We present the recently updated and expanded MASSCLEANcolors, a database of 70 million Monte Carlo models selected to match the properties (metallicity, ages and masses) of stellar clusters found in the Large Magellanic Cloud (LMC). This database shows the rather extreme and non-Guassian distribution of integrated colors and magnitudes expected with different cluster age and mass and the enormous age degeneracy of integrated colors when mass is unknown. This degeneracy could lead to catastrophic failures in estimating age with standard SSP models, particularly if most of the clusters are of intermediate or low mass, like in the LMC. Utilizing the MASSCLEANcolors database, we have developed MASSCLEANage, a statistical inference package which assigns the most likely age and mass (solved simultaneously) to a cluster based only on its integrated broad-band photometric properties. Finally, we use MASSCLEANage to derive the age and mass of LMC clusters based on integrated photometry alone. First we compare our cluster ages against those obtained for the same seven clusters using more accurate integrated spectroscopy. We find improved agreement with the integrated spectroscopy ages over the original photometric ages. A close examination of our results demonstrate the necessity of solving simultaneously for mass and age to reduce degeneracies in the cluster ages derived via integrated colors. We then selected an additional subset of 30 photometric clusters with previously well constrained ages and independently derive their age using the MASSCLEANage with the same photometry with very good agreement. The MASSCLEANage program is freely available under GNU General Public License.
We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.
It is well-known that fitting the Color Magnitude Diagrams (CMDs) to the theoretical isochrones is the main method to determine star cluster ages. However, when the CMDs are not available, the Spectral Energy Distribution (SED)-fitting technique is the only other approach, although it suffers the age-metallicity-reddening degeneracy. In this work, we gather the ages, metallicities and masses of dozens of M31 star clusters from the CMD-fitting with HST images from the literatures for comparison. We check the reliability of the SED-fitting results with different models, i.e., Bruzual \& Charlot …
The Ages of 55 Globular Clusters as Determined Using an Improved delta V_TO^HB Method Along with Color-Magnitude Diagram Constraints, and Their Implications for Broader Issues
Our picture of the age-metallicity relation for Milky Way globular clusters (MWGCs) is still highly incomplete, and the majority of MWGCs lack self-consistent age measurements. Here, we exploit deep, homogenous multi-epoch Hubble Space Telescope (HST) imaging of nine MWGCs located towards the inner Milky Way to measure their relative ages, in most cases for the first time. Our relative age measurements are designed to be directly comparable to the large set of MWGC ages presented by VandenBerg et al. (2013, V13), using identical filters, evolutionary models, and bolometric corrections, extende…
Multi-color photometry is presented for a sample of 60 dwarf ellipticals (dE) selected by morphology. The sample uses data from GALEX, SDSS and WISE to investigate the colors in filters NUV, ugri and W1 (3.4mum). We confirm the blueward shift in the color-magnitude relation for dwarf ellipticals, compared to CMR for bright ellipticals, as seen in previous studies. However, we find the deviation in color across the UV to near-IR for dE's is a strong signal of a younger age for dwarf ellipticals, one that indicates decreasing mean age with lower stellar mass. Lower mass dE's are found to have me…
Bulge globular clusters (GCs) with metallicities [Fe/H] <~ -1.0 and blue horizontal branches are candidates to harbor the oldest populations in the Galaxy. Based on the analysis of HST proper-motion-cleaned color-magnitude diagrams in filters F435W and F625W, we determine physical parameters for the old bulge globular clusters NGC 6522 and NGC 6626 (M28), both with well-defined blue horizontal branches. We compare these results with similar data for the inner halo cluster NGC 6362. These clusters have similar metallicities (-1.3 <= [Fe/H] <= -1.0) obtained from high resolution spectroscopy. We…
We present low-resolution near-infrared stacked spectra from the 3D-HST survey up to $z=2.0$ and fit them with commonly used stellar population synthesis models: BC03 (Bruzual & Charlot, 2003), FSPS10 (Flexible Stellar Population Synthesis, Conroy & Gunn 2010), and FSPS-C3K (Conroy, Kurucz, Cargile, Castelli, in prep). The accuracy of the grism redshifts allows the unambiguous detection of many emission and absorption features, and thus a first systematic exploration of the rest-frame optical spectra of galaxies up to $z=2$. We select massive galaxies ($\rm log(M_{*} / M_{\odot}) > 10.8$), we …
Globular Clusters (GCs) in the Milky Way are the primary laboratories for establishing the ages of the oldest stellar populations and for measuring the color-magnitude relation of stars. In infrared (IR) color-magnitude diagrams (CMDs), the stellar main sequence (MS) exhibits a "kink", due to opacity effects in M dwarfs, such that lower mass and cooler dwarfs become bluer in the IR color baseline. This diagnostic offers a new opportunity to model GC CMDs and to reduce uncertainties on cluster properties (e.g., their derived ages). In this context, we analyzed Hubble Space Telescope Wide Field …
The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
We use color gradients to explore the evolution of early-type galaxies in the core of the massive galaxy cluster MACS J1206.2-0847 at z = 0.44. We used data from the CLASH and CLASH-VLT surveys to perform multiwavelength optimized model fitting using Galapagos-2 from the MegaMorph project to measure their photometric parameters. We derive color gradients for $g_{475} - I_{814}$, $r_{625} - Y_{105}$, $I_{814} - H_{160}$ , and $Y_{105} - H_{160}$ at radii ranging between 0.1 - 2 $r_e$ for 79 early-type cluster galaxies. From synthetic spectral models that use simple star formation recipes, we in…
Aims. We present a new technique to estimate the relative ages of multiple stellar populations hosted by five globular clusters: NGC 104 (47 Tuc), NGC 6121 (M4), NGC 6352, NGC 6362 and NGC 6723. Methods. We used the catalogs of the database "HST UV Globular cluster Survey (HUGS)" to create color-magnitude and two-color diagrams of the Globular Clusters. We identified the multiple populations within each globular cluster, and we divided them into two main stellar populations: POPa or first generation (1G) and POPb, composed of all the successive generations of stars. The new technique allows us…
Based on updated pulsation models for Classical Cepheids, computed for various assumptions about the metallicity and helium abundance, roughly representative of pulsators in the Small Magellanic Cloud ($Z$=$0.004$ and $Y$=$0.25$), Large Magellanic Cloud ($Z$=$0.008$ and $Y$=$0.25$), and M31 ($Z$=$0.03$ and $Y$=$0.28$), and self-consistent updated evolutionary predictions, we derived Period-Age and multi-band Period-Age-Color relations that also take into account variations in the Mass-Luminosity relation. These results, combined with those previously derived for Galactic Cepheids, were used to…
Age is a fundamental parameter of stars, yet in many cases ages of individual stars are presented without robust estimates of the uncertainty. We have developed a Bayesian framework, BAFFLES, to produce the age posterior for a star from its calcium emission strength (log($R'_{HK}$)) or lithium abundance (Li EW) and $B-V$ color. We empirically determine the likelihood functions for calcium and lithium as functions of age from literature measurements of stars in benchmark clusters with well-determined ages. We use a uniform prior on age which reflects a uniform star formation rate. The age poste…
We present our new, fully-automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages…
In clusters of galaxies, the red sequence is believed to be a consequence of a correlation between stellar mass and chemical abundances, with more massive galaxies being more metal-rich and, as a consequence, redder. However, there is a color scatter around the red sequence that holds even with precision photometry, implying that the galaxy population is more complicated than as described by a mass-metallicity relation. We use precision photometry from the Cluster Lensing and Supernova survey with Hubble (CLASH) to investigate what drives this scatter. In four CLASH clusters at $z=0.355 \pm 0.…
Deep rest-optical observations are required to accurately constrain the stellar populations of $z\sim8$ galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of $z\sim8$ galaxies, we exploit the ultradeep ($\sim27$ mag, $3σ$) Spitzer/IRAC $3.6μ$m and $4.5μ$m data, probing the rest-frame optical at $z\sim8$, over $\sim200$ arcmin$^2$ of the GOODS fields from the recently completed GOODS Re-ionization Era wide…
The determination of the age of the bulge has led to two contradictory results. On the one side, the color-magnitude diagrams in different bulge fields seem to indicate a uniformly old ($>$10 Gyr) population. On the other side, individual ages derived from dwarfs observed through microlensing events seem to indicate a large spread, from $\sim$ 2 to $\sim$ 13 Gyr. Because the bulge is now recognised as being mainly a boxy peanut-shaped bar, it is suggested that disk stars are one of its main constituents, and therefore also stars with ages significantly younger than 10 Gyr. Other arguments as w…
Large samples of globular clusters (GC) with precise multi-wavelength photometry are becoming increasingly available and can be used to constrain the formation history of galaxies. We present the results of an analysis of Milky Way (MW) and Virgo core GCs based on five optical-near-infrared colors and ten synthetic stellar population models. For the MW GCs, the models tend to agree on photometric ages and metallicities, with values similar to those obtained with previous studies. When used with Virgo core GCs, for which photometry is provided by the Next Generation Virgo cluster Survey (NGVS),…
We study the stellar content in the tidal tails of three nearby merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. The tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. We compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. …
We present an investigation of the globular cluster population synthesis method of McWilliam & Bernstein (2008), focusing on the impact of NLTE modeling effects and CMD discretization. Johnson-Cousins-Bessel U-B, B-V, V-I, and J-K colors are produced for 96 synthetic integrated light spectra with two different discretization prescriptions and three degrees of NLTE treatment. These color values are used to compare NLTE and LTE derived population ages. Relative contributions of different spectral types to the integrated light spectra for different wavebands are measured. Integrated light NLTE sp…
An HST/WFPC2 survey of bright young clusters in M31. IV. Ages and mass estimates
【目标】本文介绍了利用哈勃空间望远镜（HST）上的广角行星照相机2（WFPC 2）对M31中可能的年轻大质量星团（YMC）进行成像巡天的主要结果。我们提出的图像和彩色星等图（CMD），我们所有的目标。{方法。}通过比较观测到的CMD和光度函数与理论模型，估算了团簇的红化、年龄和金属丰度。恒星质量的估计是通过与理论模型在对数（年龄）与绝对积分星等平面的比较。{结果。} 20个候选星团中有19个被证实是真正的星团。三个集群被发现不是很好的YMC候选人从新的集成光谱，实际上被发现是旧的，从他们的CMD。在剩下的16个星团中，14个星团的年龄在2500万年到28000万年之间，2个星团的年龄超过50000万年（下限）。通过纳入文献中其他10个YMC和HST测光，我们收集了25个年龄小于1 Gyr的星团样本，质量范围从0.6 x 10^4 M_sun到6 x 10^4 M_sun，平均约为3 x 10^4 M_sun。【结论】这里考虑的星团被证实有质量显着高于银河系疏散星团在相同的年龄范围。我们的分析表明，YMC在本星系群中所有最大的恒星形成星系中相对常见。
In this paper we review the operational definition of the so-called main sequence knee (MS-knee), a feature in the color-magnitude diagram (CMD) occurring at the low-mass end of the MS. The magnitude of this feature is predicted to be independent of age at fixed chemical composition. For this reason, its difference in magnitude with respect to the MS turn-off (MS-TO) point has been suggested as a possible diagnostic to estimate absolute globular cluster (GC) ages. We first demonstrate that the operational definition of the MS-knee currently adopted in the literature refers to the inflection po…
I present integrated colors and surface brightness fluctuation magnitudes in the mid-IR, derived from stellar population synthesis models that include the effects of the dusty envelopes around thermally pulsing asymptotic giant branch (TP-AGB) stars. The models are based on the Bruzual & Charlot CB* isochrones; they are single-burst, range in age from a few Myr to 14 Gyr, and comprise metallicities between $Z$= 0.0001 and $Z$ = 0.04. I compare these models to mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study the effects of varying self-consistently the mass-loss ra…
We investigate the stellar populations for a sample of 24 quiescent galaxies at 1.5 < z < 2.5 using deep rest-frame optical spectra obtained with Keck MOSFIRE. By fitting templates simultaneously to the spectroscopic and photometric data, and exploring a variety of star formation histories, we obtain robust measurements of median stellar ages and residual levels of star formation. After subtracting the stellar templates, the stacked spectrum reveals the Halpha and [NII] emission lines, providing an upper limit on the ongoing star formation rate of 0.9 +/- 0.1 Msun/yr. By combining the MOSFIRE …
This Letter examines how the sizes, structures, and color gradients of galaxies change along the quiescent sequence. Our sample consists of ~400 quiescent galaxies at $1.0\le z\le2.5$ and $10.1 \le \log{M_*/M_\odot}\le11.6$ in three CANDELS fields. We exploit deep multi-band HST imaging to derive accurate mass profiles and color gradients, then use an empirical calibration from rest-frame UVJ colors to estimate galaxy ages. We find that -- contrary to previous results -- the youngest quiescent galaxies are not significantly smaller than older quiescent galaxies at fixed stellar mass. These `po…
We use photometric and spectroscopic observations of the eclipsing binary E32 in the globular cluster 47 Tuc to derive the masses, radii, and luminosities of the component stars. The system has an orbital period of 40.9 d, a markedly eccentric orbit with e = 0.24, and is shown to be a member of or a recent escaper from the cluster. We obtain Mp = 0.862(5) Msun , Rp = 1.183(3) Rsun , Lp = 1.65(5) Lsun for the primary and Ms = 0.827(5) Msun , Rs = 1.004(4) Rsun , Ls = 1.14(4) Lsun for the secondary. Based on these data and on an earlier analysis of the binary V69 in 47 Tuc we measure the distanc…
We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449 based on multi-band imaging observations taken as part of the LEGUS and Halpha-LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of Halpha measurements, the role of stochasticity for low mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age-dating of clusters. …
We present the results of combining Hubble Space Telescope optical photometry with ground-based Ks-band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular-cluster populations in four early-type galaxies that are candidate remnants of recent mergers (NGC1700, NGC2865, NGC4382, and NGC7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIKs globular-cluster data with simple toy models of mixed cluster populations that contain three subpopulations of dif…
Local Group (LG) galaxies have relatively accurate SFHs and metallicity evolution derived from resolved CMD modeling, and thus offer a unique opportunity to explore the efficacy of estimating stellar mass M$_{\star}$ of real galaxies based on integrated stellar luminosities. Building on the SFHs and metallicity evolution of 40 LG dwarf galaxies, we carried out a comprehensive study of the influence of SFHs, metallicity evolution, and dust extinction on the UV-to-NIR color-$M/L$ (color-log$Υ_{\star}$($λ$)) relations and M$_{\star}$ estimation of local universe galaxies. We find that: The LG gal…
Red clump stars are fundamental distance indicators in astrophysics, although theoretical stellar models predict a dependence of absolute magnitudes with ages. This effect is particularly strong below 2 Gyr, but even above this limit a mild age dependence is still expected. We use seismically identified red clump stars in the Kepler field for which we have reliable distances, masses and ages from the SAGA survey to first explore this effect. By excluding red clump stars with masses larger than 1.6 Msun (corresponding to ages younger than 2 Gyr), we derive robust calibrations linking intrinsic …
The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the Universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and super-impose isochrones from different sources in th…
Globular clusters are the oldest conglomerates of stars in our Galaxy and can be useful laboratories to test theories from stellar evolution to cosmology. In this paper, we present a new method to estimate the absolute age of a globular cluster from observations of its brown dwarfs. The transition region between the end of the main sequence and the brown dwarf regime is characterized by a dearth of objects as function of magnitude. The brightest of the cooling brown dwarfs is easily identified by an increase in density in the color-magnitude diagram as you go fainter in magnitudes, and these b…
In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. We used Strömgren photometry obtained with the 4.1 m SOAR telescope and take advantage of $(b - y)$ and $m1$ colors for which there is a metallicity calibration presented in the literature. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Strömgren photometry. We confirm earlier observations that younger, more metal-ric…
A photometric and astrometric study of the two open star clusters Gulliver 18 and Gulliver 58 was carried out for the first time using the early third data release of the Gaia space observatory (Gaia-EDR3). By studying the proper motions, parallaxes, and color-magnitude diagrams of the two clusters, we determined their actual cluster membership. Therefore, ages, color excesses, and heliocentric distances of the clusters were determined. The luminosity function, mass function, total mass, mass segregation, and relaxation time of Gulliver 18 and Gulliver 58 were estimated as well.
We present the first results from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) of the Milky-Way globular clusters (GCs) NGC 3201 and NGC 2298. Using the Gemini South Adaptive Optics Imager (GSAOI), in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-meter Gemini-South telescope, we collected deep near-IR observations of both clusters, resolving their constituent stellar populations down to $K_s\simeq21$ Vega mag. Point spread function (PSF) photometry was performed on the data using spatially-variable PSFs to generate $JHK_{s}$ photometric catalogues fo…
We study the slope, intercept, and scatter of the color-magnitude and color-mass relations for a sample of ten infrared red-sequence-selected clusters at z ~ 1. The quiescent galaxies in these clusters formed the bulk of their stars above z ~ 3 with an age spread Δt ~ 1 Gyr. We compare UVJ color-color and spectroscopic-based galaxy selection techniques, and find a 15% difference in the galaxy populations classified as quiescent by these methods. We compare the color-magnitude relations from our red-sequence selected sample with X-ray- and photometric- redshift-selected cluster samples of simil…
To What Extent Are Star Cluster Ages Encoded in Their Environments? Exploring the Spatial Distribution of Age-Related Information with PHANGS-HST Imaging and Convolutional Neural Networks
Massachusetts Institute of Technology（麻省理工学院）；Space Telescope Science Institute（太空望远镜科学研究所）；The Johns Hopkins University（约翰斯·霍普金斯大学）；Instituto de Astrofísica de La Plata, CONICET–UNLP（拉普拉塔天体物理研究所，阿根廷国家科学研究委员会-拉普拉塔国立大学）；University of Virginia Astronomy Department（弗吉尼亚大学天文系）；National Radio Astronomy Observatory（美国国家无线电天文台）
We present images and spectral energy distributions (SEDs) of massive young stellar objects (YSOs) in three star-forming H II regions of the Large Magellanic Cloud: N159A, N159 Papillon, and N160. We use photometry from SOFIA/FORCAST at 25.3--37.1 um to constrain model fits to the SEDs and determine luminosities, ages, and dust content of the embedded YSOs and their local environments. By placing these sources on mid-infrared color-magnitude and color-color diagrams, we analyze their dust properties and consider their evolutionary status. Since each object in the FORCAST images has an obvious …
