abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
the observed velocity dispersion of the classical dwarf spheroidal (dsph) galaxies of the milky way (mw) requires the newtonian stellar mass-to-light (m*/l) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. using jeans analysis, we calculate the line-of-sight velocity dispersion (σlos) of stars in eight mw dsphs in the context of the modified gravity (mog) theory of moffat, assuming a constant m*/l ratio without invoking the exotic cold dark matter. first, we use the weak field approximation of mog and assume the two parameters α and μ of the theory to be constant as has already been inferred from fitting to the observed rotational data of the h i nearby galaxy survey catalogue of galaxies. we find that the derived m*/l ratios for almost all dsphs are too large to be explained by the stellar population values. in order to fit the line-of-sight velocity dispersions of the dsph with reasonable m*/l values, we must vary α and μ on a case by case basis. a common pair of values cannot be found for all dsphs. comparing with the values found from rotation curve fitting, it appears that μ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant. | testing modified gravity with dwarf spheroidal galaxies |
we use the kinematic data of the stars in eight dwarf spheroidal galaxies to assess whether f(r) gravity can fit the observed profiles of the line-of-sight velocity dispersion of these systems without resorting to dark matter. our model assumes that each galaxy is spherically symmetric and has a constant velocity anisotropy parameter β and constant mass-to-light ratio consistent with stellar population synthesis models. we solve the spherical jeans equation that includes the yukawa-like gravitational potential appearing in the weak field limit of f(r) gravity, and a plummer density profile for the stellar distribution. the f(r) velocity dispersion profiles depends on two parameters: the scale length ξ-1, below which the yukawa term is negligible, and the boost of the gravitational field δ > -1. δ and ξ are not universal parameters, but their variation within the same class of objects is expected to be limited. the f(r) velocity dispersion profiles fit the data with a value $\xi ^{-1}= 1.2^{+18.6}_{-0.9}$ mpc for the entire galaxy sample. on the contrary, the values of δ show a bimodal distribution that picks at $\overline{\delta }=-0.986\pm 0.002$ and $\overline{\delta }=-0.92\pm 0.01$. these two values disagree at 6σ and suggest a severe tension for f(r) gravity. it remains to be seen whether an improved model of the dwarf galaxies or additional constraints provided by the proper motions of stars measured by future astrometric space missions can return consistent δ's for the entire sample and remove this tension. | dynamics of dwarf galaxies in f(r) gravity |
following the collapse of their cores, some of the massive binary stars that populate our universe are expected to form merging binaries composed of black holes and neutron stars. gravitational-wave observations of the resulting compact binaries can reveal precious details on the inner workings of the supernova mechanism and the subsequent formation of compact objects. within the framework of the population-synthesis code mobse, we present the implementation of a new supernova model that relies on the compactness of the collapsing star. the model has two free parameters, namely the compactness threshold that separates the formation of black holes and that of neutron stars, and the fraction of the envelope that falls back onto the newly formed black holes. we compare this model extensively against other prescriptions that are commonly used in binary population synthesis. we find that the cleanest signatures of the role of the pre-supernova stellar compactness are (1) the relative formation rates of the different kinds of compact binaries, which mainly depend on the compactness threshold parameter, and (2) the location of the upper edge of the mass gap between the lightest black holes and the heaviest neutron stars, which mainly depends on the fallback fraction. | modeling the outcome of supernova explosions in binary population synthesis using the stellar compactness |
binary stars undergo a variety of interactions and evolutionary phases, critical for predicting and explaining observations. binary population synthesis with full simulation of stellar structure and evolution is computationally expensive, requiring a large number of mass-transfer sequences. the recently developed binary population synthesis code posydon incorporates grids of mesa binary star simulations that are interpolated to model large-scale populations of massive binaries. the traditional method of computing a high-density rectilinear grid of simulations is not scalable for higher-dimension grids, accounting for a range of metallicities, rotation, and eccentricity. we present a new active learning algorithm, psy-cris, which uses machine learning in the data-gathering process to adaptively and iteratively target simulations to run, resulting in a custom, high-performance training set. we test psy-cris on a toy problem and find the resulting training sets require fewer simulations for accurate classification and regression than either regular or randomly sampled grids. we further apply psy-cris to the target problem of building a dynamic grid of mesa simulations, and we demonstrate that, even without fine tuning, a simulation set of only ~1/4 the size of a rectilinear grid is sufficient to achieve the same classification accuracy. we anticipate further gains when algorithmic parameters are optimized for the targeted application. we find that optimizing for classification only may lead to performance losses in regression, and vice versa. lowering the computational cost of producing grids will enable new population synthesis codes such as posydon to cover more input parameters while preserving interpolation accuracies. | active learning for computationally efficient distribution of binary evolution simulations |
we present a near-infrared (near-ir) study of the spectral components of the continuum in the inner 500 × 500 pc2 of the nearby seyfert galaxy mrk 573 using adaptive optics near-ir integral field spectroscopy with the instrument near-infrared integral field spectrograph of the gemini north telescope at a spatial resolution of ∼50 pc. we performed spectral synthesis using the starlight code and constructed maps for the contributions of different age components of the stellar population: young (age ≤100 myr), young-intermediate (100 < age ≤ 700 myr), intermediate-old (700 myr < age ≤ 2 gyr) and old (age > 2 gyr) to the near-ir k-band continuum, as well as their contribution to the total stellar mass. we found that the old stellar population is dominant within the inner 250 pc, while the intermediate-age components dominate the continuum at larger distances. a young stellar component contributes up to ∼20 per cent within the inner ∼70 pc, while hot dust emission and featureless continuum components are also necessary to fit the nuclear spectrum, contributing up to 20 per cent of the k-band flux there. the radial distribution of the different age components in the inner kiloparsec of mrk 573 is similar to those obtained by our group for the seyfert galaxies mrk 1066, mrk 1157 and ngc 1068 in previous works using a similar methodology. young stellar populations (≤100 myr) are seen in the inner 200-300 pc for all galaxies contributing with ≥20 per cent of the k-band flux, while the near-ir continuum is dominated by the contribution of intermediate-age stars (t = 100 myr-2 gyr) at larger distances. older stellar populations dominate in the inner 250 pc. | disentangling the near-infrared continuum spectral components of the inner 500 pc of mrk 573: two-dimensional maps |
context. studies of extremely metal-poor stars indicate that chemical abundance ratios [x/fe] have a root mean square scatter as low as 0.05 dex (12%). it remains unclear whether this reflects observational uncertainties or intrinsic astrophysical scatter arising from physical conditions in the interstellar medium at early times.aims: we measure differential chemical abundance ratios in extremely metal-poor stars to investigate the limits of precision and to understand whether cosmic scatter or observational errors are dominant.methods: we used high-resolution (r ~ 95 000) and high signal-to-noise (s/n = 700 at 5000 å) hires/keck spectra to determine high-precision differential abundances between two extremely metal-poor stars through a line-by-line differential approach. we determined stellar parameters for the star g64-37 with respect to the standard star g64-12. we performed ew measurements for the two stars for the lines recognized in both stars and performed spectral synthesis to study the carbon abundances.results: the differential approach allowed us to obtain errors of σ(teff) = 27 k, σ(log g) = 0.06 dex, σ( [fe/h] ) = 0.02 dex and σ(vt) = 0.06 km s-1. we estimated relative chemical abundances with a precision as low as σ([x/fe]) ≈ 0.01 dex. the small uncertainties demonstrate that there are genuine abundance differences larger than the measurement errors. the observed li difference cannot be explained by the difference in mass because the less massive star has more li.conclusions: it is possible to achieve an abundance precision around ≈ 0.01-0.05 dex for extremely metal-poor stars, which opens new windows on the study of the early chemical evolution of the galaxy. table a.1 is also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/586/a67 | first high-precision differential abundance analysis of extremely metal-poor stars |
as the evolutionary link between the radio millisecond pulsars and the low-mass x-ray binaries or intermediate-mass x-ray binaries, the millisecond x-ray pulsars (msxps) are important objects in testing theories of pulsar formation and evolution. in general, neutron stars in msxps can form via core collapse supernova (cc channel) of massive stars or accretion induced collapse (aic channel) of an accreting onemg white dwarf, whose mass reaches the chandrasekhar limit. here, in addition to cc and aic channels we also consider another channel, i.e. evolution induced collapse (eic channel) of a helium star with mass between 1.4 and 2.5 m⊙. using a population synthesis code, we have studied msxps arising from three different evolutionary channels. we find that the galactic birthrates of transient msxps and persistent msxps are about 0.7-1.4 × 10-4 yr-1. our population synthesis calculations have shown that about 50-90 per cent of the msxps have undergone cc channel, about 10-40 per cent of them have undergone eic channel, and the msxps via aic channel are the least. | population synthesis of millisecond x-ray pulsars |
the nature of the progenitors of type ia supernovae (sne ia) remains a mystery. comparing theoretical rates and delay-time distributions of sne ia with those inferred observationally can constrain their progenitor models. in this work, taking thermohaline mixing into account in the helium-enriched main-sequence (hems) donor scenario, we address rates and delay times of sne ia in this channel by combining the results of self-consistent binary evolution calculations with population synthesis models. we find that the galactic sn ia rate from the hems donor scenario is around 0.6-1.2 × 10-3 yr-1, which is about 30 per cent of the observed rate. delay times of sne ia in this scenario cover a wide range of 0.1-1.0 gyr. we also present the pre-explosion properties of companion stars in the hems donor scenario, which will be helpful for placing constraints on sn ia progenitors through analysing their pre-explosion images. | rates and delay times of type ia supernovae in the helium-enriched main-sequence donor scenario |
intense, compact, star-forming galaxies are rare in the local universe but ubiquitous at high redshift. we interpret the 0.1-22 μm spectral energy distributions of a sample of 180 galaxies at 0.05 < z < 0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. by comparison with well-established stellar population synthesis models, we find that our sample comprises young (∼60-400 myr), moderate mass (∼6 × 109 m⊙) star-forming galaxies with little dust extinction (mean stellar continuum extinction econt(b - v) ∼ 0.1) and find star formation rates of a few tens of solar masses per year. we use our inferred masses to determine a mean specific star formation rate for this sample of ∼10-9 yr-1, and compare this to the specific star formation rates in distant lyman-break galaxies (lbgs), and in other low-redshift populations. we conclude that our sample's characteristics overlap significantly with those of the z ∼ 5 lbg population, making ours the first local analogue population well tuned to match those high-redshift galaxies. we consider implications for the origin and evolution of early galaxies. | physical properties of local star-forming analogues to z ∼ 5 lyman-break galaxies |
aims: we analyzed the effect of the sedimentation of 22ne on the local white dwarf luminosity function by studying scenarios under different galactic metallicity models.methods: we use an advanced population synthesis code based on monte carlo techniques to derive the synthetic luminosity function. the code incorporates the most recent and reliable cooling sequences and an accurate modeling of the observational biases under different scenarios. we first analyzed the case for a model with constant solar metallicity and compared the models with and without 22ne sedimentation with the observed luminosity function for a pure thin-disk population. then we analyzed the possible effects of a thick-disk contribution. we also studied model scenarios with different metallicities, including 22ne sedimentation. the analysis was quantified from a statistical χ2-test value for the complete and also for the most significant regions of the white dwarf luminosity function. finally, a best-fit model along with a disk age estimate was derived.results: models with constant solar metallicity cannot simultaneously reproduce the peak and cutoff of the white dwarf luminosity function. the additional release of energy due to 22ne sedimentation piles up more objects in brighter bins of the faint end of the luminosity function. the contribution of a single-burst thick-disk population increases the number of stars in the magnitude interval centered around mbol = 15.75. the metallicity model that follows a twarog profile is disposable. our best-fit model was obtained when a dispersion in metallicities of about solar metallicity was considered along with a 22ne sedimentation model, a thick-disk contribution, and an age of the thin disk of 8.8 ± 0.2 gyr.conclusions: our population synthesis model is able to reproduce the local white dwarf luminosity function with a high degree of precision when a dispersion in metallicities around a model with solar values is adopted. although the effects of 22ne sedimentation are only marginal and the contribution of a thick-disk population is minor, both of them help in better fitting the peak and the cutoff regions of the white dwarf luminosity function. | effects of 22ne sedimentation and metallicity on the local 40 pc white dwarf luminosity function |
uncertainties in stellar population models, both in terms of stellar evolution and stellar spectra, translate into uncertainties in our interpretation of stellar populations in galaxies, since stars are the source of most of the light we receive from them. observations by jwst are revealing high-redshift galaxies in great detail, which must then be compared to models. one significant source of uncertainty is in the stellar spectra used to generate composite spectra of stellar populations, which are then compared to data. confidence in theoretical models is important to enable reliable determination of the properties of these galaxies such as their ages and star formation history. here, we present a comparison of spectral synthesis carried out with six different stellar spectral libraries using the binary population and spectral synthesis framework. in photometric colours, the differences between theoretical libraries are relatively small (<0.10 mag), similar to typical observational uncertainties on individual galaxy observations. differences become more pronounced when detailed spectroscopic properties are examined. predictions for spectral line indices can vary significantly, with equivalent widths differing by a factor of 2 in some cases. with these index strengths, some of the libraries yield predictions of ages and metallicities which are unphysical. many spectral libraries lack wavelength coverage in the ultraviolet, which is of growing importance in the era of jwst observations of distant galaxies, whose flux is dominated by hot, young stars. | on the impact of spectral template uncertainties in synthetic stellar populations |
double neutron star (dns) systems are produced from massive binaries. a supernova (sn) explosion of an extremely stripped star is expected to occur at the final stage of dns formation. this type of sn is called an ultra-stripped sn (ussn). recent research revealed that a type ic sn, iptf 14gqr (sn 2014ft), has low ejecta mass (≈0.2 m ⊙) and its progenitor has a helium envelope with mass ∼0.01 m ⊙. this sn is interpreted as a ussn, and thus this is the first discovery of a ussn. furthermore, the observation of iptf 14gqr provides us with some information about its formation history. here, we perform rapid population synthesis calculations so as to estimate the detection rate of iptf 14gqr like ussne with optical transient surveys: the intermediate palomar transient factory (iptf), the zwicky transient facility (ztf), and the large synoptic survey telescope (lsst). we find that iptf, ztf, and lsst can observe iptf 14gqr like ussne at rates of 0.3, 10, and 1 yr-1, respectively. the iptf can detect 1 iptf 14gqr like ussn during its four year observation. we also investigate effects of mass-loss efficiency during roche-lobe overflow on formation channels. | the rate of iptf 14gqr like ultra-stripped supernovae and binary evolution leading to double neutron star formation |
re-creating the observed diversity in the organization of baryonic mass within dark matter haloes represents a key challenge for galaxy formation models. to address the growth of galaxy discs in dark matter haloes, we have constrained the distribution of baryonic and non-baryonic matter in a statistically representative sample of 44 nearby galaxies defined from the extended disk galaxy exploration science (edges) survey. the gravitational potentials of each galaxy are traced using rotation curves derived from new and archival radio synthesis observations of neutral hydrogen (h i). the measured rotation curves are decomposed into baryonic and dark matter halo components using 3.6 μm images for the stellar content, the h i observations for the atomic gas component, and, when available, co data from the literature for the molecular gas component. the h i kinematics are supplemented with optical integral field spectroscopic (ifs) observations to measure the central ionized gas kinematics in 26 galaxies, including 13 galaxies that are presented for the first time in this paper. distributions of baryonic-to-total mass ratios are determined from the rotation curve decompositions under different assumptions about the contribution of the stellar component and are compared to global and radial properties of the dominant stellar populations extracted from optical and near-infrared photometry. galaxies are grouped into clusters of similar baryonic-to-total mass distributions to examine whether they also exhibit similar star and gas properties. the radial distribution of baryonic-to-total mass in a galaxy does not appear to correlate with any characteristics of its star formation history. | baryonic distributions in galaxy dark matter haloes - ii. final results |
we model the present-day, observable, normal radio pulsar population of the small magellanic cloud (smc). the pulsars are generated with seba, a binary population synthesis code that evolves binaries and the constituent stellar objects up to remnant formation and beyond. we define radio pulsars by selecting neutron stars (nss) that satisfy a selection of criteria defined by galactic pulsars, and apply the detection thresholds of previous and future smc pulsar surveys. the number of synthesized and recovered pulsars is exceptionally sensitive to the assumed star formation history and applied radio luminosity model, but is not affected extensively by the assumed common-envelope model, metallicity, and ns kick velocity distribution. we estimate that the smc formed (1.6 ± 0.3) ×104 normal pulsars during the last 100 myr. we study which pulsars could have been observed by the parkes multibeam survey of the smc, by applying the survey's specific selection effects, and recover 4.0 ± 0.8 synthetic pulsars. this is in agreement with their five observed pulsars. we also apply a proposed meerkat configuration for the upcoming smc survey, and predict that the meerkat survey will detect 17.2 ± 2.5 pulsars. | the radio pulsar population of the small magellanic cloud |
we present and evaluate the prospects for detecting coherent radio counterparts to gravitational wave (gw) events using murchison widefield array (mwa) triggered observations. the mwa rapid-response system, combined with its buffering mode ( $∼$ 4 min negative latency), enables us to catch any radio signals produced from seconds prior to hours after a binary neutron star (bns) merger. the large field of view of the mwa ( $∼$ $1 000 \textrm{deg}^2$ at 120 mhz) and its location under the high sensitivity sky region of the ligo-virgo-kagra (lvk) detector network, forecast a high chance of being on-target for a gw event. we consider three observing configurations for the mwa to follow up gw bns merger events, including a single dipole per tile, the full array, and four sub-arrays. we then perform a population synthesis of bns systems to predict the radio detectable fraction of gw events using these configurations. we find that the configuration with four sub-arrays is the best compromise between sky coverage and sensitivity as it is capable of placing meaningful constraints on the radio emission from 12.6% of gw bns detections. based on the timescales of four bns merger coherent radio emission models, we propose an observing strategy that involves triggering the buffering mode to target coherent signals emitted prior to, during or shortly following the merger, which is then followed by continued recording for up to three hours to target later time post-merger emission. we expect mwa to trigger on $∼$ $5-22$ bns merger events during the lvk o4 observing run, which could potentially result in two detections of predicted coherent emission. | mwa rapid follow-up of gravitational wave transients: prospects for detecting prompt radio counterparts |
we conduct binary population synthesis to investigate the formation of wind-fed high-mass x-ray binaries containing black holes (bh-hmxbs). we evolve multiple populations of high-mass binary stars and consider bh-hmxb formation rates, masses, spins, and separations. we find that systems similar to cygnus x-1 likely form after stable case a mass transfer (mt) from the main-sequence progenitors of bhs, provided such mt is characterized by low accretion efficiency, β ≲ 0.1, with modest orbital angular momentum losses from the non-accreted material. additionally, efficient bh-hmxb formation relies on a new simple treatment for case a mt that allows donors to retain larger core masses compared to traditional rapid population-synthesis assumptions. at solar metallicity, our preferred model yields $\mathcal {o}(1)$ observable bh-hmxbs in the galaxy today, consistent with observations. in this simulation, 8 per cent of bh-hmxbs go on to merge as binary black holes or neutron star-black hole binaries within a hubble time; however, none of the merging binaries have bh-hmxb progenitors with properties similar to cygnus x-1. with our preferred settings for core mass growth, mass transfer efficiency, and angular momentum loss, accounting for an evolving metallicity, and integrating over the metallicity-specific star formation history of the universe, we find that bh-hmxbs may have contributed ≈2-5 bbh merger signals to detections reported in the third gravitational-wave transient catalogue of the ligo-virgo-kagra collaboration. we also suggest mt efficiency should be higher during stable case b mt than during case a mt. | rapid population synthesis of black hole high-mass x-ray binaries: implications for binary stellar evolution |
we present a uniform analysis of the stellar initial mass function (imf) from integrated light spectroscopy of 15 compact stellar systems (11 globular clusters in m31 and 4 ultra compact dwarfs in the virgo cluster, ucds) and two brightest coma cluster galaxies (bcgs), covering a wide range of metallicities (-1.7 < [fe/h] < 0.01) and velocity dispersions (7.4 km s-1 <σ < 275 km s-1). the s/n ~100 å-1 keck lris spectra are fitted over the range 4000 < λ/å < 10 000 with flexible full-spectrum stellar population synthesis models. we use the models to fit simultaneously for ages, metallicities, and individual elemental abundances of the population, allowing us to decouple abundance variations from variations in imf slope. we show that compact stellar systems do not follow the same trends with physical parameters that have been found for early-type galaxies. most globular clusters in our sample have an imf consistent with that of the milky way, over a wide range of [fe/h] and [mg/fe]. there is more diversity among the ucds, with some showing evidence for a bottom-heavy imf, but with no clear correlation with metallicity, abundance, or velocity dispersion. the two coma bcgs have similar velocity dispersion and metallicity, but we find the imf of ngc 4874 is consistent with that of the milky way while ngc 4889 presents evidence for a significantly bottom-heavy imf. for this sample, the imf appears to vary between objects in a way that is not explained by a single metallicity-dependent prescription. | initial mass function variability from the integrated light of diverse stellar systems |
the growing catalogue of circumbinary planets strengthens the notion that planets form in a diverse range of conditions across the cosmos. transiting circumbinary planets yield especially important insights and many examples are now known, in broadly coplanar obits with respect to their binary. studies of circumbinary discs suggest misaligned transiting examples could also plausibly exist, but their existence would exacerbate the already challenging feat of automatic detection. in this work, we synthesize populations of such planets and consider the number of transits per epoch they produce, forming integer sequences. for isotropic distributions, such sequences will appear foreign to conventional expectation, rarely (~1 per cent) producing the signature double-transits we have come to expect for circumbinaries, instead producing sparse sequences dominated by zero-transit epochs (~80 per cent). despite their strangeness, we demonstrate that these sequences will be non-random and that the two preceding epochs predict the next to high accuracy. additionally, we show that even when clustering the transits into grouped epochs, they often appear unphysical if erroneously assuming a single star, due to the missing epochs. crucially, missing epochs mean highly isotropic populations can trick the observer into assigning the wrong period in up to a quarter of cases, adding further confusion. finally, we show that the transit sequences encode the inclination distribution and demonstrate a simple inference method that successfully matches the injected truth. our work highlights how the simple act of flagging transits can be used to provide an initial, vetting-level analysis of misaligned transiting circumbinary planets. | the number of transits per epoch for transiting misaligned circumbinary planets |
using a recent homogeneous sample of 40 high-quality velocity dispersion profiles for galactic globular clusters, we study the regime of low gravitational acceleration relevant to the outskirts of these systems. we find that a simple empirical profile having a central gaussian component and a constant large-radius asymptote, σ∞, accurately describes the variety of observed velocity dispersion profiles. we use published population synthesis models, carefully tailored to each individual cluster, to estimate mass-to-light ratios from which total stellar masses, m, are inferred. we obtain a clear scaling, reminiscent of the galactic tully-fisher relation of σ _{∞}[ km s^{-1}]= 0.084^{+0.075}_{-0.040} ({m/m}_{⊙ })^{0.3 ± 0.051}, which is interesting to compare to the deep modified newtonian dynamics (mond) limit of σ _{∞} [km s^{-1}]=0.2({m/m}_{⊙ })^{0.25}. under a newtonian interpretation, our results constitute a further restriction on models where initial conditions are crafted to yield the outer flattening observed today. within a modified gravity scheme, because the globular clusters studied are not isolated objects in the deep mond regime, the results obtained point towards a modified gravity where the external field effect of mond does not appear, or is significantly suppressed. | asymptotic kinematics of globular clusters: the emergence of a tully-fisher relation |
we present a new galaxy population synthesis model, galmod. galmod is a star-count model featuring an asymmetric bar/bulge as well as spiral arms and related extinction. the model, initially introduced in pasetto et al., has been here completed with a central bar, a new bulge description, new disk vertical profiles, and several new bolometric corrections. the model can generate synthetic mock catalogs of visible portions of the milky way, external galaxies like m31, or n-body simulation initial conditions. at any given time, e.g., at a chosen age of the galaxy, the model contains a sum of discrete stellar populations, namely the bulge/bar, disk, and halo. these populations are in turn the sum of different components: the disk is the sum of the spiral arms, thin disks, a thick disk, and various gas components, while the halo is the sum of a stellar component, a hot coronal gas, and a dark-matter component. the galactic potential is computed from these population density profiles and used to generate detailed kinematics by considering up to the first four moments of the collisionless boltzmann equation. the same density profiles are then used to define the observed color-magnitude diagrams in a user-defined field of view (fov) from an arbitrary solar location. several photometric systems have been included and made available online, and no limits on the size of the fov are imposed thus allowing full-sky simulations, too. finally, we model the extinction by adopting a dust model with advanced ray-tracing solutions. the model's web page (and tutorial) can be accessed at www.galmod.org and support is provided at galaxy.model@yahoo.com. | galmod: a galactic synthesis population model |
we present a new image of the 9.0 ghz radio emission from the extended chandra deep field south. a total of 181 h of integration with the australia telescope compact array has resulted in a 0.276 deg2 image with a median sensitivity of ∼20 µjy beam-1 rms, for a synthesized beam of 4.0 × 1.3 arcsec. we present a catalogue of the 9.0 ghz radio sources, identifying 70 source components and 55 individual radio galaxies. source counts derived from this sample are consistent with those reported in the literature. the observed source counts are also generally consistent with the source counts from simulations of the faint radio population. using the wealth of multiwavelength data available for this region, we classify the faint 9 ghz population and find that 91 per cent are radio-loud active galactic nuclei (agns), 7 per cent are radio-quiet agns, and 2 per cent are star-forming galaxies. the 9.0 ghz radio sources were matched to 5.5 and 1.4 ghz sources in the literature and we find a significant fraction of flat or inverted spectrum sources, with 36 per cent of the 9 ghz sources having α _{5.5 ghz}^{9.0 ghz} > -0.3 (for s ∝ να). this flat or inverted population is not well reproduced by current simulations of radio source populations. | the atlas 9.0 ghz survey of the extended chandra deep field south: the faint 9.0 ghz radio population |
using multi-band photometric images of m51 and its companion ngc 5195 from ultraviolet to optical and infrared, we investigate spatially resolved stellar population properties of this interacting system with stellar population synthesis models. the observed infrared excess (irx) is used to constrain dust extinction. stellar mass is also inferred from the model fitting. by fitting observed spectral energy distributions (seds) with synthetical ones, we derive two-dimensional distributions of stellar age, metallicity, dust extinction and stellar mass. in m51, two grand-designed spiral arms extending from the bulge show young age, rich metallicity and abundant dust. the inter-arm regions are filled with older, metal-poorer and less dusty stellar populations. except for the spiral arm extending from m51 into ngc 5195, the stellar population properties of ngc 5195 are quite featureless. ngc 5195 is much older than m51, and its core is very dusty with av up to 1.67 mag and dense in stellar mass surface density. the close encounters might drive the dust in the spiral arm of m51 into the center of ngc 5195. | spatially-resolved stellar population properties of the m51-ngc 5195 system from multi-wavelength photometric data |
the origin of the progenitors of type ia supernovae (sne ia) is still uncertain. the core-degenerate (cd) scenario has been proposed as an alternative way for the production of sne ia. in this scenario, sne ia are formed at the final stage of common-envelope evolution from a merger of a carbon-oxygen white dwarf (co wd) with the co core of an asymptotic giant branch companion. however, the birthrates of sne ia from this scenario are still not well determined. in this work, we performed a detailed investigation on the cd scenario based on a binary population synthesis approach. the sn ia delay times from this scenario are basically in the range of 90-2500 myr, mainly contributing to the observed sne ia with short and intermediate delay times, although this scenario can also produce some old sne ia. meanwhile, our work indicates that the galactic birthrates of sne ia from this scenario are not more than 20 per cent of total sne ia due to more careful treatment of mass transfer. although the sn ia birthrates in this work are lower than those in ilkov & soker, the cd scenario cannot be ruled out as a viable mechanism for the formation of sne ia. especially, sne ia with circumstellar material from this scenario contribute to 0.7-10 per cent of total sne ia, which means that the cd scenario can reproduce the observed birthrates of sne ia like ptf 11kx. we also found that sne ia happen systemically earlier for a high value of metallicity and their birthrates increase with metallicity. | the core-degenerate scenario for the progenitors of type ia supernovae |
according to the recycling model, neutron stars in low-mass x-ray binaries were spun up to millisecond pulsars (msps), which indicates that all msps in the galactic plane ought to be harbored in binaries. however, about 20% galactic field msps are found to be solitary. to interpret this problem, we assume that the accreting neutron star in binaries may collapse and become a strange star when it reaches some critical mass limit. mass loss and a weak kick induced by asymmetric collapse during the phase transition (pt) from neutron star to strange star can result in isolated msps. in this work, we use a population-synthesis code to examine the pt model. the simulated results show that a kick velocity of ∼60 km s-1 can produce ∼6 × 103 isolated msps and birth rate of ∼6.6 × 10-7 yr-1 in the galaxy, which is approximately in agreement with predictions from observations. for the purpose of comparisons with future observation, we also give the mass distributions of radio and x-ray binary msps, along with the delay time distribution. | a strange star scenario for the formation of isolated millisecond pulsars |
context. thermonuclear supernovae (sne), a subset of which are the highly important sne type ia, remain one of the more poorly understood phenomena known to modern astrophysics. in recent years, the single degenerate helium (he) donor channel, where a white dwarf star accretes he-rich matter from a hydrogen-depleted companion, has emerged as a promising candidate progenitor scenario for these events. an unresolved question in this scenario is the fate of the companion star, which would be evident as a runaway hot subdwarf o/b stars (he sdo/b) in the aftermath of the sn event.aims: previous studies have shown that the kinematic properties of an ejected companion provide an opportunity to closer examine the properties of an sn progenitor system. however, with the number of observed objects not matching predictions by theory, the viability of this mechanism is called into question. in this study, we first synthesize a population of companion stars ejected by the aforementioned mechanism, taking into account predicted ejection velocities, the inferred population density in the galactic mass distribution, and subsequent kinematics in the galactic potential. we then discuss the astrometric properties of this population.methods: we present 106 individual ejection trajectories, which were numerically computed with a newly developed, lightweight simulation framework. initial conditions were randomly generated, but weighted according to the galactic mass density and ejection velocity data. we then discuss the bulk properties (galactic distribution and observational parameters) of our sample.results: our synthetic population reflects the galactic mass distribution. a peak in the density distribution for close objects is expected in the direction of the galactic centre. higher mass runaways should outnumber lower mass ones. if the entire considered mass range is realised, the radial velocity distribution should show a peak at 500 km s-1. if only close us 708 analogues are considered, there should be a peak at (∼750 - 850) km s-1. in either case, us 708 should be a member of the high-velocity tail of the distribution.conclusions: we show that the puzzling lack of confirmed surviving companion stars of thermonuclear sne, though possibly an observation-related selection effect, may indicate a selection against high mass donors in the sd he donor channel. | predicted spatial and velocity distributions of ejected companion stars of helium accretion-induced thermonuclear supernovae |
the temperatures of red supergiants (rsgs) are expected to depend on metallicity (z) in such a way that lower z rsgs are warmer. in this work, we investigate the z-dependence of the hayashi limit by analysing rsgs in the low-z galaxy wolf-lundmark-mellote, and compare with the rsgs in the higher z environments of the small magellanic cloud and large magellanic cloud. we determine the effective temperature (teff) of each star by fitting their spectral energy distributions, as observed by vlt + shooter, with marcs model atmospheres. we find average temperatures of $t_{\textrm {eff}_{\textrm {wlm}}}=4400\pm 202$ k, $t_{\textrm {eff}_{\textrm {smc}}}=4130\pm 103$ k, and $t_{\textrm {eff}_{\textrm {lmc}}}=4140\pm 148$ k. from population synthesis analysis, we find that although the geneva evolutionary models reproduce this trend qualitatively, the rsgs in these models are systematically too cool. we speculate that our results can be explained by the inapplicability of the standard solar mixing length to rsgs. | the temperatures of red supergiants in low-metallicity environments |
context. the fraction of field binaries on retrograde orbits about the milky way is significantly lower compared to its prograde counterpart. chemical and dynamical evidence suggests that the retrograde stellar population originates from ω centauri, which is either the most massive globular cluster (gc) of the milky way or the putative core of a former dwarf galaxy.aims: star formation conditions required to produce the retrograde binary population are constrained assuming that the retrograde stellar population originates from ω centauri's progenitor.methods: we match the observed low binary fraction with dynamical population synthesis models, including a universal initial binary population and dynamical processing in star clusters, making use of the publicly available binary population synthesis tool bipos1.results: it is found that either the gc progenitor of ω cen must have formed with a stellar density of ≈108 m⊙ pc−3 or the ω centauri dwarf galaxy's progenitor star cluster population must have formed in an extreme starburst with a star formation rate exceeding 1000 m⊙ yr−1 and probably a top-heavy embedded-cluster mass function with suppressed low-mass cluster formation. the separation and mass-ratio distribution for retrograde field binaries are predicted for comparison with future observations.conclusions: a viable solution for the deficiency of binaries on retrograde orbits is presented, and star formation conditions for ω centauri as well as orbital parameter distributions for the milky way's retrograde binary population are predicted. the dwarf galaxy origin for ω centauri is tentatively preferred within the present context. | a possible solution to the milky way's binary-deficient retrograde stellar population. evidence that ω centauri has formed in an extreme starburst |
in this work, we study the optical properties of compact radio sources selected from the literature in order to determine the impact of the radio-jet in their circumnuclear environment. our sample includes 58 compact steep spectrum (css) and gigahertz peaked spectrum (gps) and 14 megahertz-peaked spectrum (mps) radio sources located at z ≤ 1. the radio luminosity (lr) of the sample varies between log lr ~ 23.2 and 27.7 w hz-1. we obtained optical spectra for all sources from sdss-dr12 and performed a stellar population synthesis using the starlight code. we derived stellar masses (m⋆), ages ⟨t⋆⟩, star formation rates (sfr), metallicities ⟨z⋆⟩ and internal reddening av for all young agns of our sample. a visual inspection of the sdss images was made to assign a morphological class for each source. our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources. also, we found that young agns can be hosted by elliptical, spiral and interacting galaxies, confirming recent findings. when comparing the optical properties of css/gps and mps sources, we do not find any significant difference. finally, the mid-infrared wise colours analysis suggests that the compact radio sources defined as powerful agns are, in general, gas-rich systems. | optical properties of peaked spectrum radio sources |
aims: recent alma observations identified one of the most massive star-forming cores yet observed in the milky way: sdc335-mm1, within the infrared dark cloud sdc335.579-0.292. along with an accompanying core mm2, sdc335 appears to be in the early stages of its star formation process. we aim to constrain the properties of the stars forming within these two massive millimetre sources.methods: observations of sdc335 at 6, 8, 23 and 25 ghz were made with the australia telescope compact array. we report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (seds) of the compact sources in sdc335.results: three hyper-compact hii regions within sdc335 are identified, two of which are within the mm1 core. for each hchii region, we fit a free-free emission curve to the data, providing the derivation of the sources' emission measure, ionising photon flux, and electron density. using these physical properties we assign each hchii region a zero-age main sequence (zams) spectral type, finding two protostars with characteristics of spectral type b1.5 and one with a lower limit of b1-b1.5. ancillary data from infrared to mm wavelength are used to construct free-free component subtracted seds for the mm-cores, which allows us to calculate the bolometric luminosities and revise the previous gas mass estimates.conclusions: the measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the zams spectral type assigned to them. the protostars are still actively accreting, suggesting that a mechanism is limiting the accretion luminosity. we present the case for two different mechanisms capable of causing lower than expected accretion luminosity. finally, using the zams mass values as lower limit constraints, a final stellar population for sdc335 was synthesised finding sdc335 is likely to be in the process of forming a stellar cluster comparable to the trapezium cluster and ngc 6334 i(n). fits images of the atca data at 6, 8, 23, and 25 ghz used in this paper are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/577/a30 | tightening the belt: constraining the mass and evolution in sdc335 |
rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. it was demonstrated by imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. in this paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. we applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. we have used the bse (binary star evolution) population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. the validity of this approach is checked by direct mesa calculations of the evolution of a rotating 15 m⊙ star. from comparison of the calculated spin distribution of young neutron stars with the observed one, reported by popov and turolla, we infer the value τc ≃ 5 × 105 yr. we show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ∼0.1-1 per cent of the total core collapses, depending on the common envelope efficiency. | rapidly rotating neutron star progenitors |
we have identified 1027 star-forming complexes in a sample of 46 galaxies from the spirals, bridges, and tails (sb&t) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (nis) galaxies in 8 μm observations from the spitzer infrared array camera. we have used archival multi-wavelength uv-to ir observations to fit the observed spectral energy distribution of our clumps with the code investigating galaxy emission using a double exponentially declined star formation history. we derive the star formation rates (sfrs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. the resolved star formation main sequence holds on 2.5 kpc scales, although it does not hold on 1 kpc scales. we analyzed the relation between sfr, stellar mass, and age of the recent burst in the sb&t and nis samples, and we found that the sfr per stellar mass is higher in the sb&t galaxies, and the clumps are younger in the galaxy pairs. we analyzed the sfr radial profile and found that the sfr is enhanced through the disk and in the tidal features relative to normal spirals. | stellar population synthesis of star-forming clumps in galaxy pairs and non-interacting spiral galaxies |
as part of a work carried out on magellanic clouds (mcs) stellar clusters (scs), we present results in age, metallicity and reddening for hw 22, applying different methods (equivalent widths (ews), template matching and spectral synthesis) from the sc's integrated spectrum. this interesting sc would be older than previous calculations, and could harbour multiple stellar populations (mps). we present results derived by other authors and discuss them in comparison to our results. | on the magellanic clouds stellar clusters characterization from their integrated spectra |
globular clusters (gcs) have long been recognized as being amongst the oldest objects in the galaxy. as such, they have the potential of playing a pivotal role in deciphering the milky way's early history. here we present the first spectroscopic study of the low-mass system eso452-sc11 using the aaomega multifibre spectrograph at medium resolution. given the stellar sparsity of this object and the high degree of foreground contamination due to its location toward the galactic bulge, very few details are known for this cluster - there is no consensus, for instance, about its age, metallicity, or its association with the disk or bulge. we identify five member candidates based on common radial velocity, calcium-triplet metallicity, and position within the gc. using spectral synthesis, the measurement of accurate fe-abundances from fe-lines, and abundances of several α-, fe-peak, and neutron-capture elements (si, ca, ti,cr, co, ni, sr, and eu) is carried out, albeit with large uncertainties. we find that two of the five cluster candidates are likely non-members, as they have deviating iron abundances and [α/fe] ratios. the cluster mean heliocentric velocity is 19 ± 2 km s-1 with a velocity dispersion of 2.8 ± 3.4 km s-1, a low value in line with its sparse nature and low mass. the mean fe-abundance from spectral fitting is -0.88 ± 0.03 dex, where the spread is driven by observational errors. furthermore, the α-elements of the gc candidates are marginally lower than expected for the bulge at similar metallicities. as spectra of hundreds of stars were collected in a 2-degree field centered on eso452-sc11, a detailed abundance study of the surrounding field was also enabled. the majority of the non-members have slightly higher [α/fe] ratios, in line with the typical nearby bulge population. a subset of the spectra with measured fe-peak abundance ratios shows a large scatter around solar values, albeit with large uncertainties. furthermore, our study provides the first systematic measurements of strontium abundances in a galactic bulge gc. here, the eu and sr abundances of the gc candidates are broadly consistent with a disk or bulge association. recent proper motions and our orbital calculations place eso452 on an elliptical orbit in the central 3 kpc of the milky way, establishing a firm connection with the bulge. finally, while the radial velocities and preferential position of a dozen of stars outside the gc radius appear to imply the presence of extra-tidal stars, their significantly different chemical composition refutes this hypothesis. full tables 2-5 are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/604/a41 | spectroscopic study of the elusive globular cluster eso452-sc11 and its surroundings |
focusing on the remnant black holes after merging binary black holes, we show that ringdown gravitational waves of population iii binary black hole mergers can be detected at the rate of 5.9-500 events yr(sfr/(10m yr mpc))ṡ([f/(1+f)]/0.33) for various parameters and functions. this rate is estimated for events with snr>8 for second-generation gravitational wave detectors such as kagra. here, sfr and f are the peak value of the population iii star formation rate and the fraction of binaries, respectively. when we consider only events with snr>35, the event rate becomes 0.046-4.21 events yr(sfr/(10m yr mpc))ṡ([f/(1+f)]/0.33). this suggest that for a remnant black hole spin of q>0.95 we have an event rate of quasinormal modes with snr>35 of less than 0.037 events yr(sfr/(10m yr mpc))ṡ([f/(1+f)]/0.33), while it is 3-30 events yr(sfr/(10m yr mpc))ṡ([f/(1+f)]/0.33) for third-generation detectors such as the einstein telescope. if we detect many population iii binary black hole mergers, it may be possible to constrain the population iii binary evolution paths not only by the mass distribution but also by the spin distribution. | gravitational wave quasinormal mode from population iii massive black hole binaries in various models of population synthesis |
assuming all binary neutron star (bns) mergers produce short gamma-ray bursts, we combine the merger rates of bns from population synthesis studies, the sensitivities of advanced gravitational wave (gw) interferometer networks, and of the electromagnetic (em) facilities in various wavebands, to compute the detection rate of associated afterglows in these bands. using the inclination angle measured from gws as a proxy for the viewing angle and assuming a uniform distribution of jet opening angle between 3° and 30°, we generate light curves of the counterparts using the open access afterglow hydrodynamics package boxfit for x-ray, optical, and radio bands. for different em detectors, we obtain the fraction of em counterparts detectable in these three bands by imposing appropriate detection thresholds. in association with bns mergers detected by five (three) detector networks of advanced gw interferometers, assuming a bns merger rate of 0.6-774 gpc-3 yr-1 from population synthesis models, we find the afterglow detection rates (per year) to be 0.04-53 (0.02-27), 0.03-36 (0.01-19), and 0.04-47 (0.02-25) in the x-ray, optical, and radio bands, respectively. our rates represent maximum possible detections for the given bns rate since we ignore effects of cadence and field of view in em follow-up observations. | rates of short-grb afterglows in association with binary neutron star mergers |
we investigate the formation of discs within binary systems where at least one component has left the main sequence. in particular, we calculate the occurrence rates of systems that can host long-lived, massive discs that may be able to support the formation of planets. we synthesize a population based on milky way properties, using both theoretical and observational inputs to constrain key properties, such as the shape of the initial mass function, binary fraction, and mass-transfer physics. we predict 0.26 per cent of binary systems will host second-generation discs (where the primary has evolved), and 0.13 per cent of systems will host third-generation discs (where the secondary also evolves). for the milky way, this translates into 130 million and 90 million second- and third-generation systems, respectively, from an estimated total of 50 billion binary systems. of these systems that form discs, we estimate approximately 20 per cent of second-generation and 3.8 per cent of third-generation discs have enough mass to form a planetary system. we speculate on how the process of planet formation differs in these systems from conventional planet formation in protostellar discs. | the galactic rate of second- and third-generation disc and planet formation |
given the upsurge of new technologies based on nanomaterials, the development of sustainable methods to obtain functional nanostructures has become an imperative task. in this matter, several recent researches have shown that the biodegradable natural antioxidants of several plant extracts can be used simultaneously as reducing and stabilizing agents in the wet chemical synthesis of metallic nanoparticles, opening new opportunities to design greener synthesis. however, the challenge of these new techniques is to produce stable colloidal nanoparticles with controlled particle uniformity, size, shape and aggregation state, in similar manner than the well-established synthetic methods. in the present work, colloidal metallic silver nanoparticles have been synthesized using silver nitrate and extracts of illicium verum (star anise) seeds at room temperature in a facile one-step procedure. the resulting products were colloidal suspensions of two populations of silver nanoparticles, one of them with particle sizes of few nanometers and the other with particles of tens of nm. strikingly, the variation of the agno3/extract weight ratio in the reaction medium yielded to the variation of the spatial distribution of the nanoparticles: high agno3/extract concentration ratios yielded to randomly dispersed particles, whereas for lower agno3/extract ratios, the biggest particles appeared coated with the finest nanoparticles. this biosynthesized colloidal system, with controlled particle aggregation states, presents plasmonic and sers properties with potential applications in molecular sensors and nanophotonic devices. | biosynthesis of silver fine particles and particles decorated with nanoparticles using the extract of illicium verum (star anise) seeds |
in this paper we present our studies on the stellar populations and star formation histories (sfhs) for the reines et al. sample of 136 dwarf galaxies that host active galactic nuclei (agns), selected from the sloan digital sky survey data release 8. we derive stellar populations and reconstruct sfhs for these agn-host dwarfs using the stellar population synthesis code starlight. our results suggest that these agn-host dwarfs have assembled their stellar masses within a narrow period of time with the stellar mass-weighted ages in the range of 109-1010 yr, but show a wide diversity of sfhs with the luminosity-weighted stellar ages in the range of 107-1010 yr. the old population (t > 109 yr) contributes most to the galaxy light for the majority of the sample; the young population (t < 108 yr) also appears in significant but widely varying fractions, while the intermediate-age population (108 < t < 109 yr) in general contributes less to the optical continuum at 4020 å. we also find that these dwarfs follow a similar mass-metallicity relation to normal star-forming galaxies, indicating that agns have little effect on the chemical evolution of the host galaxy. we further investigate the relation between the derived sfhs and morphology of the host galaxy, and find no correlation. comparing the sfhs with the luminosity of the [o iii] λ5007 line ( ${l}_{[{\rm{o}}{\rm\small{iii}}]}$ ), we find a mild correlation exists when ${l}_{[{\rm{o}}{\rm\small{iii}}]}\gt {10}^{39}$ erg s-1, indicating a physical connection between star formation and agn activities in these dwarf galaxies. | stellar populations of a sample of optically selected agn-host dwarf galaxies |
stellar masses of galaxies are frequently obtained by fitting stellar population synthesis models to galaxy photometry or spectra. the state of the art method resolves spatial structures within a galaxy to assess the total stellar mass content. in comparison to unresolved studies, resolved methods yield, on average, higher fractions of stellar mass for galaxies. in this work we improve the current method in order to mitigate a bias related to the resolved spatial distribution derived for the mass. the bias consists in an apparent filamentary mass distribution and a spatial coincidence between mass structures and dust lanes near spiral arms. the improved method is based on iterative bayesian marginalization, through a new algorithm we have named bayesian successive priors (bsp). we have applied bsp to m51 and to a pilot sample of 90 spiral galaxies from the ohio state university bright spiral galaxy survey. by quantitatively comparing both methods, we find that the average fraction of stellar mass missed by unresolved studies is only half what previously thought. in contrast with the previous method, the output bsp mass maps bear a better resemblance to near-infrared images. | removing biases in resolved stellar mass maps of galaxy disks through successive bayesian marginalization |
we study the stellar populations and assembly of the nearby spiral galaxy ngc 2903's bulge, bar, and outer disc using the virus-p exploration of nearby galaxies ifs survey. we observe ngc 2903 with a spatial resolution of 185 pc using the mitchell spectrograph's 4.25 arcsec fibres at the 2.7 harlan j. smith telescope. bulge-bar-disc decomposition on the two micron all-sky survey (2mass) ks-band image of ngc 2903 shows that it has ∼6 per cent, 6 per cent, and 88 per cent, of its stellar mass in the bulge, bar, and outer disc, respectively, and its bulge has a low sérsic index of ∼0.27, suggestive of a discy bulge. we perform stellar population synthesis and find that the outer disc has 46 per cent of its mass in stars >5 gyr, 48 per cent in stars between 1 and 5 gyr, and <10 per cent in younger stars. its stellar bar has 65 per cent of its mass in ages 1-5 gyr and has metallicities similar to the outer disc, suggestive of the evolutionary picture where the bar forms from disc material. its bulge is mainly composed of old high-metallicity stars though it also has a small fraction of young stars. we find enhanced metallicity in the spiral arms and central region, tracing areas of high star formation as seen in the hα map. these results are consistent with the idea that galaxies of low bulge-to-total mass ratio and low bulge sérsic index like ngc 2903 has not had a recent major merger event, but has instead grown mostly through minor mergers and secular processes. | the virus-p exploration of nearby galaxies (venga): the stellar populations and assembly of ngc 2903's bulge, bar, and outer disc |
we introduce a new methodology for the direct extraction of galaxy physical parameters from multiwavelength photometry and spectroscopy. we use semianalytic models that describe galaxy evolution in the context of large-scale cosmological simulation to provide a catalog of galaxies, star formation histories, and physical parameters. we then apply models of stellar population synthesis and a simple extinction model to calculate the observable broadband fluxes and spectral indices for these galaxies. we use a linear regression analysis to relate physical parameters to observed colors and spectral indices. the result is a set of coefficients that can be used to translate observed colors and indices into stellar mass, star formation rate, and many other parameters, including the instantaneous time derivative of the star formation rate, which we denote the star formation acceleration (sfa), we apply the method to a test sample of galaxies with galex photometry and sdss spectroscopy, deriving relationships between stellar mass, specific star formation rate, and sfa. we find evidence for a mass-dependent sfa in the green valley, with low-mass galaxies showing greater quenching and higher-mass galaxies greater bursting. we also find evidence for an increase in average quenching in galaxies hosting an active galactic nucleus. a simple scenario in which lower-mass galaxies accrete and become satellite galaxies, having their star-forming gas tidally and/or ram-pressure stripped, while higher-mass galaxies receive this gas and react with new star formation, can qualitatively explain our results. | quenching or bursting: star formation acceleration—a new methodology for tracing galaxy evolution |
in this paper, we present photometry of 53 globular clusters (gcs) in the m 31 outer halo, including the galex far-ultraviolet (fuv) and near-ultraviolet (nuv), sdss ugriz, 15 intermediate-band filters of batc, and 2mass jhks bands. by comparing the multicolour photometry with stellar population synthesis models, we determine the metallicities, ages, and masses for these gcs, aiming to probe the merging/accretion history of m 31. we find no clear trend of metallicity and mass with the de-projected radius. the halo gcs younger than ∼8 gyr are mostly located at the de-projected radii around 100 kpc, but this may be due to a selection effect. we also find that the halo gcs have consistent metallicities with their spatially associated substructures, which provides further evidence of the physical association between them. both the disc and halo gcs in m 31 show a bimodal luminosity distribution. however, we should emphasise that there are more faint halo gcs which are not seen in the disc. the bimodal luminosity function of the halo gcs may reflect a different origin or evolution environment in their original hosts. the m 31 halo gcs include one intermediate metallicity group (-1.5 < [fe/h] < -0.4) and one metal-poor group ([fe/h] < -1.5), while the disc gcs have one metal-rich group more. there are considerable differences between the halo gcs in m 31 and the milky way (mw). the total number of gcs in m 31 is approximately three times greater than in the mw, however m 31 has about six times more halo gcs than the mw. compared to the halo gcs of m 31, those of the mw are mostly metal-poor. both the numerous halo gcs and the higher-metallicity component are suggestive of an active merger history of m 31. full tables 1 and 2 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/623/a65 | globular clusters in the outer halo of m 31 |
we present a new method for constraining the mass transfer evolution of low-mass x-ray binaries (lmxbs)-a reverse population synthesis technique. this is done using the detailed 1d stellar evolution code mesa (modules for experiments in stellar astrophysics) to evolve a high-resolution grid of binary systems spanning a comprehensive range of initial donor masses and orbital periods. we use the recently developed convection and rotation-boosted (carb) magnetic braking scheme. the carb magnetic braking scheme is the only magnetic braking prescription capable of reproducing an entire sample of well-studied persistent lmxbs-those with mass ratios, periods, and mass transfer rates that have been observationally determined. using the reverse population synthesis technique, where we follow any simulated system that successfully reproduces an observed lmxb backward, we have constrained possible progenitors for each observed well-studied persistent lmxb. we also determined that the minimum number of lmxb formations in the milky way is 1500 per gyr if we exclude cyg x-2. for cyg x-2, the most likely formation rate is 9000 lmxb gyr-1. the technique we describe can be applied to any observed lmxb with well-constrained mass ratio, period, and mass transfer rate. with the upcoming gaia dr3 containing information on binary systems, this technique can be applied to the data release to search for progenitors of observed persistent lmxbs. | constraining progenitors of observed low-mass x-ray binaries using convection and rotation-boosted magnetic braking |
we present a comprehensive infrared (ir) study of the iconic wolf-rayet (wr) wind-blown bubble ngc 6888 around wr 136. we use wide-field infrared survey explorer, spitzer irac, and mips and herschel pacs ir images to produce a sharp view of the distribution of dust around wr 136. we complement these ir photometric observations with spitzer irs spectra in the 5-38-μm wavelength range. the unprecedented high-resolution ir images allowed us to produce a clean spectral energy distribution, free of contamination from material along the line of sight, to model the properties of the dust in ngc 6888. we use the spectral synthesis code cloudy to produce a model for ngc 6888 that consistently reproduces its optical and ir properties. our best model requires a double distribution with the inner shell composed only of gas, whilst the outer shell requires a mix of gas and dust. the dust consists of two populations of grain sizes, one with small-sized grains asmall = [0.002-0.008] $\mu$m and another one with large-sized grains abig = [0.05-0.5] $\mu$m. the population of big grains is similar to that reported for other red supergiants stars and dominates the total dust mass, which leads us to suggest that the current mass of ngc 6888 is purely due to material ejected from wr 136, with a negligible contribution of the swept up interstellar medium. the total mass of this model is 25.5$^{+4.7}_{-2.8}$ m⊙, a dust mass of $m_\mathrm{dust} = 0.14^{+0.03}_{-0.01}$ m⊙, for a dust-to-gas ratio of 5.6 × 10-3. accordingly, we suggest that the initial stellar mass of wr 136 was ≲50 m⊙, consistent with current single stellar evolution models. | unveiling the stellar origin of the wolf-rayet nebula ngc 6888 through infrared observations |
classical wolf-rayet (wr) stars mark an important stage in the late evolution of massive stars. as hydrogen-poor massive stars, these objects have lost their outer layers, while still losing further mass through strong winds indicated by their prominent emission line spectra. wolf-rayet stars have been detected in a variety of different galaxies. their strong winds are a major ingredient of stellar evolution and population synthesis models. yet, a coherent theoretical picture of their strong mass-loss is only starting to emerge. in particular, the occurrence of wr stars as a function of metallicity (z) is still far from being understood. | the origin and impact of wolf-rayet-type mass loss |
radiation pressure on dust is an important feedback process around star clusters and may eject gas from bright subregions in star-forming galaxies. the eddington ratio has previously been constructed for galaxy-averaged observations, individual star clusters, and galactic h ii regions. here we assess the role of radiation pressure in thousands of subregions across two local star-forming galaxies, ngc 6946 and ngc 5194. using a model for the spectral energy distribution from stellar population synthesis and realistic dust grain scattering and absorption, we compute flux and radiation pressure-mean opacities and population-averaged optical depth ⟨τrp⟩. using monte-carlo calculations, we assess the momentum coupling through a dusty column to the stellar continuum. optically-thin regions around young stellar populations are 30-50 times super-eddington. we calculate the eddington ratio for the subregions including the local mass of young and old stars and cool atomic and molecular gas. we compute the fraction of the total star formation that is currently super-eddington, and provide an assessment of the role of radiation pressure in the dusty gas dynamics. depending on the assumed height of the dusty gas and the age of the stellar population, we find that ~0-10 per cent of the sightlines are super-eddington. these regions may be accelerated to ~5-15 km s-1 by radiation pressure alone. additionally, our results show that for beamed radiation, the function 1 - exp (-⟨τrp⟩) is an excellent approximation to the momentum transfer. opacities and optical depths are tabulated for seds of different stellar ages and for continuous star formation. | dust eddington ratios for star-forming galaxy subregions |
the neutron star low-mass x-ray binary (lmxb) ax j1745.6-2901 was detected with an anomalously fast decrease of its orbital period. the decreasing rate of the orbital period exceeds the contribution of all processes extracting angular momentum from the binary star in the standard model. using the scenario machine code, we conducted a population synthesis study of x-ray novae with neutron stars to investigate a possible formation and evolution of such binaries. such close lmxbs should experience a preceding common envelope stage, in which the magnetic fields of the low-mass main-sequence donor stars can be dramatically amplified. our calculations show that the magnetic stellar wind of the optical companion can efficiently extract angular momentum from the binary systems, and produce the observed orbital-period derivatives of ax j1745.6-2901 and black hole lmxbs. the estimated values of the required magnetic field induction are the following: bd ≈ 400 g (ax j1745.6-2901), bd ≈ 1500 g (kv uma), bd ≈ 400 g (a0620-00) and bd ≈ 1800 g (nova muscae). we successfully reproduced the current observational abundance of such anomalous neutron star x-ray novae, and computed the appropriate value of the parameter of magnetic braking λmsw (0.8-0.6 for roche lobe filling stars and 0.4-0.15 for binaries with partial roche lobe filling). | population synthesis of ax j1745.6-2901 x-ray nova-type binaries with rapidly decreasing orbital periods |
the advanced laser interferometer gravitational-wave observatory (aligo) has detected direct signals of gravitational waves (gws) from gw150914. the event was a merger of binary black holes whose masses are 36^{+5}_{-4} m_{{⊙}} and 29^{+4}_{-4} m_{{⊙}}. such binary systems are expected to be directly evolved from stellar binary systems or formed by dynamical interactions of black holes in dense stellar environments. here we derive the binary black hole merger rate based on the nearby ultra-luminous x-ray source (ulx) luminosity function (lf) under the assumption that binary black holes evolve through x-ray emitting phases. we obtain the binary black hole merger rate as 5.8(tulx/0.1 myr)- 1λ- 0.6exp ( - 0.30λ) gpc- 3 yr- 1, where tulx is the typical duration of the ulx phase and λ is the eddington ratio in luminosity. this is coincident with the event rate inferred from the detection of gw150914 as well as the predictions based on binary population synthesis models. although we are currently unable to constrain the eddington ratio of ulxs in luminosity due to the uncertainties of our models and measured binary black hole merger event rates, further x-ray and gw data will allow us to narrow down the range of the eddington ratios of ulxs. we also find the cumulative merger rate for the mass range of 5 m⊙ ≤ mbh ≤ 100 m⊙ inferred from the ulx lf is consistent with that estimated by the aligo collaboration considering various astrophysical conditions such as the mass function of black holes. | binary black hole merger rates inferred from luminosity function of ultra-luminous x-ray sources |
we study the mass discrepancy-acceleration relation (mdar) of 57 elliptical galaxies by their einstein rings from the sloan lens acs survey (slacs). the mass discrepancy between the lensing mass and the baryonic mass derived from population synthesis is larger when the acceleration of the elliptical galaxy lenses is smaller. the mdar is also related to surface mass density discrepancy. at the einstein ring, these lenses belong to high-surface-mass density galaxies. similarly, we find that the discrepancy between the lensing and stellar surface mass density is small. it is consistent with the recent discovery of dynamical surface mass density discrepancy in disc galaxies where the discrepancy is smaller when surface density is larger. we also find relativistic modified newtonian dynamics (mond) can naturally explain the mdar and surface mass density discrepancy in 57 einstein rings. moreover, the lensing mass, the dynamical mass and the stellar mass of these galaxies are consistent with each other in relativistic mond. | mass discrepancy-acceleration relation in einstein rings |
we investigate the compact, early-type galaxy ngc 1281 with integral field unit observations to map the stellar line-of-sight velocity distribution (losvd) out to five effective radii and construct orbit-based dynamical models to constrain its dark and luminous matter content. under the assumption of mass-follows-light, the h-band stellar mass-to-light ratio (m/l) is υ⋆ = 2.7 ± 0.1 υ⊙, and higher than expected from our stellar population synthesis fits with either a canonical kroupa (υ⋆ = 1.3 υ⊙) or salpeter (υ⋆ = 1.7 υ⊙) stellar initial mass function. such models also cannot reproduce the details of the losvd. models with a dark halo recover the kinematics well and indicate that ngc 1281 is dark matter dominated, making up ∼ 90 per cent of the total enclosed mass within the kinematic bounds. parametrized as a spherical nfw profile, the dark halo mass is 11.5 ≤ log(mdm/m⊙) ≤ 11.8 and the stellar m/l is 0.6 ≤ υ⋆/υ⊙ ≤ 1.1. however, this m/l is lower than predicted by its old stellar population. moreover, the halo mass within the kinematic extent is 10 times larger than expected based on λ-cold-dark-matter predictions, and an extrapolation yields cluster-sized dark halo masses. adopting υ⋆ = 1.7 υ⊙ yields more moderate dark halo virial masses, but these models fit the kinematics worse. a non-nfw model might solve the discrepancy between the unphysical consequences of the best-fitting dynamical models and models based on more reasonable assumptions for the dark halo and stellar m/l, which are disfavoured according to our parameter estimation. | the massive dark halo of the compact early-type galaxy ngc 1281 |
accretion induced collapse (aic) may be responsible for the formation of some interesting neutron star binaries (e.g., millisecond pulsars, intermediate-mass binary pulsars, etc). it has been suggested that oxygen-neon white dwarfs (one wds) can increase their mass to the chandrasekhar limit by multiple he-shell flashes, leading to aic events. however, the properties of he-shell flashes on the surface of one wds are still not well understood. in this article, we aim to study he-shell flashes on the surface of one wds in a systematic approach. we investigated the long-term evolution of one wds accreting he-rich materialwith various constantmass-accretion rates by time-dependent calculationswith the stellar evolution codemodules for experiments in stellar astrophysics (mesa), in which the initial onewd masses range from 1.1 to 1.35 m⊙. we found that the mass-retention efficiency increases with the one wd mass and the mass-accretion rate, whereas both the nova cycle duration and the ignition mass decrease with the one wd mass and the mass-accretion rate. we also present the nuclear products in different accretion scenarios. the results presented in this article can be used in the future binary population synthesis studies of aic events. | he-shell flashes on the surface of oxygen-neon white dwarfs |
an analysis of high-resolution near-infrared spectra of a sample of 45 asymptotic giant branch (agb) stars towards the galactic bulge is presented. the sample consists of two subsamples, a larger one in the inner and intermediate bulge, and a smaller one in the outer bulge. the data are analysed with the help of hydrostatic model atmospheres and spectral synthesis. we derive the radial velocity of all stars, and the atmospheric chemical mix ([fe/h], c/o, 12c/13c, al, si, ti, and y) where possible. our ability to model the spectra is mainly limited by the (in)completeness of atomic and molecular line lists, at least for temperatures down to teff ≈ 3100 k. we find that the subsample in the inner and intermediate bulge is quite homogeneous, with a slightly subsolar mean metallicity and only few stars with supersolar metallicity, in agreement with previous studies of non-variable m-type giants in the bulge. all sample stars are oxygen-rich, c/o < 1.0. the c/o and carbon isotopic ratios suggest that third dredge-up (3dup) is absent among the sample stars, except for two stars in the outer bulge that are known to contain technetium. these stars are also more metal-poor than the stars in the intermediate or inner bulge. current stellar masses are determined from linear pulsation models. the masses, metallicities and 3dup behaviour are compared to agb evolutionary models. we conclude that these models are partly in conflict with our observations. furthermore, we conclude that the stars in the inner and intermediate bulge belong to a more metal-rich population that follows bar-like kinematics, whereas the stars in the outer bulge belong to the metal-poor, spheroidal bulge population. | understanding agb evolution in galactic bulge stars from high-resolution infrared spectroscopy |
the evolution of symbiotic x-ray binaries in the galaxy is studied by the population synthesis method. we show that allowance for the nonstationarity of the regime of quasi-spherical subsonic accretion from the stellar wind of a giant onto slowly rotating neutron stars in these sources allows their observed positions on the neutron star spin period-x-ray luminosity diagramto be described in a wide range of stellar wind parameters. the derived distributions of sources in orbital periods, neutron star spin periods, and x-ray luminosities can be used to analyze the observations of galactic sources in the range of luminosities ∼1032-1036 erg s-1 in the planned srg/erosita all-sky survey. | symbiotic x-ray binaries systems in the galaxy |
stellar streams have become central to studies of the interaction histories of nearby galaxies. to characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 mpc) edge-on disk galaxy ngc 5907, we have obtained and analyzed new, deep gri subaru/suprime-cam and 3.6 μm spitzer/infrared array camera observations. combining the near-infrared 3.6 μm data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ∼60 kpc long segment of the stream. we have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. we conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of -0.3 inferred along the brightest parts of the stream. | metallicity and age of the stellar stream around the disk galaxy ngc 5907 |
context. a new generation of spectral synthesis models has been developed in recent years, but there is no matching set of template galaxy spectra, in terms of quality and resolution, for testing and refining the new models.aims: our main goal is to find and calibrate new near-infrared spectral indices along the hubble sequence of galaxies which will be used to obtain additional constraints to the population analysis based on medium-resolution integrated spectra of galaxies.methods: spectra of previously studied and well-understood galaxies with relatively simple stellar populations (e.g., ellipticals or bulge dominated galaxies) are needed to provide a baseline data set for spectral synthesis models.results: x-shooter spectra spanning the optical and infrared wavelengths (350-2400 nm) of bright nearby elliptical galaxies with a resolving power of r ∼ 4000-5400 were obtained. heliocentric systemic velocity, velocity dispersion, and mg, fe, and hβ line-strength indices are presented.conclusions: we present a library of very-high-quality spectra of galaxies covering a large range of age, metallicity, and morphological type. such a dataset of spectra will be crucial to addressing important questions of the modern investigation concerning galaxy formation and evolution. based on observations made with eso telescopes at the la silla paranal observatory under programme id 086.b-0900(a). the reduced spectra (fits files) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/621/a60 | near-infrared spectroscopic indices for unresolved stellar populations. i. template galaxy spectra |
we present a theoretical method for solving the chemical evolution of galaxies by assuming an instantaneous recycling approximation for chemical elements restored by massive stars and the delay time distribution formalism for delayed chemical enrichment by type ia supernovae. the galaxy gas mass assembly history, together with the assumed stellar yields and initial mass function, represents the starting point of this method. we derive a simple and general equation, which closely relates the laplace transforms of the galaxy gas accretion history and star formation history, which can be used to simplify the problem of retrieving these quantities in the galaxy evolution models assuming a linear schmidt-kennicutt law. we find that - once the galaxy star formation history has been reconstructed from our assumptions - the differential equation for the evolution of the chemical element x can be suitably solved with classical methods. we apply our model to reproduce the [o/fe] and [si/fe] versus [fe/h] chemical abundance patterns as observed at the solar neighbourhood by assuming a decaying exponential infall rate of gas and different delay time distributions for type ia supernovae; we also explore the effect of assuming a non-linear schmidt-kennicutt law, with the index of the power law being k = 1.4. although approximate, we conclude that our model with the single-degenerate scenario for type ia supernovae provides the best agreement with the observed set of data. our method can be used by other complementary galaxy stellar population synthesis models to predict also the chemical evolution of galaxies. | a simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements |
the physical properties of star cluster populations offer valuable insights into their birth, evolution, and disruption. however, individual stars in clusters beyond the nearest neighbours of the milky way are unresolved, forcing analyses of star cluster demographics to rely on integrated light, a process that is fraught with uncertainty. here infer the demographics of the cluster population in the benchmark galaxy ngc 628 using data from the legacy extra-galactic uv survey (legus) coupled to a novel bayesian forward-modelling technique. our method allows analysis of a total of 1178 clusters in the legus catalogue, roughly a factor of 4 more than previous studies that required severe completeness cuts to the data. our results indicate that the cluster mass function is truncated at $\sim 10^4$ $ \mathrm{m}_{\odot}$, consistent with proposed relations between truncation mass and star formation surface density. we find that cluster disruption begins early, $\sim 10$ myr after formation, but that it is relatively mild, with clusters requiring on average $2-3$ times their present age to disrupt; we do not find any evidence for mass dependent disruption. we also do not find convincing evidence for any radial variations in these conclusions, though we find suggestive hints that inner galaxy clusters may be more prone to disruption. confirming or refuting these hints will require future observations to increase the sample size of outer galaxy clusters. | cluster population demographics in ngc 628 derived from stochastic population synthesis models |
aims: the third gaia data release provides low-resolution spectra for around 200 million sources. it is expected that a sizeable fraction of them contain a white dwarf (wd), neither isolated, or in a binary system with a main-sequence (ms) companion, that is a white dwarf-main sequence (wdms) binary. taking advantage of a consolidated random forest algorithm used in the classification of wds, we extend it to study the feasibility of classifying gaia wdms binary spectra.methods: the random forest algorithm is first trained with a set of synthetic spectra generated by combining individual wd and ms spectra for the full range of effective temperatures and surface gravities. moreover, with the aid of a detailed population synthesis code, we simulate the gaia spectra for the abovementioned populations. for evaluating the performance of the models, a set of metrics are applied to our classifications.results: our results show that for resolving powers above ~300 the accuracy of the classification depends exclusively on the s/r of the spectra, while below that value the s/r should be increased as the resolving power is reduced to maintain a certain accuracy. the algorithm is then applied to the already classified sdss wdms catalog, revealing that the automated classification exhibits an accuracy comparable (or even higher) to previous classification methods. finally, we simulate the gaia spectra, showing that our algorithm is able to correctly classify nearly 80% the synthetic wdms spectra.conclusions: our algorithm represents a useful tool in the analysis and classification of real gaia wdms spectra. even for those spectra dominated by the flux of the ms stars, the algorithm reaches a high degree of accuracy (60%). | random forest classification of gaia dr3 white dwarf-main sequence spectra: a feasibility study |
in this population synthesis work, we study a variety of possible origin channels of supernovae type ia (sne ia). among them mergers of carbon-oxygen (co) and oxygen-neon (one) white dwarfs (wds) under the influence of gravitational waves are considered as the primary channel of sne ia formation. we estimated frequencies of mergers of wds with different chemical compositions and distributions of masses of merging wds. we computed the dependence of the ratio of merger frequencies of one and co wds as primaries in corresponding binaries on time. the scatter of masses of considered sources (up to the factor 1.5-2) of sne ia is important and should be carefully studied with other sophisticated methods from theoretical point of view. our 'game of parameters' potentially explains the increased dimming of sne ia in the redshift range z ≈ 0.5-1 by the changes in the ratio of one and co wds, i.e. to describe the observed accelerated expansion of the universe in terms of the evolution of properties of sne ia instead of cosmological explanations. this example shows the extreme importance of theoretical studies of problems concerning sne ia, because evolutionary scenario and parameter games in nature potentially lead to confusions in their empirical standardization and, therefore, they can influence on cosmological conclusions. | the evolution of relative frequencies of one and co sne ia |
we study the laser interferometer space antenna (lisa) sources that arise from isolated binary evolution, and how these depend on age and metallicity, using model stellar populations from bpass. we model these as single-aged populations which are analogous to star clusters. we calculate the combined gravitational wave (gw) spectrum of all the binaries within these model clusters, including all types of compact binaries as well as those with living stars. these results allow us to evaluate the detectability of star clusters with lisa. we find at late times the dominant sources are wd-wd binaries by factors of 50-200, but at times between 108 and 109 yr we find a significant population of ns-wd and bh-wd binaries (2-40 per 106 m⊙), which is related to the treatment of mass transfer and common-envelope events in bpass, wherein mass transfer is relatively likely to be stable. metallicity also has an effect on the gw spectrum and on the relative dominance of different types of binaries. using the information about known star clusters will aid the identification of sky locations where one could expect lisa to find gw sources. | gravitational wave spectral synthesis |
we present an updated prescription for the equilibrium tides suitable for population synthesis codes. a grid of 1d evolutionary models was created and the viscous timescale was calculated for each detailed model. a metallicity-dependent power-law relation was fitted to both the convective cores and convective envelopes of the models. the prescription was implemented into the population synthesis code binary star evolution and predicts a 16.5% reduction in the overall number of merges, with those involving main-sequence stars most affected. the new prescription also reduces the overall supernova rate by 3.6% with individual channels being differently affected. the single degenerate ia supernova occurrence is reduced by 12.8%. the merging of two carbon oxygen white dwarfs to cause a ia supernova occurs 16% less frequently. the number of subsynchronously rotating stars in close binaries is substantially increased with our prescription, as is the number of noncircularized systems at the start of common-envelope evolution. | the equilibrium tide: an updated prescription for population synthesis codes |
neutron stars can appear as sources of different nature. in this paper we address the observability of a hypothetical class of neutron stars—hot and fast non-accreting rotators, hofnars. these objects are heated due to the r-mode instability. with surface temperatures ∼106 k they are expected to be thermal soft x-ray emitters. we perform a population synthesis modeling of hofnars to predict the number of potentially detectable sources in the erosita all-sky survey. for surface temperatures ∼106 k we obtain ∼500 sources above the detection limit 0.01 cts s‑1 and ∼100 easier identifiable sources with >0.1 cts s‑1. temperatures ≳1.2 × 106 k start to be in contradiction with non-detection of hofnars by rosat. only for t ≲ 5 × 105 k numbers predicted for erosita turn out to be so low that identification does not look possible. we conclude that erosita has good chances to discover hofnars, if they exist. non-detection will put very stringent limits on the properties of this type of neutron stars. | observability of hofnars at srg/erosita |
we can learn about the formation and evolution of compact objects, such as neutron stars and black holes (bhs), by studying the x-ray emission from accreting systems in nearby star-forming galaxies. the hard (e > 10 kev) x-ray emission in particular allows strong discrimination among the accretion states and compact object types. we conducted a nustar survey (~600 ks) of the local group spiral galaxy m33 to study the distribution of x-ray binary (xrb) accretors in an actively star-forming environment. we constructed color-intensity and color-color diagrams to infer xrb accretion states. using these diagrams, we have classified 28 x-ray sources in m33 by comparing their hard x-ray colors to those of known systems. four sources lie in the parameter space occupied by x-ray pulsars, while 8, 10, and 4 sources lie in the parameter space occupied by bhs in the hard, intermediate, and soft states, respectively. the known ultraluminous x-ray source m33 x-8 is also found to be consistent with that source type. some sources overlap within the z/atoll sources due to the overlap of the two categories of bhs and z/atoll sources. in contrast to a similar nustar survey of m31 (with a low-mass xrb-dominant population), the source population in m33 is dominated by high-mass xrbs (hmxbs), allowing the study of a very different population with similar sensitivity due to the galaxy's similar distance. this characterization of a population of hmxb accretion states will provide valuable constraints for theoretical xrb population synthesis studies to their formation and evolution. | young black hole and neutron star systems in the nearby star-forming galaxy m33: the nustar view |
ss433 is an extraordinary x-ray binary that is ejecting bipolar jets at 26% the speed of light. associated with the supernova-like shell w50, ss433 is also probably one of the youngest x-ray binaries with an age of ≲105 yr. however, the masses of the two components in ss433 and even the nature of the compact object are still under debate. in this work, assuming that the compact object is a black hole, we employ a binary population synthesis method to study the formation of ss433. we use previous estimates of the age of w50 and the duration of the jet activity to constrain the evolutionary history. our calculations suggest that ss433 likely harbored a hertzsprung gap star at the beginning of the current roche-lobe overflow phase. the masses of the black hole and the optical/donor star in ss433 suggested by the simulations are around 8 m⊙ and 24 m⊙, respectively. future measurement of the donor mass and radius can help infer not only the origin of the binary but also the nature of the nebula w50. | on the formation of ss433 |
the diskmass survey recently provided measurements of the vertical velocity dispersions of disk stars in a sample of nearly face-on galaxies. by setting the disk scale-heights to be equal to those of edge-on galaxies with similar scale-lengths, it was found that these disks must be sub-maximal, with surprisingly low k-band mass-to-light ratios of the order of m⋆/lk ≃ 0.3 m⊙/l⊙. this study made use of a simple relation between the disk surface density and the measured velocity dispersion and scale height of the disk, neglecting the shape of the rotation curve and the dark matter contribution to the vertical force, which can be especially important in the case of sub-maximal disks. here, we point out that these simplifying assumptions led to an overestimation of the stellar mass-to-light ratios. relaxing these assumptions, we compute even lower values than previously reported for the mass-to-light ratios, with a median m⋆/lk ≃ 0.18 m⊙/l⊙, where 14 galaxies have m⋆/lk< 0.11. invoking prolate dark matter halos made only a small difference to the derived m⋆/lk, although extreme prolate halos (q> 1.5 for the axis ratios of the potential) might help. the cross-terms in the jeans equation are also generally negligible. these deduced k-band stellar mass-to-light ratios are even more difficult to reconcile with stellar population synthesis models than the previously reported ones. | dynamical measurement of the stellar surface density of face-on galaxies |
we use the binary module of the mesa code to study the evolution of an evolved binary system where we assume that a main-sequence companion removes the outskirts of the envelope of an asymptotic giant branch (agb) star by launching jets, and explore the characteristics of this grazing envelope evolution (gee). we base our assumption that jets launched by the secondary star remove a substantial fraction of the outskirts of the envelope of an agb star on earlier hydrodynamical simulations. we find that in many but not all cases we study, the binary system experiences the gee rather than entering the common envelope phase, under our assumptions of jet-driven mass removal. to prevent the common envelope phase, we assume the secondary star may accrete a large amount of mass in a short time while avoiding rapid inflation, the feasibility of which requires further study. because of our simplifying assumptions, we cannot yet present the parameter space for the gee. although the incorporation of the gee into population synthesis numerical codes requires further studies of the gee, we conclude that analyses of population synthesis studies of evolved binary stars should include the gee. | orbital radius during the grazing envelope evolution |
stellar population synthesis models have long struggled to reproduce observed optical through near-ir (nir) spectral energy distributions (seds) of massive quiescent galaxies. we revisit this issue using a novel approach that combines the diagnostic power of full-spectrum fitting with recently updated stellar spectral libraries. first, we perform full-spectrum fitting of continuum-normalized, stacked sdss spectra in bins of velocity dispersion to infer their stellar population properties, such as the elemental abundances and age. next, we use the resulting best-fit parameters to compute ugriz colors, which are then compared to observed colors of the same galaxies. with this approach we are able to predict the ugriz seds of low- and high-mass galaxies at the ≲0.03 mag level in nearly all cases. we find that the full optical through nir seds of quiescent galaxies can be reproduced only when the spectrum is fit with a flexibility that is able to capture the behavior of the entire optical absorption line spectrum. the models include variation in individual elemental abundances, nebular emission lines, and the presence of young stellar components. the successful prediction of the sed shape from continuum-normalized spectra implies that the continuum information is largely contained in the narrow absorption features. these results also imply that attempts to model broadband photometry of quiescent systems will suffer from potentially significant biases if the detailed abundance patterns are not taken into account. | the imprint of element abundance patterns on quiescent galaxy spectral energy distributions |
we aim to verify whether refracted gravity (rg) is capable of describing the dynamics of disk galaxies without resorting to the presence of dark matter. rg is a classical theory of gravity in which the standard poisson equation is modified with the introduction of the gravitational permittivity, which is a universal monotonic function of the local mass density. we used the rotation curves and the radial profiles of the stellar velocity dispersion perpendicular to the galactic disks of 30 disk galaxies from the diskmass survey (dms) to determine the gravitational permittivity. rg describes the rotation curves and the vertical velocity dispersions by requiring galaxy mass-to-light ratios that are in agreement with stellar population synthesis models, and disk thicknesses that are in agreement with observations, once observational biases are taken into account. our results rely on setting the three free parameters of the gravitational permittivity for each individual galaxy. however, we show that the differences of these parameters from galaxy to galaxy can, in principle, be ascribed to statistical fluctuations. we adopted an approximate procedure to estimate a single set of parameters that may properly describe the kinematics of the entire sample and suggest that the gravitational permittivity is indeed a universal function. finally, we showed that the rg models of the individual rotation curves can only partly describe the radial acceleration relation (rar) between the observed centripetal acceleration derived from the rotation curve and the newtonian gravitational acceleration originating from the baryonic mass distribution. evidently, the rg models underestimate the observed accelerations by 0.1 to 0.3 dex at low newtonian accelerations. an additional problem that ought to be considered is the strong correlation, at much more than 5σ, between the residuals of the rar models and three radially-dependent properties of the galaxies, whereas the dms data show a considerably less significant correlation, at more than 4σ, for only two of these quantities. these correlations might be the source of the non-null intrinsic scatter of the rg models: this non-null scatter is at odds with the observed intrinsic scatter of other galaxy samples different from dms, which is consistent with zero. further investigations are required to assess whether these discrepancies in the rar originate from the dms sample, which might not be ideal for deriving the rar, or whether they are genuine failures of rg. | dynamics of diskmass survey galaxies in refracted gravity |
based on the star formation histories of galaxies in halos with different masses, we develop an empirical model to grow galaxies in dark matter halos. this model has very few ingredients, any of which can be associated with observational data and thus be efficiently assessed. by applying this model to a very high resolution cosmological n-body simulation, we predict a number of galaxy properties that are a very good match to relevant observational data. namely, for both centrals and satellites, the galaxy stellar mass functions up to redshift z ≃ 4 and the conditional stellar mass functions in the local universe are in good agreement with observations. in addition, the two point correlation function is well predicted in the different stellar mass ranges explored by our model. furthermore, after applying stellar population synthesis models to our stellar composition as a function of redshift, we find that the luminosity functions in the 0.1 u, 0.1 g, 0.1 r, 0.1 i and 0.1 z bands agree quite well with the sdss observational results down to an absolute magnitude at about -17.0. the sdss conditional luminosity function itself is predicted well. finally, the cold gas is derived from the star formation rate to predict the hi gas mass within each mock galaxy. we find a remarkably good match to observed hi-to-stellar mass ratios. these features ensure that such galaxy/gas catalogs can be used to generate reliable mock redshift surveys. | an empirical model to form and evolve galaxies in dark matter halos |
we use the binary population and spectral synthesis models to test the recent suggestion that red supergiants can provide an accurate age estimate of a coeval stellar population that is unaffected by interacting binary stars. ages are estimated by using both the minimum luminosity of red supergiants and the mean luminosity of red supergiants in a cluster. we test these methods on a number of observed star clusters and find our results in agreement with previous estimates. importantly, we find the difference between the ages derived from stellar population models with and without a realistic population of interacting binary stars is only a few hundred thousand years at most. we find that the mean luminosity of red supergiants in a cluster is the best method to determine the age of a cluster because it is based on the entire red supergiant population rather than using only the least luminous red supergiant. | on ageing star clusters using red supergiants independent of the fraction of interacting binary stars |
context. one of the most important properties of a galaxy is the total stellar mass, or equivalently the stellar mass-to-light ratio (m/l). it is not directly observable, but can be estimated from stellar population synthesis. currently, a galaxy's m/l is typically estimated from global fluxes. for example, a single global g - i colour correlates well with the stellar m/l. spectral energy distribution (sed) fitting can make use of all available fluxes and their errors to make a bayesian estimate of the m/l.aims: we want to investigate the possibility of using morphology information to assist predictions of m/l. our first goal is to develop and train a method that only requires a g-band image and redshift as input. this will allows us to study the correlation between m/l and morphology. next, we can also include the i-band flux, and determine if morphology provides additional constraints compared to a method that only uses g- and i-band fluxes.methods: we used a machine learning pipeline that can be split in two steps. first, we detected morphology features with a convolutional neural network. these are then combined with redshift, pixel size and g-band luminosity features in a gradient boosting machine. our training target was the m/l acquired from the galex-sdss-wise legacy catalog, which uses global sed fitting and contains galaxies with z ∼ 0.1.results: morphology is a useful attribute when no colour information is available, but can not outperform colour methods on its own. when we combine the morphology features with global g- and i-band luminosities, we find an improved estimate compared to a model which does not make use of morphology.conclusions: while our method was trained to reproduce global sed fitted m/l, galaxy morphology gives us an important additional constraint when using one or two bands. our framework can be extended to other problems to make use of morphological information. | morphology-assisted galaxy mass-to-light predictions using deep learning |
context. galaxy evolution has been studied by interpreting the spectral energy distribution of galaxies using spectral synthesis codes. this method has been crucial in discovering different pillars of modern galaxy evolution theories. however, this analysis was mostly carried out using spectral synthesis codes that are purely stellar, that is, they assume that the nebular contribution to the total continuum is negligible. the code fado is the first publicly available population spectral synthesis tool that treats the contribution from ionised gas to the observed emission self-consistently. this is expected to have a particularly strong effect in star-forming (sf) galaxies.aims: we study the impact of the nebular contribution on the determination of the star formation rate (sfr), stellar mass, and consequent effect on the star-forming main sequence (sfms) at low redshift.methods: we applied fado to the spectral database of the sdss to derive the physical properties of galaxies. as a comparison, we used the data in the mpa-jhu catalogue, which contains the properties of sdss galaxies derived without the nebular contribution. we selected a sample of sf galaxies with hα and hβ flux measurements, and we corrected the fluxes for the nebular extinction through the balmer decrement. we then calculated the hα luminosity to estimate the sfr. then, by combining the stellar mass and sfr estimates from fado and mpa-jhu, the sfms was obtained.results: the hα flux estimates are similar between fado and mpa-jhu. because the hα flux was used as tracer of the sfr, fado and mpa-jhu agree in their sfr. the stellar mass estimates are slightly higher for fado than for mpa-jhu on average. however, considering the uncertainties, the differences are negligible. with similar sfr and stellar mass estimates, the derived sfms is also similar between fado and mpa-jhu.conclusions: our results show that for sdss normal sf galaxies, the additional modelling of the nebular contribution does not affect the retrieved fluxes and consequentially also does not influence sfr estimators based on the extinction-corrected hα luminosity. for the stellar masses, the results point to the same conclusion. these results are a consequence of the fact that the vast majority of normal sf galaxies in the sdss have a low nebular contribution. however, the obtained agreement might only hold for local sf galaxies, but higher-redshift galaxies might show different physical properties when fado is used. this would then be an effect of the expected increased nebular contribution. | an investigation of the star-forming main sequence considering the nebular continuum emission at low-z |
we report the discovery of five bright, strong gravitationally lensed galaxies at 3 < z < 4: cool j0101+2055 (z = 3.459), cool j0104-0757 (z = 3.480), cool j0145+1018 (z = 3.310), cool j0516-2208 (z = 3.549), and cool j1356+0339 (z = 3.753). these galaxies have magnitudes of r ab, z ab < 21.81 mag and are lensed by galaxy clusters at 0.26 < z < 1. this sample nearly doubles the number of known bright lensed galaxies with extended arcs at 3 < z < 4. we characterize the lensed galaxies using ground-based grz/giy imaging and optical spectroscopy. we report model-based magnitudes and derive stellar masses, dust content, and star formation rates via stellar population synthesis modeling. building lens models based on ground-based imaging, we estimate source magnifications ranging from ~29 to ~180. combining these analyses, we derive demagnified stellar masses in the range ${\mathrm{log}}_{10}({m}_{* }/{m}_{\odot })\sim 9.69-10.75$ and star formation rates in the youngest age bin in the range ${\mathrm{log}}_{10}(\mathrm{sfr}/({m}_{\odot }\,{\mathrm{yr}}^{-1}))\sim 0.39-1.46$ , placing the sample galaxies on the massive end of the star-forming main sequence in this redshift interval. in addition, three of the five galaxies have strong lyα emissions, offering unique opportunities to study lyα emitters at high redshift in future work. | cool-lamps. iv. a sample of bright strongly lensed galaxies at 3 < z < 4 |
post-asymptotic giant branch (post-agb) stars with discs are all binaries. many of these binaries have orbital periods between 100 and 1000days so cannot have avoided mass transfer between the agb star and its companion, likely through a common-envelope type interaction. we report on preliminary results of our project to model circumbinary discs around post-agb stars using our binary population synthesis code binary_c. we combine a simple analytic thin-disc model with binary stellar evolution to estimate the impact of the disc on the binary, and vice versa, fast enough that we can model stellar population and hence explore the rather uncertain parameter space involved with disc formation. we find that, provided the discs form with sufficient mass and angular momentum, and have an inner edge that is relatively close to the binary, they can both prolong the life of their parent post-agb star and pump the eccentricity of orbits of their inner binaries. | post-agb discs from common-envelope evolution |
molecular features such as the g-band, cn-band and nh-band are important diagnostics for measuring a star's carbon and nitrogen abundances, especially in metal-poor stars where atomic lines are no longer visible in stellar spectra. unlike atomic transitions, molecular features tend to form in bands, which cover large wavelength regions in a spectrum. while it is a trivial matter to compute carbon and nitrogen molecular bands under the assumption of 1d, it is extremely time consuming in 3d. in this contribution to the 2016 cobold workshop we review the improvements made to the 3d spectral synthesis code linfor3d, and discuss the new challenges found when computing molecular features in 3d. | enhanced methods for computing spectra from co5bold models using linfor3d. molecular bands in metal-poor stars |
the temperature distribution of field li-rich red giants suggests the presence of a population of li-rich red clump (rc) stars. one proposed explanation for this population is that all stars with masses near 2 m ⊙ experience a short-lived phase of li-richness at the onset of core he-burning. many of these stars have low 12c/13c, a signature of deep mixing that is presumably associated with the li regeneration. to test this purported mechanism of li enrichment, we measured abundances in 38 rc stars and 6 red giant branch (rgb) stars in four open clusters selected to have rc masses near 2 m ⊙. we find six li-rich stars (a(li) ≥ 1.50 dex) of which only two may be rc stars. none of the rc stars have li exceeding the levels observed in the rgb stars, but given the brevity of the suggested li-rich phase and the modest sample size, it is probable that stars with larger li-enrichments were missed simply by chance. however, we find very few stars in our sample with low 12c/13c. such low 12c/13c, seen in many field li-rich stars, should persist even after lithium has returned to normal low levels. thus, if li synthesis during the he flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. we estimate a conservative upper limit of the fraction of stars going through a li-rich phase to be \lt 47 % , based on stars that have low 12c/13c for their observed a(li). | lithium inventory of 2 m ⊙ red clump stars in open clusters: a test of the helium flash mechanism |
flux-calibrated integrated spectra have been obtained for a sample of 16 blue compact and high surface brightness large magellanic cloud (lmc) star clusters. the spectra cover the wavelength range 3700-6800 å, with a typical resolution and dispersion of 14 å and 3.5 å/pixel, respectively. we simultaneously derive foreground e(b - v) reddening values and ages for the clusters by comparing the line strengths and continuum distribution of their integrated spectra with those of lmc cluster spectra templates. as a first approach to obtain cluster ages, we also use the equivalent width (ew) of balmer absorption lines and some diagnostic diagrams involving the sum of the ews of selected spectral lines. through evolutionary synthesis models for simple stellar populations and using a full-spectrum fitting code, we also derive reddenings, ages, and metallicities (z/z⊙) for the cluster sample. no metallicity determinations have been previously performed for nine out of the 16 clusters here studied. we find good agreement between the cluster ages derived from the template-matching method and those ages estimated from theoretical evolutionary synthesis models. all of the studied clusters are found to be young, with ages ranging from 15 myr (ngc 1693) to 80 myr (ngc 2160), affected by reddening values typical for the lmc: 0.00< e(b-v)< 0.20. the derived metallicities z/z⊙ range from 0.2 up to 1.0 (solar metal content). we compare our results with those reported in the literature, and discuss the distribution of metallicity values. in an effort to create a spectral library at lmc metallicity level with several clusters per age range, the present cluster sample stands out as a useful complement to previous ones. | spectroscopic fundamental parameters of 16 young large magellanic cloud star clusters |
we examine the hβ lick index in a sample of ∼24 000 massive (log(m/m_{⊙})>10.75) and passive early-type galaxies extracted from the sloan digital sky survey at z < 0.3, in order to assess the reliability of this index to constrain the epoch of formation and age evolution of these systems. we further investigate the possibility of exploiting this index as `cosmic chronometer', i.e. to derive the hubble parameter from its differential evolution with redshift, hence constraining cosmological models independently of other probes. we find that the hβ strength increases with redshift as expected in passive evolution models, and shows at each redshift weaker values in more massive galaxies. however, a detailed comparison of the observed index with the predictions of stellar population synthesis models highlights a significant tension, with the observed index being systematically lower than expected. by analysing the stacked spectra, we find a weak [n ii] λ6584 emission line (not detectable in the single spectra) that anti-correlates with the mass, which can be interpreted as a hint of the presence of ionized gas. we estimated the correction of the hβ index by the residual emission component exploiting different approaches, but find it very uncertain and model dependent. we conclude that, while the qualitative trends of the observed hβ-z relations are consistent with the expected passive and downsizing scenario, the possible presence of ionized gas even in the most massive and passive galaxies prevents us to use this index for a quantitative estimate of the age evolution and for cosmological applications. | on the robustness of the hβ lick index as a cosmic clock in passive early-type galaxies |
we used gemini multi-object spectrograph in the integral field unit mode to map the stellar population, emission-line flux distributions and gas kinematics in the inner kpc of ngc 5044. from the stellar populations synthesis, we found that the continuum emission is dominated by old high metallicity stars (∼13 gyr, 2.5 z⊙). also, its nuclear emission is diluted by a non-thermal emission, which we attribute to the presence of a weak active galactic nucleus (agn). in addition, we report for the first time a broad component (fwhm ∼ 3000 km s- 1) in the h α emission line in the nuclear region of ngc 5044. by using emission-line ratio diagnostic diagrams, we found that two dominant ionization processes coexist, while the nuclear region (inner 200 pc) is ionized by a low-luminosity agn, the filamentary structures are consistent with being excited by shocks. the h α velocity field shows evidence of a rotating disc, which has a velocity amplitude of ∼240 km s-1 at ∼136 pc from the nucleus. assuming a keplerian approach, we estimated that the mass inside this radius is 1.9 × 109 m⊙, which is in agreement with the value obtained through the m-σ relation, msmbh = 1.8 ± 1.6 × 109 m⊙. modelling the ionized gas velocity field by a rotating disc component plus inflows towards the nucleus along filamentary structures, we obtain a mass inflow rate of ∼0.4 m⊙. this inflow rate is enough to power the central agns in ngc 5044. | integral field spectroscopy of the inner kpc of the elliptical galaxy ngc 5044 |
stellar population studies provide unique clues to constrain galaxy formation models. so far, detailed studies based on absorption line strengths have mainly focused on the optical spectral range although many diagnostic features are present in other spectral windows. in particular, the near-infrared (nir) can provide a wealth of information about stars, such as evolved giants, that have less evident optical signatures. due to significant advances in nir instrumentation and extension of spectral libraries and stellar population synthesis (sps) models to this domain, it is now possible to perform in-depth studies of spectral features in the nir to a high level of precision. in this work, taking advantage of state-of-the-art sps models covering the nir spectral range, we introduce a new set of nir indices constructed to be maximally sensitive to the main stellar population parameters, namely age, metallicity, and initial mass function (imf). we fully characterize the new indices against these parameters as well as their sensitivity to individual elemental abundance variations, velocity dispersion broadening, wavelength shifts, signal-to-noise ratio, and flux calibration. we also present, for the first time, a method to ensure that the analysis of spectral indices is not affected by sky contamination, which is a major challenge when dealing with nir spectroscopy. moreover, we discuss two main applications: (i) the ability of some nir spectral indices to constrain the shape of the low-mass imf and (ii) current issues in the analysis of nir spectral indices for future developments of sps modelling. | fingerprints of stellar populations in the near-infrared: an optimized set of spectral indices in the jhk bands |
radiation fields emitted by o- and b-type stars or young stellar populations (sps) are generally considered as significant central ionizing sources (ciss) of classic h ii regions. in our previous studies, we showed that the inclusion of binary interactions in stellar population synthesis models can significantly increase the ultraviolet spectrum hardness and the number of ionizing photons of intermediate-age (ia) sps (7 ≲ log(t/yr) ≲ 8). in this work, we present photoionization models of h ii regions ionized by radiation fields emitted by ia sps, including binary systems, and show that these fields are in theory possible candidates for significant ciss of classic h ii regions. when radiation fields of ia sps comprising binary systems are used as the ciss of classic h ii regions, the theoretical strengths of a number of lines (such as [o iii] λ4959', [s ii] λ6716', etc.), which are weaker than observations, are increased; the border or selection-criterion lines between star-forming galaxies and active galactic nuclei (agns) in the diagnostic diagrams (for example, [n ii] λ6583/hα versus [o iii] λ5007/hβ), move into the region occupied originally by agns; and the he ii λ1640 line, observed in lyman break and high-redshift gravitationally lensed galaxies, also can be produced. | radiation fields of intermediate-age stellar populations with binaries as ionizing sources of h ii regions. |
context. white dwarfs are the fossils left by the evolution of low- and intermediate-mass stars, and have very long evolutionary timescales. this allows us to use them to explore the properties of old populations, like the galactic halo.aims: we present a population synthesis study of the luminosity function of halo white dwarfs, aimed at investigating which information can be derived from the currently available observed data.methods: we employ an up-to-date population synthesis code based on monte carlo techniques, which incorporates the most recent and reliable cooling sequences for metal-poor progenitors as well as an accurate modeling of the observational biases.results: we find that because the observed sample of halo white dwarfs is restricted to the brightest stars, only the hot branch of the white dwarf luminosity function can be used for these purposes, and that its shape function is almost insensitive to the most relevant inputs, such as the adopted cooling sequences, the initial mass function, the density profile of the stellar spheroid, or the adopted fraction of unresolved binaries. moreover, since the cutoff of the observed luminosity has not yet been determined only the lower limits to the age of the halo population can be placed.conclusions: we conclude that the current observed sample of the halo white dwarf population is still too small to obtain definite conclusions about the properties of the stellar halo, and the recently computed white dwarf cooling sequences, which incorporate residual hydrogen burning, should be assessed using metal-poor globular clusters. | revisiting the luminosity function of single halo white dwarfs |
we investigate the formation and evolutionary sequences of galactic intermediate- and low-mass x-ray binaries (i/lmxbs) by combining binary population synthesis (bps) and detailed stellar evolutionary calculations. using an updated bps code we compute the evolution of massive binaries that leads to the formation of incipient i/lmxbs and present their distribution in the initial donor mass versus initial orbital period diagram. we then follow the evolution of the i/lmxbs until the formation of binary millisecond pulsars (bmsps). we find that the birthrate of the i/lmxb population is in the range of 9 × 10-6-3.4 × 10-5 yr-1, compatible with that of bmsps that are thought to descend from i/lmxbs. we show that during the evolution of i/lmxbs they are likely to be observed as relatively compact binaries with orbital periods ≲1 day and donor masses ≲0.3m⊙. the resultant bmsps have orbital periods ranging from less than 1 day to a few hundred days. these features are consistent with observations of lmxbs and bmsps. we also confirm the discrepancies between theoretical predictions and observations mentioned in the literature, that is, the theoretical average mass transfer rates (∼10-10 m⊙ yr-1) of lmxbs are considerably lower than observed, and the number of bmsps with orbital periods ∼0.1-10 days is severely underestimated. these discrepancies imply that something is missing in the modeling of lmxbs, which is likely to be related to the mechanisms of the orbital angular momentum loss. | formation and evolution of galactic intermediate/low-mass x-ray binaries |
aims: containing the oldest stars in the galaxy, globular clusters toward the bulge can be used to trace its dynamical and chemical evolution. in the bulge direction, there are ~50 clusters, but only about 20% have been subject of high-resolution spectroscopic investigations. so far, the sample observed at high resolution spans a moderate-to-high metallicity regime. in this sample, however, very few are located in the innermost region (rgc ≤ 1.5 kpc and | l,b | ≤ 5°). to constrain the chemical evolution enrichment of the innermost region of galaxy, accurate abundances and abundance patterns of key elements based on high-resolution spectroscopy are necessary. here we present the results we obtained for terzan 1, a metal-poor cluster located in the innermost bulge region.methods: using the near-infrared spectrograph crires at eso/vlt, we obtained high-resolution (r ≈ 50 000) h-band spectra of 16 bright giant stars in the innermost region (r ≤ 60'') of terzan 1. full spectral synthesis techniques and equivalent width measurements of selected lines, isolated and free of significant blending and/or contamination by telluric lines, allowed accurate chemical abundances and radial velocities to be derived.results: fifteen out of 16 observed stars are likely cluster members, with an average heliocentric radial velocity of +57 ± 1.8 km s-1 and mean iron abundance of [ fe/h ] = -1.26 ± 0.03 dex. for these stars we measured some [α/fe] abundance ratios, finding average values of [ o/fe ] = +0.39 ± 0.02 dex, [ mg/fe ] = +0.42 ± 0.02 dex, [ si/fe ] = +0.31 ± 0.04 dex, and [ ti/fe ] = +0.15 ± 0.04 dexconclusions: the α enhancement (≈+0.4 dex) found in the observed giant stars of terzan 1 is consistent with previous measurements on other, more metal-rich bulge clusters, which suggests a rapid chemical enrichment. based on data taken at the eso/vlt telescope, within the observing program 093.d-0179(a). | high-resolution crires spectra of terzan 1: a metal-poor globular cluster toward the inner bulge |
aims: we have endeavoured to understand the formation and evolution of the black hole (bh) x-ray binary lmc x-3. we estimated the properties of the system at four evolutionary stages: (1) at the zero-age main-sequence (zams); (2) immediately before the supernova (sn) explosion of the primary; (3) immediately after the sn; and (4) at the moment when roche-lobe overflow began.methods: we used a hybrid approach that combined detailed calculations of the stellar structure and binary evolution with approximate population synthesis models. this allowed us to estimate potential natal kicks and the evolution of the bh spin. we incorporated as model constraints the most up-to-date observational information throughout, which include the binary orbital properties, the companion star mass, effective temperature, surface gravity and radius, and the bh mass and spin.results: we find at 5% and 95% confidence, respectively, that lmc x-3 began as a zams system with the mass of the primary star in the range m1,zams = 22-31 m⊙ and a secondary star of m2,zams = 5.0-8.3 m⊙, in a wide (pzams ≳ 2.000 days) and eccentric (ezams ≳ 0.18) orbit. immediately before the sn, the primary had a mass of m1,presn = 11.1-18.0 m⊙, but the secondary star was largely unaffected. the orbital period decreased to 0.6-1.7 days and is still eccentric 0 ≤ epresn ≤ 0.44. we find that a symmetric sn explosion with no or small natal kicks (a few tens of km s-1) imparted on the bh cannot be formally excluded, but large natal kicks in excess of ≳120 km s-1 increase the estimated formation rate by an order of magnitude. following the sn, the system has a bh mbh,postsn = 6.4-8.2 m⊙ and is set on an eccentric orbit. at the onset of the roche-lobe overflow, the orbit is circular and has a period of prlo = 0.8-1.4 days. the full table 2 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/597/a12 | unraveling the formation history of the black hole x-ray binary lmc x-3 from the zero age main sequence to the present |
using new, homogeneous, long-slit spectroscopy in the wavelength range from ~0.35 to $\sim 1 \, \mu$m, we study radial gradients of optical and near-infrared (nir) initial mass function (imf)-sensitive features along the major axis of the bulge of m31, out to a galactocentric distance of ~200 arcsec (~800 pc). based on state-of-the-art stellar population synthesis models with varying na abundance ratio, we fit a number of spectral indices, from different chemical species (including tio's, ca, and na indices), to constrain the low-mass (≲0.5 m⊙) end slope (i.e. the fraction of low-mass stars) of the stellar imf, as a function of galactocentric distance. outside a radial distance of ~10 arcsec, we infer an imf similar to a milky way-like distribution, while at small galactocentric distances, an imf radial gradient is detected, with a mildly bottom-heavy imf in the few inner arcsec. we are able to fit na features (both nad and $\rm na\,{\small i}8190$), without requiring extremely high na abundance ratios. $\rm [na/fe]$ is ~0.4 dex for most of the bulge, rising up to ~0.6 dex in the innermost radial bins. our results imply an overall, luminosity-weighted, imf and mass-to-light ratio for the m31 bulge, consistent with those for a milky way-like distribution, in contrast to results obtained, in general, for most massive early-type galaxies. | mild radial variations of the stellar imf in the bulge of m31 |
most subdwarf b (sdb) + helium white dwarf (he wd) binaries are believed to be formed from a particular channel. in this channel, the he wds are produced first from red giants (rgs) with degenerate cores via stable mass transfer and sdb stars are produced from rgs with degenerate cores via common-envelope (ce) ejection. they are important for the studies of ce evolution, binary evolution, and binary population synthesis. however, the relation between wd mass and orbital period of sdb + he wd binaries has not been specifically studied. in this paper, we first use a semi-analytic method to follow their formation and find a wd mass and orbital period relation. then we use a detailed stellar evolution code to model their formation from main-sequence binaries. we find a similar relation between the wd mass and orbital period, which is in broad agreement with observations. for most sdb + he wd systems, if the wd mass (orbital period) can be determined, the orbital period (wd mass) can be inferred with this relation and then the inclination angle can be constrained with the binary mass function. in addition, we can also use this relation to constrain the ce ejection efficiency and find that a relative large ce ejection efficiency is favoured. if both the wd and sdb star masses can be determined, the critical mass ratios of dynamically unstable mass transfer for rg binaries can also be constrained. | wd mass and orbital period relation of sdb + he wd binaries |
the nature of the progenitors of type ia supernovae (sne ia) remains a mystery. binary systems consisting of a white dwarf (wd) and a main-sequence (ms) donor are potential progenitors of sne ia, in which a thermonuclear explosion of the wd may occur when its mass reaches the chandrasekhar limit during accretion of material from a companion star. in the present work, we address theoretical rates and delay times of a specific ms donor channel to sne ia, in which a helium (he) star + ms binary produced from a common envelope event subsequently forms a wd + ms system without the he star undergoing mass transfer by roche lobe overflow. by combining the results of self-consistent binary evolution calculations with population synthesis models, we find that the contribution of sne ia in this channel is around 2.0 × 10-4 yr-1. in addition, we find that delay times of sne ia in this channel cover a range of about 1.0-2.6 gyr, and almost all sne ia produced in this way (about 97%) have a delay time of ≳1 gyr. while the rate of sn ia in this work is about 10% of the overall sn ia rate, the channel represents a possible contribution to the old population (1-3 gyr) of observed sne ia. | a closer look at non-interacting he stars as a channel for producing the old population of type ia supernovae |
by considering a modified version of the evolutionary population synthesis (eps) model for stellar populations (sps) comprising binary stars, the retrieved galaxy and hii-region parameters/properties differ from the case of neglecting binary stars. the retrieved age, stellar metallicity and mass of galaxies increase (e.g. ∼ 0.2 dex when using spectral fitting algorithm), whilst the star formation rate decreases (∼0.2 dex). the radiation fields from intermediate-age sps with binary stars could be potentially important ionizing sources in hii regions. under this possibility, the theoretical division between star forming galaxy and agn on the diagnostic diagrams would move towards the up-right corner and the retrieved gaseous metallicity would decrease. | evolutionary population synthesis model with binary stars - yunnan-ii model |
the high mass x-ray binaries (hmxbs) provide an exciting framework to investigate the evolution of massive stars and the processes behind binary evolution. hmxbs have shown to be good tracers of recent star formation in galaxies and might be important feedback sources at early stages of the universe. furthermore, hmxbs are likely the progenitors of gravitational wave sources (bh-bh or bh-ns binaries that may merge producing gravitational waves). in this work, we investigate the nature and properties of hmxb population in star-forming galaxies. we combine the results from the population synthesis model mobse (giacobbo & mapelli 2018a) together with galaxy catalogs from eagle simulation (schaye et al. 2015). therefore, this method describes the hmxbs within their host galaxies in a self-consistent way. we compute the x-ray luminosity function (xlf) of hmxbs in star-forming galaxies, showing that this methodology matches the main features of the observed xlf. | the high mass x-ray binaries in star-forming galaxies |
mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (cdm) theory using the nfw dark matter halo density distribution to extract a new concentration-viral mass relation (c-mvir). the rotation curves (rcs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. although accounting for a nfw dark halo profile can explain rc observations, the implied c-mvir relation from rc analysis strongly disagrees with that resulting from different cosmological simulations. also, the m/l-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. moreover, we show that the best-fitting stellar m/l ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the λcdm theory. this can be interpreted as a serious crisis for this theory. this suggests either that the commonly used nfw halo profile, which is a natural result of λcdm cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies. | rotation curves of galaxies and the stellar mass-to-light ratio |
the metallicity distribution function of globular clusters (gcs) in galaxies is a key to understanding galactic formation and evolution. the calcium ii triplet (cat) index has recently become a popular metal abundance indicator thanks to its sensitivity to gc metallicity. here we revisit and assess the reliability of cat as a metallicity indicator using our new stellar population synthesis simulations based on empirical high-resolution fluxes. the model shows that the cat strength of old (>10 gyr) gcs is proportional to [fe/h] below -0.5. in the modest metal-rich regime, however, cat does not increase anymore with [fe/h] due to the little contribution from coolest red giant stars to the cat absorption. the nonlinear nature of the color-cat relation is confirmed by the observations of gcs in nearby early-type galaxies. this indicates that the cat should be used carefully when deriving metallicities of metal-rich stellar populations. our results offer an explanation for the observed sharp difference between the color and cat distributions of gcs in the same galaxies. we take this as an analogy to the view that metallicity-color and metallicity-lick index nonlinearity of gcs is primarily responsible for their observed “bimodal” distributions of colors and absorption indices. | nonlinear color--metallicity relations of globular clusters. vi. on calcium ii triplet based metallicities of globular clusters in early-type galaxies |
the nature of the progenitors of type ia supernovae (sne ia) is not yet fully understood. in the single-degenerate (sd) scenario, the collision of the sn ejecta with its companion star is expected to produce detectable ultraviolet emission in the first few days after the sn explosion within certain viewing angles. it was recently found that the b - v colour of the nearby sn ia sn 2012cg at about 16 d before the maximum b-band brightness was about 0.2 mag bluer than those of other normal sne ia, which was reported as the first evidence for excess blue light from the interaction of normal sn ia ejecta with its companion star. in this work, we compare current observations for sn 2012cg from its pre-explosion phase to the late-time nebular phase with theoretical predictions from binary evolution and population synthesis calculations for a variety of popular progenitor scenarios. we find that a main-sequence donor or a carbon-oxygen white dwarf donor binary system is more likely to be the progenitor of sn 2012cg. however, both scenarios also predict properties which are in contradiction to the observed features of this system. taking both theoretical and observational uncertainties into account, we suggest that it might be too early to conclude that sn 2012cg was produced from an explosion of a chandrasekhar-mass white dwarf in the sd scenario. future observations and improved detailed theoretical modelling are still required to place a more stringent constraint on the progenitor of sn 2012cg. | constraining the progenitor of the type ia supernova sn 2012cg |
we investigate the stellar populations of galaxies in clusters at different dynamical stages, aiming to identify possible effects of the relaxation state of the cluster or subcluster on the star formation histories of its galaxies. we have developed and applied a code for kinematic substructure detection to a sample of 412 galaxy clusters drawn from the tempel et al. (2012) catalogue, finding a frequency of substructures of 45 per cent. we have extracted mean stellar ages with the starlight spectral synthesis code applied to sloan digital sky survey iii spectra of the sample galaxies. we found lower mean stellar ages in unrelaxed clusters relative to relaxed clusters. for unrelaxed clusters, we separated primary and secondary subhaloes and found that, while relaxed clusters and primaries present similar masses and age distributions, secondaries present younger stellar populations, mainly due to low-mass galaxies (log m⋆/m⊙ ≲ 11 dex). an age-clustercentric radius relation is seen for all subhaloes irrespective of the presence of substructures. we also observe relations between the mean stellar age and mass of relaxed and unrelaxed clusters, massive systems presenting higher mean ages. the locus of these relations is distinct between relaxed and unrelaxed clusters, but become indistinguishable when separating primaries and secondaries. our results suggest that differences between relaxed and unrelaxed clusters are mainly driven by low-mass systems in the clusters outskirts, and that, while pre-processing can be seen in the subcomponents of dynamically young clusters, some evolution in the stellar populations must occur during the clusters relaxation. | the dynamic stage of clusters and its influence on the stellar populations of galaxies |
aims: we report the discovery of a young lithium rich giant, hd 16771, in the core-helium burning phase that does not seem to fit existing proposals of li synthesis near the luminosity function bump or during he-core flash. we aim to understand the nature of li enrichment in the atmosphere of hd 16771 by exploring various li enhancement scenarios.methods: we have collected high-resolution echelle spectra of hd 16771 and derived stellar parameters and chemical abundances for 27 elements by either line equivalent widths or synthetic spectrum analyses.results: hd 16771 is a li-rich (log ɛ(li) = + 2.67 ± 0.10 dex) intermediate mass giant star (m = 2.4 ± 0.1 m⊙) with age ~ 0.76 ± 0.13 gyr and located at the red giant clump. kinematics and chemical compositions are consistent with hd 16771 being a member of the galactic thin disk population. the non-detection of 6li (<3%), a low carbon isotopic ratio (12c/13c = 12 ± 2), and the slow rotation (vsin i = 2.8 km s-1) all suggest that lithium might have been synthesized in this star. on the contrary, hd 16771 with a mass of 2.4 m⊙ has no chance of encountering luminosity function bump and he-core flash where the possibility of fast deep-mixing for li enrichment in k giants has been suggested previously.conclusions: based of the evolutionary status of this star, we discuss the possibility that 7li synthesis in hd 16771 is triggered by the engulfment of close-in planet(s) during the rgb phase. | hd 16771: a lithium-rich giant in the red-clump stage |
we study the stellar content in the tidal tails of three nearby merging galaxies, ngc 520, ngc 2623, and ngc 3256, using bvi imaging taken with the advanced camera for surveys on board the hubble space telescope. the tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. we compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. we find a lack of very young clusters (≤10 myr old), implying that eventually star formation shuts off in the tails as the gas is used up or dispersed. there are a few clusters in each tail with estimated ages that are older than the modeled tails themselves, suggesting that these may have been stripped out from the original galaxy disks. the luminosity function of the tail clusters can be described by a single power-law, dn/dl ∝ lα, with -2.6 < α < -2.0. we find a stellar age gradient across some of the tidal tails, which we interpret as a superposition of (1) newly formed stars and clusters along the dense center of the tail and (2) a sea of broadly distributed, older stellar material ejected from the progenitor galaxies. | ages of star clusters in the tidal tails of merging galaxies |
we propose a method for confirmation of the existence of population iii (pop iii) stars with massive black hole binaries as gw150914 in gravitational wave (gw) observation. when we get enough number of events, we want to determine which model is closer to reality, with and without pop iii stars. we need to prepare various "pop i/ii models" and various "pop i/ii/iii models" and investigate which model is consistent with the events. to demonstrate our analysis, we simulate detections of gw events for some examples of population synthesis models with and without pop iii stars. we calculate the likelihood ratio with the realistic number of events and evaluate the probability of identifying the existence of pop iii stars. in typical cases, our analysis can distinguish between pop i/ii model and pop i/ii/iii model with 90% probability by 22 gw signals from black hole-black hole binary mergers. | how to confirm the existence of population iii stars by observations of gravitational waves |
we present synthetic far- and near-ultraviolet ({fuv} and {nuv}) maps of m31, both with and without dust reddening. these maps were constructed from spatially resolved star formation histories (sfhs) derived from optical hubble space telescope imaging of resolved stars, taken as part of the panchromatic hubble andromeda treasury program. we use stellar population synthesis modeling to generate synthetic uv maps with a spatial resolution of ∼100 pc (∼24 arcsec), projected. when reddening is included, these maps reproduce all of the main morphological features in the galex imaging, including rings and large star-forming complexes. the predicted uv flux also agrees well with the observed flux, with median ratios between the modeled and observed flux of {{log}}10({f}{fuv}{syn}/{f}{fuv}{obs})=0.03+/- 0.24 and {{log}}10({f}{nuv}{syn}/{f}{nuv}{obs})=-0.03+/- 0.16 in the {fuv} and {nuv}, respectively. this agreement is particularly impressive given that we used only optical photometry to construct these uv maps. having verified the synthetic reddened maps, we use the dust-free maps to examine properties of obscured flux and star formation. we compare our dust-free and reddened maps of {fuv} flux with the observed galex {fuv} flux and {fuv} + 24 μm flux to examine the fraction of obscured flux. we find that the maps of synthetic flux require that ∼90% of the {fuv} flux in m31 is obscured by dust, while the galex -based methods suggest that ∼70% of the {fuv} flux is absorbed by dust. this 30% increase in the estimate of the obscured flux is driven by significant differences between the dust-free synthetic {fuv} flux and that derived when correcting the observed {fuv} flux for dust absorption with 24 μm emission observations. the difference is further illustrated when we compare the sfrs derived from the {fuv} + 24 μm flux with the 100 myr average sfr from the cmd-based sfhs. we find that the 24 μm corrected {fuv} flux underestimates the sfr by a factor of 2.3-2.5, depending on the chosen calibration. this discrepancy could be reduced by allowing for variability in the weight applied to the 24 μm data, as has been recently suggested in the literature. based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with program #12055. | the panchromatic hubble andromeda treasury. xvii. examining obscured star formation with synthetic ultraviolet flux maps in m31. |
we simulate deep images from the hubble space telescope (hst) using semi-empirical models of galaxy formation with only a few basic assumptions and parameters. we project our simulations all the way to the observational domain, adding cosmological and instrumental effects to the images, and analyze them in the same way as real hst images ("forward modeling"). this is a powerful tool for testing and comparing galaxy evolution models, since it allows us to make unbiased comparisons between the predicted and observed distributions of galaxy properties, while automatically taking into account all relevant selection effects. our semi-empirical models populate each dark matter halo with a galaxy of determined stellar mass and scale radius. we compute the luminosity and spectrum of each simulated galaxy from its evolving stellar mass using stellar population synthesis models. we calculate the intrinsic scatter in the stellar mass-halo mass relation that naturally results from enforcing a monotonically increasing stellar mass along the merger history of each halo. the simulated galaxy images are drawn from cutouts of real galaxies from the sloan digital sky survey, with sizes and fluxes rescaled to match those of the model galaxies. the distributions of galaxy luminosities, sizes, and surface brightnesses depend on the adjustable parameters in the models, and they agree well with observations for reasonable values of those parameters. measured galaxy magnitudes and sizes have significant magnitude-dependent biases, with both being underestimated near the magnitude detection limit. the fraction of galaxies detected and fraction of light detected also depend sensitively on the details of the model. | simulating deep hubble images with semi-empirical models of galaxy formation |
in this second paper on the entire virial region of the relaxed fossil cluster rxj 1159+5531, we present a hydrostatic analysis of the azimuthally averaged hot intracluster medium (icm) using the results of su et al. for a model consisting of icm, stellar mass from the central galaxy (bcg), and an nfw dark matter (dm) halo, we obtain a good description of the projected radial profiles of icm emissivity and temperature that yield precise constraints on the total mass profile. the bcg stellar mass component is clearly detected with a k-band stellar mass-to-light ratio, {m}\star /{l}k=0.61+/- 0.11 {m}⊙ /{l}⊙ , consistent with stellar population synthesis models for a milky way initial mass function. we obtain a halo concentration, {c}200=8.4+/- 1.0, and virial mass, {m}200=(7.9+/- 0.6)× {10}13 {m}⊙ . for its mass, the inferred concentration is larger than most relaxed halos produced in cosmological simulations with planck parameters, consistent with rxj 1159+5531 forming earlier than the general halo population. the baryon fraction at r 200, {f}{{b,200}}=0.134+/- 0.007, is slightly below the planck value (0.155) for the universe. however, when we take into account the additional stellar baryons associated with non-central galaxies and the uncertain intracluster light (icl), {f}{{b,200}} increases by ≈ 0.015, consistent with the cosmic value and therefore no significant baryon loss from the system. the total mass profile is nearly a power law over a large radial range (∼0.2-10 re ), where the corresponding density slope α obeys the α -{r}e scaling relation for massive early-type galaxies. performing our analysis in the context of mond still requires a large dm fraction (85.0 % +/- 2.5 % at r = 100 kpc) similar to that obtained using the standard newtonian approach. the detection of a plausible stellar bcg mass component distinct from the nfw dm halo in the total gravitational potential suggests that ∼ {10}14 {m}⊙represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters. | the entire virial radius of the fossil cluster rxj 1159 + 5531. ii. dark matter and baryon fraction |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.