difference of flux over optical wavelength between the predicted spectra and the corresponding ones in miles and mastar is less than 5%. more verification is conducted between the magnitudes calculated from the integration of the predicted spectra and the observations in ps1 and apass bands with the same stellar parameters. no significant systematic difference is found between the predicted spectra and the photometric observations. the uncertainty is 0.08 mag in the r band for ssf-gm when comparing with the stars with the same stellar parameters selected from ps1. the uncertainty becomes 0.31 mag in the i band for ssf-dm when comparing with the stars with the same stellar parameters selected from apass. | the stellar spectra factory (ssf) based on slam |
accreting wds are very important for the studies of binary evolution, binary population synthesis and accretion physics. so far, there are a lot of accreting wd binaries with low accretion rates, such as cataclysmic variables, detected by different surveys. however, few accreting wd binaries with high accretion rates have been detected. in this paper, we studied the spectrum properties of accreting wd binaries and investigated whether accreting wd binaries with high accretion rates can be detected by the chinese space station telescope (csst). we found that some accreting wd binaries with high accretion rates can be distinguishable from other types of stars with (nuv - y, u - y), (nuv - r, u - g), (nuv - i, u - g), (nuv - z, u - g) and (nuv - y, u - g) color-color diagrams. therefore, some accreting wd binaries with high accretion rates can be detected by the csst. | possibility of searching for accreting white dwarfs with the chinese space station telescope |
understanding the properties of stellar populations and interstellar dust has important implications for galaxy evolution. in normal star-forming galaxies, stars and the interstellar medium dominate the radiation from ultraviolet (uv) to infrared (ir). in particular, interstellar dust absorbs and scatters uv and optical light, re-emitting the absorbed energy in the ir. this is a strongly nonlinear process that makes independent studies of the uv-optical and ir susceptible to large uncertainties and degeneracies. over the years, uv to ir spectral energy distribution (sed) fitting utilizing varying approximations has revealed important results on the stellar and dust properties of galaxies. yet the approximations limit the fidelity of the derived properties. there is sufficient computer power now available that it is now possible to remove these approximations and map out of landscape of galaxy seds using full dust radiative transfer. this improves upon previous work by directly connecting the uv, optical, and ir through dust grain physics. we present the dirtygrid, a grid of radiative transfer models of seds of dusty stellar populations in galactic environments designed to span the full range of physical parameters of galaxies. using the stellar and gas radiation input from the stellar population synthesis model pegase, our radiative transfer model dirty self-consistently computes the uv to far-ir/sub-mm seds for each set of parameters in our grid. dirty computes the dust absorption, scattering, and emission from the local radiation field and a dust grain model, thereby physically connecting the uv-optical to the ir. we describe the computational method and explain the choices of parameters in dirtygrid. the computation took millions of cpu hours on supercomputers, and the seds produced are an invaluable tool for fitting multi-wavelength data sets. we provide the complete set of seds in an online table. | dirtygrid i: 3d dust radiative transfer modeling of spectral energy distributions of dusty stellar populations |
organosilicon molecules such as silicon carbide (sic), silicon dicarbide (c-sic2), silicon tricarbide (c-sic3), and silicon tetracarbide (sic4) represent basic molecular building blocks connected to the growth of silicon-carbide dust grains in the outflow of circumstellar envelopes of carbon-rich asymptotic giant branch (agb) stars. yet, the fundamental mechanisms of the formation of silicon carbides and of the early processes that initiate the coupling of silicon-carbon bonds in circumstellar envelopes have remained obscure. here, we reveal in a crossed molecular beam experiment contemplated with ab initio electronic calculations that the astronomically elusive 1-ethynyl-3-silacyclopropenylidene molecule (c-sic4h2, cs, x1a') can be synthesized via a single-collision event through the barrierless reaction of the silylidyne radical (sih) with diacetylene (c4h2). this system represents a benchmark of a previously overlooked class of reactions, in which the silicon-carbon bond coupling can be initiated by a barrierless and overall exoergic reaction between the simplest silicon-bearing radical (silylidyne) and a highly hydrogen-deficient hydrocarbon (diacetylene) in the inner circumstellar envelopes of evolved carbon-rich stars such as irc+10216. considering that organosilicon molecules like 1-ethynyl-3-silacyclopropenylidene might be ultimately photolyzed to bare carbon-silicon clusters like the linear silicon tetracarbide (sic4), hydrogenated silicon-carbon clusters might represent the missing link eventually connecting simple molecular precursors such as silane (sih4) to the population of silicon-carbide based interstellar grains ejected from carbon-rich agb stars into the interstellar medium. | on the synthesis of the astronomically elusive 1-ethynyl-3-silacyclopropenylidene (c-sic4h2) molecule in circumstellar envelopes of carbon-rich asymptotic giant branch stars and its potential role in the formation of the silicon tetracarbide chain (sic4) |
we present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. long-slit spectra in the wavelength range 3440-7300 å obtained with the gemini multi-object spectrograph (gmos) at gemini south for 15 galaxies in nine close pairs were used. the spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. this result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. we interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 gyr. we also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. we compared the estimated values of stellar and nebular extinction derived from the synthesis method and the hα/hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. we did not find any correlation between nebular and stellar metallicities. neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich. | interaction effects on galaxy pairs with gemini/gmos- iii: stellar population synthesis |
possible models for the generation of electromagnetic (em) radiation during the coalescence of neutron star-black hole binaries are considered. the mass of the remnant disk around the black hole during the coalescence of neutron stars and black holes is calculated by taking into account the equation of state for neutron stars and the rotation of the binary components before the coalescence. the parameters of binary systems before the coalescence (the mass ratio, the component rotation, the neutron star magnetic field) are calculated by the population synthesis method. the derived mass of the remnant disk around the black hole after the coalescence is used to estimate the kinetic energy of the relativistic jet launched by the blandford-znajek mechanism. a disk mass of more than ∼0.05 m⊙ required for the formation of short gamma-ray bursts is shown to be obtained in no more than 1-10% of the coalescences (depending on the equation of state). less efficient common envelopes (a large parameter αce) lead to a noticeably larger percentage of events with astrophysically interesting em energy release. for binaries with a large mass ratio, in which a magnetized neutron star is not subjected to tidal disruption before the coalescence, the possibility of the formation of an electrically charged rotating black hole (wald charge) is considered and estimates of the maximum em power released by such a black hole after the coalescence are made. the conversion of the emitted gravitational waves into electromagnetic ones in the relativistic lepton plasma generated in coalescing pulsar-black hole binaries at the pre-coalescence stage is discussed. | possible electromagnetic phenomena during the coalescence of neutron star-black hole binary systems |
it is now well-established that most (if not all) ancient globular clusters host multiple populations that are characterized by distinct chemical features such as helium abundance variations along with n-c and na-o anticorrelations, at fixed [fe/h]. these very distinct chemical features are similar to what is found in the centres of the massive early-type galaxies and may influence measurements of the global properties of the galaxies. additionally, recent results have suggested that m/l variations found in the centres of massive early-type galaxies might be due to a bottom-heavy stellar initial mass function. we present an analysis of the effects of globular cluster-like multiple populations on the integrated properties of early-type galaxies. in particular, we focus on spectral features in the integrated optical spectrum and the global mass-to-light ratio that have been used to infer variations in the stellar initial mass function. to achieve this, we develop appropriate stellar population synthesis models and take into account, for the first time, an initial-final mass relation which takes into consideration a varying he abundance. we conclude that while the multiple populations may be present in massive early-type galaxies, they are likely not responsible for the observed variations in the mass-to-light ratio and imf-sensitive line strengths. finally, we estimate the fraction of stars with multiple populations chemistry that come from disrupted globular clusters within massive ellipticals and find that they may explain some of the observed chemical patterns in the centres of these galaxies. | multiple populations within globular clusters in early-type galaxies exploring their effect on stellar initial mass function estimates |
we present f775w-f850lp (rest-frame uv - u) and f850lp-f160w (rest-frame u - r) colour gradients for a sample of 17 elliptical galaxies morphologically selected in the cluster xmmu j2235.3-2557 at z = 1.39. we detected significant negative (redder inwards) u - r colour gradients in ∼70 per cent of the galaxies and flat gradients for the remaining ones. on the other hand, the uv - u gradients are significant positive (bluer inwards) for ∼80 per cent of the galaxies and flat for the remaining ones. using stellar population synthesis models, we found that the behaviour of the two colour gradients cannot be simultaneously explained by a radial variation of age, metallicity and/or dust. the observed u - r gradients are consistent with a metallicity gradient (mean value ∇z = -0.4) in agreement with the one observed in the local elliptical galaxies. the positive uv - u gradients cannot be explained with age or metallicity variations and imply an excess of uv emission towards the galaxies' central regions. this excess calls into question mechanisms able to efficiently produce uv emission. the data require either steady weak star formation ( ≲ 1 m⊙ yr-1) or an he-rich population in the cores of these galaxies in order to simultaneously reproduce both the colour gradients. on the contrary, the presence of a quasi-stellar object (qso) cannot account for the observed uv excess on its own. we discuss these hypotheses on the basis of current observations and available models. | colour gradients in cluster ellipticals at z ∼ 1.4: the hidden content of the galaxy central regions |
i present integrated colors and surface brightness fluctuation magnitudes in the mid-infrared (ir), derived from stellar population synthesis models that include the effects of the dusty envelopes around thermally pulsing asymptotic giant branch (tp-agb) stars. the models are based on the bruzual & charlot cb* isochrones; they are single-burst, range in age from a few myr to 14 gyr, and comprise metallicities between z = 0.0001 and z = 0.04. i compare these models to mid-ir data of agb stars and star clusters in the magellanic clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. i find that models with a higher than fiducial mass-loss rate are needed to fit the mid-ir colors of “extreme” single agb stars in the large magellanic cloud. surface brightness fluctuation magnitudes are quite sensitive to metallicity for 4.5 μm and longer wavelengths at all stellar population ages, and powerful diagnostics of mass-loss rate in the tp-agb for intermediate-age populations, between 100 myr and 2-3 gyr. | tracers of stellar mass-loss. ii. mid-ir colors and surface brightness fluctuations |
we investigate the effect of strong emission line galaxies on the performance of empirical photometric redshift estimation methods. in order to artificially control the contribution of photometric error and emission lines to total flux, we develop a pca-based stochastic mock catalogue generation technique that allows for generating infinite signal-to-noise ratio model spectra with realistic emission lines on top of theoretical stellar continua. instead of running the computationally expensive stellar population synthesis and nebular emission codes, our algorithm generates realistic spectra with a statistical approach, and - as an alternative to attempting to constrain the priors on input model parameters - works by matching output observational parameters. hence, it can be used to match the luminosity, colour, emission line and photometric error distribution of any photometric sample with sufficient flux-calibrated spectroscopic follow-up. we test three simple empirical photometric estimation methods and compare the results with and without photometric noise and strong emission lines. while photometric noise clearly dominates the uncertainty of photometric redshift estimates, the key findings are that emission lines play a significant role in resolving colour space degeneracies and good spectroscopic coverage of the entire colour space is necessary to achieve good results with empirical photo-z methods. template-fitting methods, on the other hand, must use a template set with sufficient variation in emission line strengths and ratios, or even better, first estimate the redshift empirically and fit the colours with templates at the best-fit redshift to calculate the k-correction and various physical parameters. | the effect of emission lines on the performance of photometric redshift estimation algorithms |
we analyse the correlations between continuum properties and emission line equivalent widths of star-forming and active galaxies from the sloan digital sky survey. since upcoming large sky surveys will make broad-band observations only, including strong emission lines into theoretical modelling of spectra will be essential to estimate physical properties of photometric galaxies. we show that emission line equivalent widths can be fairly well reconstructed from the stellar continuum using local multiple linear regression in the continuum principal component analysis (pca) space. line reconstruction is good for star-forming galaxies and reasonable for galaxies with active nuclei. we propose a practical method to combine stellar population synthesis models with empirical modelling of emission lines. the technique will help generate more accurate model spectra and mock catalogues of galaxies to fit observations of the new surveys. more accurate modelling of emission lines is also expected to improve template-based photometric redshift estimation methods. we also show that, by combining pca coefficients from the pure continuum and the emission lines, automatic distinction between hosts of weak active galactic nuclei (agns) and quiescent star-forming galaxies can be made. the classification method is based on a training set consisting of high-confidence starburst galaxies and agns, and allows for the similar separation of active and star-forming galaxies as the empirical curve found by kauffmann et al. we demonstrate the use of three important machine learning algorithms in the paper: k-nearest neighbour finding, k-means clustering and support vector machines. | quantifying correlations between galaxy emission lines and stellar continua |
while it is well known that mass transfer in binaries can pollute the surfaces of the accretors, it is still unclear whether this mechanism can reproduce the observed chemical inhomogeneities in globular clusters. we study the surface abundances of the accretors in low-mass binaries, as a first step towards understanding whether mass transfer in low-mass binaries is one of the potential origins of the aforementioned abundance anomalies in globular clusters. we use the mesa (modules for experiments in stellar astrophysics) code to calculate binary evolutionary models with different initial donor masses between 0.9 and 1.9 {m}_⊙ for an initial metallicity of z = 0.0034. the results show that in some low-mass binary systems, the accretors exhibit peculiar chemical patterns when they are still unevolved stars, e.g. c and o depletion; na and n enhancement; and constant mg, al, and c+n+o. the abundance patterns of the accretors are significantly different from their initial abundances (or that of normal single stars), and can match the observed populations. these abundance patterns strongly depend not only on the initial parameters of binaries (donor mass, mass ratio, and orbital period), but also on the assumptions regarding mass-transfer efficiency and angular momentum loss. these results support the hypothesis that mass transfer in low-mass binaries is, at least, partly responsible for the unevolved anomalous stars in globular clusters. more work on binary evolutionary models and binary population synthesis is required to fully evaluate the contribution of this scenario. | mass transfer of low-mass binaries and chemical anomalies among unevolved stars in globular clusters |
we present a new set of surface brightness fluctuation (sbf) spectra computed with the e-miles stellar population synthesis models. the model sbf spectra cover the range λλ1680-50 000 at moderately high resolution, all based on extensive empirical stellar libraries. the models span the metallicity range -2.3≤ [m/h] ≤ +0.26 for a suite of intial mass function types with varying slopes. these predictions can complement and aid fluctuation magnitude studies, permitting a first-order approximation by applying filter responses to the sbf spectra to obtain spectroscopic sbf magnitudes. we provide a recipe for obtaining the latter and discuss their uncertainties and limitations. we compare our spectroscopic sbf magnitudes to photometric data of a sample of early-type galaxies. we also show that the sbf spectra can be very useful for constraining relevant stellar population parameters. we find small (<5 per cent) mass fractions of extremely metal-poor components ([m/h] < -1) on the top of the dominant, old, and metal-rich stellar population. these results put stringent constraints on the early stages of galaxy formation in massive elliptical galaxies. this is remarkable given the high degree of degeneracy of the standard spectral analysis to such metal-poor stellar populations in the visible and in the near-infrared. the new sbf models show great potential for exploiting ongoing surveys, particularly those based on narrow-band filters. | surface brightness fluctuation spectra to constrain stellar population properties |
aims: we analyze united kingdom infrared deep sky survey (ukidss) observations of a sample of 8325 objects taken from a catalog of intrinsically red sources selected in the spitzer galactic legacy infrared mid-plane survey extraordinaire (glimpse). given the differences in angular resolution (factor >2 better in ukidss), our aim is to investigate whether there are multiple ukidss sources that might all contribute to the glimpse flux, or whether there is only one dominant ukidss counterpart. we then study possible corrections to estimates of the star formation rate (sfr) based on counts of glimpse young stellar objects (ysos). this represents an exploratory work toward the construction of a hierarchical yso catalog.methods: after performing psf fitting photometry in the ukidss data, we implemented a technique to recognize the dominant ukidss sources automatically by evaluating their match with the spectral energy distribution (sed) of the associated glimpse red sources. this is a generic method that could be robustly applied for matching seds across gaps at other wavelengths.results: we found that most (87.0 ± 1.6%) of the candidate ysos from the glimpse red source catalog have only one dominant ukidss counterpart that matches the mid-infrared sed (fainter associated ukidss sources might still be present). although at first sight this could seem surprising, given that ysos are typically in clustered environments, we argue that within the mass range covered by the glimpse yso candidates (intermediate to high masses), clustering with objects with comparable mass is unlikely at the glimpse resolution. indeed, by performing simple clustering experiments based on a population synthesis model of galactic ysos, we found that although 60% of the glimpse yso enclose at least two ukidss sources, in general only one dominates the flux.conclusions: no significant corrections are needed for estimates of the sfr of the milky way based on the assumption that the glimpse ysos are individual objects. however, we found that unresolved binaries in glimpse objects (a few of them could be resolved at the ukidss resolution) have a non-negligible effect, and would increase the sfr estimate by a factor 1.2-1.3. | do individual spitzer young stellar object candidates enclose multiple ukidss sources? |
we present a study on the stellar populations and stellar ages of a subsample of far-infrared (fir) active galactic nucleus (agn) and non-agn green valley galaxies at ${0.6\, \lt \, z\, \lt \, 1.0}$ using the data from the cosmological evolution survey field. we used long-slit spectroscopy and derived stellar populations and stellar ages using the stellar population synthesis code 'starlight' and analysed the available lick/ids indices, such as dn4000 and hδa. we find that both fir agn and non-agn green valley galaxies are dominated by intermediate stellar populations (67 per cent and 53 per cent, respectively). the median stellar ages for agns and non-agns are ${\log t\, =\, 8.5}$ and ${\, 8.4\, \rm yr}$, respectively. we found that majority of our sources (62 per cent of agns and 66 per cent of non-agns) could have experienced bursts and continuous star formation (sf). in addition, most of our fir agns (38 per cent) compared to fir non-agns (27 per cent) might have experienced a burst of sf more than 0.1 gyr ago. we also found that our fir agn and non-agn green valley galaxies have similar quenching time-scales of ~ 70 myr. therefore, the results obtained here are in line with our previous results where we do not find that our sample of fir agns in the green valley shows signs of negative agn feedback, as has been suggested previously in optical studies. | stellar populations of a sample of far-infrared agn and non-agn green valley galaxies |
yellow hypergiants (yhgs) are often presumed to represent a transitional post-red supergiant (rsg) phase for stars ~30-40 m ⊙. here we present visual-wavelength echelle spectra of six yhg candidates in the galactic cluster westerlund 1, and we compare them to known yhgs, irc +10420 and hen 3-1979. we find that the six yhg candidates do not exhibit any metal emission lines, nor do they show strong hα emission, and as such do not meet the criteria necessary to be classified as yhgs. in conjunction with their moderate luminosities of $\mathrm{log}(l/{l}_{\odot })$ = 4.7-5.4 estimated from optical/infrared photometry, we suggest instead that they are normal yellow supergiants (ysgs) with more modest initial masses around 15-20 m ⊙. this adds additional support to the hypothesis that wd1 is a multiage cluster with an older age than previously assumed, and is not a ~5 myr old cluster caught at a very specific transitional point when single-star evolution might yield wolf-rayet stars, luminous blue variables, rsgs, and yhgs in the same cluster. nevertheless, the population of ysgs in wd1 is very unusual, with ysgs outnumbering rsgs, but with both spanning a large luminosity range. here, we discuss evolutionary scenarios that might have led to the high fraction of ysgs. the number of ysgs and their significant luminosity spread cannot be explained by simple population synthesis models with single or binary stars. even with multiple ages or a large age spread, the high ysg/rsg ratio remains problematic. we suggest instead that the objects may experience a prolonged ysg phase due to evolution in triple systems. | don't believe the hype(r): the yellow supergiants of westerlund 1 |
using integral field spectroscopy, we demonstrate that gravity-sensitive absorption features in the zj band (0.9-1.35 μm) can constrain the low-mass stellar initial mass function (imf) in the cores of two elliptical galaxies, m85 and m87. compared to the visible bands, the near-infrared (nir) is more sensitive to light from low-mass dwarf stars, whose relative importance is the primary subject of the debate over imf variations in nearby galaxies. our analysis compares the observed spectra to the latest stellar population synthesis models by employing two different methods: equivalent widths and spectral fitting. we find that the imf slopes in m85 are similar to the canonical milky way imf with a median imf-mismatch parameter αk= 1.26. in contrast, we find that the imf in m87 is steeper than a salpeter imf with αk= 2.77. the derived stellar population parameters, including the imf slopes, are consistent with those from recent results in the visible bands based on spectroscopic and kinematic techniques. certain elemental abundances, e.g., na and fe, have dramatic effects on the imf-sensitive features and therefore the derived imf slopes. we show evidence for a high [na/h] ∼ 0.65 dex in the core of m85 from two independent na i absorption features. the high na abundance may be the result of a recent galactic merger involving m85. this suggests that including [na/h] in the stellar population model parameters is critical for constraining the imf slopes in m85. these results confirm the viability of using nir absorption features to investigate imf variation in nearby galaxies. | initial mass function variation in two elliptical galaxies using near-infrared tracers |
we measure and analyse galaxy clustering and the dependence on luminosity, colour, age, stellar mass, and specific star formation rate using baryon oscillation spectroscopic survey (boss) galaxies at 0.48 < z < 0.62. we fit the monopole and quadrupole moments of the two-point correlation function and its projection on scales of 0.1-60.2 h-1 mpc, after having split the catalogue in a variety of ways. we find that the clustering dependence is consistent with previous well-established results showing the broad trends expected: for example, that brighter, redder, older, more massive and quenched galaxies are more strongly clustered. we also investigate the dependence on additional parameters previously derived from stellar population synthesis model fits to the spectra. we find that galaxy clustering depends on look-back formation time at a low level, while it has little dependence on metallicity. to understand the physics behind these trends, we fit the clustering with a simulation-based emulator to simultaneously model cosmology and galaxy bias using a halo occupation distribution framework. after marginalizing parameters determining the background cosmology, galaxy bias, and a scaling parameter to decouple halo velocity field, we find that the growth rate of large-scale structure as determined by the redshift space distortions is consistent with previous analysis using the full sample, and we do not find evidence that cosmological constraints depend systematically on galaxy selection. this demonstrates that cosmological inference using small-scale clustering measurements is robust to changes in the catalogue selection. | small-scale clustering of boss galaxies: dependence on luminosity, colour, age, stellar mass, specific star formation rate, and other properties |
orbits of close-in planets can shrink significantly due to dissipation of tidal energy in a host star. this process can result in star-planet coalescence within the galactic lifetime. in some cases, such events can be accompanied by an optical or/and uv/x-ray transient. potentially, these outbursts can be observed in near future with new facilities such as lsst from distances about few mpc. we use a population synthesis model to study this process and derive the rate of star-planet mergers of different types. mostly, planets are absorbed by red giants. however, these events, happening with the rate about 3 per year, mostly do not produce detectable transients. the rate of mergers with main sequence stars depends on the effectiveness of tidal dissipation; for reasonable values of stellar tidal quality factor, such events happen in a milky way-like galaxy approximately once in 70 yr or more rarely. this rate is dominated by planets with low masses. such events do not produce bright transients having maximum luminosities ≲ 1036.5 erg s-1. brighter events, related to massive planets, with maximum luminosity ∼1037.5-1038 erg s-1, have the rate nearly five times smaller. | the rate of planet-star coalescences due to tides and stellar evolution |
we review the measurements of magnetic fields of oba stars. based on these data, we confirm that magnetic fields are distributed according to a lognormal law with mean log b = - 0.5 (b in kg) with a standard deviation σ = 0.5. the shape of the magnetic field distribution (mfd) is similar to that for neutron stars. this finding favors the hypothesis that the magnetic field of a neutron star is determined mainly by the magnetic field of its predecessor, namely the massive ob star. further, we model the evolution of an ensemble of magnetic massive stars in the galaxy. we use our own population synthesis code to obtain the distribution of stellar radii, ages, masses, temperatures, effective magnetic fields, and magnetic fluxes from the pre-main-sequence (pms) via zero-age main sequence (zams) up to the terminal-age main sequence stages. a comparison of the mfd obtained in our model with that obtained from the recent measurements of the stellar magnetic field allows us to conclude that the evolution of magnetic fields of massive stars is slow if not absent. the shape of the real mfd shows no indications of the magnetic desert proposed previously. based on this finding, we argue that the observed fraction of magnetic stars is determined by physical conditions at the pms stage of stellar evolution. | statistics of magnetic field measurements in oba stars and the evolution of their magnetic fields |
a model of the population of ultraluminous x-ray sources (ulxs) in binary systems with black hole (bh) accretors is constructed by hybrid population synthesis and is compared with the model of the population of ulxs with magnetized neutron stars (nss) that can be observed as pulsating ulxs (kuranov et al. 2020). a model of the formation of bhs whereby their mass is determined by the mass of the co core immediately before its collapse ($m_{co}$) and ``delayed'' and ``rapid'' collapse models (fryer et al. 2012) are considered. the possible transiency of ulxs due to accretion disk instability is taken into account. the parameters and evolution of ulxs in galaxies with a constant star formation rate (sfr) and in those with an old stellar population after an instantaneous star formation burst are computed. the maximum number of ulxs with bhs (${∼}10$) is reached in galaxies with a stationary $sfr=10m_{\odot}$ yr${}^{-1}$ ${∼}1$ gyr after the beginning of star formation. ulxs observed after the end of star formation are close binary systems in which bhs and/or nss formed before the end of star formation, while long-lived donors with a mass ${∼}m_{\odot}$ continue to overflow their roche lobes after its end or have filled their roche lobes even later. several gyr after the end of star formation the number of ulxs in galaxies with a mass $mg=10^{10}m_{\odot}$ is no more than 0.1, most of them are ulxs with nss. persistent sources with a roche-lobe-overflowing optical star dominate in ulxs with nss, irrespective of the adopted star formation model. the transient sources are an order of magnitude fewer. the ulxs accreting from the stellar wind of the optical component are an order of magnitude fewer than the sources with accretion via roche lobe overflow. | populations of ultraluminous x-ray sources in galaxies: origin and evolution |
gc-1 and gc-2 are two globular clusters (gcs) in the remote halo of m81 and m82 in the m81 group discovered by jang et al. using the hubble space telescope (hst) images. these two gcs were observed as part of the beijing-arizona-taiwan-connecticut (batc) multicolor sky survey using 14 intermediate-band filters covering a wavelength range of 4000-10 000 å. we accurately determine these two clusters' ages and masses by comparing their spectral energy distributions (from 2267 to 20 000 å, comprising photometric data in the near-ultraviolet of the galaxy evolution explorer, 14 batc intermediate-band and two micron all sky survey near-infrared jhks filters) with theoretical stellar population-synthesis models, resulting in ages of 15.50 ± 3.20 for gc-1 and 15.10 ± 2.70 gyr for gc-2. the masses of gc-1 and gc-2 obtained here are 1.77-2.04 × 106 and 5.20-7.11 × 106 m⊙, respectively. in addition, the deep observations with the advanced camera for surveys and wide field camera 3 on the hst are used to provide the surface brightness profiles of gc-1 and gc-2. the structural and dynamical parameters are derived from fitting the profiles to three different models; in particular, the internal velocity dispersions of gc-1 and gc-2 are derived, which can be compared with ones obtained based on spectral observations in the future. for the first time, in this paper, the rh versus mv diagram shows that gc-2 is an ultra-compact dwarf in the m81 group. | ages and structural and dynamical parameters of two globular clusters in the m81 group |
the development of human liver scaffolds retaining their 3-dimensional structure and extra-cellular matrix (ecm) composition is essential for the advancement of liver tissue engineering. we report the design and validation of a new methodology for the rapid and accurate production of human acellular liver tissue cubes (altcs) using normal liver tissue unsuitable for transplantation. the application of high shear stress is a key methodological determinant accelerating the process of tissue decellularization while maintaining ecm protein composition, 3d-architecture and physico-chemical properties of the native tissue. altcs were engineered with human parenchymal and non-parenchymal liver cell lines (hepg2 and lx2 cells, respectively), human umbilical vein endothelial cells (huvec), as well as primary human hepatocytes and hepatic stellate cells. both parenchymal and non-parenchymal liver cells grown in altcs exhibited markedly different gene expression when compared to standard 2d cell cultures. remarkably, huvec cells naturally migrated in the ecm scaffold and spontaneously repopulated the lining of decellularized vessels. the metabolic function and protein synthesis of engineered liver scaffolds with human primary hepatocytes reseeded under dynamic conditions were maintained. these results provide a solid basis for the establishment of effective protocols aimed at recreating human liver tissue in vitro. | rapid production of human liver scaffolds for functional tissue engineering by high shear stress oscillation-decellularization |
key information to understand the formation and evolution of disk galaxies are imprinted in the stellar populations of their bulges. this paper has the purpose to make available new measurements of the stellar population properties of the bulges of four spiral galaxies. both the central values and radial profiles of the line strength of some of the most common lick indices are measured along the major- and minor- axis of the bulge-dominated region of the sample galaxies. the corresponding age, metallicity, and α/fe ratio are derived by using the simple stellar population synthesis model predictions. the central values and the gradients of the stellar population properties of eso-lv 1890070, eso-lv 4460170, and eso-lv 5140100 are consistent with previous findings for bulges of spiral galaxies. on the contrary, the bulge of eso-lv 4500200 shows peculiar chemical properties possibly due to the presence of a central kinematically-decoupled component. the negative metallicity gradient found in our bulges sample indicates a relevant role for the dissipative collapse in bulge formation. however, the shallow gradients found for the age and α/fe ratio suggests that merging can not be completely ruled out for the sample bulges. this is confirmed by the properties of eso-lv 4500200 which can hardly be explained without invoking the capture of external material. based on observations made with eso telescopes at the la silla-paranal observatory under programmes 075.b-0794 and 077.b-0767. table 3 is available at the cds via http://cdsarc.u-strasbg.fr/cgi-bin/qcat?j/an/336/208. | stellar populations of the bulges of four spiral galaxies |
the analysis of multiple populations (mps) in globular clusters (gcs), both spectroscopically and photometrically, is key in understanding their formation and evolution. the relatively narrow johnson u, f336w, and stromgren and sloan u filters have been crucial in exhibiting these mps photometrically, but in paper i we showed that the broader washington c filter can more efficiently detect mps in the test case gc ngc 1851. additionally, in paper i we detected a double main sequence (ms) that has not been detected in previous observations of ngc 1851. we now match this photometry to ngc 1851's published rgb abundances and find that the two rgb branches observed in c generally exhibit different abundance characteristics in a variety of elements (e.g., ba, na, and o) and in cn band strengths, but no single element can define the two rgb branches. however, simultaneously considering [ba/fe] or cn strength with either [na/fe], [o/fe], or cn strength can separate the two photometric rgb branches into two distinct abundance groups. matches of ngc 1851's published sgb and hb abundances to the washington photometry shows consistent characterizations of the mps, which can be defined as an o-rich/n-normal population and an o-poor/n-rich population. photometric synthesis for both the washington c filter and the f336w filter finds that these abundance characteristics, with appropriate variations in he, can reproduce for both filters the photometric observations in both the rgb and the ms. this photometric synthesis also confirms the throughput advantages that the c filter has in detecting mps. | multiple populations in ngc 1851: abundance variations and uv photometric synthesis in the washington and hst/wfc3 systems |
we identify isolated galaxy triplets in a volume-limited sample from the sloan digital sky survey data release 10. our final sample has 80 galaxy systems in the redshift range 0.04 ≤ z ≤ 0.1, brighter than mr = -20.5 + 5 log h70. spectral synthesis results and whan and bpt diagnostic diagrams were employed to classify the galaxies in these systems as star-forming, active nuclei, or passive/retired. our results suggest that the brightest galaxies drive the triplet evolution, as evidenced by the strong correlations between properties as mass assembly and mean stellar population age with triplet properties. galaxies with intermediate luminosity or the faintest one within the triplet seem to play a secondary role. moreover, the relation between age and stellar mass of galaxies is similar for these galaxies but different for the brightest galaxy in the system. most of the triplet galaxies are passive or retired, according to the whan classification. low-mass triplets present different fractions of whan classes when compared to higher mass triplets. a census of whan class combinations shows the dominance of star-forming galaxies in low-mass triplets while retired and passive galaxies prevail in high-mass systems. we argue that these results suggest that the local environment, through galaxy interactions driven by the brightest galaxy, is playing a major role in triplet evolution. | dissecting galaxy triplets in the sloan digital sky survey data release 10 - i. stellar populations and emission line analysis |
we analyze the intrinsic flux ratios of various visible-near-infrared filters with respect to 3.5 μm for simple and composite stellar populations (csps), and their dependence on age, metallicity, and star formation history (sfh). uv/optical light from stars is reddened and attenuated by dust, where different sightlines across a galaxy suffer varying amounts of extinction. tamura et al. (2009) developed an approximate method to correct for dust extinction on a pixel-by-pixel basis, dubbed the “{β }v” method, by comparing the observed flux ratio to an empirical estimate of the intrinsic ratio of visible and ∼3.5 μm data. through extensive modeling, we aim to validate the “{β }v” method for various filters spanning the visible through near-infrared wavelength range, for a wide variety of simple and csps. combining starburst99 and bc03 models, we built spectral energy distributions (seds) of simple (ssp) and composite (csp) stellar populations for various realistic sfhs, while taking metallicity evolution into account. we convolve various 0.44-1.65 μm filter throughput curves with each model sed to obtain intrinsic flux ratios {β }λ ,0. when unconstrained in redshift, the total allowed range of {β }v,0 is 0.6-4.7, or almost a factor of eight. at known redshifts, and in particular at low redshifts (z ≲ 0.01), {β }v,0 is predicted to span a narrow range of 0.6-1.9, especially for early-type galaxies (0.6-0.7), and is consistent with observed {β }v values. the {β }λmethod can therefore serve as a first-order dust-correction method for large galaxy surveys that combine jwst (rest-frame 3.5 μm) and hst (rest-frame visible-near-ir) data. | analysis of the intrinsic mid-infrared l band to visible-near-infrared flux ratios in spectral synthesis models of composite stellar populations |
intergalactic medium temperature is a powerful probe of the epoch of reionization, as information is retained long after reionization itself. however, mean temperatures are highly degenerate with the timing of reionization, with the amount heat injected during the epoch, and with the subsequent cooling rates. we post-process a suite of semi-analytic galaxy formation models to characterize how different thermal statistics of the intergalactic medium can be used to constrain reionization. temperature is highly correlated with redshift of reionization for a period of time after the gas is heated. however as the gas cools, thermal memory of reionization is lost, and a power-law temperature-density relation is formed, t = t0(1 + δ)1 - γ with γ ≈ 1.5. constraining our model against observations of electron optical depth and temperature at mean density, we find that reionization likely finished at z_{reion} = 6.8 ^{+ 0.5} _{-0.8} with a soft spectral slope of α = 2.8 ^{+ 1.2} _{-1.0}. by restricting spectral slope to the range [0.5, 2.5] motivated by population ii synthesis models, reionization timing is further constrained to z_{reion} = 6.9 ^{+ 0.4} _{-0.5}. we find that, in the future, the degeneracies between reionization timing and background spectrum can be broken using the scatter in temperatures and integrated thermal history. | dark-ages reionization and galaxy formation simulation - xvi. the thermal memory of reionization |
star clusters are good tracers for formation and evolution of galaxies. we compared different fitting methods by using spectra (or by combining photometry) to determine the physical parameters. we choose a sample of 17 star clusters in m33, which previously lacked spectroscopic observations. the low-resolution spectra were taken with the xinglong 2.16 m reflector of naoc. the photometry used in the fitting includes usc and vsage bands from the sage survey, as well as the published ubvri and ugriz photometry. we first derived ages and metallicities with the ulyss (vazdekis et al. and pegase-hr) simple stellar population model and the bruzual & charlot stellar population synthesis models for the full-spectrum fitting. the fitting results of both the bc03 and ulyss models seem consistent with those of previous works as well. then, we add the sage usc and vsage photometry in the spectroscopic fitting with the bc03 models. it seems that the results become much better, especially for the padova 2000+chabrier initial mass function set. finally, we add more photometry data, ubvri and ugriz, in the fitting, and we found that the results do not improve significantly. therefore, we conclude that the photometry is useful for improving the fitting results, especially for the blue bands (λ < 4000 å), e.g., usc and vsage band. at last, we discuss the "uv excess" for the star clusters, and we find that five star clusters have uv excess, based on the galex far-uv and near-uv photometry. | comparisons of different fitting methods for the physical parameters of a star cluster sample of m33 with spectroscopy and photometry |
we present an evolutionary population synthesis model of the surface brightness fluctuation (sbf) for normal and he-enriched simple stellar populations (ssps). while our sbf model for the normal he population agrees with other existing models, the he-rich population, containing hotter horizontal branch stars and brighter red clump stars than the normal he population, entails a substantial change in the sbf of ssps. we show that the sbf magnitudes are affected by he-rich populations at least ∼0.3 mag even in i- and near-infrared bands at given colors, from which the sbf-based distances are often derived. due to uncertainties both in observations and models, however, the sbfs of galactic globular clusters and early-type galaxies do not allow verifying the he-enriched model. we propose that when combined with independent metallicity and age indicators such as mg2 and hβ, the uv and optical sbfs can readily detect underlying he-rich populations in unresolved stellar systems at a distance out to ≳20 mpc. a full set of the spectro-photometric and sbf data for ssps from the yonsei evolutionary population synthesis (yeps) model is available for download at http://cosmic.yonsei.ac.kr/yeps.htm. | yonsei evolutionary population synthesis (yeps) model. iii. surface brightness fluctuation of normal and helium-enhanced simple stellar populations |
we report the detection of lyman continuum (lyc) emission from the galaxy, cdfs-6664, at z = 3.797 in a sample of lyman break galaxies with detected [o iii] emission lines. the lyc emission is detected with a significance ~5σ in the f336w band of the hubble deep uv legacy survey, corresponding to the 650-770 å rest frame. the light centroid of the lyc emission is offset from the galaxy center by about 0.″2 (1.4 pkpc). the hubble deep images at longer wavelengths show that the emission is unlikely provided by low-redshift interlopers. the photometric and spectroscopic data show that the possible contribution of an active galactic nucleus is quite low. fitting the spectral energy distribution of this source to stellar population synthesis models, we find that the galaxy is young (~50 myr) and actively forming stars with a rate of 52.1 ± 4.9 m ⊙ yr-1. the significant star formation and the spatially offset lyc emission support a scenario where the ionizing photons escape from the low-density cavities in the ism excavated by massive young stars. from the nebular model, we estimate the escape fraction of lyc photons to be 38% ± 7% and the corresponding intergalactic medium (igm) transmission to be 60%, which deviates more than 3σ from the average transmission. the unusually high igm transmission of lyc photons in cdfs-6664 may be related to a foreground type-2 quasar, cdf-202, at z = 3.7, with a projected separation of 1.'2 only. the quasar may have photoevaporated optically thick absorbers and enhance the transmission on the sightline of cdfs-6664. | cdfs-6664: a candidate of lyman-continuum emission at z 3.8 detected by the hubble deep uv legacy survey |
the presented study gives a comprehensive overview of the theory and the evidence for a systematically varying stellar initial mass function (imf). then we focus on the impact of this paradigm change, that is, from the universal invariant imf to a variable imf, on galaxy chemical evolution (gce) studies. for this aim, we developed the first gce code, galimf, that is able to incorporate the empirically calibrated environment-dependent imf variation theory, the integrated galactic initial mass function (igimf) theory. in this theory, the galaxy-wide imf is calculated by summing all the imfs in all embedded star clusters which formed throughout the galaxy in 10 myr time epochs. the galimf code recalculates the galaxy-wide imf at each time step because the integrated galaxy-wide imf depends on the galactic star formation rate and metallicity. the resulting galaxy-wide imf and metal abundance evolve with time. using this code, we examine the chemical evolution of early-type galaxies (etgs) from dwarf to the most massive. we find that the introduction of the non-canonical imf affects the best estimation of the galaxy properties such as their mass, star formation history, and star formation efficiency. moreover, we are able to provide an independent estimation on the stellar formation timescale of galaxies, the type ia supernova production efficiency, and constrain the imf variation law of the low-mass stars. this work provides to the community the publicly available galimf code with improved constraints on the imf variation and has, for the first time, resolved the discrepancy between the galaxy formation timescales obtained from stellar population synthesis and chemical enrichment studies. | chemical evolution of galaxies with an environment-dependent stellar initial mass function |
the spatial distribution, galactic model parameters, and luminosity function of cataclysmic variables (cvs) are established using reestimated trigonometric parallaxes from gaia dr3. the data sample of 1587 cvs in this study is claimed to be suitable for galactic model parameter estimation as the distances are based on trigonometric parallaxes, and the gaia dr3 photometric completeness limits were taken into account when the sample was created. according to the analysis, the scale height of all cvs increases from 248 ± 2 to 430 ± 4 pc toward shorter periods near the lower limit of the period gap and suddenly drops to 300 ± 2 pc for the shortest orbital period cvs. the exponential scale heights of all cvs and the magnetic systems are found to be 375 ± 2 and 281 ± 3 pc, respectively, considerably larger than those suggested in previous observational studies. the local spatial density of all cvs and the magnetic systems in the sample are ${6.8}_{-1.1}^{+1.3}\times $ 10-6 and ${2.1}_{-0.4}^{+0.5}\times {10}^{-6}$ pc-3, respectively. our measurements strengthen the 1-2 order of magnitude discrepancy between the cv spatial densities predicted by population synthesis models and observations. it is likely that this discrepancy is due to objects undetected by cv surveys, such as systems with very low $\dot{m}$ and ones in the period gap. a comparison of the luminosity function of white dwarfs with the luminosity function of all cvs in this study show that 500 times the luminosity function of cvs fits very well to the luminosity function of white dwarfs. we conclude that the estimations and data sample in this study can be confidently used for further analyses of cvs. | galactic model parameters and spatial density of cataclysmic variables in the gaia era: new constraints on population models |
we present sengi, (https://christopherlovell.github.io/sengi), an online tool for viewing the spectral outputs of stellar population synthesis (sps) codes. typical sps codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. this makes it difficult to present their results in an interactive, web-friendly format. sengi uses non-negative matrix factorisation (nmf) and bilinear interpolation to estimate output spectra for arbitrary values of stellar age and metallicity. the reduced disk requirements and computational expense allows the result to be served as a client-based javascript application. in this paper we present the method for generating grids of spectra, fitting those grids with nmf, bilinear interpolation across the fitted coefficients, and finally provide estimates of the prediction and interpolation errors. | sengi: a small, fast, interactive viewer for spectral outputs from stellar population synthesis models |
the binary population in field stars and star clusters contributes to the formation of gravitational wave (gw) sources. however, the fraction of compact-object binaries (cbs), which is an important feature parameter of binary populations, is still difficult to measure and very uncertain. this paper predicts the fractions of important cbs and semi-compact object binaries (scbs) making use of an advanced stellar population synthesis technique. a comparison with the result of n-body simulation is also presented. it is found that most cbs are formed within about 500 myr after the starburst. the fractions of cbs and scbs are demonstrated to correlate with stellar metallicity. the higher the metallicity becomes, the smaller the fraction of black hole binaries (bhbs), neutron star binaries (nsbs) and scbs. this suggests that the gw sources of bhbs and nsbs are more likely to form in metal-poor environments. however, the fraction of black hole-neutron star binaries is shown to be larger for metal-rich populations on average. | fractions of compact object binaries in star clusters: theoretical predictions |
knowledge of the elemental abundances of symbiotic giants is essential to address the role of chemical composition in the evolution of symbiotic binaries, to map their parent population, and to trace their mass transfer history. however, there are few symbiotic giants for which the photospheric abundances are fairly well determined. this is the second in a series of papers on chemical composition of symbiotic giants determined from high-resolution (r ∼ 50 000) near-ir spectra. results are presented for the late-type giant star in the ae ara, bx mon, kx tra, and cl sco systems. spectrum synthesis employing standard local thermal equilibrium (lte) analysis and stellar atmosphere models were used to obtain photospheric abundances of cno and elements around the iron peak (sc, ti, fe, and ni). our analysis resulted in sub-solar metallicities in bx mon, kx tra, and cl sco by [fe/h] ∼ -0.3 or -0.5 depending on the value of microturbulence. ae ara shows metallicity closer to solar by ∼ 0.2 dex. the enrichment in 14n isotope found in all these objects indicates that the giants have experienced the first dredge-up. in the case of bx mon first dredge-up is also confirmed by the low 12c/13c isotopic ratio of ∼ 8. | chemical abundance analysis of symbiotic giants - ii. ae ara, bx mon, kx tra, and cl sco |
we present morphological analyses of post-starburst galaxies (psbs) at 0.7 < z < 0.9 in the cosmos field. we fitted ultraviolet to mid-infrared multiband photometry of objects with i < 24 from cosmos2020 catalogue with population synthesis models assuming non-parametric, piece-wise constant function of star formation history, and selected 94 of those galaxies that have high specific star formation rates (ssfrs) of more than 10-9.5 yr-1 in 321-1000 myr before observation and an order-of-magnitude lower ssfrs within recent 321 myr. we devised a new non-parametric morphological index which quantifies concentration of asymmetric features, ca, and measured it as well as concentration c and asymmetry a on the hubble space telescope/advanced camera for surveys if814w-band images. while relatively high c and low a values of psbs are similar to those of quiescent galaxies rather than star-forming galaxies, we found that psbs show systematically higher values of ca than both quiescent and star-forming galaxies; 36 per cent of psbs have log ca > 0.8, while only 16 per cent (2 per cent) of quiescent (star-forming) galaxies show such high ca values. those psbs with high ca have relatively low overall asymmetry of a ~ 0.1, but show remarkable asymmetric features near the centre. the fraction of those psbs with high ca increases with increasing ssfr in 321-1000 myr before observation rather than residual ongoing star formation. these results and their high surface stellar mass densities suggest that those galaxies experienced a nuclear starburst in the recent past, and processes that cause such starbursts could lead to the quenching of star formation through rapid gas consumption, supernova/active galactic nucleus feedback, and so on. | central concentration of asymmetric features in post-starburst galaxies at z 0.8 |
we analyse the vertical distribution of high-mass x-ray binaries (hmxbs) in ngc 55, the nearest edge-on galaxy to the milky way (mw), based on x-ray observations by chandra. adopting a statistical approach, we estimate the difference between the scale height of the vertical distribution of hmxbs and the vertical distribution of star-forming activity between 0.33 and 0.57 kpc. the spatial offsets can be explained by a momentum kick the x-ray binaries receive during the formation of the compact object after a supernova explosion of the primary star. determining the vertical distribution of hmxbs in the mw using gaia dr2 astrometry, we find that the corresponding difference is considerably lower at 0.036 ± 0.003 kpc, attributed to the greater gravitational potential of the mw. we also calculate the centre-of-mass transverse velocities of hmxbs in ngc 55, using traveltime information from binary population synthesis codes and for different star formation histories (sfhs). for a flat sfh model (typical of spiral galaxies like ngc 55), we find that hmxbs are moving with a typical transverse velocity between 34 and 48 km s-1, consistent with space velocities of mw hmxbs. for an exponentially declining sfh model, hmxbs are moving at a velocity of 21 km s-1, consistent with the corresponding velocity of hmxbs in the small magellanic cloud and large magellanic cloud. finally, we estimate the formation efficiency of hmxbs in ngc 55 at 299_{-46}^{+50} (systems/m⊙ yr-1), consistent within the errors with the magellanic clouds but significantly higher than the mw, a difference that can be explained by the subsolar metallicity of ngc 55. | vertical distribution of hmxbs in ngc 55: constraining their centre-of-mass velocity |
in the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and star clusters. systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. while fitting formulae to stellar tracks in the form of single star evolution (sse) code remain a popular choice for modelling stellar evolution in population synthesis codes, they are less adaptable to changes in the stellar tracks. hence, we have developed a method of interpolation for single star evolution (metisse) as an alternative to sse. it makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. metisse is comparable to sse in performance and can reproduce tracks from different stellar evolution codes quite accurately. in this work, we apply metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), bonn evolutionary code (bec), to study the impact of uncertainties in stellar evolution on a population of massive stars. we find that different physical ingredients used in the evolution of stars, such as the treatment of radiation dominated envelopes, can impact their evolutionary outcome, including remnant masses and maximal radial expansion. the differences in the predictions of different stellar models can help us account for the present day observations of stellar populations. | exploring uncertainties in the evolution of massive stars with metisse |
neutron stars in high-mass x-ray binaries (hmxbs) generally accrete from the wind matter of their massive companion stars. recently, shakura et al. suggested a subsonic accretion model for low-luminosity (<4 × 1036 erg s-1), wind-fed x-ray pulsars. to test the feasibility of this model, we investigate the spin period distribution of wind-fed x-ray pulsars with a supergiant companion star, using a population synthesis method. we find that the modeled distribution of supergiant hmxbs in the spin period-orbital period diagram is consistent with observations, provided that the winds from the donor stars have relatively low terminal velocities (≲1000 km s-1). the measured wind velocities in several supergiant hmxbs seem to favor this viewpoint. the predicted number ratio of wind-fed x-ray pulsars with persistent x-ray luminosities that are higher and lower than 4 × 1036 erg s-1 is about 1:10. | can the subsonic accretion model explain the spin period distribution of wind-fed x-ray pulsars? |
gemini multi-object spectrograph and its integral field unit observational data were used to study the detailed 2d gas kinematics and morphological structures within the ∼500 × 421 pc2 of the active seyfert 2 galaxy ngc 4501. we provide empirical pieces of evidence of possible outflowing material from the central zones of ngc 4501 to the observer. in addition, we performed a spectral synthesis and diagnostic diagram analysis to determine respectively the dominant stellar population in the inner disc of this galaxy and to unveil the actual nature of the central engine of ngc 4501. the principal finding of this work is that the central regions of ngc 4501 are dominated by non-circular motions connected to probable outflows of matter from the nuclear regions of this galaxy. a predominant old stellar population inhabits the internal zones of ngc 4501, excluding the possibility of ongoing starburst activity in the central parsecs of this galaxy. the latter result is confirmed by the diagnostic diagram analysis that establishes a preponderant active galactic nucleus character for ngc 4501. these outcomes together provide a general description of the gas motion and the corresponding nuclear activity in the internal disc of ngc 4501 in an attempt to elucidate the possible relation among the central activity and the induced kinematic properties of this nearby galaxy. | 2d kinematic study of the central region of ngc 4501 |
the article considers various aspects of the evolution of close binary systems (cbss). the variation in the orbital parameters of a cbs during its evolution, including the evolution of the cbs under the influence of the magnetic stellar wind and the gravitational wave radiation, is analyzed. the evolution of cbss with mass transfer is considered. evolutionary scenarios for cbss and population synthesis are discussed. modern three-dimensional models of gas flow in interacting cbss are presented. the collision of supersonic stellar winds in cbss is discussed. | close binary stars. vii: on the evolution of close binary systems |
we use three different techniques to identify hundreds of white dwarf (wd) candidates in the next generation virgo cluster survey (ngvs) based on photometry from the ngvs and guvics, and proper motions derived from the ngvs and the sloan digital sky survey (sdss). photometric distances for these candidates are calculated using theoretical color-absolute magnitude relations, while effective temperatures are measured by fitting their spectral energy distributions. disk and halo wd candidates are separated using a tangential velocity cut of 200 km s-1 in a reduced proper motion diagram, which leads to a sample of six halo wd candidates. cooling ages, calculated for an assumed wd mass of 0.6m ⊙, range between 60 myr and 6 gyr, although these estimates depend sensitively on the adopted mass. luminosity functions for the disk and halo subsamples are constructed and compared to previous results from the sdss and supercosmos survey. we compute a number density of (2.81 ± 0.52) × 10-3 pc-3 for the disk wd population—consistent with previous measurements. we find (7.85 ± 4.55) × 10-6 pc-3 for the halo, or 0.3% of the disk. observed stellar counts are also compared to predictions made by the trilegal and besançon stellar population synthesis models. the comparison suggests that the trilegal model overpredicts the total number of wds. the wd counts predicted by the besançon model agree with the observations, although a discrepancy arises when comparing the predicted and observed halo wd populations; the difference is likely due to the wd masses in the adopted model halo. | the next generation virgo cluster survey. xxviii. characterization of the galactic white dwarf population |
this paper presents ccd multicolor photometry for 304 old star clusters in the nearby spiral galaxy m31, from which the photometry of 55 star clusters is first obtained. the observations were carried out as a part of the beijing-arizona-taiwan-connecticut multicolor sky survey from 1995 february to 2008 march, using 15 intermediate-band filters covering 3000-10000 å. detailed comparisons show that our photometry is in agreement with previous measurements. based on the ages and metallicities from caldwell et al. and the photometric measurements here, we estimated the clusters’ masses by comparing their multicolor photometry with stellar population synthesis models. the results show that the sample clusters have masses between ∼ 3× {{10}4}{{m}⊙ } and ∼ {{10}7}{{m}⊙ } with a peak of ∼ 4× {{10}5}{{m}⊙ }. the masses here are in good agreement with those in previous studies. combined with the masses of young star clusters of m31 from wang et al., we find that the peak mass of the old clusters is 10 times that of young clusters. | spectral energy distributions and masses of 304 m31 old star clusters |
based on manga integral field unit (ifu) spectroscopy we search 60 agn candidates, which have stellar masses m* ⩽ 5 × 109 m⊙ and show agn ionization signatures in the bpt diagram. for these agn candidates, we derive the spatially resolved stellar population with the stellar population synthesis code starlight and measure the gradients of the mean stellar age and metallicity. we find that the gradients of mean stellar age (metallicity) of individual agn-host dwarfs are diverse in 0-0.5 re, 0.5-1 re and 0-1 re. however, the overall behavior of the mean stellar age (metallicity) profiles tend to be flat, as the median values of the gradients are close to zero. we further study the overall behavior of the mean stellar age (metallicity) by plotting the co-added radial profiles for the agn sample and compare with a control sample with similar stellar mass. we find that the median values of light-weighted mean stellar ages of the agn sample are as old as 2-3 gyr within 2 re,which are about 4-7 times older than those of the control sample. meanwhile, most of the agn candidates are low-level agns, as only eight sources have l[o iii] > 1039.5 erg s-1. hence, the agns in dwarf galaxies might accelerate the evolution of galaxies by accelerating the consumption of the gas, resulting in an overall quenching of the dwarf galaxies, and the agns also become weak due to the lack of gas. the median values of mass-weighted mean stellar age of both samples within 2 re are similar and as old as about 10 gyr, indicating that the stellar mass is mainly contributed by old stellar populations. the gradients of co-added mean stellar metallicity for both samples tend to be negative but close to zero, and the similar mean stellar metallicity profiles for both samples indicate that the chemical evolution of the host galaxy is not strongly influenced by the agn. | radial stellar populations of agn-host dwarf galaxies in sdss-iv manga survey |
context. this work uses the measured luminosity vs. displacement (lx vs. r) distribution of high-mass x-ray binaries (hmxbs) to constrain the dispersion of kick velocity σkick, which is an important parameter affecting the system velocity of a binary, and hence its spatial offset from the point of origin.aims: the aim is to constrain the natal kicks and discriminate between models by comparing the observed lx vs. r distributions with the theoretical simulations.methods: using an up-to-date evolutionary population synthesis technique, the spatial offsets of hmxbs are modeled for a range of theoretical models describing the natal kicks, including different choices of the dispersion of kick velocity σkick, as well as different theoretical treatments for black hole (bh) natal kicks.results: the study shows that the value of σkick for neutron stars (nss) is constrained to be greater than ~100 km s-1, while σkick on the order of several tens of km s-1 may be excluded, though a low or absent natal kick for electron capture supernovae nss is permitted. in particular, bh natal kicks are found not indispensable to account for the lx vs. r distributions. it is more interesting that full bh natal kicks (i.e., similar to those that nss may receive) are likely to be ruled out in this study, which is in contrast with the recent finding to explain the observed distribution of low-mass x-ray binaries hosting bhs. | displacement of x-ray binaries: constraints on the natal kicks |
we report the first measurement of the odd-isotope fractions for barium, fodd,ba in two extremely metal-poor stars: a cemp-r/s star he 0338-3945 ([fe/h] =-2.42 ± 0.11) and an r-ii star cs 31082-001 ([fe/h] =-2.90 ± 0.13). the measured fodd,ba values are 0.23 ± 0.12 corresponding to 34.3 ± 34.3% of the r-process contributions for he 0338-3945 and 0.43 ± 0.09 corresponding to 91.4 ± 25.7% of the r-process contribution to ba production for cs 31082-001. the high r-process signature of barium in cs 31082-001 (91.4 ± 25.7%) suggests that the majority of the heavy elements in this star were synthesised via an r-process path, while the lower r-process value (34.3 ± 34.3%) found in he 0338-3945 indicates that the heavy elements in this star formed through a mix of s-process and r-process synthesis. these conclusions are consistent with studies based on asymptotic giant branch star model calculations to fit their abundance distributions. based on observations carried out at the european southern observatory, paranal, chile (proposal number 170.d-0010 and 165.n-0276(a)). | the odd-isotope fractions of barium in cemp-r/s star he 0338-3945 and r-ii star cs 31082-001 |
recent hubble space telescope observations have unveiled the white dwarf cooling sequence of the galactic bulge. although the degenerate sequence can be well fitted employing the most up-to-date theoretical cooling sequences, observations show a systematic excess of red objects that cannot be explained by the theoretical models of single carbon-oxygen white dwarfs of the appropriate masses. here, we present a population synthesis study of the white dwarf cooling sequence of the galactic bulge that takes into account the populations of both single white dwarfs and binary systems containing at least one white dwarf. these calculations incorporate state-of-the-art cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, for both white dwarfs with carbon-oxygen and helium cores, and also take into account detailed prescriptions of the evolutionary history of binary systems. our monte carlo simulator also incorporates all the known observational biases. this allows us to model with a high degree of realism the white dwarf population of the galactic bulge. we find that the observed excess of red stars can be partially attributed to white dwarf plus main sequence binaries, and to cataclysmic variables or dwarf novae. our best fit is obtained with a higher binary fraction and an initial mass function slope steeper than standard values, as well as with the inclusion of differential reddening and blending. our results also show that the possible contribution of double degenerate systems or young and thick-discbulge stars is negligible. | the population of single and binary white dwarfs of the galactic bulge |
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