abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
in our best current understanding of the growth of structure in the universe, visibly complex distributions of gas and stars form and evolve into a wide range of galaxies inside overdensities of dark matter. re-creating the observed diversity in the organization of baryonic mass within dark matter halos represents a key challenge for galaxy formation models. in this dissertation, i constrain 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 to address the growth of galaxy disks in dark matter halos. i trace the gravitational potentials of each galaxy using rotation curves derived from new and archival radio synthesis observations of neutral hydrogen (hi). the measured rotation curves are decomposed into baryonic and dark matter halo components using 3.6 mum images for the stellar content, the hi observations for the atomic gas component, and, when available, co data from the literature for the molecular gas component. the hi kinematics are supplemented with optical integral field spectroscopic (ifs) observations to measure the central ionized gas kinematics in 26 galaxies. 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. this result encapsulates the challenge facing simulations to create galaxies which evolve with different star formation histories but similar distributions of mass. | baryonic distributions in galaxy dark matter halos |
califa (calar alto legacy integral field area) is a 3d spectroscopic survey of 600 nearby galaxies that we are obtaining with ppak@3.5m at calar alto (sánchez et al. 2012; husemann et al. 2012). this pioneer survey is providing valuable clues on how the mass and metallicity grow in the different galactic spatial sub-components (``bulge'' and ``disk''). processed through spectral synthesis techniques, califa datacubes allow us to, for the first time, spatially resolve the star formation history of galaxies (cid fernandes et al. 2012). the richness of this approach is already evident from the results obtained for the first ~ 100 galaxies of the sample (pérez et al. 2012). we have found that galaxies grow inside-out, and that the growth rate depends on a galaxy's mass. here, we present the radial variations of physical properties sorting galaxies by their morphological type (figure 1). we have found a good correlation between the stellar mass surface density, stellar ages and metallicities and the hubble type, but being the the early type spirals (sa-sbc) the galaxies with strong negative age and metallicity gradient from the bulge to the disk. | the growth of mass and metallicity in bulges and disks: califa perspective |
we present the atomic neutral hydrogen (hi) stacked spectra of different galaxy populations selected by colour and/or agn/star-forming properties. the hi observations were carried out with the westerbork synthesis radio telescope (wsrt) in the redshift range 0<z<0.12. in the observed volume, about 1600 galaxies have available sloan digital sky survey (sdss) spectroscopic measurement and accompanying multi-wavelength data. galaxy populations are defined using the multi-wavelength information. the hi spectra of a selected population are de-redshifted to the rest frame frequency of hi (1420.4mhz) according to the sdss redshift, and co-added in redshift/luminosity bins. (2 data files). | vizier online data catalog: global hi content from a stacking experiment (gereb+, 2015) |
feedback, a process by which gas is expelled or heated too much for new star formation to occur, is required in galaxy formation simulations to truncate star formation and form galaxies with properties that we observe today. winds from agn or supernovae after a burst of new star formation can blow out circumnuclear gas, suppressing star formation, supporting the idea that feedback is an important ingredient in galaxy evolution. agn are a potential source of this feedback, which would mean they are affecting the evolution of galaxies. yet, the timing of star forming and agn phases are not well known and as of today we do not have a complete understanding of the connection between agn and star formation. the goals of our project focus on the relationship between the supermassive black holes and their host galaxies through their active phases to understand the role of the agn in the host galaxy's evolution, from the triggering of the agn to its dormant quiescence phase. this analysis requires three elements: (1) the ability to trace an agn's history through radio spectral age dating; (2) the ability to trace a galaxy's stellar population history via full spectrum synthesis fitting; and (3) a spatially resolved view of these systems, since not all relevant information about galaxies is contained in the central core. fulfilling all three key elements can be achieved with the ongoing sdss iv manga integral field optical spectroscopic survey for spatially resolved properties of 10,000 galaxies and radio surveys such as tgss (150 mhz), wenss (330 mhz), and nvss (1.4 ghz), plus targeted ugmrt observations to fully sample the frequency range of 150-900 mhz. we present and compare agn age estimates for element (1) of 36 manga sources using brats, a software suite containing tools for radio spectral analysis. | the coevolutionary history of agn and galaxies through age estimates of radio agn |
highly obscured agn, especially compton-thick (ct) agn, likely play a key role in the galaxy-agn co-evolution scenario. they would comprise the early stages of agn activity, preceding the agn-feedback/star-formation quenching phase, during which most of both the smbh and galaxy growth take place. however, the actual ct fraction among the agn population is still largely unconstrained. the most reliable way of confirming the obscured nature of an agn by x-ray spectroscopy, but very deep observations are needed to extend local analyses to larger distances. we will present the x-ray spectral analysis of the deepest x-ray data obtained to date, the almost 7ms observation of the chandra deep field south. the unprecedented depth of this survey allow us to carry out reliable spectral analyses down to a flux limit of 10^{-16} erg cm^{-2} s^{-1} in the hard 2-8 kev band. besides the new deeper x-ray data, our approach also includes the implementation of bayesian inference in the determination of the ct fraction. our results favor x-ray background synthesis models which postulate a moderate fraction (25%) of ct objects among the obscured agn population. | the compton-thick agn fraction from the deepest x-ray spectroscopy in the cdf-s |
almost every galaxy has a supermassive black hole (smbh) residing at its center, the milky way included. recent studies suggested that these unique places are expected to host a high abundance of stellar and compact object binaries. these binaries form hierarchical triple systems with the smbh, and undergo the eccentric kozai-lidov (ekl) mechanism. here we estimate the detectability of potential gravitational wave (gw) emission from these compact objects within the frequency band of the laser interferometer space antenna (lisa) and laser interferometer gravitational-wave observatory (ligo) of the ligo-virgo collaboration (lvc). we generate a post ekl population of stars at the onset of roche limit crossing and follow their evolution to compact object binaries. as a proof-of-concept, we adopt two metallicities, solar metallicity (z = 0.02) and 15% of it (z = 0.003). we demonstrate that over the observation timescale of lisa, black hole binaries (bh-bh) and white dwarf binaries (wd-wd) provides the most prominent gw sources via the ekl assisted merger channel. systems involving neutron star (e.g., ns-bh, ns-ns) are less observable but possibly abundant through different merger channels. our population synthesis of bh-bh with z = 0.02 (z = 0.003) translate to ~4 (~24) events per year with ligo within a 1 gpc3 volume sphere. | gravitational-wave signatures from compact object binaries in the galactic center |
observations of the galaxy population throughout the cosmic time have suggested an evolution scenario where galaxies evolve from blue and star-forming, to red and quiescent as star formation is quenched and gas is consumed in stars or becomes unavailable for stellar synthesis. though multiple mechanisms have been shown to be able to quench galaxies in different ways, the interplay and relative importance of these mechanisms are still not fully understood. in this work, we study a particular quenching galaxy: ic 860, for which we have exquisite multiwavelength data to probe different activities such as outflows and agn in the galaxy. ic 860 is a quenching galaxy at a very early stage and is therefore an ideal case study for understanding the triggers of quenching. we find a multiphase outflow in molecular and neutral gas that seems unable to escape the galaxy. we also find evidence for a recent merger and a buried agn. the depletion time of the molecular gas reservoir under the current star formation rate is ~7 gyr, indicating that the galaxy could stay at the intermediate stage between the blue and red sequence for a long time. thus the timescales for quenching and gas depletion are not necessarily the same. the outflow is likely driven by the agn given the low recent star formation rate. our analysis supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling the gas and shed light on possible on-going activities in similar quenching galaxies. | a multiwavelength view of ic 860: what is in action inside quenching galaxies |
we investigate the stellar populations and ionized gas properties of a sample of central spheroidal galaxies in order to better constrain their history of star formation and gas excitation mechanism. we select galaxies from spheroids panchromatic investigation in different environmental regions (spider) catalogue and separate these galaxies in different regimes of halo and galaxy mass. to characterize the stellar population properties of these galaxies we use the stellar population synthesis method with the starlight code, and the presence of ionized gas is identified by measurements of the hα equivalent width. we analyze how these properties behave as a function of the galaxy stellar mass and the parent halo mass. a trend is observed in the sense of increased ionized gas emission for low-mass centrals in high-mass halos. we interpret this trend in a scenario of intracluster medium (icm) cooling versus active galactic nuclei (agn) feedback. | stellar populations and ionized gas in central spheroidal galaxies |
we present a detailed study of the x-ray point source populations of the nearby, star-forming, spiral galaxy m81. using deep hst data, we uniquely classify the x-ray binary (xrb) populations on the basis of their donor stars and local stellar populations. while this analysis is focused on chandra observations most sensitive to the central galactic regions, we also include preliminary analysis of new chandra observations probing the outer disk regions. these new observations importantly enable us to study xrbs across the entire disk at a range of ages. we measure the x-ray luminosity functions (xlfs) of the different xrb sub-populations (early-type main sequence, supergiant, low-mass, globular cluster), and we compare these results with predictions from xrb population synthesis models. this more robust classification (than the common, simple bulge/disk spatial separations) of xrbs minimizes contamination between different sub-populations, and it shows that high-mass xrbs have steeper xlfs than the "canonical" star-forming galaxy xlf commonly used. in the case of globular clusters, we find that more massive and denser globular clusters are more likely to be associated with xrbs. we also compare these results with the xrb populations of the prototypical starburst galaxy, m82, for which we present the deepest xlf reported for a starburst galaxy. we discuss the variations of the xrb populations in regions of m82 dominated by star-formation episodes at different ages, and in the context of predictions from xrb formation and evolution models. | the x-ray binary populations of m81 and m82 |
in asymptotic giant branch (agb) stars, 22ne plays an important role in several nucleosynthesis processes, with its production competing with the synthesis of 19f through the so called `poisoning reaction', and the following transfer into 25mg acting as the main neutron sources for the heavy element s-process, affecting the reaction rates of numerous isotopes. in this contribution, we discuss a recent neutron transfer experiment done at triumf in november 2018, directly populating 22ne, allowing for high resolution measurements of the resonance energies with the sharc silicon detector, coupled to the hpge detector array tigress for accurate measurement of the characteristic gamma rays. we will then present the method of using the angular distribution of these newly measured gamma rays and protons to determine the spins of the resonance states, allowing for further constraint on the reaction cross-section. | investigation of high-lying (alpha, gamma) resonances in 22ne through one-neutron transfer in inverse kinematics at tigress |
we have obtained deep g, r, and i-band subaru and ultra-deep 3.6 μm irac images of parts of the multiply-wrapped stellar stream around the nearby edge-on galaxy ngc 5907. we have fitted the surface brightness measurements of the stream with fsps stellar population synthesis models to derive the metallicity and age of the brightest parts of the stream. the resulting relatively high metallicity ([fe/h] = -0.3) is consistent with a major merger scenario but a satellite accretion event cannot be ruled out. | imaging of ngc 5907's stellar stream |
the origin of half of the elements heavier than iron -- the so-called r-process elements -- is a central unsolved mystery in astrophysics. these atoms include both precious metals (e.g. gold) as well as radioactive elements required for geophysical processes on the earth (e.g. thorium) and even some which are necessary on earth for advanced life (e.g. iodine). recent observations with both light and gravitational waves have demonstrated that at least some of these elements are formed through the merger of two neutron stars, but such a population struggles to reproduce the enrichment patterns seen in stars within the milky way as well apparent early enrichment in some dwarf galaxies. instead, recent work implies that the accretion disks formed in the stellar collapse that powers a long duration gamma-ray burst could in-fact be a dominant site. if this is true we should be able to observe r-process synthesis in the associated supernovae. the presence of lanthanides in r-process material creates strong opacity, such that the signature of their synthesis should be a late time infrared component visible in the supernova light. here we propose sensitive hst observations that will search for both spectroscopic and photometric evidence of the r-process, providing the opportunity to test, for the first time, if collapsars are responsible for heavy element production. | do collapsars make the heavy elements: a sensitive search in a nearby gamma-ray burst? |
we present a stellar population synthesis study of a sample of 10 post-starburst quasars (psqs) at z ∼ 0.3. these broad-lined active galactic nuclei (agns) possess the spectral signatures of massive intermediate-aged stellar populations, making them potentially useful for studying the connections between nuclear activity and host galaxy evolution. with the help of the stellar synthesis code starlight, we determine the ages of the host stellar populations, the black hole masses, and eddington fractions of the agns. we find that the psqs have m_{bh} ∼ 10^8 m_{⊙} accreting at a few percent of eddington luminosity, and the ages of host stellar populations are several hundred myr to a few gyr old. the result may support a delay between the merger-induced starburst and the quasar being triggered/becoming visible. and the estimated total ir luminosity is greater than 10^{11} l_{⊙}, which may reveal the connection between the ultra luminous infrared galaxies (ulirgs) and the psqs. we still find no significant correlations between agn and starburst properties. it's very strange, especially if the triggering mechanism of starburst also triggered the agn activity, bringing a kind of correlations between them. maybe the selection effects limit our ability to see the correlations or there could be multiple types of triggering events. the unique spectral properties of psqs hint that these objects are recently quenched starbursts. we find that virtually all of them have intermediate-age population comprising a significant fraction of the total mass of the host galaxies. | the stellar population of post-starburst quasars |
we present a hydrostatic analysis of the azimuthally averaged hot intracluster medium (icm) of the entire virial region of the relaxed fossil cluster rxj 1159+5531. 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 temperature and emission-measure 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 solar, consistent with stellar population synthesis models. we obtain a halo concentration, c_200 = 8.4 +/- 1.0, and virial mass, m_200 = 7.9 +/- 0.6 x 10^{13} m_sun. for its mass, the inferred concentrationis 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 detection of a plausible stellar bcg mass component distinct from the nfw dm halo in the total gravitational potential supports the suggestion by newman et al. (2015) that 10^{14} m_sun represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters. | the radial mass profile within the entire virial region of a fossil cluster |
observations of nearby star-forming regions suggest that binary stars are common, even representing the majority of massive stars. their evolutionary effects result in harder spectral energy distributions, generation of h i-ionizing radiation for longer times, and higher lyman continuum escape fractions from galaxies than their single star counterparts, in sum, having potentially critical implications for h i reionization and early galaxy characteristics and processes. incorporating the binary population and spectral synthesis (bpass) models into our cosmological hydrodynamic simulations with in-situ radiative transfer, we have investigated from z=5-8 the effects of binary stars on star formation, h i and early he ii reionization, the igm and cgm, and on very high redshift metals, such as those observed in quasar absorption spectra. we find that, in comparison to the single star control model, binary stars produce an accelerated h i reionization history, but simultaneously increase typical gas temperatures and in so doing reduce the global star formation rate density, leading to a slowing in the rate of he ii ionization by z=5. the line-of-sight number density of low ionization metal absorbers is reduced, while the abundance of high ionization systems is substantially increased. from these results, we conclude that while binary stars do produce the anticipated effects of aiding h i reionization and ionizing the cgm with their bluer spectra, they also introduce a more complex interplay between stellar emissivities, gas heating, and star formation whose ultimate impact is dependent on the time frame under consideration. | the effects of binary stars on galaxies and the cgm during reionization |
it is now well-established that conventional type ia supernova (sn ia) light-curve standardization techniques leave residual correlations with properties of the host galaxy. however, various studies have shown that the strength and direction of these correlations depend on the method used and sn sample being analyzed. we collect a large sample of ∼1500 spectroscopically-confirmed, nearby (median z≈0.03) sne ia that have been used in the past for cosmological analyses in order to gain a coherent understanding of these effects and how their appearance is influenced by sample selection and methodology. we assemble a large set of multi-wavelength imaging around each sn spanning the ultraviolet to infrared, identify the host galaxy in optical images, and perform matched-aperture photometry to obtain global magnitudes of these sn hosts. we generate a custom set of 150,000 flexible stellar population synthesis models which we use to fit this photometry and derive properties such as host-galaxy stellar mass, specific star formation rate, and massed-weighted age. we examine correlations between these properties and sn properties in an effort to better understand the nature of the host galaxy bias on sn luminosities. as there is evidence that environmental effects are stronger closer to the sn, in a future study we will extract physical properties of the region within a few kiloparsecs of the sn location and investigate their effects on these same sne. we also intend to expand the range of methods used to infer host galaxy properties. | investigating the sample-dependence of the host galaxy bias with ∼1500 nearby type ia supernovae used for cosmological analyses |
in the era of large scale surveys, including lsst and gaia, binary population studies will flourish due to the large influx of data. in addition to probing binary populations as a function of galactic latitude, under-sampled groups such as low mass binaries will be observed at an unprecedented rate. to prepare for these missions, binary population simulations need to be carried out at high fidelity. these simulations will enable the creation of simulated data and, through comparison with real data, will allow the underlying binary parameter distributions to be explored. in order for the simulations to be considered robust, they should reproduce observed distributions accurately. to this end we have developed a simulator which takes input models and creates a synthetic population of eclipsing binaries. starting from a galactic single star model, implemented using galaxia, a code by sharma et al. (2011), and applying observed multiplicity, mass-ratio, period, and eccentricity distributions, as reported by raghavan et al. (2010), duchêne & kraus (2013), and moe & di stefano (2017), we are able to generate synthetic binary surveys that correspond to any survey cadences. in order to calibrate our input models we compare the results of our synthesized eclipsing binary survey to the kepler eclipsing binary catalog. | synthetic survey of the kepler field |
while the imparting of velocity `kicks' to compact remnants from supernovae is widely accepted, the relationship of the `kick' to the progenitor is not. we propose the `kick' is predominantly a result of conservation of momentum between the ejected and compact remnant masses. we propose the `kick' velocity is given by v kick = α(m ejecta/m remnant)+β, where α and β are constants we wish to determine. to test this we use the bpass v2 (binary population and spectral synthesis) code to create stellar populations from both single star and binary star evolutionary pathways. we then use our remnant ejecta and progenitor explosion relationship (reaper) code to apply `kicks' to neutron stars from supernovae in these models using a grid of α and β values, (from 0 to 200 km s-1 in steps of 10 km s-1), in three different `kick' orientations, (isotropic, spin-axis aligned and orthogonal to spin-axis) and weighted by three different salpeter initial mass functions (imf's), with slopes of -2.0, -2.35 and -2.70. we compare our synthetic 2d and 3d velocity probability distributions to the distributions provided by hobbs et al. (1995). | is the link between the observed velocities of neutron stars and their progenitors a simple mass relationship? |
resolved sfh of the lmc determined from fitting models computed with the triegal population synthesis model (girardi et al, 2005a&a...436..895g) to data from the vista survey of the magellanic clouds (cioni et al., 2011a&a...527a.116c, cat. ii/351). (6 data files). | vizier online data catalog: vmc survey xliii. lmc star formation history (mazzi+, 2021) |
the data we used for this study include the galex nuv and fuv, spitzer irac 3.6um, 4.5um, 5.8um, 8.0um, and spitzer mips 24um data used in smith+ (2016aj....151...63s). for the current study, for the 37 out of 46 galaxy pairs, and the 31 out of 38 spirals with optical sloan digitized sky survey (sdss) images we used those data as well. for all of the galaxies in the sample, we also carried out clump photometry using the j, h, and ks maps from the 2mass survey. we have identified the clumps in smoothed 8um observations from the spitzer infrared array camera (irac). see section 2.2 for further details. (5 data files). | vizier online data catalog: stellar population synthesis of clumps (zaragoza-cardiel+, 2018) |
galaxies at the peak of cosmic star formation (z ∼ 2‑3) are fundamentally different from local galaxies, in terms of the properties of their massive stellar populations and physical conditions in the interstellar medium (ism). this thesis presents a detailed analysis of the stellar and nebular properties of high-redshift galaxies, using the rest-frame uv and rest-frame optical spectra of galaxies from the keck baryonic structure survey (kbss), a large, targeted spectroscopic survey of galaxies at z ∼ 2 ‑ 3.chapter 2 compares inferences of dust attenuation, star formation, and metallicity from strong nebular emission lines, the far-uv continuum, and spectral energy distribution (sed) fits. these results indicate that the majority of high-redshift galaxies display different dust properties than those at low redshift, and that the assumption of a dust attenuation curve can dramatically change inferred properties such as star formation rates (sfrs). i find that sfrs estimated from h훼 and sed fitting only agree under specific combinations of assumptions, and caution that sfr calibrations established at low redshift do not apply at z ∼ 2 ‑ 3.chapter 3 utilizes rest-uv absorption lines to study the outflow kinematics of highredshift galaxies. i compare several velocity metrics used in the literature, and search for correlations between outflow velocity and galaxy properties. these results are consistent with the picture of winds driven by momentum injected into the ism by stellar feedback. i confirm that large-scale outflows are ubiquitous at high redshift due to these galaxies' high sfrs and compact sizes.finally, chapter 4 analyzes the systematic uncertainties involved in fitting stellar population synthesis (sps) models to rest-uv spectra as well as the full seds of galaxies. i quantify differences in galaxy parameters estimated using different combinations of models and assumptions, and explore the dependence of the rest-uv portion of model spectra on stellar metallicity and population age. | leveraging the rest-ultraviolet and rest-optical spectra of galaxies at 2 < z< 3 |
x-ray binaries (xbrs) are testbeds for modeling binary and stellar evolution. be xrbs are the most numerous subclass of observed high-mass xrbs, containing be donors with neutron star (ns) and black hole (bh) companions. while the exact mechanism responsible for the be phenomenon remains under debate, stellar rotation has been identified as a key ingredient for the formation of the decretion disk. previous population synthesis studies have used the be xrb population to constrain binary evolution processes such as mass transfer and common envelope efficiency, but without selection criteria coming from rotational modeling. we use posydon, a next generation population synthesis code coupled with binary mesa models, to study galactic be xrbs. for the first time, we model the rotational evolution of the donor and use prescriptions for the decretion disk to select be xrb like systems. we can successfully match both the orbital properties of the observed sample of be xrbs, as well as the relative abundance of ns to bh bexrbs. our results demonstrate the necessity of accurately modeling stellar rotation to interpret the be xrb population. k.a.r. is supported by the gordon and betty moore foundation (pi kalogera, grant award gbmf8477) and the riedel family fellowship. k.a.r. also thanks the lsstc data science fellowship program, which is funded by lsstc, nsf cybertraining grant no. 1829740, the brinson foundation, and the moore foundation; their participation in the program has benefited this work. | modeling galactic be x-ray binaries with posydon |
one of the biggest questions in gravitational wave (gw) astronomy today is: ``how do these sources form?'' and ``what can we learn from their gws about the birth, lives and explosive deaths of massive stars?'' new gw observing runs and next-generation detectors will rapidly provide data with ever-increasing precision and volume. however, on the theoretical side, we are limited in answering these questions due to the so-called ``great gw progenitor uncertainty problem': uncertainties within the population synthesis modelling are so large, that learning about their progenitors seems completely out of reach. in this talk we will present our work on tackling this challenge. we will discuss areas within population synthesis models where we might start to learn about massive stars through cosmic time floor broekgaarden acknowledges support from a nasa finesst grant number 80nssc22k1601. | what can we learn from population synthesis and theory in the near-future big data gravitational wave era |
cosmic (compact object synthesis and monte carlo investigation code) cosmic is a rapid binary population synthesis suite with a special purpose of generating realistic compact binary populations. cosmic can also be used to evolve binaries with bse in a python environment. cosmic currently implements binary evolutionary processes using bse (hurley+2002). several modifications have been applied to bse to account for recent updates to binary evolution especially important to compact binary formation (e.g. metallicity-dependent stellar winds or black hole natal kick strengths). for a detailed discussion of these modifications, see breivik+2019 in prep. | cosmic-popsynth/cosmic: 2.0.0 |
integrated light spectroscopy from galaxies is used to study stellar populations that cannot be resolved into individual stars. these analyses often rely on stellar population synthesis (sps) techniques. however, the spectral templates available for sps methods are limited, especially in the near-infrared. we present a-list (apogee library of infrared ssp templates), a new set of high-resolution, near-ir ssp spectral templates spanning a wide range of ages (2-12 gyr), metallicities (-2.2 < [m/h] < +0.4) and alpha-element abundances (-0.2 < [alpha/m] < +0.4). this set of ssp templates is the highest resolution (r~22500) available in the near-ir, and the first such based on an empirical stellar library. our models are generated using spectra of roughly 300,000 stars from apogee spread across the milky way, with a wide range of metallicities and abundances. we show that our model spectra provide accurate fits to apogee spectra of m31 globular clusters, with best-fit metallicities agreeing with those of previous estimates to within ~0.1 dex. we also compare these model spectra to lower-resolution e-miles models and demonstrate that we recover the ages of these models to within ~1 gyr. this library is publicly available. | the apogee library of infrared ssp templates (a-list): high-resolution simple stellar population spectral models in the h-band |
the, so far, unique and well constrained trappist-1 system can be exploited for testing planet formation theories. because of observational biases, terrestrial planet formation models will, for the next decade, only be testable around low mass stars, showing the need for research in this area. we invoke the bern model of global planet formation and evolution to conduct population syntheses for 0.1 solar mass stars and compare the wealth of systems to the trappist-1 system, finding reasonable consensus for many observables. however, compositions differ significantly. | reproducing the architecture of trappist-1 using global formation and evolution models |
one of our deepest windows into the universe at far-infrared (fir) wavelengths between 70 and 500 microns is in the candels/3d-hst extragalactic fields, owing to a huge investment of the spitzer and herschel space observatory resources. while public firselected catalogs exist for almost all herschel surveys in these fields, simple crossmatching with ultraviolet (uv) to near-infrared (nir) catalogs will not yield robust photometry due to severe blending issues caused by the low-resolution nature of the data. instead, "forced photometry", which uses source positions and light profiles from a higher resolution prior to define the fir sources to be measured, identifies roughly 50% more fir-bright galaxies and enables an analysis at faint magnitudes that is otherwise impossible. here, we propose the 3d-herschel legacy program, which will produce the first comprehensive multi-wavelength (0.3-500 micron) photometric catalogs in all five candels fields by building on our existing 3d-hst photometric catalogs by adding fir forced photometry. but even with this powerhouse dataset, interpretation remains a challenge due to the complexities of galaxy formation physics: systematic uncertainties of a factor of two or more are common in key galaxy properties such as star formation rate and dust attenuation. the other truly unique aspect of our program is our proposed analysis with prospector, a new bayesian framework designed to use broad-band photometry to constrain high-dimensional (n>10) galaxy formation models. prospector provides self- consistent measurements of basic galaxy parameters with realistic error bars by simultaneously modeling the starlight at uv-nir wavelengths, together with light reprocessed by dust at mid and fir wavelengths. we will model the uv to fir photometry for 79,609 unique 3d-hst galaxies down to a limiting magnitude of jh10<26 kev) abmag, adding to the legacy value of the 3d-hst photometric and spectroscopic catalogs. we commit to a timely public release of our 3d-herschel photometric and stellar population synthesis value-added catalogs, supported by the successful track record of previous surveys our team has led (e.g., newfirm medium-band survey, 3d-hst). 3d-herschel enables an enormous range of cutting-edge research that, due to the planned public release of the catalogs, can be pursued by the community. in addition, our team will use these data to investigate several key open science questions. the focused science goal of our project is to perform a critical study of star formation in high redshift galaxies. given the reliable uncertainties on physical galaxy parameters prospector yields, we will combine our new statistical machinery with fir measurements to (1) place tighter constraints on sfr, testing the current picture of stellar mass growth in star-forming galaxies at cosmic noon, (2) disentangle the role of dust in star formation as a function of stellar mass and redshift, (3) identify a new population of low luminosity mir-bright active galactic nuclei at high redshifts, and (4) improve our efficiency of identifying quenched galaxies on the basis of rest-frame color selection techniques. such a comprehensive analysis will have important implications for our understanding of galaxy formation at cosmic noon, laying the foundation for future extragalactic studies with jwst and beyond. | 3d-herschel: completing the candels/3d-hst legacy with a new bayesian framework for deriving galaxy properties |
the study of orbital resonances allows for the constraint of planetary properties of compact systems. mean motion resonance occurs when two or more planets repeatedly exchange angular momentum and energy as they orbit their host star, since the planets will always conjunct at the same point in their orbits. we can predict a system's resonances by observing the orbital periods of the planets, as planets in or near mean motion resonance have period ratios that reduce to a ratio of small numbers. however, a period ratio near commensurability does not guarantee a resonance; we must study the system's dynamics and resonance angles to confirm resonance. because resonances require in-depth study to confirm, and because two-body resonances require a measurement of the eccentricity vector which is quite challenging, very few resonant pairs or chains have been confirmed. we thus remain in the era of small number statistics, not yet able to perform large population synthesis or informatics studies. to address this problem, we build a python package to find, confirm, and analyze mean motion resonances, primarily through n-body simulations. we verify our package by recovering the known resonances of kepler-80 and kepler-223. we then demonstrate the package's functionality and potential by confirming new resonances, characterizing the mass-eccentricity degeneracy of kepler-80g, and exploring the likelihood of an exterior giant planet in kepler-80 and kepler-223. we also study the formation history of k2-138 and constrain the planets' masses and orbital parameters. | new python package to find, confirm, and characterize mean motion resonances |
lambda boo-type stars are a group of late b to early f-type population i dwarfs that show mild to extreme deficiencies of iron-peak elements (up to 2 dex), but their c, n, o, and s abundances are near solar. we show that the international ultraviolet explorer (iue) spectra (1280-3200 a) of lambda bootis, 29 cygni (a "confirmed" lambda boo star), and vega (a "mild" lambda boo star) can be fit remarkably well by single-temperature synthetic spectra. we computed the full resolution synthetic ultraviolet (uv) spectrum covering the iue wavelength range using gray's stellar spectral synthesis program spectrum. to improve the synthetic spectra, we generated a grid of lte atmosphere models with the appropriate stellar parameters using atlas9 and the existing castelli and kurucz 2004 models. one of the improvements of their opacity distribution functions (odfs) is the addition to the line blanketing near 1400 a and 1600 a by the quasi-molecular absorptions of atomic hydrogen undergoing collisions with protons and other neutral hydrogen atoms. new-odf fluxes reproduce the ultraviolet observations of lambda boo stars in a more realistic way than previous computations. we also constructed our own uv line list for the relevant set of absorption features. modeling the uv line spectra of lambda boo stars allows us to confirm their published surface abundances, including cno and the iron group elements. it also provides further insight into their photospheric conditions (e.g., teff, log g, [m/h], micro turbulent velocity, etc.). about 40 percent of the published lambda boo candidates have existing iue spectra. we plan to follow this pilot study and perform uv spectral synthesis for all of them. | ultraviolet synthetic spectra for three lambda bootis stars |
hii regions are the archetypical tracers of high-mass star formation. because of their high luminosities, they can be seen across the entire galactic disk from mid-infrared to radio wavelengths. a uniformly sensitive survey of galactic hii regions would allow us to constrain the properties of galactic structure and star formation. we have cataloged over 8000 hii regions and candidates in the wise catalog of galactic hii regions (astro.phys.wvu.edu/wise), but only 2000 of these are confirmed hii regions to date.to bring us closer to a complete census of high-mass star formation regions in the milky way, we have several ongoing observational campaigns. these efforts include (1) green bank telescope radio recombination line (rrl) observations as part of the hii region discovery survey (hrds); (2) australia telescope compact array observations of southern hii region candidates in the southern hii region discovery survey (shrds); (3) green bank and gemini north telescope observations of star formation regions thought to reside at the edge of the star forming disk in the outer scutum-centaurus arm (osc); and (4) very large array continuum observations of the faintest hii region candidates in the second and third galactic quadrants.together, these observations will detect the rrl emission from all galactic hii regions with peak cm-wavelength flux densities > 60mjy, establish the outer edge of galactic high-mass star formation, and determine the number of hii regions in the galaxy. the hrds and shrds surveys have more than doubled the known population of galactic hii regions. we use the osc observations to determine the properties of high-mass star formation in the extreme outer galaxy and our vla observations to determine how many of our faint candidates are indeed hii regions. we combine the completeness limits we obtain through these hii region surveys with an hii region population synthesis model to estimate the total number of galactic hii regions. from this, we predict nearly 7000 hii regions in the milky way created by a central star of type b2 or earlier. | a complete census of the ~7000 milky way hii regions |
the field of gravitational-wave astronomy has been initiated by the recent observations of binary black hole mergers. these observations illuminate objects that are inaccessible with electromagnetic telescopes, and open inquiries as to how binary black hole systems form and merge. two possible formation channels proposed for such systems are isolated binary evolution in the galactic field and dynamical formation in star clusters. currently, the coarse localization of these gravitational-wave events cannot indicate the environment in which the binary formed, and simulations find that the mass distributions and merger rates of the aforementioned formation channels do not have an appreciable difference. however, the component spins of the black holes have the potential to unveil the formation history of the system. in this talk, i will discuss how to match measurements of the black hole component spin alignment with the spin distributions produced by population synthesis simulations of the galactic field and star clusters. using this framework, we will link black hole spin measurements to the formation channel of a merger, thus leading to a more detailed picture of their environments and origins. | discriminating formation channels of binary black hole systems with advanced ligo |
we have modeled the luminosity-displacement correlation of high-mass x-ray binaries (hmxbs) with an evolutionary population synthesis (eps) code. detailed properties including offsets of simulated hmxbs are presented under both common envelope prescriptions usually adopted (i.e., the αce formalism and the γ algorithm), and several theoretical models describing the natal kicks. we suggest that the distinct observational properties may be used as potential evidence to discriminate between models. | constraints from luminosity-displacement correlation of high-mass x-ray binaries |
surveys of star-forming galaxies are discovering more and more evidence that stellar populations produce harder ionizing emission than what standard spectral population synthesis models predict - sufficient to fully ionize helium and produce heii emission lines. especially in the era of jwst, this ionizing emission plays a key role in our understanding of stellar populations, yet its origin remains to be discovered. stars stripped of their h-rich envelopes via mass transfer or common envelope ejection are the exposed helium cores of their progenitors. therefore, they are extremely hot, and emit copious amounts of hard ionizing emission. we use analytical calculations to estimate the sizes of the h and he++ ionized bubbles that are expected to surround stripped stars, based on estimated ionizing emission rates from spectral models. for stripped stars of masses 3-7 m⊙, whose progenitors had masses of 10-20 m⊙, we find h-ionized bubbles of 1 pc, and doubly ionized he bubbles of 0.5 pc, assuming a typical hii region gas density of n=100 cm-3. as a result of continuous recombination, these bubbles should have nebular emission line luminosities of l(hβ) 1035-1037 erg/s and l(heii λ4686) 1032-1034 erg/s, meaning that these nebular emission features should be clearly visible in the optical spectra of observed stripped stars. as part of an ongoing observational survey of stars stripped in binaries in the magellanic clouds, we will take deep narrow-band imaging of stripped stars with masses of 3-8 m⊙, to test our theoretical predictions and map the nebular ionization structure surrounding stripped stars. with these observations, we aim to (1) constrain the role of stripped stars for the heii emission in star-forming galaxies, both nearby and in the early universe, and (2) provide a deeper understanding of their ionizing leakage into intergalactic space. | the he++ ionizing flux from stars stripped in binaries: from nearby ionized bubbles to escape into the intergalactic medium |
i will discuss recent efforts to quantify the evolution of x-ray binary (xrb) populations through cosmic time using the 6 ms chandra deep field-south (cdf-s) survey. the formation of xrbs is sensitive to galaxy properties like stellar age and metallicity---properties that have evolved significantly in the broader galaxy population throughout cosmic history. i will show that scaling relations between x-ray emission from low-mass xrbs (lmxbs) with stellar mass (lx/m) and high-mass xrbs (hmxbs) with star-formation rate (lx/sfr) change significantly with redshift, such that lx(lmxb)/m ~ (1+z)^2-3 and lx(hmxb)/sfr ~ (1+z). these findings are consistent with population synthesis models, which attribute the increase in lmxb and hmxb scaling relations with redshift as being due to declining host galaxy stellar ages and metallicities, respectively. these findings have important implications for the x-ray emission from young, low-metallicity galaxies at high redshift, which are likely to be more x-ray luminous per sfr and play a significant role in the heating of the intergalactic medium. | x-ray evolution of normal galaxies in the 6 ms chandra deep field-south |
the hubble ultra deep field and frontier fields have discovered over 1,500 galaxies at redshifts greater than 6. we present observational predictions for this high-redshift population, using the renaissance simulations, a suite of high-resolution cosmological simulations, that enables the correlation between key observables and the physical properties of the first galaxies in the universe. using a sample of over 3,000 resolved galaxies along with the formation of 10,000 massive population iii stars, we show that the luminosity function flattens above a uv magnitude of -14 but does not drop to zero even to our resolution limit of m_uv = -4. we find that dark matter halos below the atomic cooling limit (~10^8 m_sun) can form stars if they are chemically enriched, and they have similar mass-to-light ratios as local ultra-faint dwarfs. we utilize stellar population synthesis models, dust extinction using monte carlo methods, and photo-ionization modeling, all sourced from the simulation data, to obtain synthetic observations of the first galaxies. using these results, we will be able to constrain the following properties of the first galaxies: (1) star formation histories and stellar populations, (2) nebular emission and dust extinction, and (3) the faint end of the luminosity function. | physical and observable properties of the first galaxies |
in this work, our aim is to investigate the stellar populations and stellar ages of a subsample of far- infrared (fir) active galactic nucleus (agn) and non-agn green valley galaxies at 0.6 < z < 1.0 using the data from the cosmological evolution survey field. we used long-slit spectroscopy and derived stellar populations and stellar ages using the stellar population synthesis code 'starlight' and analysed the available lick/ids indices, such as dn4000 and hδa. we find that both fir agn and non-agn green valley galaxies are dominated by intermediate stellar populations (67 % and 53 %). the median stellar ages for agns and non-agns are logt = 8.5 and 8.4 yr, respectively. we found that majority of our sources (62 % of agns and 66 % of non-agns) could have experienced bursts and continuous star formation (sf). in addition, most of our fir agns (38 %) compared to fir non- agns (27 %) might have experienced a burst of sf more than 0.1 gyr ago. therefore, the results obtained here are in line with our previous results where we do not find that our sample of fir agns in the green valley shows signs of negative agn feedback, as has been suggested previously in optical studies. | stellar populations of a sample of far- infrared agn and non- agn green valley galaxies |
binary interactions, especially mass transfer and mergers, can strongly influence the evolution of massive stars and change their final properties and the occurrence of supernovae. here, we investigate how binary interactions affect predictions of the diffuse flux of neutrinos. by performing stellar population syntheses including prescriptions for binary interactions, we show that the resulting detection rates of the diffuse supernova neutrino background is enhanced by 15%-20% compared to estimates without binary considerations. a source of significant uncertainty arises due to the presently sparse knowledge of the evolution of rapidly rotating carbon-oxygen cores, especially those created as a result of mergers near the white dwarf to core collapse boundary. the enhancement effect may be as small as a few percent if the effects of rotation in postmerger systems are neglected, or as large as 75% if trends are extrapolated. our estimates serve to highlight that binary effects can be important. we acknowledge support from the university of tokyo young excellent researcher program. this work is supported by the u.s. department of energy office of science under award no. de-sc0020262 and nsf grants no.ast-1908960 and no.phy-1914409 and by the grants-in-aid for the scientific research of japan society for the promotion of science (jsps) kakenhi grant number (jp17h05206, jp17k14306, jp17h01130, jp17h06364, jp18h01212, 22k03630) and by the central research institute of explosive stellar phenomena (reisep) of fukuoka university and the associated project (no. 207002), and by joint institute for computational fundamental science (jicfus) as ``program for promoting researches on the supercomputer fugaku'' (toward a unified view of the universe: from large scale structures to planets). | impact of binary interactions on the diffuse supernova neutrino background |
using hard x-ray observations attainable with nustar, we are able to differentiate between the accretion states, and thus compact object types, of x-ray binaries (xrbs) in the andromeda galaxy, our nearest spiral neighbor. because they are directly connected to past and current stellar populations through binary synthesis modeling, studies of accreting black hole and neutron star populations can provide insights into the history of star formation and evolution in a galaxy, as well as the population of potentially detectable gravitational wave sources. this tells us not only about the xrb population of the m31 disk, but also provides hints about the population and distribution of xrbs in the milky way, where this type of characterization is more difficult due to the ambiguity of the spatial distribution of sources. using ten ~50ks observations of the disk of m31, we detect 19 xrb sources in the 4-25kev bandpass, and make classifications of 10 of those sources with the use of diagnostic color-rate and color-color diagrams, which separate sources into various neutron star and black hole regimes. we also investigate a candidate black hole associated with a globular cluster. we combine this with additional deeper observations of the disk to create x-ray luminosity functions for both the full (4-25kev) and hard (12-25kev) band luminosities. we find that they are consistent with the shapes of milky way xlfs by voss & ajello (2010), lutovinov (2013), and doroshenko (2014). we include fits of the xlfs of sub-populations of the characterized xrbs, including those in and outside of globular clusters and by compact object type. these classifications will be added to those already included in a deeper m31 survey of the bulge and a more limited coverage of the disk, expanding the knowledge of both the types of sources present in the population as well as their distribution throughout the galaxy. | a nustar view of the hard x-ray binary population of the m31 disk |
many hot jupiters (hjs) have been observed to have large obliquities or misalignments between the stellar spin axis and the orbital angular momentum of the planet. this observation hints that at least a portion of hjs formed through high-eccentricity migration, in which a cold jupiter is excited onto a highly eccentric orbit that circularizes over time due to tidal dissipation in the planet. one variety of high-e migration occurs when eccentricity oscillations are excited by an inclined stellar companion (von zeipel-kozai-lidov, or zkl oscillations). previous population studies of this mechanism assumed initial spin-orbit alignment. however, a star's obliquity may be significantly excited during the dissipation of its protoplanetary disk. by using a disk-excited obliquity for the initial condition of a new population synthesis, we demonstrate that the expected obliquity distribution from zkl-driven high-e migration has a peak near 90 degrees, similar to the recently-observed preponderance of perpendicular planets close to their host stars. | forming perpendicular hot jupiter systems via high-eccentricity migration |
we will present detailed constraints on the metallicity dependence of the high mass x-ray binary (hmxb) x-ray luminosity function (xlf). we analyze ~5 ms of chandra data for 55 actively star-forming galaxies at d < 30 mpc with gas-phase metallicities spanning 12 + log(o/h) ~ 7-9.2. within the galactic footprints, our sample contains a total of 1311 x-ray point sources. we construct a model that successfully characterizes the average hmxb xlf over the full metallicity range. we demonstrate that the sfr-normalized hmxb xlf shows clear trends with metallicity, changing in both shape and normalization across the full metallicity range. our model provides a revised scaling relation of integrated lx /sfr versus 12 + log(o/h) and a new characterization of its the sfr-dependent stochastic scatter. we compare our trends with past studies based on integrated galaxy emission and discuss the source populations that drive these integrated relations. our results have implications for binary population synthesis models, the nature of super-eddington accreting objects (e.g., ultraluminous x-ray sources), recent efforts to identify active galactic nucleus candidates in dwarf galaxies, and the x-ray radiation fields in the early universe during the epoch of cosmic heating at z > 10. | the metallicity dependence of the high-mass x-ray binary luminosity function |
many astrophysical systems, such as stellar binaries, require detailed numerical simulations to model. to explore the effects of uncertain parameters on final outcomes, we often use regularly spaced grids of simulations where the density and spacings are arbitrarily chosen using some combination of intuition, visual inspection, and computational cost per simulation. this grid-based approach becomes more inefficient and intractable for high dimensional studies. moreover, this approach falls short for studies relying on the accuracy of interpolation between simulation results. binary stellar evolution suffers from both of these problems, existing in a large parameter space and having highly non-linear evolution. we present a machine-learning approach to performing parameter studies using active learning and find improvements in classification and regression when using our algorithm compared to a regularly spaced grid. our algorithm uses parallel tempered mcmc and combines classification and regression metrics simultaneously for proposing new simulations. we apply it to optimize large grids of binary evolution simulations using the stellar evolution code mesa. our algorithm will be a key component in posydon, the next-generation binary population synthesis code we are actively developing. | a new active-learning algorithm for more efficient parameter space studies, paving the way toward next-generation binary population synthesis. |
the stellar initial mass function (imf) is a fundamental ingredient in stellar population synthesis models and for decades it was considered to be universal. however, the universality of the imf has been recently challenged by detailed stellar population modeling of massive early-type galaxies. i this talk i will present our recent efforts within the fornax3d collaboration to study and characterize spatially resolved imf variations in the fornax cluster. i will describe how the use of muse ifu data allows for an unprecedented view of the stellar population properties of nearby galaxies. i will present our sample-wide two-dimensional characterization of the imf variations, showing for the first time resolved imf maps for a sample of 23 galaxies. moreover, i will also show how the combination of detailed stellar population analysis and schwarzschild dynamical modelling provides insightful information about the origin of the observed imf variations. | imf variations in the fornax cluster |
binary population synthesis models suggest that x-ray emission from star-forming galaxies, consisting primarily of emission from x-ray binaries (xrbs) and the hot interstellar medium (ism), will be the dominant source of high-energy photons at high redshift. cosmological models further suggest that in the early universe x-ray emission from the first galaxies will be a critical source of heating for the intergalactic medium. however, a key uncertainty in these models is the form of the x-ray sed for high redshift galaxies. to date, studies of x-ray seds have focused largely on local, star-forming galaxies at solar metallicity, where the properties of the ism and xrb population may be quite different from those of the first galaxies, which are expected to be relatively metal-free. using a combination of chandra, xmm-newton, and nustar observations, we present new constraints on the 0.3-30 kev sed of the low-metallicity starburst galaxy vv 114. we find the x-ray sed of vv 114 is dominated by emission from ultra-luminous x-ray sources at energies greater than 1.5 kev, and has an elevated galaxy-integrated x-ray luminosity per unit star formation rate relative to higher-metallicity star-forming galaxies. we discuss our results in terms of the effect of metallicity on xrb populations and emission from the hot ism, and the importance of x-ray emission from star-forming galaxies in the early universe. | the x-ray spectral energy distribution of the low-metallicity starburst galaxy vv 114 |
the epoch of reionization and cosmic dawn, at (z>6) is the next big frontier for galaxy studies. however, understanding which sources are relevant to ionization at these great distances requires a more detailed investigation of star formation in young, very lowmetallicity regions. spectroscopic observations of (z>2) galaxies reveal high ionization emission lines similar to those also seen in a unique local sample of young, star-forming regions: he ii emitters (he iis), selected via signal-to-noise > 5.5 in he ii 4686a emission. in both the high-z galaxies and he iis, the high-ionization line ratios challenge our understanding about the energetic sources capable of producing such emission lines. specifically, stellar population synthesis models are unable to reproduce the observed line ratios, and recent studies found inconclusive evidence regarding the significance of x-ray binaries to the he ii emission. additionally, stellar winds and supernovae in young star clusters can produce fast (v_s > 1000 km/s) shocks, potentially traced by x-ray emission and capable of ionizing he ii in ~1 kpc nebulae for several myr. yet fast shocks have not been explored as yet in he iis. therefore, in this proposal, we aim to address: how important are hmxbs and/or fast shocks in he iis? can hmxbs, shocks and o/wr stars explain the he ii emission and high-ionization line ratios? to answer the first question, we will develop x-ray color diagnostics to measure the shape of the underlying sed to differentiate between hmxbs and/or fast shocks. these diagnostics will be applied to the 37 he ii regions in the chandra (and xmm) archival data, and yield x-ray luminosity distributions and limits on the he ii-ionizing flux from each source for use in the next step, the photoionization and shock modeling. in addition to the x-ray analysis, we will use galex, swift, sdss photometric, spitzer and wise archival data for the he iis to carry out uv-to-ir spectral energy distribution (sed)-fitting, using a state-of-the-art mcmc bayesian fitting code. the posterior distribution functions from the sed-fits (e.g., star formation histories, metallicities, and stellar seds), and the x-ray emission constraints (e.g., l_x and x-ray seds) will serve as inputs to the photoionization (including shock) modeling in order to estimate the stellar contribution to the ionizing budget. the novel aspect of this proposed work is that we will self-consistently model all the potential he ii-ionizing sources to determine whether the combination of these sources can account for the observed he ii emission or if additional source and/or more exotic stellar models are required. by accounting for all the ionizing emission from o/wr stars, xrbs, and fast shocks, we will explore the origin of the ionizing flux in these nearby high-ionization galaxies, particularly those responsible for heating and reionizing the early (z > 6) universe. these are the galaxies expected to be targeted by upcoming jwst observations. along with catalogs containing all measured and derived sed-fit parameters and l_x distributions for all 37 he iis, we will make the template x-ray seds for the he iis publicly available. we expect these may be useful in a number of studies, e.g., (1) modeling the x-ray emission from high-z galaxies, which is relevant to interpreting the 21-cm fluctuations measurable by next-generation interferometers, and, (2) modeling shocks in young, low-metallicity, star forming regions, which is another potential jwst science focus utilizing the mid-ir spectroscopic emission lines. | the nature of high ionization emission line galaxies near and far: a reckoning of all the energetic processes from stellar populations to shocks |
accreting white dwarfs (wds) in cataclysmic variables (cvs) are the critical component in the single degenerate pathway to type ia supernovae (sne ia), along with the double degenerate merger pathway, and they provide the standard candles of cosmology proving that the expansion rate of the universe is accelerating and the existence of dark energy. a key question is whether the accreting wd in a cv can grow in mass (to reach the chandrasekhar limit) despite the mass loss due to thousands of nova explosions in its lifetime. to answer this question, one needs to know precise cv white dwarf masses to determine the average wd mass above and below the cv period gap for comparison with mass distributions from theoretical evolutionary binary population synthesis models, and also angular momentum braking laws which drive mass transfer in cvs. accurate wd masses and reliable effective surface temperature teff's yield time-averaged accretion rates, < mdot>, which are tied to compressional heating over the thermal timescale of the accreted wd envelopes. however, the number of accreting wds with accurately known masses is severely limited. likewise, the rotational velocities and chemical abundances of elements are also severely limited. the only spectral region in which the wd can be studied is the far ultraviolet (fuv) because the disk dominates the optical. we propose to fill in poorly sampled regions of parameter space (teff/< mdot>) vs orbital period) by analyzing a series of fuse archival data, augmented with a subset of hst data, of 57 cvs for which the wd dominates the spectrum to derive the individual masses of accreting wds in cvs. we will use the newly available gaia dr2 and soon to be available gaia dr3 distances to obtain the scaled wd radii, and use the wd mass-radius law to derive robust wd masses. we will also derive the chemical abundances of accreted metals, evidence of metal overabundances and wd rotational velocities. the proposed archival analysis will represent the largest sample of cv wds ever analyzed from fuv spectra alone and a quantum leap ahead compared to all earlier analyses of the data. accreting white dwarfs in cataclysmic variables also provide crucial insights about the accretion of mass and angular momentum in all types of binaries including accreting neutron stars and black holes. this research should significantly impact the picture of the evolution of all compact binaries this adap proposal addresses the nasa strategic goals and science outcomes 3d: discover the origin, structure, evolution, and destiny of the universe, and search for earth- like planets. | the masses, rotational velocities and chemical abundances of white dwarfs in cataclysmic variables |
the α - elements abundance provides an important fossile signature in galactic archeology to trace the chemical evolution of the different disk populations. however, a precise abundance estimation in the metal-rich disk ([m/h] ≥ 0 dex) is still complex due to the presence of blended lines and the difficulty in the continuum placement. we present a detailed mg i abundance analysis for a sample of 2210 stars in the solar neighborhood, mostly dwarfs, observed by harps (eso spectrograph ; r ∼ 115000) and parametrised by the ambre project. the abundances were derived using the the automatic spectral synthesis code gauguin, analysing nine magnesium spectral lines in the optical range. applying a better continuum treatment, we observe both the chemical distinction between thin-thick disk populations and a decreasing trend in the magnesium abundance even at supersolar metallicities. a careful continuum placement in the normalization of the observed spectra could throw some light on chemodynamical relations (e.g. [mg/fe] as a good age proxy for the thin disk or the contribution of radial migration in the solar neighborhood). | precise magnesium abundances in the metal-rich disk |
we study the effects of including binary star evolution in population synthesis models. we use the hurley et al. (2002) code to compute binary star evolutionary tracks, and follow the procedure by han et al. (2002), in particular, the two 2hewd merger channel, to form ehb stars from a binary pair. we apply the resulting models to study uv excess etgs. | extreme horizontal branch stars in passively evolving early type galaxies |
there appears to be correlations between sn ia hubble diagram residuals and host galaxy mass, metallicity, and star formation history. an uncorrected bias may produce a systematic offset in cosmological measurements. global properties are the luminosity average of local environments, therefore the properties of local environments may hold stronger correlations than their global counterparts. there have been previous attempts at finding correlations between local environment properties and hubble residuals, but nothing without contention has been seen. looking at the host information from the sdss scene modeling data, we use mcmc to constrain the properties of the stellar population using flexible stellar population synthesis. we estimate the stellar population's age and star formation history at each resolution element of the galaxy image. the stellar population properties are then compared to the sn ia properties including the hubble residuals in the search for correlations that could lead to any systematic bias. | correlations between hubble residuals and mcmc estimated local stellar ages of type ia supernovae |
after light-curve calibration using the phillips relation, the distance to an individual type ia supernova (sn ia) can be inferred with ~5% precision. distance measurements enable type ia supernovae (sne ia), the highly luminous explosions of white dwarf stars, to be used as powerful tools to address two open questions: (1) is the local value of the hubble constant different from that inferred from the cosmic microwave background (cmb)? and (2) what is the nature of the dark energy responsible for the accelerating cosmic expansion? nearby sne ia yield a local value of the hubble constant (74.03 +- 1.42 km / s / mpc; sh0es team) that is in strong tension (~4.4 sigma) with that inferred from the cmb (67.4 +- 0.6 km / s / mpc; planck collaboration). if the tension represents a true difference, reconciling the inferred values may require new phenomena, such as an additional relativisitic species which could cause more rapid expansion during the radiation-dominated epoch. a mismatch, however, between the host-galaxy properties of sne ia in the cepheid calibration and hubble-flow sne samples used by the sh0es team could resolve the tension. the sh0es team calibrates the absolute luminosities of sne ia using massive, cepheid variable stars found only in star-forming galaxies. the value of h0, however, is measured using more distant sne ia found in both star-forming and passive galaxies. we have known for a decade from multiple, independent sn samples that sne ia luminosities, after calibration by light-curve shape and color, show a strong, ~0.05-0.1 magnitude dependence on the stellar mass of their host galaxies. the physical origin of this effect remains poorly understood, although it may be connected to progenitor age or metallicity, or the properties of the dust. if connected to progenitor age, then the current sn ia measurement of h0 by the sh0es team may be substantially biased. to explore whether the host-environment bias is linked to progenitor age, a pair of efforts have measured star-formation rates in the local environments of nearby sne ia. however, these either lack any correction for dust extinction, or rely on strong priors. we propose to combine archival uv-through-ir imaging from galex, sdss, panstarrs, 2mass, and wise with already acquired integral-field unit (ifu) optical spectra of the host galaxies of 94 sne ia in the hubble flow. we will also acquire ifu spectra of the cepheid host galaxies used by the sh0es team. modeling these data with population synthesis models will provide significantly improved measurements on the star-formation history, metallicity, and dust content of the environments of sne, and this effort will provide much more precise measurement of the environment-dependent sn ia calibration bias. moreover, we propose to construct samples of cepheid and hubble-flow sne with matching local explosion environment properties that will yield the first estimate of h0 without host-galaxy bias. in the next decade, the community will invest enormous resources in observing sne ia with the nancy grace roman space telescope to probe the nature of the dark energy. the roman space telescope will test dark-energy models by comparing the luminosity distances of nearby, low-redshift sne with those of a high-redshift sample whose host galaxies are comparatively metal poor and young. correcting host-dependent bias will not be possible using host-galaxy stellar mass, given the 10 gyrs of cosmic evolution across the sample. instead a more detailed model for the variation of calibrated sn ia luminosities is required for inferences from roman space telescope sn ia observations. our study of the local environments of low-redshift sne ia will yield posterior distributions for stellar population age and metallicity, and dust properties. these will enable us to develop the first model in terms of these physical properties, which will be needed to correct roman space telescope sn ia measurements. | an unsteady rung: matching samples of type ia supernovae in cepheid hosts and the hubble flow to measure h0 |
due to the light of their companions, binary cepheids might seem over-luminous and appear above the period-luminosity relation (plr). this systematic effect introduces a shift in the plr zero-point towards smaller magnitudes. we present quantitative results on the impact that companions to classical cepheids have on the plr zero-point. we use the binary population synthesis code startrack to evolve 200,000 binary systems for three metallicities $z$=0.004, 0.008, 0.02, which correspond respectively to the metallicities of the small and large magellanic clouds and the milky way. we narrow these populations down to stars which pass the filtering criteria for classical cepheids on their second and third crossing through the instability strip, and parametrize the impact of companions in form of the binarity fraction $f_{\rm bin} = 25, 50, 75, 100$. this yields a linear relation between the binarity fraction and the shift of the plr zero-point, and find that it is steeper at shorter wavelengths. | the impact of binary cepheids on the distance determinations |
we present a framework for estimating exoplanet occurrence rates by synthesizing constraints from radial velocity and transit surveys simultaneously. we employ forward modeling with approximate bayesian computation and mass-radius (m-r) relations of varying complexity to explore the population models describing these surveys, both separately and in a joint fit. using this approach, we fit a joint power-law planet distribution function of the form d2 n/(dlogp dlogm) ~ pb ma, with a break in the power law in mass at mb, to planets with orbital periods p = [25, 200] days and masses m = [2, 50] mearth. we find that the m-r relation from otegi et al. (2020), which splits rocky and volatile-rich planets into two populations that overlap in mass, allows us to find a model that is simultaneously consistent with both types of surveys. our joint fit gives mb = 21.6 (-3.2, +2.5) mearth, nearly a factor of three higher than the mass break from transit-only considerations and an m-r relation without such an overlap. the corresponding break in the planet-star mass ratio of qb ~ 7×10-5 may be consistent with microlensing studies (qb ~ 6×10-5 - 2×10-4). given that the microlensing detection method probes orbits far outside the kepler parameter space, this finding indicates a similar most common mass both within and beyond the snow line. the joint fit also requires that a fraction of frocky = 0.63 (-0.04, +0.04) planets in the overlap region belong to the rocky population. our results strongly suggest that future m-r relations should account for a mixture of distinct types of planets in order to describe the observed planet population. | combining transit and rv: a synthesized population model |
we request a 190 ks chandra acis-i observation of the spiral galaxy m96 to study the role of dynamics at local and global (galaxy) scales in x-ray binary (xrb) formation and evolution. we will determine if there is an enhancement in the xrb population on local scales per stellar mass and star formation rate. we will leverage the exquisite hst archival multi-band coverage of m96 to assess whether xrb populations are dynamically scattered beyond the stellar population distributions. in combination with recently updated population synthesis modeling, we will use multiwavelength data to discern the nature of any enhancements/scattering in the xrb population and study the age of stellar populations surrounding x-ray binaries and identify counterparts. | x-ray binaries 1 gyr after a collision: a chandra study of m96 (ngc 3368) |
carbon, oxygen and iron are among the most interesting elements in astrophysics. they play an important role as diagnostics of stellar populations and galactic chemical evolution. here, we present the trends of [c/h], [c/fe] and [c/mg] vs [fe/h] and [mg/h] for a large sample of about 2000 fgk dwarfs in the solar neighborhood in order to better understanding the origin of carbon and the relative importance of massive and low-to-intermediate mass stars in releasing carbon into the cosmos. in particular we use the high resolution uves spectra (uvl spectra, r~47,000) in the setup centered at 580 nm extracted from the gaia-eso survey (ges, gilmore+ 2012, randich+ 2013) idr5 release, to estimate the carbon abundances by using a spectrum synthesis technique by comparing observed spectra with "ad hoc" synthetic ones based on intrigoss (inaf-trieste grid of synthetic spectra; franchini+2018). after a cross-match with gaia dr2 archive to get proper motion and distances, we computed galactic velocities, stellar orbits and ages via a bayesian approach. sub-samples representative of the thin and the thick galactic disks, respectively, are defined by adopting three different criteria: chemical criterium (i.e. position of the stars in the [mg/fe]-[fe/h] plane), kinematical criterium (such as the ones from bensby+ 2003, 2014) or by inspecting their individual galactic orbits. the behavior of [c/h], [c/fe] and [c/mg] vs [fe/h], and age all suggest that c is primarily produced by massive stars with a contribution from low-mass stars. by using uvu ges spectra (r~54,000), oxygen abundance based on a similar spectral synthesis technique as for the c abundance but in the [oi] (630.03nm) region is planned. | carbon in the galactic disks |
binary stars are ubiquitous in the universe. measuring binary fractions and their variations in different stellar populations has important implications in the studies of a number of research fields including star formation and evolution, gravitational wave detections, galactic structure and stellar population synthesis. taking advantage of large scale surveys, statistical methods have been developed to measure binary fractions in the galaxy, but the existing studies are mainly for main-sequence stars. red giant stars and red clump stars in the late stages of stellar evolution, are ideal tracers to probe properties and evolution of binary stars. however, measurements of binary fractions for giant stars are very rarely reported. in this work, based on a large sample of red giant stars and red clumps from the 2nd value-added catalog of lamost spectroscopic survey of the galactic anti-center, we investigate the binary fractions and their variations with stellar evolution stages and metallicities, using the method of distribution of ∆rvmax. we find that there is a strong correlation between ∆rvmax and their evolution stage. the later stages the evolution is in, the lower value the binary fraction has. and the binary fraction decreases as metallicity increases. our simulation shows that binary fraction of giant stars during their main-sequence stage is about (38±2)%, slightly higher but consistent with the result of badenes et al.(2018) based on the apogee dr13. a number of 46 candidates of compact binary systems are also reported. | binary fractions based on the lamost rgb and rc data |
we describe a homogeneous catalog compilation of common proper motion stars based on gaiadr2. a preliminary list of all pairs of stars within the radius of 100pc around the sun with a separation less than a parsec was compiled. also, a subset of comoving pairs, wide binary stars, was selected. the clusters and systems with multiplicity larger than 2 were excluded from consideration. the resulting catalog contains 10358 pairs of stars. the catalog selectivity function was estimated by comparison with a set of randomly selected field stars and with a model sample obtained by population synthesis. the estimates of the star masses in the catalogued objects, both components of which belong to the main-sequence, show an excess of ''twins'', composed by stars with similar masses. this excess decreases with increasing separation between components. it is shown that such an effect cannot be a consequence of the selectivity function only and does not appear in the model where star formation of similar masses is not artificially preferred. the article is based on the talk presented at the conference ''astrometry yesterday, today, tomorrow'' (sternberg astronomical institute of the moscow state university, october 14 - 16, 2019). (1 data file). | vizier online data catalog: binary star pop. with common proper motion (sapozhnikov+, 2020) |
we present state of the art population synthesis models that improve on the following aspects with respect to most available models. (a) treatment of the uv spectral range, including new evolutionary tracks and updated treatment of the ionizing radiation emitted by the stellar population. (b) improved treatment of tp-agb stars that dominate the nir spectral range. the number of these stars present in a stellar population has been calibrated carefully by comparison with observations of the lmc/smc, and the spectra assigned to these stars include both the stellar emission and the emission from circumstellar dust. (c) definition of new diagnostics to characterize the combined stellar and nebular emission and the cold ism in galaxies. models are available in a wide range of metallicity, from z = 0 to z = 0.06, and are ready to use to interpret the spectra of galaxies of any age at low and high redshift. applications will be discussed. | state of the art population synthesis models |
the thick disc is a major component of the milky way but its epoch of formation and characteristics are still not yet well constrained. the besançon galaxy model (bgm, robin et al. 2003) is a population synthesis model based on a scenario of formation and evolution of the galaxy, a star formation history, and a set of stellar evolution models. thanks to lagarde et al. (2017), new evolutionary tracks have been introduced into the besancon galaxy model (starevol, lagarde et al. 2012) to provide global asteroseismic and surface chemical properties along the evolutionary stages. this updated galaxy model will allow us to constrain the thick disc structure and history using the markov chain monte carlo fitting method (mcmc). we show preliminary results applying this mcmc method on the 2mass photometric survey. | study of the thick disc of the milky way from a population synthesis model |
the formation of blue straggler stars (bsss), commonly categorized as stars bluer and brighter than the main sequence turnoff, has puzzled astronomers since their first detection over sixty years ago. the well-studied bss population of the old (7 gyr) open cluster ngc 188 has the potential to settle outstanding issues surrounding the frequency of different bss formation mechanisms. ngc 188 contains 21 bsss: 15 long-period single-lined binaries, two short-period double-lined binaries, and four non-velocity variables. we present results of the hubble space telescope far-ultraviolet (fuv) acs/sbc survey of the ngc 188 bss population. this survey aims to detect white dwarf (wd) companions of bsss that are indicative of a mass-transfer formation history. we directly detect fuv excesses consistent with four hot wd companions (teff ≥ 12,000 k). we infer the presence of three additional wd companions with temperatures between 11,000-12,000 k. since wds cool as they age, these results indicate that seven bsss formed through mass transfer within the past 400 myr. these wd detections set a lower limit mass-transfer formation frequency of 33%. after taking into account other potential formation mechanisms we conclude that 14 long-period binary bsss likely formed through mass transfer, setting a total ngc 188 bss mass-transfer formation frequency of 67%. comparing these results to a sophisticated n-body model of ngc 188 implies that binary population synthesis models underproduce mass transfer products, and the parameterization of stable mass transfer may need to be revisited. finally, when comparing the optical cmd position of young bsss to the zero-age main sequence (zams), we find that distance from the zams is not necessarily equivalent to bss age. one must use caution before using standard single-star isochrones to age luminous bsss.support for program number 12492 was provided by nasa through a grant from the space telescope science institute, which is operated by the association of universities for research in astronomy, incorporated, under nasa contract nas5-26555. this work was funded by the national science foundation grant ast-0908082 to the university of wisconsin-madison. | the mass-transfer formation frequency of blue straggler stars in the old open cluster ngc 188 |
the stellar classification code galclassify is a stand-alone version of galaxia (ascl:1101.007). it classifies and generates a synthetic population for each star using input containing observables in a fixed format rather than using a precomputed population over a large field. it is suitable for individual stellar classifications, but slow if you want to classify large samples of stars. | galclassify: stellar classifications using a galactic population synthesis model |
the galex ultraviolet (uv) sky surveys are uniquely sensitive to classes of astrophysical objects such as hot stars, star-forming galaxies, and z < 2.4 qsos. clean catalogs of uv sources (guvcat) were recently constructed (bianchi et al. 2017) with added flags to facilitate science applications including e.g., selection of uv-samples, maps of source density, luminosity functions, and matching with other databases. the proposed project leverages guvcat and greatly augments its scope and usefulness. by matching the uv-source catalog to corollary databases at other wavelengths, we will classify and characterize both galactic and extra-galactic uv sources and extract samples of hot white dwarfs (wd) for our science project. we will publicly deliver matched catalogs of uv sources with the latest sdss release (dr14), gaia dr2, panstarrs 3à ps1 (providing an overlap area about 3.6x that of sdss, and some indication of variability), gsc-ii, 2mass,... we leverage previous recipes and scripts for effective, fast production of the matched catalogs and useful science tags. the uv-source catalogs uniquely enable identification and characterization of objects elusive in other surveys, such as hot white dwarfs (wd), both single and in binary systems with a cooler, optically-brighter companion. hot wds are elusive at all wavelengths except the uv, owing to their very high temperatures to which optical colors are insensitive, and low optical luminosities. from the uv-matched catalogs we will extract an unbiased census of milky way hot white dwarfs. we expect an increase by two orders of magnitudes over known samples, but, more important, to extend the parameter space to the high t eff , high-mass regime, the most elusive and most relevant for the yield of chemical elements, and to include hot-wd in binaries in which the hot component is undetectable without uv data. our survey can reach small, hot wds all the way out to the halo along low-extinction sight-lines. we will characterize the uvselected hot wds with analysis of their observed analysis will provide sorely needed constraints to post-agb stellar evolution, it will clarify still uncertain aspects such as the initial-final mass relation, indispensable for understanding the yield of chemical elements from intermediate-mass stars and the chemical evolution of galaxies. our project will also provide statistics on the fraction and parameter distribution of binaries in evolved stages, complementing the abundant recent studies of binarity for stars in early evolutionary phases with information on as-yet unexplored mass ranges and late evolutionary phases. the results will inform future stellar evolution models, which in turn underpin population synthesis and chemical evolution models. the sed analysis of individual sources and the global comparison with milky way models will also yield a map of the milky way dust extinction, to which uv data are also very sensitive. the project is timely given the readiness of our uvsource catalog and complementary data, and the recent release of gaia dr2, which provides distances for most of the uv-selected stellar objects and enables us to derive 3d catalogs of this otherwise elusive stellar population. the combination allows us to build precise post-agb h-r diagrams, enabling a major step forward towards understanding post-agb evolution and binary evolution. uv-source catalogs with matched corollary data, source classification and inferred parameters, as well as analysis tools and models computed for this project, will be publicly released on the pi web site, and on mast and simbad/vizier public databases, from which they will remain permanently and widely accessible at no cost to this project. | new constraints for stellar evolution from the galex ultraviolet source catalogs |
mass loss and variability are two linked, fundamental properties of evolved stars. in this paper, i review our current understanding of these processes, with a particular focus on how observations and models are used to constrain reliable mass loss prescriptions for stellar evolution and population synthesis models. | mass loss and variability in evolved stars |
observations of the rotation curves of large galaxies like the milky way have firmly established that there is a massive unseen halo influencing the dynamics of the luminous stellar population. dark matter searches, coupled with computational models of galaxy assembly and growth, have attempted to constrain the nature of this dark halo, but gravitational lensing studies have failed to fully explain the mass observed. across the gravitational wave spectrum, there are promising observations to be made that can probe the dark halo, particularly if the dark matter emits gravitational waves. in the vicinity of the milky way and the nearby universe, lisa will be the pre-eminent gravitational wave observatory for searching for stellar-mass gravitational wave sources. in the context of binary systems, lisa will be sensitive to ultra-compact binary systems with kilosecond astrophysical periods across the entire milky way, a scale commensurate with probing the spherical halo for stellar-mass binaries that can contribute to the dark matter halo profile. this paper considers the observable gravitational-wave signature of modeled white dwarf populations in the dark halo in the parameter space that is currently unconstrained by previous searches for clumpy halo dark matter. population synthesis using cosmic is utilized to consider a wide range of models to illustrate the constraining power of lisa observations. | lisa implications of white dwarf binaries in the milky way dark matter halo |
the planets forming in the accretion disk of young stars are yet unseen by the new generation of instruments whereas their study is crucial for understanding the evolution of inner planetary systems. analysis of stellar spectra provides good proxies for studying and detecting such planetary systems. however, disentangling the signal due to the planets and to the star in stellar spectra could be cumbersome. therefore, detailed spectral synthesis in realistic simulations of star-planets-disk system are crucial for detecting planets and studying their evolution within the accretion region. this spectral synthesis requires the solution of a set of statistical equilibrium equations for the atomic species of interest. the cornerstone of non equilibrium lines formation is obtaining the levels populations pertaining to the atom for which the lines belong to. in this poster, i present how the non-lte problem for multi-level atomic systems is implemented and solved in the monte-carlo code mcfost. | non-lte atomic line formation in accretion disk around young stars |
binary neutron star mergers (nsms) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. however, modeling nsm outflows'from the total ejecta masses to their elemental yields'depends on the unknown nuclear equation of state (eos) that governs neutron-star structure. in this work, we derive a phenomenological eos by assuming that nsms are the dominant sources of the heavy-element material in metal-poor stars that display r-process abundance patterns. we start with a population synthesis model to obtain a set of merging neutron-star binaries and calculate their eos-dependent elemental yields. we then find the eos such that the yields calculated from these mergers reproduces the abundances of r-process elements derived from observations of metal-poor stars. this eos therefore represents our best prediction for what neutron stars should look like if they are to be the main progenitors of r-process material in the early universe. we present this eos and comment on how it compares to both existing eos models and results from the neutron star interior composition explorer. | a nuclear equation of state inferred from stellar r-process abundances |
we propose a major transformation of the evolutionary synthesis code starburst99 to meet the needs of the community in the coming decade. a new generation of stellar evolution models optimized for (but not limited to) massive stars has been developed. these models account for the latest progress in nuclear physics, convective processes, differential rotation, and mass loss. they cover the full abundance range from super-solar to metal-free. at the same time, we made enormous strides in exploring the stellar surfaces. the hst ullyses program provides the most complete and highest quality ultraviolet spectral library of hot, massive stars. in conjunction with ancillary optical-near-infrared spectra obtained at eso/vlt and state-of-the-art non-lte, blanketed, spherical atmospheres, a new generation of stellar-population models can be developed with the synthesis code starburst99. these models will allow us to understand the processes in star-forming galaxies in the local universe studied, e.g., by the hst treasury program classy, as well as in galaxies close to the epoch of reionization discovered by jwst. specific questions to be addressed include (i) quantifying the effects of dust attenuation on the spectral energy distribution, (ii) probing galaxy-scale outflows by providing stellar spectral templates, (iii) providing models for the hardness of the ionizing radiation fields, (iv) exploring the shape of the uppermost stellar initial mass function, and (v) detecting shortcomings in stellar models. we will also convert the current starburst99 unix solaris code into a linux compatible distribution and migrate the software and the interface to a new, user-friendly platform. | feasting on the riches of odysseus' voyage |
the aim of this study was to investigate the effects of progestins on the sex differentiation of zebrafish by measuring the sex ratio and transcriptions of genes related to sex differentiation (amh, dmrt1, figa, sox9a and sox9b genes) as well as sex hormone levels and transcriptional expression profiles along the hypothalamic-pituitary-gonadal (hpg) and hypothalamic-pituitary-adrenal (hpa) axes in juvenile zebrafish. exposure of zebrafish to 4, 33, 63 ng l-1 progesterone (p4) or 4, 34, 77 ng l-1 norgestrel (ngt) started at 20 days post fertilization (dpf) and ended at 60 dpf. the results showed that exposure to p4 caused a significant increase in proportion of females as well as significant down-regulation of amh gene and up-regulation of figa at a concentration of 63 ng l-1. however, the shift in the sex ratio toward males was observed following exposure to 34 and 77 ng l-1 ngt, which came along with the significant induction of dmrt1 gene and inhibition of figa gene. the sex hormones in exposed fish were measured with estrone being detected only in the fish exposed to the highest p4 concentration; whereas estradiol and androstenedione were detected only in the fish of the control and lowest ngt concentration. furthermore, the increase in females was associated with the significant up-regulation of several key genes controlling the synthesis of sex hormones (i.e., cyp17, cyp19a1a and hsd3b) following exposure to 63 ng l-1 p4 whereas the significant down-regulation of cyp11a1, cyp17, cyp19a1a and hsd3b genes was observed in the male-biased populations caused by 34 and 77 ng l-1 ngt. the overall results imply that both p4 and ngt could significantly affect sex differentiation in zebrafish, and that changes may be reflected by altered sex hormone levels and transcriptional expression profiles of genes related to synthesis of sex hormones. | long-term exposure to environmentally relevant concentrations of progesterone and norgestrel affects sex differentiation in zebrafish (danio rerio) |
libraries of stellar spectra find a plethora of applications, from photometric calibration to stellar population synthesis. we present low resolution spectra obtained with stis (space telescope imaging spectrograph) of 40 stars spanning 0.2 to 1.0 micrometers in spectral coverage. the stars include normal o-type stars, helium-burning stars, and post-asymptotic giant branch (pagb) stars. observations through three low resolution gratings, g230lb, g430l, and g750l enabled coverage of the wide wavelength interval. cosmic ray hits, fringing in the red, and scattered light corrections were applied. cross-correlation was used to bring the spectra to a common, final, zero velocity wavelength scale. finally, synthetic stellar spectra were used to estimate line of sight dust extinction to each star, and a five-parameter dust extinction model was fit, or a one-parameter fit in the case of low extinction. these spectra dovetail with the similar next generation stellar library (ngsl) spectra, extending the ngsl's coverage of stellar parameters, and extending to helium burning stars and stars that do not fuse. the fitted dust extinction model showed considerable variation from star to star, indicating variations in dust properties for different lines of sight. interstellar absorption lines are present in most stars, notably mg ii. the spectra are available at mast (mikulski archive for space telescopes) and the cds (centre de données astronomiques de strasbourg). support for this work was provided by nasa through grant number hst-go-14141.001-a from the space telescope science institute, which is operated by aura, inc., under nasa contract nas 5-26555. | spectral library of hot stars with hubble space telescope |
x-ray binary systems (xrbs) in the mw can exist in several different accretion states, and many have been found to vary along specific tracks on intensity-color diagrams. observationally measuring the distributions of these accretion states in a variety of environments can aid in population synthesis modeling and ultimately help us understand the formation and evolution of xrbs and their compact object components (i.e., black holes and neutron stars). recent innovative studies with nustar have demonstrated the utility of color-color and intensity-color diagrams in differentiating between xrb accretion states in extragalactic environments (ngc 253, m83, and m31). the key to nustar’s success is its sensitivity above »10kev, where spectral differences between accretion states are most pronounced. however, due to the relatively low spatial resolution and large background of nustar, the constraints from these diagrams is limited to only bright sources in nearby galaxies. in this poster, we present evidence that xmm-newton observations of m83 in the 4.0-12.0 kev range can be used to create similar color-intensity and color-color diagrams and therefore differentiate between these accretion states. we will further discuss plans to leverage xmm-newton’s vast archive and 17-year baseline to dramatically expand studies of accretion state distributions and state transitions for xrb populations in extragalactic environments. | measuring x-ray binary accretion state distributions in extragalactic environments using xmm-newton |
the thermally-pulsing asymptotic giant branch (tp-agb) phase is one of the most uncertain evolutionary phase of low- and intermediate-mass stars. the classical calibration based on magellanic clouds (mcs) clusters has proved to be unsuitable for other galaxies and the overall contribution of tp-agb stars to the integrated light of galaxies is still a matter of debate. the high-quality observations of resolved populations in the mcs offer a unique opportunity to extend and enhance the calibration of this phase. we constrain the key uncertain parameters by comparing observed star counts, luminosity functions and color distributions of the tp-agb population in the small magellanic cloud (smc) with those computed through the stellar population synthesis code trilegal, which includes the latest tp-agb evolutionary tracks from the colibri code. the strength of our approach is represented by the detailed space-resolved star formation history of the smc, derived from the deep near-infrared photometry of the vista survey of the mcs. | calibrating the tp-agb phase through resolved stellar populations in the small magellanic cloud |
python bindings to charlie conroy's flexible stellar population synthesis (fsps) fortran code | dfm/python-fsps: python-fsps v0.4.5rc1 |
dust is a key component of the interstellar medium; however, the dominant channels of dust production throughout cosmic time are uncertain. in this talk, i will discuss our analysis revisiting the impact of dust formation in the colliding winds of carbon-rich wolf-rayet (wc) binaries. by conducting a dust sed analysis of 19 galactic wc dust-producers, we find that these sources exhibit a wide range of dust production rates (dpr) from ~10-10 - ~10-5 msun yr-1. for wc systems with a known orbital period we find a decreasing dpr with increasing orbital period, which highlights the impact on the binary orbital parameters on their dust formation. we incorporate dust production into the binary population and spectral synthesis (bpass) models at a range of metallicities to study the relative dust contribution from wc binaries amongst other leading dust input sources such as agb and rsg stars and supernova ejecta. for a constant star formation history, our results suggest that wc binaries dominate the dust production over agbs and rsgs. wc binaries notably present an important dust source if supernovae are net destroyers of dust. lastly, i will discuss our planned jwst dd-ers program to investigate the formation and chemical composition of dust formed in the archetypal periodic wc binary system wr140. | revisiting the impact of dust production from wolf-rayet binaries |
the analysis is carried out using high-resolution (r=81000) and high signal-to-noise ratio (800<s/n/pixel<3400) spectrum, in the wavelength range 3700-10475, obtained with a seven-hour exposure time, using the espadons at the cfht. the calculations in lte were performed with the osmarcs 1d atmospheric model and the spectrum synthesis code turbospectrum, while the analysis in nlte is based on the multi code. we present lte abundances for 26 elements, and nlte calculations for the species ci, oi, nai, mgi, ali, ki, cai, srii, and baii lines. (3 data files). | vizier online data catalog: abundance analysis of hd 140283 (siqueira-mello+, 2015) |
the formation and evolution of local brightest cluster galaxies (bcgs) is investigated by comparing the stellar populations and dynamics of the galaxy, the intracluster light (icl), and nearby companions. integral spectroscopic data of 23 local bcgs observed out to 4 re is collected. stellar population synthesis codes are used to determine the age, metallicity, velocity, and velocity dispersion of stars within regions such as the galaxy core, the intracluster light, and the nearby companions, when available. the icl spectra are best modeled with populations that are younger and less metal-rich than those of the bcg cores. the velocity dispersion profile is seen to be rising or flat in most of the sample (17/23), and those with rising values reach the value of the host cluster's velocity dispersion in several cases. thirty-six companions to the 23 bcg are identified, 83+5-11% have dynamical friction timescales less than 0.5 gyr, and have ≥ 80% probability of bound to their respective bcg. brighter bcgs are found to have fewer companions. the results are consistent with the idea that the bcg cores and inner regions formed quickly and long ago, with the outer regions and icl forming more recently, and continuing to assemble through minor merging. | clocking the formation of today's largest galaxies: intracluster light and nearby companions |
the lyman continuum (lyc = hydrogen-ionizing radiation at wavelengths < 912 ang) of galaxies plays a fundamental role in determining the physical and observational properties of the ism and igm, including cosmic reionization. yet it is basically inaccessible to direct observations, and one therefore heavily relies on theoretical, yet untested predictions from synthesis models. furthermore the ionizing spectra differ significantly between different models, with important implications on widely used emission line diagnostics and other observables. we here propose to observe for the first time the shape of the ionizing continuum of star-forming galaxies over a wide spectral range, from ~550 to 912 angstroem. this can be achieved with cos by targeting lyc emitters at z~0.8-1. the observations will measure stellar and nebular features in the lyc, and thus provide direct constraints for stellar population models in this generally inaccessible part of the spectrum. the proposed observations will provide unique insight on the hardness of the ionizing spectra of star-forming galaxies, with numerous possible implications on our understanding of the emission line properties of distant galaxies, sources of cosmic reionization, emission line diagnostics, and related topics. | uncovering the lyman continuum sed of star-forming galaxies from550 to 912 angstroem |
population synthesis models predict the existence of large numbers of wide binaries for which the end state is a wide double white dwarf (dwd) system. i discuss the methods i used to find these systems in the sloan digital sky survey, which ultimately increased the known number of candidate binaries from ~45 to 112. i then describe an observational campaign to obtain spectra of the bright (g < 18 mag) dwd candidates; fitting these to synthetic models provided masses and cooling ages for the white dwarfs in these pairs. because these binaries are coeval but evolve as independent stars, they are unique stellar laboratories. in particular, i present a method i applied to this wide dwd sample to place new constraints on the initial-final mass relation, which relates a given main-sequence star to the mass of the white dwarf it will produce. our analysis avoids some of the difficult-to-model systematics introduced by other methods, generating independent and complementary constraints. | constraining the initial-final mass relation with wide double white dwarfs |
the origin of magnetic fields in isolated and binary white dwarfs has been investigated in a series of recent papers. one proposal is that magnetic fields are generated through an alpha-omega dynamo during common envelope evolution. here we present population synthesis calculations showing that this hypothesis is supported by observations of magnetic binaries. | the magnetic fields of white dwarfs in cataclysmic variables |
the thick disc is a major component of the milky way but, its characteristics and history are still not yet well constrained. the use of a population synthesis model, based on a scenario of formation and evolution of the galaxy, a star formation history, and a set of stellar evolution models, is a way to improve the constraints on this population. for this reason, we use the besançon galaxy model (bgm, te{robin3}). this model in constant evolution has been, thanks to te{lagarde7}, implemented with new evolutionary tracks (starevol, te{lagarde}) to provide global asteroseismic and surface chemical properties along the evolutionary stages. thanks to this updated galaxy model and the markov chain monte carlo fitting method (mcmc) we will be able to constrain the thick disc structure and history. we show preliminary results applying this mcmc method to analyse the 2mass photometric survey. | study of the structure and formation of the thick disc from stellar population modelling |
we present [fe/h] and [na/fe] abundances for 35 asymptotic giant branch (agb) stars in the galactic globular cluster 47 tucanae, using high resolution spectra obtained with the michigan/magellan fiber system (m2fs) spectrograph on the magellan-clay 6.5m telescope. the abundances and model atmosphere parameters were derived using standard equivalent width and spectrum synthesis techniques. we find an average [fe/h]=-0.68, in agreement with previous literature estimates. for sodium, we compare the [na/fe] distributions between the agb stars measured here and a similar rgb sample published previously. although the average [na/fe] abundance is lower in the agb sample, we do not find this difference to be significant. additionally, the dispersion and inter quartile range of [na/fe] are similar between the agb and rgb samples, and we argue that the distribution of na-poor and na-rich stars is equivalent between the two data sets. the data presented here offer a counter example to the case of ngc 6752, which has recently been found to exhibit a drastically different [na/fe] distribution between its agb and rgb populations. the 47 tuc data suggest that the rgb [na/fe] abundance alone is insufficient for predicting if a star will ascend the agb, and additional information, such as horizontal branch morphology or metallicity, must also be taken into account. | comparing agb and rgb sodium abundances in the globular cluster 47 tucanae (ngc 104) |
the increased interest that sparks the search for exoplanets over the last few years has resulted in the design of high-resolution spectrographs such as carmenes, installed at the 3.5 m telescope in the calar alto observatory in almería (spain), in order to improve the radial-velocity measurements and, thus, to help detect earth-type planets around stars other than the sun. among these, m dwarfs constitute ideal candidates given their ubiquity in the solar neighbourhood, low temperatures, and low masses, which favours detections by both the radial-velocity and transit techniques. in this context, the determination of stellar atmospheric parameters is an essential step to charac- terise exoplanet systems and to shed light on their formation and evolution by means of compared planetology, which tries to link the properties of exoplanets with those of their host stars. in particular, the carmenes instrument, by virtue of its high resolution and simultaneous spectral coverage in the optical and near-infrared wavelength regions, not only provides key information for the analysis of cool stars, but it also opens up the opportunity to revisit classical techniques, such as the equivalent width method and spectral synthesis, to assess the impact of the near-infrared region on the computation of stellar parameters. the prime objective of the phd thesis is the photospheric characterisation of fgkm-type stars observed with the carmenes instrument in the context of its stellar library and guaranteed time observations programme. for this aim, the equivalent width method and spectral synthesis technique were employed on high-resolution, high-s/n spectra in the optical (r = 94600, λ ∼ 5200–9600 å) and the near-infrared (r = 80400, λ ∼ 9600–17100 å). spectra of fgk-type stars were characterised with the stepar code as an implementation of the equivalent width method, while m-dwarf spectra were analysed with the steparsyn code, a bayesian implementation of spectral synthesis following a markov chain monte carlo approach. both codes are well suited for the precise computation of the stellar atmospheric parameters of late-type stars, namely the effective temperature teff, the surface gravity log g, and the stellar metallicity [m/h], where [fe/h] is often used as a proxy. as an integral part of the study, different model atmospheres, including marcs, bt-settl, and phoenix-aces, and radiative transfer codes, including turbospectrum and moog, were employed. the analysis resulted in homogenised sets of stellar parameters for 65 fgk-type stars and 343 m dwarfs observed with carmenes. the inclusion of the near-infrared region led to the selection of 653 fe i and 23 fe ii lines useful for the equivalent width method, which more than doubles the number of lines typically used in classical studies restricted to the optical region. in the same way, 75 magnetically-insensitive ti i and fe i lines were selected for the analysis of m dwarfs with spectral synthesis, along with the tio γ and ɛ bands. to avoid any degeneracy in the m-dwarf parameter spa- ce, prior probability distributions in effective temperature and surface gravity were imposed, based on the comprehensive, multi-band photometric data available for the sample. furthermore, with the aim of serving as a reference point to validate the spectroscopic determinations of the stellar atmospheric parameters, several subsets of stars included in the samples have been highlighted, including the gaia benchmark stars, fgk+m and m+m binary systems, and m dwarfs with interferometrically measured angular diameters. the stepar code has proved to be a robust implementation of the equivalent width method for the analysis of fgk-type stars with spectral types between f6 and k4. as additional limitations of the method, it is required that the spectra have a signal-to-noise ratio above 20 and a spectral resolution greater than 30 000 to prevent a suboptimal placement of the continuum level, allow for the resolution of spectral lines and correctly measure the equivalent widths of the lines. for the same reason, doubled-lined spectroscopic binaries and stars with rotational velocities greater than 15 km s‑1 have to be excluded. close examination of the impact of the near-infrared fe i and fe ii lines on parameter determinations in fgk-type stars from the carmenes stellar library has revealed a broader teff scale that appears to be linked to a higher sensitivity of these near-infrared lines to teff. however, the scarcity of fe ii lines in the near-infrared region prevented an analysis relying on this window alone. in gene- ral, there is good agreement with the parameter determinations from the literature, particularly with the 14 gaia benchmark stars included in the sample. the methodology used for the analysis of the m dwarfs is best suited in the range from m0.0 v to m7.0 v, but not beyond, due to the scarcity of ti i and fe i lines and the insensitivity of the tio bands to teff as a result of dust formation. even though the derived teff scale is in good agreement with the literature, large discrepancies in the [fe/h] scales arise, probably as a result of the different methodologies considered. nonetheless, there is agreement with the metallicity distribution of fgk- type stars in the solar neighbourhood and good correlation with the kinematic membership of the targets in the galactic populations. lastly, excellent agreement in teff is found for m dwarfs with interferometric angular diameter measurements, as well as in [fe/h] between the components in the fgk+m and m+m systems included in the m-dwarf sample. | spectroscopy of fgkm-type stars for the scientific exploitation of the carmenes exoplanet search / espectroscopía de estrellas fgkm para la explotación científica de la búsqueda de exoplanetas con carmenes |
massive stars are powerful sources of ionizing radiation and kinetic energy that shape the interstellar medium and the uv spectral morphology of host galaxies. their life-averaged feedback and their end as sn/grb make them fundamental ingredients to galactic chemodynamical evolution models and population synthesis codes. feedback from massive stars is not constant along the history of the universe: their evolution and pre-sn core size is determined to a large extent by radiation-driven winds, and these depend strongly on metallicity. in a universe of ever-increasing metal content, metal-poor massive stars and their winds are a central piece to study star-forming galaxies in past cosmic epochs. the hst archive, supported by the ullyses ddt program, stores a large collection of uv spectra of massive stars in the milky way and the magellanic clouds that will enable a thorough characterization of radiation-driven winds down to metallicities of 1/5 zsun. yet, this value is not representative of the composition of the universe earlier than redshift=1, nor at such an important landmark as the peak of the cosmic star formation history (redshift~2). we request hst-cos uv spectroscopy of 4 ob-type stars in sextans a, with 1/10 zsun metallicity, akin to blue massive stars of that period. the selection has been crafted to cover uncharted parameter space in the upper hr-diagram, where radiation-driven winds are expected to be significant. quantitative analysis of this sample together with archival data will allow us to characterize radiation-driven winds at very low metallicity and to produce the first prescriptions to be implemented into models of stellar evolution. | the winds of massive stars at the peak of the star formation history of the universe |
type ia supernovae are good standardizable candles, but their reliability as distance indicators may be limited by the imprint of their galactic origins on supernova progenitors. to investigate the connection between supernovae and their host characteristics, we have developed an improved method to estimate the stellar population age and apply it to the integrated light of the host as well as the local environment around the site of the supernova. we use a bayesian method to estimate the star-formation history of a supernova's environment by matching observed global and local spectral energy distributions (seds) to a synthesized stellar population. we apply an mcmc technique to estimate the most probable star-formation history for a given sed, its mass weighted age, and the corresponding uncertainties. applying this age estimator to a large sample of supernovae from the sloan digital sky survey ii, we find a 0.108 ± 0.035 mag 'step' in the average hubble residual at a stellar age of ~7 gyr; it is nearly twice the size of the currently popular mass step correction. this age step is seen in both the local environment age and the average age of the host galaxy at a significance of 3σ. we then apply a principal component analysis on the salt2 parameters, host stellar mass, and local environment age. we find that a new parameter, pc1, consisting of a linear combination of stretch, host stellar mass, and local age, shows a very significant (>6σ) correlation with hubble residuals. this strong correlation between hubble residuals and environment may affect the accuracy of precision cosmological measurements such as current h0 measurements and future measurements of dark energy with wfirst. | the influence of environment age and host mass on type ia supernova light curves |
most of the physical processes driving the tp-agb evolution are not yet fully understood and they need to be modelled with parameterised descriptions. we present the results of the on-going calibration of the tp-agb phase based on a complete sample of agb stars in the small magellanic cloud (sage-smc survey). we computed large grids of tp-agb models with several combinations of third dredge-up and mass-loss prescriptions with the colibri code. the smc agb population is modelled with the population synthesis code trilegal according to the space-resolved star formation history derived with the deep photometry from the vista survey of the magellanic clouds. we put quantitative constraints on the efficiencies of the third dredge-up and mass loss by requiring the models to reproduce the star counts and the luminosity functions of the observed oxygen-, carbon-rich and extreme-agb stars and we investigate the impact of the best-fitting prescriptions on the chemical yields. | calibrating tp-agb stellar models and chemical yields through resolved stellar populations in the small magellanic cloud |
employing the mesa stellar evolution code, we computed he accretion onto carbon-oxygen white dwarfs (co wds).we found two possible outcomes for models in which the wd steadily grows in mass towards the chandrasekhar limit. for relatively low he-accretion rates carbon ignition occurs in the center, leading to a type ia supernova (sn ia) explosion, whereas for relatively high accretion rates carbon is ignited off-center, probably leading to collapse. thus the parameter space producing sne ia is reduced compared to what was assumed in earlier papers, in which the possibility of off-center ignition was ignored. we then applied these results in binary population synthesis modelling, finding a modest reduction in the expected birthrate of sne ia resulting from the wd+he star channel. | the wd+he star binaries as the progenitors of type ia supernovae |
a broad effort is ongoing with large spectroscopic surveys such as apogee, eso-gaia, rave from which stellar parameters, radial velocities and detailed chemical abundances can be measured for corot, kepler, and k2 targets. in addition, asteroseismic data of red-giants stars observed by the space missions corot and kepler allow determination of stellar masses, radii, and can be used to determine the position and ages of stars. this association between spectroscopic and asteroseismic constraints provide a new way to understand galactic and stellar evolutions. to exploit all potential of this combination it would be crucial to develop our approach of synthetic populations. we compute stellar populations synthesis with the besançon galactic model including the asteroseismic and chemical properties from stellar evolution models. these synthetic populations can be compared with sinificant large surveys as apokasc (apogee+kepler) or corogee (corot+apogee). we focus here on the carbon and nitrogen surface abundances of kepler red-giant stars. we underline the importance of transport processes occurring in red-giant stars as rotation and thermohaline instability to understand chemical properties of stellar populations in the galaxy. the future for this area also starts taking shape with the launch of gaia, futur spectroscopic surveys such as 4most and weave, and the future space mission plato that will provide seismic data for more than 100 000 red-giants. such synthetic population model is a key tool to investigate future observations and better understand the evolution of the milky way. | red-giant stars: chemical clocks in the milky way |
galactic evolution at high redshifts is largely understood through stellar population synthesis (sps) modeling of spectra and photometry integrated over all starlight of a galaxy. however, complex and poorly understood stellar phases like the unstable thermally-pulsating asymptotic giant branch (tp-agb) phase make sps modeling a difficult task. recent models fail to agree on the tp-agb contribution to the infrared luminosity, leading to significant discrepancy among the properties derived from modern sps models when applied to early galaxies. here we provide a thorough assessment of each of the most widely used sps models by comparing their results and assessing their accuracy in modeling our unique dataset. we combine high-resolution spectroscopic observations from keck/mosfire with photometric data for 21 early quiescent galaxies with redshifts of z ~ 2. these galaxies are around the age of peak tp-agb activity, between ~0.3 and 2 gyr, and therefore provide an ideal test of the models. we find that models with a “light” tp-agb contribution provide much better descriptions of our galaxies at ages of ~1 gyr or less. this is true at high statistical significance and holds for models with or without dust reddening. however, contrary to previous studies, the model-dependent photometrically estimated ages are similar among the models, but they show only moderate agreement with the more model-independent spectroscopic ages derived from stellar absorption lines. the largest discrepancies are found for the charlot & bruzual (2007) models which show an artificial clustering of ages around 1 gyr. the tp-agb “light” models require more reddening, which can be independently tested by examining dust emission in the mid-infrared. the modeled fluxes are also mostly consistent with mid-infrared observations, with the exception of one model. resolving these differences among the models will substantially strengthen our estimates of the properties of early quiescent galaxies. | discriminating among stellar population synthesis models of the tp-agb phase in early quiescent galaxies |
gravitational microlensing provides a unique opportunity to probe the mass distribution of stars, black holes, and other objects in our milky way. however, population simulations are needed to interpret results from photometric microlensing surveys. the contribution from binary objects is often minimized or neglected in these simulations despite the high percentage of binary systems and the potential microlensing holds to probe binaries. in order to simulate the population effects of binary and multiple systems on microlensing, we add resolved binary parameters based on duchêne and kraus 2013 to stellar population interface for stellar evolution and atmospheres (spisea), software that simulates stellar clusters. we then inject these binaries into population synthesis for compact-object lensing events (popsycle), a package that simulates milky way microlensing surveys. in contrast to single-star results from popsycle, we find that a significant percentage of events have a binary system as either a source or lens. we also find that the addition of binaries shifts the peak of the einstein crossing time distribution to a 2x higher value. binary lensing events have, on average, longer einstein crossing times and thus significantly contaminate pools of candidate black hole lens events. as a result, microlensing searches for black holes will require larger observational samples to successfully detect astrometric microlensing signals due to black holes. | assessing the impact of binary systems on microlensing: adding binary systems to spisea and popsycle |
the present paper is devoted to the analysis of the evolution of young neutron stars (nss) in the milky way up to the death line. the methods of population synthesis have been used to study the distribution of an ensemble of young nss by their periods, period derivatives, and magnetic fields. the distribution of the initial periods and magnetic fields of the ensemble is assumed to be bimodal. relatively slowly rotating nss with initial periods p0 ∼ 1 s become magnetars, whereas nss with p0 ∼ 300 ms turn into normal pulsars. the model distributions of young nss by rotation periods, period derivatives, and magnetic fields are compared with those obtained from the atnf catalog. the location of the model ensemble of nss on the p-ṗ diagram appears to be close to the position of the real ensemble of nss. | evolution of neutron stars in the milky way |
we consider modern insights into formation and evolution of symbiotic stars. the parameters of observed population of them are compared to results of population synthesis models. we discuss the problem of reconciliation of observed number of symbiotic stars and model predictions. | symbiotic stars: formation, evolution, population |
utilizing data from the mapping nearby galaxies at apo (manga) survey (manga product launch-4, or mpl-4), of the latest generation of the sloan digital sky survey (sdss-iv), we identified nine post-starburst (e+a) systems that lie within the green valley transition zone. we identify the e+a galaxies by their sdss single fiber spectrum and u-r color, then confirmed their classification as post-starburst by coding/plotting methods and spectral synthesis codes (firefly and pipe3d), as well as with their spectral energy distributions (seds) from 0.15 µm to 22 µm, using galex, sdss, 2mass, and wise data. we produced maps of gaussian-fitted fluxes, equivalent widths, stellar velocities, metallicities and age. we also produced spectral line ratio diagrams to classify regions of stellar populations of the galaxies. we found that our sample of e+as retain their post-starburst properties across the entire galaxy, not just at their center. we detected matching a trend line in the ultraviolet and optical bands, consistent with the expected seds for an e+a galaxy, and also through the j, h and ks bands, except for one object. we classified one of the nine galaxies as a luminous infrared galaxy, unusual for a post-starburst object. our group seeks to further study stellar population properties, spectral energy distributions and quenching properties in e+a galaxies, and investigate their role in galaxy evolution as a whole. this work was supported by the alfred p. sloan foundation via the sdss-iv faculty and student team (fast) initiative, arc agreement #ssp483 to the cuny college of staten island. this work was also supported by grants to the american museum of natural history, and the cuny college of staten island through from national science foundation. | spectral analysis, synthesis, & energy distributions of nearby e+a galaxies using sdss-iv manga |
the spatially resolved stellar population content of today's galaxies holds important information for understanding the diferent processes that contribute to the star formation and mass assembly histories of galaxies. in this talk we present the results from the analysis of more than 400 nearby galaxies from the califa survey with the goal of retrieving the spatially resolved star formation history of galaxies. spectral synthesis is applied to the data cube to obtain the radial profiles of the intensity of the recent star formation rate, the local specific sfr, and also their time evolution. to emphasize the behavior of these properties for galaxies that are on and off of the main sequence of star formation we will discusse the results by attending to the galaxy mass and the hubble type. | spatially-resolved star formation history of califa galaxies: implications for galaxy formation |
we investigate here the effect of the selection function on the metallicity distribution function (mdf) as well as on the vertical metallicity gradient by studying similar lines-of-sight using four different spectroscopic surveys (apogee, lamost, rave and gaia-eso) which have different targeting strategies and therefore different selection functions. we create mock fields for each survey using two stellar population synthesis models, galaxia and trilegal. the effects of the selection function are studied in detail by applying the selection function to the two models and comparing the mdf as well as vertical metallicity gradients of the selected sources with that of the underlying sample. we find a negligible selection function effect on the mdf as well as on the vertical metallicity gradients for apogee, rave and lamost, and estimate a mean vertical metallicity gradient of -0.241+/-0.028 dex kpc-1. | the effects of the selection function on metallicity trends in spectroscopic surveys of the milky way |
relying on the complementarity of gaia proper motions with radial velocities of the rave survey, we attempt to constrain the kinematics of the milky way disc. based on the population synthesis model, we simulate the observations, applying the detailed selection functions of the observations. the dynamics is described using a global gravitational potential computed from the mass distribution of the population model, approximated by a stäckel potential (bienaymé et al. 2015). we explore a set of free parameters (solar motion, age - velocity dispersion of the disc as a function of age, the velocity gradients, vertex deviation) using a markov chain monte carlo method. we show that the fitted model reproduces very well the radial velocity and proper motion distributions, allowing to constrain the thin and thick disc secular evolution with time. | kinematics of the milky way disc from the rave survey combined with gaia dr1 |
a string of recent studies have debated the exact form and physical origin of an evolutionary trend between the peak luminosity attained by type ia supernovae (sne ia) and the properties of the galaxies that host them. we shed new light on the discussion by presenting (i) an improved statistical method to analyze the slope and correlation specific to the model assumptions of these two variables, (ii) a statistical analysis of about 200 low-redshift sne ia in which we measure the separation of hubble residuals (hr; as a probe of luminosity) between two host-galaxy morphological types (as a probe of galaxy properties), and (iii) an overview of the degree and significance of the bias introduced by different evolutionary population synthesis (eps) models that are utilized to estimate the galaxy properties. our results identify the existence of sn ia luminosity differences that are measurable in relation to a number of host-galaxy properties, including morphology, mass, age, star-formation rate, and dust, though the degree of correlation varies and the physical origin remains unclear. we find that some such parameters are strongly dependent on eps-model choice, suggesting that there are significant systematic effects to understand before claiming robust and actionable (e.g., in a cosmological sense) evolutionary trends in sn ia luminosity. | on the relationship between type ia supernova peak luminosity and host-galaxy properties |
jellyfish are the most extreme cases of galaxies undergoing ram-pressure stripping. in order to analyse the stellar populations distribution along these galaxies, we have performed stellar population synthesis in data cubes of jellyfish from the gasp programme, using both starlight and fado codes. | stellar population synthesis of jellyfish galaxies |
we present a new approach to comparing models of galaxy formation with deep images taken with the hubble space telescope (hst). in particular, we generate simulated hst images by projecting the galaxy formation models all the way into observational domain, adding cosmological and instrumental effects, and we analyze these images in the same way as real hst images ("forward modeling"). this is a powerful method for testing the models, since it allows us to make unbiased comparisons between predictions and observations, while automatically taking into account all relevant selection effects. we model the evolving galaxy population by semi-empirical techniques based on cosmological simulations of dark matter halos, in which the baryonic evolution of galaxies follows closely that of their dark halos, as specified by a constant or evolving stellar mass-halo mass (smhm) relation. we introduce a novel method to ensure that the star formation history in each simulated galaxy complies with the input smhm relation. we compute the radiative spectra of simulated galaxies from stellar population synthesis models, taking into account absorption by gas and dust in the interstellar medium and by gas in the intergalactic medium. the appearance of our simulated galaxies is based on cutout images of real galaxies in the sdss, but with luminosities and sizes rescaled to match those computed by our semi-empirical models. to determine which models are acceptable, we derive the distributions of luminosities, sizes, and surface brightnesses of galaxies in the simulated images (using sextractor and other standard analysis tools) and compare these with the corresponding distributions derived from real hst images. we find remarkably good agreement between these distributions for reasonable values of the relatively few adjustable parameters in our models. as a byproduct of this analysis, we also quantify the potential biases and selection effects in the observations. the methods presented here will be valuable in planning and interpreting future observations with hst, jwst, and wfirst. see arxiv:1501.01556 for a full account of our methods and results. | understanding galaxy formation from deep hubble images: the forward-modeling approach |
2d ultrasonic arrays have considerable application potential in lamb wave based shm systems, since they enable equivocal damage imaging and even in some cases wave-mode selection. recently, it has been shown that the 2d arrays can be used in shm applications in a synthetic focusing (sf) mode, which is much more effective than the classical phase array mode commonly used in ndt. the sf mode assumes a single element excitation of subsequent transmitters and off-line processing the acquired data. in the simplest implementation of the technique, only single multiplexed input and output channels are required, which results in significant hardware simplification. application of the sf mode for 2d arrays creates additional degrees of freedom during the design of the array topology, which complicates the array design process, however, it enables sparse array designs with performance similar to that of the fully populated dense arrays. in this paper we present the coarray concept to facilitate synthesis process of an array's aperture used in the multistatic synthetic focusing approach in lamb waves-based imaging systems. in the coherent imaging, performed in the transmit/receive mode, the sum coarray is a morphological convolution of the transmit/receive sub-arrays. it can be calculated as the set of sums of the individual sub-arrays' elements locations. the coarray framework will be presented here using a an example of a star-shaped array. the approach will be discussed in terms of beampatterns of the resulting imaging systems. both simulated and experimental results will be included. | designing of sparse 2d arrays for lamb wave imaging using coarray concept |
fossil groups are considered the end product of natural galaxy group evolution in which group members sink towards the centre of the gravitational potential due to dynamical friction, merging into a single, massive, and x-ray bright elliptical. since gravitational lensing depends on the mass of a foreground object, its mass concentration, and distance to the observer, we can expect lensing effects of such fossil groups to be particularly strong. this paper explores the exceptional system j143454.4+522850 (with a lens redshift zl = 0.625). we combine gravitational lensing with stellar population synthesis to separate the total mass of the lens into stars and dark matter. the enclosed mass profiles are contrasted with state-of-the-art galaxy formation simulations, to conclude that sw05 is likely a fossil group with a high stellar to dark matter mass fraction (0.027 ± 0.003) with respect to expectations from abundance matching (0.012 ± 0.004), indicative of a more efficient conversion of gas into stars in fossil groups. | the lens sw05 j143454.4+522850: a fossil group at redshift 0.6? |
the stellar initial mass function (imf) is a fundamental property in the measurements of stellar masses and galaxy star formation histories. i will present the stellar imf in the center of nearby massive galaxies in the massive survey based on high quality magellan/ldss-3 long-slit spectroscopy and detailed stellar synthesis modeling. i will focus on the relations among stellar imf, global galaxy properties, and stellar populations, and discuss the interesting implications of the physical processes driving the global stellar imf variation. | the stellar initial mass function in the center of massive early-type galaxies |
stellar populations synthesis models have proven to be excellent tools to learn about galaxy evolution. however, modeling small stellar populations (lower than 105 m⊙) has been an intriguing and continuous to be a field of intensive research. in this work, we have developed a new approach to form stars from clusters first, where massive stars are formed from fractions of mass of small stellar clusters. this new approximation is based on the empirical power law (mc-2) for the mass function of clusters between 20-1100 m⊙ found in recent years and the maximum stellar mass that can be formed in a cluster. incorporating this new approach to form clusters has made us upgrade the way we integrate the stellar properties and the way that the isochrone is produced with a new technique. to produce the new models we have used the most recent version of starburst99 that incorporates the most recent stellar evolution models with rotation. on the verge of solving nearby stellar populations and observing small stellar populations across the universe, this new approach brings a new scope on trying to disentangle the nature of hyper and supermassive stars in small stellar populations. in this work we present this new approach and the results when these models are applied to very energetic stellar populations such as the cluster in ngc 3603. our most important result is that we have modeled the ionizing power of this cluster and some others by forming enough supermassive stars in a cluster of ~104 m⊙. | modeling small stellar populations using starburst99 |
galaxy clusters provide a laboratory for studying the evolution of galaxies in dense environments. star formation in cluster galaxies seems to be suppressed relative to field galaxies. recent studies suggest that star formation continues in some cluster galaxies, but in a mode where a larger fraction of the light from young stars is obscured by dust. to detect this dust-obscured star formation, we use spitzer mips imaging, which is sensitive to the thermal emission from dust heated by young stars. we focus on a sample of 36 x-ray-selected clusters, all of which have high-quality masses from chandra data. for 12 of the clusters, we use extensive mmt/hectospec optical spectroscopy to identify cluster members. for galaxies without spectroscopy, we estimate photometric redshifts using sdss and irac imaging and stellar population synthesis models. we use statistical background subtraction to estimate cluster-wide star formation rates for the entire cluster sample. the optical spectra test the accuracy of these estimates for the clusters with available data. our final results will inform models of star formation within galaxy clusters. | evolution of star formation rates in clusters using spitzer mips imaging |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.