In the central few degrees of the bulge of the Milky Way there is a flattened structure of gas, dust and stars (the central molecular zone) similar to nuclear disks in other galaxies. Due to extreme foreground extinction we possess only sparse information about the (mostly old) stellar population of the nuclear disc. Here we present our KMOS spectroscopic survey of the stars in the nuclear disk reaching the old populations. In order to obtain an unbiased data set, we sample stars in the full extinction range along each line-of-sight. We also observe reference fields in neighboring regions of the Galactic bulge. Here we describe the design and execution of the survey and present first results. We obtain spectra and five spectral indices of 3113 stars with a median S/N of 67 and measure radial velocities for 3051 stars. Of those, 2735 sources have sufficient S/N to estimate temperatures and metallicities from indices. We derive metallicities using the CO 2-0 and Na I K-band spectral features, where we derive our own empirical calibration using metallicities obtained with higher resolution observations. We use 183 giant stars for calibration spanning in metallicity from -2.5 to 0.6 dex and covering temperatures of up to 5500 K. The derived index based metallicities deviate from the calibration values with a scatter of 0.32 dex. The internal uncertainty of our metallicities is likely smaller. We use these metallicity measurements together with the CO index to derive effective temperatures using literature relations. We publish the catalog here. Our data set complements Galactic surveys such as Gaia and APOGEE for the inner 200 pc radius of the Milky Way which is not readily accessible by those surveys due to extinction. We will use the derived properties in future papers for further analysis of the nuclear disk.
We present a rest-frame UV-optical stacked spectrum representative of massive quiescent galaxies at $1.0<z<1.3$ with log$(M_*/\rm{M_\odot})>10.8$. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity, [Z/H]=$-0.13\pm0.08$ with Bagpipes, and [Z/H]=$0.04\pm0.14$ with Alf, a fall of $\sim0.2-0.3$ dex compared with the local Universe. We also measure an iron abundance, [Fe/H] =$-0.18\pm0.08$, a fall of $\sim0.15$ dex compared with the the local Universe. We measure the alpha…
Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4 pc^2 of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Göttingen Spectral library of synthetic PHOENIX spec…
The Milky Way's metal-poor stars are nearby ancient objects that are used to study early chemical evolution and the assembly and structure of the Milky Way. Here we present reliable metallicities of $\sim280,000$ stars with $-3.75 \lesssim$ [Fe/H] $\lesssim -0.75$ down to $g=17$ derived using metallicity-sensitive photometry from the second data release (DR2) of the SkyMapper Southern Survey. We use the dependency of the flux through the SkyMapper $v$ filter on the strength of the Ca II K absorption features, in tandem with SkyMapper $u,g,i$ photometry, to derive photometric metallicities for …
We have observed a sample of typical z=1 star forming galaxies, selected from the HiZELS survey, with the new KMOS near-infrared, multi-IFU instrument on the VLT, in order to obtain their dynamics and metallicity gradients. The majority of our galaxies have a metallicity gradient consistent with being flat or negative (i.e. higher metallicity cores than outskirts). Intriguingly, we find a trend between metallicity gradient and specific star formation rate (sSFR), such that galaxies with a high sSFR tend to have relatively metal-poor centres, a result which is strengthened when combined with da…
We demonstrate how the metallicities of young super star clusters can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of super star clusters older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z]= +0.28 +/- 0.14 dex using a moderate resolution (R~3500) J-band spectrum and in NGC 6496 we report [Z]= -0.32 +/- 0.20 dex from…
The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also >100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8 Myr old. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and …
We present stellar metallicity measurements of more than 600 late-type stars in the central 10 pc of the Galactic centre. Together with our previously published KMOS data, this data set allows us to investigate, for the first time, spatial variations of the nuclear star cluster's metallicity distribution. Using the integral-field spectrograph KMOS (VLT) we observed almost half of the area enclosed by the nuclear star cluster's effective radius. We extract spectra at medium spectral resolution, and apply full spectral fitting utilising the PHOENIX library of synthetic stellar spectra. The stell…
Intrinsic iron abundance spreads in globular clusters, although usually small, are very common, and are signatures of self enrichment: some stars within the cluster have been enriched by supernova ejecta from other stars within the same cluster. We use the Bailin (2018) self enrichment model to predict the relationship between properties of the protocluster -- its mass and the metallicity of the protocluster gas cloud -- and the final observable properties today -- its current metallicity and the internal iron abundance spread. We apply this model to an updated catalog of Milky Way globular cl…
Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the Milky Way. Using Markov-Chain Monte-Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass--metallicity relation of the Milky …
Context: The formation and evolution of disk galaxies are long standing questions in Astronomy. Understanding the properties of globular cluster systems can lead to important insights on the evolution of its host galaxy. Aims: We aim to obtain the stellar population parameters - age and metallicity - of a sample of M31 and Galactic globular clusters. Studying their globular cluster systems is an important step towards understanding their formation and evolution in a complete way. Methods: Our analysis employs a modern pixel-to-pixel spectral fitting technique to fit observed integrated spectra…
We present an examination of the metallicity distribution function of the outermost stellar halo of the Galaxy based on an analysis of both local (within 4 kpc of the Sun, ~16,500 stars) and non-local (~21,700 stars) samples. These samples were compiled using spectroscopic metallicities from the Sloan Digital Sky Survey and photometric metallicities from the SkyMapper Southern Survey. We detect a negative metallicity gradient in the outermost halo (r > 35 kpc from the Galactic center), and find that the frequency of very metal-poor ([Fe/H] < -2.0) stars in the outer-halo region reaches up to ~…
Mapping the Distant and Metal-Poor Milky Way with SDSS-V
Department of Astronomy & Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所 (SkAI)）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Department of Astronomy, Columbia University（哥伦比亚大学天文学系）；Department of Astronomy, Boston University（波士顿大学天文学系）；Instituto de Astrofísica, Departamento de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andres Bello（安第斯贝尔托大学精确科学学院物理与天文学系天体物理研究所）；LIRA
We have used photometric data on almost 91 000 fundamental-mode RR Lyrae stars (type RRab) detected by the OGLE survey to investigate properties of old populations in the Milky Way. Based on their metallicity distributions, we demonstrate that the Galaxy is built from three distinct old components: halo, bulge, and disk. The distributions reach their maxima at approximately [Fe/H]_J95 = -1.2, -1.0, and -0.6 dex on the Jurcsik's metallicity scale, respectively. We find that, very likely, the entire halo is formed from infalling dwarf galaxies. It is evident that halo stars penetrate the inner r…
Recent advances from astronomical surveys have revealed spatial, chemical, and kinematical inhomogeneities in the inner region of the stellar halo of the Milky Way Galaxy. In particular, large spectroscopic surveys, combined with Gaia astrometric data, have provided powerful tools for analyzing the detailed abundances and accurate kinematics for individual stars. Despite these noteworthy efforts, however, spectroscopic samples are typically limited by the numbers of stars considered; their analysis and interpretation are also hampered by the complex selection functions that are often employed.…
We perform integrated spectroscopy of 24 Galactic globular clusters. Spectra are observed from one core radius for each cluster with a high wavelength resolution of ~2.0 A FWHM. In combination with two existing data sets from Puzia et al. (2002) and Schiavon et al. (2005), we construct a large database of Lick spectral indices for a total of 53 Galactic globular clusters with a wide range of metallicities, -2.4 < [Fe/H] < 0.1, and various horizontal-branch morphologies. The empirical index-to-metallicity conversion relationships are provided for the 20 Lick indices for the use of deriving meta…
We use the photometric metallicities provided by the panoramic Pristine survey to study the veracity and derive the metallicities of the numerous stellar streams found by the application of the STREAMFINDER algorithm to the Gaia EDR3 data. All 26 streams present in Pristine show a clear metallicity distribution function, which provides an independent check of the reality of these structures, supporting the reliability of STREAMFINDER in finding streams and the power of Pristine to measure precise metallicities. We further present 6 candidate structures with coherent phase-space and metallicity…
The Keck/DEIMOS Stellar Archive: I. Uniform Velocities and Metallicities for 78 Milky Way Dwarf Galaxies and Globular Clusters
Yale University（耶鲁大学）；University of California Observatories, University of California, Santa Cruz（加州大学天文台，加州大学圣克鲁兹分校）；Kavli Institute for the Physics and Mathematics of the Universe（卡弗里宇宙物理与数学研究所）；Division of Science, National Astronomical Observatory of Japan（日本国立天文台科学部）；Max-Planck-Institut für Astronomie（马克斯·普朗克天体物理学研究所）；University of California, Santa Barbara（加州大学圣塔芭芭拉分校）
Stars with unusual elemental abundances offer clues about rare astrophysical events or nucleosynthetic pathways. Stars with significantly depleted magnesium and enhanced potassium ([Mg/Fe] < -0.5; [K/Fe] > 1) have to date only been found in the massive globular cluster NGC 2419 and, to a lesser extent, NGC 2808. The origin of this abundance signature remains unknown, as does the reason for its apparent exclusivity to these two globular clusters. Here we present 112 field stars, identified from 454,180 LAMOST giants, that show significantly enhanced [K/Fe] and possibly depleted [Mg/Fe] abundanc…
There is increasing observational and theoretical evidence for a correlation between the metallicity and the mass of the stellar halo for galaxies with Milky Way-like stellar masses. Using the Illustris cosmological hydrodynamical simulations, we find that this relationship arises because a single massive massive progenitor contributes the bulk of the mass to the accreted stellar component as well as sets its metallicity. Moreover, in the Illustris simulations, this relationship extends over 3 orders of magnitude in accreted stellar mass for central galaxies. We show that for Milky Way-like ma…
We present a homogeneous set of accurate atmospheric parameters for a complete sample of very and extremely metal-poor stars in the dwarf spheroidal galaxies (dSphs) Sculptor, Ursa Minor, Sextans, Fornax, Boötes I, Ursa Major II, and Leo IV. We also deliver a Milky Way (MW) comparison sample of giant stars covering the -4 < [Fe/H] < -1.7 metallicity range. We show that, in the [Fe/H] > -3.5 regime, the non-local thermodynamic equilibrium (NLTE) calculations with non-spectroscopic effective temperature (Teff) and surface gravity (log~g) based on the photometric methods and known distance provid…
(ABRIDGED) Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. We obtain homogeneous metallicities and alpha-element enhancement for over 800 red giant stars in 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We observed R ~ 2000 spectr…
The Milky Way nuclear star cluster (MW NSC) has been used as a template to understand the origin and evolution of galactic nuclei and the interaction of nuclear star clusters with supermassive black holes. It is the only nuclear star cluster with a supermassive black hole where we can resolve individual stars to measure their kinematics and metal abundance to reconstruct its formation history. Here, we present results of the first chemo-dynamical model of the inner 1 pc of the MW NSC using metallicity and radial velocity data from the KMOS spectrograph on the Very Large Telescope. We find evid…
We used adaptive mesh refinement hydrodynamic cosmological simulations of a $z=1$ Milky Way-type galaxy and a $z=0$ Dwarf galaxy and generated synthetic quasar absorption-line spectra of their circumgalactic medium (CGM). Our goal is to assess whether standard observational spectroscopic analysis methods accurately reproduce intrinsic column densities, metallicities [Si/H], and hydrogen densities $n_{H}$, in simulated absorption-line systems. Without knowledge of the intrinsic simulated properties (blind study), we analysed synthetic COS and HIRES spectra with fixed $S/N=30$ to determine the c…
We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5m Magellan telescopes, we obtain medium resolution (R ~ 2000 - 6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallic…
The study of open cluster metallicities helps to understand the local stellar formation and evolution throughout the Milky Way. Its metallicity gradient is an important tracer for the Galactic formation in a global sense. Because open clusters can be treated in a statistical way, the error of the cluster mean is minimized. Our final goal is a semi-automatic statistical robust method to estimate the metallicity of a statistically significant number of open clusters based on Johnson BV data of their members, an algorithm that can easily be extended to other photometric systems for a systematic i…
From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars
University of Florida（佛罗里达大学）；Harvard Society of Fellows（哈佛学会）；Center for Astrophysics | Harvard & Smithsonian（天体物理中心（哈佛大学与史密森尼学会））；Université de Genève（日内瓦大学）；The Adler Planetarium（阿德勒天文馆）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)（天体物理学跨学科探索与研究中心）
Hypervelocity stars are those that have speeds exceeding the escape speed and are hence unbound from the Milky Way. We investigate a sample of low-mass hypervelocity candidates obtained using data from the high-precision SDSS Stripe 82 catalogue, which we have combined with spectroscopy from the 200-inch Hale Telescope at Palomar Observatory. We find four good candidates, but without metallicities it is difficult to pin-down their distances and therefore total velocities. Our best candidate has a significant likelihood that it is escaping the Milky Way for a wide-range of metallicities.
A Chemodynamical Census of the Milky Way's Ultra-Faint Compact Satellites. I. A First Population-Level Look at the Internal Kinematics and Metallicities of 19 Extremely-Low-Mass Halo Stellar Systems
Yale University（耶鲁大学）；University of Toronto（多伦多大学）；Dunlap Institute for Astronomy & Astrophysics（邓普勒天文学与天体物理学研究所）；University of Virginia（弗吉尼亚大学）；Carnegie Institution for Science（卡内基科学机构）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics（卡弗里宇宙物理学研究所）；Fermi National Accelerator Laboratory（费米国家加速器实验室）
A new revision of the McMaster catalog of Milky Way globular clusters is available. This is the first update since 2003 and the biggest single revision since the original version of the catalog published in 1996. The list now contains a total of 157 objects classified as globular clusters. Major upgrades have been made especially to the cluster coordinates, metallicities, and structural profile parameters, and the list of parameters now also includes central velocity dispersion. NB: This paper is a stand-alone publication available only on the astro-ph archive; it will not be published separat…
We report astrophysical properties of 12 Milky Way open clusters located beyond the circle around the Sun where the number of catalogued open clusters is thought to be statistically complete. By using deep optical photometry, we estimated their ages and metallicities on the basis of a maximum likelihood approach, using cluster members identified from Gaia DR2 data and likelihood procedures. The studied clusters turned out to be of intermediate-age (0.8 - 4.0 Gyr), with metallicities spanning the range [Fe/H] ~ -0.5 - +0.1 dex, and distributed within the general observed trend of the Milky Way …
We provide a detailed map of the ages and metallicities of turnoff stars in the Milky Way disc based on data from GALAH DR3 and Gaia EDR3. From this map, we identify previously undetected features in the age-metallicity distribution of disc stars and interpret these results as indicating a three-phase formation history of the Milky Way. In the first phase, inner disc stars form along a single age-metallicity sequence and are today kinematically hot. The end of this phase is marked by a local minimum in the inner disc age distribution 10 Gyr ago. At this time, we find the stellar populations to…
We test the performance of our analysis technique for integrated-light spectra by applying it to seven well-studied Galactic GCs that span a wide range of metallicities. Integrated-light spectra were obtained by scanning the slit of the UVES spectrograph on the ESO Very Large Telescope across the half-light diameters of the clusters. We modelled the spectra using resolved HST colour-magnitude diagrams (CMDs), as well as theoretical isochrones, in combination with standard stellar atmosphere and spectral synthesis codes. The abundances of Fe, Na, Mg, Ca, Ti, Cr, and Ba were compared with litera…
Well determined radial velocities and abundances are essential for analyzing the properties of the Globular Cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca II triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number …
(abridged) We have observed almost 1/3 of the globular clusters in the Milky Way, targeting distant and/or highly reddened objects, besides a few reference clusters. A large sample of red giant stars was observed with FORS2@VLT/ESO at R ~ 2,000. The method for derivation of stellar parameters is presented with application to six reference clusters. We aim at deriving the stellar parameters effective temperature, gravity, metallicity and alpha-element enhancement, as well as radial velocity, for membership confirmation of individual stars in each cluster. We analyse the spectra collected for th…
Context. Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ($[M/H]$). Aims. Here we provide and discuss newly obtained RV and $[M/H]$ data, which will enable us to reinvestigate potential groupings of open clusters and associations. Methods.We extracted additional RVs and $[M/H]$ from the RAdial Velocity Ex…
The spatial distribution of known globular clusters (GCs) in the Milky Way shows that the current census of GCs is incomplete in the direction of the Galactic plane. We present the discovery of two new GCs located close to the Galactic plane in the sky. These two GCs, RLGC 1 and RLGC 2, were discovered serendipitously during our new cluster survey (Ryu & Lee 2018) based on near-Infrared and mid-Infrared survey data. The two GCs show a grouping of resolved stars in their $K$ band images and a presence of faint diffuse light in their outer regions in the WISE $W1$ band images. They also show pro…
The ability to measure metallicities and α-element abundances in individual red giant branch (RGB) stars using medium-resolution spectra ($R \approx 6000$) is a valuable tool for deciphering the nature of Milky Way dwarf satellites and the history of the Galactic halo. Extending such studies to more distant systems like Andromeda is beyond the ability of the current generation of telescopes, but by co-adding the spectra of similar stars, we can attain the necessary signal-to-noise ratio to make detailed abundance measurements. In this paper, we present a method to determine metallicities and α…
We present a one-dimensional, local thermodynamic equilibrium (1D-LTE) homogeneous analysis of 132 stars observed at high-resolution with ESPaDOnS. This represents the largest sample observed at high resolution (R$\sim$40,000) from the Pristine survey. This sample is based on the first version of the Pristine catalog and covers the full range of metallicities from [Fe/H]$\sim -3$ to $\sim +0.25$, with nearly half of our sample (58 stars) composed of very metal-poor stars ([Fe/H] $\le$ $-$2). This wide range of metallicities provides the opportunity of a new detailed study of the Milky Way stel…
Estimating stellar metallicities from Gaia DR3 XP data using LAMOST DR10
Institute of Astronomy, Nicolaus Copernicus University in Toruń（托伦尼古拉·哥白尼大学天文学研究所）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
We present an analysis and comparison of the 30 micron dust features seen in the Spitzer Space Telescope spectra of 207 carbon-rich asymptotic giant branch (AGB) stars, post-AGB objects, and planetary nebulae located in the Milky Way, the Magellanic Clouds (MCs), or the Sagittarius dwarf spheroidal galaxy (Sgr dSph), which are characterised by different average metallicities. We investigated whether the formation of the 30 micron feature carrier may be a function of the metallicity. Through this study we expect to better understand the late stages of stellar evolution of carbon-rich stars in t…
Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20$^{\circ}$ across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from LAMOST and photometric rotation periods from the Zwicky Transient Facility (Z…
The structure, formation, and evolution of the Milky Way bulge is a matter of debate. Important diagnostics for discriminating between bulge models include alpha-abundance trends with metallicity, and spatial abundance and metallicity gradients. Due to the severe optical extinction in the inner Bulge region, only a few detailed investigations have been performed of this region. Here we aim at investigating the inner 2 degrees by observing the [alpha/Fe] element trends versus metallicity, and by trying to derive the metallicity gradient. [alpha/Fe] and metallicities have been determined by spec…
The nuclear stellar disc (NSD) is, together with the nuclear star cluster (NSC) and the central massive black hole, one of the main components in the central parts of our Milky Way. However, until recently, only few studies of the stellar content of the NSD have been obtained due to extreme extinction and stellar crowding. With a dedicated KMOS (VLT, ESO) spectroscopic survey, we study the kinematics and global metallicities of the NSD based on the observations of K/M giant stars. We trace radial velocities and metallicities which were derived based on spectral indices (Na I and CO) along the …
I present the mean metallicity distribution of stars in the Milky Way Galaxy based on photometry from the Sloan Digital Sky Survey. I utilize an empirically calibrated set of stellar isochrones developed in previous work to estimate the metallicities of individual stars to a precision of $0.2$ dex for reasonably bright stars across the survey area. I also obtain more precise metallicity estimates using priors from the $Gaia$ parallaxes for relatively nearby stars. Close to the Galactic mid-plane ($|Z|<2$ kpc), a mean metallicity map reveals deviations from the mirror symmetry between the north…
We present stellar age distributions of the Milky Way (MW) bulge region using ages for $\sim$6,000 high-luminosity ($\log(g) < 2.0$), metal-rich ($\rm [Fe/H] \ge -0.5$) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Ages are derived using {\it The Cannon} label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars ($>$8 Gyr). We find evidence that the planar region of the b…
