We present an analysis of $UBVRI$ data from the Selected Area SA 141. By applying recalibrated methods of measuring ultraviolet excess (UVX), we approximate abundances and absolute magnitudes for 368 stars over 1.3 square degrees out to distances over 10 kpc. With the density distribution constrained from our previous photometric parallax investigations and with sufficient accounting for the metallicity bias in the UVX method, we are able to compare the vertical abundance distribution to those measured in previous studies. We find that the abundance distribution has an underlying uniform component consistent with previous spectroscopic results that posit a monometallic thick disk and halo with abundances of $[Fe/H]$ = $-$0.8 and $-$1.4, respectively. However, there are a number of outlying data points that may indicate contamination by more metal-rich halo streams. The absence of vertical abundance gradients in the Galactic stellar populations and the possible presence of interloping halo streams would be consistent with expectations from merger models of Galaxy formation. We find that our UVX method has limited sensitivity in exploring the metallicity distribution of the distant Galactic halo, owing to the poor constraint on the $UBV$ properties of very metal-poor stars. The derivation of metallicities from broadband $UBV$ photometry remains fundamentally sound for the exploration of the halo but is in need of both improved calibration and superior data.
Stellar Ages and Metallicities of Central and Satellite Galaxies: Implications for Galaxy Formation and Evolution
利用一个大型SDSS星系群星表，我们研究了恒星年龄和中心星系和卫星星系的金属丰度如何依赖于恒星质量和晕质量。我们发现卫星比相同恒星质量的中心更古老且金属含量更丰富。此外，年龄-恒星质量和金属度-恒星质量关系的斜率在密度较大的环境中变浅。这是由于低质量卫星星系的平均年龄和金属丰度随着它们所在的晕的质量而增加。与Wang et al.（2008）的半解析模型的比较表明，它成功地再现了卫星比相同恒星质量的中心更老的事实，并且年龄差异随着卫星晕质量的增加而增加。这是扼杀的结果，它使卫星的恒星星族被动地进化，而中心恒星的长期恒星形成活动使它们的平均年龄更年轻。在质量更大的环境中，所产生的年龄偏移更大，因为它们的卫星更早地被吸积。然而，该模型未能再现晕质量的低质量卫星的金属丰度的依赖性，产生的金属丰度恒星质量和年龄恒星质量的关系是太浅，并预测卫星星系具有相同的金属丰度中心相同的恒星质量，在不同意的数据。我们认为，这些差异可能表明需要（i）修改超新星反馈和活动星系核反馈的配方，（ii）使用更现实的描述扼杀，（iii）包括适当的处理潮汐剥离，加热和卫星星系的破坏。[摘要]
Context. Determining the metallicities and ages of M31 clusters is fundamental to the study of the formation and evolution of M31 itself. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has carried out a systematic spectroscopic campaign of clusters and candidates in M31. Aims. We constructed a catalogue of 346 M31 clusters observed by LAMOST. By combining the information of the LAMOST spectra and the multi-band photometry, we developed a new algorithm to estimate the metallicities and ages of these clusters. Methods. We distinguish young clusters from old using random f…
We explore how the star formation and metal enrichment histories of present-day galaxies have been affected by environment combining stellar population parameter estimates and group environment characterization for SDSS DR7. We compare stellar ages, stellar metallicities and element abundance ratios [alpha/Fe] of satellite and central galaxies, as a function of their stellar and host group halo mass, controlling for the current star formation rate and for the infall epoch. We confirm that below log(Mstar/Msun)=10.5 satellites are older and metal-richer than equally-massive central galaxies. On…
We infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low-z observed with HST and 19 at z~2 from the Megasaura sample. We fit each stellar continuum with a linear combination of up to 50 single age and single metallicity Starburst99 models. From these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. Inferred light-weighted stellar metallicities span 0.05-1.5 Z$_\odot$ and are sim…
We report results that show that the straightforwardly star cluster metallicities obtained from Strömgren $vby$ photometry is age-dependent and need to be corrected for further use. This outcome arises from the comparison of [Fe/H] values derived from Strömgren photometry with those metallicities published in the literature for 26 Large and Small Magellanic Cloud star clusters, whose ages range from $\sim$ 1 Gyr up to the known oldest globular clusters' ages in these galaxies. While deriving mean star cluster metallicities we carried out a thorough selection of red giant branch candidates to c…
Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc
A deep understanding of the Milky Way galaxy, its formation and evolution requires observations of huge numbers of stars. Stellar photometry, therefore, provides an economical method to obtain intrinsic stellar parameters. With the addition of distance information - deriving reliable ages from photometry is a possibility. We have developed a Bayesian method that generates 2D probability maps of a star's age and metallicity from photometry and parallax using isochrones. Our synthetic tests show that including a near-UV passband enables us to break the degeneracy between a star's age and metalli…
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…
Massive stars are the main objects that illuminate H II regions and they evolve quickly to end their lives in core-collapse supernovae (CCSNe). Thus it is important to investigate the association between CCSNe and H II regions. In this paper, we present emission line diagnostics of the stellar populations around nearby CCSNe, that include their host H II regions, from the PMAS/PPAK Integral-field Supernova hosts COmpilation (PISCO). We then use BPASS stellar population models to determine the age, metallicity and gas parameters for H II regions associated with CCSNe, contrasting models that co…
The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
We use deep \textit{Hubble Space Telescope} spectroscopy to constrain the metallicities and (\editone{light-weighted}) ages of massive ($\log M_\ast/M_\odot\gtrsim10$) galaxies selected to have quiescent stellar populations at $1.0<z<1.8$. The data include 12--orbit depth coverage with the WFC3/G102 grism covering $\sim$ $8,000<λ<11,500$~Å\, at a spectral resolution of $R\sim 210$ taken as part of the CANDELS Lyman-$α$ Emission at Reionization (CLEAR) survey. At $1.0<z<1.8$, the spectra cover important stellar population features in the rest-frame optical. We simulate a suite of stellar popula…
We study 147 star clusters in the Large Magellanic Cloud (LMC) in order to determine their mean metallicities and ages, as well as the mean metallicities of 80 surrounding fields. We construct an age-metallicity relation (AMR) for the clusters in the LMC. For this purpose, we used Strömgren photometry obtained with the SOI camera on the 4.1 m SOAR telescope. We found the mean metallicity and age for 110 star clusters. For the remaining 37, we provide an age estimation only. To the best of our knowledge, for 29 clusters from our sample, we provide both the metallicity and age for the first time…
A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF7, DF44 and DF17, which have central surface brightnesses of $μ_g \approx 24.4-25.1$ mag arcsec$^{-2}$. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hours of on-source integration we achieved a mean signal-to-noise ratio (S/N) in the optical of $9.5$Å$^{-1}$, $7.9$Å$^{-1}$ and $5.0$Å$^{-1}$,…
Globular clusters (GCs) are important tools to rebuild the accretion history of a galaxy. There are newly discovered GCs in the Sagittarius (Sgr) dwarf galaxy, that can be used as probes of the accretion event onto the Milky Way (MW). Our main aim is to characterize the Sgr GC system by measuring its main physical parameters. We build the optical and near-IR color-magnitude diagrams (CMDs) for 21 new Sgr GCs using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-IR database combined with the Gaia EDR3 optical database. We derive metallicities and ages for all targets, using th…
White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyse 1372 WDs found in wide binaries with MS companions, and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can …
We exploit the [Mg/Mn]-[Al/Fe] chemical abundance plane to help identify nearby halo stars in the 14th data release from the APOGEE survey that have been accreted on to the Milky Way. Applying a Gaussian Mixture Model, we find a `blob' of 856 likely accreted stars, with a low disc contamination rate of ~7%. Cross-matching the sample with the second data release from Gaia gives us access to parallaxes and apparent magnitudes, which place constraints on distances and intrinsic luminosities. Using a Bayesian isochrone pipeline, this enables us to estimate new ages for the accreted stars, with typ…
We present spatially-resolved measurements of star formation histories (SFHs), metallicities, and distances in three nearby elliptical galaxies and the bulge of M31 derived using the pixel color-magnitude diagram (pCMD) technique. We compute pCMDs from archival $\textit{HST}$ photometry of M87, M49, NGC 3377 and M31, and fit the data using the new code $\texttt{PCMDPy}$. We measure distances to each system that are accurate to $\sim 10\%$. The recovered non-parametric SFHs place reasonable ($\pm 1$ dex) constraints on the recent (< 2 Gyr) star formation in M31 and NGC 3377, both of which show …
We present updated stellar population models appropriate for old ages (>1 Gyr) and covering a wide range in metallicities (-1.5<[Fe/H]<0.3). These models predict the full spectral variation associated with individual element abundance variation as a function of metallicity and age. The models span the optical-NIR wavelength range (0.37-2.4um), include a range of initial mass functions (IMFs) and contain the flexibility to vary 18 individual elements including C, N, O, Mg, Si, Ca, Ti, and Fe. To test the fidelity of the models we fit them to integrated light optical spectra of 41 Galactic globu…
Molecular clouds at very high latitudes ($b > 60^o$) away from the Galactic plane are considered rare and not conventional sites of star formation. Contrary to this, the recent discovery of high latitude embedded Clusters can possibly change our understanding of the Galaxy formation, evolution and dynamics and the role of the halo in the Galactic evolutionary process. This article reviews a study of nine embedded clusters (ECs) reported in recent literature with ages less than 5 Myr and vertical distances from the galactic disc ranging from 1.8 to 5 kpc. It discusses the processes that could c…
SN1991bg-like supernovae are a distinct subclass of thermonuclear supernovae (SNe Ia). Their spectral and photometric peculiarities indicate their progenitors and explosion mechanism differ from `normal' SNe Ia. One method of determining information about supernova progenitors we cannot directly observe is to observe the stellar population adjacent to the apparent supernova explosion site to infer the distribution of stellar population ages and metallicities. We obtain integral field observations and analyse the spectra extracted from regions of projected radius $\sim\,\mathrm{kpc}$ about the …
We determined the ages, the kinematic parameters and Galactic orbital parameters of six metal-poor (-2.4<[Fe/H]<-1 dex) F-type high proper motion (HPM) stars to investigate their HPM nature and origin. For the kinematical procedure, the astrometric data from the Gaia DR2 was used. High resolution ELODIE spectra of the six dwarfs were also used to obtain accurate [Fe/H] abundances and up-to-date [$α$/Fe] abundances. The calculations for stellar ages were based on Bayesian statistics, with the computed ages falling in the range 9.5-10.1 Gyrs. On the basis of the metallicities and ages, six HMP s…
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文学与空间科学学院）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕尔马大学天体物理学系）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Zhejiang Lab（浙江实验室）；China West Normal University（西华师范大学）
