Science.gov

Sample records for age stellar populations

  1. INTERMEDIATE-AGE STELLAR POPULATIONS IN CLASSICAL QUASI-STELLAR OBJECT HOST GALAXIES

    SciTech Connect

    Canalizo, Gabriela; Stockton, Alan E-mail: stockton@ifa.hawaii.edu

    2013-08-01

    Although mergers and starbursts are often invoked in the discussion of quasi-stellar object (QSO) activity in the context of galaxy evolution, several studies have questioned their importance or even their presence in QSO host galaxies. Accordingly, we are conducting a study of z {approx} 0.2 QSO host galaxies previously classified as passively evolving elliptical galaxies. We present deep Keck/LRIS spectroscopy of a sample of 15 hosts and model their stellar absorption spectra using stellar synthesis models. The high signal-to-noise ratio of our spectra allows us to break various degeneracies that arise from different combinations of models, varying metallicities, and contamination from QSO light. We find that none of the host spectra can be modeled by purely old stellar populations and that the majority of the hosts (14/15) have a substantial contribution from intermediate-age populations with ages ranging from 0.7 to 2.4 Gyr. An average host spectrum is strikingly well fit by a combination of an old population and a 2.1 (+0.5, -0.7) Gyr population. The morphologies of the host galaxies suggest that these aging starbursts were induced during the early stages of the mergers that resulted in the elliptical-shaped galaxies that we observe. The current active galactic nucleus activity likely corresponds to the late episodes of accretion predicted by numerical simulations, which occur near the end of the mergers, whereas earlier episodes may be more difficult to observe due to obscuration. Our off-axis observations prevent us from detecting any current star formation or young stellar populations that may be present in the central few kiloparsecs.

  2. Uv Imaging of Intermediate-Age Magellanic Cloud Clusters: Hot Stellar Populations in Composite Stellar Systems

    NASA Astrophysics Data System (ADS)

    Freedman, Wendy

    1994-01-01

    Hot stars were first recognized to be an important component of galactic spheroids with early vacuum ultraviolet observations of ellipticals and spiral bulges that were made with OAO. Now, 20 years later, we still do not have a full understanding of the VUV evolution of intermediate and old age stellar populations. Using the WFPC2, we therefore propose to undertake an ultraviolet survey of a sample of star clusters spanning a range in age in the Large Magellanic Cloud. The objective of this investigation is to determine the nature of the hot stellar components in rich, intermediate-to-old age LMC clusters. Ground-based optical/IR studies suggest the presence of short-lived hot horizontal branch and post-asymptotic giant branch stars in these clusters but detailed characterizations of the stars require the ultraviolet capability of HST. In this effort we will be aided by the absence of red leaks in the WFPC2 Woods filter and very high angular resolution of the HST. Although old star clusters in the Galaxy and M31 are, and will be, the subjects of intense investigation by HST, OUR SURVEY WILL BE THE FIRST OF ITS KIND FOR POPULATIONS OF INTERMEDIATE AGE. Such systems are critical for interpreting the spectra and colors of high redshift galaxies, and will provide important support to these studies.

  3. Stellar Populations

    NASA Astrophysics Data System (ADS)

    Peletier, Reynier F.

    2013-10-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on nearby galaxies, which are best suited to study this theme. Of course, the understanding of stellar populations is intimately connected to understanding the formation and evolution of galaxies, one of the great outstanding problems of astronomy. We are currently in a situation where very large observational advances have been made in recent years. Galaxies have been detected up to a redshift of ten. A huge effort has to be made so that stellar population theory can catch up with observations. Since most galaxies are far away, information about them has to come from stellar population synthesis of integrated light. Here I will discuss how stellar evolution theory, together with observations in our Milky Way and Local Group, are used as building blocks to analyse these integrated stellar populations.

  4. Modeling tracers of young stellar population age in star-forming galaxies

    SciTech Connect

    Levesque, Emily M.; Leitherer, Claus

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  5. AGE AND MASS SEGREGATION OF MULTIPLE STELLAR POPULATIONS IN GALACTIC NUCLEI AND THEIR OBSERVATIONAL SIGNATURES

    SciTech Connect

    Perets, Hagai B.; Mastrobuono-Battisti, Alessandra

    2014-04-01

    Nuclear stellar clusters (NSCs) are known to exist around massive black holes in galactic nuclei. They are thought to have formed through in situ star formation following gas inflow to the nucleus of the galaxy and/or through the infall of multiple stellar clusters. Here we study the latter, and explore the composite structure of the NSC and its relation to the various stellar populations originating from its progenitor infalling clusters. We use N-body simulations of cluster infalls and show that this scenario may produce observational signatures in the form of age segregation: the distribution of the stellar properties (e.g., stellar age and/or metallicity) in the NSCs reflects the infall history of the different clusters. The stellar populations of clusters, infalling at different times (dynamical ages), are differentially segregated in the NSC and are not fully mixed even after a few gigayears of evolution. Moreover, the radial properties of stellar populations in the progenitor cluster are mapped to their radial distribution in the final NSC, potentially leading to efficient mass segregation in NSCs, even those where relaxation times are longer than a Hubble time. Finally, the overall structures of the stellar populations present non-spherical configurations and show significant cluster to cluster population differences.

  6. Colour pairs for constraining the age and metallicity of stellar populations

    NASA Astrophysics Data System (ADS)

    Li, Zhongmu; Han, Zhanwen

    2008-04-01

    Using a widely used stellar-population synthesis model, we study the possibility of using pairs of AB system colours to break the well-known stellar age-metallicity degeneracy and to give constraints on two luminosity-weighted stellar-population parameters (age and metallicity). We present the relative age and metallicity sensitivities of the AB system colours that relate to the u,B,g,V,r,R,i, I,z,J,H and K bands, and we quantify the ability of various colour pairs to break the age-metallicity degeneracy. Our results suggest that a few pairs of colours can be used to constrain the above two stellar-population parameters. This will be very useful for exploring the stellar populations of distant galaxies. In detail, colour pairs [(r-K), (u-R)] and [(r-K), (u-r)] are shown to be the best pairs for estimating the luminosity-weighted stellar ages and metallicities of galaxies. They can constrain two stellar-population parameters on average with age uncertainties less than 3.89 Gyr and metallicity uncertainties less than 0.34 dex for typical colour uncertainties. The typical age uncertainties for young populations (age < 4.6 Gyr) and metal-rich populations (Z >= 0.001) are small (about 2.26 Gyr) while those for old populations (age >= 4.6 Gyr) and metal-poor populations (Z < 0.001) are much larger (about 6.88 Gyr). However, the metallicity uncertainties for metal-poor populations (about 0.0024) are much smaller than for other populations (about 0.015). Some other colour pairs can also possibly be used for constraining the two parameters. On the whole, the estimation of stellar-population parameters is likely to be reliable only for early-type galaxies with small colour errors and globular clusters, because such objects contain less dust. In fact, no galaxy is totally dust-free and early-type galaxies are also likely have some dust [e.g. E(B- V) ~ 0.05], which can change the stellar ages by about 2.5 Gyr and metallicities (Z) by about 0.015. When we compare the

  7. Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

    SciTech Connect

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L.; Naylor, Tim; Povich, Matthew S.; Garmire, Gordon P.

    2014-06-01

    A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

  8. Ages and metallicities for quiescent galaxies in the Shapley supercluster: driving parameters of the stellar populations

    NASA Astrophysics Data System (ADS)

    Smith, Russell J.; Lucey, John R.; Hudson, Michael J.

    2009-12-01

    We use high signal-to-noise spectroscopy for a sample of 232 quiescent galaxies in the Shapley supercluster, to investigate how their stellar populations depend on velocity dispersion (σ), luminosity and stellar mass. The sample spans a large range in velocity dispersion (30-300kms-1) and in luminosity (MR from -18.7 to -23.2). Estimates of age, total metallicity (Z/H) and α-element abundance ratio (α/Fe) were derived from absorption-line analysis, using single-burst models of Thomas and collaborators. Using the Rose CaII index, we conclude that recent star formation (frosting) events are not responsible for the intermediate ages observed in some of the galaxies. Age, Z/H and α/Fe are correlated positively with velocity dispersion, but we also find significant residual trends with luminosity: at given σ, the brighter galaxies are younger, less α-enriched and have higher Z/H. At face value, these results might suggest that the stellar populations depend on stellar mass as well as on velocity dispersion. However, we show that the observed trends can be reproduced by models in which the stellar populations depend systematically only on σ, and are independent of stellar mass M*. For age, the observed luminosity correlation arises because young galaxies are brighter, at fixed M*. For metallicity, the observed luminosity dependence arises because metal-rich galaxies, at fixed mass, tend also to be younger, and hence brighter. We find a good match to the observed luminosity correlations with age ~σ+0.40, Z/H~σ+0.35,α/Fe ~σ+0.20, where the slopes are close to those found when fitting traditional scaling relations. We conclude that the star formation and enrichment histories of galaxies are determined primarily by the depth of their gravitational potential wells. The observed residual correlations with luminosity do not imply a corresponding dependence on stellar mass.

  9. Comprehensive stellar population models and the disentanglement of age and metallicity effects

    NASA Technical Reports Server (NTRS)

    Worthey, Guy

    1994-01-01

    The construction of detailed models for intermediate and old stellar populations is described. Input parameters include metallicity (-2 less than (Fe/H) less than 0.5), single-burst age (between 1.5 and 17 Gyr), and initial mass function (IMF) exponent. Quantities output include broadband magnitudes, spectral energy distributions, surface brightness fluctuation magnitudes, and a suite of 21 absorption feature indices. The models are checked against a wide variety of available observations. Examinations of model output yield the following conclusions. (1) If the percentage change delta age/delta Z approximately equals 3/2 for two populations, they will appear almost identical in most indices. A few indices break this degeneracy by being either more abundance sensitive (Fe4668, Fe5015, Fe5709, and Fe5782) or more age sensitive (G4300, H beta, and presumably higher order Balmer lines) than usual. (2) Present uncertainties in stellar evolution are of the same magnitude as the effects of IMF and Y in the indices studied. (3) Changes in abundance ratios (like (Mg/Fe)) are predicted to be readily apparent in the spectra of old stellar populations. (4) The I-band flux of a stellar population is predicted to be nearly independent of metallicity and only modestly sensitive to age. The I band is therefore recommended for standard candle work or studies of M/L in galaxies. Other conclusions stem from this work. (1) Intercomparison of models and observations of two TiO indices seem to indicate variation of the (V/Ti) ratio among galaxies, but it is not clear how this observation ties into the standard picture of chemical enrichment. (2) Current estimates of (Fe/H) for the most metal-rich globulars that are based on integrated indices are probably slightly too high. (3) Colors of population models from different authors exhibit a substantial range. At solar metallicity and 13 Gyr, this range corresponds to an age error of roughly +/- 7 Gyr. Model colors from different authors

  10. RESEARCH PAPER: Old stellar population synthesis: new age and mass estimates for Mayall II = G1

    NASA Astrophysics Data System (ADS)

    Ma, Jun; de Grijs, Richard; Fan, Zhou; Rey, Soo-Chang; Wu, Zhen-Yu; Zhou, Xu; Wu, Jiang-Hua; Jiang, Zhao-Ji; Chen, Jian-Sheng; Lee, Kyungsook; Sohn, Sangmo Tony

    2009-06-01

    Mayall II = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKS 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20 000 Å. A quantitative comparison with a variety of simple stellar population (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ~1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 107 Modot) indicate that G1 is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 102 Lodot far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.

  11. The tight subgiant branch of the intermediate-age star cluster NGC 411 implies a single-aged stellar population

    NASA Astrophysics Data System (ADS)

    Li, C.; de Grijs, R.; Bastian, N.; Deng, L.; Niederhofer, F.; Zhang, C.

    2016-09-01

    The presence of extended main-sequence turn-off (eMSTO) regions in intermediate-age star clusters in the Large and Small Magellanic Clouds is often interpreted as resulting from extended star formation histories (SFHs), lasting ≥300 Myr. This strongly conflicts with the traditional view of the dominant star formation mode in stellar clusters, which are thought of as single-aged stellar populations. Here we present a test of this interpretation by exploring the morphology of the subgiant branch (SGB) of NGC 411, which hosts possibly the most extended eMSTO among all known intermediate-age star clusters. We show that the width of the NGC 411 SGB favours the single-aged stellar population interpretation and rules out an extended SFH. In addition, when considering the red clump (RC) morphology and adopting the unproven premise that the widths of all features in the colour-magnitude diagram are determined by an underlying range in ages, we find that the SFH implied is still very close to that resulting from a single-aged stellar population, with a minor fraction of stars scattering to younger ages compared with the bulk of the population. The SFHs derived from the SGB and RC are both inconsistent with the SFH derived from the eMSTO region. NGC 411 has a very low escape velocity and it has unlikely undergone significant mass-loss at an early stage, thus indicating that it may lack the capacity to capture most of its initial, expelled gas from stellar evolutionary processes, a condition often required for extended SFHs to take root.

  12. Constraining Stellar Population Models. I. Age, Metallicity and Abundance Pattern Compilation for Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.; Courteau, Stéphane; Graves, Genevieve; Schiavon, Ricardo P.

    2014-01-01

    We present an extensive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. Our compilation constitutes a notable improvement over previous similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavors, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the α elements. When paired with the ages of our clusters, we find evidence that supports a scenario whereby the Milky Way obtained its globular clusters through two channels: in situ formation and accretion of satellite galaxies. The distributions of C, N, O, and Na abundances and the dispersions thereof per cluster corroborate the known fact that all GGCs studied so far with respect to multiple stellar populations have been found to harbor them. Finally, using data on individual stars, we verify that stellar atmospheres become progressively polluted by CN(O)-processed material after they leave the main sequence. We also uncover evidence which suggests that the α elements Mg and Ca may originate from more than one nucleosynthetic production site. We estimate that our compilation incorporates all relevant analyses from the literature up to mid-2012. As an aid to investigators in the fields named above, we provide detailed electronic tables of the data upon which our work is based at http

  13. Cosmic Evolution of X-ray Binary Populations: Probes of Changing Chemistry and Aging Stellar Populations in the Universe

    NASA Astrophysics Data System (ADS)

    Lehmer, Bret; Basu-Zych, Antara; Mineo, Stefano; Brandt, W. Niel; Eufrasio, Rafael T.; Fragos, Tassos; Hornschemeier, Ann E.; Luo, Bin; Xue, Yongquan; Bauer, Franz E.; Gilfanov, Marat; Kalogera, Vassiliki; Ranalli, Piero; Schneider, Donald P.; Shemmer, Ohad; Tozzi, Paolo; Trump, Jonathan; Vignali, Cristian; Wang, JunXian; Yukita, Mihoko; Zezas, Andreas

    2016-01-01

    The 2-10 keV emission from normal galaxies is dominated by X-ray binary (XRB) populations. 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. The 6 Ms Chandra Deep Field-South (CDF-S) allows us to study how XRB emission has evolved over a significant fraction of cosmic history (since z ~ 4), without significant contamination from AGN. Using constraints from the CDF-S, I will show that the X-ray emission from normal galaxies from z = 0-7 depends not only on star-formation rate (SFR), but also on stellar mass (M) and redshift. Our analysis shows the that low-mass X-ray binary emission scales with stellar mass and evolves as LX(LMXB)/M ~ (1+z)^3, and high-mass X-ray binaries scale with SFR and evolve as LX(HMXB)/SFR ~ (1+z), consistent with predictions from 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.

  14. Age and metallicity effects in single stellar populations: application to M 31 clusters.

    NASA Astrophysics Data System (ADS)

    de Freitas Pacheco, J. A.

    1997-03-01

    We have recently calculated (Borges et al. 1995AJ....110.2408B) integrated metallicity indices for single stellar populations (SSP). Effects of age, metallicity and abundances were taken into account. In particular, the explicit dependence of the indices Mg_2_ and NaD respectively on the ratios [Mg/Fe] and [Na/Fe] was included in the calibration. We report in this work an application of those models to a sample of 12 globular clusters in M 31. A fitting procedure was used to obtain age, metallicity and the [Mg/Fe] ratio for each object, which best reproduce the data. The mean age of the sample is 15+/-2.8Gyr and the mean [Mg/Fe] ratio is 0.35+/-0.10. These values and the derived metallicity spread are comparable to those found in galactic counterparts.

  15. Age and Abundance Discrimination in Old Stellar Populations Using Mid-Ultraviolet Colors

    NASA Astrophysics Data System (ADS)

    Dorman, Ben; O'Connell, Robert W.; Rood, Robert T.

    2003-07-01

    The rest-frame mid-ultraviolet spectral region (2000-3200 Å) is important in analyzing the stellar populations of the ``red envelope'' systems observed at high redshifts. Here we explore the usefulness of the mid-UV for determining ages and abundances of old populations. We work with a theoretical set of low-resolution spectra and broadband colors because tests show that these are at present more realistic than high-resolution models. A mid-UV to optical/IR wavelength baseline provides good separation of population components because the main-sequence turnoff dominates the integrated light between 2500 and 4000 Å. Mid-UV spectral features are not sensitive to the dwarf/giant mixture in the population, unlike those in the optical region. We find a 6 mag difference in the mid-UV continuum level (normalized at V) over the metallicity range -1.5ages in the range 4-16 Gyr. Logarithmic derivatives of mid-UV colors with respect to age or metal abundance are 3-10 times larger than for the UBV region. Most of the spectral information on old populations therefore resides below 4000 Å. Measurement of a single mid-UV color is capable of placing a strong lower bound on the mean metallicity of an old population. We investigate the capability of UBV and mid-UV broadband colors to separately determine age and abundance, taking into account precision in the color measurements. We find that the mid-UV improves resolution in logt, logZ space by about a factor of 3 for a given observational precision. Contamination by hot, post-He flash evolutionary phases can seriously affect the mid-UV spectra of old populations. A simple estimate shows that contamination can reach over 80% in some cases. However, this is straightforward to remove as long as far-UV measurements are available. We find that extinction should have relatively small effects on parameters derived for old populations from the mid-UV. Finally, we show

  16. Stellar Populations of Shell Galaxies

    NASA Astrophysics Data System (ADS)

    Carlsten, Scott; Zenteno, Alfredo

    2016-01-01

    We present a study of the inner (out to ˜1 effective radius) stellar populations in a sample of 9 shell galaxies. We derive stellar population parameters from long slit spectra by both analyzing the Lick indices of the galaxies and by fitting high resolution SSP model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. We find the presence of young stellar populations in several of the galaxies, implying recent star formation and allowing us to speculate on the age of the shells. Analyzing the metallicity gradients in our sample, we find an average metallicity gradient of -0.16±0.10 dex/decade in radius. Finally, we compare this with galaxy evolution models to try to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers in their past but it is unclear whether the shells formed from these events or from separate minor mergers.

  17. Spectroscopic age and metallicity for a sample of Globular Clusters from Stellar Population Models

    NASA Astrophysics Data System (ADS)

    Stock, M. J.; Calderón, P.

    2009-05-01

    We present spectroscopic age and metallicity predictions for a sample of 20 Globular Clusters in the massive E0 galaxy NGC 1407 (data from Cenarro et al. 2007, AJ, 134, 391) and for the Galacic Globular Clusters data from the Library of Integrated Spectra of Galactic Globular Clusters (GGC's) from Schiavon et al. (2005, ApJS, 160, 163) including the widely studied 47 Tuc cluster. Using index-index plots we compared model Single Stellar Populations (SSP's) spectra to the integrated spectra of both samples of Globular Clusters using high resolution line strength indices (Stock, in prep.) and the syntethic SSP's models from P. Coelho (2007, private comm.) as well as the CB07 solar models. For the GC's in NGC1407, the predictions from the syntethic models's with [α /Fe]=0.4 are in good agreement with the results from Cenarro et al. (2007, AJ, 134, 391), taking into account that the dispersion is partially due to the fact that the mean [α/Fe] ratio of the sample is ≈ 0.3 dex, resulting in younger ages and lower metallicities (Thomas et al. 2003, A&A, 401, 429). We observe a bimodal distribution of the Fe4383+ index which is in turn an indicator of metallicity, also seen in Cenarro et al. (2005). The CB07 models predict ages that are widely spread over the plot yielding ages greater than 14 Gyrs. The metallicity derived from these models are very low for almost all the objects (Z < 0.008). The distribution of the GGC's on the syntethic model grid shows a trend in the sense that metal poor clusters are younger than metal rich ones, but this effect might not be real (de Angeli et al. 2005, AJ, 130, 116). For 47 Tuc we estimate an age of ≈ 10 Gyr, and metallicity Z < 0.011 (<[Fe/H]= -0.5) which are both comparable with the values reported in the literature (Carretta et al. 2000; Liu & Chaboyer 2000, ApJ, 544, 818; Schiavon et al. 2002, ApJ, 580, 873; Gratton et al. 2003, A&A, 408, 529).

  18. Magellanic Clouds: Stellar Populations

    NASA Astrophysics Data System (ADS)

    Mould, J.; Murdin, P.

    2000-11-01

    The Magellanic Clouds (figure 1) have long been seen as the prototypical young STELLAR POPULATION. The presence of young GLOBULAR CLUSTERS in the Clouds spoke to southern hemisphere observers of the opportunity to study close up processes which have not occurred in the Milky Way for a long time. Young globulars are also seen in other gas-rich, highly disturbed environments, such as merging galaxi...

  19. Inside out and Upside down: Tracing the Assembly of a Simulated Disk Galaxy Using Mono-age Stellar Populations

    NASA Astrophysics Data System (ADS)

    Bird, Jonathan C.; Kazantzidis, Stelios; Weinberg, David H.; Guedes, Javiera; Callegari, Simone; Mayer, Lucio; Madau, Piero

    2013-08-01

    We analyze the present day structure and assembly history of a high-resolution hydrodynamic simulation of the formation of a Milky-Way-(MW)-like disk galaxy, from the "Eris" simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. At z = 0, stars with t form < 2 Gyr mainly occupy the stellar spheroid, with the oldest (earliest forming) stars having more centrally concentrated profiles. The younger age cohorts populate disks of progressively longer radial scale lengths and shorter vertical scale heights. At a given radius, the vertical density profiles and velocity dispersions of stars vary smoothly as a function of age, and the superposition of old, vertically extended and young, vertically compact cohorts gives rise to a double-exponential profile like that observed in the MW. Turning to formation history, we find that the trends of spatial structure and kinematics with stellar age are largely imprinted at birth, or immediately thereafter. Stars that form during the active merger phase at z > 3 are quickly scattered into rounded, kinematically hot configurations. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms "inside out" in a radial sense and "upside down" in a vertical sense. Secular heating and radial migration influence the final state of each age cohort, but the changes they produce are small compared to the trends established at formation. The predicted correlations of stellar age with spatial and kinematic structure are in good qualitative agreement with the correlations observed for mono-abundance stellar populations in the MW.

  20. INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS

    SciTech Connect

    Bird, Jonathan C.; Kazantzidis, Stelios; Weinberg, David H.; Guedes, Javiera; Callegari, Simone; Mayer, Lucio; Madau, Piero

    2013-08-10

    We analyze the present day structure and assembly history of a high-resolution hydrodynamic simulation of the formation of a Milky-Way-(MW)-like disk galaxy, from the ''Eris'' simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. At z = 0, stars with t{sub form} < 2 Gyr mainly occupy the stellar spheroid, with the oldest (earliest forming) stars having more centrally concentrated profiles. The younger age cohorts populate disks of progressively longer radial scale lengths and shorter vertical scale heights. At a given radius, the vertical density profiles and velocity dispersions of stars vary smoothly as a function of age, and the superposition of old, vertically extended and young, vertically compact cohorts gives rise to a double-exponential profile like that observed in the MW. Turning to formation history, we find that the trends of spatial structure and kinematics with stellar age are largely imprinted at birth, or immediately thereafter. Stars that form during the active merger phase at z > 3 are quickly scattered into rounded, kinematically hot configurations. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms ''inside out'' in a radial sense and ''upside down'' in a vertical sense. Secular heating and radial migration influence the final state of each age cohort, but the changes they produce are small compared to the trends established at formation. The predicted correlations of stellar age with spatial and kinematic structure are in good qualitative agreement with the correlations observed for mono-abundance stellar populations in the MW.

  1. CHARACTERIZING ULTRAVIOLET AND INFRARED OBSERVATIONAL PROPERTIES FOR GALAXIES. I. INFLUENCES OF DUST ATTENUATION AND STELLAR POPULATION AGE

    SciTech Connect

    Mao Yewei; Kong Xu; Kennicutt, Robert C. Jr.; Hao, Cai-Na; Zhou Xu E-mail: xkong@ustc.edu.cn

    2012-09-20

    The correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color (or ultraviolet spectral slope), i.e., the IRX-UV (or IRX-{beta}) relation, found in studies of starburst galaxies is a prevalent recipe for correcting extragalactic dust attenuation. Considerable dispersion in this relation discovered for normal galaxies, however, complicates its usability. In order to investigate the cause of the dispersion and to have a better understanding of the nature of the IRX-UV relation, in this paper, we select five nearby spiral galaxies, and perform spatially resolved studies on each of the galaxies, with a combination of ultraviolet and infrared imaging data. We measure all positions within each galaxy and divide the extracted regions into young and evolved stellar populations. By means of this approach, we attempt to discover separate effects of dust attenuation and stellar population age on the IRX-UV relation for individual galaxies. In this work, in addition to dust attenuation, stellar population age is interpreted to be another parameter in the IRX-UV function, and the diversity of star formation histories is suggested to disperse the age effects. At the same time, strong evidence shows the need for more parameters in the interpretation of observational data, such as variations in attenuation/extinction law. Fractional contributions of different components to the integrated luminosities of the galaxies suggest that the integrated measurements of these galaxies, which comprise different populations, would weaken the effect of the age parameter on IRX-UV diagrams. The dependence of the IRX-UV relation on luminosity and radial distance in galaxies presents weak trends, which offers an implication of selective effects. The two-dimensional maps of the UV color and the infrared-to-ultraviolet ratio are displayed and show a disparity in the spatial distributions between the two galaxy parameters, which offers a spatial interpretation of the scatter

  2. EVIDENCE FOR INTERMEDIATE-AGE STELLAR POPULATIONS IN EARLY-TYPE GALAXIES FROM K-BAND SPECTROSCOPY

    SciTech Connect

    Marmol-Queralto, E.; Cardiel, N.; Gorgas, J.; Sanchez-Blazquez, P.; Cenarro, A. J.; Vazdekis, A.; Kuntschner, H.; Silva, D. R.

    2009-11-10

    The study of stellar populations in early-type galaxies in different environments is a powerful tool for constraining their star formation histories. This study has been traditionally restricted to the optical range, where dwarfs around the turn-off and stars at the base of the red giant branch dominate the integrated light at all ages. The near-infrared spectral range is especially interesting since in the presence of an intermediate-age population, asymptotic giant branch stars are the main contributors. In this Letter, we measure the near-infrared indices Na I and D {sub CO} for a sample of 12 early-type galaxies in low-density environments and compare them with the Fornax galaxy sample presented by Silva et al.. The analysis of these indices in combination with Lick/IDS indices in the optical range reveals that (1) the Na I index is a metallicity indicator as good as C4668 in the optical range, and (2) D {sub CO} is a tracer of intermediate-age stellar populations. We find that low-mass galaxies in low-density environments show higher Na I and D {sub CO} than those located in the Fornax cluster, which points toward a late stage of star formation for the galaxies in less dense environments, in agreement with results from other studies using independent methods.

  3. THE MAGELLANIC INTER-CLOUD PROJECT (MAGIC). I. EVIDENCE FOR INTERMEDIATE-AGE STELLAR POPULATIONS IN BETWEEN THE MAGELLANIC CLOUDS

    SciTech Connect

    Noeel, N. E. D.; Read, J. I.; Conn, B. C.; Rix, H.-W.; Carrera, R.

    2013-05-10

    The origin of the gas in between the Magellanic Clouds (MCs)-known as the ''Magellanic Bridge'' (MB)-is puzzling. Numerical simulations suggest that the MB formed from tidally stripped gas and stars in a recent interaction between the MCs. However, the apparent lack of stripped intermediate- or old-age stars associated with the MB is at odds with this picture. In this paper, we present the first results from the MAGellanic Inter-Cloud program (MAGIC) aimed at probing the stellar populations in the inter-Cloud region. We present observations of the stellar populations in two large fields located in between the Large and Small Magellanic Clouds (LMC/SMC), secured using the WFI camera on the 2.2 m telescope in La Silla. Using a synthetic color-magnitude diagram technique, we present the first quantitative evidence for the presence of intermediate-age and old stars in the inter-Cloud region. The intermediate-age stars-which make up {approx}28% of all stars in the region-are not present in fields at a similar distance from the SMC in a direction pointing away from the LMC. This provides potential evidence that these intermediate-age stars could have been tidally stripped from the SMC. However, spectroscopic studies will be needed to confirm or rule out the tidal origin for the inter-Cloud gas and stars.

  4. On the local stellar populations

    NASA Astrophysics Data System (ADS)

    Fuhrmann, Klaus; Chini, Rolf; Kaderhandt, Lena; Chen, Zhiwei

    2016-10-01

    We present a study of the local stellar populations from a volume-complete all-sky survey of the about 500 bright stars with distances less than 25 pc and down to main-sequence effective temperatures Teff ≥ 5300~K. The sample is dominated by a 93 % fraction of Population I stars, only 22 sources (5 %) are Population II stars, and 9 sources (2 %) are intermediate disc stars. No source belongs to the halo. By following the mass of the stars instead of their light, the resulting subset of 136 long-lived stars distributes as 22 (16.2 %) : 6 (4.4 %) : 108 (79.4 %) for the Population II : intermediate disc : Population I, respectively. Along with the much larger scaleheight reached by Population II, this unbiased census of long-lived stars provides plain evidence for a starburst epoch in the early Milky Way, with the formation of a massive, rotationally-supported, and dark Population II. The same conclusion arises from the substantial early chemical enrichment levels, exemplified here by the elements magnesium and iron, as it arises also from the local Population II white dwarfs. The kinematics, metallicity distribution functions, star formation rates, age-metallicity relations, the inventory of young stars, and the occurrence of blue straggler stars are discussed. A potentially new aspect of the survey is the possibility for substructure among the local Population II stars that may further subdivide into metal-poor and metal-rich sources.

  5. Radiation fields of intermediate-age stellar populations with binaries as ionizing sources of H II regions

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Li, L.; Cheng, L.; Wang, L.; Kang, X.; Zhuang, Y.; Han, Z.

    2015-02-01

    Radiation fields emitted by O- and B-type stars or young stellar populations (SPs) are generally considered as significant central ionizing sources (CISs) of classic H II regions. In our previous studies, we showed that the inclusion of binary interactions in stellar population synthesis models can significantly increase the ultraviolet spectrum hardness and the number of ionizing photons of intermediate-age (IA) SPs (7 ≲ log(t/yr) ≲ 8). In this work, we present photoionization models of H II regions ionized by radiation fields emitted by IA SPs, including binary systems, and show that these fields are in theory possible candidates for significant CISs of classic H II regions. When radiation fields of IA SPs comprising binary systems are used as the CISs of classic H II regions, the theoretical strengths of a number of lines (such as [O III] λ4959', [S II] λ6716', etc.), which are weaker than observations, are increased; the border or selection-criterion lines between star-forming galaxies and active galactic nuclei (AGNs) in the diagnostic diagrams (for example, [N II] λ6583/Hα versus [O III] λ5007/Hβ), move into the region occupied originally by AGNs; and the He II λ1640 line, observed in Lyman break and high-redshift gravitationally lensed galaxies, also can be produced.

  6. Stellar populations of stellar halos: Results from the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Conroy, C.; Pillepich, A.; Hernquist, L.

    2016-08-01

    The influence of both major and minor mergers is expected to significantly affect gradients of stellar ages and metallicities in the outskirts of galaxies. Measurements of observed gradients are beginning to reach large radii in galaxies, but a theoretical framework for connecting the findings to a picture of galactic build-up is still in its infancy. We analyze stellar populations of a statistically representative sample of quiescent galaxies over a wide mass range from the Illustris simulation. We measure metallicity and age profiles in the stellar halos of quiescent Illustris galaxies ranging in stellar mass from 1010 to 1012 M ⊙, accounting for observational projection and luminosity-weighting effects. We find wide variance in stellar population gradients between galaxies of similar mass, with typical gradients agreeing with observed galaxies. We show that, at fixed mass, the fraction of stars born in-situ within galaxies is correlated with the metallicity gradient in the halo, confirming that stellar halos contain unique information about the build-up and merger histories of galaxies.

  7. STELLAR POPULATION VARIATIONS IN THE MILKY WAY's STELLAR HALO

    SciTech Connect

    Bell, Eric F.; Xue Xiangxiang; Rix, Hans-Walter; Ruhland, Christine; Hogg, David W.

    2010-12-15

    If the stellar halos of disk galaxies are built up from the disruption of dwarf galaxies, models predict highly structured variations in the stellar populations within these halos. We test this prediction by studying the ratio of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor populations) to main-sequence turn-off stars (MSTO stars; a feature of all populations) in the stellar halo of the Milky Way using data from the Sloan Digital Sky Survey. We develop and apply an improved technique to select BHB stars using ugr color information alone, yielding a sample of {approx}9000 g < 18 candidates where {approx}70% of them are BHB stars. We map the BHB/MSTO ratio across {approx}1/4 of the sky at the distance resolution permitted by the absolute magnitude distribution of MSTO stars. We find large variations of the BHB/MSTO star ratio in the stellar halo. Previously identified, stream-like halo structures have distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo features, e.g., the low-latitude structure, appear to be almost completely devoid of BHB stars, whereas other structures appear to be rich in BHB stars. The Sagittarius tidal stream shows an apparent variation in the BHB/MSTO ratio along its extent, which we interpret in terms of population gradients within the progenitor dwarf galaxy. Our detection of coherent stellar population variations between different stellar halo substructures provides yet more support to cosmologically motivated models for stellar halo growth.

  8. STELLAR POPULATIONS OF ULTRALUMINOUS INFRARED GALAXIES

    SciTech Connect

    Hou, L. G.; Han, J. L.; Kong, M. Z.; Wu Xuebing

    2011-05-10

    Ultraluminous infrared galaxies (ULIRGs) are classified into several types depending on the dominance of starburst or active galactic nucleus (AGN) components. We conducted a stellar population analysis for a sample of 160 ULIRGs to study the evolution of ULIRGs. We found that the dominance of intermediate-age and old stellar populations increases along the sequence of H II-like ULIRGs, Seyfert-H II composite ULIRGs, and Seyfert 2 ULIRGs. Consequently, the typical mean stellar age and stellar mass increase along the sequence. Comparing the gas mass estimated from the CO measurements to the stellar mass estimated from the optical spectra, we found that the gas fraction is anti-correlated with stellar mass. Even so, the total masses of H II-like ULIRGs with small stellar masses and a large fraction of gas are not comparable to the small masses of Seyfert 2 ULIRGs. This indicates that H II-like ULIRGs with small stellar masses have no evolutionary connections with massive Seyfert 2 ULIRGs. Only massive ULIRGs may follow the evolution sequence toward AGNs, and massive H II-like ULIRGs are probably in an earlier stage of the sequence.

  9. Ubiquitous time variability of integrated stellar populations.

    PubMed

    Conroy, Charlie; van Dokkum, Pieter G; Choi, Jieun

    2015-11-26

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

  10. Ubiquitous time variability of integrated stellar populations.

    PubMed

    Conroy, Charlie; van Dokkum, Pieter G; Choi, Jieun

    2015-11-26

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models. PMID:26570999

  11. Ubiquitous time variability of integrated stellar populations

    NASA Astrophysics Data System (ADS)

    Conroy, Charlie; van Dokkum, Pieter G.; Choi, Jieun

    2015-11-01

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected ‘pixel shimmer’ in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

  12. Galactic stellar populations: current and new perspectives

    NASA Astrophysics Data System (ADS)

    Haywood, M.

    2014-11-01

    Present studies on the evolution of the Milky Way are driven and shaped by how we conceive its stellar populations, in an on going process started by W. Baade seventy years ago. Despite much progress and advances in our understanding of these populations, inspection of their main properties is however hardly indicative of the path the Milky Way has followed to build up its mass. This is not only a matter of (stellar) age measurement, but more so the consequence of how we interprete the structures that we see in our Galaxy, often through the filter of our definitions of stellar populations. The panorama presented in the following pages opens the possibility that the present "filter" is not fully adequate. I start these Lectures with a summary of the main properties of the disks, bulge, and halo, and then present some of the new directions in the interpretation of the structure and evolution of the disk(s), with emphasis on chemical evolution. I discuss recent results in our understanding of the bulge, its stellar components and chemical evolution. Finally, I present the ideas currently proposed to explain the formation of the Galactic stellar halo. I conclude by examining how deeply all these new results question our present definition of stellar populations.

  13. Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars

    NASA Astrophysics Data System (ADS)

    Das, Payel; Williams, Angus; Binney, James

    2016-08-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that trace the phase-space kinematics and chemistry out to ˜70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fit EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ˜2 kpc to -4 in the outer halo, with an axis ratio ˜0.7 throughout. There is no indication for rotation in the BHBs, although this is highly uncertain. A moderate level of radial anisotropy is detected, with βs varying from isotropic to between ˜0.1 and ˜0.3 in the outer halo depending on latitude. The BHB data are consistent with an age gradient of -0.03 Gyr kpc-1, with some uncertainty in the distribution of the larger ages. These results are consistent with a scenario in which older, larger systems contribute to the inner halo, whilst the outer halo is primarily comprised of younger, smaller systems.

  14. Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

    SciTech Connect

    Li, Chengyuan; De Grijs, Richard; Deng, Licai E-mail: grijs@pku.edu.cn

    2014-04-01

    Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of the clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.

  15. Stellar Populations in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    MacArthur, L. A.; Courteau, S.; Bell, E. F.; Holtzman, J. A.

    2004-12-01

    We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0--Irr. The colors are compared to stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Relative trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends level off for T ⪉ 4 (Sbc and earlier), V {rot} ⪆ 120 km s-1, MK ⪉ -23 mag, and μ 0 ⪉ 18.5 mag arcsec-2. Outer disk gradients are weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Relative trends in gradients with galaxy parameters do not agree with predictions of semi-analytic models of hierarchical galaxy formation, possibly as a result of bar-induced radial flows. However, the observed trends are in agreement with chemo-spectro photometric models of spiral galaxy evolution based on CDM-motivated scaling laws but including none of the hierarchical merging characteristics. This implies a strong dependence of the star formation history of spiral galaxies on the galaxy potential and halo spin parameter. L.A.M. and S.C acknowledge support

  16. The Carina Project. X. On the Kinematics of Old and Intermediate-age Stellar Populations1,2

    NASA Astrophysics Data System (ADS)

    Fabrizio, M.; Bono, G.; Nonino, M.; Łokas, E. L.; Ferraro, I.; Iannicola, G.; Buonanno, R.; Cassisi, S.; Coppola, G.; Dall’Ora, M.; Gilmozzi, R.; Marconi, M.; Monelli, M.; Romaniello, M.; Stetson, P. B.; Thévenin, F.; Walker, A. R.

    2016-10-01

    We present new radial velocity (RV) measurements of old (horizontal branch) and intermediate-age (red clump) stellar tracers in the Carina dwarf spheroidal. They are based on more than 2200 low-resolution spectra collected with VIMOS at Very Large Telescope (VLT). The targets are faint (20 ≲ V ≲ 21.5 mag), but the accuracy at the faintest limit is ≤9 km s‑1. These data were complemented with RV measurements either based on spectra collected with FORS2 and FLAMES/GIRAFFE at VLT or available in the literature. We ended up with a sample of 2748 stars and among them, 1389 are candidate Carina stars. We found that the intermediate-age stellar component shows a well-defined rotational pattern around the minor axis. The western and the eastern side of the galaxy differ by +5 and ‑4 km s‑1 when compared with the main RV peak. The old stellar component is characterized by a larger RV dispersion and does not show evidence of the RV pattern. We compared the observed RV distribution with N-body simulations for a former disky dwarf galaxy orbiting a giant Milky Way–like galaxy. We rotated the simulated galaxy by 60° with respect to the major axis, we kept the observer on the orbital plane of the dwarf and extracted a sample of stars similar to the observed one. Observed and predicted {V}{rot}/σ ratios across the central regions are in remarkable agreement. This evidence indicates that Carina was a disky dwarf galaxy that experienced several strong tidal interactions with the Milky Way. Owing to these interactions, Carina transformed from a disky to a prolate spheroid and the rotational velocity transformed into random motions.

  17. Colour and stellar population gradients in galaxies

    NASA Astrophysics Data System (ADS)

    Tortora, C.; Napolitano, N. R.; Cardone, V. F.; Capaccioli, M.; Jetzer, P.; Molinaro, R.

    We discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario.

  18. The Age of the Young Bulge-like Population in the Stellar System Terzan 5: Linking the Galactic Bulge to the High-z Universe

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Massari, D.; Dalessandro, E.; Lanzoni, B.; Origlia, L.; Rich, R. M.; Mucciarelli, A.

    2016-09-01

    The Galactic bulge is dominated by an old, metal-rich stellar population. The possible presence and the amount of a young (a few gigayears old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 was found to harbor three sub-populations with iron content varying by more than one order of magnitude (from 0.2 up to two times the solar value), with chemical abundance patterns strikingly similar to those observed in bulge field stars. Here we report on the detection of two distinct main-sequence turnoff points in Terzan 5, providing the age of the two main stellar populations: 12 Gyr for the (dominant) sub-solar component and 4.5 Gyr for the component at super-solar metallicity. This discovery classifies Terzan 5 as a site in the Galactic bulge where multiple bursts of star formation occurred, thus suggesting a quite massive progenitor possibly resembling the giant clumps observed in star-forming galaxies at high redshifts. This connection opens a new route of investigation into the formation process and evolution of spheroids and their stellar content. Based on data obtained with (1) the ESA/NASA HST, under programs GO-14061, GO-12933, GO-10845, (2) the Very Large Telescope of the European Southern Observatory during the Science Verification of the camera MAD; (3) the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA.

  19. INTEGRATED STELLAR POPULATIONS: CONFRONTING PHOTOMETRY WITH SPECTROSCOPY

    SciTech Connect

    MacArthur, Lauren A.; McDonald, Michael; Courteau, Stephane; Gonzalez, J. Jesus

    2010-08-01

    We investigate the ability of spectroscopic techniques to yield realistic star formation histories (SFHs) for the bulges of spiral galaxies based on a comparison with their observed broadband colors. Full spectrum fitting to optical spectra indicates that recent (within {approx}1 Gyr) star formation activity can contribute significantly to the V-band flux, whilst accounting for only a minor fraction of the stellar mass budget which is made up primarily of old stars. Furthermore, recent implementations of stellar population (SP) models reveal that the inclusion of a more complete treatment of the thermally pulsating asymptotic giant branch (TP-AGB) phase to SP models greatly increases the NIR flux for SPs of ages 0.2-2 Gyr. Comparing the optical-NIR colors predicted from population synthesis fitting, using models which do not include all stages of the TP-AGB phase, to the observed colors reveals that observed optical-NIR colors are too red compared to the model predictions. However, when a 1 Gyr SP from models including a full treatment of the TP-AGB phase is used, the observed and predicted colors are in good agreement. This has strong implications for the interpretation of stellar populations, dust content, and SFHs derived from colors alone.

  20. Stellar Populations. A User Guide from Low to High Redshift

    NASA Astrophysics Data System (ADS)

    Greggio, Laura; Renzini, Alvio

    2011-09-01

    This textbook is meant to illustrate the specific role played by stellar population diagnostics in our attempt to understand galaxy formation and evolution. The book starts with a rather unconventional summary of the results of stellar evolution theory (Chapter 1), as they provide the basis for the construction of synthetic stellar populations. Current limitations of stellar models are highlighted, which arise from the necessity to parametrize all those physical processes that involve bulk mass motions, such as convection, mixing, mass loss, etc. Chapter 2 deals with the foundations of the theory of synthetic stellar populations, and illustrates their energetics and metabolic functions, providing basic tools that will be used in subsequent chapters. Chapters 3 and 4 deal with resolved stellar populations, first addressing some general problems encountered in photometric studies of stellar fields. Then some highlights are presented illustrating our current capacity of measuring stellar ages in Galactic globular clusters, in the Galactic bulge and in nearby galaxies. Chapter 5 is dedicated to the exemplification of synthetic spectra of simple as well as composite stellar populations, drawing attention to those spectral features that may depend on less secure results of stellar evolution models. Chapter 6 illustrates how synthetic stellar populations are used to derive basic galaxy properties, such as star formation rates, stellar masses, ages and metallicities, and does so for galaxies at low as well as at high redshifts. Chapter 7 is dedicated to supernovae, distinguishing them in core collapse and thermonuclear cases, describing the evolution of their rates for various star formation histories, and estimating the supernova productivity of stellar populations and their chemical yields. In Chapter 8 the stellar initial mass function (IMF) is discussed, first showing how even apparently small IMF variations may have large effects on the demo! graphy of stellar

  1. Star clusters as simple stellar populations.

    PubMed

    Bruzual A, Gustavo

    2010-02-28

    In this paper, I review to what extent we can understand the photometric properties of star clusters, and of low-mass, unresolved galaxies, in terms of population-synthesis models designed to describe 'simple stellar populations' (SSPs), i.e. groups of stars born at the same time, in the same volume of space and from a gas cloud of homogeneous chemical composition. The photometric properties predicted by these models do not readily match the observations of most star clusters, unless we properly take into account the expected variation in the number of stars occupying sparsely populated evolutionary stages, owing to stochastic fluctuations in the stellar initial mass function. In this case, population-synthesis models reproduce remarkably well the full ranges of observed integrated colours and absolute magnitudes of star clusters of various ages and metallicities. The disagreement between the model predictions and observations of cluster colours and magnitudes may indicate problems with or deficiencies in the modelling, and does not necessarily tell us that star clusters do not behave like SSPs. Matching the photometric properties of star clusters using SSP models is a necessary (but not sufficient) condition for clusters to be considered SSPs. Composite models, characterized by complex star-formation histories, also match the observed cluster colours.

  2. THE C+N+O ABUNDANCE OF {omega} CENTAURI GIANT STARS: IMPLICATIONS FOR THE CHEMICAL-ENRICHMENT SCENARIO AND THE RELATIVE AGES OF DIFFERENT STELLAR POPULATIONS

    SciTech Connect

    Marino, A. F.; Milone, A. P.; Aparicio, A.; Piotto, G.; Cassisi, S.; D'Antona, F.; Anderson, J.; Bedin, L. R.; Renzini, A.; Villanova, S. E-mail: milone@iac.es E-mail: giampaolo.piotto@unipd.it E-mail: dantona@oa-roma.inaf.it E-mail: luigi.bedin@oapd.inaf.it E-mail: svillanova@astro-udec.cl

    2012-02-10

    We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster by studying how the total C+N+O content varies among the different metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find that the (anti)correlations among the light elements that would be expected on theoretical grounds for matter that has been nuclearly processed via high-temperature proton captures. The overall [(C+N+O)/Fe] increases by {approx}0.5 dex from [Fe/H] {approx}-2.0 to [Fe/H] {approx}-0.9. Our results provide insight into the chemical-enrichment history of the cluster, and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations.

  3. Stellar population model dependence in optical AGN identification

    NASA Astrophysics Data System (ADS)

    Chen, Yanping; Zaw, Ingyin; Farrar, Glennys

    2016-08-01

    The choice of stellar templates plays an important role in optical spectroscopic AGN classification, because the host galaxy contribution must be accurately subtracted in order to isolate the true contribution of the AGN. Up to now, simple stellar population models such as BC03, have been used as templates in doing the stellar component analysis. As more stellar population models become available, systematic study of the impact of the stellar population modeling becomes possible. This is important not only for finding the best template but also for understanding the merits and limitations of the templates. We analyzed the SDSS DR8 spectra, using different empirical, theoretical, and mixed stellar population models. We found that some templates lead to systematic biases in the identification of AGN candidates. We investigated the effects of the range of age,metallicity, and the total wavelength used in full-spectrum fitting. We found that the completeness of parameter space in the template model plays a vital role in classifying AGN candidates; the wavelength range used to analyze the spectra also affects the result but in a relative minor way. Empirical stellar models can be expected to yield the most reliable estimate of the absorption features in the host galaxies, since there will be less model dependence (e.g., on opacity assumption, line profile representation).

  4. PN populations in the local group and distant stellar populations

    NASA Astrophysics Data System (ADS)

    Reid, Warren

    2016-08-01

    Our understanding of galactic structure and evolution is far from complete. Within the past twelve months we have learnt that the Milky Way is about 50% wider than was previously thought. As a consequence, new models are being developed that force us to reassess the kinematic structure of our Galaxy. Similarly, we need to take a fresh look at the halo structure of external galaxies in our Local Group. Studies of stellar populations, star-forming regions, clusters, the interstellar medium, elemental abundances and late stellar evolution are all required in order to understand how galactic assembly has occurred as we see it. PNe play an important role in this investigation by providing a measure of stellar age, mass, abundances, morphology, kinematics and synthesized matter that is returned to the interstellar medium (ISM). Through a method of chemical tagging, halo PNe can reveal evidence of stellar migration and galactic mergers. This is an outline of the advances that have been made towards uncovering the full number of PNe in our Local Group galaxies and beyond. Current numbers are presented and compared to total population estimates based on galactic mass and luminosity. A near complete census of PNe is crucial to understanding the initial-to-final mass relation for stars with mass >1 to <8 times the mass of the sun. It also allows us to extract more evolutionary information from luminosity functions and compare dust-to-gas ratios from PNe in different galactic locations. With new data provided by the Gaia satellite, space-based telescopes and the rise of giant and extra-large telescopes, we are on the verge of observing and understanding objects such as PNe in distant galaxies with the same detail we expected from Galactic observations only a decade ago.

  5. Stellar population models based on new generation stellar library

    NASA Astrophysics Data System (ADS)

    Koleva, M.; Vazdekis, A.

    The spectral predictions of stellar population models are not as accurate in the ultra-violet (UV) as in the optical wavelength domain. One of the reasons is the lack of high-quality stellar libraries. The New Generation Stellar Library (NGSL), recently released, represents a significant step towards the improvement of this situation. To prepare NGSL for population synthesis, we determined the atmospheric parameters of its stars, we assessed the precision of the wavelength calibration and characterised its intrinsic resolution. We also measured the Galactic extinction for each of the NGSL stars. For our analyses we used Ulyss, a full spectrum fitting package, fitting the NGSL spectra against the MILES interpolator. As a second step we build preliminary single stellar population models using Vazdekis (2003) synthesis code. We find that the wavelength calibration is precise up to 0.1 px, after correcting a systematic effect in the optical range. The spectral resolution varies from 3 Å in the UV to 10 Å in the near-infrared (NIR), corresponding to a roughly constant reciprocal resolution R=λ/δλ ≈1000 and an instrumental velocity dispersion σ_{ins} ≈ 130 kms. We derived the atmospheric parameters homogeneously. The precision for the FGK stars is 42 K, 0.24 and 0.09 dex for teff, logg and feh, respectively. The corresponding mean errors are 150 K, 0.50 and 0.48 dex for the M stars, and for the OBA stars they are 4.5 percent, 0.44 and 0.18 dex. The comparison with the literature shows that our results are not biased. Our first version of models compares well with models based on optical libraries, having the advantages to be free from artifacts due to the atmosphere. In future we will fine-tune our models by comparing to different models and observations of globular clusters.

  6. Intergalactic stellar populations in intermediate redshift clusters

    NASA Astrophysics Data System (ADS)

    Melnick, J.; Giraud, E.; Toledo, I.; Selman, F.; Quintana, H.

    2012-11-01

    A substantial fraction of the total stellar mass in rich clusters of galaxies resides in a diffuse intergalactic component usually referred to as the intracluster light (ICL). Theoretical models indicate that these intergalactic stars originate mostly from the tidal interaction of the cluster galaxies during the assembly history of the cluster, and that a significant fraction of these stars could have formed in situ from the late infall of cold metal-poor gas clouds on to the cluster. However, these models also overpredict the fraction of stellar mass in the ICL by a substantial margin, something that is still not well understood. The models also make predictions about the age distribution of the ICL stars, which may provide additional observational constraints. Here we present population synthesis models for the ICL of an intermediate redshift (z = 0.29) X-ray cluster that we have extensively studied in previous papers. The advantage of observing intermediate redshift clusters rather than nearby ones is that the former fit the field of view of multi-object spectrographs in 8-m telescopes and therefore permit us to encompass most of the ICL with only a few well-placed slits. In this paper we show that by stacking spectra at different locations within the ICL it is possible to reach sufficiently high signal-to-noise ratios to fit population synthesis models and derive meaningful results. The models provide ages and metallicities for the dominant populations at several different locations within the ICL and the brightest cluster galaxies (BCG) halo, as well as measures of the kinematics of the stars as a function of distance from the BCG. We thus find that the ICL in our cluster is dominated by old metal-rich stars, at odds with what has been found in nearby clusters where the stars that dominate the ICL are old and metal poor. While we see weak evidence of a young, metal-poor component, if real, these young stars would amount to less than 1 per cent of the total ICL

  7. UNUSUAL PAH EMISSION IN NEARBY EARLY-TYPE GALAXIES: A SIGNATURE OF AN INTERMEDIATE-AGE STELLAR POPULATION?

    SciTech Connect

    Vega, O.; Bressan, A.; Panuzzo, P.; Granato, G. L.; Silva, L.; Zeilinger, W. W.

    2010-10-01

    We present the analysis of Spitzer-IRS spectra of four early-type galaxies (ETGs), NGC 1297, NGC 5044, NGC 6868, and NGC 7079, all classified as LINERs in the optical bands. Their IRS spectra present the full series of H{sub 2} rotational emission lines in the range 5-38 {mu}m, atomic lines, and prominent polycyclic aromatic hydrocarbon (PAH) features. We investigate the nature and origin of the PAH emission, characterized by unusually low 6-9/11.3 {mu}m interband ratios. After the subtraction of a passive ETG template, we find that the 7-9 {mu}m spectral region requires dust features not normally present in star-forming galaxies. Each spectrum is then analyzed with the aim of identifying their components and origin. In contrast to normal star-forming galaxies, where cationic PAH emission prevails, our 6-14 {mu}m spectra seem to be dominated by large and neutral PAH emission, responsible for the low 6-9/11.3 {mu}m ratios, plus two broad dust emission features peaking at 8.2 {mu}m and 12 {mu}m. These broad components, observed until now mainly in evolved carbon stars and usually attributed to pristine material, contribute approximately 30%-50% of the total PAH flux in the 6-14 {mu}m region. We propose that the PAH molecules in our ETGs arise from fresh carbonaceous material that is continuously released by a population of carbon stars, formed in a rejuvenation episode that occurred within the last few Gyr. The analysis of the MIR spectra allows us to infer that, in order to maintain the peculiar size and charge distributions biased to large and neutral PAHs, this material must be shocked and excited by the weak UV interstellar radiation field of our ETGs.

  8. PN populations in the Local Group and distant stellar populations

    NASA Astrophysics Data System (ADS)

    Reid, Warren Alfred

    2015-08-01

    Our understanding of galactic structure and evolution is far from complete. Within the past twelve months we have learnt that the Milky Way is about 50% wider than was previously thought. As a consequence, new models are being developed that force us to reassess the kinematic structure of our Galaxy. Similarly, we need to take a fresh look at the halo structure of external galaxies in our Local Group. Studies of stellar populations, star-forming regions, clusters, the interstellar medium, elemental abundances and late stellar evolution are all required in order to understand how galactic assembly has occurred as we see it.PNe play an important role in this investigation by providing a measure of stellar age, mass, abundances, morphology, kinematics and synthesized matter that is returned to the interstellar medium (ISM). PN populations in the halos can be compared to those deeper within each galaxy to reveal any differences in chemical composition that may, through a method of chemical tagging show signs of stellar migration and galactic entwining.In this talk I will outline the advances that have been made in uncovering the full number of PNe in our Local Group galaxies. Current numbers will be presented and compared to total population estimates based on galactic mass and luminosity. A near complete census of PNe is crucial to understanding the initial-to-final mass relation for stars with mass >1 to <8 times the mass of the sun. It also allows us to extract more evolutionary information from luminosity functions and compare dust-to-gas ratios from PNe in different galactic locations. Nucleosynthesised material returned to the ISM during the PN phase can be compared to non-synthesised matter to expose the role PNe play in enriching the galactic environment.With new data provided by the Gaia satellite, space-based telescopes and the rise of giant and extra-large telescopes supplementing future space telescope missions, we are on the verge of observing and

  9. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-02-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 12 NFGS galaxies observable from Cerro Tololo in 2014A. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  10. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-08-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 19 NFGS galaxies observable from Cerro Tololo in 2014B. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  11. The Information Content of Stellar Halos: Accretion Histories and Stellar Population Gradients in Quiescent Illustris Galaxies

    NASA Astrophysics Data System (ADS)

    Cook, Benjamin A.; Conroy, Charlie; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Hernquist, Lars

    2016-06-01

    Long dynamical timescales in the outskirts of galaxies are thought to preserve the information content of their accretion histories, in the form of stellar population gradients. We present a detailed analysis of the stellar halo properties of a statistically representative sample of quiescent galaxies from the Illustris simulation, and show that stellar population gradients at large radii can indeed be used to infer galactic accretion histories. We measure metallicity, age, and surface-brightness profiles in the halos of Illustris galaxies ranging from 1010 to 1012 solar masses. We find that the ex-situ mass fraction – the fraction of stars that were accreted from smaller bodies – at large radius is correlated with the gradients of both metallicity and surface-brightness between 2-10 effective radii. There is a tight relation between the two gradients, suggesting that the information content of hierarchical accretion is predominantly the same between the two. The residuals from this mean relation are correlated with the mean (mass-weighted) merger mass ratio, which implies that major and minor mergers leave slightly different signatures in the stellar populations of stellar halos.

  12. The stellar population of the Lupus clouds

    NASA Technical Reports Server (NTRS)

    Hughes, Joanne; Hartigan, Patrick; Krautter, Joachim; Kelemen, Janos

    1994-01-01

    We present photometric and spectroscopic observations of the H alpha emission stars in the Lupus dark cloud complex. We estimate the effective temperatures of the stars from their spectral types and calculate the reddening towards each object from the (R-I) colors. From these data, we derive mass and age distributions for the Lupus stars using a new set of pre-main sequence evolutionar tracks. We compare the results for the Lupus stars with those for a similar population of young stellar objects in Taurus-Auriga and Chamaeleon and with the initial mass function for field stars in the solar neighborhood. From the H-R diagrams, Lupus appears to contain older stars than Taurus. The Lupus dark clouds form a greater proportion of low mass stars than the Taurus complex. Also, the proportion of low mass stars in Lupus is higher than that predicted by the Miller-Scalo initial mass function, and the lowest mass stars in Lupus are less active than similar T Tauri stars in other regions.

  13. Stellar Populations with the LSST

    NASA Astrophysics Data System (ADS)

    Saha, Abhijit; Olsen, K.; LSST Stellar Populations Collaboration

    2006-12-01

    The LSST will produce a multi-color map and photometric object catalog of half the sky to g 27.5(5σ). Strategically cadenced time-space sampling of each field spanning ten years will allow variability, proper motion and parallax measurements for objects brighter than g 25. As part of providing an unprecedented map of the Galaxy, the accurate multi-band photometry will permit photometric parallaxes, chemical abundances and a handle on ages via colors at turn-off for main-sequence stars at all distances within the Galaxy, permitting a comprehensive study of star formation histories (SFH) and chemical evolution for field stars. With a geometric parallax accuracy of 1mas, LSST will produce a robust complete sample of the solar neighborhood stars. While delivering parallax accuracy comparable to HIPPARCOS, LSST will extend the catalog to more than a 10 magnitudes fainter limit, and will be complete to MV 15. In the Magellanic Clouds too, the photometry will reach MV +8, allowing the SFH and chemical signatures in the expansive outer extremities to be gleaned from their main sequence stars. This in turn will trace the detailed interaction of the Clouds with the Galaxy halo. The LSST time sampling will identify and characterize variable stars of all types, from time scales of 1hr to several years, a feast for variable star astrophysics. Cepheids and LPVs in all galaxies in the Sculptor, M83 and Cen-A groups are obvious data products: comparative studies will reveal systematic differences with galaxy properties, and help to fine tune the rungs of the distance ladder. Dwarf galaxies within 10Mpc that are too faint to find from surface brightness enhancements will be revealed via over-densities of their red giants: this systematic census will extend the luminosity function of galaxies to the faint limit. Novae discovered by LSST time sampling will trace intergalactic stars out to the Virgo and Fornax clusters.

  14. The stellar population of the Rosat North Ecliptic Pole survey

    NASA Astrophysics Data System (ADS)

    Micela, G.; Affer, L.; Favata, F.; Henry, J. P.; Gioia, I.; Mullis, C. R.; Sanz Forcada, J.; Sciortino, S.

    2007-01-01

    Context: X-ray surveys are a very efficient mean of detecting young stars and therefore allow us to study the young stellar population in the solar neighborhood and the local star formation history in the last billion of years. Aims: We want to study the young stellar population in the solar neighborhood, to constrain its spatial density and scale height as well as the recent local star formation history. Methods: We analyze the stellar content of the ROSAT North Ecliptic Pole survey, and compare the observations with the predictions derived from stellar galactic model. Since the ROSAT NEP survey is sensitive at intermediate fluxes is able to sample both the youngest stars and the intermediate age stars (younger than 109 years), linking the shallow and deep flux surveys already published in the literature. Results: We confirm the existence of an excess of yellow stars in our neighborhood previously seen in shallow survey, which is likely due to a young star population not accounted for in the model. However the excellent agreement between observations and predictions of dM stars casts some doubt on the real nature of this active population.

  15. Multiple Stellar Populations in Star Clusters

    NASA Astrophysics Data System (ADS)

    Piotto, G.

    2013-09-01

    For half a century it had been astronomical dogma that a globular cluster (GC) consists of stars born at the same time out of the same material, and this doctrine has borne rich fruits. In recent years, high resolution spectroscopy and high precision photometry (from space and ground-based observations) have shattered this paradigm, and the study of GC populations has acquired a new life that is now moving it in new directions. Evidence of multiple stellar populations have been identified in the color-magnitude diagrams of several Galactic and Magellanic Cloud GCs where they had never been imagined before.

  16. Stellar populations in Active Galactic Nuclei III

    NASA Astrophysics Data System (ADS)

    Boisson, C.; Joly, M.; Pelat, D.; Ward, M. J.

    2004-12-01

    In this paper we apply the stellar population synthesis method previously described in Boisson et al. (\\cite{Boisson2000}) to five more AGN. The analysis of these new data strengthen our previous conclusions: i) homogeneity of the stellar population within a class of nuclear activity regardless of the morphological type of the host galaxy; ii) populations within the nuclear regions of LINERs and Seyfert 2s are different: LINERs have a very old metal-rich population while in the Seyfert 2s a contribution of a weak burst of star formation is observed together with the old high metallicity component; iii) in the circum-nuclar region (200 pc ≤D≤1 kpc) of all the active galaxies in our sample, except for NGC 2992, we detect an old burst of star formation (0.2-1 Gyr),which is contrary to what is observed in normal galaxies. We note that the broad OIλ8446 Å emission line detected in the spectrum of the nucleus of NGC 2992 confirms its classification as a Seyfert 1. Based on observations collected at the New Technology Telescope of the European Southern Observatory, La Silla, Chile.

  17. KINEMATICS OF STELLAR POPULATIONS IN POSTSTARBURST GALAXIES

    SciTech Connect

    Hiner, Kyle D.; Canalizo, Gabriela E-mail: khiner@astro-udec.cl

    2015-01-20

    Poststarburst galaxies host a population of early-type stars (A or F) but simultaneously lack indicators of ongoing star formation such as [O II] emission. Two distinct stellar populations have been identified in these systems: a young poststarburst population superimposed on an older host population. We present a study of nine poststarburst galaxies with the following objectives: (1) to investigate whether and how kinematical differences between the young and old populations of stars can be measured, and (2) to gain insight into the formation mechanism of the young population in these systems. We fit high signal-to-noise spectra with two independent populations in distinct spectral regions: the Balmer region, the Mg IB region, and the Ca triplet when available. We show that the kinematics of the two populations largely track one another if measured in the Balmer region with high signal-to-noise data. Results from examining the Faber-Jackson relation and the fundamental plane indicate that these objects are not kinematically disturbed relative to more evolved spheroids. A case study of the internal kinematics of one object in our sample shows it to be pressure supported and not rotationally dominated. Overall our results are consistent with merger-induced starburst scenarios where the young population is observed during the later stages of the merger.

  18. Revealing the Stellar POPULATION{S} of Andromeda IV

    NASA Astrophysics Data System (ADS)

    Ferguson, Annette

    1996-07-01

    Andromeda IV is an enigmatic object, first identified by van den Bergh {1972}, during his photographic survey for dwarf spheroidal galaxy companions to M31, as either an `old star cloud' in the outer disk of M31, or possibly a background dwarf galaxy. We here propose deep WFPC2 V and I imaging of And IV to V> 27, which will resolve stars down to M_V +3, and determine main sequence turnoffs of < 5 * 10^9yr. The mean color of the red giant branch will provide a mean metallicity estimate, while the width constrains the dispersion in metallicity. The AGB and BHB stars provide further age and metallicity constraints. A reliable distance is necessary to establish the location of And IV in the M31 disk; this will be obtained from the I-band magnitude of the tip of the RGB. Ground-based observations are hampered by the proximity of a relatively bright star and by the combination of faintness and crowding in And IV. The extant ground-based CCD photometry for this object, to V 23 {Jones 1993}, have been interpreted as representing a young population with a narrow range of ages, an `unusually large' open cluster. And IV may be large enough that it could represent the transition stage between a single-age star cluster, and a self-enriched, many-generation stellar system. If indeed in the disk of M31, And IV lies beyond 4 disk scalelengths, a typical `edge' of optical disks. It thus could provide a unique example of a large star cluster in the outer regions of a disk, where there is little on-going or past star formation.

  19. The Stellar Populations of Lyman Break Galaxies at z ~ 5

    NASA Astrophysics Data System (ADS)

    Yabe, Kiyoto; Ohta, Kouji; Iwata, Ikuru; Sawicki, Marcin; Tamura, Naoyuki; Akiyama, Masayuki; Aoki, Kentaro

    2009-03-01

    We present the results of spectral energy distribution (SED) fitting analysis for Lyman break galaxies (LBGs) at z ~ 5 in the Great Observatories Origins Deep Survey North (GOODS-N) and its flanking fields (the GOODS-FF). With the publicly available Infrared Array Camera (IRAC) images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z ~ 5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of the sample LBGs. The derived stellar masses range from 108 to 1011 M sun with a median value of 4.1 × 109 M sun. Comparison with z = 2-3 LBGs shows that the stellar masses of z ~ 5 LBGs are systematically smaller by a factor of 3-4 than those of z = 2-3 LBGs in a similar rest-frame UV luminosity range. The star formation ages are relatively younger than those of the z = 2-3 LBGs. We also compared the results for our sample with other studies for the z = 5-6 galaxies. Although there seem to be similarities and differences in the properties, we could not conclude its significance. We also derived a stellar mass function of our sample by correcting for incompletenesses. Although the number densities in the massive end are comparable to the theoretical predictions from semianalytic models involving active galactic nucleus feedback, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 108 M sun, the stellar mass density at z ~ 5 is calculated to be (0.7-2.4) ×107 M sun Mpc-3. The stellar mass density at z ~ 5 is dominated by the massive part of the stellar mass function. Compared with other observational studies and the model predictions, the mass density of our sample is consistent with general trend of the increase of the stellar mass density with time.

  20. Comparing Stellar Populations Across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Loeffler, Shane; Kaleida, Catherine C.; Parkash, Vaishali

    2015-01-01

    Previous work (Jansen et al., 2000, Taylor et al., 2005) has revealed trends in the optical wavelength radial profiles of galaxies across the Hubble Sequence. Radial profiles offer insight into stellar populations, metallicity, and dust concentrations, aspects which are deeply tied to the individual evolution of a galaxy. The Nearby Field Galaxy Survey (NFGS) provides a sampling of nearby galaxies that spans the range of morphological types, luminosities, and masses. Currently available NFGS data includes optical radial surface profiles and spectra of 196 nearby galaxies. We aim to look for trends in the infrared portion of the spectrum for these galaxies, but find that existing 2MASS data is not sufficiently deep. Herein, we expand the available data for the NGFS galaxy IC1639 deeper into the infrared using new data taken with the Infrared Sideport Imager (ISPI) on the 4-m Blanco Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. Images taken in J, H, and Ks were reduced using standard IRAF and IDL procedures. Photometric calibrations were completed by using the highest quality (AAA) 2MASS stars in the field. Aperture photometry was then performed on the galaxy and radial profiles of surface brightness, J-H color, and H-Ks color were produced. For IC1639, the new ISPI data reveals flat color gradients and surface brightness gradients that decrease with radius. These trends reveal an archetypal elliptical galaxy, with a relatively homogeneous stellar population, stellar density decreasing with radius, and little-to-no obscuration by dust. We have obtained ISPI images for an additional 8 galaxies, and further reduction and analysis of these data will allow for investigation of radial trends in the infrared for galaxies across the Hubble Sequence.

  1. The galaxy population of Abell 1367: the stellar mass-metallicity relation

    NASA Astrophysics Data System (ADS)

    Mouhcine, M.; Kriwattanawong, W.; James, P. A.

    2011-04-01

    Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

  2. YONSEI EVOLUTIONARY POPULATION SYNTHESIS (YEPS) MODEL. I. SPECTROSCOPIC EVOLUTION OF SIMPLE STELLAR POPULATIONS

    SciTech Connect

    Chung, Chul; Yoon, Suk-Jin; Lee, Sang-Yoon; Lee, Young-Wook

    2013-01-15

    We present a series of papers on the 2012 version of the Yonsei Evolutionary Population Synthesis (YEPS) model, which was constructed based on over 20 years of research. This first paper delineates the spectroscopic aspect of integrated light from stellar populations older than 1 Gyr. The standard YEPS is based on the most up-to-date Yonsei-Yale stellar evolutionary tracks and BaSel 3.1 flux libraries, and provides absorption line indices of the Lick/IDS system and high-order Balmer lines for simple stellar populations as functions of stellar parameters, such as metallicity, age, and {alpha}-element mixture. Special care has been taken to incorporate a systematic contribution from horizontal-branch (HB) stars, which alters the temperature-sensitive Balmer lines significantly, resulting in up to a 5 Gyr difference in the age estimation of old, metal-poor stellar populations. We also find that HBs exert an appreciable effect not only on the Balmer lines but also on the metallicity-sensitive lines, including the magnesium index. This is critical in explaining the intriguing bimodality found in index distributions of globular clusters in massive galaxies and to accurately derive spectroscopic metallicities from various indices. A full set of the spectroscopic and photometric YEPS model data of the entire parameter space is currently downloadable at http://web.yonsei.ac.kr/cosmic/data/YEPS.htm.

  3. Stellar mass and population diagnostics of cluster galaxies

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.

    2013-12-01

    We conduct a broad investigation about stellar mass and population diagnostics in order to formulate novel constraints related to the formation and evolution of galaxies from a nearby cluster environment. Our work is powered by the use of stellar population models which transform galaxy colours and/or absorption line strengths into estimates of its stellar properties. As input to such models, we assemble an extensive compilation of age and chemical abundance information for Galactic globular clusters. This compilation allows a confident expansion of these models into new regions of parameter space that promise to refine our knowledge of galactic chemical evolution. We then draw upon a state-of-the-art spectroscopic and photometric survey of the Virgo galaxy cluster in order to constrain spatial variations of the stellar ages, metallicities, and masses within its member galaxies, and their dynamical masses. We interpret these data in the context of the histories of star formation, chemical enrichment, and stellar mass assembly to formulate a broad picture of the build-up of this cluster's content over time. In it, the giant early-type galaxies formed through highly dissipational processes at early times that built up most of their stellar mass and drew significant amounts of dark matter within their optical radii. Conversely, dwarf early-types experienced environmental processes that quenched their star formation during either the early stages of cluster assembly or upon infall at later times. Somewhat perplexing is our finding that the internal dynamics of these galaxies are largely explained by their stellar masses. Lastly, Virgo spirals also suffer from their dense environment, through ram pressure stripping and/or tidal harrassment. In addition to quenching, these effects leave an imprint on their internal dynamical evolution too. Late-type spirals exhibit evidence of having ejected significant amounts of baryons from their inner regions, likely via energetic

  4. The AIMSS Project - III. The stellar populations of compact stellar systems

    NASA Astrophysics Data System (ADS)

    Janz, Joachim; Norris, Mark A.; Forbes, Duncan A.; Huxor, Avon; Romanowsky, Aaron J.; Frank, Matthias J.; Escudero, Carlos G.; Faifer, Favio R.; Forte, Juan Carlos; Kannappan, Sheila J.; Maraston, Claudia; Brodie, Jean P.; Strader, Jay; Thompson, Bradley R.

    2016-02-01

    In recent years, a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilized discriminant, their stellar population properties. Based on new spectroscopy from 8-10m telescopes, we derive ages, metallicities, and [α/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals (cEs) larger than M32. Together with a literature compilation, this provides a panoramic view of the stellar population characteristics of early-type systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the cEs depart from the mass-metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultracompact dwarfs (UCDs) changes at a few times 107 M⊙, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS internal escape velocities.

  5. Kinematics and Stellar Populations in Isolated Lenticular Galaxies

    NASA Astrophysics Data System (ADS)

    Katkov, Ivan Yu.; Kniazev, Alexei Yu.; Sil'chenko, Olga K.

    2015-07-01

    By combining new long-slit spectral data obtained with the Southern African Large Telescope for nine galaxies with our previously published observations for 12 additional galaxies, we study the stellar and gaseous kinematics as well as radially resolved stellar population properties and ionized-gas metallicity and excitation for a sample of isolated lenticular galaxies. We have found that there is no particular time frame of formation for the isolated lenticular galaxies: the mean stellar ages of the bulges and disks are distributed between 1 and \\gt 13 Gyr, and the bulge and the disk in every galaxy formed synchronously demonstrate similar stellar ages and magnesium-to-iron ratios. Extended ionized-gas disks are found in the majority of the isolated lenticular galaxies, in 72% ±11%. Half of all extended gaseous disks demonstrate a visible counterrotation with respect to their stellar counterparts. We argue that just such a fraction of projected counterrotation is expected if all of the gas in isolated lenticular galaxies is accreted from outside, under the assumption of isotropically distributed external sources. The very narrow range of the gas oxygen abundances we found for the outer ionized-gas disks excited by young stars, [O/H] from 0.0 to +0.2 dex, gives evidence for satellite merging as the most probable source of this accretion. Last, we formulate a hypothesis that the morphological type of a field disk galaxy is completely determined by the outer cold-gas accretion regime. Based on observations made with the Southern African Large Telescope (SALT), programs 2011-3-RSA_OTH-001, 2012-1-RSA_OTH-002 and 2012-2-RSA_OTH-002.

  6. Stellar populations of galaxies in the ALHAMBRA survey up to z ~ 1. I. MUFFIT: A multi-filter fitting code for stellar population diagnostics

    NASA Astrophysics Data System (ADS)

    Díaz-García, L. A.; Cenarro, A. J.; López-Sanjuan, C.; Ferreras, I.; Varela, J.; Viironen, K.; Cristóbal-Hornillos, D.; Moles, M.; Marín-Franch, A.; Arnalte-Mur, P.; Ascaso, B.; Cerviño, M.; González Delgado, R. M.; Márquez, I.; Masegosa, J.; Molino, A.; Pović, M.; Alfaro, E.; Aparicio-Villegas, T.; Benítez, N.; Broadhurst, T.; Cabrera-Caño, J.; Castander, F. J.; Cepa, J.; Fernández-Soto, A.; Husillos, C.; Infante, L.; Aguerri, J. A. L.; Martínez, V. J.; del Olmo, A.; Perea, J.; Prada, F.; Quintana, J. M.; Gruel, N.

    2015-10-01

    Aims: We present MUFFIT, a new generic code optimized to retrieve the main stellar population parameters of galaxies in photometric multi-filter surveys, and check its reliability and feasibility with real galaxy data from the ALHAMBRA survey. Methods: Making use of an error-weighted χ2-test, we compare the multi-filter fluxes of galaxies with the synthetic photometry of mixtures of two single stellar populations at different redshifts and extinctions, to provide the most likely range of stellar population parameters (mainly ages and metallicities), extinctions, redshifts, and stellar masses. To improve the diagnostic reliability, MUFFIT identifies and removes from the analysis those bands that are significantly affected by emission lines. The final parameters and their uncertainties are derived by a Monte Carlo method, using the individual photometric uncertainties in each band. Finally, we discuss the accuracies, degeneracies, and reliability of MUFFIT using both simulated and real galaxies from ALHAMBRA, comparing with results from the literature. Results: MUFFIT is a precise and reliable code to derive stellar population parameters of galaxies in ALHAMBRA. Using the results from photometric-redshift codes as input, MUFFIT improves the photometric-redshift accuracy by ~10-20%. MUFFIT also detects nebular emissions in galaxies, providing physical information about their strengths. The stellar masses derived from MUFFIT show excellent agreement with the COSMOS and SDSS values. In addition, the retrieved age-metallicity locus for a sample of z ≤ 0.22 early-type galaxies in ALHAMBRA at different stellar mass bins are in very good agreement with the ones from SDSS spectroscopic diagnostics. Moreover, a one-to-one comparison between the redshifts, ages, metallicities, and stellar masses derived spectroscopically for SDSS and by MUFFIT for ALHAMBRA reveals good qualitative agreements in all the parameters, hence reinforcing the strengths of multi-filter galaxy data

  7. CALIBRATING STELLAR POPULATION MODELS WITH MAGELLANIC CLOUD STAR CLUSTERS

    SciTech Connect

    Noeel, N. E. D.; Carollo, C. M.; Greggio, L.; Renzini, A.; Maraston, C.

    2013-07-20

    Stellar population models are commonly calculated using star clusters as calibrators for those evolutionary stages that depend on free parameters. However, discrepancies exist among different models, even if similar sets of calibration clusters are used. With the aim of understanding these discrepancies, and of improving the calibration procedure, we consider a set of 43 Magellanic Cloud (MC) clusters, taking age and photometric information from the literature. We carefully assign ages to each cluster based on up-to-date determinations, ensuring that these are as homogeneous as possible. To cope with statistical fluctuations, we stack the clusters in five age bins, deriving for each of them integrated luminosities and colors. We find that clusters become abruptly red in optical and optical-infrared colors as they age from {approx}0.6 to {approx}1 Gyr, which we interpret as due to the development of a well-populated thermally pulsing asymptotic giant branch (TP-AGB). We argue that other studies missed this detection because of coarser age binnings. Maraston and Girardi et al. models predict the presence of a populated TP-AGB at {approx}0.6 Gyr, with a correspondingly very red integrated color, at variance with the data; Bruzual and Charlot and Conroy models run within the error bars at all ages. The discrepancy between the synthetic colors of Maraston models and the average colors of MC clusters results from the now obsolete age scale adopted. Finally, our finding that the TP-AGB phase appears to develop between {approx}0.6 and 1 Gyr is dependent on the adopted age scale for the clusters and may have important implications for stellar evolution.

  8. Stellar population effects on the inferred photon density at reionization

    NASA Astrophysics Data System (ADS)

    Stanway, Elizabeth R.; Eldridge, J. J.; Becker, George D.

    2016-02-01

    The relationship between stellar populations and the ionizing flux with which they irradiate their surroundings has profound implications for the evolution of the intergalactic medium (IGM). We quantify the ionizing flux arising from synthetic stellar populations which incorporate the evolution of interacting binary stars. We determine that these show ionizing flux boosted by 60 per cent at 0.05 ≤ Z ≤ 0.3 Z⊙ and a more modest 10-20 per cent at near-solar metallicities relative to star-forming populations in which stars evolve in isolation. The relation of ionizing flux to observables such as 1500 Å continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age, star formation history and initial mass function (IMF). For a galaxy forming 1 M⊙ yr-1, observed at >100 Myr after the onset of star formation, we predict a production rate of photons capable of ionizing hydrogen, Nion = 1.4 × 1053 s-1 at Z = Z⊙ and 3.5 × 1053 s-1 at 0.1 Z⊙, assuming a Salpeter-like IMF. We evaluate the impact of these issues on the ionization of the IGM, finding that the known galaxy populations can maintain the ionization state of the Universe back to z ˜ 9, assuming that their luminosity functions continue to MUV = -10, and that constraints on the IGM at z ˜ 2-5 can be satisfied with modest Lyman-continuum photon escape fractions of 4-24 per cent depending on assumed metallicity.

  9. Binary interactions and multiple stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Dengkai

    2015-08-01

    Observations revealed the presence of multiple stellar populations in globular clusters (GCs) that exhibit wide abundance variations and multiple sequences in Hertzsprung-Russell diagram. We present a scenario for the formation of multiple stellar populations in GCs. In this scenario, initial GCs are single-generation clusters, and our model predicts that the abundance anomalous stars observed in GCs are the merged stars and the accretor stars produced by binary interactions, which are rapidly rotating stars at the moment of their formation. The stellar population with binaries can reproduce two important observational evidences of multiple stellar populations, the Na-O anticorrelation and the multiple sequences in HR diagram. This suggests that binary interactions may be a possible scenario for the formation of multiple stellar populations in GCs.

  10. Evolutionary Stellar Population Synthesis at 2 Å Spectral Resolution

    NASA Astrophysics Data System (ADS)

    Vazdekis, A.

    2001-03-01

    I present an evolutionary stellar population synthesis model which predicts spectral energy distributions, SEDs, for simple old single-metallicity stellar populations, SSPs, in the wavelength intervals λλ 3856-4476Å and 4795-5465Å at a resolution of FWHM$equals;1.8 $Aring;, on the basis of an extensive empirical spectral library composed of ~550 stars. The synthesized model spectra can be used to analyse observed galaxy spectra in a very easy and flexible way, allowing us to adapt the theoretical predictions to the characteristics of the data instead of proceeding in the opposite direction (as we must do,for example, when transforming observational data to a particular system of indices at specific resolution/s, such as Lick, which is heavily instrument-dependent). The SSP spectra, with flux-calibrated response curves, can be smoothed to the same resolution as that of the data or to galaxy internal velocity dispersion, allowing us to analyse the observed spectra in their own system, and with no need to correct the index measurements for velocity dispersion. Thus, we are able to use all the information contained in the data, at their higher spectral resolution. Excellent fits are obtained for various metal-rich globular clusters at relatively high resolution, and well known spectral peculiarities such as the strong CN absorption features are detected. When applied to early-type galaxies the model also shows its potential for studying element ratios such as the Mg/Fe overabundance. The model spectra provided robust age indicators for old stellar populations which do not depend on metallicity and therefore have a great potential for solving the age-metallicity degeneracy of galaxy spectra.

  11. Stellar populations in the bulges of isolated galaxies

    NASA Astrophysics Data System (ADS)

    Morelli, L.; Parmiggiani, M.; Corsini, E. M.; Costantin, L.; Dalla Bontà, E.; Méndez-Abreu, J.; Pizzella, A.

    2016-09-01

    We present photometry and long-slit spectroscopy for 12 S0 and spiral galaxies selected from the Catalogue of Isolated Galaxies. The structural parameters of the sample galaxies are derived from the Sloan Digital Sky Survey i-band images by performing a two-dimensional photometric decomposition of the surface brightness distribution. This is assumed to be the sum of the contribution of a Sérsic bulge, an exponential disc, and a Ferrers bar characterized by elliptical and concentric isophotes with constant ellipticity and position angles. The rotation curves and velocity dispersion profiles of the stellar component are measured from the spectra obtained along the major axis of galaxies. The radial profiles of the Hβ, Mg and Fe line-strength indices are derived too. Correlations between the central values of the Mg 2 and line-strength indices and the velocity dispersion are found. The mean age, total metallicity and total α/Fe enhancement of the stellar population in the centre and at the radius where the bulge gives the same contribution to the total surface brightness as the remaining components are obtained using stellar population models with variable element abundance ratios. We identify intermediate-age bulges with solar metallicity and old bulges with a large spread in metallicity. Most of the sample bulges display super-solar α/Fe enhancement, no gradient in age and negative gradients of metallicity and α/Fe enhancement. These findings support a formation scenario via dissipative collapse where environmental effects are remarkably less important than in the assembly of bulges of galaxies in groups and clusters.

  12. Carbon and oxygen abundances in stellar populations

    NASA Astrophysics Data System (ADS)

    Nissen, P. E.; Chen, Y. Q.; Carigi, L.; Schuster, W. J.; Zhao, G.

    2014-08-01

    Context. Carbon and oxygen abundances in stars are important in many fields of astrophysics including nucleosynthesis, stellar structure, evolution of galaxies, and formation of planetary systems. Still, our knowledge of the abundances of these elements in different stellar populations is uncertain because of difficulties in observing and analyzing atomic and molecular lines of C and O. Aims: Abundances of C, O, and Fe are determined for F and G main-sequence stars in the solar neighborhood with metallicities in the range -1.6 < [Fe/H] < +0.4 in order to study trends and possible systematic differences in the C/Fe, O/Fe, and C/O ratios for thin- and thick-disk stars as well as high- and low-alpha halo stars. In addition, we investigate if there is any connection between C and O abundances in stellar atmospheres and the occurrence of planets. Methods: Carbon abundances are determined from the λλ 5052,5380 C i lines and oxygen abundances from the λ7774 O i triplet and the forbidden [O i] line at 6300 Å. MARCS model atmospheres are applied and non-LTE corrections for the O i triplet are included. Results: Systematic differences between high- and low-alpha halo stars and between thin- and thick-disk stars are seen in the trends of [C/Fe] and [O/Fe]. The two halo populations and thick-disk stars show the same trend of [C/O] versus [O/H], whereas the thin-disk stars are shifted to higher [C/O] values. Furthermore, we find some evidence of higher C/O and C/Fe ratios in stars hosting planets than in stars for which no planets have been detected. Conclusions: The results suggest that C and O in both high- and low-alpha halo stars and in thick-disk stars are made mainly in massive (M> 8 M⊙) stars, whereas thin-disk stars have an additional carbon contribution from low-mass AGB and massive stars of high metallicity causing a rising trend of the C/O ratio with increasing metallicity. However, at the highest metallicities investigated ([Fe/H] ≃ + 0.4), C/O does not

  13. Unresolved versus resolved: testing the validity of young simple stellar population models with VLT/MUSE observations of NGC 3603

    NASA Astrophysics Data System (ADS)

    Kuncarayakti, H.; Galbany, L.; Anderson, J. P.; Krühler, T.; Hamuy, M.

    2016-09-01

    Context. Stellar populations are the building blocks of galaxies, including the Milky Way. The majority, if not all, extragalactic studies are entangled with the use of stellar population models given the unresolved nature of their observation. Extragalactic systems contain multiple stellar populations with complex star formation histories. However, studies of these systems are mainly based upon the principles of simple stellar populations (SSP). Hence, it is critical to examine the validity of SSP models. Aims: This work aims to empirically test the validity of SSP models. This is done by comparing SSP models against observations of spatially resolved young stellar population in the determination of its physical properties, that is, age and metallicity. Methods: Integral field spectroscopy of a young stellar cluster in the Milky Way, NGC 3603, was used to study the properties of the cluster as both a resolved and unresolved stellar population. The unresolved stellar population was analysed using the Hα equivalent width as an age indicator and the ratio of strong emission lines to infer metallicity. In addition, spectral energy distribution (SED) fitting using STARLIGHT was used to infer these properties from the integrated spectrum. Independently, the resolved stellar population was analysed using the colour-magnitude diagram (CMD) to determine age and metallicity. As the SSP model represents the unresolved stellar population, the derived age and metallicity were tested to determine whether they agree with those derived from resolved stars. Results: The age and metallicity estimate of NGC 3603 derived from integrated spectroscopy are confirmed to be within the range of those derived from the CMD of the resolved stellar population, including other estimates found in the literature. The result from this pilot study supports the reliability of SSP models for studying unresolved young stellar populations. Based on observations collected at the European Organisation

  14. Evolutionary Stellar Population Synthesis at 2 Å Spectral Resolution

    NASA Astrophysics Data System (ADS)

    Vazdekis, A.

    1999-03-01

    In this paper we develop an evolutionary stellar population synthesis model to predict spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) at resolution ~1.8 Å in two reduced but very important spectral regions around 4000 and 5000 Å. The input stellar database is composed of a subsample of ~500 stars selected from the original Jones spectral library This is the first time that such an evolutionary model has employed such an extensive empirical stellar spectral library, at such high resolution, for supporting its SED predictions. A spectral library corresponding to simple old stellar populations with metallicities in the range -0.7<=[Fe/H]<=+0.2 is presented here, as well as an extensive discussion about the most popular system of absorption indices at intermediate resolution, the Lick system, showing the advantages of using the new model predictions. Also, we show for the first time the behavior of the Rose system of indices, at higher resolution, as a function of the age and the metallicity of the stellar population. The newly synthesized model spectra can be used to analyze the observed galaxy spectrum in a very easy and flexible way, allowing us to adapt the theoretical predictions to the characteristics of the data instead of proceeding in the opposite direction as, for example, we must do when transforming the observational data for using model predictions based on a particular instrument-dependent system of indices at a specific resolution. The synthetic SSP spectra, with flux-calibrated spectral response, can be smoothed to the same resolution as the observations or to the measured galaxy internal velocity dispersion, allowing us to analyze the observed spectrum in its own system. Therefore, we are able to utilize all the information contained in the data at their spectral resolution. After performing this step, the entire observational spectrum can be compared at one time, or the analysis can be done by

  15. Binary Populations and Stellar Dynamics in Young Clusters

    NASA Astrophysics Data System (ADS)

    Vanbeveren, D.; Belkus, H.; Van Bever, J.; Mennekens, N.

    2008-06-01

    We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, η Car, ζ Pup, γ2 Velorum and WR 140.

  16. The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk

    NASA Astrophysics Data System (ADS)

    Haywood, Misha; Di Matteo, Paola; Lehnert, Matthew D.; Katz, David; Gómez, Ana

    2013-12-01

    We analyze a sample of solar neighborhood stars that have high-quality abundance determinations and show that there are two distinct regimes of [α/Fe] versus age, which we identify as the epochs of the thick and thin disk formation. A tight correlation between metallicity and [α/Fe] versus age is clearly identifiable for thick disk stars, implying that this population formed from a well mixed interstellar medium, probably initially in starburst and then more quiescently, over a time scale of 4-5 Gyr. Thick disk stars have vertical velocity dispersions which correlate with age, with the youngest objects of this population having small scale heights similar to those of thin disk stars. A natural consequence of these two results is that a vertical metallicity gradient is expected in this population. We suggest that the youngest thick disk set the initial conditions from which the inner thin disk started to form about 8 Gyr ago, at [Fe/H] in the range of (-0.1, +0.1) dex and [α/Fe] ~ 0.1 dex. This also provides an explanation for the apparent coincidence between the existence of a step in metallicity at 7-10 kpc in the thin disk and the confinement of the thick disk within R < 10 kpc. We suggest that the outer thin disk developed outside the influence of the thick disk, giving rise to a separate structure, but also that the high alpha-enrichment of those regions may originate from a primordial pollution of the outer regions by the gas expelled from the forming thick disk. Metal-poor thin disk stars ([Fe/H] < -0.4 dex) in the solar vicinity, whose properties are best explained by them originating in the outer disk, are shown to be as old as the youngest thick disk (9-10 Gyr). This implies that the outer thin disk started to form while the thick disk was still forming stars in the inner parts of the Galaxy. Hence, while the overall inner (thick+thin) disk is comprised of two structures with different scale lengths and whose combination may give the impression of an

  17. Kinematics and stellar population of the lenticular galaxy NGC 4124

    NASA Astrophysics Data System (ADS)

    Zasov, A. V.; Sil'chenko, O. K.; Katkov, I. Yu.; Dodonov, S. N.

    2013-01-01

    Results of spectroscopic and photometric studies for the locally isolated lenticular galaxy NGC 4124 are presented. A model of the mass distribution consistent with photometric data has been constructed on the basis of a kinematic analysis. In this model, the halo mass within the optical radius is almost half the diskmass. The disk is shown to be in a dynamical state close to amarginally stable one. This rules out dynamical disk heating for the galaxy through a strong external action or a merger with a massive system. However, the presence of a gaseous disk inclined to the main plane of the galaxy in the central kiloparsec region suggests probable cannibalization of a small satellite that also produced a late starburst in the central region. This is confirmed by the younger mean age (˜2 Gyr) of the stellar population in the galaxy's central region than the disk age (5-7 Gyr).

  18. Probing Multiple Stellar Populations In The Open Cluster Trumpler 20

    NASA Astrophysics Data System (ADS)

    Platais, Imants; Melo, C. H. F.; Fulbright, J. P.; Clem, J. L.; Kozhurina-Platais, V.; Barnes, S.; Bedin, L. R.; Bellini, A.; Figueira, P.

    2010-01-01

    Ignoring the globular clusters, multiple stellar populations have been discovered in some intermediate-age LMC star clusters but not yet in any Galactic open cluster. However, a recently-unveiled rich, 1.3-Gyr old Galactic open cluster Trumpler 20 appears to offer propitious clues about the bimodality of its main sequence. We present new BVI observations obtained with the CTIO 1-m telescope. We also present comprehensive VLT/FLAMES high-resolution spectroscopic observations obtained at the ESO/Paranal. Kinematic membership in Trumpler 20 is derived from a single epoch radial velocities for more than 900 stars. The color-magnitude diagram of Trumpler 20 indicates a double main sequence turn-off and a considerable extension of the red clump. The distribution of [Fe/H] values for 87 red giants is consistent with Trumpler 20 having a single metallicity. The cluster is conspicuously rich with fast rotators (vsin i > 100 km/s), many of whom are located near the main sequence turn-off, thus lending support to the suggestion by Bastian & de Mink that for intermediate age (1-2 Gyr) clusters the effects of stellar rotation have direct implications on the structure of main sequence near the turn-off. Trumpler 20 is the first known Galactic open cluster to show this phenomenon. This work is supported in part by a NSF grant 09-08114 to JHU.

  19. EARLY-TYPE GALAXIES AT z {approx} 1.3. II. MASSES AND AGES OF EARLY-TYPE GALAXIES IN DIFFERENT ENVIRONMENTS AND THEIR DEPENDENCE ON STELLAR POPULATION MODEL ASSUMPTIONS

    SciTech Connect

    Raichoor, A.; Mei, S.; Huertas-Company, M.; Nakata, F.; Kodama, T.; Stanford, S. A.; Rettura, A.; Jee, M. J.; Holden, B. P.; Illingworth, G.; Rosati, P.; Blakeslee, J. P.; Demarco, R.; Eisenhardt, P.; Tanaka, M.

    2011-05-01

    We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z {approx} 1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multi-wavelength (0.6-4.5 {mu}m; KPNO, Palomar, Keck, Hubble Space Telescope, Spitzer) data sets. At this redshift the contribution of the thermally pulsing asymptotic giant branch (TP-AGB) phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot and Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual and Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using the Maraston and Charlot and Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M {approx}> 10{sup 11} M{sub sun}) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses.

  20. The Dark Energy Survey: Prospects for resolved stellar populations

    SciTech Connect

    Rossetto, Bruno M.; Santiago, Basílio X.; Girardi, Léo; Camargo, Julio I. B.; Balbinot, Eduardo; da Costa, Luiz N.; Yanny, Brian; Maia, Marcio A. G.; Makler, Martin; Ogando, Ricardo L. C.; Pellegrini, Paulo S.; Ramos, Beatriz; de Simoni, Fernando; Armstrong, R.; Bertin, E.; Desai, S.; Kuropatkin, N.; Lin, H.; Mohr, J. J.; Tucker, D. L.

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  1. Stellar populations in spiral galaxies: broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    2006-06-01

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  2. Stellar populations in spiral galaxies: Broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  3. Stellar Populations and the Star Formation Histories of LSB Galaxies: III. Stellar Population Models

    NASA Astrophysics Data System (ADS)

    Schombert, James; McGaugh, Stacy

    2014-09-01

    A series of population models are designed to explore the star formation history of gas-rich, low surface brightness (LSB) galaxies. LSB galaxies are unique in having properties of very blue colors, low Hα emission and high gas fractions that indicated a history of constant star formation (versus the declining star formation models used for most spirals and irregulars). The model simulations use an evolving multi-metallicity composite population that follows a chemical enrichment scheme based on Milky Way observations. Color and time sensitive stellar evolution components (i.e., BHB, TP-AGB and blue straggler stars) are included, and model colors are extended into the Spitzer wavelength regions for comparison to new observations. In general, LSB galaxies are well matched to the constant star formation scenario with the variation in color explained by a fourfold increase/decrease in star formation over the last 0.5 Gyrs (i.e., weak bursts). Early-type spirals, from the S4G sample, are better fit by a declining star formation model where star formation has decreased by 40% in the last 12 Gyrs.

  4. A Study of Stellar Population Synthesis of Post-starburst Quasars

    NASA Astrophysics Data System (ADS)

    Zhang-hu, Chu; Qiu-sheng, Gu

    2016-07-01

    We present a study of stellar population synthesis of a sample of 10 post-starburst quasars (PSQs) at z ∼ 0.3. These PSGs posses the spectral signatures of massive intermediate-aged stellar populations, making them potentially useful for studying the connections between the galactic nuclear activity and the host galaxy evolution. With the help of the stellar synthesis code STARLIGHT, we have determined the stellar population ages, black hole masses, and Eddington ratios of their host galaxies. We find that the PSQs have the black hole mass MBH ∼ 108 M⊙, the bolometric luminosity of a few percent of Eddington luminosity, and the ages of host stellar populations from several hundred Myr to a few Gyr. The result may support a time delay existed between the merge-induced starburst and the quasar being triggered/becoming visible. The synthetical spectral energy distribution (SED) of the PSQs indicates that they are closely related with the Ultra Luminous Infrared Galaxies (ULIRGs), and for these PSQs, the derived infrared luminosity has attained the level of a luminous infrared galaxy, implying that very possibly, these quasars selected by their optical spectra are undergoing the evolution from ULIRGs to optical quasars.

  5. Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars

    NASA Technical Reports Server (NTRS)

    Worthey, Guy; Faber, S. M.; Gonzalez, J. Jesus; Burstein, D.

    1994-01-01

    Twenty-one optical absorption features, 11 of which have been previously defined, are automatically measured in a sample of 460 stars. Following Gorgas et al., the indices are summarized in fitting functions that give index strengths as functions of stellar temperature, gravity, and (Fe/H). This project was carried out with the purpose of predicting index strengths in the integrated light of stellar populations of different ages and metallicities, but the data should be valuable for stellar studies in the Galaxy as well. Several of the new indices appear to be promising indicators of metallicity for old stellar populations. A complete list of index data and atmospheric parameters is available in computer-readable form.

  6. Fluctuation spectroscopy: a new probe of old stellar populations

    SciTech Connect

    Van Dokkum, Pieter G.; Conroy, Charlie

    2014-12-10

    We introduce a new method to determine the relative contributions of different types of stars to the integrated light of nearby early-type galaxies. As is well known, the surface brightness of these galaxies shows pixel-to-pixel fluctuations due to Poisson variations in the number of giant stars. Differential spectroscopy of pixels as a function of fluctuation strength ({sup f}luctuation spectroscopy{sup )} effectively measures the spectral variation of stars as a function of their luminosity, information that is otherwise difficult to obtain for individual stars outside of the Local Group. We apply this technique to the elliptical galaxy NGC 4472, using Hubble Space Telescope/Advanced Camera for Surveys imaging in six narrow-band ramp filters tuned to spectral features in the range 0.8 μm-1.0 μm. Pixels with ±5% broad-band variations show differential color variations of 0.1%-1.0% in the narrow-band filters. These variations are primarily due to the systematic increase in TiO absorption strength with increasing luminosity on the upper giant branch. The data are very well reproduced by the same Conroy and van Dokkum stellar population synthesis model that is the best fit to the integrated light, with residuals in the range 0.03%-0.09%. Models with ages or metallicities that are significantly different from the integrated-light values do not yield good fits. We can also rule out several modifications to the underlying model, including the presence of a significant (>3% of the light) population of late M giants. The current observations constitute a powerful test of the expected luminosities and temperatures of metal-rich giants in massive early-type galaxies. Studies of pixels with much larger (negative) fluctuations will provide unique information on main sequence stars and the stellar initial mass function.

  7. Stellar population properties for a sample of hard X-ray AGNs

    NASA Astrophysics Data System (ADS)

    Morelli, L.; Calvi, V.; Masetti, N.; Parisi, P.; Landi, R.; Maiorano, E.; Minniti, D.; Galaz, G.

    2013-08-01

    Aims: The aim of this paper is to study the stellar population of galaxies hosting an active galactic nucleus (AGN). We studied a subsample of hard X-ray emitting AGNs from the INTEGRAL and Swift catalogs, which were previously identified and characterized through optical spectroscopy. Our analysis provides complementary information, namely age and metallicity, which is necessary to complete the panoramic view of these interesting objects. Methods: We selected hard X-ray emitting objects, identified as AGNs, by checking their optical spectra in search of absorption lines suitable for the stellar population analysis. We obtained a final sample consisting of 20 objects with a redshift lower than 0.3. We used the full-spectrum fitting method; particularly, we use penalized pixel method and apply the PPXF code. After masking all the regions affected by emission lines, we fitted the spectra with the MILES single stellar population templates, and we derived mass-weighted ages and metallicities. Results: Most of the objects in our sample show an old stellar population; however, three of them are characterized by a bimodal distribution with a non-negligible contribution from young stars. The values of the mass-weighted metallicity span a wide range with most of them slightly above the solar value. No relations between the stellar population properties and the morphological ones have been found. Table 1 and Figs. 3-5 are available in electronic form at http://www.aanda.org

  8. The accretion histories of brightest cluster galaxies from their stellar population gradients

    NASA Astrophysics Data System (ADS)

    Oliva-Altamirano, Paola; Brough, Sarah; Jimmy, Tran, Kim-Vy; Couch, Warrick J.; McDermid, Richard M.; Lidman, Chris; von der Linden, Anja; Sharp, Rob

    2015-06-01

    We analyse the spatially resolved stellar populations of nine local (z < 0.1) Brightest Cluster Galaxies (BCGs) observed with VIMOS in Integral Field Unit mode. Our sample is composed of seven slow-rotating and two fast-rotating BCGs. We do not find a connection between stellar kinematics and stellar populations in this small sample. The BCGs have shallow metallicity gradients (median Δ[Fe/H] = -0.11 ± 0.1), high central metallicities (median [Fe/H][α/Fe] = 0 = 0.13 ± 0.07), and a wide range of central ages (from 5 to 15 Gyr). We propose that the reason for this is diverse evolutionary paths in BCGs. 67 per cent of the sample (6/9) show ˜7 Gyr old central ages, which reflects an active accretion history, and 33 per cent of the sample (3/9) have central ages older than 11 Gyr, which suggest no star formation since z = 2. The BCGs show similar central stellar populations and stellar population gradients to early-type galaxies of similar mass (Mdyn > 1011.3 M⊙) from the ATLAS3D survey (median [Z/H] = 0.04 ± 0.07, Δ[Z/H] = -0.19 ± 0.1). However, massive early-type galaxies from ATLAS3D have consistently old ages (median Age = 12.0 ± 3.8 Gyr). We also analyse the close massive companion galaxies of two of the BCGs. These galaxies have similar stellar populations to their respective BCGs.

  9. Uncovered: Progenitors of globular clusters showing off their multiple stellar populations

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Li, Chengyuan; Deng, Licai; Geller, Aaron M.; Xin, Yu; Hu, Yi; Faucher-Giguere, Claude-Andre

    2016-01-01

    Stars in star clusters are thought to form in a single burst from a common progenitor cloud of molecular gas, resulting in so-called simple stellar populations. However, old, massive globular clusters—with ages greater than 10 billion years—often host multiple stellar populations, indicating that more than one star-forming event may have occurred during their lifetimes. The most popular scenario for their formation invokes colliding stellar winds from late-stage, asymptotic-giant-branch stars. If this were correct, the initial globular cluster masses should be at least 10 times more massive than their current masses of typically a few x 105 Msun. However, large populations of clusters with masses greater than a few x 106 Msun are not found in the local Universe. Here we present Hubble Space Telescope observations of three 1-2 billion-year-old, massive star clusters in the Magellanic Clouds which show unequivocal evidence of burst-like star-formation activity that occurred a few x 108 years after their initial formation era. The spatial distributions of the younger stellar generations suggest that they may have originated from ambient gas clouds accreted by the clusters while orbiting in the disks of their host galaxies rather than from colliding stellar winds. Simple models imply that such clusters could indeed accrete sufficient gas reservoirs to form these stars. This may eventually give rise to the appearance of multiple stellar populations in globular clusters.

  10. Metallicity and Age of the Stellar Stream around the Disk Galaxy NGC 5907

    NASA Astrophysics Data System (ADS)

    Laine, Seppo; Grillmair, Carl J.; Capak, Peter; Arendt, Richard G.; Romanowsky, Aaron J.; Martínez-Delgado, David; Ashby, Matthew L. N.; Davies, James E.; Majewski, Stephen R.; Brodie, Jean P.; GaBany, R. Jay; Arnold, Jacob A.

    2016-09-01

    Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μm Spitzer/Infrared Array Camera observations. Combining the near-infrared 3.6 μm data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ∼60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of ‑0.3 inferred along the brightest parts of the stream.

  11. Metallicity and Age of the Stellar Stream around the Disk Galaxy NGC 5907

    NASA Astrophysics Data System (ADS)

    Laine, Seppo; Grillmair, Carl J.; Capak, Peter; Arendt, Richard G.; Romanowsky, Aaron J.; Martínez-Delgado, David; Ashby, Matthew L. N.; Davies, James E.; Majewski, Stephen R.; Brodie, Jean P.; GaBany, R. Jay; Arnold, Jacob A.

    2016-09-01

    Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μm Spitzer/Infrared Array Camera observations. Combining the near-infrared 3.6 μm data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ˜60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of -0.3 inferred along the brightest parts of the stream.

  12. Formation of multiple stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Dengkai

    2014-09-01

    Observations reveal the presence of multiple stellar populations (MSPs) in globular clusters (GCs) that exhibit wide abundance variations and multiple sequences in their Hertzsprung-Russell diagrams. We present a scenario for the formation of MSPs in GCs. In this scenario, initial GCs are single-generation clusters, and our model predicts that the anomalous-abundance stars observed in GCs are the merged and accreted stars produced by binary interactions, which are rapidly rotating stars at the moment of their formation. A stellar population with binaries can reproduce two important observational pieces of evidence of MSPs, the Na-O anticorrelation and the multiple sequences in the HR diagram.

  13. Stellar populations of the recent merger NGC 5128

    NASA Astrophysics Data System (ADS)

    Rejkuba, M.; Silva, D. R.; Minniti, D.; Bedding, T.

    2000-12-01

    Using the VLT with FORS1 and ISAAC we resolve stars in the halo and NE shell of the nearest giant elliptical galaxy NGC 5128. The shell is likely to be the stellar debris of a smaller galaxy accreted by NGC 5128 approximately 160 to 500 Myr ago (Quinn 1984, ApJ, 297, 596; Israel 1998, A&ARv, 8, 237). We indeed observe a higher stellar density at the position of the shell. On the shell a string of young blue stars is superimposed (see also Graham 1998, ApJ, 502, 245 and Mould et al. 2000, ApJ, 536, 266). Comparison of our UV color-magnitude diagram (CMD) with the theoretical isochrones of the Padua group gives an age of 10-15 Myr for this recent star formation. The bluest stars (U-V<-0.75) are mainly aligned with the direction of the radio and X-ray jet, but there is also a vertical structure located at the edge of the large HI cloud found next to the shell (Schiminovich 1994, ApJ, 432, L101). The optical (U-V) and near-IR (V-Ks) CMDs for the rest of the shell stars are consistent with an old population similar to the one observed in the halo field of NGC 5128. The halo population of NGC 5128 is mainly old and has a significant metallicity spread. The optical-near IR (V-Ks) CMDs reveal stars as metal-poor as [Fe/H] ~-2 dex. Unfortunately, the incompleteness in the V-band photometry prevents the determination of the upper end of the metallicity distribution. At the assumed distance of 3.6 Mpc (Soria et al. 1996, ApJ, 465, 79), the K-band magnitude of the tip of the RGB is expected to be found at K ~21. We observe a large number of stars between 19.5 and 21 mag in Ks, corresponding to a significant intermediate-age AGB population. This work was partially sponsored by FONDECYT grants No. 07990048 and 01990440.

  14. Women and population aging.

    PubMed

    Kunugi, T

    1989-06-01

    In 1985, there were approximately 427 million persons aged 60 and over in the world, accounting for about 9% of the world's population. By 2020, the elderly population will comprise 13% of the world's population and 70% of these people will live in developing countries. Governments and international agencies should increase their efforts and activities to improve care for the elderly within the family unit. The socioeconomic implications of aging are greater for females because of their higher life expectancy. In the year 2000, 11% of the world's female population will be aged 60 and over. By 2025, there will be 604 million elderly women in the world, 70% of whom will be living in developing countries, and among them, 70% in rural areas. An important issue requiring both research and policy attention is the interdependence among women's economic, health, and social concerns, which increase with age. The author calls for more specific policies that aim to eliminate discrimination against disabled persons, the elderly, and particularly elderly women. The author urges governmental and nongovernmental organizations to implement these recommendations: 1) promote research studies and the collection and analysis of information on the socioeconomic, health, legal, and demographic situation of elderly women; 2) promote awareness of elderly women's contribution to society; 3) eliminate discriminatory treatment of elderly women; 4) develop health promotion programs and services to meet elderly women's long-term care needs; 5) promote wider appreciation of continued participation of elderly women in social and cultural activities; 6) promote the development of elderly women's organizations and self-help groups; 7) promote and assure the participation of elderly women in the process of development; and 8) develop literacy programs and training programs for elderly women.

  15. CONNECTION BETWEEN DYNAMICALLY DERIVED INITIAL MASS FUNCTION NORMALIZATION AND STELLAR POPULATION PARAMETERS

    SciTech Connect

    McDermid, Richard M.; Cappellari, Michele; Bayet, Estelle; Bureau, Martin; Davies, Roger L.; Alatalo, Katherine; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Duc, Pierre-Alain; Davis, Timothy A.; De Zeeuw, P. T.; Emsellem, Eric; Kuntschner, Harald; Khochfar, Sadegh; Krajnović, Davor; Morganti, Raffaella; Oosterloo, Tom; Naab, Thorsten; and others

    2014-09-10

    We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the ATLAS{sup 3D} project. We study trends between our dynamically derived IMF normalization α{sub dyn} ≡ (M/L){sub stars}/(M/L){sub Salp} and absorption line strengths, and interpret these via single stellar population-equivalent ages, abundance ratios (measured as [α/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalization of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of α{sub dyn} at a given population parameter. As a result, we find weak α{sub dyn}-[α/Fe] and α{sub dyn} –Age correlations and no significant α{sub dyn} –[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalization via the low-mass star demographics inferred through stellar spectral analysis.

  16. THE EFFECTS OF STELLAR ROTATION. I. IMPACT ON THE IONIZING SPECTRA AND INTEGRATED PROPERTIES OF STELLAR POPULATIONS

    SciTech Connect

    Levesque, Emily M.; Leitherer, Claus; Ekstrom, Sylvia; Meynet, Georges; Schaerer, Daniel

    2012-05-20

    We present a sample of synthetic massive stellar populations created using the Starburst99 evolutionary synthesis code and new sets of stellar evolutionary tracks, including one set that adopts a detailed treatment of rotation. Using the outputs of the Starburst99 code, we compare the populations' integrated properties, including ionizing radiation fields, bolometric luminosities, and colors. With these comparisons we are able to probe the specific effects of rotation on the properties of a stellar population. We find that a population of rotating stars produces a much harder ionizing radiation field and a higher bolometric luminosity, changes that are primarily attributable to the effects of rotational mixing on the lifetimes, luminosities, effective temperatures, and mass-loss rates of massive stars. We consider the implications of the profound effects that rotation can have on a stellar population, and discuss the importance of refining stellar evolutionary models for future work in the study of extragalactic, and particularly high-redshift, stellar populations.

  17. A SPECTROSCOPIC CENSUS OF THE M82 STELLAR CLUSTER POPULATION

    SciTech Connect

    Konstantopoulos, I. S.; Westmoquette, M. S.; Bastian, N.; Smith, L. J.; Trancho, G.

    2009-08-20

    We present a spectroscopic study of the stellar cluster population of M82, the archetype starburst galaxy, based primarily on new Gemini-North multi-object spectroscopy of 49 star clusters. These observations constitute the largest to date spectroscopic data set of extragalactic young clusters, giving virtually continuous coverage across the galaxy; we use these data to deduce information about the clusters as well as the M82 post-starburst disk and nuclear starburst environments. Spectroscopic age dating places clusters in the nucleus and disk between (7, 15) and (30, 270) Myr, with distribution peaks at {approx}10 and 140 Myr, respectively. We find cluster radial velocities (RVs) in the range v{sub R} in (-160, 220)km s{sup -1} (with respect to the galaxy center), and line-of-sight Na I D interstellar absorption line velocities v {sup NaID}{sub R} in (-75, 200) km s{sup -1}, in many cases entirely decoupled from the clusters. As the disk cluster RVs lie on the flat part of the galaxy rotation curve, we conclude that they comprise a regularly orbiting system. Our observations suggest that the largest part of the population was created as a result of the close encounter with M81 {approx}220 Myr ago. Clusters in the nucleus are found in solid body rotation on the bar. The possible detection of Wolf-Rayet features in their spectra indicates that cluster formation continues in the central starburst zone. We also report the potential discovery of two old populous clusters in the halo of M82, aged {approx}>8 Gyr. Using these measurements and simple dynamical considerations, we derive a toy model for the invisible physical structure of the galaxy, and confirm the existence of two dominant spiral arms.

  18. Stellar populations in the Carina region. The Galactic plane at l = 291°

    NASA Astrophysics Data System (ADS)

    Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

    2016-08-01

    Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the

  19. Exploring Stellar Populations in the Tidal Tails of NGC3256

    NASA Astrophysics Data System (ADS)

    Rodruck, Michael; Konstantopoulos, Iraklis; Charlton, Jane C.

    2015-01-01

    Galaxy interactions can inject material into the intergalactic medium via violent gravitational dynamics, often visualized in tidal tails. The composition of these tails has remained a mystery, as previous studies have focused on detecting tidal features, rather than the composite material itself. With this in mind, we have developed an observing program using deep, multiband imaging to probe the chaotic regions of tidal tails in search for an underlying stellar population. NGC3256's Western and Eastern tidal tails serve as a case study for this new technique. Our results show median color values of u - g = 1.12 and r - i = 0.09 for the Western tail, and u - g = 1.29 and r - i = 0.21 for the Eastern tail, corresponding to ages of approximately 450 Myr and 900 Myr for the tails, respectively. A u - g color gradient is seen in the Western tail as well, running from 1.32 to 1.08 (~2000 Myr to 400 Myr), suggesting ages inside tidal tails can have significant variations.

  20. Measurement of stellar age from uranium decay.

    PubMed

    Cayrel, R; Hill, V; Beers, T C; Barbuy, B; Spite, M; Spite, F; Plez, B; Andersen, J; Bonifacio, P; François, P; Molaro, P; Nordström, B; Primas, F

    2001-02-01

    The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope 232Th (half-life 14 Gyr) has been used to date Galactic stars, but it decays by only a factor of two over the lifetime of the Universe. 238U (half-life 4.5 Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957 nm, has previously not been detected in stars. Here we report a measurement of this line in the very metal-poor star CS31082-001, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7 +/- 0.14 +/- 0.12 yields an age of 12.5 +/- 3 Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe.

  1. Exploring the stellar populations of nearby and high redshift galaxies with ELTs

    NASA Astrophysics Data System (ADS)

    Gullieuszik, M.; Falomo, R.; Greggio, L.; Uslenghi, M.; Fantinel, D.

    The high sensitivity and spatial resolution of future ELTs facilities will offer the unique opportunity to probe directly the stellar populations of the very inner regions of galaxies in the local Universe and to derive morphological and photometric information for high redshift galaxies. We present our project aimed at assessing the expected capabilities of ELTs in the study of nearby and high-redshift stellar populations. To this end, we simulated imaging observations of different stellar populations in the local Universe and in high-redhshift galaxies with the MICADO camera at the E-ELT. Detailed photometric analyses of these images were used to probe the feasibility of science cases dealing with photometry of resolved stars in crowded fields, and with surface photometry of distant galaxies. We find that the future facilities will allow us to greatly improve our knowledge of the stellar populations in galaxies, especially in the innermost and most crowded regions. Accurate photometry of turn-off stars in nuclear star clusters of intermediate age will be possible up to distances of ˜ 3 Mpc. The exquisite spacial resolution will also drive great progress in unresolved stellar populations studies, enabling the detailed measurement of structural parameters, colour profiles, and the detection of signature of star formation sub-structures in galaxies at redshifts up to z=3.

  2. Signatures of multiple stellar populations in unresolved extragalactic globular/young massive star clusters

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.; Finzell, Thomas

    2013-06-01

    We present an investigation of potential signatures of the formation of multiple stellar populations in recently formed extragalactic star clusters. All of the Galactic globular clusters for which good samples of individual stellar abundances are available show evidence for multiple populations. This appears to require that multiple episodes of star formation and light element enrichment are the norm in the history of a globular cluster. We show that there are detectable observational signatures of multiple formation events in the unresolved spectra of massive, young extragalactic star clusters. We present the results of a pilot program to search for one of the cleanest signatures that we identify—the combined presence of emission lines from a very recently formed population and absorption lines from a somewhat older population. A possible example of such a system is identified in the Antennae galaxies. This source's spectrum shows evidence of two stellar populations with ages of 8 Myr and 80 Myr. Further investigation shows that these populations are in fact physically separated, but only by a projected distance of 59 pc. We show that the clusters are consistent with being bound and discuss the possibility that their coalescence could result in a single globular cluster hosting multiple stellar populations. While not the prototypical system proposed by most theories of the formation of multiple populations in clusters, the detection of this system in a small sample is both encouraging and interesting. Our investigation suggests that expanded surveys of massive young star clusters should detect more clusters with such signatures.

  3. OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION

    SciTech Connect

    Radburn-Smith, David J.; Dalcanton, Julianne J.; Roskar, Rok; Debattista, Victor P.; Streich, David; De Jong, Roelof S.; Vlajic, Marija; Holwerda, Benne W.; Purcell, Chris W.; Dolphin, Andrew E.; Zucker, Daniel B.

    2012-07-10

    We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars of NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.

  4. Tracing galaxy evolution through resolved stellar populations and star clusters

    NASA Astrophysics Data System (ADS)

    Silva-Villa, E.

    2011-09-01

    Field stars and star clusters contain a big part of the galaxy’s history. To understand galaxy formation and evolution we need then to understand the parts of which galaxies are composed. It has commonly been assumed that most stars formed in clusters. However, the connection between these two systems is not clear, and the fraction of actual star formation happening in clusters is still uncertain. Through this thesis, we aim to use field stars and star clusters to attack different problems regarding galaxy formation and evolution, named: 1. the cluster formation efficiency and its (co-)relation with environment (i.e. the host galaxy), 2. the star formation rate in the arms and inter-arm regions of spiral galaxies, and 3. the indications of a possible interaction between two galaxies observed through their resolved stellar populations. We performed a systematic and homogeneous study over the galaxies NGC45, NGC1313, NGC4395, NGC5236 and NGC7793, where star clusters and field stars are analyze separately. For this aim, we used Hubble Space Telescope observations in the optical bands U, B, V and I, using the Advanced Camera for Surveys and the Wide Field Planetary Camera 2. Standard photometric procedures are use to study the properties of these two main parts of the galaxies. However, incompleteness constrains our results to ages younger than 100 Myr. Following the synthetic CMD method we recovered the star formation history for the last 100 Myr over the five galaxies. Comparing observed clusters properties with simple stellar population models, we estimate ages and masses of star clusters. We observe that the galaxies NGC5236 and NGC1313 show higher star and cluster formation rates, while NGC45, NGC4395 and NGC7793 show lower values. We found that the actual fraction of star formation happening in clusters presents low values (< 10%), contrary to common assumptions, however in agreement with studies in other galaxies. Observations of the surface star formation

  5. The Stellar Population Structure of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Bovy, Jo; Rix, Hans-Walter; Schlafly, Edward F.; Nidever, David L.; Holtzman, Jon A.; Shetrone, Matthew; Beers, Timothy C.

    2016-05-01

    The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering 4 {kpc}≲ R≲ 15 {kpc}, to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in [α /{Fe}] and [{Fe}/{{H}}]—accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced [α /{Fe}] are centrally concentrated and are well-described as exponentials with a scale length of 2.2+/- 0.2 {kpc} over the whole radial range of the disk. We discover that the surface-density profiles of low-[α /{Fe}] MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from ≈ 5 to ≈ 13 {kpc} at low [{Fe}/{{H}}]. The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high-[α /{Fe}] MAPs have constant scale heights, low-[α /{Fe}] MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale height and that low-[{Fe}/{{H}}], low-[α /{Fe}] and high-[{Fe}/{{H}}], high-[α /{Fe}] MAPs have intermediate ({h}Z≈ 300{--}600 {pc}) scale heights that smoothly bridge the traditional thin- and thick-disk divide. That the high-[α /{Fe}], thick disk components do not flare is strong evidence against their thickness being caused by radial migration. The correspondence between the radial structure and chemical-enrichment age of stellar populations is clear confirmation of the inside-out growth of galactic disks. The details of these relations will constrain the variety of physical conditions under which stars form throughout the MW disk.

  6. THE STELLAR POPULATION AND STAR FORMATION PROPERTIES OF BLUE COMPACT DWARF GALAXIES

    SciTech Connect

    Zhao Yinghe; Gao Yu; Gu Qiusheng E-mail: yugao@pmo.ac.cn

    2011-02-15

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger ({approx}10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10{sup -3} to {approx}1 M{sub sun} yr{sup -1}, with a median value of {approx}0.1 M{sub sun} yr{sup -1}. We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  7. Cosmic Infrared Background and Early Stellar Populations

    NASA Technical Reports Server (NTRS)

    Kashlinsky, A.

    2005-01-01

    Cosmic infrared background (CIB) contains information about galaxy luminosities over the entire history of the Universe and can be a powerful diagnostic of the early populations otherwise inaccessible to telescopic studies. Its measurements are very difficult because of the strong IR foregrounds from the Solar system and the Galaxy. Nevertheless, substantial recent progress in measuring the CIB and its structure has been made. The measurements now allow to set significant constraints on early galaxy evolution and, perhaps, even detect the elusive Population III era. We discuss briefly the theory behind the CIB, review the latest measurements of the CIB and its structure, and discuss their implications for detecting and/or constraining the first stars and their epochs.

  8. Physical properties of young stellar populations in 24 starburst galaxies observed with FUSE

    NASA Astrophysics Data System (ADS)

    Pellerin, Anne; Robert, Carmelle

    2007-10-01

    We present the main physical properties of very young stellar populations seen with the Far Ultraviolet Spectroscopic Explorer in 24 individual starbursts. These characteristics have been obtained using the evolutionary spectral synthesis technique in the far-ultraviolet range with the LAVALSB code. For each starburst, quantitative values for age, metallicity, initial mass function slope, stellar mass and internal extinction have been obtained and discussed in details. Limits of the code have been tested. One main conclusion is that most starbursts (and probably all of them) cannot be represented by any continuous star formation burst in the far ultraviolet. Also, quantitative values of various optical diagnostics related to these stellar populations have been predicted. Underlying stellar populations, dominated by B-type stars, have been detected in NGC1140, NGC4449 and possibly NGC3991. We characterized the young stellar populations of less than 5Myr in Seyfert2 nuclei. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. Far Ultraviolet Spectroscopic Explorer (FUSE) is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985. E-mail: pellerin@stsci.edu (AP); carobert@phy.ulaval.ca (CR)

  9. The Spatial Structure of Young Stellar Clusters. II. Total Young Stellar Populations

    NASA Astrophysics Data System (ADS)

    Kuhn, Michael A.; Getman, Konstantin V.; Feigelson, Eric D.

    2015-03-01

    We investigate the intrinsic stellar populations (estimated total numbers of OB and pre-main-sequence stars down to 0.1 {{M}⊙ }) that are present in 17 massive star-forming regions (MSFRs) surveyed by the MYStIX project. The study is based on the catalog of >31,000 MYStIX Probable Complex Members with both disk-bearing and disk-free populations, compensating for extinction, nebulosity, and crowding effects. Correction for observational sensitivities is made using the X-ray luminosity function and the near-infrared initial mass function—a correction that is often not made by infrared surveys of young stars. The resulting maps of the projected structure of the young stellar populations, in units of intrinsic stellar surface density, allow direct comparison between different regions. Several regions have multiple dense clumps, similar in size and density to the Orion Nebula Cluster. The highest projected density of ˜34,000 stars pc-2 is found in the core of the RCW 38 cluster. Histograms of surface density show different ranges of values in different regions, supporting the conclusion of Bressert et al. that no universal surface-density threshold can distinguish between clustered and distributed star formation. However, a large component of the young stellar population of MSFRs resides in dense environments of 200-10,000 stars pc-2 (including within the nearby Orion molecular clouds), and we find that there is no evidence for the B10 conclusion that such dense regions form an extreme “tail” of the distribution. Tables of intrinsic populations for these regions are used in our companion study of young cluster properties and evolution.

  10. An isochrone data base and a rapid model for stellar population synthesis

    NASA Astrophysics Data System (ADS)

    Li, Zhongmu; Han, Zhanwen

    2008-06-01

    We first presented an isochrone data base that can be widely used for stellar population synthesis studies and colour-magnitude diagram (CMD) fitting. The data base consists of the isochrones of both single-star and binary-star simple stellar populations (ss-SSPs and bs-SSPs). The ranges for the age and metallicity of populations are 0-15 Gyr and 0.0001-0.03, respectively. All data are available for populations with two widely used initial mass functions (IMFs), that is, Salpeter IMF and Chabrier IMF. The uncertainty caused by the data base (about 0.81 per cent) is designed to be smaller than those caused by the Hurley code and widely used stellar spectra libraries (e.g. BaSeL 3.1) when it is used for stellar population synthesis. Based on the isochrone data base, we then built a rapid stellar population synthesis (RPS) model and calculated the high-resolution (0.3-Å) integrated spectral energy distributions, Lick indices and colour indices for bs-SSPs and ss-SSPs. In particular, we calculated the UBVRIJHKLM colours, ugriz colours and some composite colours that consist of magnitudes on different systems. These colours are useful for disentangling the well-known stellar age-metallicity degeneracy according to our previous work. As an example for applying the isochrone data base for CMD fitting, we fitted the CMDs of two star clusters (M67 and NGC1868) and obtained their distance moduli, colour excesses, stellar metallicities and ages. The results showed that the isochrones of bs-SSPs are closer to those of real star clusters. It suggests that we should take the effects of binary interactions into account in stellar population synthesis. We also discussed on the limitations of the application of the isochrone data base and the results of the RPS model. All the data are available at the CDS or on request to the authors. E-mail: zhongmu.li@gmail.com

  11. Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

    NASA Astrophysics Data System (ADS)

    Xin, Yu; Deng, Licai

    Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are very important in our context when considering the integrated spectral properties of a cluster, or a simple stellar population. In this chapter, we are going to describe how important the contribution of BSSs is to the total light of a cluster.

  12. Quantifying the impact of AGN and nebular emission on stellar population properties with REBETIKO

    NASA Astrophysics Data System (ADS)

    Cardoso, L. S. M.; Gomes, J. M.; Papaderos, P.

    2016-06-01

    Spectral synthesis enables the reconstruction of the star formation and chemical evolution histories (SFH & CEH) of a galaxy that are encoded in its spectral energy distribution (SED). Most state-of-the-art population synthesis codes however consider only purely stellar emission and are hence inadequate for modelling studies of galaxies where non-stellar emission components contribute significantly to the SED. This work combines evolutionary and population synthesis techniques to quantify the impact of active galactic nucleus (AGN) and nebular emission on the determination of the stellar population properties in galaxies. We have developed an evolutionary synthesis code called REBETIKO - Reckoning galaxy Emission By means of Evolutionary Tasks with Input Key Observables - to compute and study the time evolution of the SED of AGN-hosts and starburst galaxies. Our code takes into account the main ingredients of a galaxy's SED (e.g. non-thermal emission and/or nebular continuum and lines) for various commonly used parameterizations of the SFH, such as instantaneous burst, constant, exponentially decreasing, and gradually increasing peaking at a redshift between 1-10. Synthetic SEDs computed with REBETIKO have been subsequently fitted with the STARLIGHT population synthesis code (PSC) which can be regarded as representative for currently available state-of-the-art (i.e. purely stellar) PSCs. The objective is to study the impact of non-stellar SED components on the recovery of the true total stellar mass M_{star} and SFH of a galaxy, as well as other evolutionary properties, such as CEH and light- and mass-weighted mean stellar age and metallicity. We find that purely stellar fits in galaxies with a strong non-stellar continuum (e.g. Seyfert and/or starburst galaxies) can for instance overestimate M_{star} by up to 3 orders of magnitude, while the mean stellar age and metallicity can deviate from their true values up to 2 and 4 dex, respectively. These results imply

  13. A tale of two tails: exploring stellar populations in the tidal tails of NGC 3256

    NASA Astrophysics Data System (ADS)

    Rodruck, Michael; Konstantopoulos, Iraklis; Knierman, Karen; Fedotov, Konstantin; Mullan, Brendan; Gallagher, Sarah; Durrell, Patrick; Ciardullo, Robin; Gronwall, Caryl; Charlton, Jane

    2016-09-01

    We have developed an observing programme using deep, multiband imaging to probe the chaotic regions of tidal tails in search of an underlying stellar population, using NGC 3256's 400 Myr twin tidal tails as a case study. These tails have different colours of u - g = 1.05 ± 0.07 and r - i = 0.13 ± 0.07 for NGC 3256W, and u - g = 1.26 ± 0.07 and r - i = 0.26 ± 0.07 for NGC 3256E, indicating different stellar populations. These colours correspond to simple stellar population ages of 288^{+11}_{-54} and 841^{+125}_{-157} Myr for NGC 3256W and NGC 3256E, respectively, suggesting that NGC 3256W's diffuse light is dominated by stars formed after the interaction, while light in NGC 3256E is primarily from stars that originated in the host galaxy. Using a mixed stellar population model, we break our diffuse light into two populations: one at 10 Gyr, representing stars pulled from the host galaxies, and a younger component, whose age is determined by fitting the model to the data. We find similar ages for the young populations of both tails (195^{-13}_{+0} and 170^{-70}_{+44} Myr for NGC 3256W and NGC 3256E, respectively), but a larger percentage of mass in the 10 Gyr population for NGC 3256E (98^{+1}_{-3} per cent versus 90^{+5}_{-6} per cent). Additionally, we detect 31 star cluster candidates in NGC 3256W and 19 in NGC 2356E, with median ages of 141 and 91 Myr, respectively. NGC 3256E contains several young (<10 Myr), low-mass objects with strong nebular emission, indicating a small, recent burst of star formation.

  14. P-MaNGA: full spectral fitting and stellar population maps from prototype observations

    NASA Astrophysics Data System (ADS)

    Wilkinson, David M.; Maraston, Claudia; Thomas, Daniel; Coccato, Lodovico; Tojeiro, Rita; Cappellari, Michele; Belfiore, Francesco; Bershady, Matthew; Blanton, Mike; Bundy, Kevin; Cales, Sabrina; Cherinka, Brian; Drory, Niv; Emsellem, Eric; Fu, Hai; Law, David; Li, Cheng; Maiolino, Roberto; Masters, Karen; Tremonti, Christy; Wake, David; Wang, Enci; Weijmans, Anne-Marie; Xiao, Ting; Yan, Renbin; Zhang, Kai; Bizyaev, Dmitry; Brinkmann, Jonathan; Kinemuchi, Karen; Malanushenko, Elena; Malanushenko, Viktor; Oravetz, Daniel; Pan, Kaike; Simmons, Audrey

    2015-05-01

    MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yr SDSS-IV (Sloan Digital Sky Survey IV) survey that will obtain resolved spectroscopy from 3600 to 10 300 Å for a representative sample of over 10 000 nearby galaxies. In this paper, we derive spatially resolved stellar population properties and radial gradients by performing full spectral fitting of observed galaxy spectra from P-MaNGA, a prototype of the MaNGA instrument. These data include spectra for 18 galaxies, covering a large range of morphological type. We derive age, metallicity, dust, and stellar mass maps, and their radial gradients, using high spectral-resolution stellar population models, and assess the impact of varying the stellar library input to the models. We introduce a method to determine dust extinction which is able to give smooth stellar mass maps even in cases of high and spatially non-uniform dust attenuation. With the spectral fitting, we produce detailed maps of stellar population properties which allow us to identify galactic features among this diverse sample such as spiral structure, smooth radial profiles with little azimuthal structure in spheroidal galaxies, and spatially distinct galaxy sub-components. In agreement with the literature, we find the gradients for galaxies identified as early type to be on average flat in age, and negative (-0.15 dex/Re) in metallicity, whereas the gradients for late-type galaxies are on average negative in age (-0.39 dex/Re) and flat in metallicity. We demonstrate how different levels of data quality change the precision with which radial gradients can be measured. We show how this analysis, extended to the large numbers of MaNGA galaxies, will have the potential to shed light on galaxy structure and evolution.

  15. An analysis of the composite stellar population in M32

    NASA Astrophysics Data System (ADS)

    Coelho, P.; Mendes de Oliveira, C.; Cid Fernandes, R.

    2009-06-01

    We obtained long-slit spectra of high signal-to-noise ratio of the galaxy M32 with the Gemini Multi-Object Spectrograph at the Gemini-North telescope. We analysed the integrated spectra by means of full spectral fitting in order to extract the mixture of stellar populations that best represents its composite nature. Three different galactic radii were analysed, from the nuclear region out to 2arcmin from the centre. This allows us to compare, for the first time, the results of integrated light spectroscopy with those of resolved colour-magnitude diagrams from the literature. As a main result we propose that an ancient and an intermediate-age population co-exist in M32, and that the balance between these two populations change between the nucleus and outside one effective radius (1reff) in the sense that the contribution from the intermediate population is larger at the nuclear region. We retrieve a smaller signal of a young population at all radii whose origin is unclear and may be a contamination from horizontal branch stars, such as the ones identified by Brown et al. in the nuclear region. We compare our metallicity distribution function for a region 1 to 2arcmin from the centre to the one obtained with photometric data by Grillmair et al. Both distributions are broad, but our spectroscopically derived distribution has a significant component with [Z/Zsolar] <= -1, which is not found by Grillmair et al. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina) (observing run ID: GN-2004B-Q-74). E-mail: pcoelho@iap.fr (PC); oliveira

  16. Photometry of Multiple Stellar Populations in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Milone, Antonino

    2012-05-01

    An increasing number of observations over the last years have shown the existence of distinct sub-populations in many (maybe all) globular clusters and shattered the paradigm of globulars hosting single, simple stellar populations. These multiple populations manifest themselves in a split of different evolutionary sequences in the cluster color-magnitude diagrams. Using filters covering an appropriate range of wavelengths, photometry splits the main sequence into two or more branches, and in many cases this bimodality is repeated in the subgiant and red giant regions, and on the horizontal branch. In this talk I will summarize the main results from photometric studies.

  17. UV-extended E-MILES stellar population models: young components in massive early-type galaxies

    NASA Astrophysics Data System (ADS)

    Vazdekis, A.; Koleva, M.; Ricciardelli, E.; Röck, B.; Falcón-Barroso, J.

    2016-09-01

    We present UV-extended E-MILES stellar population synthesis models covering the spectral range λλ 1680 - 50000 Å at moderately high resolution. We employ the NGSL space-based stellar library to compute spectra of single-age, single-metallicity stellar populations in the wavelength range from 1680 to 3540 Å. These models represent a significant improvement in resolution and age/metallicity coverage over previous studies based on earlier space-based libraries. These model spectra were joined with those we computed in the visible using MILES, and other empirical libraries for redder wavelengths. The models span the metallicity range -1.79⩽ {[M/H]}}⩽ +0.26 and ages above 30 Myr, for a suite of IMF types with varying slopes. We focus on the behaviour of colours, spectra and line-strength indices in the UV range as a function of relevant stellar population parameters. Whereas some indices strengthen with increasing age and metallicity, as most metallicity indicators in the visible, other indices peak around 3 Gyr for metal-rich stellar populations, such as Mg at 2800 Å. Our models provide reasonably good fits to the integrated colours and most line-strengths of the stellar clusters of the Milky-Way and LMC. Our full-spectrum fits in the UV range for a representative set of ETGs of varying mass yield age and metallicity estimates in very good agreement with those obtained in the optical range. The comparison of UV colours and line-strengths of massive ETGs with our models reveals the presence of young stellar components, with ages in the range 0.1 - 0.5 Gyr and mass fractions 0.1 - 0.5%, on the top of an old stellar population.

  18. Understanding the size growth of massive galaxies through stellar populations

    NASA Astrophysics Data System (ADS)

    Ferreras, Ignacio

    2015-08-01

    The growth of massive galaxies remains an open problem. The observational evidence seems to converge on a two-stage scenario, where a compact massive core is formed during an early, intense burst, followed by a more extended process of mass and size growth at intermediate redshift (z<2). This talk focuses on the latter, exploring the growth of massive galaxies through a detailed analysis of the stellar populations in close pairs, to study their formation history. Two surveys are explored (SHARDS and GAMA), probing the stellar populations of pre-merging systems out to z~1.3, and down to a mass ratio ~1:100. We will compare the results between medium band spectral fitting (SHARDS) and those from a more targeted analysis of line strengths in the GAMA data. The combination of the two datasets provide a unique insight of the growth channel of massive galaxies via mergers.

  19. Ultraviolet to Mid-Infrared Observations of Star-forming Galaxies at z~2: Stellar Masses and Stellar Populations

    NASA Astrophysics Data System (ADS)

    Shapley, Alice E.; Steidel, Charles C.; Erb, Dawn K.; Reddy, Naveen A.; Adelberger, Kurt L.; Pettini, Max; Barmby, Pauline; Huang, Jiasheng

    2005-06-01

    We present the broadband UV through mid-infrared spectral energy distributions (SEDs) of a sample of 72 spectroscopically confirmed star-forming galaxies at z=2.30+/-0.3. Located in a 72 arcmin2 field centered on the bright background QSO, HS 1700+643, these galaxies were preselected to lie at z~2 solely on the basis of their rest-frame UV colors and luminosities and should be representative of UV-selected samples at high redshift. In addition to deep ground-based photometry spanning from 0.35 to 2.15 μm, we make use of Spitzer IRAC data, which probe the rest-frame near-IR at z~2. The range of stellar populations present in the sample is investigated with simple, single-component stellar population synthesis models. The inability to constrain the form of the star formation history limits our ability to determine the parameters of extinction, age, and star formation rate without using external multiwavelength information. Emphasizing stellar mass estimates, which are much less affected by these uncertainties, we find =10.32+/-0.51 for the sample. The addition of Spitzer IRAC data as a long-wavelength baseline reduces stellar mass uncertainties by a factor of 1.5-2 relative to estimates based on optical-Ks photometry alone. However, the total stellar mass estimated for the sample is remarkably insensitive to the inclusion of IRAC data. We find correlations between stellar mass and rest-frame R band (observed Ks) and rest-frame 1.4 μm (observed 4.5 μm) luminosities, although with significant scatter. Even at rest-frame 1.4 μm, the mass-to-light ratio varies by a factor of 15 indicating that even the rest-frame near-IR, when taken alone, is a poor indicator of stellar mass in star-forming galaxies at z~2. Allowing for the possibility of episodic star formation, we find that typical galaxies in our sample could contain up to 3 times more stellar mass in an old underlying burst than what was inferred from single-component modeling. In contrast, mass

  20. A Study of the Stellar Population in Selected SO Galaxies

    NASA Technical Reports Server (NTRS)

    Perez, M.; Danks, A.

    1997-01-01

    The goal of this program was to observe at least two SO galaxies with abnormal colors in the blue and clear optical signatures of dust and gas. The galaxies NGC 2217 and NGC 1808 were observed at least in one of the IUE cameras (1200-200 and 2000-3200 A) during the 13th episode, using the 4 US1 shifts assigned to this program. The galaxy NGC 2217 had been found to be part of a subgroup of SO galaxies with external gas rotating in retrograde motion with respect to the stars. This galaxy is a face-on object with indications of large amount of gas, quite rare for a SO galaxy. We observed this object on three different occasions with IUE at different positions of the large aperture (spacecraft roll angle) with respect to the nuclear region. These exposures allowed us to take full advantage of the spatial resolution of IUE by mapping nuclear and bulge region of this galaxy. We found that the data point to a marginally earlier stellar population toward the central region. The UV light as a whole is dominated by a late-type stellar population of principally G and K stars. The almost face-on view of this galaxy appears optically thick to UV light. It is conceivable that in analogy to out own Galaxy, the stellar populations weakly detected in NGC 2217, are mostly halo and late-type stars in the center with an increasing contribution of dust and early stellar populations (so far undetected) as we move outward along the faint spiral arms. This result is contrary to our initial expectation, since the counterrotating gas does not appear to be enhancing star formation in this galaxy. Even more interesting were the observations of NGC 1808; galaxy which has been classified, with a handful of other objects, both as a starburst and Seyfert galaxy. Attachment: 'The White-Dwarf Companions of 56 Persei and HR 3643.'

  1. A Study of the Stellar Population in Selected SO Galaxies

    NASA Astrophysics Data System (ADS)

    Perez, M.; Danks, A.

    1997-03-01

    The goal of this program was to observe at least two SO galaxies with abnormal colors in the blue and clear optical signatures of dust and gas. The galaxies NGC 2217 and NGC 1808 were observed at least in one of the IUE cameras (1200-200 and 2000-3200 A) during the 13th episode, using the 4 US1 shifts assigned to this program. The galaxy NGC 2217 had been found to be part of a subgroup of SO galaxies with external gas rotating in retrograde motion with respect to the stars. This galaxy is a face-on object with indications of large amount of gas, quite rare for a SO galaxy. We observed this object on three different occasions with IUE at different positions of the large aperture (spacecraft roll angle) with respect to the nuclear region. These exposures allowed us to take full advantage of the spatial resolution of IUE by mapping nuclear and bulge region of this galaxy. We found that the data point to a marginally earlier stellar population toward the central region. The UV light as a whole is dominated by a late-type stellar population of principally G and K stars. The almost face-on view of this galaxy appears optically thick to UV light. It is conceivable that in analogy to out own Galaxy, the stellar populations weakly detected in NGC 2217, are mostly halo and late-type stars in the center with an increasing contribution of dust and early stellar populations (so far undetected) as we move outward along the faint spiral arms. This result is contrary to our initial expectation, since the counterrotating gas does not appear to be enhancing star formation in this galaxy. Even more interesting were the observations of NGC 1808; galaxy which has been classified, with a handful of other objects, both as a starburst and Seyfert galaxy. Attachment: 'The White-Dwarf Companions of 56 Persei and HR 3643.'

  2. Shaping Disk Galaxy Stellar Populations via Internal and External Processes

    NASA Astrophysics Data System (ADS)

    Roškar, Rok

    2015-03-01

    In recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

  3. MILES extended: Stellar population synthesis models from the optical to the infrared

    NASA Astrophysics Data System (ADS)

    Röck, B.; Vazdekis, A.; Ricciardelli, E.; Peletier, R. F.; Knapen, J. H.; Falcón-Barroso, J.

    2016-05-01

    We present the first single-burst stellar population models, which covers the optical and the infrared wavelength range between 3500 and 50 000 Å and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [ Fe / H ] = - 0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis of two different sets of isochrones. They are available to the scientific community on the MILES web page. We checked the internal consistency of our models and compared their colour predictions to those of other models that are available in the literature. Optical and near infrared colours that are measured from our models are found to reproduce the colours well that were observed for various samples of early-type galaxies. Our models will enable a detailed analysis of the stellar populations of observed galaxies.

  4. THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS

    SciTech Connect

    Wise, John H.; Turk, Matthew J.; Norman, Michael L.; Abel, Tom

    2012-01-20

    By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10{sup -6}-10{sup -3.5} Z{sub Sun }. We present an adaptive mesh refinement radiation hydrodynamics simulation that follows the transition from Population III to Population II star formation. The maximum spatial resolution of 1 comoving parsec allows for individual molecular clouds to be well resolved and their stellar associations to be studied in detail. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5% to nearly the cosmic fraction in halos with merger histories rich in halos above 10{sup 7} M{sub Sun }. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10{sup -3} Z{sub Sun} and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Ly{alpha} systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.

  5. VizieR Online Data Catalog: Rosat North Ecliptic survey stellar population (Micela+, 2007)

    NASA Astrophysics Data System (ADS)

    Micela, G.; Affer, L.; Favata, F.; Henry, J. P.; Gioia, I.; Mullis, C. R.; Sanz-Forcada, J.; Sciortino, D.

    2006-11-01

    X-ray surveys are a very efficient mean of detecting young stars and therefore allow us to study the young stellar population in the solar neighborhood and the local star formation history in the last billion of years. We want to study the young stellar population in the solar neighborhood, to constrain its spatial density and scale height as well as the recent local star formation history. We analyze the stellar content of the ROSAT North Ecliptic Pole survey, and compare the observations with the predictions derived from stellar galactic model. Since the ROSAT NEP survey is sensitive at intermediate fluxes is able to sample both the youngest stars and the intermediate age stars (younger than 109years), linking the shallow and deep flux surveys already published in the literature. We confirm the existence of an excess of yellow stars in our neighborhood previously seen in shallow survey, which is likely due to a young star population not accounted for in the model. However the excellent agreement between observations and predictions of dM stars casts some doubt on the real nature of this active population. (2 data files).

  6. A Tale of Two Tails: Exploring Stellar Populations in the Tidal Tails of NGC 3256

    NASA Astrophysics Data System (ADS)

    Rodruck, Michael; Charlton, Jane C.; Konstantopoulos, Iraklis

    2016-01-01

    Galaxy interactions can inject material into the intergalactic medium via violent gravitational dynamics, often visualized in tidal tails. The composition of these tails has remained a mystery, as previous studies have focused on detecting tidal features, rather than the composite material itself. We have developed an observing program using deep, multiband imaging to probe the chaotic regions of tidal tails in search for an underlying stellar population. NGC 3256's twin tidal tails serve as a case study for this new technique. Our results show color values of u - g = 1.15 and r - i = 0.08 for the Western tail, and u - g = 1.33 and r - i = 0.22 for the Eastern tail, corresponding to discrepant ages between the tails of approximately 320 Myr and 785 Myr, respectively. With the interaction age of the system measured at 400 Myr, we find the stellar light in Western tail to be dominated by disrupted star clusters formed during and after the interaction, whereas the light from the Eastern tail is dominated by a 10 Gyr population originating from the host galaxies. We fit the Eastern tail color to a Mixed Stellar Population (MSP) model comprised 94% by mass of a 10 Gyr stellar population, and 6% of a 309 Myr population. We find 52% of the bolometric flux originating from this 10 Gyr population. We also detect a blue to red color gradient in each tail, running from galactic center to tail tip. In addition to tidal tail light, we detect 29 star cluster candidates (SCCs) in the Western tail and 19 in the Eastern, with mean ages of 282 Myr and 98 Myr respectively. Interestingly, we find an excess of very blue SCCs in the Eastern tail as compared to the Western tail, marking a recent, small episode of star formation.

  7. The CALIFA survey across the Hubble sequence. Spatially resolved stellar population properties in galaxies

    NASA Astrophysics Data System (ADS)

    González Delgado, R. M.; García-Benito, R.; Pérez, E.; Cid Fernandes, R.; de Amorim, A. L.; Cortijo-Ferrero, C.; Lacerda, E. A. D.; López Fernández, R.; Vale-Asari, N.; Sánchez, S. F.; Mollá, M.; Ruiz-Lara, T.; Sánchez-Blázquez, P.; Walcher, C. J.; Alves, J.; Aguerri, J. A. L.; Bekeraité, S.; Bland-Hawthorn, J.; Galbany, L.; Gallazzi, A.; Husemann, B.; Iglesias-Páramo, J.; Kalinova, V.; López-Sánchez, A. R.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mast, D.; Méndez-Abreu, J.; Mendoza, A.; del Olmo, A.; Pérez, I.; Quirrenbach, A.; Zibetti, S.

    2015-09-01

    Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different processes on galaxy evolution is the study of the stellar population content of today's galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. These cover a wide range of Hubble types, from spheroids to spiral galaxies, while stellar masses range from M⋆ ~ 109 to 7 × 1011 M⊙. We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies: the stellar mass surface density (μ⋆), stellar extinction (AV), light-weighted and mass-weighted ages (⟨log age⟩L, ⟨log age⟩M), and mass-weighted metallicity (⟨log Z⋆⟩M). To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd). We confirm that more massive galaxies are more compact, older, moremetal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M⋆, which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of ⟨log age⟩L are consistent with an inside-out growth of galaxies, with the largest ⟨log age⟩L gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and bulges are

  8. Stellar Populations of Highly Magnified Lensed Galaxies Young Starburst at Z to Approximately 2

    NASA Technical Reports Server (NTRS)

    Wuyts, Eva; Rigby, Jane R.; Gladders, Michael D.; Gilbank, David G.; Sharon, Keren; Gralla, Megan B.; Bayliss, Matthew B.

    2011-01-01

    We present a comprehensive analysis of the rest-frame UV to near-IR spectral energy distributions and rest-frame optical spectra of four of the brightest gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at z = 170, MS1512-cB58 at z = 2.73, SGAS J152745.1+065219 at z = 2.76 and SGAS J12265L3+215220 at z = 2.92. This includes new Spitzer imaging for RCSGA0327 as well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of the stellar populations and physical conditions. We compare star formation rates as measured from the SED fit, the Ha and [O II] .(lambda)3727 emission lines, and the UV+IR bolometric luminosity where 24micron photometry is available. The SFR estimate from the SED fit is consistently higher than the other indicators, which suggests that the Calzetti dust extinction law used in the SED fitting is too flat for young star-forming galaxies at z approx. 2. Our analysis finds similar stellar population parameters for all four lensed galaxies: stellar masses 3 - 7 x 10(exp 9) Stellar mass, young ages approx. 100 Myr, little dust content E(B - V)=0.10-0.25, and star formation rates around 20- 100 Stellar mass/y. Compared to typical values for the galaxy population at z approx. 2, this suggests we are looking at newly formed, starbursting systems that have only recently started the build-up of stellar mass. These results constitute the first detailed, uniform analysis of a sample of the growing number of strongly lensed galaxies known at z approx. 2. Subject headings: galaxies: high-redshift, strong gravitational lensing, infrared: galaxies

  9. Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters. I. Statistical and Computational Methods

    NASA Astrophysics Data System (ADS)

    Stenning, D. C.; Wagner-Kaiser, R.; Robinson, E.; van Dyk, D. A.; von Hippel, T.; Sarajedini, A.; Stein, N.

    2016-07-01

    We develop a Bayesian model for globular clusters composed of multiple stellar populations, extending earlier statistical models for open clusters composed of simple (single) stellar populations. Specifically, we model globular clusters with two populations that differ in helium abundance. Our model assumes a hierarchical structuring of the parameters in which physical properties—age, metallicity, helium abundance, distance, absorption, and initial mass—are common to (i) the cluster as a whole or to (ii) individual populations within a cluster, or are unique to (iii) individual stars. An adaptive Markov chain Monte Carlo (MCMC) algorithm is devised for model fitting that greatly improves convergence relative to its precursor non-adaptive MCMC algorithm. Our model and computational tools are incorporated into an open-source software suite known as BASE-9. We use numerical studies to demonstrate that our method can recover parameters of two-population clusters, and also show how model misspecification can potentially be identified. As a proof of concept, we analyze the two stellar populations of globular cluster NGC 5272 using our model and methods. (BASE-9 is available from GitHub: https://github.com/argiopetech/base/releases).

  10. SNLS: Relating the properties of type Ia supernovae to the stellar populations of their host galaxies

    NASA Astrophysics Data System (ADS)

    Sullivan, M.; Pritchet, C. J.; Le Borgne, D.; Hodsman, A.; Howell, D. A.; Astier, P.; Aubourg, E.; Balam, D.; Basa, S.; Carlberg, R.; Conley, A.; Fabbro, S.; Fouchez, D.; Guy, J.; Hook, I.; Lafoux, H.; Neill, J. D.; Pain, R.; Palanque-Delabrouille, N.; Perrett, K.; Regnault, N.; Rich, J.; Taillet, R.; Baumont, S.; Bronder, J.; Filliol, M.; Perlmutter, S.; Tao, C.; SNLS Collaboration

    2005-12-01

    We examine the rates and properties of type Ia supernovae (SNe Ia) in relation to the physical parameters defining their host galaxy stellar populations. Using a sample of 114 spectroscopically confirmed SNe Ia discovered via the Supernova Legacy Survey (SNLS) distributed over 0.2stellar mass and the current total SFRs of the host systems, suggesting SNe Ia can be generated from both very young and old stellar populations. We further demonstrate a dependence of SN light-curve shapes on the mean age of the stellar population from which the progenitor is drawn -- older systems preferentially host faster/dimmer SNe Ia, as observed in the local Universe. Though with current sample sizes, existing analysis techniques adequately account for these trends when using SNe Ia to constrain cosmological parameters, identifying and understanding the relationship between SNe Ia and their environments will lead to a future improved cosmological candle.

  11. A hierarchical Bayesian approach for reconstructing the Initial Mass Function of Single Stellar Populations

    NASA Astrophysics Data System (ADS)

    Dries, M.; Trager, S. C.; Koopmans, L. V. E.

    2016-08-01

    Recent studies based on the integrated light of distant galaxies suggest that the initial mass function (IMF) might not be universal. Variations of the IMF with galaxy type and/or formation time may have important consequences for our understanding of galaxy evolution. We have developed a new stellar population synthesis (SPS) code specifically designed to reconstruct the IMF. We implement a novel approach combining regularization with hierarchical Bayesian inference. Within this approach we use a parametrized IMF prior to regulate a direct inference of the IMF. This direct inference gives more freedom to the IMF and allows the model to deviate from parametrized models when demanded by the data. We use Markov Chain Monte Carlo sampling techniques to reconstruct the best parameters for the IMF prior, the age, and the metallicity of a single stellar population. We present our code and apply our model to a number of mock single stellar populations with different ages, metallicities, and IMFs. When systematic uncertainties are not significant, we are able to reconstruct the input parameters that were used to create the mock populations. Our results show that if systematic uncertainties do play a role, this may introduce a bias on the results. Therefore, it is important to objectively compare different ingredients of SPS models. Through its Bayesian framework, our model is well-suited for this.

  12. A hierarchical Bayesian approach for reconstructing the initial mass function of single stellar populations

    NASA Astrophysics Data System (ADS)

    Dries, M.; Trager, S. C.; Koopmans, L. V. E.

    2016-11-01

    Recent studies based on the integrated light of distant galaxies suggest that the initial mass function (IMF) might not be universal. Variations of the IMF with galaxy type and/or formation time may have important consequences for our understanding of galaxy evolution. We have developed a new stellar population synthesis (SPS) code specifically designed to reconstruct the IMF. We implement a novel approach combining regularization with hierarchical Bayesian inference. Within this approach, we use a parametrized IMF prior to regulate a direct inference of the IMF. This direct inference gives more freedom to the IMF and allows the model to deviate from parametrized models when demanded by the data. We use Markov chain Monte Carlo sampling techniques to reconstruct the best parameters for the IMF prior, the age and the metallicity of a single stellar population. We present our code and apply our model to a number of mock single stellar populations with different ages, metallicities and IMFs. When systematic uncertainties are not significant, we are able to reconstruct the input parameters that were used to create the mock populations. Our results show that if systematic uncertainties do play a role, this may introduce a bias on the results. Therefore, it is important to objectively compare different ingredients of SPS models. Through its Bayesian framework, our model is well suited for this.

  13. THE EVOLUTION OF STELLAR POPULATIONS IN THE OUTER DISKS OF SPIRAL GALAXIES

    SciTech Connect

    Alberts, Stacey; Calzetti, Daniela; Dong Hui; Johnson, L. C.; Dale, Daniel A.; Bianchi, Luciana; Thilker, David; Chandar, Rupali; Kennicutt, Robert C.; Meurer, Gerhardt R.; Regan, Michael

    2011-04-10

    We investigate recent star formation in the extended ultraviolet (XUV) disks of five nearby galaxies (NGC 0628, NGC 2090, NGC 2841, NGC 3621, and NGC 5055) using a long wavelength baseline comprised of ultraviolet and mid-infrared imaging from the Galaxy Evolution Explorer and the Spitzer Infrared Array Camera. We identify 229 unresolved stellar complexes across targeted portions of their XUV disks and utilize spectral energy distribution fitting to measure their stellar ages and masses through comparison with Starburst99 population synthesis models of instantaneous burst populations. We find that the median age of outer-disk associations in our sample is {approx}100 Myr with a large dispersion that spans the entire range of our models (1 Myr to 1 Gyr). This relatively evolved state for most associations addresses the observed dearth of H{alpha} emission in some outer disks, as H{alpha} can only be observed in star-forming regions younger than {approx}10 Myr. The large age dispersion is robust against variations in extinction (in the range E(B - V) = 0-0.3 mag) and variations in the upper end of the stellar initial mass function (IMF). In particular, we demonstrate that the age dispersion is insensitive to steepening of the IMF, up to extreme slopes.

  14. A NEW METHOD FOR DERIVING THE STELLAR BIRTH FUNCTION OF RESOLVED STELLAR POPULATIONS

    SciTech Connect

    Gennaro, M.; Brown, T. M.; Gordon, K. D.; Tchernyshyov, K.

    2015-07-20

    We present a new method for deriving the stellar birth function (SBF) of resolved stellar populations. The SBF (stars born per unit mass, time, and metallicity) is the combination of the initial mass function (IMF), the star formation history (SFH), and the metallicity distribution function (MDF). The framework of our analysis is that of Poisson Point Processes (PPPs), a class of statistical models suitable when dealing with points (stars) in a multidimensional space (the measurement space of multiple photometric bands). The theory of PPPs easily accommodates the modeling of measurement errors as well as that of incompleteness. Our method avoids binning stars in the color–magnitude diagram and uses the whole likelihood function for each data point; combining the individual likelihoods allows the computation of the posterior probability for the population's SBF. Within the proposed framework it is possible to include nuisance parameters, such as distance and extinction, by specifying their prior distributions and marginalizing over them. The aim of this paper is to assess the validity of this new approach under a range of assumptions, using only simulated data. Forthcoming work will show applications to real data. Although it has a broad scope of possible applications, we have developed this method to study multi-band Hubble Space Telescope observations of the Milky Way Bulge. Therefore we will focus on simulations with characteristics similar to those of the Galactic Bulge.

  15. The Young Stellar Population of LYNDS 1340. An Infrared View

    NASA Astrophysics Data System (ADS)

    Kun, M.; Wolf-Chase, G.; Moór, A.; Apai, D.; Balog, Z.; O'Linger-Luscusk, J.; Moriarty-Schieven, G. H.

    2016-06-01

    We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of ≲100 members, including both pre-main-sequence stars and embedded protostars. New Herbig-Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.

  16. Stellar Populations, Outflows, and Morphologies of High-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Kornei, Katherine Anne

    Understanding the regulation and environment of star formation across cosmic time is critical to tracing the build-up of mass in the Universe and the interplay between the stars and gas that are the constituents of galaxies. Three studies are presented in this thesis, each examining a different aspect of star formation at a specific epoch. The first study presents the results of a photometric and spectroscopic survey of 321 Lyman break galaxies (LBGs) at z ˜ 3 to investigate systematically the relationship between Lyalpha emission and stellar populations. Lyalpha equivalent widths were calculated from rest-frame UV spectroscopy and optical/near-infrared/Spitzer photometry was used in population synthesis modeling to derive the key properties of age, dust extinction, star formation rate (SFR), and stellar mass. Using a variety of statistical tests, we find that Lyalpha equivalent width and age, SFR, and dust extinction, respectively, are significantly correlated in the sense that objects with strong Lyalpha emission also tend to be older, lower in star formation rate, and less dusty than objects with weak Lyalpha emission, or the line in absorption. We accordingly conclude that, within the LBG sample, objects with strong Lyalpha emission represent a later stage of galaxy evolution in which supernovae-induced outflows have reduced the dust covering fraction. The second study focuses specifically on galactic-scale outflowing winds in 72 star-forming galaxies at z ˜ 1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging available for the Extended Groth Strip, we examine galaxies on a per-object basis in order to better understand both the prevalence of galactic outflows at z ˜ 1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from

  17. Probing the Mass Distribution and Stellar Populations of M82

    NASA Astrophysics Data System (ADS)

    Greco, Johnny; Martini, P.; Thompson, T. A.

    2012-01-01

    M82 is often considered the archetypical starburst galaxy because of its spectacular starbust-driven superwind. Its close proximity of 3.6 Mpc and nearly edge-on geometry make it a unique laboratory for studying the physics of rapid star formation and violent galactic winds. In addition, there is evidence that it has been tidally-truncated by its interaction with M81 and therefore has essentially no dark matter halo. The mass distribution of this galaxy is needed to estimate the power of its superwind, as well as determine if a dark matter halo is still present. Numerous studies have used stellar and gas dynamics to estimate the mass distribution, yet the substantial dust attenuation has been a significant challenge. We have measured the stellar kinematics in the near-infrared K-band with the LUCI-1 spectrograph at the Large Binocular Telescope. We used the '2CO stellar absorption bandhead at 2.29µm to measure the stellar rotation curve out to ˜4kpc, and our results confirm that the dark matter halo is still present. This is in stark contrast with the nearly Keplerian gas dynamics measured with HI and CO emission from the interstellar medium. We estimate M82's dynamical mass to be ˜1010 M⊙. We have also measured the equivalent width of the 12CO bandhead to provide new constraints on the spatial extent of the red supergiant population. The variation in the CO equivalent width with radius clearly shows that supergiants dominate the light within 0.5kpc radius. The superwind is likely launched from this region, where we estimate the enclosed mass is 2×109 M⊙.

  18. Stellar populations in local star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Perez-Gonzalez, P. G.

    2003-11-01

    The main goal of this thesis work is studying the main properties of the stellar populations embedded in a statistically complete sample of local active star-forming galaxies: the Universidad Complutense de Madrid (UCM) Survey of emission-line galaxies. This sample contains 191 local star-forming galaxies at an average redshift of 0.026. The survey was carried out using an objective-prism technique centered at the wavelength of the Halpha nebular emission-line (a common tracer of recent star formation). (continues)

  19. The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

    NASA Astrophysics Data System (ADS)

    Tailo, M.; Di Criscienzo, M.; D'Antona, F.; Caloi, V.; Ventura, P.

    2016-04-01

    We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch (HB) data. The reproduction of the observed colour-magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: (1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed, we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ˜0.5 Gyr time interval; in particular the most metal-rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y ˜ 0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = +0.7); (2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub-giant data; (3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal-poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

  20. Young Nearby Suns and Stellar Jitter Dependence on Age

    NASA Astrophysics Data System (ADS)

    Cabrera, Nicole; White, Russel; Delfosse, Xavier; Noah Quinn, Samuel; Latham, David W.

    2015-01-01

    Finding the nearest young planets offers the most direct way to improve our understanding of how planets form, how they migrate, and how they evolve. However, most radial velocity (RV) surveys have avoided young stars because of their problematic characteristics, including high levels of stellar activity. Recent advancements in infrared (IR) detectors as well as wavelength calibration methods have provided new ways of pursuing high-precision RV measurements of young stars. While this work has been successfully applied to many young late-K and M dwarfs, much less RV work has been done on young Sun-like stars, with the very recent exception of adolescent stars (~600 Myr) in open clusters. In order to better understand the dynamical and structural forces that shaped our own Solar system, we must begin to explore the more massive realm of Sun-like stars.We present precision optical radial velocity data of 5 young, nearby, Sun-like stars in AB Dor and assess our ability to detect young planets with current spectroscopic methods. The data were obtained with the TRES spectrograph on the 1.5-m Tillinghast Reflector at the Fred L. Whipple Observatory and with SOPHIE on the 1.95 m Telescope at the Observatoire de Haute Provence. We obtained a RV precision of ~8 m/s with TRES and ~7 m/s precision with SOPHIE; average observed dispersions are 38 m/s and 33 m/s, respectively. We combine our results with spectroscopic data of Sun-like stars spanning a broad range of youthful ages (< 1 Gyr) from the literature to investigate the relationship between stellar jitter and stellar age. The results suggest that the jitter of Sun-like stars decreases below 100 m/s for stars older than ~30 Myr, which would enable the discovery of hot Jupiters orbiting these adolescent age stars.

  1. Young Stellar Populations and Star Clusters in NGC 1705

    NASA Astrophysics Data System (ADS)

    Annibali, F.; Tosi, M.; Monelli, M.; Sirianni, M.; Montegriffo, P.; Aloisi, A.; Greggio, L.

    2009-07-01

    We present Hubble Space Telescope (HST) photometry of the late-type dwarf galaxy NGC 1705 observed with the Wide-Field Planetary Camera 2 (WFPC2) in the F380W and F439W bands and with the Advanced Camera for Surveys/High-Resolution Channel (HRC) in the F330W, F555W, and F814W broad-band filters. We cross-correlate these data with previous ones acquired with the WFPC2 in the F555W, F814W bands, and derive multiband color-magnitude diagrams (CMDs) of the cross-identified individual stars and candidate star clusters. For the central regions of the galaxy, where HST-NICMOS F110W and F160W photometry is also available, we present U, B, V, I, J, H CMDs of the 256 objects with magnitudes measured in all bands. While our previous study based on F555W, F814W, F110W, and F160W data allowed us to trace the star formation history of NGC 1705 back to a Hubble time, the new data provide a better insight on its recent evolution. With the method of the synthetic CMDs, we confirm the presence of two strong bursts of star formation (SF). The older of the two bursts (B1) occurred between ~10 and 15 Myr ago, coeval to the age of the central super star cluster (SSC). The younger burst (B2) started ~3 Myr ago, and it is still active. The stellar mass produced by B2 amounts to ~106 M sun, and it is a factor of ~3 lower for B1. The interburst phase was likely characterized by a much lower level of SF rather than by its complete cessation. The two bursts show distinct spatial distributions: while B1 is centrally concentrated, B2 is more diffused, and presents ring and arclike structures that remind of an expanding shell. This suggests a feedback mechanism, in which the expanding superbubble observed in NGC 1705, likely generated by the 10-15 Myr burst, triggered the current strong SF activity. The excellent spatial resolution of the HRC allowed us to reliably identify 12 star clusters (plus the SSC) in the central ~26'' × 29'' region of NGC 1705, 10 of which have photometry in all the

  2. YOUNG STELLAR POPULATIONS AND STAR CLUSTERS IN NGC 1705

    SciTech Connect

    Annibali, F.; Greggio, L.; Tosi, M.; Montegriffo, P.; Monelli, M.; Sirianni, M.; Aloisi, A.

    2009-07-15

    We present Hubble Space Telescope (HST) photometry of the late-type dwarf galaxy NGC 1705 observed with the Wide-Field Planetary Camera 2 (WFPC2) in the F380W and F439W bands and with the Advanced Camera for Surveys/High-Resolution Channel (HRC) in the F330W, F555W, and F814W broad-band filters. We cross-correlate these data with previous ones acquired with the WFPC2 in the F555W, F814W bands, and derive multiband color-magnitude diagrams (CMDs) of the cross-identified individual stars and candidate star clusters. For the central regions of the galaxy, where HST-NICMOS F110W and F160W photometry is also available, we present U, B, V, I, J, H CMDs of the 256 objects with magnitudes measured in all bands. While our previous study based on F555W, F814W, F110W, and F160W data allowed us to trace the star formation history of NGC 1705 back to a Hubble time, the new data provide a better insight on its recent evolution. With the method of the synthetic CMDs, we confirm the presence of two strong bursts of star formation (SF). The older of the two bursts (B1) occurred between {approx}10 and 15 Myr ago, coeval to the age of the central super star cluster (SSC). The younger burst (B2) started {approx}3 Myr ago, and it is still active. The stellar mass produced by B2 amounts to {approx}10{sup 6} M {sub sun}, and it is a factor of {approx}3 lower for B1. The interburst phase was likely characterized by a much lower level of SF rather than by its complete cessation. The two bursts show distinct spatial distributions: while B1 is centrally concentrated, B2 is more diffused, and presents ring and arclike structures that remind of an expanding shell. This suggests a feedback mechanism, in which the expanding superbubble observed in NGC 1705, likely generated by the 10-15 Myr burst, triggered the current strong SF activity. The excellent spatial resolution of the HRC allowed us to reliably identify 12 star clusters (plus the SSC) in the central {approx}26'' x 29'' region of NGC

  3. Exotic populations in globular clusters: blue stragglers as tracers of the internal dynamical evolution of stellar systems

    NASA Astrophysics Data System (ADS)

    Ferraro, Francesco R.

    2016-02-01

    In this paper I present an overview of the main observational properties of a special class of exotic objects (the so-called Blue Straggler Stars, BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency and their radial distribution are discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical evolution of stellar systems, thus allowing the definition of an empirical ``clock''able to measure the dynamical age of stellar aggregates from pure observational properties.

  4. OGLE-ing the Magellanic system: stellar populations in the Magellanic Bridge

    SciTech Connect

    Skowron, D. M.; Jacyszyn, A. M.; Udalski, A.; Szymański, M. K.; Skowron, J.; Poleski, R.; Kozłowski, S.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Mróz, P.; Pietrukowicz, P.; Ulaczyk, K.; Wyrzykowski, Ł.

    2014-11-10

    We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This finding is based on number density maps for stellar populations found in data gathered by OGLE-IV that fully cover over 270 deg{sup 2} of the sky in the Magellanic Bridge area. This is the most extensive optical survey of this region to date. We find that the young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along δ ∼ –73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. These overdensities are well matched by H I surface density contours, although the newly found young population in the eastern Bridge is offset by ∼2 deg north from the highest H I density contour. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. Red clump stars are present mainly in the southern and central parts of the Magellanic Bridge, below its gaseous part, and their presence is reflected by a strong deviation from the radial density profiles of the two galaxies. This may indicate either a tidal stream of stars, or that the stellar halos of the two galaxies overlap. On the other hand, we do not observe such an overlap within an intermediate-age population represented by the top of the red giant branch and the asymptotic giant branch stars. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.

  5. Spiral arm kinematics for Milky Way stellar populations

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Natale, G.; Kawata, D.; Chiosi, C.; Hunt, J. A. S.; Brogliato, C.

    2016-09-01

    We present a new theoretical population synthesis model (the Galaxy model) to examine and deal with large amounts of data from surveys of the Milky Way and to decipher the present and past structure and history of our own Galaxy. We assume the Galaxy to consist of a superposition of many composite stellar populations belonging to the thin and thick discs, the stellar halo and the bulge, and to be surrounded by a single dark matter halo component. A global model for the Milky Way's gravitational potential is built up self-consistently with the density profiles from the Poisson equation. In turn, these density profiles are used to generate synthetic probability distribution functions (PDFs) for the distribution of stars in colour-magnitude diagrams (CMDs). Finally, the gravitational potential is used to constrain the stellar kinematics by means of the moment method on a (perturbed)-distribution function. Spiral arms perturb the axisymmetric disc distribution functions in the linear response framework of density-wave theory where we present an analytical formula of the so-called `reduction factor' using hypergeometric functions. Finally, we consider an analytical non-axisymmetric model of extinction and an algorithm based on the concept of probability distribution function to handle CMDs with a large number of stars. A genetic algorithm is presented to investigate both the photometric and kinematic parameter space. This galaxy model represents the natural framework to reconstruct the structure of the Milky Way from the heterogeneous data set of surveys such as Gaia-ESO, SEGUE, APOGEE2, RAVE and the Gaia mission.

  6. 3D mapping of stellar populations in galaxies as a function of environment

    NASA Astrophysics Data System (ADS)

    Thomas, Daniel

    2015-08-01

    MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a6-year SDSS-IV survey that will obtain resolved spectroscopy from 3600A to 10300 A for a representative sample of 10,000 nearby galaxies. MaNGA will allow the internal kinematics and spatially-resolved properties of stellar populations and gas inside galaxies to be studied as a function of local environment and halo mass for the very first time. I will present results from our analysis of the first year MaNGA data. The main focus is on the 3-dimensional distribution of stellar population properties in galaxies - formation age, element abundance, IMF slope - studying how these vary spatially in galaxies as a function of galaxy environment and dark matter halo mass.

  7. THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. III. MEASURING AGES AND MASSES OF PARTIALLY RESOLVED STELLAR CLUSTERS

    SciTech Connect

    Beerman, Lori C.; Johnson, L. Clifton; Fouesneau, Morgan; Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Ben F.; Seth, Anil C.; Bell, Eric F.; Bianchi, Luciana C.; Caldwell, Nelson; Dolphin, Andrew E.; Gouliermis, Dimitrios A.; Kalirai, Jason S.; Larsen, Soren S.; Melbourne, Jason L.; Rix, Hans-Walter; Skillman, Evan D.

    2012-12-01

    The apparent age and mass of a stellar cluster can be strongly affected by stochastic sampling of the stellar initial mass function (IMF), when inferred from the integrated color of low-mass clusters ({approx}<10{sup 4} M {sub Sun }). We use simulated star clusters to show that these effects are minimized when the brightest, rapidly evolving stars in a cluster can be resolved, and the light of the fainter, more numerous unresolved stars can be analyzed separately. When comparing the light from the less luminous cluster members to models of unresolved light, more accurate age estimates can be obtained than when analyzing the integrated light from the entire cluster under the assumption that the IMF is fully populated. We show the success of this technique first using simulated clusters, and then with a stellar cluster in M31. This method represents one way of accounting for the discrete, stochastic sampling of the stellar IMF in less massive clusters and can be leveraged in studies of clusters throughout the Local Group and other nearby galaxies.

  8. Old Stellar Populations of The VGS Void Galaxies

    NASA Astrophysics Data System (ADS)

    Beygu, Burcu; Jarrett, Thomas; Jarrett, Tom; van de Weygaert, Rien; Kreckel, Kathryn; van der Hulst, Thijs; van Gorkom, Jacqueline

    2011-05-01

    Cosmic voids form an essential ingredient of the Cosmic Web and may harbour a systematically different population of galaxies. Largely unaffected by the complex processes modifying galaxies in high-density environments, the pristine and isolated void regions must hold important clues to the intrinsic process of formation and evolution of galaxies. The Void Galaxy Survey (VGS) is a multi-wavelength program to study 60 void galaxies. Each has been selected from the deepest interior regions of identified voids in the SDSS redshift survey on the basis of a unique geometric technique, with no a prior selection of intrinsic properties of the void galaxies. The project intends to study in detail the gas content, star formation history and stellar content, as well as kinematics and dynamics of void galaxies and their companions in a broad sample of void environments. It involves the HI imaging of the gas distribution in each of the VGS galaxies. Amongst its most tantalizing findings is the possible evidence for cold gas accretion in some of the most interesting objects, amongst which are a polar ring galaxy and a filamentary configuration of void galaxies. An essential aspect for understanding the formation and evolution of void galaxies concerns their star formation history. The current IRAC proposal is meant to study the older stellar population of void galaxies to constrain their assembly history.

  9. Stellar Population Maps of High-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Fetherolf, Tara; Reddy, Naveen; MOSDEF

    2016-06-01

    A comprehensive study of resolved galaxy structure can shed light on the formation and evolution of galactic properties, such as the distribution of stars and interstellar dust that obscures starlight. This requires high-resolution, multi-waveband photometry and spectroscopy to completely characterize the galaxies. Previous studies lacked key spectroscopic information, were comprised of small samples, or focused on the local universe. We use HST ACS/WFC3 high-resolution, multi-waveband imaging from the CANDELS project in parallel with moderate-resolution Keck I MOSFIRE spectra from the MOSFIRE Deep Evolution Field (MOSDEF) survey to produce resolved stellar population and dust maps of ~500 galaxies at redshifts 1.4 < z < 2.6—covering the key epoch when galaxies accreted most of their mass. For data preparation and analysis we develop an automated Python program to process our large, comprehensive dataset. From the multi-waveband imaging and spectroscopic redshifts, we model the spectral energy distribution for every resolution element within each galaxy and compare these results to the spectroscopically measured global properties. From our stellar population and dust maps we identify resolved structures within these galaxies. We also investigate if spectroscopically measured galaxy properties are biased when compared with that of localized sub-galactic structures.

  10. A DYNAMICAL SIGNATURE OF MULTIPLE STELLAR POPULATIONS IN 47 TUCANAE

    SciTech Connect

    Richer, Harvey B.; Heyl, Jeremy; Anderson, Jay; Kalirai, Jason S.; Shara, Michael M.; Dotter, Aaron; Fahlman, Gregory G.; Rich, R. Michael E-mail: heyl@phas.ubc.ca E-mail: jkalarai@stsci.edu E-mail: aaron.dotter@gmail.com E-mail: rmr@astro.ucla.edu

    2013-07-01

    Based on the width of its main sequence, and an actual observed split when viewed through particular filters, it is widely accepted that 47 Tucanae contains multiple stellar populations. In this contribution, we divide the main sequence of 47 Tuc into four color groups, which presumably represent stars of various chemical compositions. The kinematic properties of each of these groups are explored via proper motions, and a strong signal emerges of differing proper-motion anisotropies with differing main-sequence color; the bluest main-sequence stars exhibit the largest proper-motion anisotropy which becomes undetectable for the reddest stars. In addition, the bluest stars are also the most centrally concentrated. A similar analysis for Small Magellanic Cloud stars, which are located in the background of 47 Tuc on our frames, yields none of the anisotropy exhibited by the 47 Tuc stars. We discuss implications of these results for possible formation scenarios of the various populations.

  11. Spectral analysis of the nuclear stellar population and gas emission in NGC 6240

    NASA Astrophysics Data System (ADS)

    Schmitt, Henrique R.; Bica, Edurado; Pastoriza, Miriani G.

    1996-02-01

    We analyse the nuclear stellar population and emission-line spectrum in the range lambdalambda 3100-9700A of the infrared luminous merger galaxy NGC 6240. Two spectral extractions from CCD frames are studied: one corresponding to the double nucleus and the other from a light peak 4 arcsec east of the nucleus. The double nucleus is DeltaE(B-V)~=0.30 mag more reddened and has a stronger interstellar NaI D absorption as compared to the eastern peak; otherwise the two extractions present similar spectral properties, in particular the dereddened continuum distribution and emission-line ratios. The population synthesis of the double nucleus, which has age and metallicity as free parameters and is based on spectral properties of a library of star clusters, indicates that the coninuum flux fraction at 5870A owing to an old bulge/halo component is ~=75 per cent, that of intermediate-age components (1 to 5 Gyr) is ~=5 per cent, and that associated with young ones (50 to 500 Myr) is ~=20 per cent. Currently star-forming regions do not contribute more than 1-2 per cent to the continuum at 5870A, and this amount is contributed only if they are differentially reddened from the rest of the stellar components by DeltaE(B-V)_i<~1.00. The age distribution of the nuclear stellar population, when compared to that found in normal nuclei, sets constraints on the age of the dynamical interaction that led to the present merger; the synthesis suggests that the interaction has been operating for ~=1 Gyr. We derive an internal reddening affecting the nuclear stellar population of E(B-V)_sp=0.48. The population-subtracted optical emission-line spectrum is typical of a shock-heated gas. We derive an internal reddening for the emitting gas clouds of E(B-V)_g=0.60. We conclude that in the central 2-3 kpc of NGC 6240 the old (bulge) and 1-Gyr to 50-Myr stellar components are homogeneously mixed, and they coexist with colliding gas clouds from the discs of the merging spirals. The continuum and

  12. Anomalous Growth of Aging Populations

    NASA Astrophysics Data System (ADS)

    Grebenkov, Denis S.

    2016-04-01

    We consider a discrete-time population dynamics with age-dependent structure. At every time step, one of the alive individuals from the population is chosen randomly and removed with probability q_k depending on its age, whereas a new individual of age 1 is born with probability r. The model can also describe a single queue in which the service order is random while the service efficiency depends on a customer's "age" in the queue. We propose a mean field approximation to investigate the long-time asymptotic behavior of the mean population size. The age dependence is shown to lead to anomalous power-law growth of the population at the critical regime. The scaling exponent is determined by the asymptotic behavior of the probabilities q_k at large k. The mean field approximation is validated by Monte Carlo simulations.

  13. Uncertainties in stellar ages provided by grid techniques

    NASA Astrophysics Data System (ADS)

    Prada Moroni, P. G.; Valle, G.; Dell'Omodarme, M.; Degl'Innocenti, S.

    2016-09-01

    The determination of the age of single stars by means of grid-based techniques is a well established method. We discuss the impact on these estimates of the uncertainties in several ingredients routinely adopted in stellar computations. The systematic bias on age determination caused by varying the assumed initial helium abundance, the mixing-length and convective core overshooting parameters, and the microscopic diffusion are quantified and compared with the statistical error owing to the current uncertainty in the observations. The typical uncertainty in the observations accounts for 1 σ statistical relative error in age determination ranging on average from about -35 % to +42 %, depending on the mass. However, the age's relative error strongly depends on the evolutionary phase and can be higher than 120 % for stars near the zero-age main-sequence, while it is typically about 20 % or lower in the advanced main-sequence phase. A variation of ± 1 in the helium-to-metal enrichment ratio induces a quite modest systematic bias on age estimates. The maximum bias due to the presence of the convective core overshooting is -7 % for β = 0.2 and -13 % for β = 0.4. The main sources of bias are the uncertainty in the mixing-length value and the neglect of microscopic diffusion, which account each for a bias comparable to the random error uncertainty.

  14. Single stellar populations in the near-infrared. I. Preparation of the IRTF spectral stellar library

    NASA Astrophysics Data System (ADS)

    Meneses-Goytia, S.; Peletier, R. F.; Trager, S. C.; Falcón-Barroso, J.; Koleva, M.; Vazdekis, A.

    2015-10-01

    We present a detailed study of the stars of the NASA InfraRed Telescope Facility (IRTF) spectral library to understand its full extent and reliability for use with stellar population (SP) modeling. The library consist of 210 stars, with a total of 292 spectra, covering the wavelength range of 0.94 to 2.41 μm at a resolution R ≈ 2000. For every star we infer the effective temperature (Teff), gravity (log g) and metallicity ([Z/Z⊙]) using a full-spectrum fitting approach in a section of the K-band (2.19 to 2.34 μm) and temperature-NIR colour relations. We test the flux calibration of these stars by calculating their integrated colours and comparing them with the Pickles library colour-temperature relations. We also investigate the NIR colours as a function of the calculated effective temperature and compared them in colour-colour diagrams with the Pickles library. This latter test shows a good broad-band flux calibration, important for the SP models. Finally, we measure the resolution R as a function of wavelength. We find that the resolution increases as a function of lambda from about 6 Å in J to 10 Å in the red part of the K-band. With these tests we establish that the IRTF library, the largest currently available general library of stars at intermediate resolution in the NIR, is an excellent candidate to be used in stellar population models. We present these models in the next paper of this series. The IRTF spectral library is available at irtfweb.ifa.hawaii.edu/spex/IRTF_Spectral_Library/

  15. A New Method for Deriving the Stellar Birth Function of Resolved Stellar Populations.

    NASA Astrophysics Data System (ADS)

    Gennaro, M.; Tchernyshyov, K.; Brown, T. M.; Gordon, K. D.

    2015-07-01

    We present a new method for deriving the stellar birth function (SBF) of resolved stellar populations. The SBF (stars born per unit mass, time, and metallicity) is the combination of the initial mass function (IMF), the star formation history (SFH), and the metallicity distribution function (MDF). The framework of our analysis is that of Poisson Point Processes (PPPs), a class of statistical models suitable when dealing with points (stars) in a multidimensional space (the measurement space of multiple photometric bands). The theory of PPPs easily accommodates the modeling of measurement errors as well as that of incompleteness. Our method avoids binning stars in the color–magnitude diagram and uses the whole likelihood function for each data point; combining the individual likelihoods allows the computation of the posterior probability for the population's SBF. Within the proposed framework it is possible to include nuisance parameters, such as distance and extinction, by specifying their prior distributions and marginalizing over them. The aim of this paper is to assess the validity of this new approach under a range of assumptions, using only simulated data. Forthcoming work will show applications to real data. Although it has a broad scope of possible applications, we have developed this method to study multi-band Hubble Space Telescope observations of the Milky Way Bulge. Therefore we will focus on simulations with characteristics similar to those of the Galactic Bulge. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  16. Economics of an aging population.

    PubMed Central

    Jackson, P M

    1985-01-01

    Throughout this century, as in many other countries, the proportion of the British population in the older age groups has increased. The effect this has on the economy is discussed. Topics covered include the determinants of the economic status of old people; the reasons for the choice of retirement ages; the burden of the aged on younger generations; the costs of pension schemes; the disincentive effects of pensions on savings; and poverty in old age. PMID:4009105

  17. Evidence for Distributed Young Stellar Populations in Strong AGN at z 1

    NASA Astrophysics Data System (ADS)

    Ammons, Mark; Melbourne, J.; Koo, D.; Max, C.

    2008-09-01

    We present stellar populations analysis of 8 AGN hosts at z 1 and derive stellar age trends that compare to local AGN host samples. We utilize laser guide star adaptive optics imaging in K-band, taken at the Keck Observatory, of hosts in the Great Observatories Origins Deep Survey (GOODS) South. Combination of these data with imaging in B, V, i, z from the HST Advanced Camera for Surveys (ACS) gives multi-color photometry with comparable spatial resolution of better than 100 mas in all bands. The AGN nature of these hosts is implied from their large X-ray luminosities (log L > 42 in ergs/s, 2-10 keV) as measured by Chandra. We fit Bruzual & Charlot (2003) stellar populations models to the 5-band photometry. Our use of near-IR fluxes in the fitting process gives tighter constraints on the dust extinction. The strongest conclusion is that the presence of distributed younger stellar populations (age less than 100 Myr) is correlated with the [OIII] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. However, we also find that strong Type II AGN hosts at this redshift are more likely to have some disk component or be irregulars than all Type I sources, which tend to be of earlier type. The mid-IR SEDs of the strong Type II AGN indicates that they are excited to LIRG status via galactic starbursting, while the strong Type I AGN are excited to LIRG status via hot dust surrounding the central engine. This suggests that the obscured nature of Type II AGN at this redshift is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are byproducts of this starbursting. This study is funded by the Bachmann family and the NSF.

  18. Teaching Astronomy with an Inquiry Activity on Stellar Populations

    NASA Astrophysics Data System (ADS)

    Rafelski, M.; Foley, M.; Graves, G. J.; Kretke, K. A.; Mills, E.; Nassir, M.; Patel, S.

    2010-12-01

    We describe a new inquiry design aimed at teaching advanced high-school to senior college students the basics of stellar populations. The inquiry is designed to have students come up with their own version of the Hertzsprung-Russell diagram as a tool to understand how stars evolve based on their color, mass, and luminosity. The inquiry makes use of pictures and spectra of stars, which the students analyze and interpret to answer the questions they come up with at the beginning. The students undergo a similar experience to real astronomers, using the same tools and methods to figure out the phenomena they are trying to understand. Specifically, they use images and spectra of stars, and organize the data via tables and plots to find trends that will then enable them to answer their questions. The inquiry also includes a "thinking tool" to help connect the trends students observe to the larger picture of stellar evolution. We include a description of the goals of the inquiry, the activity description, the motivations and thoughts that went into the design of the inquiry, and reflections on how the inquiry activity worked in practice.

  19. STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

    SciTech Connect

    Roediger, Joel C.; Courteau, Stephane; Sanchez-Blazquez, Patricia; McDonald, Michael E-mail: courteau@astro.queensu.ca E-mail: mcdonald@space.mit.edu

    2012-10-10

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely

  20. Stellar populations in the Lynx Super Cluster at redshift 1.26

    NASA Astrophysics Data System (ADS)

    Jorgensen, Inger; Bergmann, Marcel; Chiboucas, Kristin; Toft, Sune; Zirm, Andrew; Gruetzbauch, Ruth; Schiavon, Richardo

    2013-08-01

    We propose to continue our investigation of stellar populations in rich galaxy clusters at z>1.2 by obtaining deep optical spectroscopy of 25 member galaxies in the cluster Lynx E (z=1.26). This proposal is part of our larger project aimed at constraining models for galaxy evolution in dense environments from observations of stellar populations in rich z=1.2-2 galaxy clusters. The main objective is to establish the star formation (SF) history over this epoch during which large changes in SF rates and galaxy structure are expected to take place in cluster galaxies. The proposed observations will reach S/N=20 for galaxies 2 mag fainter than the brightest cluster galaxy. The spectra will be used to determine SF rates, ages and metallicities as well as measure the velocity dispersions. Combining the spectroscopy with available HST/ACS imaging, we will test models for evolution of the Fundamental Plane and of galaxy size. The analysis will also utilize data from the Gemini/HST Cluster Galaxy Project, which covers rich clusters at z=0.2-1.0. The E2V DD CCDs in GMOS make possible this unprecedented probe of distant cluster galaxies, as no prior stellar population studies based on high S/N spectra exist for clusters at z>1.

  1. The Pure Noncollisional Blue Straggler Population in the Giant Stellar System ω Centauri

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Sollima, A.; Rood, R. T.; Origlia, L.; Pancino, E.; Bellazzini, M.

    2006-02-01

    We have used high spatial resolution data from the Hubble Space Telescope (HST) and wide-field ground-based observations to search for blue straggler stars (BSSs) over the entire radial extent of the large stellar system ω Centauri. We have detected the largest population of BSSs ever observed in any stellar system. Even though the sample is restricted to the brightest portion of the BSS sequence, more than 300 candidates have been identified. BSSs are thought to be produced by the evolution of binary systems (formed either by stellar collisions or mass exchange in binary stars). Since systems like Galactic globular clusters (GGCs) and ω Cen evolve dynamically on timescales significantly shorter than their ages, binaries should have settled toward the center, showing a more concentrated radial distribution than the ordinary, less massive single stars. Indeed, in all GGCs that have been surveyed for BSSs, the BSS distribution is peaked at the center. Conversely, in ω Cen we find that the BSSs share the same radial distribution as the adopted reference populations. This is the cleanest evidence ever found that such a stellar system is not fully relaxed even in the central region. We further argue that the absence of central concentration in the BSS distribution rules out a collisional origin. Thus, the ω Cen BSSs are the purest and largest population of noncollisional BSSs ever observed. Our results allow the first empirical quantitative estimate of the production rate of BSSs via this channel. BSSs in ω Cen may represent the best local template for modeling the BSS populations in distant galaxies where they cannot be individually observed. Based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. Also based on WFI observations collected at the European Southern Observatory, La Silla, Chile, within the observing programs 62.L-0354 and 64.L-0439.

  2. Population ageing and dental care.

    PubMed

    Harford, Jane

    2009-04-01

    Population ageing is a fact in both developed and developing countries. The concern about population ageing largely arises from the combination of a greater number of older people requiring greater amounts of healthcare services and pensions, and relatively fewer people working to pay for them. Oral health and dental care are important aspects of health and health care. Lower rates of edentulism and an ageing population mean that older people will feature more prominently in dental services. Traditionally, economic studies of ageing have focused on the fiscal implications of ageing, projecting the increased burden on health and welfare services that accompanies ageing. It assumed that ageing is the major driver of recent changes and those past trends will simply be amplified by faster population ageing in the future. Less work has been done to understand other past drivers of increased healthcare spending and their implications for the future. The conclusion of these reports is usually that population ageing is unaffordable with current policy settings. They have proposed policies to deal with population ageing which focused on increasing workforce participation and worker productivity to increase the tax base and reducing entitlements. However, the affordability question is as much political as a numerical. There are no clearly articulated criteria for affordability and little opportunity for public discourse about what citizens are willing to pay in taxes to support an ageing population. While the reports do not necessarily reflect public opinion, they will certainly shape it. Predicting the future for oral health is more fraught than for general health, as oral health is in the midst of an epidemiological transition from high rates of edentulism and tooth loss to low rates. Changes in the pattern of dental expenditure in the past do not mirror the experience of rapid increases in per capita expenditure on older age groups as regards general health. Dentistry

  3. The MASSIVE Survey. II. Stellar Population Trends Out to Large Radius in Massive Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Greene, Jenny E.; Janish, Ryan; Ma, Chung-Pei; McConnell, Nicholas J.; Blakeslee, John P.; Thomas, Jens; Murphy, Jeremy D.

    2015-07-01

    We examine stellar population gradients in ˜100 massive early-type galaxies spanning 180\\lt {σ }*\\lt 370 km s-1 and MK of -22.5 to -26.5 mag, observed as part of the MASSIVE survey. Using integral-field spectroscopy from the Mitchell Spectrograph on the 2.7 m telescope at McDonald Observatory, we create stacked spectra as a function of radius for galaxies binned by their stellar velocity dispersion, stellar mass, and group richness. With excellent sampling at the highest stellar mass, we examine radial trends in stellar population properties extending to beyond twice the effective radius (˜ 2.5 {R}{e}). Specifically, we examine trends in age, metallicity, and abundance ratios of Mg, C, N, and Ca, and discuss the implications for star formation histories and elemental yields. At a fixed physical radius of 3-6 kpc (the likely size of the galaxy cores formed at high redshift), stellar age and [α/Fe] increase with increasing {σ }* and depend only weakly on stellar mass, as we might expect if denser galaxies form their central cores earlier and faster. If we instead focus on 1-1.5 {R}{e}, the trends in abundance and abundance ratio are washed out, as might be expected if the stars at large radius were accreted by smaller galaxies. Finally, we show that when controlling for {σ }*, there are only very subtle differences in stellar population properties or gradients as a function of group richness; even at large radius, internal properties matter more than environment in determining star formation history.

  4. Rotating Stellar Models Can Account for the Extended Main-sequence Turnoffs in Intermediate-age Clusters

    NASA Astrophysics Data System (ADS)

    Brandt, Timothy D.; Huang, Chelsea X.

    2015-07-01

    We show that the extended main-sequence turnoffs seen in intermediate-age Large Magellanic Cloud (LMC) clusters, often attributed to age spreads of several 100 Myr, may be easily accounted for by variable stellar rotation in a coeval population. We compute synthetic photometry for grids of rotating stellar evolution models and interpolate them to produce isochrones at a variety of rotation rates and orientations. An extended main-sequence turnoff naturally appears in color-magnitude diagrams at ages just under 1 Gyr, peaks in extent between ˜1 and 1.5 Gyr, and gradually disappears by around 2 Gyr in age. We then fit our interpolated isochrones by eye to four LMC clusters with very extended main-sequence turnoffs: NGC 1783, 1806, 1846, and 1987. In each case, stellar populations with a single age and metallicity can comfortably account for the observed extent of the turnoff region. The new stellar models predict almost no correlation of turnoff color with rotational v{sin}i. The red part of the turnoff is populated by a combination of slow rotators and edge-on rapid rotators, while the blue part contains rapid rotators at lower inclinations.

  5. Characterizing the Milky Way's Stellar Populations by Understanding Stars Inside and Out

    NASA Astrophysics Data System (ADS)

    Epstein, Courtney Rose

    Understanding the mass assembly process and star formation history of galaxies is an open question in cosmology. In comparison with studying high-redshift galaxies, the Milky Way provides a laboratory for studying the formation and evolution of one system in detail. The Milky Way's star formation history may be reconstructed from the kinematics and chemistry of its stars, but accurate stellar ages are required to define the chronology of events. This dissertation explores two promising techniques for inferring field star ages based on (1) the decline in rotation rates due to stellar winds on the main sequence, and (2) the combination of asteroseismic mass and spectroscopic abundance constraints for red giant branch stars. Low-mass main sequence stars with a deep surface convection zone lose angular momentum due to a magnetically-driven wind and spin down over time, making rotation a potential age indicator. I investigate both theoretical and observational uncertainties in the rotation-mass-age relationship. Because the functional form of the angular momentum loss law is not well established, two different prescriptions are compared; both have the feature that solar mass stars forget their initial conditions and converge to a narrow rotation sequence more quickly than lower mass stars do. Even for a perfect angular momentum loss model, I find that the initial spread in rotation rates dominates the age uncertainty for young and low-mass (M ≤ 0.6 MSun) stars, while latitudinal surface differential rotation sets a ~20% minimum uncertainty in rotation-based ages. Rotation periods are predicted to be a useful clock and detectable by ground-based surveys for field populations as old as 1--2 Gyr, and detectable by space-based telescopes for stars as old as the Galactic disk. Rotation provides better leverage than other age diagnostics for unevolved dwarfs because the spin down timescale is much faster than the nuclear-burning timescale. However, for solar-like dwarfs and

  6. Stellar Populations of Highly Magnified Lensed Galaxies: Young Starbursts at Z approximately 2

    NASA Technical Reports Server (NTRS)

    Wuyts, Eva; Rigby, Jane R.; Gladders, Michael D.; Gilbank, David G.; Sharon, Keren; Gralla, Megan B.; Bayliss, Matthew B.

    2012-01-01

    We present a comprehensive analysis of the rest-frame UV to near-IR spectral energy distributions (SEDs) and rest-frame optical spectra of four of the brightest gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at z = 1.70, MS1512-cB58 at z = 2.73, SGAS J152745.1+065219 at z = 2.76, and SGAS J122651.3+215220 at z = 2.92. This includes new Spitzer imaging for RCSGA0327 as well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and SGAS1226. Lensing magnifications of 3-4 mag allow a detailed study of the stellar populations and physical conditions. We compare star formation rates (SFRs) as measured from the SED fit, the Ha and [O II] ?3727 emission lines, and the UV+IR bolometric luminosity where 24 micron photometry is available. The SFR estimate from the SED fit is consistently higher than the other indicators, which suggests that the Calzetti dust extinction law used in the SED fitting is too flat for young star-forming galaxies at z 2. Our analysis finds similar stellar population parameters for all four lensed galaxies: stellar masses (3-7) ? 10(exp 9)Solar M young ages approx 100 Myr, little dust content E(B - V) = 0.10-0.25, and SFRs around 20-100 solar M/ yr. Compared to typical values for the galaxy population at z approx. 2, this suggests we are looking at newly formed, starbursting systems that have only recently started the buildup of stellar mass. These results constitute the first detailed, uniform analysis of a sample of the growing number of strongly lensed galaxies known at z approx 2.

  7. Formation of new stellar populations from gas accreted by massive young star clusters.

    PubMed

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters. PMID:26819043

  8. Formation of new stellar populations from gas accreted by massive young star clusters.

    PubMed

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  9. Stellar acoustic radii, mean densities, and ages from seismic inversion techniques

    NASA Astrophysics Data System (ADS)

    Buldgen, G.; Reese, D. R.; Dupret, M. A.; Samadi, R.

    2015-01-01

    Context. Determining stellar characteristics such as the radius, mass or age is crucial when studying stellar evolution or exoplanetary systems, or when characterising stellar populations in the Galaxy. Asteroseismology is the golden path to accurately obtain these characteristics. In this context, a key question is how to make these methods less model-dependent. Aims: Building on the previous work of Daniel Reese, we wish to extend the Substractive Optimally Localized Averages (SOLA) inversion technique to new stellar global characteristics beyond the mean density. The goal is to provide a general framework in which to estimate these characteristics as accurately as possible in low-mass main-sequence stars. Methods: First, we describe our framework and discuss the reliability of the inversion technique and possible sources of error. We then apply this methodology to the acoustic radius, an age indicator based on the sound speed derivative and the mean density, and compare it to estimates based on the average large and small frequency separations. These inversions are carried out for several test cases including various metallicities, different mixing-lengths, non-adiabatic effects, and turbulent pressure. Results: We observe that the SOLA method yields accurate results in all test cases whereas results based on the large and small frequency separations are less accurate and more sensitive to surface effects and structural differences in the models. If we include the surface corrections of Kjeldsen et al. (2008, ApJ, 683, L175), we obtain results of comparable accuracy for the mean density. Overall, the mean density and acoustic radius inversions are more robust than the inversions for the age indicator. Moreover, the current approach is limited to relatively young stars with radiative cores. Increasing the number of observed frequencies improves the reliability and accuracy of the method. Appendices are available in electronic form at http://www.aanda.org

  10. Gradients of stellar population properties and evolution clues in a nearby galaxy M101

    SciTech Connect

    Lin, Lin; Kong, Xu; Lin, Xuanbin; Mao, Yewei; Cheng, Fuzhen; Zou, Hu; Jiang, Zhaoji; Zhou, Xu E-mail: xkong@ustc.edu.cn

    2013-06-01

    Multiband photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of the nearby Scd-type galaxy M101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-A {sub FUV} relation, found to depend on a second parameter of birth rate b (ratio of present- and past-averaged star formation rates), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an 'inside-out' disk growth scenario. Two distinct disk regions with different gradients of age and color are discovered, similar to another late-type galaxy, NGC 628. The metallicity gradient of the stellar content is flatter than that of H II regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower compared with galaxies of similar and earlier morphological type. We note that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar which is relatively young, metal-rich, and contains much dust.

  11. Images in the rocket ultraviolet - The stellar population in the central bulge of M31

    NASA Technical Reports Server (NTRS)

    Bohlin, R. C.; Cornett, R. H.; Hill, J. K.; Hill, R. S.; Oconnell, R. W.; Stecher, T. P.

    1985-01-01

    Imagery of the bulge of M31 obtained with a rocket-borne telescope in two broad bands centered at 1460 A and 2380 A is discussed. The UV spatial profiles over a region about 200 arcsec wide are identical with those at visible wavelengths. The absence of detectable point sources indicates that main-sequence stars hotter than B0 V are not present in the bulge. It is suggested that the far-UV flux in old stellar populations originates in post-AGB stars. The UV flux from such stars is extremely sensitive to age and the physics of their previous mass loss.

  12. The stellar population in the core of M15

    NASA Technical Reports Server (NTRS)

    De Marchi, Guido; Paresce, Francesco

    1994-01-01

    The inner core of the globular cluster M15 within approximately 2 sec of the geometrical center has been explored with high-resolution images taken through several broad-band UV filter with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). Approximately 210 stars in this region down to a 5 sigma detection limit of m(sub 220) = 21.5 were reliably identified and located on a UV - U color magnitude diagram for the first time. A majority of stars (about 70% of the total) observed this way lie above the expected main-sequence turn-off of this cluster and below the sparsely populated horizontal branch. The extension of the main sequence above the turn-off separates this population in two roughly equal components situated to the right and left of this line. Most of the former must be classical blue stragglers while the rest belong to a new, as yet unidentified, population of very blue stars. Possibilities include, but are not restricted to, well-mixed single stars, subdwarfs, and helium white dwarfs. Similar objects are also found just outside the core out to approximately 6 sec from the center, but the brighter, presumably more massive ones, are sharply confined to the core itself. The measured excess of bright blue stars and the relative deficiency of bright red giants in the core are consistent with the blue inward color gradient measured from the ground and imply that dynamical evolution can significantly affect the stellar population in the very dense central regions of a high-concentration globular cluster like M15.

  13. Recovering galaxy stellar population properties from broad-band spectral energy distribution fitting

    NASA Astrophysics Data System (ADS)

    Pforr, Janine; Maraston, Claudia; Tonini, Chiara

    2012-06-01

    We explore the dependence of galaxy stellar population properties that are derived from broad-band spectral energy distribution fitting - such as age, stellar mass, dust reddening, etc. - on a variety of parameters, such as star formation histories, age grid, metallicity, initial mass function (IMF), dust reddening and reddening law, filter setup and wavelength coverage. Mock galaxies are used as test particles. We confirm our earlier results based on real z= 2 galaxies, that usually adopted τ-models lead to overestimate the star formation rate and to underestimate the stellar mass. Here, we show that - for star-forming galaxies - galaxy ages, masses and reddening can be well determined simultaneously only when the correct star formation history is identified. This is the case for inverted-τ models at high-z, for which we find that the mass recovery (at fixed IMF) is as good as ˜0.04 dex. However, since the right star formation history is usually unknown, we quantify the offsets generated by adopting standard fitting setups. Stellar masses are generally underestimated, which results from underestimating the age. For mixed fitting setups with a variety of star formation histories the median mass recovery at z˜ 2-3 is as decent as ˜0.1 dex (at fixed IMF), albeit with large scatter. The situation worsens towards lower redshifts, because of the variety of possible star formation histories and ages. At z˜ 0.5 the stellar mass can be underestimated by as much as ˜0.6 dex (at fixed IMF). A practical trick to improve upon this figure is to exclude reddening from the fitting parameters, as this helps to avoid unrealistically young and dusty solutions. Stellar masses are underestimated by a smaller amount (˜0.3 dex at z˜ 0.5). Reddening and the star formation rate should then be determined via a separate fitting. As expected, the recovery of properties is better for passive galaxies, for which e.g. the mass can be fully recovered (within ˜0.01 dex at fixed IMF

  14. THE AGE AND STELLAR PARAMETERS OF THE PROCYON BINARY SYSTEM

    SciTech Connect

    Liebert, James; Arnett, David; Fontaine, Gilles; Young, Patrick A.; Williams, Kurtis A. E-mail: darnett@as.arizona.edu E-mail: pyoung.3@asu.edu

    2013-05-20

    The Procyon AB binary system (orbital period 40.838 yr, a newly refined determination) is near and bright enough that the component radii, effective temperatures, and luminosities are very well determined, although more than one possible solution to the masses has limited the claimed accuracy. Preliminary mass determinations for each component are available from Hubble Space Telescope imaging, supported by ground-based astrometry and an excellent Hipparcos parallax; we use these for our preferred solution for the binary system. Other values for the masses are also considered. We have employed the TYCHO stellar evolution code to match the radius and luminosity of the F5 IV-V primary star to determine the system's most likely age as 1.87 {+-} 0.13 Gyr. Since prior studies of Procyon A found its abundance indistinguishable from solar, the solar composition of Asplund, Grevesse, and Sauval (Z = 0.014) is assumed for the Hertzsprung-Russell diagram fitting. An unsuccessful attempt to fit using the older solar abundance scale of Grevesse and Sauval (Z = 0.019) is also reported. For Procyon B, 11 new sequences for the cooling of non-DA white dwarfs have been calculated to investigate the dependences of the cooling age on (1) the mass, (2) core composition, (3) helium layer mass, and (4) heavy-element opacities in the helium envelope. Our calculations indicate a cooling age of 1.19 {+-} 0.11 Gyr, which implies that the progenitor mass of Procyon B was 2.59{sub -0.26}{sup +0.44} M{sub Sun }. In a plot of initial versus final mass of white dwarfs in astrometric binaries or star clusters (all with age determinations), the Procyon B final mass lies several {sigma} below a straight line fit.

  15. Stellar age dating with thorium, uranium and lead

    NASA Astrophysics Data System (ADS)

    Frebel, Anna; Kratz, Karl-Ludwig

    2009-06-01

    We present HE 1523-0901, a metal-poor star in which the radioactive elements Th and U could be detected. Only three stars have measured U abundances, of which HE 1523-0901 has the most confidently determined value. From comparing the stable Eu, Os, and Ir abundances with measurements of Th and U, stellar ages can be derived. Based on seven such chronometer abundance ratios, the age of HE 1523-0901 was found to be ~13 Gyr. Only an upper limit for Pb could be measured so far. Knowing all three abundances of Th, U, and Pb would provide a self-consistent test for r-process calculations. Pb is the beta- plus alpha-decay end-product of all decay chains in the mass region between Pb and the onset of dominant spontaneous fission above Th and U. Hence, in addition to Th/U also Th, U/Pb should be used to obtain a consistent picture for actinide chronometry. From recent r-process calculations within the classical “waiting-point” model, for a 13 Gyr old star we predict the respective abundance ratios of logγ(Th/U) = 0.84, logγ(Th/Pb) = -1.32 and logγ(U/Pb) = -2.16. We compare these values with the measured abundance ratios in HE 1523-0901 of logγ(Th/U) = 0.86, logγ(Th/Pb) > -1.0 and logγ(U/Pb) > -1.9. With this good level of agreement, HE 1523-0901 is already a vital probe for observational “near-field” cosmology by providing an independent lower limit for the age of the Universe.

  16. Stellar Archaeology with Gaia: The Galactic White Dwarf Population

    NASA Astrophysics Data System (ADS)

    Gänsicke, B.; Tremblay, P.; Barstow, M.; Bono, G.; Burleigh, M.; Casewell, S.; Dhillon, V.; Farihi, J.; Garcia-Berro, E.; Geier, S.; Gentile-Fusillo, N.; Hermes, J.; Hollands, M.; Istrate, A.; Jordan, S.; Knigge, C.; Manser, C.; Marsh, T.; Nelemans, G.; Pala, A.; Raddi, R.; Tauris, T.; Toloza, O.; Veras, D.; Werner, K.; Wilson, D.

    2016-10-01

    Gaia will identify several 105 white dwarfs, most of which will be in the solar neighborhood at distances of a few hundred parsecs. Ground-based optical follow-up spectroscopy of this sample of stellar remnants is essential to unlock the enormous scientific potential it holds for our understanding of stellar evolution, and the Galactic formation history of both stars and planets.

  17. Stellar populations in ω Centauri: a multivariate analysis

    NASA Astrophysics Data System (ADS)

    Fraix-Burnet, D.; Davoust, E.

    2015-07-01

    We have performed multivariate statistical analyses of photometric and chemical abundance parameters of three large samples of stars in the globular cluster ω Centauri. The statistical analysis of a sample of 735 stars based on seven chemical abundances with the method of Maximum Parsimony (cladistics) yields the most promising results: seven groups are found, distributed along three branches with distinct chemical, spatial and kinematical properties. A progressive chemical evolution can be traced from one group to the next, but also within groups, suggestive of an inhomogeneous chemical enrichment of the initial interstellar matter. The adjustment of stellar evolution models shows that the groups with metallicities [Fe/H] > -1.5 are Helium enriched, thus presumably of second generation. The spatial concentration of the groups increases with chemical evolution, except for two groups, which stand out in their other properties as well. The amplitude of rotation decreases with chemical evolution, except for two of the three metal-rich groups, which rotate fastest, as predicted by recent hydrodynamical simulations. The properties of the groups are interpreted in terms of star formation in gas clouds of different origins. In conclusion, our multivariate analysis has shown that metallicity alone cannot segregate the different populations of ω Centauri.

  18. STELLAR POPULATIONS AND THE STAR FORMATION HISTORIES OF LOW SURFACE BRIGHTNESS GALAXIES. II. H II REGIONS

    SciTech Connect

    Schombert, James; McGaugh, Stacy; Maciel, Tamela E-mail: stacy.mcgaugh@case.edu

    2013-08-01

    The luminosities, colors, and H{alpha} emission for 429 H II regions in 54 low surface brightness (LSB) galaxies are presented. While the number of H II regions per galaxy is lower in LSB galaxies compared to star-forming irregulars and spirals, there is no indication that the size or luminosity function of H II regions differs from other galaxy types. The lower number of H II regions per galaxy is consistent with their lower total star formation rates. The fraction of the total L{sub H{alpha}} contributed by H II regions varies from 10% to 90% in LSB galaxies (the rest of the H{alpha} emission being associated with a diffuse component) with no correlation with galaxy stellar or gas mass. Bright H II regions have bluer colors, similar to the trend in spirals; their number and luminosities are consistent with the hypothesis that they are produced by the same H II luminosity function as spirals. Comparison with stellar population models indicates that the brightest H II regions in LSB galaxies range in cluster mass from a few 10{sup 3} M{sub Sun} (e.g., {rho} Oph) to globular-cluster-sized systems (e.g., 30 Dor) and that their ages are consistent with clusters from 2 to 15 Myr old. The faintest H II regions are comparable to those in the LMC powered by a single O or B star. Thus, star formation in LSB galaxies covers the full range of stellar cluster mass.

  19. The ATLAS3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Cappellari, Michele; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2015-04-01

    We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, R^maj_e), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ˜ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions.

  20. Merger traces in the spatial distribution of stellar populations in the Fornax dSph galaxy

    NASA Astrophysics Data System (ADS)

    del Pino, Andrés; Aparicio, Antonio; Hidalgo, Sebastian L.

    2015-12-01

    We present a comprehensive and detailed study of the stellar populations of the Fornax dwarf spheroidal galaxy. We analyse their spatial distributions along the main body of the galaxy, obtaining their surface density maps, together with their radial density profiles. Results are based on the largest and most complete catalogue of stars in Fornax, with more than 3.5 × 105 stars covering the main body of the galaxy up to V ˜ 24. We find a differentiated structure in Fornax depending on the stellar ages. Old stars (≳10 Gyr) follow an elliptical distribution well fitted by King profiles with relatively large core radius (rc = 760 ± 60 pc). On another hand, young populations (≲3 Gyr) concentrate in the central region of the galaxy (rc = 210 ± 10 pc), and are better fitted by Sérsic profiles with 0.8 < n < 1.2, indicating some discy shape. These stars show strong asymmetries and substructures not aligned with the main optical axes of Fornax. This together with the observed differences between metallicity and age distribution maps strongly suggests accretion of material with different angular momentum. These results lead us to propose a scenario in which Fornax has suffered a major merger at z ˜ 1.

  1. Combined Effects of Binaries and Stellar Rotation on the Color-Magnitude Diagrams of Intermediate-age Star Clusters

    NASA Astrophysics Data System (ADS)

    Li, Zhongmu; Mao, Caiyan; Chen, Li; Zhang, Qian

    2012-12-01

    About 70% of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turnoffs, and dual red giant clumps. The observed result seems to be at odds with the classical idea that such clusters are simple stellar populations. Although many models have been used to explain the results via factors such as prolonged star formation history, metallicity spread, differential reddening, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows "golf club" color-magnitude diagrams with broad or multiple turnoffs, dual red clumps, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams, including extended turnoff or multiple turnoffs, can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.

  2. COMBINED EFFECTS OF BINARIES AND STELLAR ROTATION ON THE COLOR-MAGNITUDE DIAGRAMS OF INTERMEDIATE-AGE STAR CLUSTERS

    SciTech Connect

    Li Zhongmu; Mao Caiyan; Chen Li; Zhang Qian

    2012-12-20

    About 70% of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turnoffs, and dual red giant clumps. The observed result seems to be at odds with the classical idea that such clusters are simple stellar populations. Although many models have been used to explain the results via factors such as prolonged star formation history, metallicity spread, differential reddening, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows 'golf club' color-magnitude diagrams with broad or multiple turnoffs, dual red clumps, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams, including extended turnoff or multiple turnoffs, can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.

  3. RemoveYoung: A tool for the removal of the young stellar component in galaxies within an adjustable age cutoff

    NASA Astrophysics Data System (ADS)

    Gomes, J. M.; Papaderos, P.

    2016-10-01

    The optical morphology of galaxies holds the cumulative record of their assembly history, and techniques for its quantitative characterization offer a promising avenue toward understanding galaxy formation and evolution. However, the morphology of star-forming galaxies is generally dictated by the youngest stellar component, which can readily overshine faint structural/morphological features in the older underlying stellar background (e.g., relics from recent minor mergers) that could hold important insights into the galaxy build-up process. Stripping off galaxy images from the emission from stellar populations younger than an adjustable age cutoff tcut can therefore provide a valuable tool in extragalactic research. RemoveYoung (), a publicly available tool that is presented here, exploits the combined power of integral field spectroscopy (IFS) and spectral population synthesis (SPS) toward this goal. Two-dimensional (2D) post-processing of SPS models to IFS data cubes with permits computation of the spectral energy, surface brightness, and stellar surface density distribution of stellar populations older than a user-defined tcut. This suggests a variety of applications of star-forming galaxies, such as interacting or merging galaxy pairs and lower mass starburst galaxies near and far; these include blue compact and tidal dwarf galaxies.

  4. Being WISE. I. Validating stellar population models and M {sub *}/L ratios at 3.4 and 4.6 μm

    SciTech Connect

    Norris, Mark A.; Meidt, Sharon; Van de Ven, Glenn; Schinnerer, Eva; Groves, Brent; Querejeta, Miguel

    2014-12-10

    Using data from the Wide-field Infrared Survey Explorer mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 μm (W2) photometry of stellar populations have been examined. We find that the W1 – W2 colors of intermediate and old (>2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 – W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 μm bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

  5. The Hydra I cluster core. I. Stellar populations in the cD galaxy NGC 3311

    NASA Astrophysics Data System (ADS)

    Barbosa, C. E.; Arnaboldi, M.; Coccato, L.; Hilker, M.; Mendes de Oliveira, C.; Richtler, T.

    2016-05-01

    Context. The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. Aims: We provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radii. We wish to characterize the processes that drove the build-up of the stellar light at all these radii. Methods: We obtained the spectra from several regions in NGC 3311 covering an area of ~3 arcmin2 in the wavelength range 4800 ≲ λ(Å) ≲ 5800, using the FORS2 spectrograph at the Very Large Telescope in the MXU mode. We measured the equivalent widths of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. Results: The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC 3311 may be divided in two radial regimes, one within and the another beyond one effective radius, Re = 8.4 kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC 3311 velocity dispersion profile. The inner galaxy (R ≤ Re) is old (age ~14 Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0°< PA < 90° has higher metallicity with respect to the symmetric external halo. Conclusions: The different stellar populations in the inner galaxy and extended halo

  6. IN-SYNC. IV. The Young Stellar Population in the Orion A Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Da Rio, Nicola; Tan, Jonathan C.; Covey, Kevin R.; Cottaar, Michiel; Foster, Jonathan B.; Cullen, Nicholas C.; Tobin, John J.; Kim, Jinyoung S.; Meyer, Michael R.; Nidever, David L.; Stassun, Keivan G.; Chojnowski, S. Drew; Flaherty, Kevin M.; Majewski, Steve; Skrutskie, Michael F.; Zasowski, Gail; Pan, Kaike

    2016-02-01

    We present the results of the Sloan Digital Sky Survey APOGEE INfrared Spectroscopy of Young Nebulous Clusters program (IN-SYNC) survey of the Orion A molecular cloud. This survey obtained high-resolution near-infrared spectroscopy of about 2700 young pre-main-sequence stars on a ˜ 6^\\circ field of view. We have measured accurate stellar parameters ({T}{{eff}}, {log}g, v{sin}i) and extinctions and placed the sources in the Hertzsprung-Russel diagram (HRD). We have also extracted radial velocities for the kinematic characterization of the population. We compare our measurements with literature results to assess the performance and accuracy of the survey. Source extinction shows evidence for dust grains that are larger than those in the diffuse interstellar medium: we estimate an average RV = 5.5 in the region. Importantly, we find a clear correlation between HRD inferred ages and spectroscopic surface-gravity-inferred ages and between extinction and disk presence; this strongly suggests a real spread of ages larger than a few Myr. Focusing on the young population around NGC 1980/ι Ori, which has previously been suggested to be a separate, foreground, older cluster, we confirm its older (˜5 Myr) age and low AV, but considering that its radial velocity distribution is indistinguishable from Orion A’s population, we suggest that NGC 1980 is part of Orion A’s star formation activity. Based on their stellar parameters and kinematic properties, we identify 383 new candidate members of Orion A, most of which are diskless sources in areas of the region poorly studied by previous works.

  7. THE EFFECT OF HELIUM-ENHANCED STELLAR POPULATIONS ON THE ULTRAVIOLET-UPTURN PHENOMENON OF EARLY-TYPE GALAXIES

    SciTech Connect

    Chung, Chul; Yoon, Suk-Jin; Lee, Young-Wook

    2011-10-20

    Recent observations and modeling of globular clusters (GCs) with multiple populations strongly indicate the presence of super-helium-rich subpopulations in old stellar systems. Motivated by this, we have constructed new population synthesis models with and without helium-enhanced subpopulations to investigate their impact on the UV-upturn phenomenon of quiescent early-type galaxies (ETGs). We find that our models with helium-enhanced subpopulations can naturally reproduce the strong UV-upturns observed in giant elliptical galaxies assuming an age similar to that of old GCs in the Milky Way. The major source of far-UV (FUV) flux, in this model, is relatively metal-poor and helium-enhanced hot horizontal-branch stars and their progeny. The Burstein et al. relation of the FUV - V color with metallicity is also explained either by the variation of the fraction of helium-enhanced subpopulations or by the spread in mean age of stellar populations in ETGs.

  8. A multiwavelength investigation of the H II region S311: young stellar population and star formation

    NASA Astrophysics Data System (ADS)

    Yadav, Ram Kesh; Pandey, A. K.; Sharma, Saurabh; Ojha, D. K.; Samal, M. R.; Mallick, K. K.; Jose, J.; Ogura, K.; Richichi, Andrea; Irawati, Puji; Kobayashi, N.; Eswaraiah, C.

    2016-09-01

    We present a multiwavelength investigation of the young stellar population and star formation activities around the H II region Sharpless 311. Using our deep near-infrared observations and archival Spitzer-IRAC observations, we have detected a total of 125 young stellar objects (YSOs) in an area of ˜86 arcmin2. The YSO sample includes eight Class I and 117 Class II candidate YSOs. The mass completeness of the identified YSO sample is estimated to be 1.0 M⊙. The ages and masses of the majority of the candidate YSOs are estimated to be in the range ˜0.1-5 Myr and ˜0.3-6 M⊙, respectively. The 8-μm image of S311 displays an approximately spherical cavity around the ionizing source, which was possibly created by the expansion of the H II region. The spatial distribution of the candidate YSOs reveals that a significant number of them are distributed systematically along the 8-μm emission with a majority clustered around the eastern border of the H II region. Four clumps/compact H II regions are detected in the radio continuum observations at 1280 MHz, which may have been formed during the expansion of the H II region. The estimated dynamical age of the region, main-sequence lifetime of the ionizing source, the spatial distribution and ages of the candidate YSOs indicate triggered star formation in the complex.

  9. THE YOUNG STELLAR POPULATION OF THE CYGNUS-X DR15 REGION

    SciTech Connect

    Rivera-Gálvez, S.; Román-Zúñiga, C. G.; Jiménez-Bailón, E.; Ybarra, J. E.; Alves, J. F.

    2015-12-15

    We present a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region. We studied young stars that were forming or recently formed at and around the tip of a prominent molecular pillar and an infrared dark cloud. Using a combination of ground-based near-infrared, space-based infrared, and X-ray data, we constructed a point source catalog from which we identified 226 young stellar sources, which we classified into evolutionary classes. We studied their spatial distributions across the molecular gas structures and identified several groups that possibly belong to distinct young star clusters. We obtained samples of these groups and constructed K-band luminosity functions that we compared with those of artificial clusters, allowing us to make first order estimates of the mean ages and age spreads of the groups. We used a {sup 13}CO(1-0) map to investigate the gas kinematics at the prominent gaseous envelope of the central cluster in DR15, and we inferred that the removal of this envelope is relatively slow compared to other cluster regions, in which the gas dispersal timescale could be similar or shorter than the circumstellar disk dissipation timescale. The presence of other groups with slightly older ages, associated with much less prominent gaseous structures, may imply that the evolution of young clusters in this part of the complex proceeds in periods that last 3–5 Myr, perhaps after a slow dissipation of their dense molecular cloud birthplaces.

  10. Formation of the first galaxies under Population III stellar feedback

    NASA Astrophysics Data System (ADS)

    Jeon, Myoungwon

    2015-01-01

    will discuss key physical quantities of the first galaxies derived from our simulations, such as their stellar population mix, star formation rates, metallicities, and resulting broad-band color and recombination spectra.

  11. Theory of stellar population synthesis with an application to N-body simulations

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Chiosi, C.; Kawata, D.

    2012-09-01

    Aims: We present here a new theoretical approach to population synthesis. The aim is to predict colour magnitude diagrams (CMDs) for huge numbers of stars. With this method we generate synthetic CMDs for N-body simulations of galaxies. Sophisticated hydrodynamic N-body models of galaxies require equal quality simulations of the photometric properties of their stellar content. The only prerequisite for the method to work is very little information on the star formation and chemical enrichment histories, i.e. the age and metallicity of all star-particles as a function of time. The method takes into account the gap between the mass of real stars and that of the star-particles in N-body simulations, which best correspond to the mass of star clusters with different age and metallicity, i.e. a manifold of single stellar sopulations (SSP). Methods: The theory extends the concept of SSP to include the phase-space (position and velocity) of each star. Furthermore, it accelerates the building up of simulated CMD by using a database of theoretical SSPs that extends to all ages and metallicities of interest. Finally, it uses the concept of distribution functions to build up the CMD. The technique is independent of the mass resolution and the way the N-body simulation has been calculated. This allows us to generate CMDs for simulated stellar systems of any kind: from open clusters to globular clusters, dwarf galaxies, or spiral and elliptical galaxies. Results: The new theory is applied to an N-body simulation of a disc galaxy to test its performance and highlight its flexibility.

  12. EARLY-TYPE GALAXIES IN THE PEARS SURVEY: PROBING THE STELLAR POPULATIONS AT MODERATE REDSHIFT

    SciTech Connect

    Ferreras, Ignacio; Pasquali, Anna; Malhotra, Sangeeta; Rhoads, James; Cohen, Seth; Windhorst, Rogier; Pirzkal, Nor; Grogin, Norman; Koekemoer, Anton M.; Panagia, Nino; Lisker, Thorsten; Daddi, Emanuele; Hathi, Nimish P.

    2009-11-20

    Using Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) slitless grism spectra from the PEARS program, we study the stellar populations of morphologically selected early-type galaxies in the GOODS North and South fields. The sample-extracted from a visual classification of the (v2.0) HST/ACS images and restricted to redshifts z > 0.4-comprises 228 galaxies (i {sub F775W} < 24 mag, AB) out to z approx< 1.3 over 320 arcmin{sup 2}, with a median redshift z {sub M} = 0.75. This work significantly increases our previous sample from the GRAPES survey in the HUDF (18 galaxies over approx11 arcmin{sup 2}). The grism data allow us to separate the sample into 'red' and 'blue' spectra, with the latter comprising 15% of the total. Three different grids of models parameterizing the star formation history are used to fit the low-resolution spectra. Over the redshift range of the sample-corresponding to a cosmic age between 5 and 10 Gyr-we find a strong correlation between stellar mass and average age, whereas the spread of ages (defined by the root mean square of the distribution) is roughly approx1 Gyr and independent of stellar mass. The best-fit parameters suggest that it is the formation epoch and not the formation timescale that best correlates with mass in early-type galaxies. This result-along with the recently observed lack of evolution of the number density of massive galaxies-motivates the need for a channel of (massive) galaxy formation bypassing any phase in the blue cloud, as suggested by the simulations of Dekel et al.

  13. Near-Infrared Surface Brightness Fluctuations as Diagnostics of Unresolved Stellar Populations

    NASA Astrophysics Data System (ADS)

    González L., R. A.; Liu, M. C.

    Surface brightness fluctuations (SBFs) are already a very powerful tool for deriving cosmological distances. However, their promise as diagnostics of unresolved stellar populations has not yet been fulfilled. Here, we present an ongoing project to mine the 2MASS database with exactly that purpose. This work should help 1) explain the observed dispersion of measured SBFs in nearby galaxy clusters; 2) calibrate the stellar population synthesis models that are used, in combination with observational data, to derive cosmological distances; and 3) expand the capabilities of the largest telescopes, like the GTC, to study very distant stellar populations.

  14. POPULATIONS OF YOUNG STELLAR OBJECTS IN NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Hsieh, Tien-Hao; Lai, Shih-Ping E-mail: slai@phys.nthu.edu.tw

    2013-03-01

    We develop a new method for identifying young stellar objects (YSOs) from star-forming regions using the photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying statistical properties such as the star formation rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle in identifying YSOs comes from background galaxies with similar spectral energy distributions to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in color-color diagrams and color-magnitude diagrams (CMDs), those criteria may exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in a multi-dimensional (multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sources from molecular clouds to Spitzer's SWIRE data, which have a negligible amount of YSOs, we can naturally identify YSO candidates (YSOc) located outside of the galaxy-populated regions in the multi-D space. In the five c2d surveyed clouds, we select 322 new YSOc and miss/exclude 33 YSOc compared to Evans et al., and this results in 1313 YSOc in total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stages remain unchanged. Compared to theories by Krumholz and McKee, our derived SFR suggests that star formation at a large scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify seven new very low luminosity objects.

  15. CORE-COLLAPSE SUPERNOVAE AND HOST GALAXY STELLAR POPULATIONS

    SciTech Connect

    Kelly, Patrick L.; Kirshner, Robert P.

    2012-11-10

    We have used images and spectra of the Sloan Digital Sky Survey to examine the host galaxies of 519 nearby supernovae (SN). The colors at the sites of the explosions, as well as chemical abundances, and specific star formation rates (SFRs) of the host galaxies provide circumstantial evidence on the origin of each SN type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple spectroscopic fibers, we select the fiber with host radial offset most similar to that of the SN. Type Ic SN explode at small host offsets, and their hosts have exceptionally strongly star-forming, metal-rich, and dusty stellar populations near their centers. The SN Ic-BL and SN IIb explode in exceptionally blue locations, and, in our sample, we find that the host spectra for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb host fiber spectra are also more metal-poor than those for SN Ib, although a significant difference exists for only one of two strong-line diagnostics. SN Ic-BL host galaxy emission lines show strong central specific SFRs. In contrast, we find no strong evidence for different environments for SN IIn compared to the sites of SN II. Because our SN sample is constructed from a variety of sources, there is always a risk that sampling methods can produce misleading results. We have separated the SN discovered by targeted surveys from those discovered by galaxy-impartial searches to examine these questions and show that our results do not depend sensitively on the discovery technique.

  16. The stellar accretion origin of stellar population gradients at large radii in massive, early-type galaxies

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; Naab, Thorsten

    2015-08-01

    We investigate the differential impact of physical mechanisms, mergers (stellar accretion) and internal energetic phenomena, on the evolution of stellar population gradients in massive, present-day galaxies employing a set of high-resolved, cosmological zoom simulations. We demonstrate that negative metallicity and color gradients at large radii (>2Reff) originate from the accretion of metal-poor stellar systems. At larger radii, galaxies become typically more dominated by stars accreted from satellite galaxies in major and minor mergers. However, only strong galactic winds can sufficiently reduce the metallicity content of the accreted stars to realistically steepen the outer metallicity and colour gradients in agreement with present-day observations. In contrast, the gradients of the models without winds are inconsistent with observations (too flat). In the wind model, colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This analysis greatly highlights the importance of both energetic processes and merger events for stellar population properties of massive galaxies at large radii. Our results are expected to significantly contribute to the interpretation of current and up-coming IFU surveys (like MaNGA and Califa), which in turn can help to constrain models for energetic processes in simulations.

  17. The Connection between Stellar Populations and the Baryon Cycle and Ionizing Escape Fractions of Galaxies at High Redshift

    NASA Astrophysics Data System (ADS)

    Reddy, Naveen; Steidel, Charles

    2016-08-01

    We propose Spitzer IRAC 3.6 micron observations to cover the three remaining fields of a large spectroscopic survey of galaxies, AGN, and QSOs in the same cosmic volumes at z~2-3. The IRAC data will be used to probe the stellar populations in these galaxies and to understand how galaxy properties (e.g., stellar masses, ages, reddening, star-formation rates) depend on the flow of baryons into and out of galaxies, as well as identify those properties of galaxies that are conducive to the escape of ionizing radiation at high redshift. The dense spectroscopic sampling of the targeted fields have provided unique insights into metal enrichment as a function of galactocentric radius and the statistical correlation between galaxies and metals in the inter-galactic medium. Our goal is to quantify how the distribution of metals in the circum-galactic and inter-galactic media (CGM/IGM) depend on the stellar masses, ages, and star formation rates of galaxies. Moreover, in an effort to clarify the role of galaxies in reionizing the Universe (and keeping it ionized), we wish to understand the types of stellar populations (e.g., stellar masses, ages) that influence the propensity of galaxies to leak ionizing radiation. Our preliminary observations suggest that bluer galaxies with lower star-formation rates have larger escape fractions, but the results are tentative without the inclusion of the IRAC data proposed here. A modest investment of just 13.1 hours (including overhead), divided among the three fields will cover a total of approximately 200 spectroscopically-confirmed z~2-3 galaxies that span two orders of magnitude in bolometric luminosity and stellar mass. The proposed IRAC imaging will allow us to fully leverage the existing spectroscopic samples that form the backbone of our survey of the baryon cycle and escaping ionizing radiation at high redshift.

  18. Testing Density Wave Theory with Resolved Stellar Populations around Spiral Arms in M81

    NASA Astrophysics Data System (ADS)

    Choi, Yumi; Dalcanton, Julianne J.; Williams, Benjamin F.; Weisz, Daniel R.; Skillman, Evan D.; Fouesneau, Morgan; Dolphin, Andrew E.

    2015-09-01

    Stationary density waves rotating at a constant pattern speed {{{Ω }}}{{P}} would produce age gradients across spiral arms. We test whether such age gradients are present in M81 by deriving the recent star formation histories (SFHs) of 20 regions around one of M81's grand-design spiral arms. For each region, we use resolved stellar populations to determine the SFH by modeling the observed color-magnitude diagram constructed from archival Hubble Space Telescope F435W and F606W imaging. Although we should be able to detect systematic time delays in our spatially resolved SFHs, we find no evidence of star formation propagation across the spiral arm. Our data therefore provide no convincing evidence for a stationary density wave with a single pattern speed in M81, and instead favor the scenario of kinematic spiral patterns that are likely driven by tidal interactions with the companion galaxies M82 and NGC 3077.

  19. The reliability of age measurements for Young Stellar Objects from Hertzsprung-Russell or color-magnitude diagrams

    NASA Astrophysics Data System (ADS)

    Preibisch, Thomas

    2012-01-01

    The possibility to estimate ages and masses of Young Stellar Objects (YSOs) from their location in the Hertzsprung-Russell diagram (HRD) or a color-magnitude diagram provides a very important tool for the investigation of fundamental questions related to the processes of star formation and early stellar evolution. Age estimates are essential for studies of the temporal evolution of circumstellar material around YSOs and the conditions for planet formation. The characterization of the age distribution of the YSOs in a star forming region allows researchers to reconstruct the star formation history and provides important information on the fundamental question of whether star formation is a slow or a fast process. However, the reliability of these age measurements and the ability to detect possible age spreads in the stellar population of star forming regions are fundamentally limited by several factors. The variability of YSOs, unresolved binary components, and uncertainties in the calibrations of the stellar parameters cause uncertainties in the derived luminosities that are usually much larger than the typical photometry errors. Furthermore, the pre-main sequence evolution track of a YSO depends to some degree on the initial conditions and the details of its individual accretion history. I discuss how these observational and model uncertainties affect the derived isochronal ages, and demonstrate how neglecting or underestimating these uncertainties can easily lead to severe misinterpretations, gross overestimates of the age spread, and ill-based conclusions about the star formation history. These effects are illustrated by means of Monte-Carlo simulations of observed star clusters with realistic observational uncertainties. The most important points are as follows. First, the observed scatter in the HRD must not be confused with a genuine age spread, but is always just an upper limit to the true age spread. Second, histograms of isochronal ages naturally show a

  20. The VMC survey. XI. Radial stellar population gradients in the galactic globular cluster 47 Tucanae

    SciTech Connect

    Li, Chengyuan; De Grijs, Richard; Deng, Licai; Rubele, Stefano; Girardi, Leo; Gullieuszik, Marco; Wang, Chuchu; Bekki, Kenji; For, Bi-Qing; Cioni, Maria-Rosa L.; Clementini, Gisella; Emerson, Jim; Groenewegen, Martin A. T.; Guandalini, Roald; Marconi, Marcella; Ripepi, Vincenzo; Piatti, Andrés E.; Van Loon, Jacco Th. E-mail: grijs@pku.edu.cn

    2014-07-20

    We present a deep near-infrared color-magnitude diagram of the Galactic globular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, K{sub s} survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red giant branches exhibit apparent, continuous variations in color-magnitude space as a function of radius. Subgiant branch stars at larger radii are systematically brighter than their counterparts closer to the cluster core; similarly, red-giant-branch stars in the cluster's periphery are bluer than their more centrally located cousins. The observations can very well be described by adopting an age spread of ∼0.5 Gyr as well as radial gradients in both the cluster's helium abundance (Y) and metallicity (Z), which change gradually from (Y = 0.28, Z = 0.005) in the cluster core to (Y = 0.25, Z = 0.003) in its periphery. We conclude that the cluster's inner regions host a significant fraction of second-generation stars, which decreases with increasing radius; the stellar population in the 47 Tuc periphery is well approximated by a simple stellar population.

  1. Massive open star clusters using the VVV survey. V. Young clusters with an OB stellar population

    NASA Astrophysics Data System (ADS)

    Ramírez Alegría, S.; Borissova, J.; Chené, A.-N.; Bonatto, C.; Kurtev, R.; Amigo, P.; Kuhn, M.; Gromadzki, M.; Carballo-Bello, J. A.

    2016-04-01

    Context. The ESO public survey VISTA Variables in the Vía Láctea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 sq. deg. More than a hundred cluster candidates have been reported thanks to this survey. Aims: We present the fifth article in a series of papers focused on young and massive clusters discovered in the VVV survey. In this paper, we present the physical characterization of five clusters with a spectroscopically confirmed OB-type stellar population. Methods: To characterize the clusters, we used near-infrared photometry (J, H, and KS) from the VVV survey and near-infrared K-band spectroscopy from ISAAC at VLT, following the methodology presented in the previous articles of the series. Results: All clusters in our sample are very young (ages between 1-20 Myr), and their total mass are between (1.07+0.40-0.30)×102 M⊙ and (4.17+4.15-2.08)×103 M⊙. We observed a relation between the clusters total mass Mecl and the mass of their most massive stellar member mmax, for clusters with an age <10 Myr. Based on observations taken within the ESO VISTA Public Survey VVV (programme ID 179.B-2002), and with ISAAC/VLT (programme 087.D-0341(A)).

  2. Multiple stellar populations in Magellanic Cloud clusters. II. Evidence also in the young NGC 1844?

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Bedin, L. R.; Cassisi, S.; Piotto, G.; Anderson, J.; Pietrinferni, A.; Buonanno, R.

    2013-07-01

    We used Hubble Space Telescope observations to study the young cluster NGC 1844 in the Large Magellanic Cloud (LMC). We estimated the fraction and the mass-ratio distribution of photometric binaries and report that the main sequence presents an intrinsic breadth which cannot be explained only in terms of photometric errors, and is unlikely because of differential reddening. We attempted different interpretations of this feature, including stellar rotation, binary stars, and the presence of multiple stellar populations of different ages, metallicity, helium, or C+N+O abundance. Although we have excluded age, helium, and C+N+O variations of being responsible for the main-sequence spread, none of the other interpretations is conclusive. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555, under GO-12219.Figures 1-3, 9, and 10 are available in electronic form at http://www.aanda.orgPhotometric data is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A143

  3. FAST STAR, SLOW STAR; OLD STAR, YOUNG STAR: SUBGIANT ROTATION AS A POPULATION AND STELLAR PHYSICS DIAGNOSTIC

    SciTech Connect

    Van Saders, Jennifer L.; Pinsonneault, Marc H.

    2013-10-20

    Stellar rotation is a strong function of both mass and evolutionary state. Missions such as Kepler and CoRoT provide tens of thousands of rotation periods, drawn from stellar populations that contain objects at a range of masses, ages, and evolutionary states. Given a set of reasonable starting conditions and a prescription for angular momentum loss, we address the expected range of rotation periods for cool field stellar populations (∼0.4-2.0 M{sub ☉}). We find that cool stars fall into three distinct regimes in rotation. Rapid rotators with surface periods less than 10 days are either young low-mass main sequence (MS) stars, or higher mass subgiants which leave the MS with high rotation rates. Intermediate rotators (10-40 days) can be either cool MS dwarfs, suitable for gyrochronology, or crossing subgiants at a range of masses. Gyrochronology relations must therefore be applied cautiously, since there is an abundant population of subgiant contaminants. The slowest rotators, at periods greater than 40 days, are lower mass subgiants undergoing envelope expansion. We identify additional diagnostic uses of rotation periods. There exists a period-age relation for subgiants distinct from the MS period-age relations. There is also a period-radius relation that can be used as a constraint on the stellar radius, particularly in the interesting case of planet host stars. The high-mass/low-mass break in the rotation distribution on the MS persists onto the subgiant branch, and has potential as a diagnostic of stellar mass. Finally, this set of theoretical predictions can be compared to extensive datasets to motivate improved modeling.

  4. The Chemical Properties of Milky Way and M31 Globular Clusters. II. Stellar Population Model Predictions

    NASA Astrophysics Data System (ADS)

    Beasley, Michael A.; Brodie, Jean P.; Strader, Jay; Forbes, Duncan A.; Proctor, Robert N.; Barmby, Pauline; Huchra, John P.

    2005-03-01

    We derive ages, metallicities, and abundance ratios ([α/Fe]) from the integrated spectra of 23 globular clusters in M31 by employing multivariate fits to two different stellar population models. We also perform a parallel analysis on 21 Galactic globular clusters as a consistency check and in order to facilitate a differential analysis. Our analysis shows that the M31 globular clusters separate into three distinct components in age and metallicity; we identify an old, metal-poor group (seven clusters), an old, metal-rich group (10 clusters), and an intermediate-age (3-6 Gyr), intermediate-metallicity ([Z/H]~-1) group (six clusters). This third group is not identified in the Galactic globular cluster sample. We also see evidence that the old, metal-rich Galactic globular clusters are 1-2 Gyr older than their counterparts in M31. The majority of globular clusters in both samples appear to be enhanced in α-elements, but the degree of enhancement is rather model-dependent. The intermediate-age globular clusters appear to be the most enhanced, with [α/Fe]~0.4. These clusters are clearly depressed in CN with respect to the models and the bulk of the M31 and Milky Way sample. Compared with the bulge of M31, M32, and NGC 205, these clusters most resemble the stellar populations in NGC 205 in terms of age, metallicity, and CN abundance. We infer horizontal branch morphologies for the M31 clusters using the Rose Ca II index and demonstrate that blue horizontal branches are not leading to erroneous age estimates in our analysis. We discuss and reject as unlikely the hypothesis that these objects are in fact foreground stars contaminating the optical catalogs. The intermediate-age clusters have generally higher velocities than the bulk of the M31 cluster population. Spatially, three of these clusters are projected onto the bulge region, and the remaining three are distributed at large radii. We discuss these objects within the context of the build-up of the M31 halo and

  5. Report on the Workshop Resolved and Unresolved Stellar PopUlaTIoNs (RASPUTIN)

    NASA Astrophysics Data System (ADS)

    Bono, G.; Valenti, E.

    2014-12-01

    The workshop aimed at sharing and discussing observations and diagnostics, together with models and simulations, of the resolved and unresolved stellar populations in galaxies from the Milky Way to the distant Universe. Special attention was paid to recent results concerning galaxy formation and evolution, fostering the exchange of ideas and techniques in dealing with nearby stellar populations. There will be no published proceedings, but presentations are available for download from the workshop web page (www.eso.org/sci/meetings/2014/rasputin2014).

  6. Breathing FIRE: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    El-Badry, Kareem; Wetzel, Andrew; Geha, Marla; Hopkins, Philip F.; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André

    2016-04-01

    We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (Mstar = 2 × 106 - 5 × 1010 M⊙) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ˜1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the global potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ˜200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed Mstar. Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly. This age-dependent radial migration mixes—and even inverts—intrinsic age and metallicity gradients. Thus, the galactic-archaeology approach of calculating radial star formation histories from stellar populations at z = 0 can be severely biased. These effects are strongest at Mstar ≈ 107-9.6 M⊙, the same regime where feedback most efficiently cores galaxies. Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in ΛCDM.

  7. Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters III: Analysis of 30 Clusters

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, R.; Stenning, D. C.; Sarajedini, A.; von Hippel, T.; van Dyk, D. A.; Robinson, E.; Stein, N.; Jefferys, W. H.

    2016-09-01

    We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic Globular Clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of ˜0.04 to 0.11. Because adequate models varying in CNO are not presently available, we view these spreads as upper limits and present them with statistical rather than observational uncertainties. Evidence supports previous studies suggesting an increase in helium content concurrent with increasing mass of the cluster and also find that the proportion of the first population of stars increases with mass as well. Our results are examined in the context of proposed globular cluster formation scenarios. Additionally, we leverage our Bayesian technique to shed light on inconsistencies between the theoretical models and the observed data.

  8. The massive stellar population of W49: A spectroscopic survey

    NASA Astrophysics Data System (ADS)

    Wu, Shi-Wei; Bik, Arjan; Bestenlehner, Joachim M.; Henning, Thomas; Pasquali, Anna; Brandner, Wolfgang; Stolte, Andrea

    2016-05-01

    Context. Massive stars form on different scales that range from large, dispersed OB associations to compact, dense starburst clusters. The complex structure of regions of massive star formation and the involved short timescales provide a challenge for our understanding of their birth and early evolution. As one of the most massive and luminous star-forming region in our Galaxy, W49 is the ideal place to study the formation of the most massive stars. Aims: By classifying the massive young stars that are deeply embedded in the molecular cloud of W49, we aim to investigate and trace the star formation history of this region. Methods: We analyse near-infrared K-band spectroscopic observations of W49 from LBT/LUCI combined with JHK images obtained with NTT/SOFI and LBT/LUCI. Based on JHK-band photometry and K-band spectroscopy, the massive stars are placed in a Hertzsprung Russell diagram. By comparison with evolutionary models, their age and hence the star formation history of W49 can be investigated. Results: Fourteen O-type stars, as well as two young stellar objects (YSOs), are identified by our spectroscopic survey. Eleven O stars are main sequence stars with subtypes ranging from O3 to O9.5 and masses ranging from ~20 M⊙ to ~120 M⊙. Three of the O stars show strong wind features and are considered to be Of-type supergiants with masses beyond 100 M⊙. The two YSOs show CO emission, which is indicative of the presence of circumstellar disks in the central region of the massive cluster. The age of the cluster is estimated as ~1.5 Myr, with star formation continuing in different parts of the region. The ionising photons from the central massive stars have not yet cleared the molecular cocoon surrounding the cluster. W49 is comparable to extragalactic star-forming regions, and it provides us with a unique chance to study a starburst in detail. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among

  9. [Telemedicine and the ageing population].

    PubMed

    Otto, Ulrich; Brettenhofer, Marlene; Tarnutzer, Silvan

    2015-09-01

    Telemedicine aims to create new forms of health care delivery by the use of information and communication technologies (ICT),for example, to improve the access to health care for patients in rural regions. There is a need for assistive technologies and innovative technological solutions due to the demographic change. Population trends of western societies show concurrently an ageing population and the wish of elderly people to live at home as long as possible while there is a tendency that older people live in greater distances to their kin nowadays. More complex diseases and multimorbidity urge improved interconnectedness between different health care professionals. Hence, different health systems pursue e-health strategies with the aim to implement electronic patient records (EPR) and similar technological solutions as a first approach to tackle those challenges. Telemedicine represents an open and evolving concept which is subject to a regular process of further development as a consequence of accelerated technological progress. The increased articulated demand for patient centered health care is one driver for the use of telemedicine. In the context of the trend of shorter hospital stays technological solutions can provide an opportunity for better support and care at home to reduce health risks and improve caregiving quality after hospital discharges. Despite the still prevalent reservations of elderly people about the use of ICT research shows that acceptance and the willingness to use technical devices is increasing. The article describes different aspects of telemedicine in the context of the aging population: definitions, an overview of trends and various fields of use with specific practical examples. A synoptic view of research results of evaluations of telemedicine applications regarding their effectiveness and cost-benefit analysis complement the paper.

  10. [Telemedicine and the ageing population].

    PubMed

    Otto, Ulrich; Brettenhofer, Marlene; Tarnutzer, Silvan

    2015-09-01

    Telemedicine aims to create new forms of health care delivery by the use of information and communication technologies (ICT),for example, to improve the access to health care for patients in rural regions. There is a need for assistive technologies and innovative technological solutions due to the demographic change. Population trends of western societies show concurrently an ageing population and the wish of elderly people to live at home as long as possible while there is a tendency that older people live in greater distances to their kin nowadays. More complex diseases and multimorbidity urge improved interconnectedness between different health care professionals. Hence, different health systems pursue e-health strategies with the aim to implement electronic patient records (EPR) and similar technological solutions as a first approach to tackle those challenges. Telemedicine represents an open and evolving concept which is subject to a regular process of further development as a consequence of accelerated technological progress. The increased articulated demand for patient centered health care is one driver for the use of telemedicine. In the context of the trend of shorter hospital stays technological solutions can provide an opportunity for better support and care at home to reduce health risks and improve caregiving quality after hospital discharges. Despite the still prevalent reservations of elderly people about the use of ICT research shows that acceptance and the willingness to use technical devices is increasing. The article describes different aspects of telemedicine in the context of the aging population: definitions, an overview of trends and various fields of use with specific practical examples. A synoptic view of research results of evaluations of telemedicine applications regarding their effectiveness and cost-benefit analysis complement the paper. PMID:26323956

  11. Fundamental Parameters of Nearby Red Dwarfs: Stellar Radius as an Indicator of Age

    NASA Astrophysics Data System (ADS)

    Silverstein, Michele L.; Henry, Todd J.; Winters, Jennifer G.; Jao, Wei-Chun; Riedel, Adric R.; Dieterich, Sergio; RECONS Team

    2016-01-01

    Red dwarfs dominate the Galactic population, yet determining one of their most fundamental characteristics --- age --- has proven difficult. The characterization of red dwarfs in terms of their age is fundamental to mapping the history of star and, ultimately, planet formation in the Milky Way. Here we report on a compelling technique to evaluate the radii of red dwarfs, which can be used to provide leverage in estimating their ages. These radii are also particularly valuable in the cases of transiting exoplanet hosts because accurate stellar radii are required to determine accurate planetary radii.In this work, we use the BT-Settl models in combination with Johnson-Kron-Cousins VRI, 2MASS JHK, and WISE All-Sky Release photometry to produce spectral energy distributions (SEDs) to determine the temperatures and bolometric fluxes for 500 red dwarfs, most of which are in the southern sky. The full suites of our photometric and astrometric data (including hundreds of accurate new parallaxes from the RECONS team at the CTIO/SMARTS 0.9m) allow us to also determine the bolometric luminosities and radii. This method of radius determination is validated by a comparison of our measurements to those found using the CHARA Array (Boyajian et al. 2012), which match within a few percent.In addition to a compilation of red dwarf fundamental parameters, our findings provide a snapshot of relative stellar ages in the solar neighborhood. Of particular interest are the cohorts of very young and very old stars identified within 50 pc. These outliers exemplify the demographic extremes of the nearest stars.This effort has been supported by the NSF through grants AST-0908402, AST-1109445, and AST-1412026, and via observations made possible by the SMARTS Consortium.

  12. The structure and Stellar Populations of Nuclear Star Clusters in Late-type Spiral Galaxies From HST/WFC3 Imaging

    NASA Astrophysics Data System (ADS)

    Carson, Daniel

    2016-06-01

    Luminous, compact stellar systems known as nuclear clusters (NCs) are commonly found in the centers of galaxies across the entire Hubble sequence. I present an analysis of the structure and stellar populations of a sample of ten of the nearest and brightest NCs residing in late-type spiral galaxies, using imaging data from Hubble Space Telescope Wide Field Camera 3 in seven bands that span the near-ultraviolet to the near-infrared. The intrinsic shapes and sizes of the NCs, disentangled from the effects of point spread function (PSF) blurring, were measured using GALFIT. For six of the ten NCs in our sample, we find changes in the effective radius with wavelength, which suggests that many NCs contain radially varying stellar populations. There is also a general trend of increasing roundness of the NCs at longer wavelengths, suggesting that the youngest stars in NCs typically form in disks. I developed a Monte Carlo code to fit linear combinations of simple stellar population models to the observed spectral energy distribution (SED) of each NC and assess the uncertainties in the fit parameters. Tests using mock SEDs with known input parameters demonstrate that although the method is susceptible to degeneracies between model SEDs, the code is robust and accurately recovers the total stellar mass for a wide range of NC colors and ages. I present global star formation histories and stellar mass estimates for each cluster, which are in good agreement with previous dynamical studies. The clusters are generally dominated by an old (> 1 Gyr) population, but are best described by multi-age models. The spatially resolved properties of the stellar populations of each NC were also studied by performing SED fits on a pixel-by-pixel basis. These fits reveal radial age gradients in the same NCs that exhibited variation in the effective radius with wavelength. Finally, I present deprojected density profiles and estimates of the central stellar density of each cluster.

  13. The fossil record of the stellar populations at redshifts above 1.5

    NASA Astrophysics Data System (ADS)

    Walcher, C. Jakob; Coelho, Paula; Gallazzi, Anna; Charlot, Stephane; Bruzual, Gustavo

    2015-08-01

    Recent advances in stellar population modeling allow to determine physical properties such as mean age, iron and alpha-element abundances from integrated spectra using not only specific wavelength ranges as in traditional Lick-index-type methods, but from the full available spectrum. I will present an extension of this technique for low-redshift, massive early-type galaxies allowing to determine the [Fe/H] and [alpha/Fe] of only the stars older than 9.5 Gyr on a per galaxy basis. We find that these stars show uniformly high [alpha/Fe] abundances, allowing us to constrain the timescales over which star formation takes place in high-redshift galaxies that are being targeted directly by this symposium. I will also present analysis of the mass and environment dependancies of these properties.

  14. Stellar populations in (U)LIRGs and post-starburst QSOs

    NASA Astrophysics Data System (ADS)

    Cortijo-Ferrero, Clara

    2011-11-01

    Within the hierarchical model, it is believed that galactic mergers (like those happening in Ultraluminous Infrared Galaxies, ULIRGs) could generate starburst processes (SBs) that would feed a central AGN. The final stage, once the gas has been dissipated, is the formation of elliptical galaxies. In other words, we want to investigate the evolutionary sequence: (U)LIRGs -> POST-SBs -> QSOs -> ellipticals. For doing so we are are studying the stellar populations (SPs) in two samples of (U)LIRGs and POST-SBs QSOs galaxies for which we have optical integral field spectroscopy (IFS-PMAS@CAHA) data and HST high resolution multiwavelength imaging (from NUV to NIR). Using the ages of the SPs as a clock we can check whether or not an evolutionary link exists between them. In this poster we present the first results of the analysis of these data.

  15. STRUCTURE AND POPULATION OF THE ANDROMEDA STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY

    SciTech Connect

    Tanaka, Mikito; Chiba, Masashi; Komiyama, Yutaka; Iye, Masanori; Guhathakurta, Puragra

    2010-01-10

    We present a photometric survey of the stellar halo of the nearest giant spiral galaxy, Andromeda (M31), using Suprime-Cam on the Subaru Telescope. A detailed analysis of VI color-magnitude diagrams of the resolved stellar population is used to measure properties such as line-of-sight distance, surface brightness, metallicity, and age. These are used to isolate and characterize different components of the M31 halo: (1) the giant southern stream (GSS); (2) several other substructures; and (3) the smooth halo. First, the GSS is characterized by a broad red giant branch (RGB) and a metal-rich/intermediate-age red clump (RC). The I magnitude of the well-defined tip of the RGB suggests that the distance to the observed GSS field is (m - M){sub 0} = 24.73 +- 0.11 (883 +- 45 kpc) at a projected radius of R approx 30 kpc from M31's center. The GSS shows a high metallicity peaked at [Fe/H]approx>-0.5 with a mean (median) of -0.7 (-0.6), estimated via comparison with theoretical isochrones. Combined with the luminosity of the RC, we estimate the mean age of its stellar population to be approx8 Gyr. The mass of its progenitor galaxy is likely in the range of 10{sup 7}-10{sup 9} M{sub sun}. Second, we study M31's halo substructure along the northwest/southeast minor axis out to R approx 100 kpc and the southwest major-axis region at R approx 60 kpc. We confirm two substructures in the southeast halo reported by Ibata et al. and discover two overdense substructures in the northwest halo. We investigate the properties of these four substructures as well as other structures including the western shelf and find that differences in stellar populations among these systems, thereby suggesting each has a different origin. Our statistical analysis implies that the M31 halo as a whole may contain at least 16 substructures, each with a different origin, so its outer halo has experienced at least this many accretion events involving dwarf satellites with mass 10{sup 7}-10{sup 9} M{sub sun

  16. Ultraviolet Spectral Diagnostics of the Age of Old Stellar Systems

    NASA Astrophysics Data System (ADS)

    Peterson, Ruth

    2007-05-01

    For our Hubble Treasury program GO-9455, we are modeling the mid- and near-ultraviolet regions of old stars across the color-magnitude diagram. After revising the list of input atomic and molecular line parameters from 2200A to 9000A, we are calculating spectra of individual stars from first principles, and combining their weighted fluxes to form composite spectra representing single-age, single-metallicity populations older than 1Gyr. We are doing this for metallicities from one-hundredth to three times solar, and for three different ratios of the abundances of light versus iron-peak elements. We show plots comparing the calculated spectra with observations of stars, M31 globular clusters, and more distant galaxies. We find that the light-element ratio affects not only the strengths of individual lines and bands, but also the blue continuum in cool stars of near-solar metallicity and higher, as the continuous opacity is increased by high magnesium abundance. We also note that at such metallicities, the mid-ultraviolet spectrum of composite systems is suppressed below 2500A, and the near-ultraviolet becomes the spectral region providing the strongest observable constraints on age, metallicity, and abundance ratio.

  17. Constraining the solutions of an inverse method of stellar population synthesis

    NASA Astrophysics Data System (ADS)

    Moultaka, J.; Boisson, C.; Joly, M.; Pelat, D.

    2004-06-01

    In three previous papers (Pelat \\cite{Pelat97}, MNRAS, 284, 365; Pelat \\cite{Pelat98}, MNRAS, 299, 877; Moultaka & Pelat \\cite{Moultaka00}, MNRAS, 314, 409), we set out an inverse stellar population synthesis method that uses a database of stellar spectra. Unlike other methods, this one provides full knowledge of all possible solutions as well as a good estimation of their stability; moreover, it provides the unique approximate solution, when the problem is overdetermined, using a rigorous minimization procedure. In Boisson et al. (\\cite{Boisson00}, A&A, 357, 850), this method was applied to 10 active and 2 normal galaxies. In this paper we analyse the results of the method after constraining the solutions. Adding {a priori} physical conditions to the solutions constitutes a good way to regularize the synthesis problem. As an illustration we introduce physical constraints on the relative number of stars taking into account our present knowledge of the initial mass function in galaxies. To avoid biases on the solutions due to such constraints, we use constraints involving only inequalities between the number of stars, after dividing the H-R diagram into various groups of stellar masses. We discuss the results for a well-known globular cluster of the galaxy M 31 and discuss some of the galaxies studied in Boisson et al. (\\cite{Boisson00}, A&A, 357, 850). We find that, given the spectral resolution and the spectral domain, the method is very stable according to such constraints (i.e. the constrained solutions are almost the same as the unconstrained one). However, additional information can be derived about the evolutionary stage of the last burst of star formation, but the precise age of this particular burst seems to be questionable. Appendix A, Figs. 2-5 and Tables 4-6 are only available in electronique form at http://www.edpsciences.org moultaka@ph1.uni-koeln.de

  18. Heart of darkness: dust obscuration of the central stellar component in globular clusters younger than ˜100 Myr in multiple stellar population models

    NASA Astrophysics Data System (ADS)

    Longmore, S. N.

    2015-03-01

    To explain the observed anomalies in stellar populations within globular clusters, many globular cluster formation theories require two independent episodes of star formation. A fundamental prediction of these models is that the clusters must accumulate large gas reservoirs as the raw material to form the second stellar generation. We show that young clusters containing the required gas reservoir should exhibit the following observational signatures: (i) a dip in the measured luminosity profile or an increase in measured reddening towards the cluster centre, with AV > 10 mag within a radius of a few pc; (ii) bright (sub)mm emission from dust grains; (iii) bright molecular line emission once the gas is dense enough to begin forming stars. Unless the initial mass function is anomalously skewed towards low-mass stars, the clusters should also show obvious signs of star formation via optical emission lines (e.g. Hα) after the stars have formed. These observational signatures should be readily observable towards any compact clusters (radii of a few pc) in the nearby Universe with masses ≳106 M⊙ and ages ≲100 Myr. This provides a straightforward way to directly test globular cluster formation models which predict large gas reservoirs are required to form the second stellar generation. The fact that no such observational evidence exists calls into question whether such a mechanism happens regularly for young massive clusters in galaxies within a few tens of Mpc.

  19. A stellar-mass black hole population in the globular cluster NGC 6101?

    NASA Astrophysics Data System (ADS)

    Peuten, M.; Zocchi, A.; Gieles, M.; Gualandris, A.; Hénault-Brunet, V.

    2016-11-01

    Dalessandro et al. observed a similar distribution for blue straggler stars and main-sequence turn-off stars in the Galactic globular cluster NGC 6101, and interpreted this feature as an indication that this cluster is not mass-segregated. Using direct N-body simulations, we find that a significant amount of mass segregation is expected for a cluster with the mass, radius and age of NGC 6101. Therefore, the absence of mass segregation cannot be explained by the argument that the cluster is not yet dynamically evolved. By varying the retention fraction of stellar-mass black holes, we show that segregation is not observable in clusters with a high black hole retention fraction (>50 per cent after supernova kicks and >50 per cent after dynamical evolution). Yet all model clusters have the same amount of mass segregation in terms of the decline of the mean mass of stars and remnants with distance to the centre. We also discuss how kinematics can be used to further constrain the presence of a stellar-mass black hole population and distinguish it from the effect of an intermediate-mass black hole. Our results imply that the kick velocities of black holes are lower than those of neutron stars. The large retention fraction during its dynamical evolution can be explained if NGC 6101 formed with a large initial radius in a Milky Way satellite.

  20. Stellar populations in local group dwarf elliptical galaxies. I - NGC 147

    NASA Technical Reports Server (NTRS)

    Mould, J. R.; Kristian, J.; Da Costa, G. S.

    1983-01-01

    A color-magnitude diagram of NGC 147 to an I magnitude of 23 is presented. The stellar population in the outer parts of this elliptical galaxy resembles that of the globular clusters of the Milky Way. Quantitative comparison of the giant branch with those of globular clusters yields a mean metallicity of -1.2 + or - 0.2, making NGC 147 a part of the general correlation between mass and metallicity seen in ellipticals. The giant branch appears to be broad, which suggests a metallicity dispersion. The absence of asymptotic giant branch stars at luminosities above that of the red giant branch tip sets an upper limit of 10 percent for the fraction of stars in this NGC 147 field that have ages less than 12 Gyr. This result contrasts with the situation in some of the related, but less massive, dwarf spheroidal systems. If the choice is made to assume, rather than determine the stellar content of NGC 147, a distance of 630 + or - 50 kpc is derived, similar to that of M31.

  1. Ionizing stellar population in the disc of NGC 3310 - II. The Wolf-Rayet population

    NASA Astrophysics Data System (ADS)

    Miralles-Caballero, D.; Rosales-Ortega, F. F.; Díaz, A. I.; Otí-Floranes, H.; Pérez-Montero, E.; Sánchez, S. F.

    2014-12-01

    We use integral field spectroscopy to study in detail the Wolf-Rayet (WR) population in NGC 3310, spatially resolving 18 star-forming knots with typical sizes of 200-300 pc in the disc of the galaxy hosting a substantial population of WRs. The detected emission in the so-called blue bump is attributed mainly to late-type nitrogen WRs (WNL), ranging from a few dozens to several hundreds of stars per region. Our estimated WNL/(WNL+O) ratio is comparable to reported empirical relations once the extinction-corrected emission is further corrected by the presence of dust grains inside the nebula that absorb a non-negligible fraction of UV photons. Comparisons of observables with stellar population models show disagreement by factors larger than 2-3. However, if the effects of interacting binaries and/or photon leakage are taken into account, observations and predictions tend to converge. We estimate the binary fraction of the H II regions hosting WRs to be significant in order to recover the observed X-ray flux, hence proving that the binary channel can be critical when predicting observables. We also explore the connection of the environment with the current hypothesis that WRs can be progenitors to long-duration gamma-ray bursts (GRBs). Galaxy interactions, which can trigger strong episodes of star formation in the central regions, may be a plausible environment where WRs may act as progenitors of GRBs. Finally, even though the chemical abundance is generally homogeneous, we also find weak evidence for rapid N pollution by WR stellar winds at scales of ˜200 pc.

  2. A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752

    SciTech Connect

    Milone, A. P.; Marino, A. F.; Yong, D. E-mail: amarino@mso.anu.edu.au; and others

    2013-04-20

    Multi-band Hubble Space Telescope photometry reveals that the main sequence, sub-giant, and the red-giant branch of the globular cluster NGC 6752 splits into three main components in close analogy with the three distinct segments along its horizontal branch stars. These triple sequences are consistent with three stellar groups: a stellar population with a chemical composition similar to field-halo stars (Population a), a Population (c) with enhanced sodium and nitrogen, depleted carbon and oxygen, and an enhanced helium abundance ({Delta}Y {approx} 0.03), and a Population (b) with an intermediate (between Populations a and c) chemical composition and slightly enhanced helium ({Delta}Y {approx} 0.01). These components contain {approx}25% (Population a), {approx}45% (Population b), and {approx}30% (Population c) of the stars. No radial gradient for the relative numbers of the three populations has been identified out to about 2.5 half-mass radii.

  3. Stellar

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation.' As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules.' The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 7,000 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly-ionized oxygen atoms.

  4. THE PROGENITOR MASS OF SN 2011dh FROM STELLAR POPULATION ANALYSIS

    SciTech Connect

    Murphy, Jeremiah W.; Jennings, Zachary G.; Williams, Benjamin; Dalcanton, Julianne J.; Dolphin, Andrew E. E-mail: adolphin@raytheon.com

    2011-11-20

    Using Hubble Space Telescope photometry, we characterize the age of the stellar association in the vicinity of supernova (SN) 2011dh and use it to infer the zero-age main-sequence mass (M{sub ZAMS}) of the progenitor star. We find two distinct and significant star formation (SF) events with ages of <6 and 17{sup +3}{sub -4} Myr, and the corresponding M{sub ZAMS} are >29 and 13{sup +2}{sub -1} M{sub Sun }, respectively. These two bursts represent 18{sup +4}{sub -9}% (young) and 64{sup +10}{sub -14}% (old) of the total SF in the last 50 Myr. Adopting these fractions as probabilities suggests that the most probable M{sub ZAMS} is 13{sup +2}{sub -1} M{sub Sun }. These results are most sensitive to the luminosity function along the well-understood main sequence (MS) and are less sensitive to uncertain late-stage stellar evolution. Therefore, they stand even if the progenitor suffered disruptive post-MS evolution (e.g., eruptive mass loss or binary Roche-lobe overflow). Progenitor identification will help to further constrain the appropriate population. Even though pre-explosion images show a yellow supergiant (YSG) at the site of the SN, panchromatic SN light curves suggest a more compact star as the progenitor. In spite of this, our results suggest an association between the YSG and the SN. Not only was the star located at the SN site, but reinforcing an association, the star's bolometric luminosity is consistent with the final evolutionary stage of the 17 Myr old starburst. If the YSG disappears, then M{sub ZAMS} = 13{sup +2}{sub -1} M{sub Sun }, but if it persists, then our results allow the possibility that the progenitor was an unseen star of >29 M{sub Sun }.

  5. Fiscal implications of population ageing.

    PubMed

    Johnson, P

    1997-12-29

    In all developed countries the fiscal ties of the tax and benefit system serve to complement, and sometimes substitute for, traditional family bonds between young and old. Older people are major recipients of public pensions and public health care systems. Since these public transfers and services are financed primarily from the taxes paid by people of working age, the welfare system in effect transfers resources from young to old. But rather than see the fiscal interdependency between young and old as being analogous to the ties that bind children, parents and grandparents together in familial networks, it is often interpreted as an oppressive burden that the old place on the young. This paper examines arguments that population ageing will exacerbate this burden, and may lead to the collapse of public welfare systems. It shows that the financial problems currently associated with public pensions are a function of system design rather than demographic change, and that wholesale privatization of pension systems will do little to solve the major dilemma--of persuading people to transfer a larger part of their lifetime income to their later years in order to sustain a reasonable standard of living throughout an ever lengthening period of retirement. PMID:9460075

  6. Fiscal implications of population ageing.

    PubMed Central

    Johnson, P

    1997-01-01

    In all developed countries the fiscal ties of the tax and benefit system serve to complement, and sometimes substitute for, traditional family bonds between young and old. Older people are major recipients of public pensions and public health care systems. Since these public transfers and services are financed primarily from the taxes paid by people of working age, the welfare system in effect transfers resources from young to old. But rather than see the fiscal interdependency between young and old as being analogous to the ties that bind children, parents and grandparents together in familial networks, it is often interpreted as an oppressive burden that the old place on the young. This paper examines arguments that population ageing will exacerbate this burden, and may lead to the collapse of public welfare systems. It shows that the financial problems currently associated with public pensions are a function of system design rather than demographic change, and that wholesale privatization of pension systems will do little to solve the major dilemma--of persuading people to transfer a larger part of their lifetime income to their later years in order to sustain a reasonable standard of living throughout an ever lengthening period of retirement. PMID:9460075

  7. STELLAR POPULATION PROPERTIES AND EVOLUTION ANALYSIS OF NGC 628 WITH PANCHROMATIC PHOTOMETRY

    SciTech Connect

    Zou Hu; Zhang Wei; Yang Yanbin; Zhou Xu; Jiang Zhaoji; Ma Jun; Wu Zhenyu; Wu Jianghua; Zhang Tianmeng; Fan Zhou

    2011-07-15

    Panchromatic spectral energy distribution from the ultraviolet, optical to infrared photometry of NGC 628, combined with evolutionary stellar population synthesis, is used to derive the spatially resolved age, metallicity, and reddening maps. These parameter distributions show that the bulge of this galaxy is a disk-like pseudobulge, which has a Sersic index close to the exponential law, rich gas, and a young circumnuclear ring structure. We also discover that the disk has two distinct regions with different radial age and metallicity gradients. The inner region is older and has a much steeper age gradient than the outer region of the disk. Both these two regions and the central young structure can be seen in the radial profile of the optical color. Based on the age and reddening distributions, we conclude that the pseudobulge and disk are likely to have grown via secular evolution, which is the redistribution of mass and energy through the angular momentum transport caused by the non-axisymmetric potential of the spirals. However, possible gas accretion events could affect the outer region of the disk due to abundant H I gas accumulating in the outer disk.

  8. VELOCITY DISPERSIONS AND STELLAR POPULATIONS OF THE MOST COMPACT AND MASSIVE EARLY-TYPE GALAXIES AT REDSHIFT {approx}1

    SciTech Connect

    Martinez-Manso, Jesus; Guzman, Rafael; Barro, Guillermo; Cardiel, Nicolas; Gallego, Jesus; Cenarro, Javier; Perez-Gonzalez, Pablo; Sanchez-Blazquez, Patricia; Trujillo, Ignacio; Balcells, Marc; Hempel, Angela; Prieto, Mercedes

    2011-09-10

    We present Gran-Telescopio-Canarias/OSIRIS optical spectra of four of the most compact and massive early-type galaxies (ETGs) in the Groth Strip Survey at redshift z {approx} 1, with effective radii R{sub e} = 0.5-2.4 kpc and photometric stellar masses M{sub *} = (1.2-4) x 10{sup 11} M{sub sun}. We find that these galaxies have velocity dispersions {sigma} = 156-236 km s{sup -1}. The spectra are well fitted by single stellar population models with approximately 1 Gyr of age and solar metallicity. We find that (1) the dynamical masses of these galaxies are systematically smaller by a factor of {approx}6 than the published stellar masses using BRIJK photometry, and (2) when estimating stellar masses as 0.7x M{sub dyn}, a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of ETGs.

  9. SLUG - stochastically lighting up galaxies - III. A suite of tools for simulated photometry, spectroscopy, and Bayesian inference with stochastic stellar populations

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.; Fumagalli, Michele; da Silva, Robert L.; Rendahl, Theodore; Parra, Jonathan

    2015-09-01

    Stellar population synthesis techniques for predicting the observable light emitted by a stellar population have extensive applications in numerous areas of astronomy. However, accurate predictions for small populations of young stars, such as those found in individual star clusters, star-forming dwarf galaxies, and small segments of spiral galaxies, require that the population be treated stochastically. Conversely, accurate deductions of the properties of such objects also require consideration of stochasticity. Here we describe a comprehensive suite of modular, open-source software tools for tackling these related problems. These include the following: a greatly-enhanced version of the SLUG code introduced by da Silva et al., which computes spectra and photometry for stochastically or deterministically sampled stellar populations with nearly arbitrary star formation histories, clustering properties, and initial mass functions; CLOUDY_SLUG, a tool that automatically couples SLUG-computed spectra with the CLOUDY radiative transfer code in order to predict stochastic nebular emission; BAYESPHOT, a general-purpose tool for performing Bayesian inference on the physical properties of stellar systems based on unresolved photometry; and CLUSTER_SLUG and SFR_SLUG, a pair of tools that use BAYESPHOT on a library of SLUG models to compute the mass, age, and extinction of mono-age star clusters, and the star formation rate of galaxies, respectively. The latter two tools make use of an extensive library of pre-computed stellar population models, which are included in the software. The complete package is available at http://www.slugsps.com.

  10. Dissecting Kinematics and Stellar Populations of Counter-Rotating Galaxies with 2-Dimensional Spectroscopy

    NASA Astrophysics Data System (ADS)

    Coccato, L.; Morelli, L.; Pizzella, A.; Corsini, E. M.; Dalla Bontá, E.; Buson, L. M.

    2014-05-01

    We present a spectral decomposition technique and its applications to a sample of galaxies hosting large-scale counter-rotating stellar disks. Our spectral decomposition technique allows to separate and measure the kinematics and the properties of the stellar populations of both the two counter-rotating disks in the observed galaxies at the same time. Our results provide new insights on the epoch and mechanism of formation of these galaxies.

  11. Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters. II. NGC 5024, NGC 5272, and NGC 6352

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, R.; Stenning, D. C.; Robinson, E.; von Hippel, T.; Sarajedini, A.; van Dyk, D. A.; Stein, N.; Jefferys, W. H.

    2016-07-01

    We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival Advanced Camera for Surveys Treasury observations of Galactic Globular Clusters to find and characterize two stellar populations in NGC 5024 (M53), NGC 5272 (M3), and NGC 6352. For these three clusters, both single and double-population analyses are used to determine a best fit isochrone(s). We employ a sophisticated Bayesian analysis technique to simultaneously fit the cluster parameters (age, distance, absorption, and metallicity) that characterize each cluster. For the two-population analysis, unique population level helium values are also fit to each distinct population of the cluster and the relative proportions of the populations are determined. We find differences in helium ranging from ˜0.05 to 0.11 for these three clusters. Model grids with solar α-element abundances ([α/Fe] = 0.0) and enhanced α-elements ([α/Fe] = 0.4) are adopted.

  12. Stellar population properties of the most massive globular clusters and ultra-compact dwarf galaxies of the Fornax cluster

    NASA Astrophysics Data System (ADS)

    Hilker, Michael

    2015-08-01

    Most of the massive globular clusters (GCs) of our Milky Way show evidence of multiple stellar populations with distinct light element abundances. A few GCs even exhibit spreads in iron abundance and probably age. Those are nuclear star cluster candidates whose host galaxies were disrupted during the assembly history of the Milky Way. In galaxy clusters, disruption of low mass, nucleated galaxies was very common in the past. Indeed, in the Virgo and Fornax clusters there exists a large population of very massive and compact star cluster-like objects, often called ultra-compact dwarf galaxies (UCDs). If one postulates that the complex GCs omega Centauri and M54 in the Milky Way and G1 in Andromeda are low-mass UCDs, one would expect that UCDs in general should also have complex star formation and chemical enrichment histories. However, due to the large distance and thus unresolved nature of UCDs, multiple stellar populations in them are very difficult to detect and quantify. I will present our most recent attempts to constrain the stellar content, dynamical state and origin of UCDs in the Fornax cluster. Multi-band imaging as well as low to medium resolution spectroscopy is used to derive ages, metallicites and [alpha/Fe] abundances, as well as to constrain their IMFs and find hints for multiple stellar populations through UV to NIR SED fitting.Our recent simulations on the disruption process of nucleated dwarf galaxies in cluster environments showed that more than 50% of the most massive UCDs should originate from nuclear star clusters. Some Fornax UCDs actually show evidence for this scenario, as revealed by extended low surface brightness disks around them and onsets of tidal tails.

  13. SPATIAL DISTRIBUTION AND EVOLUTION OF THE STELLAR POPULATIONS AND CANDIDATE STAR CLUSTERS IN THE BLUE COMPACT DWARF I ZWICKY 18

    SciTech Connect

    Contreras Ramos, R.; Annibali, F.; Fiorentino, G.; Tosi, M.; Clementini, G.; Aloisi, A.; Van der Marel, R. P.; Marconi, M.; Musella, I.; Saha, A.

    2011-10-01

    The evolutionary properties and spatial distribution of I Zwicky 18 (IZw18) stellar populations are analyzed by means of Hubble Space Telescope/Advanced Camera for Surveys deep and accurate photometry. A comparison of the resulting color-magnitude diagrams (CMDs) with stellar evolution models indicates that stars of all ages are present in all the system's components, including objects possibly up to 13 Gyr old, intermediate-age stars, and very young ones. The CMDs show evidence of thermally pulsing asymptotic giant branch and carbon stars. classical and ultra-long-period Cepheids as well as long-period variables have been measured. About 20 objects could be unresolved star clusters; these are mostly concentrated in the northwest (NW) portion of the main body (MB). If interpreted with simple stellar population models, these objects indicate a particularly active star formation over the past 100 Myr in IZw18. The stellar spatial distribution shows that the younger ones are more centrally concentrated, while old and intermediate-age stars are distributed homogeneously over the two bodies, although they are more easily detectable at the system's periphery. The oldest stars are most visible in the secondary body (SB) and in the southeast (SE) portion of the MB, where crowding is less severe, but are also present in the rest of the MB, where they are measured with larger uncertainties. The youngest stars are a few Myr old, are located predominantly in the MB, and are mostly concentrated in its NW portion. The SE portion of the MB appears to be in a similar, but not as young, evolutionary stage as the NW, while the SB stars are older than at least 10 Myr. There is then a sequence of decreasing age of the younger stars from the SB to the SE portion of the MB to the NW portion. All our results suggest that IZw18 is not atypical compared to other blue compact dwarfs.

  14. SODIUM-OXYGEN ANTICORRELATION AND NEUTRON-CAPTURE ELEMENTS IN OMEGA CENTAURI STELLAR POPULATIONS

    SciTech Connect

    Marino, A. F.; Milone, A. P.; Piotto, G.; Bellini, A.; Villanova, S.; Geisler, D.; Gratton, R.; Renzini, A.; D'Antona, F.; Anderson, J.; Bedin, L. R.; Cassisi, S.; Zoccali, M. E-mail: anna.marino@unipd.it

    2011-04-10

    Omega Centauri is no longer the only globular cluster known to contain multiple stellar populations, yet it remains the most puzzling. Due to the extreme way in which the multiple stellar population phenomenon manifests in this cluster, it has been suggested that it may be the remnant of a larger stellar system. In this work, we present a spectroscopic investigation of the stellar populations hosted in the globular cluster {omega} Centauri to shed light on its still puzzling chemical enrichment history. With this aim, we used FLAMES+GIRAFFE-VLT to observe 300 stars distributed along the multimodal red giant branch of this cluster, sampling with good statistics the stellar populations of different metallicities. We determined chemical abundances for Fe, Na, O, and n-capture elements Ba and La. We confirm that {omega} Centauri exhibits large star-to-star variations in iron with [Fe/H] ranging from {approx}-2.0 to {approx}-0.7 dex. Barium and lanthanum abundances of metal-poor stars are correlated with iron, up to [Fe/H] {approx}-1.5, while they are almost constant (or at least have only a moderate increase) in the more metal-rich populations. There is an extended Na-O anticorrelation for stars with [Fe/H] {approx}<-1.3 while more metal-rich stars are almost all Na-rich. Sodium was found to mildly increase with iron over the entire metallicity range.

  15. Binary interactions as a possible scenario for the formation of multiple stellar populations in globular clusters

    SciTech Connect

    Jiang, Dengkai; Han, Zhanwen; Li, Lifang E-mail: zhanwenhan@ynao.ac.cn

    2014-07-01

    Observations have revealed the presence of multiple stellar populations in globular clusters (GCs) that exhibit wide abundance variations and multiple sequences in the Hertzsprung-Russell (HR) diagram. We present a scenario for the formation of multiple stellar populations in GCs. In this scenario, initial GCs are single-generation clusters, and our model predicts that the stars with anomalous abundances observed in GCs are merged stars and accretor stars produced by binary interactions—rapidly rotating stars at the moment of their formation—and that these stars are more massive than normal single stars in the same evolutionary stage. We find that, due to their own evolution, these rapidly rotating stars have surface abundances, effective temperatures, and luminosities that are different from normal single stars in the same evolutionary stage. This stellar population of binaries reproduces two important points of observational evidence of multiple stellar populations: a Na-O anticorrelation and multiple sequences in the HR diagram. This evidence suggests that binary interactions may be a possible scenario for the formation of multiple stellar populations in GCs.

  16. RECOVERING STELLAR POPULATION PROPERTIES AND REDSHIFTS FROM BROADBAND PHOTOMETRY OF SIMULATED GALAXIES: LESSONS FOR SED MODELING

    SciTech Connect

    Wuyts, Stijn; Cox, Thomas J.; Hernquist, Lars; Franx, Marijn; Hopkins, Philip F.; Robertson, Brant E.; Van Dokkum, Pieter G.

    2009-05-01

    We present a detailed analysis of our ability to determine stellar masses, ages, reddening, and extinction values, and star formation rates (SFRs) of high-redshift galaxies by modeling broadband spectral energy distributions (SEDs) with stellar population synthesis. In order to do so, we computed synthetic optical-to-NIR SEDs for model galaxies taken from hydrodynamical merger simulations placed at redshifts 1.5 {<=} z {<=} 2.9. Viewed under different angles and during different evolutionary phases, the simulations represent a wide variety of galaxy types (disks, mergers, spheroids). We show that simulated galaxies span a wide range in SEDs and color, comparable to those of observed galaxies. In all star-forming phases, dust attenuation has a large effect on colors, SEDs, and fluxes. The broadband SEDs were then fed to a standard SED modeling procedure, and resulting stellar population parameters were compared to their true values. Disk galaxies generally show a decent median correspondence between the true and estimated mass and age, but suffer from large uncertainties ({delta}log M = -0.06{sup +0.06} {sub -0.13}, {delta}log age {sub w} = +0.03{sup +0.19} {sub -0.42}). During the merger itself, we find larger offsets: {delta}log M = -0.13{sup +0.10} {sub -0.14} and {delta}log age {sub w} = -0.12{sup +0.40} {sub -0.26}. E(B - V) values are generally recovered well, but the estimated total visual absorption A{sub V} is consistently too low, increasingly so for larger optical depths ({delta}A{sub V} = -0.54{sup +0.40} {sub -0.46} in the merger regime). Since the largest optical depths occur during the phases of most intense star formation, it is for the highest SFRs that we find the largest underestimates ({delta}log SFR = -0.44{sup +0.32} {sub -0.31} in the merger regime). The masses, ages, E(B - V), A{sub V} , and SFRs of merger remnants (spheroids) are very well reproduced. We discuss possible biases in SED modeling results caused by mismatch between the true and

  17. Multiple stellar populations in Magellanic Cloud clusters - IV. The double main sequence of the young cluster NGC 1755

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Marino, A. F.; D'Antona, F.; Bedin, L. R.; Da Costa, G. S.; Jerjen, H.; Mackey, A. D.

    2016-06-01

    Nearly all the star clusters with ages of ˜1-2 Gyr in both Magellanic Clouds exhibit an extended main-sequence turn-off (eMSTO) whose origin is under debate. The main scenarios suggest that the eMSTO could be either due to multiple generations of stars with different ages or to coeval stellar populations with different rotation rates. In this paper we use Hubble Space Telescope images to investigate the ˜80-Myr old cluster NGC 1755 in the LMC. We find that the MS is split with the blue and the red MS hosting about the 25 per cent and the 75 per cent of the total number of MS stars, respectively. Moreover, the MSTO of NGC 1755 is broadened in close analogy with what is observed in the ˜300-Myr-old NGC 1856 and in most intermediate-age Magellanic-Cloud clusters. We demonstrate that both the split MS and the eMSTO are not due to photometric errors, field-stars contamination, differential reddening, or non-interacting binaries. These findings make NGC 1755 the youngest cluster with an eMSTO. We compare the observed CMD with isochrones and conclude that observations are not consistent with stellar populations with difference in age, helium, or metallicity only. On the contrary, the split MS is well reproduced by two stellar populations with different rotation, although the fit between the observed eMSTO and models with different rotation is not fully satisfactory. We speculate whether all stars in NGC 1755 were born rapidly rotating, and a fraction has slowed down on a rapid time-scale, or the dichotomy in rotation rate was present already at star formation. We discuss the implication of these findings on the interpretation of eMSTO in young and intermediate-age clusters.

  18. THE LOW-MASS STELLAR POPULATION IN L1641: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF THE STELLAR INITIAL MASS FUNCTION

    SciTech Connect

    Hsu, Wen-Hsin; Hartmann, Lee; Allen, Lori; Hernandez, Jesus; Megeath, S. T.; Mosby, Gregory; Tobin, John J.; Espaillat, Catherine

    2012-06-10

    We present results from an optical photometric and spectroscopic survey of the young stellar population in L1641, the low-density star-forming region of the Orion A cloud south of the Orion Nebula Cluster (ONC). Our goal is to determine whether L1641 has a large enough low-mass population to make the known lack of high-mass stars a statistically significant demonstration of environmental dependence of the upper mass stellar initial mass function (IMF). Our spectroscopic sample consists of IR-excess objects selected from the Spitzer/IRAC survey and non-excess objects selected from optical photometry. We have spectral confirmation of 864 members, with another 98 probable members; of the confirmed members, 406 have infrared excesses and 458 do not. Assuming the same ratio of stars with and without IR excesses in the highly extincted regions, L1641 may contain as many as {approx}1600 stars down to {approx}0.1 M{sub Sun }, comparable within a factor of two to the ONC. Compared to the standard models of the IMF, L1641 is deficient in O and early B stars to a 3{sigma}-4{sigma} significance level, assuming that we know of all the massive stars in L1641. With a forthcoming survey of the intermediate-mass stars, we will be in a better position to make a direct comparison with the neighboring, dense ONC, which should yield a stronger test of the dependence of the high-mass end of the stellar IMF on environment.

  19. Environment, morphology, and stellar populations of bulgeless low surface-brightness galaxies

    NASA Astrophysics Data System (ADS)

    Shao, X.; Disseau, K.; Yang, Y. B.; Hammer, F.; Puech, M.; Rodrigues, M.; Liang, Y. C.; Deng, L. C.

    2015-07-01

    Based on the Sloan Digital Sky Survey DR 7, we investigate the environment, morphology, and stellar population of bulgeless low surface-brightness (LSB) galaxies in a volume-limited sample with redshift ranging from 0.024 to 0.04 and Mr≤-18.8. The local density parameter Σ5 is used to trace their environments. We find that, for bulgeless galaxies, the surface brightness does not depend on the environment. The stellar populations are compared for bulgeless LSB galaxies in different environments and for bulgeless LSB galaxies with different morphologies. The stellar populations of LSB galaxies in low-density regions are similar to those of LSB galaxies in high-density regions. Irregular LSB galaxies have more young stars and are more metal-poor than regular LSB galaxies. These results suggest that the evolution of LSB galaxies may be driven by their dynamics, including mergers rather than by their large-scale environment.

  20. Empirical calibration of the near-infrared CaII triplet - IV. The stellar population synthesis models

    NASA Astrophysics Data System (ADS)

    Vazdekis, A.; Cenarro, A. J.; Gorgas, J.; Cardiel, N.; Peletier, R. F.

    2003-04-01

    We present a new evolutionary stellar population synthesis model, which predicts spectral energy distributions for single-age single-metallicity stellar populations (SSPs) at resolution 1.5 Å (FWHM) in the spectral region of the near-infrared CaII triplet feature. The main ingredient of the model is a new extensive empirical stellar spectral library that has been recently presented by Cenarro et al., which is composed of more than 600 stars with an unprecedented coverage of the stellar atmospheric parameters. Two main products of interest for stellar population analysis are presented. The first is a spectral library for SSPs with metallicities -1.7 < [Fe/H] < +0.2, a large range of ages (0.1-18 Gyr) and initial mass function (IMF) types. They are well suited to modelling galaxy data, since the SSP spectra, with flux-calibrated response curves, can be smoothed to the resolution of the observational data, taking into account the internal velocity dispersion of the galaxy, allowing the user to analyse the observed spectrum in its own system. We also produce integrated absorption-line indices (namely CaT*, CaT and PaT) for the same SSPs in the form of equivalent widths. We find the following behaviour for the CaII triplet feature in old-aged SSPs: (i) the strength of the CaT* index does not change much with time for all metallicities for ages larger than ~3 Gyr; (ii) this index shows a strong dependence on metallicity for values below [M/H]~-0.5 and (iii) for larger metallicities this feature does not show a significant dependence either on age or on the metallicity, being more sensitive to changes in the slope of power-like IMF shapes. The SSP spectra have been calibrated with measurements for globular clusters by Armandroff & Zinn, which are well reproduced, probing the validity of using the integrated CaII triplet feature for determining the metallicities of these systems. Fitting the models to two early-type galaxies of different luminosities (NGC 4478 and 4365

  1. TRIGGERED STAR FORMATION AND YOUNG STELLAR POPULATION IN BRIGHT-RIMMED CLOUD SFO 38

    SciTech Connect

    Choudhury, Rumpa; Bhatt, H. C.; Mookerjea, Bhaswati E-mail: hcbhatt@iiap.res.i

    2010-07-10

    We have investigated the young stellar population in and around SFO 38, one of the massive globules located in the northern part of the Galactic H II region IC 1396, using the Spitzer IRAC and MIPS observations (3.6-24 {mu}m), and followed up with ground-based optical photometric and spectroscopic observations. Based on the IRAC and MIPS colors and H{alpha} emission, we identify {approx}45 young stellar objects (Classes 0/I/II) and 13 probable pre-main-sequence candidates. We derive the spectral types (mostly K- and M-type stars), effective temperatures, and individual extinction of the relatively bright and optically visible Class II objects. Most of the Class II objects show variable H{alpha} emission as well as optical and near-infrared photometric variability, which confirm their 'youth'. Based on optical photometry and theoretical isochrones, we estimate the spread in stellar ages to be between 1 and 8 Myr with a median age of 3 Myr and a mass distribution of 0.3-2.2 M{sub sun} with a median value around 0.5 M{sub sun}. Using the width of the H{alpha} emission line measured at 10% peak intensity, we derive the mass accretion rates of individual objects to be between 10{sup -10} and 10{sup -8} M{sub sun} yr{sup -1}. From the continuum-subtracted H{alpha} line image, we find that the H{alpha} emission of the globule is not spatially symmetric with respect to the O-type ionizing star HD 206267, and the interstellar extinction toward the globule is also anomalous. We clearly detect an enhanced concentration of YSOs closer to the southern rim of SFO 38 and identify an evolutionary sequence of YSOs from the rim to the dense core of the cloud, with most of the Class II objects located at the bright rim. The YSOs appear to be aligned along two different directions toward the O6.5V type star HD 206267 and the B0V type star HD 206773. This is consistent with the Radiation Driven Implosion (RDI) model for triggered star formation. Further, the apparent speed of

  2. The stellar populations of the globular cluster M55

    NASA Astrophysics Data System (ADS)

    Mandushev, Georgi

    1999-10-01

    New broad-band, ground-based photometry in four filters (UBVI ) for two fields in the sparse, metal-poor Galactic globular duster M55 (NGC 6809) is presented and analyzed. New values are derived for the reddening (EB-V = 0.13 +/- 0.02 and E V-I = 0.17 +/- 0.02), distance modulus ((m - M)v = 14.02 +/- 0.08) and age (14 +/- 1.2 Gyr) of M55. The main- sequence luminosity function of M55 is found to be different from the luminosity functions of the metal-poor dusters M15, M30 and M92 and this difference is interpreted as a deficiency of low-mass stars, by about 50% compared to the other three clusters. The mass function of M55 for masses below 0.4 Msolar is found to be fairly flat and. consequently low-mass stars do not dominate the cluster mass. The red giant branch of M55 has been observed from nearly its tip to the subgiant branch. In all passbands the observed luminosity of the red giant dump it lower than the predictions of theoretical models. The ratios of the number of stars on the red giant branch, the horizontal branch and the asymptotic giant branch are found to be in a good agreement with theoretical models. Neither the V-band nor the I-band luminosity functions for the evolved: populations in M55 show any significant deviation from the theoretical luminosity functions. In particular, no evidence is found for a deficiency of main-sequence stars compared to the number of stars on the subgiant and giant branches. M55 is the only well- studied, metal-poor duster for which no discrepancy between observations and canoniocal luminosity functions is found. A large sample of blue stragglers in the core of M55 is identified and analyzed. It is concluded that the blue stragglers in M55 are born with helium-enriched cores but not envelopes, thus resembling stars that have already evolved away from the main sequence. IT is also suggested that the observed blue straggler sequence represents the equivalent of a core helium-enriched main sequence where the blue stragglers

  3. SPIDER - VII. Revealing the stellar population content of massive early-type galaxies out to 8Re

    NASA Astrophysics Data System (ADS)

    La Barbera, F.; Ferreras, I.; de Carvalho, R. R.; Bruzual, G.; Charlot, S.; Pasquali, A.; Merlin, E.

    2012-11-01

    Radial trends of stellar populations in galaxies provide a valuable tool to understand the mechanisms of galaxy growth. In this paper, we present the first comprehensive analysis of optical-optical and optical-NIR colours, as a function of galaxy mass, out to the halo region (8Re) of early-type galaxies (ETGs). We select a sample of 674 massive ETGs (M★ ≳ 3 × 1010 M⊙) from the Sloan Digital Sky Survey (SDSS)-based SPIDER survey. By comparing with a large range of population synthesis models, we derive robust constraints on the radial trends in age and metallicity. Metallicity is unambiguously found to decrease outwards, with a measurable steepening of the slope in the outer regions (Re < R < 8Re). The gradients in stellar age are found to be more sensitive to the models used, but in general, the outer regions of ETGs feature older populations compared to the cores. This trend is strongest for the most massive galaxies in our sample (M★ ≳ 1011 M⊙). Furthermore, when segregating with respect to large-scale environment, the age gradient is more significant in ETGs residing in higher density regions. These results shed light on the processes leading from the formation of the central core to the growth of the stellar envelope of massive galaxies. The fact that the populations in the outer regions are older and more metal-poor than in the core suggests a process whereby the envelope of massive galaxies is made up of accreted small satellites (i.e. minor mergers) whose stars were born during the first stages of galaxy formation.

  4. Apparent age spreads in clusters and the role of stellar rotation

    NASA Astrophysics Data System (ADS)

    Niederhofer, F.; Georgy, C.; Bastian, N.; Ekström, S.

    2015-10-01

    We use the Geneva SYCLIST isochrone models that include the effects of stellar rotation to investigate the role that rotation has on the resulting colour-magnitude diagram of young and intermediate age clusters. We find that if a distribution of rotation velocities exists within the clusters, rotating stars will remain on the main sequence for longer, appearing to be younger than non-rotating stars within the same cluster. This results in an extended main sequence turn-off (eMSTO) that appears at young ages (˜30 Myr) and lasts beyond 1 Gyr. If this eMSTO is interpreted as an age spread, the resulting age spread is proportional to the age of the cluster, i.e. young clusters (<100 Myr) appear to have small age spreads (tens of Myr) whereas older clusters (˜1 Gyr) appear to have much large spreads, up to a few hundred Myr. We compare the predicted spreads for a sample of rotation rates to observations of young and intermediate age clusters, and find a strong correlation between the measured `age spread' and the age of the cluster, in good agreement with models of stellar rotation. This suggests that the `age spreads' reported in the literature may simply be the result of a distribution of stellar rotation velocities within clusters.

  5. The large scale view of the young stellar populations in the Orion OB1 Association

    NASA Astrophysics Data System (ADS)

    Briceno, Cesar; Calvet, Nuria

    2016-06-01

    The Orion OB1 association, at ~400 pc and with a wide range of ages (~1-10 Myr) and environmental conditions, is an ideal place to look at how stars form, first evolve and disperse among the general population of field stars. Also to study disk dispersal and the duration of the planet formation phase.However, despite spanning nearly 200 deg2 on the sky, almost all we know about Orion comes from studies of a limited fraction of the entire region, mostly of the youngest objects (~<1 Myr) in the A and B molecular clouds and the ~3 Myr old sigma Ori cluster.We will present here the results of our 180 sq deg photometric multi-epoch survey across the Orion OB1 association, using the known variability of T Tauri stars to pick them among the general field population, and following with spectroscopy to confirm members and characterize them.The ~2000 newly identified young low-mass stars are mostly located away from the molecular clouds, across tens of sq. deg. in the Orion OB1a and OB1b sub-associations, with ages in the range ~4-10 Myr. But within this general population we identify a significant fraction concentrated in distinct overdensities, most notably the ~7 Myr old 25 Orionis cluster. These stellar aggregates point to a previously unknown degree of substructure that has survived the dissipation of the parent molecular clouds. We also find that the Orion Nebula Cluster is surrounded by a few sq.deg. halo of young stars, as has been suggested by recent sudies.

  6. Oral medicine and the ageing population.

    PubMed

    Yap, T; McCullough, M

    2015-03-01

    The oral cavity is subject to age related processes such as cellular ageing and immunosenescence. The ageing population bears an increased burden of intraoral pathology. In oral medicine, the majority of presenting patients are in their fifth to seventh decade of life. In this review, we discuss the ageing population's susceptibility to mucosal disorders and the increased prevalence of potentially malignant disorders and oral squamous cell carcinoma, as well as dermatoses including oral lichen planus and immunobullous conditions. We also address the ageing population's susceptibility to oral discomfort and explore salivary secretion, ulceration and the symptoms of oral burning. Finally, we will describe orofacial pain conditions which are more likely encountered in an older population. This update highlights clinical presentations which are more likely to be encountered in the ageing population in a general practice setting and the importance of screening both new and long-term patients.

  7. Oral medicine and the ageing population.

    PubMed

    Yap, T; McCullough, M

    2015-03-01

    The oral cavity is subject to age related processes such as cellular ageing and immunosenescence. The ageing population bears an increased burden of intraoral pathology. In oral medicine, the majority of presenting patients are in their fifth to seventh decade of life. In this review, we discuss the ageing population's susceptibility to mucosal disorders and the increased prevalence of potentially malignant disorders and oral squamous cell carcinoma, as well as dermatoses including oral lichen planus and immunobullous conditions. We also address the ageing population's susceptibility to oral discomfort and explore salivary secretion, ulceration and the symptoms of oral burning. Finally, we will describe orofacial pain conditions which are more likely encountered in an older population. This update highlights clinical presentations which are more likely to be encountered in the ageing population in a general practice setting and the importance of screening both new and long-term patients. PMID:25762041

  8. Population aging and its strategic options.

    PubMed

    Zhang, W

    1997-12-01

    Since population aging will challenge all societies in the future, all countries need to give priority attention to the matter. In 2000, more than 130 million of China's population will be aged 60 years, 10% of the total population. The proportion of China's population in that age group will then grow to 25% in 2050. Developing the economy is the most fundamental way to increase the country's population carrying capacity and to cope with population aging. Only a developed economy can solve the problems inherent to population aging. A relatively low total dependency ratio and an annual net increase of about 6 million working-age population during 1982-2025 will facilitate economic development in China. Complementary strategies to handle population aging in China include supporting and continuing the tradition of families supporting their elderly, developing a community-based support system, updating the existing social security system, and improving the legal system on aging to ensure that it protects the rights and interests of the elderly.

  9. THE AGE, STELLAR CONTENT, AND STAR FORMATION TIMESCALE OF THE B59 DENSE CORE

    SciTech Connect

    Covey, K. R.; Lada, C. J.; Muench, A. A.; Forbrich, J.; Ascenso, J.; Roman-Zuniga, C.

    2010-10-20

    We have investigated the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Using the SpeX spectrograph on the NASA Infrared Telescope Facility, we obtained moderate resolution, near-infrared (NIR) spectra for 20 candidate young stellar objects (YSOs) in B59 and a representative sample of NIR and mid-IR bright sources distributed throughout the Pipe. Measuring luminosity and temperature sensitive features in these spectra, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. To measure B59's age, we place its candidate YSOs in the Hertzsprung-Russell diagram and compare their location to YSOs in several well-studied star-forming regions, as well as predictions of pre-main-sequence (PMS) evolutionary models. We find that B59 is composed of late-type (K4-M6) low-mass (0.9-0.1 M{sub sun}) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the {rho} Oph, Taurus, and Chameleon star-forming regions. Deriving absolute age estimates from PMS models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6 {+-} 0.8 Myr. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6{sup +4.1}{sub -2.6} Myr. We also find that the relative age orderings implied by PMS evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependences. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggests that the B59 dense core has been stable against global collapse for roughly six dynamical timescales and is actively forming stars with a star formation efficiency per dynamical time of {approx}6%. While the {approx}150% uncertainties associated with our age measurement propagate directly into these

  10. The young stellar population of IC 1613. II. Physical properties of OB associations

    NASA Astrophysics Data System (ADS)

    Garcia, M.; Herrero, A.; Castro, N.; Corral, L.; Rosenberg, A.

    2010-11-01

    Context. To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We ultimately aim to study the metallicity-dependent driving mechanism of the winds of blue massive stars and use metal-poor massive stars of the Local Volume as a proxy for the stars in the early Universe. Aims: In a previous paper we produced a list of OB associations in IC 1613. Their properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the structure and recent star formation history of the galaxy. We characterize these OB associations and study their connection with the galactic global properties. Methods: The reddening-free Q parameter is a powerful tool in the photometric analysis of young populations of massive stars, since it exhibits a smaller degree of degeneracy with OB spectral types than the B-V color. The color-magnitude diagram (Q vs. V) of the OB associations in IC 1613 is studied to determine their age and mass, and confirm the population of young massive stars. Results: We identified more than 10 stars with M ≥ 50 M⊙. Spectral classification available for some of them confirm their massive nature, yet we find the common discrepancy with the spectroscopically derived masses. There is a general increasing trend of the mass of the most massive member with the number of members of each association, but not with the stellar density. The average diameter of the associations of this catalog is 40 pc, half the historically considered typical size of OB associations. Size increases with the association population. The distribution of the groups strongly correlates with that of neutral and ionized hydrogen. We find the largest dispersion of association

  11. PMAS optical integral field spectroscopy of luminous infrared galaxies. II. Spatially resolved stellar populations and excitation conditions

    NASA Astrophysics Data System (ADS)

    Alonso-Herrero, A.; García-Marín, M.; Rodríguez Zaurín, J.; Monreal-Ibero, A.; Colina, L.; Arribas, S.

    2010-11-01

    Context. The general properties (e.g., activity class, star formation rates, metallicities, extinctions, average ages, etc.) of luminous (LIRGs) and ultraluminous infrared galaxies (ULIRGs) in the local universe are well known because large samples of these objects have been the subject of numerous spectroscopic works over the past three decades. There are, however, relatively few studies of the spatially-resolved spectroscopic properties of large samples of LIRGs and ULIRGs using integral field spectroscopy (IFS). Aims: We are carrying out an IFS survey of local (z<0.26) samples of LIRGs and ULIRGs to characterize their two-dimensional spectroscopic properties. The main goal of this paper is to study the spatially resolved properties of the stellar populations and the excitation conditions in a sample of LIRGs. Methods: We analyze optical (3800-7200 Å) IFS data taken with the Potsdam Multi-Aperture Spectrophotometer (PMAS) of the central few kiloparsecs of eleven LIRGs. To study these stellar populations, we fit the optical stellar continuum and the hydrogen recombination lines of selected regions in the galaxies. We analyzed the excitation conditions of the gas using the spatially resolved properties of the brightest optical emission lines. We complemented the PMAS observations with existing HST/NICMOS near-infrared continuum and Paα imaging. Results: The optical continua of selected regions in our LIRGs are well fitted with a combination of an evolved (~0.7-10 Gyr) stellar population with an ionizing stellar population (1-20 Myr). The latter population is more obscured than the evolved population, and has visual extinctions in good agreement with those obtained from the Balmer decrement. Except for NGC 7771, we find no clear that there is an important contribution to the optical light from an intermediate-aged stellar population (~100-500 Myr). Even after correcting for the presence of stellar absorption, a large number of spaxels with low observed equivalent

  12. Extragalactic stellar populations in the near and mid-infrared: 1-30 mum emission from evolved populations, young and dusty star forming regions and the earliest stellar populations

    NASA Astrophysics Data System (ADS)

    Mentuch, Erin

    2010-11-01

    The near- through mid-infrared offers a unique and, as this thesis aims to show, essential view of extragalactic stellar populations both nearby, at intermediate redshifts and at very high redshift. In chapter 2, I demonstrate that rest-frame near-IR photometry obtained by the Spitzer Space Telescope provides more robust stellar mass estimates for a spectroscopic sample of ˜ 100 galaxies in the redshift desert (0:5 < z < 2), and is crucial for modeling galaxies with young star-forming populations. From this analysis, a surprising result emerges in the data. Although the rest-frame light short of 2 mum improves stellar mass estimates, the models and observations disagree beyond 2 mum and emission from non-stellar sources becomes significant. At wavelengths from 1--30 mum, stellar and non-stellar emission contribute equally to a galaxy's global spectral energy distribution. This is unlike visible wavelengths where stellar emission dominates or the far-IR where dust emission provides the bulk of a galaxy's luminosity. Using the sample of high-z galaxies, in chapter 3, I quantify the statistical significance of the excess emission at 2-5 mum and find the emission to correlate with the O II luminosity, suggesting a link between the excess emission and star formation. The origin of the excess emission is not clear, although I explore a number of non-stellar candidates in this chapter. Nearby resolved observations provide a clearer picture of the excess by spatially resolving 68 nearby galaxies. By analyzing the pixel-by-pixel near-IR colours within each galaxy at ˜1-5 mum, increasingly red near-IR colors are mapped to spatial regions in chapter 4. For regions with red NIR colors and high star formation rates, I find the broad near- through mid-IR spectrum is constant, varying only in amplitude as a function of the intensity of star formation, suggesting the infrared emission of a young, dusty stellar populations can be added to stellar population synthesis models as an

  13. Chemical abundances in LMC stellar populations. II. The bar sample

    NASA Astrophysics Data System (ADS)

    Van der Swaelmen, M.; Hill, V.; Primas, F.; Cole, A. A.

    2013-12-01

    Aims: This paper compares the chemical evolution of the Large Magellanic Cloud (LMC) to that of the Milky Way (MW) and investigates the relation between the bar and the inner disc of the LMC in the context of the formation of the bar. Methods: We obtained high-resolution and mid signal-to-noise ratio spectra with FLAMES/GIRAFFE at ESO/VLT and performed a detailed chemical analysis of 106 and 58 LMC field red giant stars (mostly older than 1 Gyr), located in the bar and the disc of the LMC respectively. To validate our stellar parameter determinations and abundance measurement procedures, we performed thorough tests using the well-known mildly metal-poor Milky-Way thick disc giant Arcturus (HD 124897, α Boo). We measured elemental abundances for O, Mg, Si, Ca, Ti (α-elements), Na (light odd element), Sc, V, Cr, Co, Ni, Cu (iron-peak elements), Y, Zr, Ba, La, and Eu (s- and r-elements). Results: We find that the α-element ratios [Mg/Fe] and [O/Fe] are lower in the LMC than in the MW while the LMC has similar [Si/Fe], [Ca/Fe], and [Ti/Fe] to the MW. As for the heavy elements, [Ba,La/Eu] exhibit a strong increase with increasing metallicity starting from [Fe/H] ≈ -0.8 dex, and the LMC has lower [Y + Zr/Ba + La] ratios than the MW. Cu is almost constant over all metallicities and about 0.5 dex lower in the LMC than in the MW. The LMC bar and inner disc exhibit differences in their [α/ Fe] (slightly larger scatter for the bar in the metallicity range [-1, -0.5]), their Eu (the bar trend is above the disc trend for [Fe/H] ≥ -0.5 dex), their Y and Zr, their Na and their V (offset between the bar and the disc distributions). Conclusions: Our results show that the chemical history of the LMC experienced a strong contribution from type Ia supernovae as well as a strong s-process enrichment from metal-poor AGB winds. Massive stars made a smaller contribution to the chemical enrichment compared to the MW. The observed differences between the bar and the disc speak in

  14. Ultracompact Blue Dwarf Galaxies: Hubble Space Telescope Imaging and Stellar Population Analysis

    NASA Astrophysics Data System (ADS)

    Corbin, Michael R.; Vacca, William D.; Cid Fernandes, Roberto; Hibbard, John E.; Somerville, Rachel S.; Windhorst, Rogier A.

    2006-11-01

    We present deep Hubble Space Telescope (HST) Advanced Camera for Surveys/High Resolution Channel U-, narrow-V-, and I-band images of nine ``ultracompact'' blue dwarf galaxies (UCBDs) selected from the Sloan Digital Sky Survey (SDSS). We define UCBDs as local (z<0.01) star-forming galaxies having angular diameters less than 6" and physical diameters <1 kpc. They are also among the most metal-poor galaxies known, including objects having 12+log(O/H)<7.65, and are found to reside within voids. Both the HST images and the objects' SDSS optical spectra reveal that they are composites of young (~1-10 Myr) populations that dominate their light and older (~10 Gyr) populations that dominate their stellar masses, which we estimate to be ~107-108 Msolar. An intermediate-age (~107-109 yr) population is also indicated in most objects. The objects do not appear to be as dynamically disturbed as the prototype UCBD, POX 186, but the structure of several of them suggests that their current star formation has been triggered by the collisions/mergers of smaller clumps of stars. In one case, HS 0822+3542, the images resolve what may be two small (~100 pc) components that have recently collided, supporting this interpretation. In six of the objects much of the star formation is concentrated in young massive clusters, contributing to their compactness in ground-based images. The evidence that the galaxies consist mainly of ~10 Gyr old stars establishes that they are not protogalaxies, forming their first generation of stars. Their low metallicities are more likely to be the result of the escape of supernova ejecta, rather than youth.

  15. Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution.

    PubMed

    Stanghellini; Shaw; Balick; Blades

    2000-05-10

    Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system. PMID:10813674

  16. Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution.

    PubMed

    Stanghellini; Shaw; Balick; Blades

    2000-05-10

    Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.

  17. Galaxy evolution through resolved stellar populations in the nearby Centaurus A group .

    NASA Astrophysics Data System (ADS)

    Crnojević, D.; Grebel, E. K.; Ferguson, A. M. N.; Koch, A.; Rejkuba, M.; Da Costa, G.; Jerjen, H.; Irwin, M. J.; Bernard, E. J.; Arimoto, N.; Jablonka, P.; Kobayashi, C.

    The CenA group is a nearby dense complex (˜4 Mpc) dominated by an active elliptical galaxy, hosting more than 60 dwarf companions with a variety of morphological types and stellar contents. We study the resolved stellar populations of a sample of dwarfs using optical and near-infrared data from ACS/HST and ISAAC/VLT. We characterize their recent star formation histories and metallicity content, and compare them to what is known for Local Group dwarfs, underlining similarities and differences. Our results probe the fu ndamental interplay between nature and nurture in the evolution of dwarfs in such a dense environment. We further present the results of the first deep survey of resolved stellar populations in the remote outer halo of our nearest giant elliptical, CenA (VIMOS/VLT optical data). Tracing its halo structure (radial profile, extent and metallicity) out to a remarkable ˜85 kpc and comparing the halo stellar populations to those of CenA's dwarf companions enables us to constrain the mechanisms that contributed to the build-up of CenA in the context of cosmological galaxy formation models.

  18. The X-Ray Luminosity Functions of Field Low-Mass X-Ray Binaries in Early-Type Galaxies: Evidence for a Stellar Age Dependence

    NASA Technical Reports Server (NTRS)

    Lehmer, B. D.; Berkeley, M.; Zezas, A.; Alexander, D. M.; Basu-Zych, A.; Bauer, F. E.; Brandt, W. N.; Fragos, T.; Hornschemeier, A. E.; Kalogera, V.; Ptak, A.; Sivakoff, G. R.; Tzanavaris, P.; Yukita, M.

    2014-01-01

    We present direct constraints on how the formation of low-mass X-ray binary (LMXB) populations in galactic fields depends on stellar age. In this pilot study, we utilize Chandra and Hubble Space Telescope (HST) data to detect and characterize the X-ray point source populations of three nearby early-type galaxies: NGC 3115, 3379, and 3384. The luminosity-weighted stellar ages of our sample span approximately equal to 3-10 Gyr. X-ray binary population synthesis models predict that the field LMXBs associated with younger stellar populations should be more numerous and luminous per unit stellar mass than older populations due to the evolution of LMXB donor star masses. Crucially, the combination of deep Chandra and HST observations allows us to test directly this prediction by identifying and removing counterparts to X-ray point sources that are unrelated to the field LMXB populations, including LMXBs that are formed dynamically in globular clusters, Galactic stars, and background AGN/galaxies. We find that the "young" early-type galaxy NGC 3384 (approximately equals 2-5 Gyr) has an excess of luminous field LMXBs (L(sub x) approximately greater than (5-10) × 10(exp 37) erg s(exp -1)) per unit K-band luminosity (L(sub K); a proxy for stellar mass) than the "old" early-type galaxies NGC 3115 and 3379 (approximately equals 8-10 Gyr), which results in a factor of 2-3 excess of L(sub X)/L(sub K) for NGC 3384. This result is consistent with the X-ray binary population synthesis model predictions; however, our small galaxy sample size does not allow us to draw definitive conclusions on the evolution field LMXBs in general. We discuss how future surveys of larger galaxy samples that combine deep Chandra and HST data could provide a powerful new benchmark for calibrating X-ray binary population synthesis models.

  19. The X-ray luminosity functions of field low-mass X-ray binaries in early-type galaxies: Evidence for a stellar age dependence

    SciTech Connect

    Lehmer, B. D.; Tzanavaris, P.; Yukita, M.; Berkeley, M.; Basu-Zych, A.; Hornschemeier, A. E.; Ptak, A.; Zezas, A.; Alexander, D. M.; Bauer, F. E.; Brandt, W. N.; Fragos, T.; Kalogera, V.; Sivakoff, G. R.

    2014-07-01

    We present direct constraints on how the formation of low-mass X-ray binary (LMXB) populations in galactic fields depends on stellar age. In this pilot study, we utilize Chandra and Hubble Space Telescope (HST) data to detect and characterize the X-ray point source populations of three nearby early-type galaxies: NGC 3115, 3379, and 3384. The luminosity-weighted stellar ages of our sample span ≈3-10 Gyr. X-ray binary population synthesis models predict that the field LMXBs associated with younger stellar populations should be more numerous and luminous per unit stellar mass than older populations due to the evolution of LMXB donor star masses. Crucially, the combination of deep Chandra and HST observations allows us to test directly this prediction by identifying and removing counterparts to X-ray point sources that are unrelated to the field LMXB populations, including LMXBs that are formed dynamically in globular clusters, Galactic stars, and background active galactic nuclei/galaxies. We find that the 'young' early-type galaxy NGC 3384 (≈2-5 Gyr) has an excess of luminous field LMXBs (L {sub X} ≳ (5-10) × 10{sup 37} erg s{sup –1}) per unit K-band luminosity (L{sub K} ; a proxy for stellar mass) than the 'old' early-type galaxies NGC 3115 and 3379 (≈8-10 Gyr), which results in a factor of ≈2-3 excess of L {sub X}/L{sub K} for NGC 3384. This result is consistent with the X-ray binary population synthesis model predictions; however, our small galaxy sample size does not allow us to draw definitive conclusions on the evolution field LMXBs in general. We discuss how future surveys of larger galaxy samples that combine deep Chandra and HST data could provide a powerful new benchmark for calibrating X-ray binary population synthesis models.

  20. A stellar population synthesis approach to the Oosterhoff dichotomy

    NASA Astrophysics Data System (ADS)

    Sollima, A.; Cassisi, S.; Fiorentino, G.; Gratton, R. G.

    2014-10-01

    We use colour-magnitude diagram synthesis together with theoretical relations from non-linear pulsation models to approach the long-standing problem of the Oosterhoff dichotomy related to the distribution of the mean periods of fundamental RR Lyrae variables in globular clusters. By adopting the chemical composition determined from spectroscopic observations and a criterion to account for the hysteresis mechanism, we tuned age and mass loss to simultaneously reproduce the morphology of both the turn-off and the horizontal branch of a sample of 17 globular clusters of the Milky Way and of nearby dwarf galaxies in the crucial metallicity range (-1.9 < [Fe/H] < -1.4) where the Oostheroff transition is apparent. We find that the Oosterhoff dichotomy among Galactic globular clusters is naturally reproduced by models. The analysis of the relative impact of the various involved parameters indicates that the main responsibles of the dichotomy are the peculiar distribution of clusters in the age-metallicity plane and the hysteresis. In particular, there is a clear connection between the two main branches of the age-metallicity relation for Galactic globular clusters and the Oosterhoff groups. The properties of clusters' RR Lyrae belonging to other Oostheroff groups (OoInt and OoIII) are instead not well reproduced. While for OoIII clusters a larger helium abundance for a fraction of the cluster's stars can reconcile the model prediction with observations, some other parameter affecting both the horizontal branch morphology and the RR Lyrae periods is required to reproduce the behaviour of OoInt clusters.

  1. The incidence of binaries in globular cluster stellar populations

    NASA Astrophysics Data System (ADS)

    Lucatello, S.; Sollima, A.; Gratton, R.; Vesperini, E.; D'Orazi, V.; Carretta, E.; Bragaglia, A.

    2015-12-01

    Binary fraction and orbital characteristics provide indications on the conditions of star formation, as they shed light on the environment they were born in. Multiple systems are more common in low density environments than in higher density environments. In the current debate about the formation of globular clusters and their multiple populations, studying the binary incidence in the populations they host offers a crucial piece of information on the environment of their birth and their subsequent dynamical evolution. Through a multiyear observational campaign using FLAMES at VLT, we monitored the radial velocity of 968 red-giant-branch stars located around the half-light radii in a sample of ten Galactic globular clusters. We found a total of 21 radial velocity variables identified as bona fide binary stars, for a binary fraction of 2.2% ± 0.5%. When separating the sample into first generation and second generation stars, we find a binary fraction of 4.9% ± 1.3% and 1.2% ± 0.4%, respectively. Through simulations that take possible sources of bias into account in detecting radial velocity variations in the two populations, we show that the difference is significant and only marginally affected by these effects. This kind of different binary fraction strongly suggests different conditions in the environment of formation and evolution of first and second generations stars, with the latter being born in a much denser environment. Our result hence strongly supports the idea that the second generation forms in a dense subsystem at the center of the loosely distributed first generation, where (loose) binaries are efficiently destroyed. Based on data obtained with the Very Large Telescope at the European Southern Observatory, programs: 073.D-0100, 073.D-0211 and 083.D-0208.Full Tables 1, 3, and table of the individual radial velocities are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc

  2. Variable Stars and Stellar Populations in Andromeda XXI. II. Another Merged Galaxy Satellite of M31?

    NASA Astrophysics Data System (ADS)

    Cusano, Felice; Garofalo, Alessia; Clementini, Gisella; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Musella, Ilaria; Ripepi, Vincenzo; Speziali, Roberto; Sani, Eleonora; Merighi, Roberto

    2015-06-01

    B and V time-series photometry of the M31 dwarf spheroidal satellite Andromeda XXI (And XXI) was obtained with the Large Binocular Cameras at the Large Binocular Telescope. We have identified 50 variables in And XXI, of which 41 are RR Lyrae stars (37 fundamental-mode—RRab, and 4 first-overtone-RRc, pulsators) and 9 are Anomalous Cepheids (ACs). The average period of the RRab stars (< {P}{ab}> =0.64 days) and the period-amplitude diagram place And XXI in the class of Oosterhoff II—Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derived the galaxy distance modulus of (m - M)0 = 24.40 ± 0.17 mag, which is smaller than previous literature estimates, although still consistent with them within 1σ. The galaxy color-magnitude diagram shows evidence for the presence of three different stellar generations in And XXI: (1) an old (˜12 Gyr) and metal-poor ([Fe/H] = -1.7 dex) component traced by the RR Lyrae stars; (2) a slightly younger (10-6 Gyr) and more metal-rich ([Fe/H] = -1.5 dex) component populating the red horizontal branch, and (3) an intermediate age (˜1 Gyr) component with the same metallicity that produced the ACs. Finally, we provide hints that And XXI could be the result of a minor merging event between two dwarf galaxies. Based on data collected with the LBC at the LBT.

  3. Evidence of an interaction from resolved stellar populations: the curious case of NGC 1313

    NASA Astrophysics Data System (ADS)

    Silva-Villa, E.; Larsen, S. S.

    2012-06-01

    The galaxy NGC 1313 has attracted the attention of various studies due to the peculiar morphology observed in optical bands, although it is classified as a barred, late-type galaxy with no apparent close-by companions. However, the velocity field suggests an interaction with a satellite companion. Using resolved stellar populations, we study different parts of the galaxy to understand further its morphology. Based on Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) images, we estimated star formation histories by means of the synthetic colour-magnitude diagram method in different areas in the galaxy. Incompleteness limits our analysis to ages younger than ˜100 Myr. Stars in the red and blue He-burning phases are used to trace the distribution of recent star formation. Star formation histories suggest a burst in the south-western region. We support the idea that NGC 1313 is experiencing an interaction with a satellite companion, observed as a tidally disrupted satellite galaxy in the south-west of NGC 1313. However, we do not observe any indication of a perturbation due to the interaction with the satellite galaxy at other locations across the galaxy, suggesting that only a modest-sized companion that did not trigger a global starburst was involved.

  4. Ultra-diffuse Galaxies in Clusters and the Field: Masses and Stellar Populations

    NASA Astrophysics Data System (ADS)

    Romanowsky, Aaron; Laine, Seppo; Krick, Jessica; van Dokkum, Pieter; Villaume, Alexa; Brodie, Jean

    2016-08-01

    Ultra-diffuse galaxies (UDGs) were recognized only last year as a novel class of galaxies, with luminosities like dwarfs but sizes like giants. Although some UDGs appear to be just unusually extended dwarfs, others show evidence of being very different and unexpected: their dark matter halos are overmassive by factors of ~10, with one UDG even being arguably a 'failed Milky Way.' These exotic galaxies might be a byproduct of environmental processes within galaxy clusters, but UDGs have also now been found in the field. It is crucial for understanding their origins to test if UDGs have the same properties in cluster and field environments. Here we propose studying the stellar populations (ages and metallicities) of seven UDGs using Spitzer/IRAC 3.6- and 4.5-micron imaging combined with optical photometry, along with mass estimation of three of the UDGs using HST/ACS imaging to provide globular cluster number counts and colors (proxies for halo mass). This ultra low surface brightness photometry in the near infrared, on an important new class of galaxies, could become a legacy result from the Spitzer mission.

  5. On the Incorporation of Metallicity Data into Measurements of Star Formation History from Resolved Stellar Populations

    NASA Astrophysics Data System (ADS)

    Dolphin, Andrew E.

    2016-07-01

    The combination of spectroscopic stellar metallicities and resolved star color–magnitude diagrams (CMDs) has the potential to constrain the entire star formation history (SFH) of a galaxy better than fitting CMDs alone (as is most common in SFH studies using resolved stellar populations). In this paper, two approaches to incorporating external metallicity information into CMD-fitting techniques are presented. Overall, the joint fitting of metallicity and CMD information can increase the precision of measured age–metallicity relationships (AMRs) and star formation rates by 10% over CMD fitting alone. However, systematics in stellar isochrones and mismatches between spectroscopic and photometric determinations of metallicity can reduce the accuracy of the recovered SFHs. I present a simple mitigation of these systematics that can reduce their amplitude to the level obtained from CMD fitting alone, while ensuring that the AMR is consistent with spectroscopic metallicities. As is the case in CMD-fitting analysis, improved stellar models and calibrations between spectroscopic and photometric metallicities are currently the primary impediment to gains in SFH precision from jointly fitting stellar metallicities and CMDs.

  6. Characterizing Pre-Main Sequence Populations in Stellar Associations of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios

    2007-07-01

    The Large Magellanic Cloud {LMC} offers an extremely rich sample of resolved low-mass stars {below 1 Solar Mass} in the act of formation that has not been explored sufficiently yet. These pre-main sequence {PMS} stars provide a unique snapshot of the star formation process, as it is being recorded for the last 20 Myr, and they give important information on the low-mass Initial Mass Function {IMF} of their host stellar systems. Studies of young, rich LMC clusters like 30 Doradus are crowding limited, even at the angular resolution facilitated by HST in the optical. To learn more about low-mass PMS stars in the LMC, one has to study less crowded regions like young stellar assocations. We propose to employ WFPC2 to obtain deep photometry {V 25.5 mag} of four selected LMC stellar associations in order to perform an original optical analysis of their red PMS and blue bright MS stellar populations. With these observations we aim at a comprehensive study, which will add substantial information on the most recent star formation and the IMF in the LMC. The data reduction and analysis will be performed with a 2D photometry software package especially developped by us for WFPC2 imaging of extended stellar associations with variable background. Our targets have been selected optimizing a combination of criteria, namely spatial resolution, crowding, low extinction, nebular contamination, and background confusion in comparison to other regions in the Local Group. Parallel NICMOS imaging will provide additional information on near-infrared properties of the stellar population in the regions surrounding these systems.

  7. Stellar populations and Star Formation Rates in NGC 6872, the Condor galaxy

    NASA Astrophysics Data System (ADS)

    Eufrasio, Rafael T.; De Mello, D. F.; Dwek, E.; Arendt, R. G.; Gadotti, D. A.

    2014-01-01

    We present a detailed analysis of the Spectral Energy Distributions (SEDs) of 10 kpc regions across the giant spiral galaxy NGC 6872, the Condor galaxy. We made use of archival data from the FUV (GALEX) to 22 μm (WISE). In order to find any signature of the recent interaction 130 Myr) with its companion, the S0 galaxy IC 4970, we inspected the SED of Condor's bar. One possibility is that is would have been formed by passage of the companion. We find that it is a particularly long bar (9 kpc semi-major axis), with a size almost twice as large as the average found in other barred galaxies (4.5 kpc median in the local universe, Gadotti 2011). A bulge/bar/disk 2D decomposition using the Spitzer 3.6 μm image and the budda package (de Souza et al. 2004; Gadotti 2008) reveals that the ratio of the bar semi-major axis to the disk scale-length is 1.4, which is a value typically found in other barred galaxies (see Fig. 1 in Gadotti 2011). The disk scale-length is ~ 7 kpc, which is extremely large (2.8 kpc median in local galaxies, Gadotti 2009). Our analysis also shows that there are no signs of recent star formation along the bar. We find no signs of a box-peanut structure near the central regions, which is also another signature of an evolved bar. Taken altogether, the evidence points to a bar formed at least a few billion years ago and the stars in the bar seem to be a fossil record of the stellar population in the galaxy before the interaction with its companion. Then, we modeled the SFH of each 10 kpc region as constant Star Formation Rate (SFR) for the past 100 Myr superposed on an exponentially decaying, longstanding SFR. We find a single exponential SFH to account for all the recent SFR of the galaxy, with no need for an additional SFR due to the interaction. Av is low all across the galaxy 0.25), but increases near 0.7) the point of collision. The SFH of the arms are asymmetric. The northeastern arm having older ages 5 Gyr) and SFH closer to constant, while the

  8. THE RESOLVED STELLAR POPULATION IN 50 REGIONS OF M83 FROM HST/WFC3 EARLY RELEASE SCIENCE OBSERVATIONS

    SciTech Connect

    Kim, Hwihyun; Cohen, Seth H.; Windhorst, Rogier A.; Whitmore, Bradley C.; Mutchler, Max; Bond, Howard E.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Calzetti, Daniela; O'Connell, Robert W.; Balick, Bruce; Carollo, Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; and others

    2012-07-01

    We present a multi-wavelength photometric study of {approx}15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  9. The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

    NASA Technical Reports Server (NTRS)

    Kim, Hwihyun; Whitmore, Bradley C.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Mutchler, Max; Cohen, Seth H.; Calzetti, Daniela; O’Connell, Robert W.; Windhorst, Rogier A.; Balick, Bruce; Bond, Howard E.; Carollo, Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; Paresce, Francesco; Silk, Joe I; Trauger, John T.; Walker, Alistair R.; Young, Erick T.

    2012-01-01

    We present a multi-wavelength photometric study of approximately 15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones.We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations ofWolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  10. The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

    NASA Astrophysics Data System (ADS)

    Kim, Hwihyun; Whitmore, Bradley C.; Chandar, Rupali; Saha, Abhijit; Kaleida, Catherine C.; Mutchler, Max; Cohen, Seth H.; Calzetti, Daniela; O'Connell, Robert W.; Windhorst, Rogier A.; Balick, Bruce; Bond, Howard E.; Carollo, Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; Paresce, Francesco; Silk, Joe I.; Trauger, John T.; Walker, Alistair R.; Young, Erick T.

    2012-07-01

    We present a multi-wavelength photometric study of ~15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

  11. STELLAR POPULATIONS IN THE OUTER HALO OF THE MASSIVE ELLIPTICAL M49

    SciTech Connect

    Mihos, J. Christopher; Harding, Paul; Rudick, Craig S.; Feldmeier, John J. E-mail: paul.harding@case.edu E-mail: jjfeldmeier@ysu.edu

    2013-02-20

    We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49's stellar halo out to {approx}100 kpc (7r{sub e}), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B - V {approx} 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.

  12. Which processes shape stellar population gradients of massive galaxies at large radii?

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela

    2016-08-01

    We investigate the differential impact of physical mechanisms, mergers (stellar accretion) and internal energetic phenomena, on the evolution of stellar population gradients in massive, present-day galaxies employing a set of high-resolution, cosmological zoom simulations. We demonstrate that negative metallicity and color gradients at large radii (>2Reff) originate from the accretion of metal-poor stellar systems. At larger radii, galaxies become typically more dominated by stars accreted from satellite galaxies in major and minor mergers. However, only strong galactic winds can sufficiently reduce the metallicity content of the accreted stars to realistically steepen the outer metallicity and colour gradients in agreement with present-day observations. In contrast, the gradients of the models without winds are inconsistent with observations (too flat). In the wind model, colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This analysis greatly highlights the importance of both energetic processes and merger events for stellar population properties of massive galaxies at large radii. Our results are expected to significantly contribute to the interpretation of current and up-coming IFU surveys (like MaNGA and Califa), which in turn can help to better constrain still uncertain models for energetic processes in simulations.

  13. INTER- AND INTRA-CLUSTER AGE GRADIENTS IN MASSIVE STAR FORMING REGIONS AND INDIVIDUAL NEARBY STELLAR CLUSTERS REVEALED BY MYStIX

    NASA Astrophysics Data System (ADS)

    Getman, Konstantin V.; Feigelson, Eric; Kuhn, Michael A.; Broos, Patrick S; Townsley, Leisa K.; Naylor, Tim; Povich, Matthew S.; Luhman, Kevin; Garmire, Gordon

    2014-08-01

    The MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) project seeks to characterize 20 OB-dominated young star forming regions (SFRs) at distances <4 kpc using photometric catalogs from the Chandra X-ray Observatory, Spitzer Space Telescope, UKIRT and 2MASS surveys. As part of the MYStIX project, we developed a new stellar chronometer that employs near-infrared and X-ray photometry data, AgeJX. Computing AgeJX averaged over MYStIX (sub)clusters reveals previously unknown age gradients across most of the MYStIX regions as well as within some individual rich clusters. Within the SFRs, the inferred AgeJX ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed stellar populations. Noticeable intra-cluster gradients are seen in the NGC 2024 (Flame Nebula) star cluster and the Orion Nebula Cluster (ONC): stars in cluster cores appear younger and thus were formed later than stars in cluster halos. The latter result has two important implications for the formation of young stellar clusters. Clusters likely form slowly: they do not arise from a single nearly-instantaneous burst of star formation. The simple models where clusters form inside-out are likely incorrect, and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  14. Spatially Resolved Stellar Populations Of Nearby Post-Starburst Galaxies In SDSS-IV MaNGA

    NASA Astrophysics Data System (ADS)

    Liu, Charles; Betances, Ashley; Bonilla, Alaina Marie; Gonzalez, Andrea; Migliore, Christina; Goddard, Daniel; Masters, Karen; SDSS-IV MaNGA Team

    2016-01-01

    We have selected five galaxies in the Mapping Nearby Galaxies at APO (MaNGA) project of the latest generation of the Sloan Digital Sky Survey (SDSS-IV) identified as post-starburst (E+A) systems, in the transition between "blue cloud" and "red sequence" galaxies. We measure the equivalent widths of the Balmer series, D4000 break, and metal lines across each galaxy, and produce maps of the stellar age, stellar mass, and metallicities of each galaxy using FIREFLY, a full spectral analysis code. We have found that the measured properties of the galaxies overall generally matches well with single-aperture SDSS spectra from which the original post-starburst identifications were made. The variation in the spatial distributions of the stellar populations, in particular the A-stars, give us insight into the details of the transitional E+A quenching phase. This work was supported by the Alfred P. Sloan Foundation via the SDSS-IV Faculty and Student Team (FAST) initiative, ARC Agreement No. SSP483 to the CUNY College of Staten Island.

  15. Quantitative chemical tagging, stellar ages and the chemo-dynamical evolution of the Galactic disc

    NASA Astrophysics Data System (ADS)

    Mitschang, A. W.; De Silva, G.; Zucker, D. B.; Anguiano, B.; Bensby, T.; Feltzing, S.

    2014-03-01

    The early science results from the new generation of high-resolution stellar spectroscopic surveys, such as Galactic Archaeology with HERMES (GALAH) and the Gaia European Southern Observatory survey (Gaia-ESO), will represent major milestones in the quest to chemically tag the Galaxy. Yet this technique to reconstruct dispersed coeval stellar groups has remained largely untested until recently. We build on previous work that developed an empirical chemical tagging probability function, which describes the likelihood that two field stars are conatal, that is, they were formed in the same cluster environment. In this work, we perform the first ever blind chemical tagging experiment, i.e. tagging stars with no known or otherwise discernible associations, on a sample of 714 disc field stars with a number of high-quality high-resolution homogeneous metal abundance measurements. We present evidence that chemical tagging of field stars does identify coeval groups of stars, yet these groups may not represent distinct formation sites, e.g. as in dissolved open clusters, as previously thought. Our results point to several important conclusions, among them that group finding will be limited strictly to chemical abundance space, e.g. stellar ages, kinematics, colours, temperature and surface gravity do not enhance the detectability of groups. We also demonstrate that in addition to its role in probing the chemical enrichment and kinematic history of the Galactic disc, chemical tagging represents a powerful new stellar age determination technique.

  16. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    SciTech Connect

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; De Koter, A.; Sana, H.; Gvaramadze, V. V.; Liermann, A.

    2014-01-10

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range

  17. UV light from old stellar populations: the HST and GALEX eyes on globular clusters.

    NASA Astrophysics Data System (ADS)

    Dalessandro, Emanuele

    The UV properties of old stellar populations have been subject of intense scrutiny from the late sixties, when the UV-upturn in early type galaxies was first discovered. Because of their proximity and relative simplicity, Galactic globular clusters (GGCs) are ideal local templates to understand how the integrated UV light is driven by hot stellar populations, primarily horizontal branch stars and their progeny. Our understanding of such stars is still plagued by theoretical uncertainties, which are partly due to the absence of an accurate, comprehensive, statistically representative homogeneous data-set. To move a step forward on this subject, we have combined the HST and GALEX capabilities and collected the largest data-base ever obtained for GGCs in UV. This data-base is best suited to provide insights on the HB second parameter problem and on the first stages of GCs formation and chemical evolution and to understand how they are linked to the observed properties of extragalactic systems.

  18. MEASUREMENT OF THE MASS AND STELLAR POPULATION DISTRIBUTION IN M82 WITH THE LBT

    SciTech Connect

    Greco, Johnny P.; Martini, Paul; Thompson, Todd A.

    2012-09-20

    We present a K-band spectroscopic study of the stellar and gas kinematics, mass distribution, and stellar populations of the archetypical starburst galaxy M82. Our results are based on a single spectrum at a position angle of 67.{sup 0}5 through the K-band nucleus. We used the {sup 12}CO stellar absorption band head at 2.29 {mu}m (CO{sub 2.29}) to measure the rotation curve out to nearly 4 kpc radius on both the eastern and western sides of the galaxy. Our data show that the rotation curve is flat from 1 to 4 kpc. This stands in sharp contrast to some previous studies, which have interpreted H I and CO emission-line position-velocity diagrams as evidence for a declining rotation curve. The kinematics of the Br{gamma}, H{sub 2}, and He I emission lines are consistent with, although characterized by slightly higher velocities than, the stellar kinematics. We derived M82's mass distribution from our stellar kinematic measurements and estimate that its total dynamical mass is {approx}10{sup 10} M{sub Sun }. We measured the equivalent width of CO{sub 2.29} (W{sub 2.29}) as a function of distance from the center of the galaxy to investigate the spatial extent of the red supergiant (RSG) population. The variation in W{sub 2.29} with radius clearly shows that RSGs dominate the light inside 500 pc radius. M82's superwind is likely launched from this region, where we estimate that the enclosed mass is {approx}<2 Multiplication-Sign 10{sup 9} M{sub Sun }.

  19. PRE-MAIN-SEQUENCE STELLAR POPULATIONS ACROSS SHAPLEY CONSTELLATION III. I. PHOTOMETRIC ANALYSIS AND IDENTIFICATION ,

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Henning, Thomas; Da Rio, Nicola; Brandner, Wolfgang; Dolphin, Andrew E.; Robberto, Massimo; Panagia, Nino; Gruendl, Robert A.; Chu, You-Hua; Rosa, Michael; Romaniello, Martino; De Marchi, Guido; Zinnecker, Hans

    2011-09-10

    We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope Wide-Field Planetary Camera 2. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double-Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63, and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.

  20. A census of young stellar populations in the warm ULIRG PKS 1345+12

    NASA Astrophysics Data System (ADS)

    Rodríguez Zaurín, J.; Holt, J.; Tadhunter, C. N.; González Delgado, R. M.

    2007-03-01

    We present a detailed investigation of the young stellar populations (YSP) in the radio-loud ultraluminous infrared galaxy (ULIRG), PKS1345+12 (z = 0.12), based on high-resolution Hubble Space Telescope (HST) imaging and long-slit spectra taken with the William Herschel Telescope (WHT) at La Palma. While the images clearly show bright knots suggestive of super star clusters (SSCs), the spectra reveal the presence of YSP in the diffuse light across the full extent of the halo of the merging double nucleus system. Spectral synthesis modelling has been used to estimate the ages of the YSP for both the SSC and the diffuse light sampled by the spectra. For the SSC, we find ages tSSC < 6Myr with reddenings 0.2 < E(B - V) < 0.5 and masses 106 < MYSPSSC < 107Msolar. In the region to the south of the western nucleus that contains the SSC our modelling of the spectrum of the diffuse light is also consistent with a relatively young age for the YSP (~5Myr), although older YSP ages cannot be ruled out. However, in other regions of the galaxy we find that the spectra of the diffuse light component can only be modelled with a relatively old post-starburst YSP (0.04-1.0Gyr) or with a disc galaxy template spectrum. The results demonstrate the importance of accounting for reddening in photometric studies of SSC and highlight the dangers of focusing on the highest surface brightness regions when trying to obtain a general impression of the star formation activity in the host galaxies of ULIRGs. The case of PKS1345+12 provides clear evidence that the star formation histories of the YSP in ULIRGs are complex. While the SSC represent the vigorous phase of star formation associated with the final stages of the merger, the YSP in the diffuse light are likely to represent star formation in one or more of the merging galaxies at an earlier stage or prior to the start of the merger. Intriguingly, our long-slit spectra show line splitting at the locations of the SSC, indicating that they are

  1. Ages, chemistry, and type 1A supernovae: Clues to the formation of the galactic stellar halo

    NASA Technical Reports Server (NTRS)

    Smecker-Hane, Tammy A.; Wyse, Rosemary F. G.

    1993-01-01

    We endeavor to resolve two conflicting constraints on the duration of the formation of the Galactic stellar halo - 2-3 Gyr age differences in halo stars, and the time scale inferred from the observed constant values of chemical element abundance ratios characteristic of enrichment by Type II supernovae - by investigating the time scale for the onset of Type Ia supernovae (SNIa) in the currently favored progenitor model - mergers of carbon and oxygen white dwarfs (CO WDs).

  2. STELLAR POPULATIONS AND STRUCTURAL PROPERTIES OF ULTRA FAINT DWARF GALAXIES, CANES VENATICI I, BOOeTES I, CANES VENATICI II, AND LEO IV

    SciTech Connect

    Okamoto, Sakurako; Arimoto, Nobuo; Yamada, Yoshihiko; Onodera, Masato

    2012-01-10

    We take deep images of four ultra faint dwarf (UFD) galaxies, Canes Venatici I (CVn I), Booetes I (Booe I), Canes Venatici II (CVn II), and Leo IV, using the Suprime-Cam on the Subaru Telescope. Color-magnitude diagrams (CMDs) extend below main-sequence turnoffs (MSTOs) and yield measurements of the ages of stellar populations. The stellar populations of three faint galaxies, the Booe I, CVn II, and Leo IV dwarf spheroidal galaxies (dSphs), are estimated to be as old as the Galactic globular cluster M92. We confirm that Booe I dSph has no intrinsic color spread in the MSTO and no spatial difference in the CMD morphology, which indicates that Booe I dSph is composed of an old single stellar population. One of the brightest UFDs, CVn I dSph, shows a relatively younger age ({approx}12.6 Gyr) with respect to Booe I, CVn II, and Leo IV dSphs, and the distribution of red horizontal branch (HB) stars is more concentrated toward the center than that of blue HB stars, suggesting that the galaxy contains complex stellar populations. Booe I and CVn I dSphs show the elongated and distorted shapes. CVn II dSph has the smallest tidal radius of a Milky Way satellite and has a distorted shape, while Leo IV dSph shows a less concentrated spherical shape. The simple stellar population of faint UFDs indicates that the gases in their progenitors were removed more effectively than those of brighter dSphs at the occurrence of their initial star formation. This is reasonable if the progenitors of UFDs belong to less massive halos than those of brighter dSphs.

  3. Population II Li-6 as a probe of nucleosynthesis and stellar structure and evolution

    NASA Technical Reports Server (NTRS)

    Steigman, Gary; Fields, Brian D.; Olive, Keith A.; Schramm, David N.; Walker, Terry P.

    1993-01-01

    We discuss the importance of Population II Li-6 as a diagnostic for models of primordial nucleosynthesis, cosmic-ray nucleosyntheses in the early Galaxy, and the structure and evolution of metal-poor solar-type stars. The observation of Li-6 in the subdwarf HD 84937 is shown to be consistent with the existing Population II LiBeB data within the context of a simple three-component model: (1) standard big bang nucleosynthesis, (2) Population II cosmic-ray nucleosynthesis, (3) standard (nonrotating) stellar LiBeB depletion. If this interpretation is correct, we predict a potentially detectable boron abundance for this star: about 2 x 10 exp -12. Subsequent Population II LiBeB observations, and in particular further observations of Population II Li-6, are shown to be crucial to our understanding of the primordial and early galactic creation and destruction mechanisms for light elements.

  4. The aging population: demographics and the biology of aging.

    PubMed

    Kanasi, Eleni; Ayilavarapu, Srinivas; Jones, Judith

    2016-10-01

    Epidemiologic studies show that 11% of the world's population is over 60 years of age; this is projected to increase, by 2050, to 22% of the population. Oral aging is a current focus of several organizations including the Federation Dentaire Internationale, the World Health Organization and the American and Japanese Dental Associations. In their Tokyo Declaration, the Japanese Association identified the elderly population as one of its main target groups. One of the WHO goals is for each person to retain more than 20 teeth by age 80, despite the fact that the prevalence of periodontal disease is continuously rising as the population is aging. Every species has its own characteristic lifespan, which is determined by its evolutionary history and is modified by multiple diverse factors, including biological mechanisms. In humans, the gradual accumulation of products of cellular metabolism and extensive DNA damage contribute to the aging process. Aging is thought to be associated with a low-grade inflammatory phenotype in mammals, called 'inflammaging', and is the result of autophagic capacity impairing so-called 'housekeeping activities' in the cells, resulting in protein aggregation, mitochondrial dysfunction and oxidative stress. Delayed stem-cell proliferation, associated with aging, may impact the maintenance and survival of a living being, but excessive proliferation could also result in depleted reserves of stem cells. Studies are needed to address the association of delayed cell proliferation and wound healing with the onset of periodontal diseases and response to treatment. The effects of systemic diseases, medications, psychological effects and decreased interest or ability in performing oral-hygiene practices are thought to result in periodontal diseases, and ultimately in tooth loss, in aged individuals. Together with an aging population comes a responsibility for 'healthy' and 'successful' aging. This article describes the changing global demographic

  5. Dissecting galaxy triplets in the Sloan Digital Sky Survey Data Release 10 - I. Stellar populations and emission line analysis

    NASA Astrophysics Data System (ADS)

    Costa-Duarte, M. V.; O'Mill, A. L.; Duplancic, F.; Sodré, L.; Lambas, D. G.

    2016-07-01

    We identify isolated galaxy triplets in a volume-limited sample from the Sloan Digital Sky Survey Data Release 10. Our final sample has 80 galaxy systems in the redshift range 0.04 ≤ z ≤ 0.1, brighter than Mr = -20.5 + 5 log h70. Spectral synthesis results and WHAN and BPT diagnostic diagrams were employed to classify the galaxies in these systems as star-forming, active nuclei, or passive/retired. Our results suggest that the brightest galaxies drive the triplet evolution, as evidenced by the strong correlations between properties as mass assembly and mean stellar population age with triplet properties. Galaxies with intermediate luminosity or the faintest one within the triplet seem to play a secondary role. Moreover, the relation between age and stellar mass of galaxies is similar for these galaxies but different for the brightest galaxy in the system. Most of the triplet galaxies are passive or retired, according to the WHAN classification. Low-mass triplets present different fractions of WHAN classes when compared to higher mass triplets. A census of WHAN class combinations shows the dominance of star-forming galaxies in low-mass triplets while retired and passive galaxies prevail in high-mass systems. We argue that these results suggest that the local environment, through galaxy interactions driven by the brightest galaxy, is playing a major role in triplet evolution.

  6. No Evidence for Multiple Stellar Populations in the Low-mass Galactic Globular Cluster E 3

    NASA Astrophysics Data System (ADS)

    Salinas, Ricardo; Strader, Jay

    2015-08-01

    Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M˜ 1.4× {10}4 {M}⊙ ) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found. Based on observations obtained at the Southern Astrophysical Research (SOAR) Telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  7. Did globular clusters contribute to the stellar population of the Galactic halo?

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Krause, Martin

    2016-08-01

    The origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

  8. THE INTRIGUING STELLAR POPULATIONS IN THE GLOBULAR CLUSTERS NGC 6388 AND NGC 6441

    SciTech Connect

    Bellini, A.; Anderson, J.; Piotto, G.; Nardiello, D.; Milone, A. P.; King, I. R.; Renzini, A.; Bedin, L. R.; Cassisi, S.; Pietrinferni, A.; Sarajedini, A.

    2013-03-01

    NGC 6388 and NGC 6441 are two massive Galactic bulge globular clusters that share many properties, including the presence of an extended horizontal branch (HB), quite unexpected because of their high metal content. In this paper we use Hubble Space Telescope's WFPC2, ACS, and WFC3 images and present a broad multicolor study of their stellar content, covering all main evolutionary branches. The color-magnitude diagrams (CMDs) give compelling evidence that both clusters host at least two stellar populations, which manifest themselves in different ways. NGC 6388 has a broadened main sequence (MS), a split sub-giant branch (SGB), and a split red giant branch (RGB) that becomes evident above the HB in our data set; its red HB is also split into two branches. NGC 6441 has a split MS, but only an indication of two SGB populations, while the RGB clearly splits in two from the SGB level upward, and no red HB structure. The multicolor analysis of the CMDs confirms that the He difference between the two main stellar populations in the two clusters must be similar. This is observationally supported by the HB morphology, but also confirmed by the color distribution of the stars in the MS optical band CMDs. However, a MS split becomes evident in NGC 6441 using UV colors, but not in NGC 6388, indicating that the chemical patterns of the different populations are different in the two clusters, with C, N, and O abundance differences likely playing a major role. We also analyze the radial distribution of the two populations.

  9. Stellar age spreads in clusters as imprints of cluster-parent clump densities

    SciTech Connect

    Parmentier, G.; Grebel, E. K.; Pfalzner, S.

    2014-08-20

    It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, ε{sub ff}, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our model predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: ε{sub ff} = 0.1 and ε{sub ff} = 0.01. When ε{sub ff} = 0.1, the half-life time is of the order of the clump free-fall time, τ{sub ff}. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τ{sub ff}, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star

  10. Stellar Age Spreads in Clusters as Imprints of Cluster-parent Clump Densities

    NASA Astrophysics Data System (ADS)

    Parmentier, G.; Pfalzner, S.; Grebel, E. K.

    2014-08-01

    It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, epsilonff, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our model predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: epsilonff = 0.1 and epsilonff = 0.01. When epsilonff = 0.1, the half-life time is of the order of the clump free-fall time, τff. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τff, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star-forming regions

  11. The progenitors of local ultra-massive galaxies across cosmic time: from dusty star-bursting to quiescent stellar populations

    SciTech Connect

    Marchesini, Danilo; Marsan, Cemile Z.; Muzzin, Adam; Franx, Marijn; Stefanon, Mauro; Brammer, Gabriel G.; Vulcani, Benedetta; Fynbo, J. P. U.; Milvang-Jensen, Bo; Dunlop, James S.; Buitrago, Fernando

    2014-10-10

    Using the UltraVISTA catalogs, we investigate the evolution in the 11.4 Gyr since z = 3 of the progenitors of local ultra-massive galaxies (log (M {sub star}/M {sub ☉}) ≈ 11.8; UMGs), providing a complete and consistent picture of how the most massive galaxies at z = 0 have assembled. By selecting the progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56{sub −0.25}{sup +0.35} dex, 0.45{sub −0.20}{sup +0.16} dex, and 0.27{sub −0.12}{sup +0.08} dex from z = 3, z = 2, and z = 1, respectively, to z = 0. At z < 1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At z > 1, the contribution from star-forming galaxies progressively increases, with the progenitors at 2 < z < 3 being dominated by massive (M {sub star} ≈ 2 × 10{sup 11} M {sub ☉}), dusty (A {sub V} ∼ 1-2.2 mag), star-forming (SFR ∼ 100-400 M {sub ☉} yr{sup –1}) galaxies with a large range in stellar ages. At z = 2.75, ∼15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that at least half of the stellar content of local UMGs was assembled at z > 1, whereas the remaining was assembled via merging from z ∼ 1 to the present. Most of the quenching of the star-forming progenitors happened between z = 2.75 and z = 1.25, in good agreement with the typical formation redshift and scatter in age of z = 0 UMGs as derived from their fossil records. The progenitors of local UMGs, including the star-forming ones, never lived on the blue cloud since z = 3. We propose an alternative path for the formation of local UMGs that refines previously proposed pictures and that is fully consistent with our findings.

  12. Core-halo age gradients and star formation in the Orion Nebula and NGS 2024 young stellar clusters

    SciTech Connect

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

    2014-06-01

    We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age{sub JX} , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age{sub JX} estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  13. A LARGE STELLAR EVOLUTION DATABASE FOR POPULATION SYNTHESIS STUDIES. VI. WHITE DWARF COOLING SEQUENCES

    SciTech Connect

    Salaris, M.; Cassisi, S.; Pietrinferni, A.; Kowalski, P. M.; Isern, J. E-mail: cassisi@oa-teramo.inaf.i

    2010-06-20

    We present a new set of cooling models and isochrones for both H- and He-atmosphere white dwarfs (WDs), incorporating accurate boundary conditions from detailed model atmosphere calculations, and carbon-oxygen chemical abundance profiles based on updated stellar evolution calculations from the BaSTI stellar evolution archive-a theoretical data center for the Virtual Observatory. We discuss and quantify the uncertainties in the cooling times predicted by the models, arising from the treatment of mixing during the central H- and He-burning phases, the number of thermal pulses experienced by the progenitors, progenitor metallicity, and the {sup 12}C({alpha}, {gamma}){sup 16}O reaction rate. The largest sources of uncertainty turn out to be related to the treatment of convection during the last stages of the progenitor central He-burning phase and the {sup 12}C({alpha}, {gamma}){sup 16}O reaction rate. We compare our new models to previous calculations performed with the same stellar evolution code, and discuss their application to the estimate of the age of the solar neighborhood and the interpretation of the observed number ratios between H- and He-atmosphere WDs. The new WD sequences and an extensive set of WD isochrones that cover a large range of ages and progenitor metallicities are made publicly available at the official BaSTI Web site.

  14. How good a clock is rotation? The stellar rotation-mass-age relationship for old field stars

    SciTech Connect

    Epstein, Courtney R.; Pinsonneault, Marc H. E-mail: pinsono@astronomy.ohio-state.edu

    2014-01-10

    The rotation-mass-age relationship offers a promising avenue for measuring the ages of field stars, assuming the attendant uncertainties to this technique can be well characterized. We model stellar angular momentum evolution starting with a rotation distribution from open cluster M37. Our predicted rotation-mass-age relationship shows significant zero-point offsets compared to an alternative angular momentum loss law and published gyrochronology relations. Systematic errors at the 30% level are permitted by current data, highlighting the need for empirical guidance. We identify two fundamental sources of uncertainty that limit the precision of rotation-based ages and quantify their impact. Stars are born with a range of rotation rates, which leads to an age range at fixed rotation period. We find that the inherent ambiguity from the initial conditions is important for all young stars, and remains large for old stars below 0.6 M {sub ☉}. Latitudinal surface differential rotation also introduces a minimum uncertainty into rotation period measurements and, by extension, rotation-based ages. Both models and the data from binary star systems 61 Cyg and α Cen demonstrate that latitudinal differential rotation is the limiting factor for rotation-based age precision among old field stars, inducing uncertainties at the ∼2 Gyr level. We also examine the relationship between variability amplitude, rotation period, and age. Existing ground-based surveys can detect field populations with ages as old as 1-2 Gyr, while space missions can detect stars as old as the Galactic disk. In comparison with other techniques for measuring the ages of lower main sequence stars, including geometric parallax and asteroseismology, rotation-based ages have the potential to be the most precise chronometer for 0.6-1.0 M {sub ☉} stars.

  15. Understanding the formation and evolution of early-type galaxies based on newly developed single-burst stellar population synthesis models in the infrared

    NASA Astrophysics Data System (ADS)

    Roeck, Benjamin

    2015-12-01

    The detailed study of the different stellar populations which can be observed in galaxies is one of the most promising methods to shed light on the evolutionary histories of galaxies. So far, stellar population analysis has been carried out mainly in the optical wavelength range. The infrared spectral range, on the other hand, has been poorly studied so far, although it provides very important insights, particularly into the cooler stellar populations which are present in galaxies. However, in the last years, space telescopes like the Spitzer Space Telescope or the Wide-field Infrared Survey Explorer and instruments like the spectrograph X-Shooter on the Very Large Telescope have collected more and more photometric and spectroscopic data in this wavelength range. In order to analyze these observations, it is necessary to dispose of reliable and accurate stellar population models in the infrared. Only a small number of stellar population models in the infrared exist in the literature. They are mostly based on theoretical stellar libraries and very often cover only the near-infrared wavelength range at a rather low resolution. Hence, we developed new single-burst stellar population models between 8150 and 50000Å which are exclusively based on 180 spectra from the empirical Infrared Telescope Facility stellar library. We computed our single stellar population models for two different sets of isochrones and various types of initial mass functions of different slopes. Since the stars of the Infrared Telescope Facility library present only a limited coverage of the stellar atmospheric parameter space, our models are of sufficient quality only for ages larger than 1 Gyr and metallicities between [Fe/H] = 0.40 and 0.26. By combining our single stellar population models in the infrared with the extended medium-resolution Isaac Newton Telescope library of empirical spectra in the optical spectral range, we created the first single stellar population models covering the

  16. SOME MACROECONOMIC ASPECTS OF GLOBAL POPULATION AGING*

    PubMed Central

    LEE, RONALD; MASON, ANDREW

    2012-01-01

    Across the demographic transition, declining mortality followed by declining fertility produces decades of rising support ratios as child dependency falls. These improving support ratios raise per capita consumption, other things equal, but eventually deteriorate as the population ages. Population aging and the forces leading to it can produce not only frightening declines in support ratios but also very substantial increases in productivity and per capita income by raising investment in physical and human capital. Longer life, lower fertility, and population aging all raise the demand for wealth needed to provide for old-age consumption. This leads to increased capital per worker even as aggregate saving rates fall. However, capital per worker may not rise if the increased demand for wealth is satisfied by increased familial or public pension transfers to the elderly. Thus, institutions and policies matter for the consequences of population aging. The accumulation of human capital also varies across the transition. Lower fertility and mortality are associated with higher human capital investment per child, also raising labor productivity. Together, the positive changes due to human and physical capital accumulation will likely outweigh the problems of declining support ratios. We draw on estimates and analyses from the National Transfer Accounts project to illustrate and quantify these points. PMID:21302431

  17. Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

    NASA Astrophysics Data System (ADS)

    Barnes, S. A.; Spada, F.; Weingrill, J.

    2016-09-01

    Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

  18. Kinematics and stellar populations of low-luminosity early-type galaxies in the Abell 496 cluster

    NASA Astrophysics Data System (ADS)

    Chilingarian, I. V.; Cayatte, V.; Durret, F.; Adami, C.; Balkowski, C.; Chemin, L.; Laganá, T. F.; Prugniel, P.

    2008-07-01

    Context: The morphology and stellar populations of low-luminosity early-type galaxies in clusters have until now been limited to a few relatively nearby clusters such as Virgo or Fornax. Scenarii for the formation and evolution of dwarf galaxies in clusters are therefore not well constrained. Aims: We investigate here the morphology and stellar populations of low-luminosity galaxies in the relaxed richness class 1 cluster Abell 496 (z = 0.0330). Methods: Deep multiband imaging obtained with the CFHT Megacam allowed us to select a sample of faint galaxies, defined here as objects with magnitudes 18 < r' < 22 mag within a 1.2 arcsec fibre (-18.8 < MB < -15.1 mag). We observed 118 galaxies spectroscopically with the ESO VLT FLAMES/Giraffe spectrograph with a resolving power R = 6300. We present structural analysis and colour maps for the 48 galaxies belonging to the cluster. We fit the spectra of 46 objects with PEGASE.HR synthetic spectra to estimate the ages, metallicities, and velocity dispersions. We estimated possible biases by similarly analysing spectra of ~1200 early-type galaxies from the Sloan Digital Sky Survey Data Release 6 (SDSS DR6). We computed values of α/Fe abundance ratios from the measurements of Lick indices. We briefly discuss effects of the fixed aperture size on the measurements. Results: For the first time, high-precision estimates of stellar population properties have been obtained for a large sample of faint galaxies in a cluster, allowing for the extension of relations between stellar populations and internal kinematics to the low-velocity dispersion regime. We have revealed a peculiar population of elliptical galaxies in the core of the cluster, resembling massive early-type galaxies by their stellar population properties and velocity dispersions, but having luminosities of about 2 mag fainter. Conclusions: External mechanisms of gas removal (ram pressure stripping and gravitational harassment) are more likely to have occurred than

  19. STELLAR POPULATIONS OF Ly{alpha} EMITTERS AT z = 4.86: A COMPARISON TO z {approx} 5 LYMAN BREAK GALAXIES

    SciTech Connect

    Yuma, Suraphong; Ohta, Kouji; Yabe, Kiyoto; Shimasaku, Kazuhiro; Yoshida, Makiko; Ouchi, Masami; Iwata, Ikuru; Sawicki, Marcin

    2010-09-10

    We present a study of a stellar population of Ly{alpha} emitters (LAEs) at z = 4.86 in the Great Observatories Origins Deep Survey North (GOODS-N) field and its flanking field. The LAEs are selected based on optical narrowband (NB711) and broadband (V, I{sub c} , and z') observations by the Suprime-Cam attached to the Subaru Telescope. With the publicly available Infrared Array Camera (IRAC) data in GOODS-N and further IRAC observations in the flanking fields, we select five LAEs that are not contaminated by neighboring objects in IRAC images and construct their observed spectral energy distributions (SEDs) with I{sub c} , z', IRAC 3.6 {mu}m, and 4.5 {mu}m band photometries. The SEDs cover the rest-frame UV-to-optical wavelengths. We derive the stellar masses, ages, color excesses, and star formation rates (SFRs) of the five LAEs using an SED fitting method. Assuming a constant star formation history, we find that the stellar masses range from 10{sup 8} to 10{sup 10} M {sub sun} with the median value of 2.5 x 10{sup 9} M{sub sun}. The derived ages range from very young (7.4 Myr) to 437 Myr, with a median age of 25 Myr. The color excess E(B - V) is between 0.1and0.4 mag. SFRs are 55-209 M{sub sun} yr{sup -1}. A comparison of the stellar populations is made between 3 LAEs and 88 Lyman break galaxies (LBGs) selected at the same redshift, in the same observed field, and down to the same limit of the rest-frame UV luminosity. These three LAEs are the brightest and reddest samples of all the LAE samples at z = 4.86. The LAEs are distributed at the relatively faint part of the UV-luminosity distribution of LBGs. Deriving the stellar properties of the LBGs by fitting their SEDs with the same model ensures that model difference does not affect the comparison. It is found that the stellar properties of the LAEs are located in the region where the properties of LBGs are distributed. On average, the LAEs show less dust extinction and lower SFRs than LBGs, while the stellar

  20. Walter Baade: Father of the Two Stellar Populations and Pioneer Supernova Researcher

    NASA Astrophysics Data System (ADS)

    Osterbrock, D. E.

    2001-05-01

    Walter Baade was the great observational astronomer of the middle part of the past century. He lived and worked in Pasadena, where he ``discovered" the two stellar populations and did outstanding pioneer research on supernovae at Mount Wilson and Palomar Observatories from 1931 until 1959, when he returned to his native Germany, and died the following year. Baade was born in a little town in northwest Germany, and educated at Goettingen University, where he received his Ph.D. in 1919, just after the end of World War I. He got a research position at Hamburg Observatory, and quickly jumped into globular cluster and galactic structure work with its 40-in reflector, then the largest telescope in Europe. Baade recognized very early the great importance of the extremely rare ``highly luminous novae" which Heber D. Curtis and Knut Lundmark isolated in 1919-21. In 1929 Baade called these ``Hauptnovae" the key to measuring distances of faint galaxies. We call them supernovae today, a term he and Fritz Zwicky began using in 1932. Similarly Baade's first inkling that there was a spherically symmetric distribution of stars in our Galaxy, which he named Population II in his two great 1944 papers, came when he began picking up field RR Lyrae variables in 1926. Baade's research on the two stellar populations and supernovae was extremely important in opening up the whole fields of stellar and galactic evolution. His invited lectures at meetings and symposia, and his courses as a visiting professor inspired a whole generation of research astrophysicists. Baade's attractive personality made it possible for him to make his great discoveries in a land in which he was officially an enemy alien during World War II.

  1. Nitrogen abundances and multiple stellar populations in the globular clusters of the Fornax dSph

    SciTech Connect

    Larsen, Søren S.; Strader, Jay

    2014-12-10

    We use measurements of nitrogen abundances in red giants to search for multiple stellar populations in the four most metal-poor globular clusters (GCs) in the Fornax dwarf spheroidal galaxy (Fornax 1, 2, 3, and 5). New imaging in the F343N filter, obtained with the Wide Field Camera 3 on the Hubble Space Telescope, is combined with archival F555W and F814W observations to determine the strength of the NH band near 3370 Å. After accounting for observational errors, the spread in the F343N-F555W colors of red giants in the Fornax GCs is similar to that in M15 and corresponds to an abundance range of Δ[N/Fe] ∼ 2 dex, as observed also in several Galactic GCs. The spread in F555W-F814W is, instead, fully accounted for by observational errors. The stars with the reddest F343N-F555W colors (indicative of N-enhanced composition) have more centrally concentrated radial distributions in all four clusters, although the difference is not highly statistically significant within any individual cluster. From double-Gaussian fits to the color distributions, we find roughly equal numbers of 'N-normal' and 'N-enhanced' stars (formally ∼40% N-normal stars in Fornax 1, 3, and 5 and ∼60% in Fornax 2). We conclude that GC formation, in particular, regarding the processes responsible for the origin of multiple stellar populations, appears to have operated similarly in the Milky Way and in the Fornax dSph. Combined with the high ratio of metal-poor GCs to field stars in the Fornax dSph, this places an important constraint on scenarios for the origin of multiple stellar populations in GCs.

  2. Using narrow-band J-PAS photometry to assess the properties of the stellar population in galaxies

    NASA Astrophysics Data System (ADS)

    Bruzual, Gustavo; Mejia-Narvaez, Alfredo; Magris C., Gladis

    2015-08-01

    We study the uncertainties and biases on the properties of the stellar population content of galaxies retrieved from narrow-band (J-PAS) photometry using the non-parametric method of spectral fitting dubbed DynBaS. We construct a star formation history library à la Chen et al. (2012), and then SED-fit a selection of synthetic spectra with observational properties similar to SDSS galaxies. We confront the results obtained from the photometric fits to those obtained from spectroscopic data for synthetic and real galaxies at various redshift ranges. Since no assumption on the star formation history is made, the so called template mismatch biases are naturally overcome. We find that biases in our estimations are the consequence of the several degeneracies between mass, age, metallicity, and internal dust extinction present in galaxy properties.

  3. The economics of population aging in China.

    PubMed

    Yu, X

    1996-01-01

    This article relies on a Marxist framework for discussing the relationship between economic development and population aging in China. China places value on correctly understanding the causes, processes, trends, and socioeconomic consequences of population aging during the development of its socialist market economy. Many policies have an impact on the aged. Marxist theories of economic operations identify four key features--production, distribution, exchange, and consumption--which are affected by human activity. The age structure of population affects socioeconomic operations. An increase in accumulated capital means a decrease in consumption capital. China must maintain its high level of annual economic growth (6.0%-6.5%). 30% of China's national income must be used for accumulation of capital and investment, but the increase in the aged has led to growth in consumption capital. By 2050, it is expected that there will be over 100 million retirees needing about 800 billion RMB in pensions (20 times the amount in 1993). As the number of elderly grows, savings decline. The growth of the elderly will place demands on social security funds, which will in turn rely on an increased proportion of consumption capital. The increased labor force and the increased number of aged will both vie for a share in the national economy until about 2020, and then the problem will be declines in productivity in some areas. It is generally believed that support of the elderly should not rise above 10% of national income. In 1993, the elderly's share was 3.7%, and at the present rate of growth, it is expected that the share will be above 10% by 2030. Working families will have to carry a heavy domestic burden of care for their aged. Productivity will have to increase in order to offset the decline in per capita consumption capital due to aging. The author offers countermeasures at the macro- and microlevel for dealing with the demographic changes.

  4. Transition of the stellar initial mass function explored using binary population synthesis

    NASA Astrophysics Data System (ADS)

    Suda, Takuma; Komiya, Yutaka; Yamada, Shimako; Katsuta, Yutaka; Aoki, Wako; Gil-Pons, Pilar; Doherty, Carolyn L.; Campbell, Simon W.; Wood, Peter R.; Fujimoto, Masayuki Y.

    2013-05-01

    The stellar initial mass function (IMF) plays a crucial role in the determination of the number of surviving stars in galaxies, of the chemical composition of the interstellar medium and of the distribution of light in galaxies. A key unsolved question is whether the IMF is universal in time and space. Here, we use the state-of-the-art results of stellar evolution to show that the IMF of our Galaxy made a transition from an IMF dominated by massive stars to the present-day IMF at an early phase of the Galaxy formation. Updated results from stellar evolution in a wide range of metallicities have been implemented in a binary population synthesis code, and compared with the observations of carbon-enhanced metal-poor (CEMP) stars in our Galaxy. We find that the application of the present-day IMF to Galactic halo stars causes serious contradictions with four observable quantities connected with the evolution of asymptotic giant branch (AGB) stars. Furthermore, a comparison between our calculations and the observations of CEMP stars might help us to constrain the transition metallicity for the IMF, which we tentatively set at [Fe/H] ≈-2. A novelty of the current study is the inclusion of mass-loss suppression in intermediate-mass AGB stars at low metallicity. This significantly reduces the overproduction of nitrogen-enhanced stars, which was a major problem in previous studies when using the IMF dominated by high-mass stars. Our results also demonstrate that the use of the present-day IMF for all time in chemical evolution models results in the overproduction of Type I.5 supernovae. More data on stellar abundances will help us to understand how the IMF has changed, and what caused such a transition.

  5. Binaries, cluster dynamics and population studies of stars and stellar phenomena

    NASA Astrophysics Data System (ADS)

    Vanbeveren, Dany

    2005-10-01

    The effects of binaries on population studies of stars and stellar phenomena have been investigated over the past 3 decades by many research groups. Here we will focus mainly on the work that has been done recently in Brussels and we will consider the following topics: the effect of binaries on overall galactic chemical evolutionary models and on the rates of different types of supernova, the population of point-like X-ray sources where we distinguish the standard high mass X-ray binaries and the ULXs, a UFO-scenario for the formation of WR+OB binaries in dense star systems. Finally we critically discuss the possible effect of rotation on population studies.

  6. The nature of the red disc-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations

    NASA Astrophysics Data System (ADS)

    Pierini, D.; Maraston, C.; Gordon, K. D.; Witt, A. N.

    2005-10-01

    We investigate which conditions of dust attenuation and stellar populations allow models of dusty, continuously star-forming, bulge-less disc galaxies at 0.8 <~z<~ 3.2 to meet the different colour selection criteria of high-z`red' galaxies (e.g. RC-K > 5.3, IC-K > 4, J-K > 2.3). As a main novelty, we use stellar population models that include the thermally pulsating asymptotic giant branch (TP-AGB) phase of stellar evolution. The star formation rate of the models declines exponentially as a function of time, the e-folding time being longer than 3 Gyr. In addition, we use calculations of radiative transfer of the stellar and scattered radiation through different dusty interstellar media in order to explore the wide parameter space of dust attenuation. We find that synthetic discs can exhibit red optical/near-infrared colours because of reddening by dust, but only if they have been forming stars for at least ~1 Gyr. Extremely few models barely exhibit RC-K > 5.3, if the inclination i= 90° and if the opacity 2 ×τV>~ 6. Hence, RC-K-selected galaxies at 1 <~z<~ 2 most probably are either systems with an old, passively evolving bulge or starbursts. Synthetic discs at 1 <~z<~ 2 exhibit 4 < IC-K < 4.8, if they are seen edge on (i.e. at i~ 90°) and if 2 ×τV>~ 0.5. This explains the large fraction of observed, edge-on disc-like galaxies with Ks < 19.5 and F814W-Ks>~ 4. Finally, models with 2 <~z<~ 3.2 exhibit 2.3 < J-K < 3, with no bias towards i~ 90° and for a large range in opacity (e.g. 2 ×τV > 1 for i~ 70°). In conclusion, red disc-like galaxies at 0.8 <~z<~ 3.2 may not necessarily be dustier than nearby disc galaxies (with 0.5 <~ 2 ×τV<~ 2) and/or much older than ~1 Gyr. This result is due both to a realistic description of dust attenuation and to the emission contribution by TP-AGB stars, with ages of 0.2 to 1-2 Gyr and intrinsically red colours.

  7. Population ageing: what should we worry about?

    PubMed Central

    Turner, Adair

    2009-01-01

    Approximately half the world's population now has replacement-level fertility or below. The UK experience in accommodating to a changing dependency ratio provides some generalizable insights. A mechanistic approach assuming a fixed retirement age and a need to raise fertility or increase immigration in order to maintain pensions at a fixed proportion of the gross domestic product (GDP) is overstated and wrong. It needs to be replaced by a welfare optimizing model, which takes into account the increasing years of healthy life, a slow rise in the pensionable age, capital inheritance and wider welfare considerations of population density that are not reflected in GDP measures. A combined replacement ratio (CRR) is suggested for developed countries combining the impact of the fertility rate and immigration rate. A CRR above 2 implies continued population growth. The current UK CRR of 2.48 is higher than needed for pension reasons, and it is suggested that it exceeds the welfare maximizing level. PMID:19770152

  8. ASTEROSEISMIC CLASSIFICATION OF STELLAR POPULATIONS AMONG 13,000 RED GIANTS OBSERVED BY KEPLER

    SciTech Connect

    Stello, Dennis; Bedding, Timothy R.; Benomar, Othman; White, Timothy R.; Huber, Daniel; Bildsten, Lars; Paxton, Bill; Elsworth, Yvonne P.; Gilliland, Ronald L.; Mosser, Benoit

    2013-03-10

    Of the more than 150,000 targets followed by the Kepler Mission, about 10% were selected as red giants. Due to their high scientific value, in particular for Galaxy population studies and stellar structure and evolution, their Kepler light curves were made public in late 2011. More than 13,000 (over 85%) of these stars show intrinsic flux variability caused by solar-like oscillations making them ideal for large-scale asteroseismic investigations. We automatically extracted individual frequencies and measured the period spacings of the dipole modes in nearly every red giant. These measurements naturally classify the stars into various populations, such as the red giant branch, the low-mass (M/M{sub Sun} {approx}< 1.8) helium-core-burning red clump, and the higher-mass (M/M{sub Sun} {approx}> 1.8) secondary clump. The period spacings also reveal that a large fraction of the stars show rotationally induced frequency splittings. This sample of stars will undoubtedly provide an extremely valuable source for studying the stellar population in the direction of the Kepler field, in particular when combined with complementary spectroscopic surveys.

  9. Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at Z approx. 2

    NASA Technical Reports Server (NTRS)

    Tease, Katherine Whitaker; VanDokkum, Pieter G.; Brammer, Gabriel; Momcheva, Ivelina G.; Skelton, Rosalind; Franx, Marijn; Kriek, Mariska; Labbe, Ivo; Fumagalli, Mattia; Lundgren, Britt F.; Nelson, Erica J.; Patel, Shannon G.; Rix, Hans-Walter

    2013-01-01

    Quiescent galaxies at zeta approximately 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 less than z less than 2.2 from the 3D-HST grism survey. In addition to H(Beta) (lambda 4861 Angstroms), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (lambda 4304 Angstroms), Mg I (lambda 5175 Angstroms), and Na i (lambda 5894 Angstroms). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approximately 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3(+0.1/-0.3) Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6(+0.5/-0.4) Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9(+0.2/-0.1) Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and Hß emission. Interestingly, this emission is more centrally concentrated than the continuum with L(sub OIII) = 1.7 +/- 0.3 × 10(exp 40 erg s-1, indicating residual central star formation or nuclear activity.

  10. Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies With Relatively Old Stellar Populations at z Approx. 2

    NASA Technical Reports Server (NTRS)

    Tease, Katherine Whitaker; vanDokkum, Pieter G.; Brammer, Gabriel; Momcheva, Ivelina; Skelton, Rosalind; Franx, Marijin; Kriek, Mariska; Labbe, Ivo; Fumagalli, Mattia; Lundgren, Britt F.; Nelson, Erica J.; Patel, Shannon G.; Rix, Hans-Walter

    2013-01-01

    Quiescent galaxies at z approx. 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 < z < 2.2 from the 3D-HST grism survey. In addition to H (4861 ),we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (4304 ),Mgi (5175 ), and Na i (5894 ). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approx. 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3+0.10.3 Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80 of galaxies are dominated by metal lines and have a relatively old mean age of 1.6+0.50.4 Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9+0.20.1 Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O iii] and H emission. Interestingly, this emission is more centrally concentrated than the continuum with LOiii = 1.7+/- 0.3 x 10(exp 40) erg/s, indicating residual central star formation or nuclear activity.

  11. QUIESCENT GALAXIES IN THE 3D-HST SURVEY: SPECTROSCOPIC CONFIRMATION OF A LARGE NUMBER OF GALAXIES WITH RELATIVELY OLD STELLAR POPULATIONS AT z {approx} 2

    SciTech Connect

    Whitaker, Katherine E.; Van Dokkum, Pieter G.; Momcheva, Ivelina G.; Skelton, Rosalind; Nelson, Erica J.; Brammer, Gabriel; Franx, Marijn; Labbe, Ivo; Fumagalli, Mattia; Patel, Shannon G.; Kriek, Mariska; Lundgren, Britt F.; Rix, Hans-Walter

    2013-06-20

    Quiescent galaxies at z {approx} 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 < z < 2.2 from the 3D-HST grism survey. In addition to H{beta} ({lambda}4861 A), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band ({lambda}4304 A), Mg I ({lambda}5175 A), and Na I ({lambda}5894 A). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was {approx}3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3{sup +0.1}{sub -0.3} Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6{sup +0.5}{sub -0.4} Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9{sup +0.2}{sub -0.1} Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and H{beta} emission. Interestingly, this emission is more centrally concentrated than the continuum with L{sub OIII}=1.7{+-}0.3 Multiplication-Sign 10{sup 40} erg s{sup -1}, indicating residual central star formation or nuclear activity.

  12. Predicting Intrinsic mid-IR to optical flux ratios for galaxies of different types using Spectral Synthesis Models of Composite Stellar Populations

    NASA Astrophysics Data System (ADS)

    Kim, Duho; Jansen, Rolf A.; Windhorst, Rogier A.

    2016-01-01

    We analyze the intrinsic flux ratios of simple and composite stellar populations for various visible--near-infrared filters with respect to ˜3.5μm (L-band), and their dependence on metallicity, star-formation history, and effective mean age. This study is motivated by the fact that light from galaxies is reddened and attenuated by dust via scattering and absorption, where different sightlines across the face of a galaxy suffer various amounts of extinction. Ignoring the effects of this extinction could lead one to infer lower stellar mass, and SFR, or higher metallicity. Tamura et al. (2009) developed an approximate method, dubbed the "βV" method, which corrects for dust-extinction on a pixel-by-pixel basis, by comparing the observed flux ratio and empirical estimate of the intrinsic flux ratio of optical and ˜3.5μm broadband data. Here, we aim to validate and test the limits of the βV method for various filters spanning the visible through near-infrared wavelength range. Through extensive modeling, we test their assumptions for the intrinsic flux ratios for a wide variety of simple and composite stellar populations. We build spectral energy distributions (SEDs) of simple stellar populations (SSPs), by adopting Starburst99 and BC03 models for young (<9Myr) and old (>100Myr) stellar populations, respectively, and linear combinations of these for intermediate ages. We then construct composite stellar population (CSP) SEDs by combining SSP SEDs for various realistic star-formation histories (SFHs). We convolve filter response curves of visible--near-infrared filters for HST imaging surveys and mid-infrared filters in current (WISE, Spitzer/IRAC) and near-future use (JWST/NIRCam) with each model SED, to obtain intrinsic flux ratios (βλ,0). We find that βNIR,0 is only varying slightly as a function of metallicity but is insensitive to SFH or redshift (z≤2). We also find a narrow range of βV,0 (0.7+0.05-0.08) for early Hubble type galaxies (E and S0) using

  13. Stellar Populations in the Kepler and K2 fields: APOGEE-KASC Collaboration

    NASA Astrophysics Data System (ADS)

    Johnson, Jennifer; APOKASC Collaboration

    2016-01-01

    The age distribution, both absolute and relative, of stars throughout the Milky Way reveals the history of star formation and migration and is a key constraint on galaxy formation models. The combination of spectroscopic and asteroseismic information for stars observed by both the APOGEE survey and the Kepler/K2 missions provides ages for field red giants along many lines of sight through the Galaxy. The fundamental stellar properties derived from these data are used to test theories of the formation of the thin and thick disks, the role of radial migration, and the timescales for nucleosynthesis in our Galaxy. We also explore correlations between asteroseismic mass and spectroscopic abundances, with a view towards age calibrations for large current and future spectroscopic surveys.

  14. STELLAR POPULATIONS OF ULTRAVIOLET-SELECTED ACTIVE GALACTIC NUCLEI HOST GALAXIES AT z {approx} 2-3

    SciTech Connect

    Hainline, Kevin N.; Shapley, Alice E.; Greene, Jenny E.; Steidel, Charles C.; Reddy, Naveen A.; Erb, Dawn K.

    2012-11-20

    We use stellar population synthesis modeling to analyze the host-galaxy properties of a sample of 33 UV-selected, narrow-lined active galactic nuclei (AGNs) at z {approx} 2-3. In order to quantify the contribution of AGN emission to host galaxy broadband spectral energy distributions (SEDs), we use the subsample of 11 AGNs with photometric coverage spanning from rest-frame UV through near-IR wavelengths. Modeling the SEDs of these objects with a linear combination of stellar population and AGN templates, we infer the effect of the AGN on derived stellar population parameters. We also estimate the typical bias in derived stellar populations for AGNs lacking rest-frame near-IR wavelength coverage, and develop a method for inferring the true host-galaxy properties. We compare AGN host-galaxy properties to those of a sample of UV-selected, star-forming non-AGNs in the same redshift range, including a subsample carefully matched in stellar mass. Although the AGNs have higher masses and star-formation rates than the full non-active sample, their stellar population properties are consistent with those of the mass-selected sample, suggesting that the presence of an AGN is not connected with the cessation of star formation activity in star-forming galaxies at z {approx} 2-3. We suggest that a correlation between M {sub BH} and galaxy stellar mass is already in place at this epoch. Assuming a roughly constant Eddington ratio for AGNs at all stellar masses, we are unable to detect the AGNs in low-mass galaxies because they are simply too faint.

  15. The young stellar population in the Serpens Cloud Core: An ISOCAM survey

    NASA Astrophysics Data System (ADS)

    Kaas, A. A.; Olofsson, G.; Bontemps, S.; André, P.; Nordh, L.; Huldtgren, M.; Prusti, T.; Persi, P.; Delgado, A. J.; Motte, F.; Abergel, A.; Boulanger, F.; Burgdorf, M.; Casali, M. M.; Cesarsky, C. J.; Davies, J.; Falgarone, E.; Montmerle, T.; Perault, M.; Puget, J. L.; Sibille, F.

    2004-07-01

    We present results from an ISOCAM survey in the two broad band filters LW2 (5-8.5 μm) and LW3 (12-18 μm) of a 0.13 square degree coverage of the Serpens Main Cloud Core. A total of 392 sources were detected in the 6.7 μm band and 139 in the 14.3 μm band to a limiting sensitivity of ˜2 mJy. We identified 53 Young Stellar Objects (YSOs) with mid-IR excess from the single colour index [14.3/6.7], and 8 additional YSOs from the H-K/K-m6.7 diagram. Only 32 of these 61 sources were previously known to be YSO candidates. Only about 50% of the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the 48 square arcmin field covering the central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10 times larger than in other young embedded clusters such as ρ Ophiuchi or Chamaeleon. The mid-IR fluxes of the Class I and flat-spectrum sources are found to be on the average larger than those of Class II sources. Stellar luminosities are estimated for the Class II sample, and its luminosity function is compatible with a coeval population of about 2 Myr which follows a three segment power-law IMF. For this age about 20% of the Class IIs are found to be young brown dwarf candidates. The YSOs are in general strongly clustered, the Class I sources more than the Class II sources, and there is an indication of sub-clustering. The sub-clustering of the protostar candidates has a spatial scale of 0.12 pc. These sub-clusters are found along the NW-SE oriented ridge and in very good agreement with the location of dense cores traced by millimeter data. The smallest clustering scale for the Class II sources is about 0.25 pc, similar to what was found for ρ Ophiuchi. Our data show evidence that star formation in Serpens has proceeded in several phases, and that a ``microburst'' of star formation has taken place very recently, probably within the last 105 yrs. Based on observations with ISO, an ESA project with instruments funded by ESA Member States

  16. Energy implications of an aging population

    SciTech Connect

    Not Available

    1980-08-01

    This study provides various demographic, medical, and economic information relative to energy usage on a segment of the population, the elderly, which is growing in absolute numbers and relative population percentage. This growth is expected to continue well into the twenty-first century. The US aging population numbered 3.1 million in 1900, and by 1977 it had climbed to 23.5 million. It can be stated with reasonable certainty that this figure will rise to 31 million in the year 2000 and 43 million in the year 2020. These figures, corresponding to more than 10% of our population, are by no means insignificant. As our fossil-fuel reserves are being depleted and the cost of energy mounts, it becomes apparent that the elderly will become increasingly vulnerable to the energy crisis, primarily beause of their physical tendency to infirmity, their economic and social situation, and their susceptibility to psychological depression. This white paper concentrates on those aspects of aging and the nation's energy problem which are not usually related in our everyday consideration of these as separable problems. It seeks to identify the peculiar energy problems of the aged and to consider alternatives in the solution of these problems in light of modern technology.

  17. The stellar kinematics and populations of boxy bulges: cylindrical rotation and vertical gradients

    NASA Astrophysics Data System (ADS)

    Williams, Michael J.; Zamojski, Michel A.; Bureau, Martin; Kuntschner, Harald; Merrifield, Michael R.; de Zeeuw, P. Tim; Kuijken, Konrad

    2011-07-01

    Boxy and peanut-shaped bulges are seen in about half of edge-on disc galaxies. Comparisons of the photometry and major-axis gas and stellar kinematics of these bulges to simulations of bar formation and evolution indicate that they are bars viewed in projection. If the properties of boxy bulges can be entirely explained by assuming that they are bars, then this may imply that their hosts are pure disc galaxies with no classical bulge. A handful of these bulges, including that of the Milky Way, have been observed to rotate cylindrically, i.e. with a mean stellar velocity independent of height above the disc. In order to assess whether such behaviour is ubiquitous in boxy bulges, and whether a pure disc interpretation is consistent with their stellar populations, we have analysed the stellar kinematics and populations of the boxy or peanut-shaped bulges in a sample of five edge-on galaxies. We placed slits along the major axis of each galaxy and at three offset but parallel positions to build up spatial coverage. The boxy bulge of NGC 3390 rotates perfectly cylindrically within the spatial extent and uncertainties of the data. This is consistent with the metallicity and α-element enhancement of the bulge, which are the same as in the disc. This galaxy is thus a pure disc galaxy. The boxy bulge of ESO 311-G012 also rotates very close to cylindrically. The boxy bulge of NGC 1381 is neither clearly cylindrically nor non-cylindrically rotating, but it has a negative vertical metallicity gradient and is α-enhanced with respect to its disc, suggesting a composite bulge comprised of a classical bulge and bar (and possibly a discy pseudo-bulge). The rotation of the peanut-shaped bulge of NGC 5746 is difficult to classify, but the peanut-shaped bulge of IC 4767 does not rotate cylindrically. Thus, even this relatively small sample is sufficient to demonstrate that boxy bulges display a range of rotational and population properties, indicating that they do not form a

  18. Population genomics of Bronze Age Eurasia.

    PubMed

    Allentoft, Morten E; Sikora, Martin; Sjögren, Karl-Göran; Rasmussen, Simon; Rasmussen, Morten; Stenderup, Jesper; Damgaard, Peter B; Schroeder, Hannes; Ahlström, Torbjörn; Vinner, Lasse; Malaspinas, Anna-Sapfo; Margaryan, Ashot; Higham, Tom; Chivall, David; Lynnerup, Niels; Harvig, Lise; Baron, Justyna; Della Casa, Philippe; Dąbrowski, Paweł; Duffy, Paul R; Ebel, Alexander V; Epimakhov, Andrey; Frei, Karin; Furmanek, Mirosław; Gralak, Tomasz; Gromov, Andrey; Gronkiewicz, Stanisław; Grupe, Gisela; Hajdu, Tamás; Jarysz, Radosław; Khartanovich, Valeri; Khokhlov, Alexandr; Kiss, Viktória; Kolář, Jan; Kriiska, Aivar; Lasak, Irena; Longhi, Cristina; McGlynn, George; Merkevicius, Algimantas; Merkyte, Inga; Metspalu, Mait; Mkrtchyan, Ruzan; Moiseyev, Vyacheslav; Paja, László; Pálfi, György; Pokutta, Dalia; Pospieszny, Łukasz; Price, T Douglas; Saag, Lehti; Sablin, Mikhail; Shishlina, Natalia; Smrčka, Václav; Soenov, Vasilii I; Szeverényi, Vajk; Tóth, Gusztáv; Trifanova, Synaru V; Varul, Liivi; Vicze, Magdolna; Yepiskoposyan, Levon; Zhitenev, Vladislav; Orlando, Ludovic; Sicheritz-Pontén, Thomas; Brunak, Søren; Nielsen, Rasmus; Kristiansen, Kristian; Willerslev, Eske

    2015-06-11

    The Bronze Age of Eurasia (around 3000-1000 BC) was a period of major cultural changes. However, there is debate about whether these changes resulted from the circulation of ideas or from human migrations, potentially also facilitating the spread of languages and certain phenotypic traits. We investigated this by using new, improved methods to sequence low-coverage genomes from 101 ancient humans from across Eurasia. We show that the Bronze Age was a highly dynamic period involving large-scale population migrations and replacements, responsible for shaping major parts of present-day demographic structure in both Europe and Asia. Our findings are consistent with the hypothesized spread of Indo-European languages during the Early Bronze Age. We also demonstrate that light skin pigmentation in Europeans was already present at high frequency in the Bronze Age, but not lactose tolerance, indicating a more recent onset of positive selection on lactose tolerance than previously thought.

  19. Population genomics of Bronze Age Eurasia.

    PubMed

    Allentoft, Morten E; Sikora, Martin; Sjögren, Karl-Göran; Rasmussen, Simon; Rasmussen, Morten; Stenderup, Jesper; Damgaard, Peter B; Schroeder, Hannes; Ahlström, Torbjörn; Vinner, Lasse; Malaspinas, Anna-Sapfo; Margaryan, Ashot; Higham, Tom; Chivall, David; Lynnerup, Niels; Harvig, Lise; Baron, Justyna; Della Casa, Philippe; Dąbrowski, Paweł; Duffy, Paul R; Ebel, Alexander V; Epimakhov, Andrey; Frei, Karin; Furmanek, Mirosław; Gralak, Tomasz; Gromov, Andrey; Gronkiewicz, Stanisław; Grupe, Gisela; Hajdu, Tamás; Jarysz, Radosław; Khartanovich, Valeri; Khokhlov, Alexandr; Kiss, Viktória; Kolář, Jan; Kriiska, Aivar; Lasak, Irena; Longhi, Cristina; McGlynn, George; Merkevicius, Algimantas; Merkyte, Inga; Metspalu, Mait; Mkrtchyan, Ruzan; Moiseyev, Vyacheslav; Paja, László; Pálfi, György; Pokutta, Dalia; Pospieszny, Łukasz; Price, T Douglas; Saag, Lehti; Sablin, Mikhail; Shishlina, Natalia; Smrčka, Václav; Soenov, Vasilii I; Szeverényi, Vajk; Tóth, Gusztáv; Trifanova, Synaru V; Varul, Liivi; Vicze, Magdolna; Yepiskoposyan, Levon; Zhitenev, Vladislav; Orlando, Ludovic; Sicheritz-Pontén, Thomas; Brunak, Søren; Nielsen, Rasmus; Kristiansen, Kristian; Willerslev, Eske

    2015-06-11

    The Bronze Age of Eurasia (around 3000-1000 BC) was a period of major cultural changes. However, there is debate about whether these changes resulted from the circulation of ideas or from human migrations, potentially also facilitating the spread of languages and certain phenotypic traits. We investigated this by using new, improved methods to sequence low-coverage genomes from 101 ancient humans from across Eurasia. We show that the Bronze Age was a highly dynamic period involving large-scale population migrations and replacements, responsible for shaping major parts of present-day demographic structure in both Europe and Asia. Our findings are consistent with the hypothesized spread of Indo-European languages during the Early Bronze Age. We also demonstrate that light skin pigmentation in Europeans was already present at high frequency in the Bronze Age, but not lactose tolerance, indicating a more recent onset of positive selection on lactose tolerance than previously thought. PMID:26062507

  20. The LMC geometry and outer stellar populations from early DES data

    SciTech Connect

    Balbinot, Eduardo; Plazas, A.; Santiago, B. X.; Girardi, L.; Pieres, A.; da Costa, L. N.; Maia, M. A. G.; Gruendl, R. A.; Walker, A. R.; Yanny, B.; Drlica-Wagner, A.; Benoit-Levy, A.; Abbott, T. M. C.; Allam, S. S.; Annis, J.; Bernstein, J. P.; Bernstein, R. A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Rosell, A. Carnero; Cunha, C. E.; Depoy, D. L.; Desai, S.; Diehl, H. T.; Doel, P.; Estrada, J.; Evrard, A. E.; Fausti Neto, A.; Finley, D. A.; Flaugher, B.; Frieman, J. A.; Gruen, D.; Honscheid, K.; James, D.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; March, M.; Marshall, J. L.; Miller, C.; Miquel, R.; Ogando, R.; Peoples, J.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Tucker, D. L.; Wechsler, R.; Zuntz, J.

    2015-03-20

    The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey. The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 magnitudes fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = –38.14°±0.08° (near side in the North) and a position angle for the line of nodes of θ₀ = 129.51°±0.17°. We find that stars younger than ~4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R>4Gyr = 1.41 ± 0.01 kpc, while the younger population has R<4Gyr = 0.72 ± 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of Rt = 13.5 ± 0.8 kpc. If this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is ≃24+9–6 times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fit LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. As a result, our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.

  1. The LMC geometry and outer stellar populations from early DES data

    DOE PAGES

    Balbinot, Eduardo; Plazas, A.; Santiago, B. X.; Girardi, L.; Pieres, A.; da Costa, L. N.; Maia, M. A. G.; Gruendl, R. A.; Walker, A. R.; Yanny, B.; et al

    2015-03-20

    The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey. The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 magnitudes fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = –38.14°±0.08° (near side in the North) and a position angle for the line of nodes of θ₀ = 129.51°±0.17°. Wemore » find that stars younger than ~4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R>4Gyr = 1.41 ± 0.01 kpc, while the younger population has R<4Gyr = 0.72 ± 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of Rt = 13.5 ± 0.8 kpc. If this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is ≃24+9–6 times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fit LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. As a result, our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.« less

  2. International Conference on Population Aging. Keynote address.

    PubMed

    Tabone, V

    1992-11-01

    This is the keynote address of H.E.Dr. Vincent Tabone, President of Malta, at the International Conference on Aging, which was held in San Diego in September 1992. He states that the conference celebrates the tenth anniversary of the Vienna International Plan of Action, and provides an opportunity to evaluate progress and plan future direction. Dr. Tabone, as Minister of Foreign Affairs, first introduced the question of aging at the UN General Assembly over twenty years ago; the United Nations Secretariat established its first program in the field of aging in 1970. At the World Assembly on Aging in 1982, all members adopted the International Plan of Action, which defined guidelines for policies and programs in support of the aging populations. As a direct result of this, and in support of the needs of developing countries, the UN signed an agreement with the government of Malta that established the International Institute on Aging as an autonomous body under the auspices of the UN; it is the major expression of the Vienna Plan of Action. Concern for aging populations has developed enough maturity and momentum to oversee its own progress. Although current events may relegate the social and economic implications of the aged to the sphere of rhetoric, they demand thinking in terms of generations and transcend all political boundaries. This conference will evaluate progress toward deflecting a situation where the elderly constitute an increasing proportion of the population, without adequate and appropriate provision for their livelihood, and could have direct bearing on encouraging and ensuring the continuity of the family's vital and traditional role in preserving the dignity, status, and well-being of its aging members. A nation which begrudges its dues to the elderly, the successful products of society and triumphs of life, denies its past. This conference is a reaffirmation of commitment to the United Nations Principles for Older Persons, an omen of the review of

  3. International Conference on Population Aging. Keynote address.

    PubMed

    Tabone, V

    1992-11-01

    This is the keynote address of H.E.Dr. Vincent Tabone, President of Malta, at the International Conference on Aging, which was held in San Diego in September 1992. He states that the conference celebrates the tenth anniversary of the Vienna International Plan of Action, and provides an opportunity to evaluate progress and plan future direction. Dr. Tabone, as Minister of Foreign Affairs, first introduced the question of aging at the UN General Assembly over twenty years ago; the United Nations Secretariat established its first program in the field of aging in 1970. At the World Assembly on Aging in 1982, all members adopted the International Plan of Action, which defined guidelines for policies and programs in support of the aging populations. As a direct result of this, and in support of the needs of developing countries, the UN signed an agreement with the government of Malta that established the International Institute on Aging as an autonomous body under the auspices of the UN; it is the major expression of the Vienna Plan of Action. Concern for aging populations has developed enough maturity and momentum to oversee its own progress. Although current events may relegate the social and economic implications of the aged to the sphere of rhetoric, they demand thinking in terms of generations and transcend all political boundaries. This conference will evaluate progress toward deflecting a situation where the elderly constitute an increasing proportion of the population, without adequate and appropriate provision for their livelihood, and could have direct bearing on encouraging and ensuring the continuity of the family's vital and traditional role in preserving the dignity, status, and well-being of its aging members. A nation which begrudges its dues to the elderly, the successful products of society and triumphs of life, denies its past. This conference is a reaffirmation of commitment to the United Nations Principles for Older Persons, an omen of the review of

  4. The Structure and Stellar Populations of Nuclear Star Clusters in Late-type Spiral Galaxies From HST/WFC3 Imaging

    NASA Astrophysics Data System (ADS)

    Carson, Daniel; Barth, Aaron J.; Seth, Anil; den Brok, Mark; Cappelari, Michele; Greene, Jenny E.; Ho, Luis C.; Neumayer, Nadine

    2015-01-01

    Luminous, compact stellar systems known as nuclear clusters (NCs) are commonly found in the centers of galaxies across the entire Hubble sequence. We present a detailed analysis of the two-dimensional (2D) structure of of ten of the nearest and brightest NCs residing in late-type spiral galaxies, using imaging data from Hubble Space Telescope Wide Field Camera 3 in seven bands that span the near-ultraviolet to the near-infrared. The intrinsic shapes and sizes of the NCs, disentangled from the effects of point spread function (PSF) blurring, were measured by fitting PSF convolved, 2D surface brightness profiles to each image using GALFIT. The clusters exhibit a wide range of structural properties, with F814W absolute magnitudes that range from -11.2 mag to -15.1 mag and F814W effective radii that range from 1.4 to 8.3 pc. For six of the ten NCs in our sample, we find changes in the effective radius with wavelength, which suggests that many NCs contain radially varying stellar populations. We also find a general trend of increasing roundness of the NCs at longer wavelengths, suggesting that the youngest stars in NCs typically form in disks.The stellar populations of the clusters were studied by comparing their observed colors to simple stellar population (SSP) models. In color-color diagrams spanning the near-UV through the near-IR, most of the clusters lie far from single-burst evolutionary tracks, showing evidence for complex star formation histories. Most of the NCs have integrated colors consistent with the presence of both an old population (> 1 Gyr) and a young population (˜100-300 Myr). The wide wavelength coverage of our data provides a sensitivity to populations with a mix of ages that would not be possible to achieve with imaging in optical bands only.

  5. Designing new meals for an ageing population.

    PubMed

    Costa, Ana I A; Jongen, Wim M F

    2010-06-01

    Today's ageing population is an ever-increasing, highly diverse group of people wanting to live a healthy and enjoyable life. Seniors increasingly see the importance of eating healthy and delicious food in a pleasant environment in achieving happiness and well-being. Up until now, the food industry has been rather slow in transforming the wealth of available knowledge regarding the nutritional needs and sensory perception of the ageing into new food products. Based on our own and the published research of others, we discuss here how the design of new meals for an ageing population can be tackled by a consumer-led approach to food product development. After a brief overview of the underlying concepts and practices, a detailed description is given of how this approach could be used in the design of Home Meal Replacements for senior households. This description includes also a comprehensive review of the major determinants of food preference and meal choice behavior in a later age. Finally, relevant implications are derived from the work presented and future trends in the technological development of foods for the ageing highlighted.

  6. Studying the nature of runaway stars using Andromeda's massive stellar population

    NASA Astrophysics Data System (ADS)

    Bulkley, Jordan; Seth, Anil; Johnson, Cliff; Dalcanton, Julianne; Guhathakurta, Raja; Dorman, Claire; Hamren, Katie; Caldwell, Nelson; Williams, Ben

    2016-03-01

    Theory of the formation of massive stars remains incomplete, the question of the environments required have yet to be answered. An agreement on whether all massive stars must form in cluster type environments, or if isolated formation is viable has yet to be reached. This is further complicated by the presence of runaway stars, stellar objects which have been ejected from their host cluster. Studying the nature of these isolated runaway stars becomes paramount in the larger goal of developing a more comprehensive massive star formation theory. Creating a survey of runaway star candidates is possible thanks to Panchromatic Hubble Andromeda Treasury's UV and optical photometry, and the identified clusters from the Andromeda Project. A first glimpse into the data suggests large body of massive stars are 50 parsecs or more from the closest cluster and roughly half of the entire massive stellar population is found outside of defined cluster boundaries. Additional analysts shows a stark difference between the velocity dispersion of massive stars and appropriately young clusters, the stars exhibiting a inflated dispersion. Using this result in conjunction with artificial clusters and star populations, constrains on the percentage of expected runaway objects can be made.

  7. Nuclear activity and stellar population of a sample of interacting galaxies

    NASA Astrophysics Data System (ADS)

    Pastoriza, M. G.; Donzelli, C. J.; Bonatto, C.

    1999-07-01

    In this paper we investigate the nuclear activity and stellar population in a sample of 27 physical galaxy pairs. Equivalent widths of absorption features are used to characterise the nuclear stellar population according to templates: most galaxies of the sample have important flux contributions from stars younger than 10(8) years. According to classical diagnostic-diagrams the galaxies in our sample are either classified as H II regions or have emission line ratios near the transition zone between H II regions and LINERs. Based on the observed spectra, only 4 galaxies show LINER properties and 1 nucleus is a Seyfert 2. We found that the spectrum of a transition object (38% of the sample) can be described by a combination of an AGN with an H II region. As a result, 20 galaxies of the present sample may host a low-luminosity active nucleus. Based on observations made at CASLEO and CTIO. Complejo Astronómico El Leoncito (CASLEO) is operated under agreement between the Consejo Nacional de Investigaciones Cient\\'\\i ficas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan.

  8. A population dynamics approach to biological aging

    NASA Astrophysics Data System (ADS)

    de Almeida, R. M. C.

    A dynamical model for aging in biological population is discussed where asexual reproduction is considered. The maximum life span is inherited from parent to offspring with some random mutations described by a transition matrix, and the fertile period begins at a defined age R. The intra species competition is modeled through a Verhulst-like factor. Discrete time evolution equations are iterated and the transient and asymptotic solutions are obtained. When only bad mutations are taken into account, the stationary solutions are obtained analytically. The results are applied to the Penna model.

  9. Tracing the evolution of NGC 6397 through the chemical composition of its stellar populations

    NASA Astrophysics Data System (ADS)

    Lind, K.; Charbonnel, C.; Decressin, T.; Primas, F.; Grundahl, F.; Asplund, M.

    2011-03-01

    Context. The chemical compositions of globular clusters provide important information on the star formation that occurred at very early times in the Galaxy. In particular the abundance patterns of elements with atomic number z ≤ 13 may shed light on the properties of stars that early on enriched parts of the star-forming gas with the rest-products of hydrogen-burning at high temperatures. Aims: We analyse and discuss the chemical compositions of a large number of elements in 21 red giant branch stars in the metal-poor globular cluster NGC 6397. We compare the derived abundance patterns with theoretical predictions in the framework of the "wind of fast rotating massive star"-scenario. Methods: High-resolution spectra were obtained with the FLAMES/UVES spectrograph on the VLT. We determined non-LTE abundances of Na, and LTE abundances for the remaining 21 elements, including O (from the [OI] line at 630 nm), Mg, Al, α, iron-peak, and neutron-capture elements, many of which had not been previously analysed for this cluster. We also considered the influence of possible He enrichment in the analysis of stellar spectra. Results: We find that the Na abundances of evolved, as well as unevolved, stars in NGC 6397 show a distinct bimodality, which is indicative of two stellar populations: one primordial stellar generation of composition similar to field stars, and a second generation that is polluted with material processed during hydrogen-burning, i.e., enriched in Na and Al and depleted in O and Mg. The red giant branch exhibits a similar bimodal distribution in the Strömgren colour index cy = c1 - (b - y), implying that there are also large differences in the N abundance. The two populations have the same composition for all analysed elements heavier than Al, within the measurement uncertainty of the analysis, with the possible exception of [Y/Fe]. Using two stars with almost identical stellar parameters, one from each generation, we estimate the difference in He

  10. MULTI-WAVELENGTH HUBBLE SPACE TELESCOPE PHOTOMETRY OF STELLAR POPULATIONS IN NGC 288

    SciTech Connect

    Piotto, G.; Milone, A. P.; Marino, A. F.; Jerjen, H.; Bedin, L. R.; Anderson, J.; Bellini, A.; Cassisi, S. E-mail: luigi.bedin@oapd.inaf.it E-mail: amarino@mso.anu.edu.au E-mail: jayander@stsci.edu E-mail: cassisi@oa-teramo.inaf.it

    2013-09-20

    We present new UV observations for NGC 288, taken with the WFC3 detector on board the Hubble Space Telescope, and combine them with existing optical data from the archive to explore the multiple-population phenomenon in this globular cluster (GC). The WFC3's UV filters have demonstrated an uncanny ability to distinguish multiple populations along all photometric sequences in GCs thanks to their exquisite sensitivity to the atmospheric changes that are telltale signs of second-generation enrichment. Optical filters, on the other hand, are more sensitive to stellar-structure changes related to helium enhancement. By combining both UV and optical data, we can measure the helium variation. We quantify this enhancement for NGC 288 and find that the variation is typical of what we have come to expect in other clusters.

  11. Dynamical evolution effects on the hot stellar populations in globular clusters

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Piotto, Giampaolo

    1992-01-01

    Results of a study of FUV properties of Galactic globular clusters are presented. The spatially resolved spectra measured with the IUE satellite are used to find indications of color gradients in two clusters with the postcore-collapse (PCC) morphology, NGC 6752 and NGC 7099, but not in the case of NTGC 6093, a cluster with the classical King-model-type morphology. These FUV color gradients may be caused by the presence of a highly concentrated population of hot objects, such as the extreme BHB stars, blue stragglers, etc. This result extends to the FUV regime the trends seen in the ground-based data in the visible regime. PCC or highly concentrated small-core lusters are found to have bluer HB morphologies and bluer FUV colors, and the bluest FUV colors at a given metallicity. These trends indicate that dynamical evolution of clusters played some role in determining the net abundance and the spatial distribution of their hot stellar populations.

  12. Population aging and endogenous economic growth.

    PubMed

    Prettner, Klaus

    2013-04-01

    We investigate the consequences of population aging for long-run economic growth perspectives. Our framework incorporates endogenous growth models and semi-endogenous growth models as special cases. We show that (1) increases in longevity have a positive impact on per capita output growth, (2) decreases in fertility have a negative impact on per capita output growth, (3) the positive longevity effect dominates the negative fertility effect in case of the endogenous growth framework, and (4) population aging fosters long-run growth in the endogenous growth framework, while its effect depends on the relative change between fertility and mortality in the semi-endogenous growth framework.Electronic supplementary material The online version of this article (doi:10.1007/s00148-012-0441-9) contains supplementary material, which is available to authorized users.

  13. Using diffusion k-means for simple stellar population modeling of low S/N quasar host galaxy spectra

    NASA Astrophysics Data System (ADS)

    Mosby, Gregory; Tremonti, Christina A.; Hooper, Eric; Wolf, Marsha J.; Sheinis, Andrew; Richards, Joseph

    2016-01-01

    Quasar host galaxies (QHGs) represent a unique stage in galaxy evolution that can provide a glimpse into the relationship between an active supermassive black hole (SMBH) and its host galaxy. However, observing the hosts of high luminosity, unobscured quasars in the optical is complicated by the large ratio of quasar to host galaxy light. One strategy in optical spectroscopy is to use offset longslit observations of the host galaxy. This method allows the centers of QHGs to be analyzed apart from other regions of their host galaxies. But light from the accreting black hole's point spread function still enters the host galaxy observations, and where the contrast between the host and intervening quasar light is favorable, the host galaxy is faint, producing low signal-to-noise (S/N) data. This stymies traditional stellar population methods that might rely on high S/N features in galaxy spectra to recover key galaxy properties like its star formation history (SFH). In response to this challenge, we have developed a method of stellar population modeling using diffusion k-means (DFK) that can recover SFHs from rest frame optical data with S/N ~ 5 Å^-1. Specifically, we use DFK to cultivate a reduced stellar population basis set. This DFK basis set of four broad age bins is able to recover a range of SFHs. With an analytic description of the seeing, we can use this DFK basis set to simultaneously model the SFHs and the intervening quasar light of QHGs as well. We compare the results of this method with previous techniques using synthetic data and find that our new method has a clear advantage in recovering SFHs from QHGs. On average, the DFK basis set is just as accurate and decisively more precise. This new technique could be used to analyze other low S/N galaxy spectra like those from higher redshift or integral field spectroscopy surveys.This material is based upon work supported by the National Science Foundation under grant no. DGE -0718123 and the Advanced

  14. Investigation of multiple stellar populations in globular clusters with the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Smolinski, Jason P.

    This dissertation describes the study of abundance variations among stars in Galactic globular clusters using the large set of spectroscopic data collected by the Sloan Digital Sky Survey (SDSS). Globular clusters have typically been considered to be simple stellar populations---groups of stars that are coeval and chemically homogeneous. Observations within the last forty years have shed light on the possibility that they are not so simple after all by revealing the presence of star-to-star variations in light-element abundances. Additionally, several globular clusters are known to harbor multiple populations of stars by the presence of multiple sequences on a color-magnitude diagram. In this study, the procedure for membership selection is first described. Stars are selected from the vast data set available from SDSS Data Release 7 and several cuts are made to reduce the sample down to only those stars that are members of the globular clusters in this sample. This procedure is also performed on three open clusters as well and is further used to validate the current SEGUE Stellar Parameter Pipeline. CN and CH molecular absorption indices are then measured for all globular cluster member stars and their distributions are analyzed. Bimodal distributions in CN are seen on the red giant branch in all clusters with [Fe/H] > -2.1, and hints of bimodality are seen for two metal-poor clusters as well. CN-CH anticorrelations are also seen and the implications are discussed. The observed distributions of CN absorption bandstrengths are examined and compared to theoretical predictions from two-population models. These results are combined with radial distributions and positions on the color-magnitude diagram as evidence for the presence of multiple populations of stars within the clusters in this sample.

  15. Understanding the formation and evolution of early-type galaxies based on newly developed single-burst stellar population synthesis models in the infrared

    NASA Astrophysics Data System (ADS)

    Roeck, Benjamin

    2015-12-01

    The detailed study of the different stellar populations which can be observed in galaxies is one of the most promising methods to shed light on the evolutionary histories of galaxies. So far, stellar population analysis has been carried out mainly in the optical wavelength range. The infrared spectral range, on the other hand, has been poorly studied so far, although it provides very important insights, particularly into the cooler stellar populations which are present in galaxies. However, in the last years, space telescopes like the Spitzer Space Telescope or the Wide-field Infrared Survey Explorer and instruments like the spectrograph X-Shooter on the Very Large Telescope have collected more and more photometric and spectroscopic data in this wavelength range. In order to analyze these observations, it is necessary to dispose of reliable and accurate stellar population models in the infrared. Only a small number of stellar population models in the infrared exist in the literature. They are mostly based on theoretical stellar libraries and very often cover only the near-infrared wavelength range at a rather low resolution. Hence, we developed new single-burst stellar population models between 8150 and 50000Å which are exclusively based on 180 spectra from the empirical Infrared Telescope Facility stellar library. We computed our single stellar population models for two different sets of isochrones and various types of initial mass functions of different slopes. Since the stars of the Infrared Telescope Facility library present only a limited coverage of the stellar atmospheric parameter space, our models are of sufficient quality only for ages larger than 1 Gyr and metallicities between [Fe/H] = 0.40 and 0.26. By combining our single stellar population models in the infrared with the extended medium-resolution Isaac Newton Telescope library of empirical spectra in the optical spectral range, we created the first single stellar population models covering the

  16. Using modern stellar observables to constrain stellar parameters and the physics of the stellar interior

    NASA Astrophysics Data System (ADS)

    van Saders, Jennifer L.

    2014-05-01

    stellar parameters and the physics of the interior. I examine how the acoustic signature of the location of the base of stellar convective envelopes can be used as an absolute abundance indicator, and describe a novel 3He-burning instability in low mass stars along with the observational signatures of such a process. Finally, I examine the manner in which stellar rotation, observed in a population of objects, can be used as a means to distinguish between different evolutionary states, masses, and ages. I emphasize that rotation periods can be used as age indicators (as often discussed in the literature), but that the interpretation of rotation periods must be made within the context of the full stellar population to arrive at accurate results.

  17. Uncertainties in asteroseismic grid-based estimates of stellar ages. SCEPtER: Stellar CharactEristics Pisa Estimation gRid

    NASA Astrophysics Data System (ADS)

    Valle, G.; Dell'Omodarme, M.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2015-03-01

    Context. Stellar age determination by means of grid-based techniques that adopt asteroseismic constraints is a well established method nowadays. However some theoretical aspects of the systematic and statistical errors affecting these age estimates still have to be investigated. Aims: We study the impact on stellar age determination of the uncertainty in the radiative opacity, in the initial helium abundance, in the mixing-length value, in the convective core overshooting, and in the microscopic diffusion efficiency adopted in stellar model computations. Methods: We extended our SCEPtER grid to include stars with mass in the range [0.8; 1.6] M⊙ and evolutionary stages from the zero-age main sequence to the central hydrogen depletion. For the age estimation we adopted the same maximum likelihood technique as described in our previous work. To quantify the systematic errors arising from the current uncertainty in model computations, many synthetic grids of stellar models with perturbed input were adopted. Results: We found that the current typical uncertainty in the observations accounts for 1σ statistical relative error in age determination, which on average ranges from about -35% to +42%, depending on the mass. However, owing to the strong dependence on the evolutionary phase, the age's relative error can be higher than 120% for stars near the zero-age main sequence, while it is typically of the order of 20% or lower in the advanced main-sequence phase. The systematic bias on age determination due to a variation of ±1 in the helium-to-metal enrichment ratio ΔY/ΔZ is about one-fourth of the statistical error in the first 30% of the evolution, while it is negligible for more evolved stages. The maximum bias due to the presence of the convective core overshooting is -7% and -13% for mild and strong overshooting scenarios. For all the examined models, the impact of a variation of ±5% in the radiative opacity was found to be negligible. The most important source

  18. Stellar rotation at young ages: new results from Corot's monitoring NGC 2264

    NASA Astrophysics Data System (ADS)

    Favata, F.; Micela, G.; Alencar, S.; Aigrain, S.; Zwintz, K.

    2010-11-01

    Stellar rotation at young ages: new results from Corot's Angular momentum is one of the driving forces in the early evolution of stars. Issues such as the coupling between the star and the accretion disk (the so-called disk regulation paradigm), are traced by the evolution of rotational momentum, but affect the star-forming process as a whole. One of the features observed in star-forming regions (e.g. ONC and NGC 2264) of age between 1 and few Myr, for masses above 0.25 solar masses, is a bimodality of the rotational period distribution, with a peak around 1 day and the other at around 4 to 7 days. This bimodality has been interpreted as the smoking gun of the disk-locking mechanism (with the fast rotators having lost their disk and the slow ones still being regulated by their disks).

  19. Slowed ageing, welfare, and population problems.

    PubMed

    Wareham, Christopher

    2015-10-01

    Biological studies have demonstrated that it is possible to slow the ageing process and extend lifespan in a wide variety of organisms, perhaps including humans. Making use of the findings of these studies, this article examines two problems concerning the effect of life extension on population size and welfare. The first--the problem of overpopulation--is that as a result of life extension too many people will co-exist at the same time, resulting in decreases in average welfare. The second--the problem of underpopulation--is that life extension will result in too few people existing across time, resulting in decreases in total welfare. I argue that overpopulation is highly unlikely to result from technologies that slow ageing. Moreover, I claim that the problem of underpopulation relies on claims about life extension that are false in the case of life extension by slowed ageing. The upshot of these arguments is that the population problems discussed provide scant reason to oppose life extension by slowed ageing.

  20. Perioperative Cognitive Decline in the Aging Population

    PubMed Central

    Terrando, Niccolò; Brzezinski, Marek; Degos, Vincent; Eriksson, Lars I.; Kramer, Joel H.; Leung, Jacqueline M.; Miller, Bruce L.; Seeley, William W.; Vacas, Susana; Weiner, Michael W.; Yaffe, Kristine; Young, William L.; Xie, Zhongcong; Maze, Mervyn

    2011-01-01

    Elderly patients who have an acute illness or who undergo surgery often experience cognitive decline. The pathophysiologic mechanisms that cause neurodegeneration resulting in cognitive decline, including protein deposition and neuroinflammation, also play a role in animal models of surgery-induced cognitive decline. With the aging of the population, surgical candidates of advanced age with underlying neurodegeneration are encountered more often, raising concerns that, in patients with this combination, cognitive function will precipitously decline postoperatively. This special article is based on a symposium that the University of California, San Francisco, convened to explore the contributions of surgery and anesthesia to the development of cognitive decline in the aged patient. A road map to further elucidate the mechanisms, diagnosis, risk factors, mitigation, and treatment of postoperative cognitive decline in the elderly is provided. PMID:21878601

  1. The BaLROG project - II. Quantifying the influence of bars on the stellar populations of nearby galaxies

    NASA Astrophysics Data System (ADS)

    Seidel, M. K.; Falcón-Barroso, J.; Martínez-Valpuesta, I.; Sánchez-Blázquez, P.; Pérez, I.; Peletier, R.; Vazdekis, A.

    2016-08-01

    We continue the exploration of the BaLROG (Bars in Low Redshift Optical Galaxies) sample: 16 large mosaics of barred galaxies observed with the integral field unit Spectrographic Areal Unit for Research on Optical Nebulae. We quantify the influence of bars on the composition of the stellar component. We derive line-strength indices of H β, Fe5015 and Mgb. Based on single stellar population (SSP) models, we calculate ages, metallicities and [Mg/Fe] abundances and their gradients along the bar major and minor axes. The high spatial resolution of our data allows us to identify breaks among index and SSP profiles, commonly at 0.13 ± 0.06 bar length, consistent with kinematic features. Inner gradients are about 10 times steeper than outer gradients and become larger when there is a central rotating component, implying that the gradients are not independent of dynamics and orbits. Central ages appear to be younger for stronger bars. Yet, the bar regions are usually old. We find a flattening of the iron (Fe5015) and magnesium (Mgb) outer gradients along the bar major axis, translating into a flattening of the metallicity gradient. This gradient is found to be 0.03 ± 0.07 dex kpc-1 along the bar major axis while the mean value of the bar minor axis compares well with that of an unbarred control sample and is significantly steeper, namely -0.20 ± 0.04 dex kpc-1. These results confirm recent simulations and discern the important localized influence of bars. The elevated [Mg/Fe] abundances of bars and bulges compared to the lower values of discs suggest an early formation, in particular for early-type galaxies.

  2. Mass-loss From Evolved Stellar Populations In The Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Riebel, David

    2012-01-01

    I have conducted a study of a sample of 30,000 evolved stars in the Large Magellanic Cloud (LMC) and 6,000 in the Small Magellanic Cloud (SMC), covering their variability, mass-loss properties, and chemistry. The initial stages of of my thesis work focused on the infrared variability of Asymptotic Giant Branch (AGB) stars in the LMC. I determined the period-luminosity (P-L) relations for 6 separate sequences of 30,000 evolved star candidates at 8 wavelengths, as a function of photometrically assigned chemistry, and showed that the P-L relations are different for different chemical populations (O-rich or C-rich). I also present results from the Grid of Red supergiant and Asymptotic giant branch star ModelS (GRAMS) radiative transfer (RT) model grid applied to the evolved stellar population of the LMC. GRAMS is a pre-computed grid of RT models of RSG and AGB stars and surrounding circumstellar dust. Best-fit models are determined based on 12 bands of photometry from the optical to the mid-infrared. Using a pre-computed grid, I can present the first reasonably detailed radiative transfer modeling for tens of thousands of stars, allowing me to make statistically accurate estimations of the carbon-star luminosity function and the global dust mass return to the interstellar medium from AGB stars, both key parameters for stellar population synthesis models to reproduce. In the SAGE-Var program, I used the warm Spitzer mission to take 4 additional epochs of observations of 7500 AGB stars in the LMC and SMC. These epochs, combined with existing data, enable me to derive mean fluxes at 3.6 and 4.5 microns, that will be used for tighter constraints for GRAMS, which is currently limited by the variability induced error on the photometry. This work is support by NASA NAG5-12595 and Spitzer contract 1415784.

  3. THE STELLAR POPULATION OF h AND {chi} PERSEI: CLUSTER PROPERTIES, MEMBERSHIP, AND THE INTRINSIC COLORS AND TEMPERATURES OF STARS

    SciTech Connect

    Currie, Thayne; Irwin, Jonathan; Kenyon, Scott J.; Tokarz, Susan; Hernandez, Jesus; Balog, Zoltan; Bragg, Ann; Berlind, Perry; Calkins, Mike E-mail: jirwin@cfa.harvard.edu

    2010-02-01

    From photometric observations of {approx} 47,000 stars and spectroscopy of {approx} 11,000 stars, we describe the first extensive study of the stellar population of the famous Double Cluster, h and {chi} Persei, down to subsolar masses. By analyzing optical spectra and optical/infrared photometry, we constrain the distance moduli (dM), reddening (E(B - V)), and ages for h Persei, {chi} Persei, and the low-density halo population surrounding both cluster cores. With the exception of mass and spatial distribution, the clusters are nearly identical in every measurable way. Both clusters have E(B - V) {approx} 0.52-0.55 and dM = 11.8-11.85; the halo population, while more poorly constrained, likely has identical properties. As determined from the main-sequence turnoff, the luminosity of M supergiants, and pre-main-sequence isochrones, ages for h Persei, {chi} Persei, and the halo population all converge on {approx}14 Myr, thus showing a stunning agreement between estimates based on entirely different physics. From these data, we establish the first spectroscopic and photometric membership lists of cluster stars down to early/mid M dwarfs. At minimum, there are {approx} 5000 members within 10' of the cluster centers, while the entire h and {chi} Persei region has at least {approx} 13,000 and as many as 20,000 members. The Double Cluster contains {approx} 8400 M {sub sun} of stars within 10' of the cluster centers. We estimate a total mass of at least 20,000 M {sub sun}. We conclude our study by outlining outstanding questions regarding the past and present properties of h and {chi} Persei. From comparing recent work, we compile a list of intrinsic colors and derive a new effective temperature scale for O-M dwarfs, giants, and supergiants.

  4. A Kinematic Study of the Nuclear Stellar Populations in Seyfert Galaxies

    NASA Astrophysics Data System (ADS)

    García-Rissmann, Aurea; Cid Fernandes, Roberto; Asari, N. V.; Vega, Luis Rodolfo; Schmitt, Henrique; González Delgado, Rosa

    2005-05-01

    Recent studies in the optical and UV have detected circumnuclear starbursts in 40% of nearby Seyfert-2 galaxies; about half of the remaining 60% present a UV excess whose nature is not well known, mainly because of the limitations of the current stellar population analysis techniques in the optical and UV domains. A possible way to circumvent these difficulties is to use a determination of the mass-to-light (M/L) ratio, obtained with a combination of velocity dispersion measurements and photometric information. Dynamical information in AGN (particularly in type 2) is better determined from NIR spectroscopic data, where the stellar absorption features are less affected by the nuclear continuum dilution. In this work, we present preliminary results of a spectroscopic survey of more than 60 Seyfert nuclei (mainly Seyfert 2s), conducted at ESO/La Silla and at KPNO. For many of these objects we have complementary data, such as HST images, optical and (in some cases) UV spectroscopy. The long-slit spectroscopy for the purpose of this project was performed around the NIR Ca II triplet lines at 8498, 8542 and 8662Å. Here we describe the analysis steps taken so far, and present the first results concerning velocity dispersion measurements in nuclear regions. With these data we aim to investigate the ambiguous Seyfert 2 nuclei nature, thus contributing to a better understanding of the AGN-starburst connection.

  5. Kinematics and chemical properties of the Galactic stellar populations. The HARPS FGK dwarfs sample

    NASA Astrophysics Data System (ADS)

    Adibekyan, V. Zh.; Figueira, P.; Santos, N. C.; Hakobyan, A. A.; Sousa, S. G.; Pace, G.; Delgado Mena, E.; Robin, A. C.; Israelian, G.; González Hernández, J. I.

    2013-06-01

    Aims: We analyzed chemical and kinematical properties of about 850 FGK solar neighborhood long-lived dwarfs observed with the HARPS high-resolution spectrograph. The stars in the sample have log g ≥ 4 dex, 5000 ≤ Teff ≤ 6500 K, and - 1.39 ≤ [Fe/H] ≤ 0.55 dex. The aim of this study is to characterize and explore the kinematics and chemical properties of stellar populations of the Galaxy in order to understand their origins and evolution. Methods: We applied a purely chemical analysis approach based on the [α/Fe] vs. [Fe/H] plot to separate Galactic stellar populations into the thin disk, thick disk, and high-α metal-rich (hαmr). Then, we explored the population's stellar orbital eccentricity distributions, their correlation with metallicity, and rotational velocity gradients with metallicity in the Galactic disks to provide constraints on the various formation models. Results: We identified a gap in the [α/Fe]-[Fe/H] plane for the α-enhanced stars, and by performing a bootstrapped Monte Carlo test we obtained a probability higher than 99.99% that this gap is not due to small-number statistics. Our analysis shows a negative gradient of the rotational velocity of the thin disk stars with [Fe/H] (-17 km s-1 dex-1), and a steep positive gradient for both the thick disk and hαmr stars with the same magnitude of about +42 km s-1 dex-1. For the thin disk stars we observed no correlation between orbital eccentricities and metallicity, but observed a steep negative gradient for the thick disk and hαmr stars with practically the same magnitude (≈-0.18 dex-1). The correlations observed for the nearby stars (on average 45 pc) using high-precision data, in general agree well with the results obtained for the SDSS sample of stars located farther from the Galactic plane. Conclusions: Our results suggest that radial migration played an important role in the formation and evolution of the thin disk. For the thick disk stars it is not possible to reach a firm

  6. The economic consequences of ageing populations.

    PubMed Central

    Mirrlees, J A

    1997-01-01

    The effect of low birth rates and lengthening lives on the economy is discussed. Two extreme cases are examined: where pensions are entirely on a pay-as-you-go basis, and where they are entirely funded. It is argued that the economy would grow faster in the latter case. The impact on the levels of consumption of each age cohort during its lifetime is assessed. The possible magnitude of changes in consumption as a result of an increase in the retired part of the population is illustrated. It is shown that, comparing later cohorts to earlier cohorts, the former are better off under a funded system. An argument is then sketched showing that a pay-as-you-go system favours earlier cohorts too much; while most probably, but not certainly, a fully funded system favours the later cohorts excessively. It is claimed that a gradual introduction of partial funding, and some increase in the length of working lives, can deal with the effects of an ageing population without an excessive burden on any cohort or age-group. PMID:9460073

  7. Observing Resolved Stellar Populations with the JWST Near-Infrared Spectrograph

    NASA Astrophysics Data System (ADS)

    Gilbert, K. M.; Beck, T. L.; Karakla, D. M.

    2016-10-01

    The James Webb Space Telescope's (JWST) Near Infrared Spectrograph (NIRSpec) will provide a multi-object spectroscopy (MOS) mode through the Micro-Shutter Array (MSA). Each MSA quadrant is a grid of contiguous shutters that can be configured to form slits on more than 100 astronomical targets simultaneously. The combination of JWST's sensitivity and superb resolution in the infrared and NIRSpec's full wavelength coverage over 0.6 to 5 μm will open new parameter space for studies of galaxies and resolved stellar populations alike. We describe a NIRSpec MSA observing scenario of spectroscopy of individual stars in an external galaxy, and investigate the technical challenges posed by this scenario. This use case and others, including a deep galaxy survey and observations of Galactic HII regions, are guiding development of the NIRSpec user interfaces including proposal planning and pipeline calibrations.

  8. Observations of Resolved Stellar Populations with the JWST Near Infrared Spectrograph

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline; Beck, Tracy L.; Karakla, Diane M.

    2015-01-01

    The James Webb Space Telescope's (JWST) Near Infrared Spectrograph (NIRSpec) will provide a multi-object spectroscopy mode through the four Micro-Shutter Arrays (MSAs). Each MSA is a grid of contiguous shutters that can be configured to form slits on more than 100 astronomical targets simultaneously. The combination of JWST's sensitivity and superb resolution in the infrared and NIRSpec's full wavelength coverage over 1 to 5 micrometers will open new parameter space for studies of galaxies and resolved stellar populations alike. We present a NIRSpec MSA observing scenario for obtaining spectroscopy of individual stars in external galaxies. We examine the multiplexing capability of the MSA as a function of the possible MSA configuration design choices, and investigate the primary sources of error in velocity measurements and the prospects for minimizing them. We discuss how this and other use cases are being used to guide development of the NIRSpec user interfaces, including proposal planning and pipeline calibrations.

  9. Food and Addiction among the Ageing Population

    PubMed Central

    Murray, Susan; Kroll, Cindy; Avena, Nicole M.

    2014-01-01

    Obesity among the elderly is a growing public health concern. Among the various factors that may contribute to the current rates of obesity is the rewarding aspect of highly palatable foods and beverages, which may lead to overconsumption and excess caloric intake. The present review describes recent research supporting the hypothesis that, for some individuals, the consumption these highly palatable foods and beverages may lead to the development of addictive-like behaviors. In particular, the authors consider the relevance of this hypothesis to the ageing population. PMID:25449527

  10. Food and addiction among the ageing population.

    PubMed

    Murray, Susan; Kroll, Cindy; Avena, Nicole M

    2015-03-01

    Obesity among the elderly is a growing public health concern. Among the various factors that may contribute to the current rates of obesity is the rewarding aspect of highly palatable foods and beverages, which may lead to overconsumption and excess caloric intake. The present review describes recent research supporting the hypothesis that, for some individuals, the consumption these highly palatable foods and beverages may lead to the development of addictive-like behaviors. In particular, the authors consider the relevance of this hypothesis to the ageing population.

  11. Stellar population gradients in the cores of nearby field E+A galaxies

    NASA Astrophysics Data System (ADS)

    Pracy, Michael B.; Owers, Matt S.; Couch, Warrick J.; Kuntschner, Harald; Bekki, Kenji; Briggs, Frank; Lah, Philip; Zwaan, Martin

    2012-03-01

    We have selected a sample of local E+A galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 for follow-up integral field spectroscopy with the Wide Field Spectrograph (WiFeS) on the Australian National University's (ANU) 2.3-m telescope. The sample was selected using the Hα line in place of the [O II] λ3727 line as the indicator of ongoing star formation (or lack thereof). This allowed us to select a lower redshift sample of galaxies than available in the literature since the [O II] λ3727 falls off the blue end of the wavelength coverage in the SDSS for the very lowest redshift objects. This low-redshift selection means that the galaxies have a large angular to physical scale which allows us to resolve the central ˜1 kpc region of the galaxies; the region where stellar population gradients are expected. Such observations have been difficult to make using other higher redshift samples because even at redshifts z˜ 0.1 the angular to physical scale is similar to the resolution provided by ground-based seeing. Our integral field spectroscopy has enabled us to make the first robust detections of Balmer line gradients in the centres of E+A galaxies. Six out of our sample of seven, and all the galaxies with regular morphologies, are observed to have compact and centrally concentrated Balmer line absorption. This is evidence for compact young cores and stellar population gradients which are predicted from models of mergers and tidal interactions which funnel gas into the galaxy core. Given the generally isolated nature of our sample, this argues for the galaxies being seen in the late stage of a merger where the progenitors have already coalesced.

  12. The panchromatic Hubble Andromeda Treasury. V. Ages and masses of the year 1 stellar clusters

    SciTech Connect

    Fouesneau, Morgan; Johnson, L. Clifton; Weisz, Daniel R.; Dalcanton, Julianne J.; Williams, Benjamin F.; Bell, Eric F.; Bianchi, Luciana; Caldwell, Nelson; Gouliermis, Dimitrios A.; Guhathakurta, Puragra; Larsen, Søren S.; Rix, Hans-Walter; Seth, Anil C.; Skillman, Evan D.

    2014-05-10

    We present ages and masses for 601 star clusters in M31 from the analysis of the six filter integrated light measurements from near-ultraviolet to near-infrared wavelengths, made as part of the Panchromatic Hubble Andromeda Treasury (PHAT). We derive the ages and masses using a probabilistic technique, which accounts for the effects of stochastic sampling of the stellar initial mass function. Tests on synthetic data show that this method, in conjunction with the exquisite sensitivity of the PHAT observations and their broad wavelength baseline, provides robust age and mass recovery for clusters ranging from ∼10{sup 2} to 2 × 10{sup 6} M {sub ☉}. We find that the cluster age distribution is consistent with being uniform over the past 100 Myr, which suggests a weak effect of cluster disruption within M31. The age distribution of older (>100 Myr) clusters falls toward old ages, consistent with a power-law decline of index –1, likely from a combination of fading and disruption of the clusters. We find that the mass distribution of the whole sample can be well described by a single power law with a spectral index of –1.9 ± 0.1 over the range of 10{sup 3}-3 × 10{sup 5} M {sub ☉}. However, if we subdivide the sample by galactocentric radius, we find that the age distributions remain unchanged. However, the mass spectral index varies significantly, showing best-fit values between –2.2 and –1.8, with the shallower slope in the highest star formation intensity regions. We explore the robustness of our study to potential systematics and conclude that the cluster mass function may vary with respect to environment.

  13. The Rho Ophiuchi cloud young stellar population - Results of a near-infrared study

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.; Young, Erick T.

    1991-01-01

    An imaging survey of 1.4 sq pc of the Rho Ophiuchi dark cloud in the J, H, and K near-infrared photometric bands was conducted. Approximately 332 of the 481 detected sources are associated with the cloud, and 30 percent of these have near-infrared excesses, indicative of disks or circumstellar material surrounding these young stellar objects (YSOs). The K-band luminosity function is significantly different in different regions of the survey area, suggesting that YSOs in these regions have different ages or mass functions. The entire survey area has a high star formation efficiency of about 23 percent. Finally, many newly detected sources provide a relatively large, uniformly sensitive sample of objects for study at longer wavelengths to better determine true source luminosities and evolutionary lifetimes.

  14. A Systematic Study of Effects of Stellar Rotation, Age Spread, and Binaries on Color-Magnitude Diagrams with Extended Main-sequence Turnoffs

    NASA Astrophysics Data System (ADS)

    Li, Zhongmu; Mao, Caiyan; Zhang, Liyun; Zhang, Xi; Chen, Li

    2016-07-01

    Stellar rotation, age spread, and binary stars are thought to be the three most possible causes of the peculiar color-magnitude diagrams (CMDs) of some star clusters, which exhibit extended main-sequence turnoffs (eMSTOs). The answer is far from clear. This paper studies the effects of the three above causes on the CMDs of star clusters systematically. A rapid stellar evolutionary code and a recently published database of rotational effects of single stars have been used, via an advanced stellar population synthesis technique. As a result, we find a similar result for rotation to recent works, which suggests that rotation is able to explain, at least partially, the eMSTOs of clusters, if clusters are not too old (<2.0 Gyr). In addition, an age spread of 200-500 Myr reproduces extended turnoffs for all clusters younger than 2.5 Gyr, in particular, for those younger than 2.2 Gyr. Age spread also results in extended red clumps (eRCs) for clusters younger than 0.5 Gyr. The younger the clusters, the clearer the eRC structures. Moreover, it is shown that binaries (including interactive binaries) affect the spread of MSTOs slightly for old clusters, but they can contribute to the eMSTOs of clusters younger than 0.5 Gyr. Our result suggests a possible way to disentangle the roles of stellar rotation and age spread, i.e., checking the existence of CMDs with both eMSTOs and eRCs in clusters younger than 0.5 Gyr.

  15. RX J0848.6+4453: The Evolution of Galaxy Sizes and Stellar Populations in a z = 1.27 Cluster

    NASA Astrophysics Data System (ADS)

    Jørgensen, Inger; Chiboucas, Kristin; Toft, Sune; Bergmann, Marcel; Zirm, Andrew; Schiavon, Ricardo P.; Grützbauch, Ruth

    2014-12-01

    RX J0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of galaxies. We present an analysis of the stellar populations and star formation history for a sample of 24 members of the cluster. Our study is based on deep optical spectroscopy obtained with Gemini North combined with imaging data from Hubble Space Telescope. Focusing on the 13 bulge-dominated galaxies for which we can determine central velocity dispersions, we find that these show a smaller evolution with redshift of sizes and velocity dispersions than reported for field galaxies and galaxies in poorer clusters. Our data show that the galaxies in RX J0848.6+4453 populate the fundamental plane (FP) similar to that found for lower-redshift clusters. The zero-point offset for the FP is smaller than expected if the cluster's galaxies are to evolve passively through the location of the FP we established in our previous work for z = 0.8-0.9 cluster galaxies and then to the present-day FP. The FP zero point for RX J0848.6+4453 corresponds to an epoch of last star formation at z_form= 1.95+0.22-0.15. Further, we find that the spectra of the galaxies in RX J0848.6+4453 are dominated by young stellar populations at all galaxy masses and in many cases show emission indicating low-level ongoing star formation. The average age of the young stellar populations as estimated from the strength of the high-order Balmer line Hζ is consistent with a major star formation episode 1-2 Gyr prior, which in turn agrees with z form = 1.95. These galaxies dominated by young stellar populations are distributed throughout the cluster. We speculate that low-level star formation has not yet been fully quenched in the center of this cluster, possibly because the cluster is significantly poorer than other clusters previously studied at similar redshifts, which appear to have very little ongoing star formation in their centers. The mixture in RX J0848.6+4453 of passive galaxies with young stellar populations and massive

  16. RX J0848.6+4453: The evolution of galaxy sizes and stellar populations in A z = 1.27 cluster

    SciTech Connect

    Jørgensen, Inger; Chiboucas, Kristin; Schiavon, Ricardo P.; Toft, Sune; Zirm, Andrew; Bergmann, Marcel; Grützbauch, Ruth E-mail: kchiboucas@gemini.edu E-mail: sune@dark-cosmology.dk E-mail: marcelbergmann@gmail.com

    2014-12-01

    RX J0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of galaxies. We present an analysis of the stellar populations and star formation history for a sample of 24 members of the cluster. Our study is based on deep optical spectroscopy obtained with Gemini North combined with imaging data from Hubble Space Telescope. Focusing on the 13 bulge-dominated galaxies for which we can determine central velocity dispersions, we find that these show a smaller evolution with redshift of sizes and velocity dispersions than reported for field galaxies and galaxies in poorer clusters. Our data show that the galaxies in RX J0848.6+4453 populate the fundamental plane (FP) similar to that found for lower-redshift clusters. The zero-point offset for the FP is smaller than expected if the cluster's galaxies are to evolve passively through the location of the FP we established in our previous work for z = 0.8-0.9 cluster galaxies and then to the present-day FP. The FP zero point for RX J0848.6+4453 corresponds to an epoch of last star formation at z{sub form}=1.95{sub −0.15}{sup +0.22}. Further, we find that the spectra of the galaxies in RX J0848.6+4453 are dominated by young stellar populations at all galaxy masses and in many cases show emission indicating low-level ongoing star formation. The average age of the young stellar populations as estimated from the strength of the high-order Balmer line Hζ is consistent with a major star formation episode 1-2 Gyr prior, which in turn agrees with z {sub form} = 1.95. These galaxies dominated by young stellar populations are distributed throughout the cluster. We speculate that low-level star formation has not yet been fully quenched in the center of this cluster, possibly because the cluster is significantly poorer than other clusters previously studied at similar redshifts, which appear to have very little ongoing star formation in their centers. The mixture in RX J0848.6+4453 of passive galaxies with young stellar

  17. Stellar populations and morphology on the red sequence at z~1

    NASA Astrophysics Data System (ADS)

    Mei, Simona; Holden, Brad P.; Blakeslee, John P.; Ford, Holland C.; Franx, Marijn; Illingworth, Garth D.; Jee, Myungkook J.; Overzier, Roderik; Postman, Marc; Rosati, Piero; van der Wel, Arjen; Bartlett, James G.

    2010-06-01

    We present results from a detailed study of cluster red sequence at z~1 from the ACS Intermediate Redshift Cluster Survey (Mei et al. 2009). Our analysis shows that the red sequence is well defined at z~1 and elliptical and lenticular galaxies lie on similar color-magnitude relations. We analyze the parameters of the early-type color-magnitude relations -scatter, slope and zero-point-as a function of redshift, galaxy properties and cluster mass. Our results suggest that bright elliptical galaxies in cluster cores are on average older than S0 galaxies and peripheral elliptical galaxies (by about 0.5 Gyr, using a simple, single burst solar metallicity Bruzual & Charlot (2003) stellar population model). The red sequence does not show significant evolution out to redshift z~1.3 nor significant dependence on cluster mass. The fraction of morphological early-type galaxies on the red sequence is 80% to 90% of the total red sequence population for most of our clusters. In the highest redshift, low mass cluster of our sample, early-type/late-type fractions on the red sequence are similar (~50%), with most of the late-type population composed of galaxies classified as S0/a. This trend is not correlated with the cluster's X-ray luminosity, nor with its velocity dispersion, and could be a real evolution with redshift.

  18. THE YOUNG STELLAR OBJECT POPULATION IN THE VELA-D MOLECULAR CLOUD

    SciTech Connect

    Strafella, F.; Maruccia, Y.; Maiolo, B.; Lorenzetti, D.; Giannini, T.; Elia, D.; Molinari, S.; Pezzuto, S.; Massi, F.; Olmi, L.

    2015-01-10

    We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D, a star-forming region observed by both the Spitzer/NASA and Herschel/ESA space telescopes. The point-source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSOs), also including sources detected in less than four IRAC bands. Bona fide YSOs are selected by using appropriate color-color and color-magnitude criteria aimed at excluding both Galactic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other star-forming clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far-IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources intended to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 of which are starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both the Spitzer and Herschel lists, it follows that in the investigated region we find 53 protostars and that the Spitzer-selected protostars account for approximately two-thirds of the total.

  19. On the origins of enigmatic stellar populations in Local Group galactic nuclei

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan W. C.; Antonini, Fabio; Stone, Nicholas C.; Shara, Michael M.; Merritt, David

    2016-08-01

    We consider the origins of enigmatic stellar populations in four Local Group galactic nuclei, specifically the Milky Way, M31, M32 and M33. These are centrally concentrated blue stars, found in three out of the four nuclear star clusters (NSCs) considered here. Their origins are unknown, but could include blue straggler (BS) stars, extended horizontal branch stars and young recently formed stars. Here, we calculate order-of-magnitude estimates for various collision rates, as a function of the host NSC environment and distance from the cluster centre. These rates are sufficiently high that BSs, formed via collisions between main sequence (MS) stars, could contribute non-negligibly (˜ 1-10% in mass) to every surface brightness profile, with the exception of the Milky Way. Stellar evolution models show that the envelopes of red giant branch (RGB) stars must be nearly completely stripped to significantly affect their photometric appearance, which requires multiple collisions. Hence, the collision rates for individual RGB stars are only sufficiently high in the inner ≲ 0.1 pc of M31 and M32 for RGB destruction to occur. Collisions between white dwarfs and MS stars, which should ablate the stars, could offer a steady and significant supply of gas in every NSC in our sample. The gas could either fragment to form new stars, or accrete onto old MS stars already present. Thus, collisional processes could contribute significantly to the observed blue excesses in M31 and M33; future studies should be aimed at better constraining theoretical predictions to compliment existing and future observational data.

  20. Physical Properties of Spectroscopically Confirmed Galaxies at z ≥ 6. III. Stellar Populations from SED Modeling with Secure Lyα Emission and Redshifts

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; Finlator, Kristian; Cohen, Seth H.; Egami, Eiichi; Windhorst, Rogier A.; Fan, Xiaohui; Davé, Romeel; Kashikawa, Nobunari; Mechtley, Matthew; Ouchi, Masami; Shimasaku, Kazuhiro; Clément, Benjamin

    2016-01-01

    We present a study of stellar populations in a sample of spectroscopically confirmed Lyman-break galaxies (LBGs) and Lyα emitters (LAEs) at 5.7\\lt z\\lt 7. These galaxies have deep images from Subaru, the Hubble Space Telescope, and Spitzer/IRAC. We focus on 27 galaxies with IRAC detections, and characterize their stellar populations based on the multi-band data and secure redshifts. By estimating nebular emission from the observed Lyα flux, we break the strong model degeneracy between young galaxies with prominent nebular emission and older galaxies with strong Balmer breaks. The results show that our galaxies cover a wide range of ages from several to a few hundred million years (Myr), and stellar masses from ˜108 to ˜10{}11 {M}⊙ . These galaxies can be roughly divided into two subsamples: an “old” subsample consisting of galaxies older than 100 Myr, with stellar masses higher than {10}9 {M}⊙ , and a “young” subsample consisting of galaxies younger than ˜30 Myr, with masses ranging between ˜108 and ˜ 3× {10}9 {M}⊙ . Both subsamples display a correlation between stellar mass and star formation rate (SFR), but with very different normalizations. The average specific SFR (sSFR) of the “old” subsample is 3-4 Gyr-1, consistent with previous studies of “normal” star-forming galaxies at z≥slant 6. The average sSFR of the “young” subsample is an order of magnitude higher, likely due to starburst activity. Our results also indicate little dust extinction in the majority of the galaxies, as already suggested by their steep rest-frame UV slopes. Finally, LAEs and LBGs with strong Lyα emission are indistinguishable in terms of age, stellar mass, and SFR. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based in part on

  1. Physical Properties of Spectroscopically Confirmed Galaxies at z ≥ 6. III. Stellar Populations from SED Modeling with Secure Lyα Emission and Redshifts

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; Finlator, Kristian; Cohen, Seth H.; Egami, Eiichi; Windhorst, Rogier A.; Fan, Xiaohui; Davé, Romeel; Kashikawa, Nobunari; Mechtley, Matthew; Ouchi, Masami; Shimasaku, Kazuhiro; Clément, Benjamin

    2016-01-01

    We present a study of stellar populations in a sample of spectroscopically confirmed Lyman-break galaxies (LBGs) and Lyα emitters (LAEs) at 5.7stellar populations based on the multi-band data and secure redshifts. By estimating nebular emission from the observed Lyα flux, we break the strong model degeneracy between young galaxies with prominent nebular emission and older galaxies with strong Balmer breaks. The results show that our galaxies cover a wide range of ages from several to a few hundred million years (Myr), and stellar masses from ˜108 to ˜10{}11 {M}⊙ . These galaxies can be roughly divided into two subsamples: an "old" subsample consisting of galaxies older than 100 Myr, with stellar masses higher than {10}9 {M}⊙ , and a "young" subsample consisting of galaxies younger than ˜30 Myr, with masses ranging between ˜108 and ˜ 3× {10}9 {M}⊙ . Both subsamples display a correlation between stellar mass and star formation rate (SFR), but with very different normalizations. The average specific SFR (sSFR) of the "old" subsample is 3-4 Gyr-1, consistent with previous studies of "normal" star-forming galaxies at z≥slant 6. The average sSFR of the "young" subsample is an order of magnitude higher, likely due to starburst activity. Our results also indicate little dust extinction in the majority of the galaxies, as already suggested by their steep rest-frame UV slopes. Finally, LAEs and LBGs with strong Lyα emission are indistinguishable in terms of age, stellar mass, and SFR. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based in part on observations made with the

  2. Ultraviolet, Optical, and Infrared Constraints on Models of Stellar Populations and Dust Attenuation

    NASA Astrophysics Data System (ADS)

    Johnson, Benjamin D.; Schiminovich, David; Seibert, Mark; Treyer, Marie; Martin, D. Christopher; Barlow, Tom A.; Forster, Karl; Friedman, Peter G.; Morrissey, Patrick; Neff, Susan G.; Small, Todd; Wyder, Ted K.; Bianchi, Luciana; Donas, José; Heckman, Timothy M.; Lee, Young-Wook; Madore, Barry F.; Milliard, Bruno; Rich, R. Michael; Szalay, Alex S.; Welsh, Barry Y.; Yi, Sukyoung K.

    2007-12-01

    The color of galaxies is a fundamental property, easily measured, that constrains models of galaxies and their evolution. Dust attenuation and star formation history (SFH) are the dominant factors affecting the color of galaxies. Here we explore the empirical relation between SFH, attenuation, and color for a wide range of galaxies, including early types. These galaxies have been observed by GALEX, SDSS, and Spitzer, allowing the construction of measures of dust attenuation from the ratio of infrared (IR) to ultraviolet (UV) flux and measures of SFH from the strength of the 4000 Å break. The empirical relation between these three quantities is compared to models that separately predict the effects of dust and SFH on color. This comparison demonstrates the quantitative consistency of these simple models with the data and hints at the power of multiwavelength data for constraining these models. The UV color is a strong constraint; we find that a Milky Way extinction curve is disfavored, and that the UV emission of galaxies with large 4000 Å break strengths is likely to arise from evolved populations. We perform fits to the relation between SFH, attenuation, and color. This relation links the production of starlight and its absorption by dust to the subsequent reemission of the absorbed light in the IR. Galaxy models that self-consistently treat dust absorption and emission as well as stellar populations will need to reproduce these fitted relations in the low-redshift universe.

  3. Probing the dusty inhabitants of the Local Group Galaxies: JWST/MIRI colors of infrared stellar populations

    NASA Astrophysics Data System (ADS)

    Jones, Olivia; Meixner, Margaret

    2016-01-01

    The assembly of galaxies involves the life cycle of mass, metal enrichment and dust that JWST will probe. Detailed studies of nearby galaxies provides guidance for interpreting the more distant forming galaxies. JWST/MIRI will enable stellar population studies akin to work done with HST on the Local Group galaxies but over a new wavelength range. MIRI's imaging capability over nine photometric bands from 5 to 28 microns is particularly suited to survey stars with an infrared excess and to detangle the extinction or thermal emission from various species of dust. These dusty stellar populations include young stellar objects, evolved stars and supernovae that are bright in the infrared. Using the rich Spitzer-IRS spectroscopic dataset and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)-Spectroscopic survey of over a thousand objects in the Magellanic Clouds, we calculate the expected flux -densities and colors in the MIRI broadband filters for these prominent infrared sources. We uses these fluxes to illustrate what JWST will see in stellar population studies for other Local Group galaxies. JWST/MIRI observations of infrared sources in Local Group Galaxies will constrain the life cycle of galaxies through their dust emission. For example, how much of the interstellar dust is supplied by dying stars? Do the number of young stellar objects agree with star formation diagnostic for the galaxy? We discuss the locations of the post- and pre-main-sequence populations in MIRI color-color and color-magnitude space and examine which filters are best for identifying populations of sources. We connect these results to existing galaxies with HST data for instance Andromeda and M33.

  4. 11 CFR 110.18 - Voting age population.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 11 Federal Elections 1 2012-01-01 2012-01-01 false Voting age population. 110.18 Section 110.18... PROHIBITIONS § 110.18 Voting age population. There is annually published by the Department of Commerce in the Federal Register an estimate of the voting age population based on an estimate of the voting...

  5. 11 CFR 110.18 - Voting age population.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 11 Federal Elections 1 2010-01-01 2010-01-01 false Voting age population. 110.18 Section 110.18... PROHIBITIONS § 110.18 Voting age population. There is annually published by the Department of Commerce in the Federal Register an estimate of the voting age population based on an estimate of the voting...

  6. 11 CFR 110.18 - Voting age population.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 11 Federal Elections 1 2013-01-01 2012-01-01 true Voting age population. 110.18 Section 110.18... PROHIBITIONS § 110.18 Voting age population. There is annually published by the Department of Commerce in the Federal Register an estimate of the voting age population based on an estimate of the voting...

  7. 11 CFR 110.18 - Voting age population.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 11 Federal Elections 1 2014-01-01 2014-01-01 false Voting age population. 110.18 Section 110.18... PROHIBITIONS § 110.18 Voting age population. There is annually published by the Department of Commerce in the Federal Register an estimate of the voting age population based on an estimate of the voting...

  8. 11 CFR 110.18 - Voting age population.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 11 Federal Elections 1 2011-01-01 2011-01-01 false Voting age population. 110.18 Section 110.18... PROHIBITIONS § 110.18 Voting age population. There is annually published by the Department of Commerce in the Federal Register an estimate of the voting age population based on an estimate of the voting...

  9. The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2013-07-01

    We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mag. We utilize these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local Vesc derived from the surface brightness. We find that the local Vesc is tightly correlated with the Mg b and Fe5015 line strengths and optical colours, and anti-correlated with the Hβ line strength. In the case of the Mg b and colour-Vesc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We also make use of single stellar population (SSP) modelling to transform our line strength index measurements into the SSP-equivalent parameters age (t), metallicity ([Z/H]) and α-enhancement [α/Fe]. The residuals from the relation are correlated with age, [α/Fe], molecular gas mass and local environmental density. We identify a population of galaxies that occur only at low Vesc that exhibit negative gradients in the Mg b- and Colour-Vesc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mg b-Vesc relation to constrain the possible number of dry mergers experienced by

  10. Developing vaccines for an aging population.

    PubMed

    Black, Steven; De Gregorio, Ennio; Rappuoli, Rino

    2015-04-01

    The demographics of the world's population are changing, with many adults now surviving into their 80s. With this change comes the need to protect the aging and other underserved populations not only against infectious diseases but also against cancer and other chronic conditions. New technologies derived from recent advances in the fields of immunology, structural biology, synthetic biology, and genomics have brought a revolution in the vaccine field. Among them, vaccine adjuvants have the potential to harness the immune system to provide protection against new types of diseases, improve protection in young children, and expand this protection to adults and the elderly. However, in order to do so we need also to overcome the nontechnical challenges that could limit the implementation of innovative vaccines, including controversies regarding the safety of adjuvants, increasing regulatory complexity, the inadequate methods used to assess the value of novel vaccines, and the resulting industry alienation from future investment. This Perspective summarizes the outcome of a recent multidisciplinary symposium entitled "Enhancing Vaccine Immunity and Value," held in Siena, Italy, in July 2014, that addressed two related questions: how to improve vaccine efficacy by using breakthrough technologies and how to capture the full potential of novel vaccines.

  11. Influence of the Stellar Population on Type IA Supernovae: Consequences for the Determination of Ω

    NASA Astrophysics Data System (ADS)

    Höflich, P.; Nomoto, K.; Umeda, H.; Wheeler, J. C.

    2000-01-01

    The influence of the metallicity on the main sequence on the chemical structure of the exploding white dwarf, the nucleosynthesis during the explosion, and the light curves of an individual Type Ia supernovae have been studied. Detailed calculations of the stellar evolution, the explosion, and light curves of delayed detonation models are presented. Detailed stellar evolution calculations with a main-sequence mass MMS of 7 Msolar have been performed to test the influence of the metallicity Z on the structure of the progenitor. A change of Z influences the central helium burning and, consequently, the size of the C/O core that becomes a C/O white dwarf and its C/O ratio. Subsequently, the white dwarf may grow to the Chandrasekhar mass and explode as a Type Ia supernova. Consequently, the C/O structure of the exploding white dwarf depends on Z. Since C and O are the fuel for the thermonuclear explosion, Z indirectly changes the energetics of the explosion. In our example, changing Z from Population I to Population II causes a change in the zero point of the maximum brightness/decline relation by about 0.1 mag and a change in the rise time by about 1 day. Combined with previous studies, the offset in the maximum brightness/decline ΔM~0.1Δt, where Δt is the change of the rise time in days. Systematic effects of the size discussed here may well make the results from the SNe Ia searches consistent with a universe with ΩM=0.2 and ΩΛ=0 but hardly will change the conclusion that we live in a universe with low ΩM. Variations of the expected size may prove to be critical if, in the future, SNe Ia are used to measure large-scale scalar fields because Z may show large local variations. Evolutionary effects will not change substantially the counting rates for SNe Ia even at very large redshifts. Evolutionary effects may be of the same order as the brightness changes related to cosmological parameters, but we have shown ways how the effects of evolution can be detected.

  12. A new type of compact stellar population: “dark star clusters”

    NASA Astrophysics Data System (ADS)

    Banerjee, Sambaran; Kroupa, Pavel

    2015-08-01

    The possibility of the presence of large populations of stellar mass black holes (BHs) in star clusters has currently come into focus as an increasing number of BHs are being detected in globular clusters from X-ray and radio observations. By virtue of their ~10 times higher mass than the average stellar mass, these BHs strongly segregate towards the center of their parent star cluster. In that way they become dynamically highly active and potentially invoke a wide variety of physical phenomena; the most important ones being emission of gravitational waves (GWs), formation of X-ray binaries, and expansion of the cluster. However, closer to the Galactic center, a different manifestation of the BH population within a star cluster can take place. We propose, for the first time, that rapid removal of stars from the outer parts of a cluster by the strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster. The remaining system would apparently be a super-virial star cluster that is gravitationally held compact by an invisible mass. We study the formation and properties of such systems through direct N-body computations and estimate that they can be present in significant numbers (~100) in the inner region of the Milky Way. We call such objects “dark star clusters” (DSCs) as they appear dimmer than normal star clusters of similar total mass and they comprise a predicted, new class of entities. Dark Star Clusters are a natural outcome of star clusters’ evolution in a strong tidal field provided a substantial number of BHs (and neutron stars) are formed with low natal kicks and are retained in them. Hence, the discovery of DSCs will not only constrain the uncertain natal kicks of BHs, thereby scenarios of BH formation, but will also reassure star clusters as potential sites for GW emission for forthcoming ground-based detectors such as the Advanced LIGO. Finally, we discuss whether the Galactic-central IRS 13E can possibly be a DSC.

  13. Pixel Color Magnitude Diagrams for Semi-resolved Stellar Populations: The Star Formation History of Regions within the Disk and Bulge of M31

    NASA Astrophysics Data System (ADS)

    Conroy, Charlie; van Dokkum, Pieter G.

    2016-08-01

    The analysis of stellar populations has, by and large, been developed for two limiting cases: spatially resolved stellar populations in the color–magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resolved regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Here we develop the concept of pixel color–magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity versus pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, {N}{{pix}}. Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and have the potential to break degeneracies between age, metallicity and dust based on two filter data for values of {N}{{pix}} up to at least 104. We extract pCMDs from Hubble Space Telescope optical imaging of M31 and derive SFHs with seven independent age bins from 106 to 1010 year for both the crowded disk and bulge regions (where {N}{{pix}}≈ 30{--}{10}3). From analyzing a small region of the disk we find a SFH that is smooth and consistent with an exponential decay timescale of 4 Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-based facilities.

  14. Pixel Color Magnitude Diagrams for Semi-resolved Stellar Populations: The Star Formation History of Regions within the Disk and Bulge of M31

    NASA Astrophysics Data System (ADS)

    Conroy, Charlie; van Dokkum, Pieter G.

    2016-08-01

    The analysis of stellar populations has, by and large, been developed for two limiting cases: spatially resolved stellar populations in the color-magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resolved regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Here we develop the concept of pixel color-magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity versus pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, {N}{{pix}}. Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and have the potential to break degeneracies between age, metallicity and dust based on two filter data for values of {N}{{pix}} up to at least 104. We extract pCMDs from Hubble Space Telescope optical imaging of M31 and derive SFHs with seven independent age bins from 106 to 1010 year for both the crowded disk and bulge regions (where {N}{{pix}}≈ 30{--}{10}3). From analyzing a small region of the disk we find a SFH that is smooth and consistent with an exponential decay timescale of 4 Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-based facilities.

  15. The regulation of star formation in cool-core clusters: imprints on the stellar populations of brightest cluster galaxies

    NASA Astrophysics Data System (ADS)

    Loubser, S. I.; Babul, A.; Hoekstra, H.; Mahdavi, A.; Donahue, M.; Bildfell, C.; Voit, G. M.

    2016-02-01

    A fraction of brightest cluster galaxies (BCGs) show bright emission in the ultraviolet and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broad-band photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 stellar populations as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (˜200 Myr) stellar populations in four of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star-forming BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1 and 3 per cent, but rising to 7 per cent in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibits a ratio of the radiative cooling-to-free-fall time (tc/tff) of ≤10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and active galactic nucleus feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter tc/tff falls below ˜10, leading to the condensation and precipitation of cold gas. The number of galaxies in our sample where the host cluster satisfies all the

  16. The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

    NASA Astrophysics Data System (ADS)

    Michielsen, D.; Boselli, A.; Conselice, C. J.; Toloba, E.; Whiley, I. M.; Aragón-Salamanca, A.; Balcells, M.; Cardiel, N.; Cenarro, A. J.; Gorgas, J.; Peletier, R. F.; Vazdekis, A.

    2008-04-01

    Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP. In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [α/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity-weighted mean age, the large-scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram-pressure stripping of the gas in short time-scales, and in the transformation of discy dwarfs to more spheroidal objects by harassment over longer time-scales. This points towards a continuing infalling scenario for the evolution of dEs.

  17. The Solar Twin Planet Search. III. The [Y/Mg] clock: estimating stellar ages of solar-type stars

    NASA Astrophysics Data System (ADS)

    Tucci Maia, M.; Ramírez, I.; Meléndez, J.; Bedell, M.; Bean, J. L.; Asplund, M.

    2016-05-01

    Context. Solar twins are stars with similar stellar (surface) parameters to the Sun that can have a wide range of ages. This provides an opportunity to analyze the variation of their chemical abundances with age. Nissen (2015, A&A, 579, A52) recently suggested that the abundances of the s-process element Y and the α-element Mg could be used to estimate stellar ages. Aims: This paper aims to determine with high precision the Y, Mg, and Fe abundances for a sample of 88 solar twins that span a broad age range (0.3-10.0 Gyr) and investigate their use for estimating ages. Methods: We obtained high-quality Magellan Inamori Kyocera Echelle (MIKE) spectra and determined Y and Mg abundances using equivalent widths and a line-by-line differential method within a 1D LTE framework. Stellar parameters and iron abundances were measured in Paper I of this series for all stars, but a few (three) required a small revision. Results: The [Y/Mg] ratio shows a strong correlation with age. It has a slope of -0.041 ± 0.001 dex/Gyr and a significance of 41σ. This is in excellent agreement with the relation first proposed by Nissen (2015). We found some outliers that turned out to be binaries where mass transfer may have enhanced the yttrium abundance. Given a precise measurement of [Y/Mg] with typical error of 0.02 dex in solar twins, our formula can be used to determine a stellar age with ~0.8 Gyr precision in the 0 to 10 Gyr range. Based on observations obtained at the Clay Magellan Telescopes at Las Campanas Observatory, Chile and at the 3.6 m Telescope at the La Silla ESO Observatory, Chile (program ID 188.C-0265).

  18. HORIZONTAL BRANCH MORPHOLOGY AND MULTIPLE STELLAR POPULATIONS IN THE ANOMALOUS GLOBULAR CLUSTER M 22

    SciTech Connect

    Marino, A. F.; Milone, A. P.; Lind, K. E-mail: milone@iac.es

    2013-05-01

    M 22 is an anomalous globular cluster that hosts two groups of stars with different metallicity and s-element abundance. The star-to-star light-element variations in both groups, with the presence of individual Na-O and C-N anticorrelations, demonstrates that this Milky Way satellite has experienced a complex star formation history. We have analyzed FLAMES/UVES spectra for seven stars covering a small color interval on the reddest horizontal branch (HB) portion of this cluster and investigated possible relations between the chemical composition of a star and its location along the HB. Our chemical abundance analysis takes into account effects introduced by deviations from the local thermodynamic equilibrium (NLTE effects), which are significant for the measured spectral lines in the atmospheric parameters range spanned by our stars. We find that all the analyzed stars are barium-poor and sodium-poor, thus supporting the idea that the position of a star along the HB is strictly related to the chemical composition, and that the HB morphology is influenced by the presence of different stellar populations.

  19. Characterizing stellar halo populations - I. An extended distribution function for halo K giants

    NASA Astrophysics Data System (ADS)

    Das, Payel; Binney, James

    2016-08-01

    We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ˜80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ˜-2 to ˜-4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ˜-0.001 dex kpc-1, a small gradient in the dispersion in [Fe/H] of ˜0.001 dex kpc-1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ˜-1.5 and ˜-2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.

  20. Ultraviolet Properties of Primeval Galaxies: Theoretical Models from Stellar Population Synthesis

    NASA Astrophysics Data System (ADS)

    Buzzoni, Alberto

    2002-03-01

    The ultraviolet luminosity evolution of star-forming galaxies is explored from the theoretical point of view, especially focusing on the theory of UV energetics in simple and composite stellar populations and its relationship to the star formation rate and other main evolutionary parameters. Galaxy emission below λ<3000 Å directly correlates with actual star formation, not depending on the total mass of the system. A straightforward calibration is obtained, in this sense, from the theoretical models at 1600, 2000, and 2800 Å, and a full comparison is carried out with IUE data and other balloon-borne observations for local galaxies. The claimed role of late-type systems as prevailing contributors to the cosmic UV background is reinforced by our results; at 2000 Å, Im irregulars are found in fact nearly 4 orders of magnitude brighter than ellipticals, per unit luminous mass. The role of dust absorption in the observation of high-redshift galaxies is assessed, comparing the model output and observed spectral energy distribution of local galaxy samples. Similar to what we observe in our own galaxy, a quick evolution in the dust environment might be envisaged in primeval galaxies, with an increasing fraction of luminous matter that would escape the regions of harder and ``clumpy'' dust absorption on a timescale of some 107 yr, comparable to the lifetime of stars of 5-10 Msolar.

  1. Spectra of late type dwarf stars of known abundance for stellar population models

    NASA Technical Reports Server (NTRS)

    Oconnell, R. W.

    1990-01-01

    The project consisted of two parts. The first was to obtain new low-dispersion, long-wavelength, high S/N IUE spectra of F-G-K dwarf stars with previously determined abundances, temperatures, and gravities. To insure high quality, the spectra are either trailed, or multiple exposures are taken within the large aperture. Second, the spectra are assembled into a library which combines the new data with existing IUE Archive data to yield mean spectral energy distributions for each important type of star. My principal responsibility is the construction and maintenance of this UV spectral library. It covers the spectral range 1200-3200A and is maintained in two parts: a version including complete wavelength coverage at the full spectral resolution of the Low Resolution cameras; and a selected bandpass version, consisting of the mean flux in pre-selected 20A bands. These bands are centered on spectral features or continuum regions of special utility - e.g. the C IV lambda 1550 or Mg II lambda 2800 feature. In the middle-UV region, special emphasis is given to those features (including continuum 'breaks') which are most useful in the study of F-G-K star spectra in the integrated light of old stellar populations.

  2. HST/WFC3 Near-Infrared Spectroscopy of Quenched and Mildly Star Forming Galaxies at 1.4 from WISPs: Stellar Population Properties

    NASA Astrophysics Data System (ADS)

    Bedregal, Alejandro; Scarlata, C.; WISP Survey Team

    2013-01-01

    We combine HST G102 and G141 near-IR grism spectroscopy with HST/UVIS, HST/WFC3 and Spitzer/IRAC[3.6 micron] photometry to assemble a sample of massive (M_star/M_sun = 11.0 dex) and rather passive galaxies at 1.4. After restricting to masses above 10.65 dex, this sample of 80 sources is the largest with homogeneous near-IR spectroscopy for this kind of galaxies at these redshifts. In contrast to the local Universe, we find the mass range above 10.65 dex is populated by galaxies with a wide range of properties. Although our color selection excludes from the sample typical SF massive galaxies, we still find two populations characterized by distinctive average luminosity-weighted ages and star-formation time-scales, but having similar mass and redshift distributions. The spectral energy distributions of Quenched galaxies (SSFR=<10^-2Gyr^-1) are well fitted with exponentially decreasing SFHs, and short star-formation timescales (tau=10-100Myr). They also show a wide distribution in ages, between 1 and 3 Gyrs. On the other hand, we also find a population of low SSFR galaxies (SSFR >10^-2Gyr.^-1) which show more extended SFHs (tau=0.1-1Gyr), being mostly old 3Gyr), and with higher A_V extinctions than the quenched galaxies. Given the stellar mass range covered by our SF galaxies, we find that their SFRs are low compared to normal SF galaxies at these redshifts (median SF 7M_sun yr^-1). We find that the old and massive population of mild-SF galaxies has properties inconsistent with them being a rejuvenated version of the quenched population at the same redshift. This possibly implies that the two samples originate from different mechanisms. In particular, the stellar-population properties of the quenched galaxies are consistent with being the result of gas-rich major mergers, well before the epoch of observation, and with a quick truncation of the SF after the merger. Instead, the properties of the old and mild-SF galaxies are in better agreement with a more extended

  3. Self-consistent physical parameters for five intermediate-age SMC stellar clusters from CMD modelling

    NASA Astrophysics Data System (ADS)

    Dias, B.; Kerber, L. O.; Barbuy, B.; Santiago, B.; Ortolani, S.; Balbinot, E.

    2014-01-01

    Context. Stellar clusters in the Small Magellanic Cloud (SMC) are useful probes for studying the chemical and dynamical evolution of this neighbouring dwarf galaxy, enabling inspection of a large period covering over 10 Gyr. Aims: The main goals of this work are the derivation of age, metallicity, distance modulus, reddening, core radius, and central density profiles for six sample clusters, in order to place them in the context of the Small Cloud evolution. The studied clusters are AM 3, HW 1, HW 34, HW 40, Lindsay 2, and Lindsay 3; HW 1, HW 34, and Lindsay 2 are studied for the first time. Methods: Optical colour-magnitude diagrams (V,B - V CMDs) and radial density profiles were built from images obtained with the 4.1 m Southern Astrophysical Research (SOAR) telescope, reaching V ~ 23. The determination of structural parameters were carried out by applying King profile fitting. The other parameters were derived in a self-consistent way by means of isochrone fitting, which uses likelihood statistics to identify the synthetic CMDs that best reproduce the observed ones. Membership probabilities were determined comparing the cluster and control field CMDs. Completeness and photometric uncertainties were obtained by performing artificial star tests. Results: The results confirm that these clusters (except HW 34, identified as a field fluctuation) are intermediate-age clusters, with ages between 1.2 Gyr (Lindsay 3) and ~5.0 Gyr (HW 1). In particular HW 1, Lindsay 2 and Lindsay 3 are located in a region that we called West Halo, where studies of ages and metallicity gradients are still lacking. Moreover, Lindsay 2 was identified as a moderately metal-poor cluster with [Fe/H] = -1.4 ± 0.2 dex, lower than expected from the age-metallicity relation by Pagel & Tautvaisiene (1998). We also found distances varying from ~53 kpc to 66 kpc, compatible with the large depth of the SMC. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which

  4. Variable Stars and Stellar Populations in Andromeda XXV. III. A Central Cluster or the Galaxy Nucleus?

    NASA Astrophysics Data System (ADS)

    Cusano, Felice; Garofalo, Alessia; Clementini, Gisella; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Ripepi, Vincenzo; Musella, Ilaria; Testa, Vincenzo; Carini, Roberta; Faccini, Marco

    2016-09-01

    We present B and V time series photometry of Andromeda XXV, the third galaxy in our program on the Andromeda’s satellites, which we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 62 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 57 RR Lyrae variables (46 fundamental-mode—RRab, and 11 first-overtone—RRc, pulsators), 3 anomalous Cepheids, 1 eclipsing binary system, and 1 unclassified variable. The average period of the RRab stars (< {Pab}> =0.60 σ = 0.04 days) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m-M)0 = 24.63 ± 0.17 mag. The color-magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poor ([Fe/H] = -1.8 dex) stellar population as old as ˜10-12 Gyr, traced by a conspicuous red giant branch and the large population of RR Lyrae stars. We discovered a spherically shaped high density of stars near the galaxy center. This structure appears to be at a distance consistent with Andromeda XXV and we suggest it could either be a star cluster or the nucleus of Andromeda XXV. We provide a summary and compare the number and characteristics of the pulsating stars in the M31 satellites analyzed so far for variability. Based on data collected with the Large Binocular Cameras at the Large Binocular Telescope.

  5. TESTING STELLAR POPULATION SYNTHESIS MODELS WITH SLOAN DIGITAL SKY SURVEY COLORS OF M31's GLOBULAR CLUSTERS

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.; Maccarone, Thomas J.; Kundu, Arunav

    2011-08-10

    Accurate stellar population synthesis models are vital in understanding the properties and formation histories of galaxies. In order to calibrate and test the reliability of these models, they are often compared with observations of star clusters. However, relatively little work has compared these models in the ugriz filters, despite the recent widespread use of this filter set. In this paper, we compare the integrated colors of globular clusters in the Sloan Digital Sky Survey (SDSS) with those predicted from commonly used simple stellar population (SSP) models. The colors are based on SDSS observations of M31's clusters and provide the largest population of star clusters with accurate photometry available from the survey. As such, it is a unique sample with which to compare SSP models with SDSS observations. From this work, we identify a significant offset between the SSP models and the clusters' g - r colors, with the models predicting colors which are too red by g - r {approx} 0.1. This finding is consistent with previous observations of luminous red galaxies in the SDSS, which show a similar discrepancy. The identification of this offset in globular clusters suggests that it is very unlikely to be due to a minority population of young stars. The recently updated SSP model of Maraston and Stroembaeck better represents the observed g - r colors. This model is based on the empirical MILES stellar library, rather than theoretical libraries, suggesting an explanation for the g - r discrepancy.

  6. Color and Stellar Population Gradients in Passively Evolving Galaxies at z ~ 2 from HST/WFC3 Deep Imaging in the Hubble Ultra Deep Field

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Giavalisco, Mauro; Cassata, Paolo; Ferguson, Henry C.; Dickinson, Mark; Renzini, Alvio; Koekemoer, Anton; Grogin, Norman A.; Papovich, Casey; Tundo, Elena; Fontana, Adriano; Lotz, Jennifer M.; Salimbeni, Sara

    2011-07-01

    We report the detection of color gradients in six massive (stellar mass (M star) > 1010 M ⊙) and passively evolving (specific star formation rate <10-11 yr-1) galaxies at redshift 1.3 < z < 2.5 identified in the Hubble Ultra Deep Field using ultra-deep Hubble Space Telescope (HST) Advanced Camera for Surveys and WFC3/IR images. After carefully matching the different point-spread functions, we obtain color maps and multi-band optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest resolved radial distance (≈1.7 kpc) up to several times the H-band effective radius. We find that the inner regions of these galaxies have redder rest-frame UV-optical colors (U - V, U - B, and B - V) than the outer parts. The slopes of the color gradient have no obvious dependence on the redshift and on the stellar mass of the galaxies. They do mildly depend, however, on the overall dust obscuration (E(B - V)) and rest-frame (U - V) color, with more obscured or redder galaxies having steeper color gradients. The z ~ 2 color gradients are also steeper than those of local early-type ones. The gradient of a single parameter (age, extinction, or metallicity) cannot fully explain the observed color gradients. Fitting the spatially resolved HST seven-band photometry to stellar population synthesis models, we find that, regardless of assumptions on the metallicity gradient, the redder inner regions of the galaxies have slightly higher dust obscuration than the bluer outer regions, implying that dust partly contributes to the observed color gradients, although the magnitude depends on the assumed extinction law. Due to the age-metallicity degeneracy, the derived age gradient depends on the assumptions for the metallicity gradient. We discuss the implications of a number of assumptions for metallicity gradients on the formation and evolution of these galaxies. We find that the evolution of the mass-size relationship from z ~ 2 to the present cannot be driven by in situ

  7. Extreme Stellar Populations in the Universe: Backsplash Dwarf Galaxies and Wandering Stars

    NASA Astrophysics Data System (ADS)

    Teyssier, Maureen

    We demonstrate that stars beyond the virial radii of galaxies may be generated by the gravitational impulse received by a satellite as it passes through the pericenter of its orbit around its parent. These stars may become energetically unbound (escaped stars), or may travel to further than a few virial radii for longer than a few Gyr, but still remain energetically bound to the system (wandering stars). Larger satellites (10-100% the mass of the parent), and satellites on more radial orbits are responsible for the majority of this ejected population. Wandering stars could be observable on Mpc scales via classical novae, and on 100 Mpc scales via SNIa. The existence of such stars would imply a corresponding population of barely-bound, old, high velocity stars orbiting the Milky Way, generated by the same physical mechanism during the Galaxy's formation epoch. Sizes and properties of these combined populations should place some constraints on the orbits and masses of the progenitor objects from which they came, providing insight into the merging histories of galaxies in general and the Milky Way in particular. We distinguish between Local Group field galaxies which may have passed through the virial volume of the Milky Way, and those which have not, via a statistical comparison against populations of dark matter haloes in the Via Lactea II (VLII) simulation with known orbital histories. Analysis of VLII provides expectations for this escaped population: they contribute 13 per cent of the galactic population between 300 and 1500 kpc from the Milky Way, and hence we anticipate that about 7 of the 54 known Local Group galaxies in that distance range are likely to be Milky Way escapees. These objects can be of any mass below that of the Milky Way, and they are expected to have positive radial velocities with respect to the Milky Way. Comparison of the radius-velocity distributions of VLII populations and measurements of Local Group galaxies presents a strong likelihood

  8. High-precision abundances of Sc, Mn, Cu, and Ba in solar twins. Trends of element ratios with stellar age

    NASA Astrophysics Data System (ADS)

    Nissen, P. E.

    2016-09-01

    Aims: A previous study of correlations between element abundances and ages of solar twin stars in the solar neighborhood is extended to include Sc, Mn, Cu, and Ba to obtain new information on the nucleosynthetic history of these elements. Methods: HARPS spectra with S/N ≳ 600 are used to derive very precise (σ ~ 0.01 dex) differential abundances of Sc, Mn, Cu, and Ba for 21 solar twins and the Sun. The analysis is based on MARCS model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Stellar ages with internal errors less than 1 Gyr are obtained by interpolation in the log g - Teff diagram between isochrones based on the Aarhus Stellar Evolution Code. Results: For stars younger than 6 Gyr, [Sc/Fe], [Mn/Fe], [Cu/Fe], and [Ba/Fe] are tightly correlated with stellar age, which is also the case for the other elements previously studied; linear relations between [X/Fe] and age have χ^2red ˜ 1, and for most stars the residuals do not depend on elemental condensation temperature. For ages between 6 and 9 Gyr, the [X/Fe] - age correlations break down and the stars split up into two groups having respectively high and low [X/Fe] for the odd-Z elements Na, Al, Sc, and Cu. Conclusions: While stars in the solar neighborhood younger than ~ 6 Gyr were formed from interstellar gas with a smooth chemical evolution, older stars seem to have originated from regions enriched by supernovae with different neutron excesses. Correlations between abundance ratios and stellar age suggest that: (i) Sc is made in Type II supernovae along with the α-capture elements; (ii) the Type II to Ia yield ratio is about the same for Mn and Fe; (iii) Cu is mainly made by the weak s-process in massive stars; (iv) the Ba/Y yield ratio for asymptotic giant branch stars increases with decreasing stellar mass; (v) [Y/Mg] and [Y/Al] can be used as chemical clocks when determining ages of solar metallicity stars. Based on data products from observations made

  9. Older and colder: The impact of starspots on stellar masses, ages, and lithium during the pre-main sequence

    NASA Astrophysics Data System (ADS)

    Somers, Garrett

    2016-01-01

    Starspots are ubiquitously found on young, active stars on the pre-main sequence (pre-MS), and may cover up to ~50% of their surfaces, but their effects on early stellar evolution have never been fully explored. I study the impact of such extreme spot coverage on pre-MS stellar evolution by modifying an existing stellar evolution code to account for spot effects on both the surface boundary conditions and the transport of energy in the interior. I show that heavy spot coverage systematically increases the radii of young stars, while reducing their luminosity and average surface temperature. Such increased radii may underlie the well-known radius inflation of some young, active stars, while the decreased luminosity and effective temperature displace stars on the HR diagram, leading to systematic under-estimation of stellar masses by up to 2x, and of stellar ages by up to 10x, if spotted stars are interpreted with un-spotted isochrones. The inhomogeneous surfaces of spotted stars also distort the emission spectrum, and can thus explain the anomalous colors of the rapidly rotating K dwarfs of the Pleiades, a young open cluster. I further find that spots reduce the central temperature of stars, leading to a suppression of lithium burning during the pre-MS. As a result, pre-MS stars of equal mass but differing spot properties reach the zero-age main sequence with different surface lithium abundances. I show that this effect can account for the previously unexplained lithium abundance dispersions observed at fixed Teff in the Pleiades, and other young clusters.Synthesizing these results, I argue that the inclusion of spots, a prominent phenomenon on the pre-MS, can explain several outstanding mysteries associated with young stars: inflated radii, age spreads in young clusters, the anomalous colors of rapid rotators, and the lithium abundance dispersions in young star clusters. I discuss implications of under-estimated masses and ages for measuring age spreads in young

  10. Identifying Contributions to the Stellar Halo from Accreted, Kicked-out, and In Situ Populations

    NASA Astrophysics Data System (ADS)

    Sheffield, Allyson A.; Majewski, Steven R.; Johnston, Kathryn V.; Cunha, Katia; Smith, Verne V.; Cheung, Andrew M.; Hampton, Christina M.; David, Trevor J.; Wagner-Kaiser, Rachel; Johnson, Marshall C.; Kaplan, Evan; Miller, Jacob; Patterson, Richard J.

    2012-12-01

    We present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30° < |b| < 60°), designed to probe the properties of this population to distances of ~9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk (lang[Fe/H]rang ~ -0.6) with some contribution from the metal-rich component of the nearby halo. Here we report first results for 1799 stars. The distribution of radial velocity (RV) as a function of l for these stars shows (1) the expected thick disk population and (2) local metal-rich halo stars moving at high speeds relative to the disk, which in some cases form distinct sequences in RV-l space. High-resolution echelle spectra taken for 34 of these "RV outliers" reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: 17 of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way, 8 have abundances coincident with those of the Galactic disk and a more metal-rich halo, and 9 of the stars fall on the locus defined by the majority of stars in the halo. The chemical abundance trends of the RV outliers suggest that this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas in situ on their current orbits. These results are consistent with scenarios where the stellar halo, at least as probed by M giants, arises from multiple formation mechanisms; however, when

  11. Grids of stellar models with rotation. II. WR populations and supernovae/GRB progenitors at Z = 0.014

    NASA Astrophysics Data System (ADS)

    Georgy, C.; Ekström, S.; Meynet, G.; Massey, P.; Levesque, E. M.; Hirschi, R.; Eggenberger, P.; Maeder, A.

    2012-06-01

    Context. In recent years, many very interesting observations have appeared concerning the positions of Wolf-Rayet (WR) stars in the Hertzsprung-Russell diagram (HRD), the number ratios of WR stars, the nature of Type Ibc supernova (SN) progenitors, long and soft gamma ray bursts (LGRB), and the frequency of these various types of explosive events. These observations represent key constraints on massive star evolution. Aims: We study, in the framework of the single-star evolutionary scenario, how rotation modifies the evolution of a given initial mass star towards the WR phase and how it impacts the rates of Type Ibc SNe. We also discuss the initial conditions required to obtain collapsars and LGRB. Methods: We used a recent grid of stellar models computed with and without rotation to make predictions concerning the WR populations and the frequency of different types of core-collapse SNe. Current rotating models were checked to provide good fits to the following features: solar luminosity and radius at the solar age, main-sequence width, red-giant and red-supergiant (RSG) positions in the HRD, surface abundances, and rotational velocities. Results: Rotating stellar models predict that about half of the observed WR stars and at least half of the Type Ibc SNe may be produced through the single-star evolution channel. Rotation increases the duration of the WNL and WNC phases, while reducing those of the WNE and WC phases, as was already shown in previous works. Rotation increases the frequency of Type Ic SNe. The upper mass limit for Type II-P SNe is ~19.0 M⊙ for the non rotating models and ~16.8 M⊙ for the rotating ones. Both values agree with observations. Moreover, present rotating models provide a very good fit to the progenitor of SN 2008ax. We discuss future directions of research for further improving the agreement between the models and the observations. We conclude that the mass-loss rates in the WNL and RSG phases are probably underestimated at present

  12. Galactic globular cluster NGC 6752 and its stellar population as inferred from multicolor photometry

    SciTech Connect

    Kravtsov, Valery; Alcaíno, Gonzalo; Marconi, Gianni; Alvarado, Franklin E-mail: inewton@terra.cl E-mail: gmarconi@eso.org

    2014-03-01

    This paper is devoted to photometric study of the Galactic globular cluster (GGC) NGC 6752 in UBVI, focusing on the multiplicity of its stellar population. We emphasize that our U passband is (1) narrower than the standard one due to its smaller extension blueward and (2) redshifted by ∼300 Å relative to its counterparts, such as the HST F336W filter. Accordingly, both the spectral features encompassed by it and photometric effects of the multiplicity revealed in our study are somewhat different than in recent studies of NGC 6752. Main sequence stars bluer in U – B are less centrally concentrated, as red giants are. We find a statistically significant increasing luminosity of the red giant branch (RGB) bump of ΔU ≈ 0.2 mag toward the cluster outskirts with no so obvious effect in V. The photometric results are correlated with spectroscopic data: the bluer RGB stars in U – B have lower nitrogen abundances. We draw attention to a larger width of the RGB than the blue horizontal branch (BHB) in U – B. This seems to agree with the effects predicted to be caused by molecular bands produced by nitrogen-containing molecules. We find that brighter BHB stars, especially the brightest ones, are more centrally concentrated. This implies that red giants that are redder in U – B, i.e., more nitrogen enriched and centrally concentrated, are the main progenitors of the brighter BHB stars. However, such a progenitor-progeny relationship disagrees with theoretical predictions and with the results on the elemental abundances in horizontal branch stars. We isolated the asymptotic giant branch clump and estimated the parameter ΔV{sub ZAHB}{sup clump} = 0.98 ± 0.12.

  13. Classifying the embedded young stellar population in Perseus and Taurus and the LOMASS database

    NASA Astrophysics Data System (ADS)

    Carney, M. T.; Yıldız, U. A.; Mottram, J. C.; van Dishoeck, E. F.; Ramchandani, J.; Jørgensen, J. K.

    2016-02-01

    Context. The classification of young stellar objects (YSOs) is typically done using the infrared spectral slope or bolometric temperature, but either can result in contamination of samples. More accurate methods to determine the evolutionary stage of YSOs will improve the reliability of statistics for the embedded YSO population and provide more robust stage lifetimes. Aims: We aim to separate the truly embedded YSOs from more evolved sources. Methods: Maps of HCO+J = 4-3 and C18O J = 3-2 were observed with HARP on the James Clerk Maxwell Telescope (JCMT) for a sample of 56 candidate YSOs in Perseus and Taurus in order to characterize the presence and morphology of emission from high density (ncrit > 106 cm-3) and high column density gas, respectively. These are supplemented with archival dust continuum maps observed with SCUBA on the JCMT and Herschel PACS to compare the morphology of the gas and dust in the protostellar envelopes. The spatial concentration of HCO+J = 4-3 and 850 μm dust emission are used to classify the embedded nature of YSOs. Results: Approximately 30% of Class 0+I sources in Perseus and Taurus are not Stage I, but are likely to be more evolved Stage II pre-main sequence (PMS) stars with disks. An additional 16% are confused sources with an uncertain evolutionary stage. Outflows are found to make a negligible contribution to the integrated HCO+ intensity for the majority of sources in this study. Conclusions: Separating classifications by cloud reveals that a high percentage of the Class 0+I sources in the Perseus star forming region are truly embedded Stage I sources (71%), while the Taurus cloud hosts a majority of evolved PMS stars with disks (68%). The concentration factor method is useful to correct misidentified embedded YSOs, yielding higher accuracy for YSO population statistics and Stage timescales. Current estimates (0.54 Myr) may overpredict the Stage I lifetime on the order of 30%, resulting in timescales down to 0.38 Myr for the

  14. Optimal lineage principle for age-structured populations

    NASA Astrophysics Data System (ADS)

    Kussell, Edo

    2012-02-01

    Populations whose individuals exhibit age-dependent growth have often been studied using temporal dynamics of age distributions. In this talk, I examine the dynamics of age along lineages. We will see that the lineage point-of-view provides fundamental insights into evolutionary pressures on individuals' aging profiles. I will describe a variational principle that enables exact results for lineage statistics, in a variety of models. I will also discuss measurements on continuously dividing bacterial populations growing in microfluidics devices.

  15. Rethinking Leisure Services in an Aging Population.

    ERIC Educational Resources Information Center

    Godbey, Geoffrey; And Others

    1982-01-01

    A survey examined fear of crime among an elderly population as it related to leisure behavior and the use of public recreation facilities. Response to the survey showed that, although the elderly population was surprisingly mobile, reasons preventing respondents from using parks and senior centers included: lack of interest, fear of crime, health,…

  16. STECKMAP: STEllar Content and Kinematics via Maximum A Posteriori likelihood

    NASA Astrophysics Data System (ADS)

    Ocvirk, P.

    2011-08-01

    STECKMAP stands for STEllar Content and Kinematics via Maximum A Posteriori likelihood. It is a tool for interpreting galaxy spectra in terms of their stellar populations through the derivation of their star formation history, age-metallicity relation, kinematics and extinction. The observed spectrum is projected onto a temporal sequence of models of single stellar populations, so as to determine a linear combination of these models that best fits the observed spectrum. The weights of the various components of this linear combination indicate the stellar content of the population. This procedure is regularized using various penalizing functions. The principles of the method are detailed in Ocvirk et al. 2006.

  17. The importance of stellar feedback for high-redshift galaxy populations in hierarchical formation models

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; De Lucia, Gabriella

    2015-08-01

    One major deficiency of most state-of-the-art galaxy formation models consists in their inability of capturing the observed galaxy downsizing trend as they significantly over-estimate the number density of low-mass galaxies at high redshifts. This points towards fundamental modifications in modeling the interplay between star formation and stellar feedback. Employing an enhanced galaxy formation model with a full chemical enrichment scheme, we present an improved model for stellar feedback (based on parametrizations extracted from cosmological zoom simulations), in which strong gas outflows happen due to bursty star formation at high redshift, while star formation is mainly "quiescent" not causing any significant outflows anymore at low redshift. Due to the stronger gas outflows at high z, early star formation is strongly delayed towards later times in good agreement with abundance matching predictions. As a consequence, also metal enrichment gets significantly delayed, resulting in a much more realistic redshift evolution of the gaseous metallicity. Overall, with our new stellar feedback model, we can successfully reproduce many observational constraints, such as the redshift evolution of the stellar mass function and of the SFR function, the gaseous and stellar metallicity content, the cold gas fractions and the fraction of quiescent/red galaxies at both low and high redshifts. The resulting new-generation galaxy catalogues based on that model are expected to significantly contribute to the interpretation of current and up-coming large-scale surveys (HST, JWST, Euclid) which in turn may also help to further constrain feedback models.

  18. CHANDRA/ACIS-I STUDY OF THE X-RAY PROPERTIES OF THE NGC 6611 AND M16 STELLAR POPULATIONS

    SciTech Connect

    Guarcello, M. G.; Drake, J. J.; Caramazza, M.; Micela, G.; Sciortino, S.; Prisinzano, L.

    2012-07-10

    Mechanisms regulating the origin of X-rays in young stellar objects and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow us to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC 6611. At 1750 pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age {<=}3 Myr. We study an archival 78 ks Chandra/ACIS-I observation of NGC 6611 and two new 80 ks observations of the outer region of M16, one centered on the Column V and the other on a region of the molecular cloud with ongoing star formation. We detect 1755 point sources with 1183 candidate cluster members (219 disk-bearing and 964 disk-less). We study the global X-ray properties of M16 and compare them with those of the Orion Nebula Cluster. We also compare the level of X-ray emission of Class II and Class III stars and analyze the X-ray spectral properties of OB stars. Our study supports the lower level of X-ray activity for the disk-bearing stars with respect to the disk-less members. The X-ray luminosity function (XLF) of M16 is similar to that of Orion, supporting the universality of the XLF in young clusters. Eighty-five percent of the O stars of NGC 6611 have been detected in X-rays. With only one possible exception, they show soft spectra with no hard components, indicating that mechanisms for the production of hard X-ray emission in O stars are not operating in NGC 6611.

  19. Chandra/ACIS-I Study of the X-Ray Properties of the NGC 6611 and M16 Stellar Populations

    NASA Astrophysics Data System (ADS)

    Guarcello, M. G.; Caramazza, M.; Micela, G.; Sciortino, S.; Drake, J. J.; Prisinzano, L.

    2012-07-01

    Mechanisms regulating the origin of X-rays in young stellar objects and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow us to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC 6611. At 1750 pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age <=3 Myr. We study an archival 78 ks Chandra/ACIS-I observation of NGC 6611 and two new 80 ks observations of the outer region of M16, one centered on the Column V and the other on a region of the molecular cloud with ongoing star formation. We detect 1755 point sources with 1183 candidate cluster members (219 disk-bearing and 964 disk-less). We study the global X-ray properties of M16 and compare them with those of the Orion Nebula Cluster. We also compare the level of X-ray emission of Class II and Class III stars and analyze the X-ray spectral properties of OB stars. Our study supports the lower level of X-ray activity for the disk-bearing stars with respect to the disk-less members. The X-ray luminosity function (XLF) of M16 is similar to that of Orion, supporting the universality of the XLF in young clusters. Eighty-five percent of the O stars of NGC 6611 have been detected in X-rays. With only one possible exception, they show soft spectra with no hard components, indicating that mechanisms for the production of hard X-ray emission in O stars are not operating in NGC 6611.

  20. Herschel far-infrared observations of the Carina Nebula complex - The embedded young stellar and protostellar population

    NASA Astrophysics Data System (ADS)

    Gaczkowski, Benjamin; Preibisch, Thomas; Ratzka, Thorsten; Roccatagliata, Veronica; Ohlendorf, Henrike; Pekruhl, Stephanie

    2013-07-01

    At a distance of 2.3 kpc, the Carina Nebula is the nearest southern region with a large enough massive stellar population to sample the top of the IMF and displays all phenomena of massive star formation. We have performed a 9 square-degree Herschel far-infrared survey of the Carina Nebula complex (CNC) which revealed, for the first time, the very complex and filamentary small-scale structure of the dense clouds. We discovered 642 objects that are independently detected as point-like sources in at least two of the five Herschel bands. About 75% of these are Class 0 protostars with masses between about one and ten solar masses estimated from radiative transfer modeling. Taking the observational limits into account and extrapolating the observed number of Herschel-detected protostars over the stellar initial mass function suggests that the star formation rate of the CNC is about 0.017 solar masses per year. The spatial distribution of the Herschel young stellar objects (YSO) candidates is highly inhomogeneous and does not follow the distribution of cloud mass. Rather, most Herschel YSO candidates are found at the irradiated edges of clouds and pillars. The currently ongoing star formation process forms only low-mass and intermediate-mass stars, but no massive stars. The characteristic spatial configuration of the YSOs provides support to the picture that the formation of this latest stellar generation is triggered by the advancing ionization fronts. Around the bubble-shaped HII region Gum 31 (containing the young stellar cluster NGC 3324) in the north-western part of the CNC we identified 752 candidate YSOs from Spitzer, WISE, and Herschel data and analyzed their spectral energy distributions. Their location in the rim of the bubble is suggestive of their being triggered by a 'collect and collapse' scenario, which agrees well with the observed parameters of the region which we obtained from density and temperature maps from our Herschel data.

  1. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. III. A Quintuple Stellar Population in NGC 2808

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Marino, A. F.; Piotto, G.; Renzini, A.; Bedin, L. R.; Anderson, J.; Cassisi, S.; D'Antona, F.; Bellini, A.; Jerjen, H.; Pietrinferni, A.; Ventura, P.

    2015-07-01

    In this study we present the first results from multi-wavelength Hubble Space Telescope (HST) observations of the Galactic globular cluster (GC) NGC 2808 as an extension of the Hubble Space Telescope UV Legacy Survey of Galactic GCs (GO-13297 and previous proprietary and HST archive data). Our analysis allowed us to disclose a multiple-stellar-population phenomenon in NGC 2808 even more complex than previously thought. We have separated at least five different populations along the main sequence and the red giant branch (RGB), which we name A, B, C, D, and E (though an even finer subdivision may be suggested by the data). We identified the RGB bump in four out of the five RGBs. To explore the origin of this complex color-magnitude diagram, we have combined our multi-wavelength HST photometry with synthetic spectra, generated by assuming different chemical compositions. The comparison of observed colors with synthetic spectra suggests that the five stellar populations have different contents of light elements and helium. Specifically, if we assume that NGC 2808 is homogeneous in [Fe/H] (as suggested by spectroscopy for Populations B, C, D, E, but lacking for Population A) and that population A has a primordial helium abundance, we find that populations B, C, D, E are enhanced in helium by ΔY ˜ 0.03, 0.03, 0.08, 0.13, respectively. We obtain similar results by comparing the magnitude of the RGB bumps with models. Planned spectroscopic observations will test whether Population A also has the same metallicity, or whether its photometric differences with Population B can be ascribed to small [Fe/H] and [O/H] differences rather than to helium. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  2. THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. III. A QUINTUPLE STELLAR POPULATION IN NGC 2808

    SciTech Connect

    Milone, A. P.; Marino, A. F.; Jerjen, H.; Piotto, G.; Renzini, A.; Bedin, L. R.; Anderson, J.; Bellini, A.; Cassisi, S.; Pietrinferni, A.; D’Antona, F.; Ventura, P.

    2015-07-20

    In this study we present the first results from multi-wavelength Hubble Space Telescope (HST) observations of the Galactic globular cluster (GC) NGC 2808 as an extension of the Hubble Space Telescope UV Legacy Survey of Galactic GCs (GO-13297 and previous proprietary and HST archive data). Our analysis allowed us to disclose a multiple-stellar-population phenomenon in NGC 2808 even more complex than previously thought. We have separated at least five different populations along the main sequence and the red giant branch (RGB), which we name A, B, C, D, and E (though an even finer subdivision may be suggested by the data). We identified the RGB bump in four out of the five RGBs. To explore the origin of this complex color–magnitude diagram, we have combined our multi-wavelength HST photometry with synthetic spectra, generated by assuming different chemical compositions. The comparison of observed colors with synthetic spectra suggests that the five stellar populations have different contents of light elements and helium. Specifically, if we assume that NGC 2808 is homogeneous in [Fe/H] (as suggested by spectroscopy for Populations B, C, D, E, but lacking for Population A) and that population A has a primordial helium abundance, we find that populations B, C, D, E are enhanced in helium by ΔY ∼ 0.03, 0.03, 0.08, 0.13, respectively. We obtain similar results by comparing the magnitude of the RGB bumps with models. Planned spectroscopic observations will test whether Population A also has the same metallicity, or whether its photometric differences with Population B can be ascribed to small [Fe/H] and [O/H] differences rather than to helium.

  3. Ultraviolet radiation from evolved stellar populations. 2: The ultraviolet upturn phenomenon in elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Dorman, Ben; O'Connell, Robert W.; Rood, Robert T.

    1995-01-01

    We discuss the far-ultraviolet upturn phenomenon (UVX) observed in elliptical galaxies and spiral galaxy bulges. Our premise is the UV radiation from these systems emanates primarily from extreme horizontal branch (EHB) stars and their progeny. We derive the broad-band UV colors 1500-V and 2500-V for globular clusters and elliptical galaxies from the available satellite data and investigate color-color and color-line strength correlation. Clusters can be bluer than any galaxy in 15-V and 25-V, implying larger hot star populations, but galaxies are significantly bluer than clusters in 15-25 at a given 15-V. We attribute this primarily to the effect of metal abundance on the mid-UV (2500 A) light. These redder colors of the galaxies also imply that the UVX in galaxies is not produced by metal-poor subpopulations similar to the clusters. We devlop a simple spectral synthesis formulation for all phases of single star evolution from the zero-age main sequence (ZAMS) to the white dwarf cooling track that requires only one or two parameters for each choice of age and abundance. We provide the ingredients necessary for constructing models with arbitrary horizontal branch (HB) morphologies in the age range 2 less than t less than 20 Gyr and for six metallicities in the range -2.26 less than (Fe/H) less than 0.58; we also consider the efect of enhanced Y in metal-rich models. The maximum lifetime UV output is produced by EHB stars with (M(sub env))(sup 0) approximately 0.02 solar mass and can be up to 30 times higher than for post-asymptotic giant branch (P-AGB) stars. The ultraviolet output of old populations is governed primarily by the distribution of (M(sub env))(sup 0)P(M(sub env))(sup 0), on the ZAHB. The UV output is not very sensitive to (Fe/H) or to Y, but it can change very rapidly with (M(sub env))(sup 0). Thus it is extremely sensitive to the precise nature of giant-branch mass loss. Our models use simple descriptions of P(M(sub env))(sup 0) to bracket the colors

  4. The puzzle of metallicity and multiple stellar populations in the globular clusters in Fornax

    NASA Astrophysics Data System (ADS)

    D'Antona, F.; Caloi, V.; D'Ercole, A.; Tailo, M.; Vesperini, E.; Ventura, P.; Di Criscienzo, M.

    2013-09-01

    All models for the formation of multiple populations in globular clusters (GCs) imply an initial mass of the systems several times greater than the present mass. A recent study of the dwarf spheroidal galaxy Fornax, where the low-metallicity ([Fe/H] ≲ -2) stars contained in GCs appear to account for ˜20 per cent of the total number, seems to constrain the initial mass of the four low-metallicity GCs in Fornax to be at most a factor of 5-6 greater than their present mass. We examine the photometric data for Fornax clusters, focusing our attention on their horizontal branch (HB) colour distribution and, when available, on the fraction and period distribution of RR Lyrae variables. Based on our understanding of the HB morphology in terms of varying helium content (and red giant mass-loss rate) in the context of multiple stellar generations, we show that the clusters F2, F3 and F5 must contain substantial fractions of second-generation stars (˜54-65 per cent). On the basis of a simple chemical evolution model we show that the helium distribution in these clusters can be reproduced by models with cluster initial masses ranging from values equal to ˜4 to ˜10 times greater than the current masses. Models with a very short second-generation star formation episode can also reproduce the observed helium distribution but require greater initial masses up to about 20 times the current mass. While the lower limit of this range of possible initial GC masses is consistent with those suggested by observations of the low-metallicity field stars, we also discuss the possibility that the metallicity scale of field stars (based on Ca II triplet spectroscopy) and the metallicities derived for the clusters in Fornax may not be consistent with each other. In this case, observational constraints would allow greater initial cluster masses. Two interesting hypotheses are needed in order to reproduce the HB morphology of the clusters F2, F3 and F5. (i) The first-generation HB stars all

  5. China: Awakening Giant Developing Solutions to Population Aging

    ERIC Educational Resources Information Center

    Zhang, Ning Jackie; Guo, Man; Zheng, Xiaoying

    2012-01-01

    As the world's most populous country with the largest aging population and a rapidly growing economy, China is receiving increased attention from both the Chinese government and the governments of other countries that face low fertility and aging problems. This unprecedented shift of demographic structure has repercussions for many aspects of…

  6. The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)

    NASA Astrophysics Data System (ADS)

    Carretta, E.; Bragaglia, A.; Gratton, R. G.; D'Orazi, V.; Lucatello, S.; Sollima, A.; Momany, Y.; Catanzaro, G.; Leone, F.

    2015-06-01

    We present the abundance analysis of 82 red giant branch stars in the dense, metal-poor globular cluster NGC 6093 (M 80), the largest sample of stars analysed in this way for this cluster. From high-resolution UVES spectra of 14 stars and intermediate resolution GIRAFFE spectra for the other stars we derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu. On our UVES metallicity scale the mean metal abundance of M 80 is [Fe/H] = -1.791 ± 0.006 ± 0.076 (±statistical ±systematic error) with σ = 0.023 (14 stars). M 80 shows star-to-star variations in proton-capture elements, and the extension of the Na-O anti-correlation perfectly fit the relations with (i) total cluster mass; (ii) horizontal branch morphology; and (iii) cluster concentration previously found by our group. The chemistry of multiple stellar populations in M 80 does not look extreme. The cluster is also a representative of halo globular clusters concerning the pattern of α-capture and Fe-group elements. However we found that a significant contribution from the s-process is required to account for the distribution of neutron-capture elements. A minority of stars in M 80 seem to exhibit slightly enhanced abundances of s-process species, compatible with those observed in M 22 and NGC 1851, although further confirmation from larger samples is required. Based on observations collected at ESO telescopes under programme 083.D-0208.Full Tables 2, 3, 5-9 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A116Appendix A is available in electronic form at http://www.aanda.org

  7. Comparisons of the galaxy age, stellar velocity dispersion and K-band luminosity distributions between grouped galaxies and isolated ones

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Deng, Xin-Fa

    2016-02-01

    In two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we compare the age, stellar velocity dispersion and K-band luminosity distributions of grouped galaxies with those of isolated galaxies, to explore the environmental dependence of these properties of galaxies. It is found that grouped galaxies have preferentially larger stellar velocity dispersions and are preferentially older than isolated galaxies. We also note apparent difference of K-band luminosity distribution at both extremes of density in the luminous volume-limited Main galaxy sample: grouped galaxies are preferentially more luminous than isolated galaxies, while this difference in the faint volume-limited Main galaxy sample is very small.

  8. Realistic ionizing fluxes for young stellar populations from 0.05 to 2 Zsolar

    NASA Astrophysics Data System (ADS)

    Smith, Linda J.; Norris, Richard P. F.; Crowther, Paul A.

    2002-12-01

    We present a new grid of ionizing fluxes for O and Wolf-Rayet (W-R) stars for use with evolutionary synthesis codes and single-star HII region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Zsolar) using the WM-BASIC code of Pauldrach, Hoffmann & Lennon for O stars and the CMFGEN code of Hillier & Miller for W-R stars. The stellar wind parameters are scaled with metallicity for both O and W-R stars. We compare the ionizing fluxes of the new models with the CoStar models of Schaerer & de Koter and the pure helium W-R models of Schmutz, Leitherer & Gruenwald. We find significant differences, particularly above 54 eV, where the emergent flux is determined by the wind density as a function of metallicity. The new models have lower ionizing fluxes in the HeI continuum with important implications for nebular line ratios. We incorporate the new models into the evolutionary synthesis code STARBURST99 and compare the ionizing outputs for an instantaneous burst and continuous star formation with the work of Schaerer & Vacca (SV98), and Leitherer et al. The changes in the output ionizing fluxes as a function of age are dramatic. We find that, in contrast to previous studies, nebular HeIIλ4686 will be at, or just below, the detection limit in low metallicity starbursts during the W-R phase. The new models have lower fluxes in the HeI continuum for Z>= 0.4 Zsolar and ages <=7 Myr because of the increased line blanketing. We test the accuracy of the new model atmosphere grid by constructing photoionization models for simple HII regions, and assessing the impact of the new ionizing fluxes on important nebular diagnostic line ratios. For the case of an HII region where the ionizing flux is given by the WM-basic dwarf O star grid, we show that HeIλ5786/Hβ decreases between 1 and 2 Zsolar in a similar manner to observations. We find that this decline is caused by the increased

  9. Age-structured optimal control in population economics.

    PubMed

    Feichtinger, Gustav; Prskawetz, Alexia; Veliov, Vladimir M

    2004-06-01

    This paper brings both intertemporal and age-dependent features to a theory of population policy at the macro-level. A Lotka-type renewal model of population dynamics is combined with a Solow/Ramsey economy. We consider a social planner who maximizes an aggregate intertemporal utility function which depends on per capita consumption. As control policies we consider migration and saving rate (both age-dependent). By using a new maximum principle for age-structured control systems we derive meaningful results for the optimal migration and saving rate in an aging population. The model used in the numerical calculations is calibrated for Austria.

  10. Estimating ages of open star clusters using stellar lumionosity and colour

    NASA Astrophysics Data System (ADS)

    Williams, Chris

    2004-12-01

    This paper was designed for the 'armchair' astronomer who is interested in 'amateur research' by utilising the vast amount of images placed on the Internet from various places. Open star clusters are groups of stars that are physically related, bound by mutual gravitational attraction, populate a limited region of space and are all roughly at the same distance from us. We believe they originate from large cosmic gas and dust clouds within the Milky Way and the process of formation takes only a short time, so therefore all members of the cluster are of similar age. Also, as all the stars in a cluster formed from the same cloud, they are all of similar (initial) chemical composition. This 'family' of stars may be of similar birth age but their evolutionary ages differ due to the variation in their masses. High mass stars evolve much quicker than low mass stars they consume their fuel faster, have higher luminosities and die in a very short time (astronomical speaking) compared to a fractional solar mass star.

  11. The Flynn Effect and Population Aging

    ERIC Educational Resources Information Center

    Skirbekk, Vegard; Stonawski, Marcin; Bonsang, Eric; Staudinger, Ursula M.

    2013-01-01

    Although lifespan changes in cognitive performance and Flynn effects have both been well documented, there has been little scientific focus to date on the net effect of these forces on cognition at the population level. Two major questions moving beyond this finding guided this study: (1) Does the Flynn effect indeed continue in the 2000s for…

  12. The Resolved Stellar Halo and Dwarf Satellite Population of NGC 3109

    NASA Astrophysics Data System (ADS)

    Hargis, Jonathan R.; Crnojevic, Denija; Sand, David J.; Willman, Beth; Spekkens, Kristine; Grillmair, Carl J.; Strader, Jay

    2016-01-01

    The stellar halo and halo substructure of dwarf galaxies provides an important window into both LCDM cosmology and galaxy formation theory on the smallest scales. We are undertaking a deep, wide-field imaging survey of nearby, isolated sub-Milky Way mass galaxies in order to (1) map the substructure, spatial extent, and metallicity of their stellar halos in resolved stars, and (2) search for faint dwarf satellite companions (i.e., the ``dwarfs of dwarfs"). These studies will allow us to explore the role of in-situ versus accretion processes in forming stellar halos in dwarfs, as well as constrain the faint end of the satellite galaxy luminosity function. This work presents a preliminary analysis of the pilot galaxy in our survey: NGC 3109 (Mv = -15 mag), a nearby (d = 1.3 Mpc) dwarf irregular, approximately 1/6th the stellar mass of the SMC. We imaged ~40 sq. deg around NGC 3109 (projected radius of ~100 kpc) using CTIO 4m/DECam to depths ~2 mag below the TRGB. We disovered a new gas-rich dwarf satellite of NGC 3109, dubbed Antlia B (Mv = -9.7 mag), similar to the recently-discovered Leo P. We also discovered five candidate dwarf satellites, with sizes (~100 pc) and luminosities (Mv ~ -6 mag) consistent with being ultra-faint dwarfs at the distance of NGC 3109. Lastly, we present stellar halo maps of resolved RGB stars on both large and small scales. We discuss the various substructures found in these maps and the future directions of our survey. This work was supported by NSF AST-1151462.

  13. Inferences about ungulate population dynamics derived from age ratios

    USGS Publications Warehouse

    Harris, N.C.; Kauffman, M.J.; Mills, L.S.

    2008-01-01

    Age ratios (e.g., calf:cow for elk and fawn:doe for deer) are used regularly to monitor ungulate populations. However, it remains unclear what inferences are appropriate from this index because multiple vital rate changes can influence the observed ratio. We used modeling based on elk (Cervus elaphus) life-history to evaluate both how age ratios are influenced by stage-specific fecundity and survival and how well age ratios track population dynamics. Although all vital rates have the potential to influence calf:adult female ratios (i.e., calf:xow ratios), calf survival explained the vast majority of variation in calf:adult female ratios due to its temporal variation compared to other vital rates. Calf:adult female ratios were positively correlated with population growth rate (??) and often successfully indicated population trajectories. However, calf:adult female ratios performed poorly at detecting imposed declines in calf survival, suggesting that only the most severe declines would be rapidly detected. Our analyses clarify that managers can use accurate, unbiased age ratios to monitor arguably the most important components contributing to sustainable ungulate populations, survival rate of young and ??. However, age ratios are not useful for detecting gradual declines in survival of young or making inferences about fecundity or adult survival in ungulate populations. Therefore, age ratios coupled with independent estimates of population growth or population size are necessary to monitor ungulate population demography and dynamics closely through time.

  14. Delivering Library Services to an Aging Population.

    ERIC Educational Resources Information Center

    Katz, Ruth M.

    This study guide was prepared to assist library personnel in using the VINTAGE series, which consists of five color videocassette programs and two slide/sound shows on topics relating to public library services to the aging. The guide to these programs, which were designed for use in staff development programs and to promote community involvement,…

  15. On Constructing Ageing Rural Populations: "Capturing" the Grey Nomad

    ERIC Educational Resources Information Center

    Davies, Amanda

    2011-01-01

    The world's population is ageing, with forecasts predicting this ageing is likely to be particularly severe in the rural areas of more developed countries. These forecasts are developed from nationally aggregated census and survey data and assume spatial homogeneity in ageing. They also draw on narrow understandings of older people and construct…

  16. Asteroseismology for "à la carte" stellar age-dating and weighing. Age and mass of the CoRoT exoplanet host HD 52265

    NASA Astrophysics Data System (ADS)

    Lebreton, Y.; Goupil, M. J.

    2014-09-01

    Context. In the context of the space missions CoRoT, Kepler, Gaia, TESS, and PLATO, precise and accurate stellar ages, masses, and radii are of paramount importance. For instance, they are crucial for constraining scenarii of planetary formation and evolution. Aims: We aim at quantifying how detailed stellar modelling can improve the accuracy and precision on age and mass of individual stars. To that end, we adopt a multifaceted approach where we carefully examine how the number of observational constraints as well as the uncertainties on observations and on model input physics affect the results of age-dating and weighing. Methods: We modelled in detail the exoplanet host-star HD 52265, a main-sequence, solar-like oscillator that CoRoT observed for four months. We considered different sets of observational constraints (Hertzsprung-Russell data, metallicity, various sets of seismic constraints). For each case, we determined the age, mass, and properties of HD 52265 inferred from stellar models, and we quantified the impact of the model input physics and free parameters. We also compared model ages with ages derived by empirical methods or Hertzsprung-Russell diagram inversion. Results: For our case study HD 52265, our seismic analysis provides an age A = 2.10-2.54 Gyr, a mass M = 1.14-1.32 M⊙, and a radius R = 1.30-1.34 R⊙, which corresponds to age, mass, and radius uncertainties of ~10, ~7, and ~1.5 per cent, respectively. These uncertainties account for observational errors and current state-of-the-art stellar model uncertainties. Our seismic study also provides constraints on surface convection properties through the mixing-length, which we find to be 12-15 per cent lower than the solar value. On the other hand, because of helium-mass degeneracy, the initial helium abundance is determined modulo the mass value. Finally, we evaluate the seismic mass of the exoplanet to be Mpsini = 1.17-1.26 MJupiter, much more precise than what can be derived by Hertzsprung

  17. Star Cluster Properties in Two LEGUS Galaxies Computed with Stochastic Stellar Population Synthesis Models

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.; Adamo, Angela; Fumagalli, Michele; Wofford, Aida; Calzetti, Daniela; Lee, Janice C.; Whitmore, Bradley C.; Bright, Stacey N.; Grasha, Kathryn; Gouliermis, Dimitrios A.; Kim, Hwihyun; Nair, Preethi; Ryon, Jenna E.; Smith, Linda J.; Thilker, David; Ubeda, Leonardo; Zackrisson, Erik

    2015-10-01

    We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar.

  18. STAR CLUSTER PROPERTIES IN TWO LEGUS GALAXIES COMPUTED WITH STOCHASTIC STELLAR POPULATION SYNTHESIS MODELS

    SciTech Connect

    Krumholz, Mark R.; Adamo, Angela; Fumagalli, Michele; Wofford, Aida; Calzetti, Daniela; Grasha, Kathryn; Lee, Janice C.; Whitmore, Bradley C.; Bright, Stacey N.; Ubeda, Leonardo; Gouliermis, Dimitrios A.; Kim, Hwihyun; Nair, Preethi; Ryon, Jenna E.; Smith, Linda J.; Zackrisson, Erik E-mail: adamo@astro.su.se

    2015-10-20

    We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar.

  19. A reinterpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disc

    NASA Astrophysics Data System (ADS)

    Price-Whelan, Adrian M.; Johnston, Kathryn V.; Sheffield, Allyson A.; Laporte, Chervin F. P.; Sesar, Branimir

    2015-09-01

    The Triangulum-Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of concentric ring- or shell-like overdensities at large R (≈30 kpc) and Z (≈-10 kpc) in the Galactic halo that are thought to have been formed from the accretion and disruption of a satellite galaxy. This paper critically reexamines this formation scenario by comparing the number ratio of RR Lyrae to M giant stars associated with the TriAnd clouds with other structures in the Galaxy. The current data suggest a stellar population for these overdensities (fRR: MG < 0.38 at 95 per cent confidence) quite unlike any of the known satellites of the Milky Way (fRR: MG ≈ 0.5 for the very largest and fRR: MG ≫ 1 for the smaller satellites) and more like the population of stars born in the much deeper potential well inhabited by the Galactic disc (fRR: MG < 0.01). N-body simulations of a Milky Way-like galaxy perturbed by the impact of a dwarf galaxy demonstrate that, in the right circumstances, concentric rings propagating outwards from that Galactic disc can plausibly produce similar overdensities. These results provide dramatic support for the recent proposal by Xu et al. that, rather than stars accreted from other galaxies, the TriAnd clouds could represent stars kicked out from our own disc. If so, these would be the first populations of disc stars to be found in the Galactic halo and a clear signature of the importance of this second formation mechanism for stellar haloes more generally. Moreover, their existence at the very extremities of the disc places strong constraints on the nature of the interaction that formed them.

  20. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    SciTech Connect

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J.; Basu, S.; Deheuvels, S.; Brandao, I. M.; Cunha, M. S.; Sousa, S. G.; Dogan, G.; Metcalfe, T. S.; Serenelli, A. M.; Garcia, R. A.; Ballot, J.; Weiss, A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.; Lebreton, Y.; Noels, A.; and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  1. LSD: Lyman-break galaxies Stellar populations and Dynamics - I. Mass, metallicity and gas at z ~ 3.1

    NASA Astrophysics Data System (ADS)

    Mannucci, F.; Cresci, G.; Maiolino, R.; Marconi, A.; Pastorini, G.; Pozzetti, L.; Gnerucci, A.; Risaliti, G.; Schneider, R.; Lehnert, M.; Salvati, M.

    2009-10-01

    We present the first results of a project, Lyman-break galaxies Stellar populations and Dynamics (LSD), aimed at obtaining spatially resolved, near-infrared (IR) spectroscopy of a complete sample of Lyman-break galaxies at z ~ 3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as [OII] λ3727, Hβ and [OIII] λ5007, which are used to study sizes, star formation rates (SFRs), morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/Infrared Array Camera photometry are used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10-50 per cent solar, with a strong evolution of the mass-metallicity relation from lower redshifts. Stellar masses, gas fraction and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass-metallicity relation. We conclude that a large fraction of these galaxies is actively creating stars after major episodes of gas infall or merging. Based on observations collected with European Southern Observatory/Very Large Telescope (ESO/VLT) (proposals 075.A-0300 and 076.A-0711), with the Italian TNG, operated by FGG (INAF) at the Spanish Observatorio del Roque de los Muchachos, and with the Spitzer Space Telescope, operated by JPL (Caltech) under a contract with NASA.

  2. STELLAR POPULATIONS FROM SPECTROSCOPY OF A LARGE SAMPLE OF QUIESCENT GALAXIES AT Z > 1: MEASURING THE CONTRIBUTION OF PROGENITOR BIAS TO EARLY SIZE GROWTH

    SciTech Connect

    Belli, Sirio; Ellis, Richard S.; Newman, Andrew B.

    2015-02-01

    We analyze the stellar populations of a sample of 62 massive (log M {sub *}/M {sub ☉} > 10.7) galaxies in the redshift range 1 < z < 1.6, with the main goal of investigating the role of recent quenching in the size growth of quiescent galaxies. We demonstrate that our sample is not biased toward bright, compact, or young galaxies, and thus is representative of the overall quiescent population. Our high signal-to-noise ratio Keck/LRIS spectra probe the rest-frame Balmer break region that contains important absorption line diagnostics of recent star formation activity. We obtain improved measures of the various stellar population parameters, including the star formation timescale τ, age, and dust extinction, by fitting templates jointly to both our spectroscopic and broadband photometric data. We identify which quiescent galaxies were recently quenched and backtrack their individual evolving trajectories on the UVJ color-color plane finding evidence for two distinct quenching routes. By using sizes measured in the previous paper of this series, we confirm that the largest galaxies are indeed among the youngest at a given redshift. This is consistent with some contribution to the apparent growth from recent arrivals, an effect often called progenitor bias. However, we calculate that recently quenched objects can only be responsible for about half the increase in average size of quiescent galaxies over a 1.5 Gyr period, corresponding to the redshift interval 1.25 < z < 2. The remainder of the observed size evolution arises from a genuine growth of long-standing quiescent galaxies.

  3. Linear age-dependent population growth with seasonal harvesting.

    PubMed

    Sánchez, D A

    1980-06-01

    A population growth is modelled by the Von Foerster PDE with accompanying Lotka-Volterra integral equation describing the birth rate; the age specific death and fertility rates are assumed to depend only on age and not time. A harvesting policy where a fraction of the population of age greater than a given age is harvested for a fraction of a given season. This introduces a time dependence, but this difficulty is circumvented by devising approximate time-independent models whose birthrates bracket the true birthrate--the standard renewal equation theory applies to the approximate models so quantitative results can be obtained.

  4. US population aging and demand for inpatient services.

    PubMed

    Pallin, Daniel J; Espinola, Janice A; Camargo, Carlos A

    2014-03-01

    US inpatient capacity increased until the 1970s, then declined. The US Census Bureau expects the population aged ≥65 years to more than double by 2050. The implications for national inpatient capacity requirements have not been quantified. Our objective was to calculate the number of hospital admissions that will be necessitated by population aging, ceteris paribus. We estimated 2011 nationwide age-specific hospitalization rates using data from the Nationwide Inpatient Sample and Census data. We applied these rates to the population expected by the Census Bureau to exist through 2050. By 2050, the US population is expected to increase by 41%. Our analysis suggests that based on expected changes in the population age structure by then, the annual number of hospitalizations will increase by 67%. Thus, inpatient capacity would have to expand 18% more than population growth to meet demand. Total aggregate inpatient days is projected to increase 22% more than population growth. The total projected growth in required inpatient capacity is 72%, accounting for both number of admissions and length of stay. This analysis accounts only for changes in the population's age structure. Other factors could increase or decrease demand, as discussed in the article. PMID:24464735

  5. School Age Populations Research Needs - NCS Dietary Assessment Literature Review

    Cancer.gov

    Drawing conclusions about the validity of available dietary assessment instruments in school age children is hampered by the differences in instruments, research design, reference methods, and populations in the validation literature.

  6. Modeling the brain morphology distribution in the general aging population

    NASA Astrophysics Data System (ADS)

    Huizinga, W.; Poot, D. H. J.; Roshchupkin, G.; Bron, E. E.; Ikram, M. A.; Vernooij, M. W.; Rueckert, D.; Niessen, W. J.; Klein, S.

    2016-03-01

    Both normal aging and neurodegenerative diseases such as Alzheimer's disease cause morphological changes of the brain. To better distinguish between normal and abnormal cases, it is necessary to model changes in brain morphology owing to normal aging. To this end, we developed a method for analyzing and visualizing these changes for the entire brain morphology distribution in the general aging population. The method is applied to 1000 subjects from a large population imaging study in the elderly, from which 900 were used to train the model and 100 were used for testing. The results of the 100 test subjects show that the model generalizes to subjects outside the model population. Smooth percentile curves showing the brain morphology changes as a function of age and spatiotemporal atlases derived from the model population are publicly available via an interactive web application at agingbrain.bigr.nl.

  7. Measuring the speed of aging across population subgroups.

    PubMed

    Sanderson, Warren C; Scherbov, Sergei

    2014-01-01

    People in different subgroups age at different rates. Surveys containing biomarkers can be used to assess these subgroup differences. We illustrate this using hand-grip strength to produce an easily interpretable, physical-based measure that allows us to compare characteristic-based ages across educational subgroups in the United States. Hand-grip strength has been shown to be a good predictor of future mortality and morbidity, and therefore a useful indicator of population aging. Data from the Health and Retirement Survey (HRS) were used. Two education subgroups were distinguished, those with less than a high school diploma and those with more education. Regressions on hand-grip strength were run for each sex and race using age and education, their interactions and other covariates as independent variables. Ages of identical mean hand-grip strength across education groups were compared for people in the age range 60 to 80. The hand-grip strength of 65 year old white males with less education was the equivalent to that of 69.6 (68.2, 70.9) year old white men with more education, indicating that the more educated men had aged more slowly. This is a constant characteristic age, as defined in the Sanderson and Scherbov article "The characteristics approach to the measurement of population aging" published 2013 in Population and Development Review. Sixty-five year old white females with less education had the same average hand-grip strength as 69.4 (68.2, 70.7) year old white women with more education. African-American women at ages 60 and 65 with more education also aged more slowly than their less educated counterparts. African American men with more education aged at about the same rate as those with less education. This paper expands the toolkit of those interested in population aging by showing how survey data can be used to measure the differential extent of aging across subpopulations.

  8. Measuring the speed of aging across population subgroups.

    PubMed

    Sanderson, Warren C; Scherbov, Sergei

    2014-01-01

    People in different subgroups age at different rates. Surveys containing biomarkers can be used to assess these subgroup differences. We illustrate this using hand-grip strength to produce an easily interpretable, physical-based measure that allows us to compare characteristic-based ages across educational subgroups in the United States. Hand-grip strength has been shown to be a good predictor of future mortality and morbidity, and therefore a useful indicator of population aging. Data from the Health and Retirement Survey (HRS) were used. Two education subgroups were distinguished, those with less than a high school diploma and those with more education. Regressions on hand-grip strength were run for each sex and race using age and education, their interactions and other covariates as independent variables. Ages of identical mean hand-grip strength across education groups were compared for people in the age range 60 to 80. The hand-grip strength of 65 year old white males with less education was the equivalent to that of 69.6 (68.2, 70.9) year old white men with more education, indicating that the more educated men had aged more slowly. This is a constant characteristic age, as defined in the Sanderson and Scherbov article "The characteristics approach to the measurement of population aging" published 2013 in Population and Development Review. Sixty-five year old white females with less education had the same average hand-grip strength as 69.4 (68.2, 70.7) year old white women with more education. African-American women at ages 60 and 65 with more education also aged more slowly than their less educated counterparts. African American men with more education aged at about the same rate as those with less education. This paper expands the toolkit of those interested in population aging by showing how survey data can be used to measure the differential extent of aging across subpopulations. PMID:24806337

  9. Population ageing in ghana: research gaps and the way forward.

    PubMed

    Mba, Chuks J

    2010-09-29

    This paper attempts to highlight research gaps and what should be done concerning population ageing in the Ghanaian context. The proportion of the elderly increased from 4.9 percent in 1960 to 7.2 percent in 2000, while the number rose from 0.3 million to 1.4 million over the same period (an increase of 367 percent). Projection results indicate that by 2050, the aged population will account for 14.1 percent of the total population. Very little is known about the living arrangements and health profile of Ghana's older population. With increasing urbanization and modernization, it is important to know something about intergenerational transfers from adult children to their elderly parents, and characterize the elderly persons' food security strategies. Training of researchers will be important in terms of strengthening Ghana's capacity to monitor trends, as well as to conduct research and explore new directions in population ageing research.

  10. Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.; Johnson, K. E.; Tzanavaris, Panayiotis; Gronwall, C.

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  11. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    SciTech Connect

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

    2013-06-20

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended memb