Asymmetric spatial distribution of sub-solar metallicity stars in the Milky Way nuclear star cluster
A. Feldmeier-Krause, W. Kerzendorf, T. Do, F. Nogueras-Lara, N. Neumayer, C. J. Walcher, A. Seth, R. Schödel, P. T. de Zeeuw, M. Hilker, Nora Lützgendorf, H. Ku… 展开作者
A. Feldmeier-Krause, W. Kerzendorf, T. Do, F. Nogueras-Lara, N. Neumayer, C. J. Walcher, A. Seth, R. Schödel, P. T. de Zeeuw, M. Hilker, Nora Lützgendorf, H. Kuntschner, M. Kissler-Patig
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 stellar metallicities range from [M/H]=-1.25 dex to [M/H]> +0.3 dex, with most of the stars having super-solar metallicity. We are able to measure an anisotropy of the stellar metallicity distribution. In the Galactic North, the portion of sub-solar metallicity stars with [M/H]<0.0 dex is more than twice as high as in the Galactic South. One possible explanation for different fractions of sub-solar metallicity stars in different parts of the cluster is a recent merger event. We propose to test this hypothesis with high-resolution spectroscopy, and by combining the metallicity information with kinematic data.
We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars were obtained with the medium-spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guide star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is large variation in metallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity. About 6\% of the stars have [M/H] $<$ -0.5. This result is in contrast to previous observations, with smaller samples, that show stars…
Observations show a clear vertical metallicity gradient in the Galactic bulge, which is often taken as a signature of dissipative processes in the formation of a classical bulge. Various evidence shows, however, that the Milky Way is a barred galaxy with a boxy bulge representing the inner three-dimensional part of the bar. Here we show with a secular evolution N-body model that a boxy bulge formed through bar and buckling instabilities can show vertical metallicity gradients similar to the observed gradient, if the initial axisymmetric disk had a comparable radial metallicity gradient. In thi…
We investigate the vertical metallicity gradients of five mono-age stellar populations between 0 and 11 Gyr for a sample of 18 435 dwarf stars selected from the cross-matched Tycho-Gaia Astrometric Solution (TGAS) and RAdial Velocity Experiment (RAVE) Data Release 5. We find a correlation between the vertical metallicity gradients and age, with no vertical metallicity gradient in the youngest population and an increasingly steeper negative vertical metallicity gradient for the older stellar populations. The metallicity at disc plane remains almost constant between 2 and 8 Gyr, and it becomes s…
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…
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…
Metallicity gradients derived from planetary nebulae (PNe) using O, Ne, and Ar abundances are studied and compared to those from HII regions in the galaxies M31, M33, NGC 300 and the Milky Way. Galactocentric radii and chemical abundances were collected from the literature, carefully selecting a homogeneous sample for each galaxy. Metallicity gradients shown by PNe are flatter than those of HII regions in all cases. The extreme case is M31 where PN abundances are not related to galactocentric distances and the gradients are consistent with zero. To analyze the evolution of gradients with time …
We investigate the large scale metallicity distribution in the Galactic bulge, using a large spatial coverage, in order to constrain the bulge formation scenario. We use the VISTA variables in the Via Lactea (VVV) survey data and 2MASS photometry, covering 320 sqdeg of the Galactic bulge, to derive photometric metallicities by interpolating of the (J-Ks)0 colors of individual Red Giant Branch stars based on a set of globular cluster ridge lines. We then use this information to construct the first global metallicity map of the bulge with a resolution of 30'x45'. The metallicity map of the bulge…
We present a low metallicity map of the Milky Way consisting of $\sim$111,000 giants with $-3.5 \lesssim$ [Fe/H] $\lesssim -$0.75, based on public photometry from the second data release of the SkyMapper survey. These stars extend out to $\sim$7kpc from the solar neighborhood and cover the main Galactic stellar populations, including the thick disk and the inner halo. Notably, this map can reliably differentiate metallicities down to [Fe/H] $\sim -3.0$, and thus provides an unprecedented view into the ancient, metal-poor Milky Way. Among the more metal-rich stars in our sample ([Fe/H] $> -2.0$…
We use a high resolution cosmological zoom simulation of a Milky Way-sized halo to study the observable features in velocity and metallicity space associated with the dynamical influence of spiral arms. For the first time, we demonstrate that spiral arms, that form in a disc in a fully cosmological environment with realistic galaxy formation physics, drive large-scale systematic streaming motions. In particular, on the trailing edge of the spiral arms the peculiar galacto-centric radial and azimuthal velocity field is directed radially outward and azimuthally backward, whereas it is radially i…
Using the stellar atmospheric parameters such as effective temperature and metallicity derived from SDSS spectra for 2200 main sequence (MS) stars which were also observed by Beijing - Arizona - Taiwan - Connecticut (BATC) photometric system, we develop the polynomial photometric calibration method to evaluate the stellar effective temperature and metallicity for BATC multi-color photometric data. This calibration method has been applied to about 160 000 MS stars from 67 BATC observed fields. Those stars have colors and magnitudes in the ranges 0.1 < d - h < 1.4 and 14.0 < d < 21.0. We find th…
Recovering the birth radii of observed stars in the Milky Way is one of the ultimate goals of Galactic Archaeology. One method to infer the birth radius and the evolution of the ISM metallicity assumes a linear relation between the ISM metallicity with radius at any given look-back time. Here we test the reliability of this assumption by using 4 zoom-in cosmological hydrodynamic simulations from the NIHAO-UHD project. We find that one can infer precise birth radii only when the stellar disk starts to form, which for our modeled galaxies happens ~ 10 Gyr ago, in agreement with recent estimates …
Recent analysis of the SDSS-III/APOGEE Data Release 12 stellar catalogue has revealed that the Milky Way's metallicity distribution function (MDF) changes shape as a function of radius, transitioning from being negatively skewed at small Galactocentric radii to positively skewed at large Galactocentric radii. Using a high resolution, N-body+SPH simulation, we show that the changing skewness arises from radial migration - metal-rich stars form in the inner disk and subsequently migrate to the metal-poorer outer disk. These migrated stars represent a large fraction (> 50%) of the stars in the ou…
Globular clusters can form inside their host galaxies at high redshift when gas densities were higher and gas-rich mergers were common. They can also form inside lower-mass galaxies that have since been accreted and tidally disrupted, leaving their globular cluster complement bound to higher-mass halos. We argue that the age-metallicity-specific orbital energy relation in a galaxy's globular cluster system can be used to identify its origin. Gas-rich mergers should produce tightly bound systems in which metal-rich clusters are younger than metal-poor clusters. Globular clusters formed in massi…
Metallicity Structure in Galactic Longitude-Velocity Diagrams of the Milky Way Disk and FIRE-2 Simulations
National Radio Astronomy Observatory（国家射电天文台）；Pennsylvania State University（宾夕法尼亚州立大学）；University of Wisconsin–Madison（威斯康星大学麦迪逊分校）；California State University, Chico（加州州立大学奇科分校）
The metallicity structure of the Milky Way disk stems from the chemodynamical evolutionary history of the Galaxy. We use the National Radio Astronomy Observatory Karl G. Jansky Very Large Array to observe ~8-10 GHz hydrogen radio recombination line and radio continuum emission toward 82 Galactic HII regions. We use these data to derive the electron temperatures and metallicities for these nebulae. Since collisionally excited lines from metals (e.g., oxygen, nitrogen) are the dominant cooling mechanism in HII regions, the nebular metallicity can be inferred from the electron temperature. Includ…
We examine the metallicity trends in the Milky Way (MW) bulge - using APOGEE DR13 data - and explore their origin by comparing two N-body models of isolated galaxies which develop a bar and a boxy/peanut (b/p) bulge. Both models have been proposed as scenarios for reconciling a disc origin of the MW bulge with a negative vertical metallicity gradient. The first model is a superposition of co-spatial, i.e. overlapping, disc populations with different scaleheights, kinematics and metallicities. In this model the thick, metal-poor, and centrally concentrated disc populations contribute significan…
Milky Way's hot gaseous halo extends up to the Galactic virial radius ($\sim 200$ kpc) and contains a significant component of baryon mass of the Galaxy. The halo properties can be constrained from X-ray spectroscopic observations and from satellite galaxies' ram-pressure stripping studies. Results of the former method crucially depend on the gas metallicity assumptions while the latter one's are insensitive to them. Here, a joint analysis of both kinds of data is presented to constrain electron density and metallicity of the gas. The power law is assumed for the electron density radial profil…
Radial metallicity gradients are observed in the disks of the Milky Way and in several other spiral galaxies. In the case of the Milky Way, many objects can be used to determine the gradients, such as HII regions, B stars, Cepheids, open clusters and planetary nebulae. Several elements can be studied, such as oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other elements in cepheids, open clusters and stars. As a consequence, the number of observational characteristics inferred from the study of abundance gradients is very large, so that in the past few years they have b…
Galactic and extragalactic studies have shown that metal-rich globular clusters (GCs) are approximately three times more likely to host bright low-mass X-ray binaries (LMXBs) than metal-poor GCs. There is no satisfactory explanation for this metallicity effect. We tested the hypothesis that the number density of red giant branch (RGB) stars is larger in metal-rich GCs, and thus potentially the cause of the metallicity effect. Using Hubble Space Telescope photometry for 109 unique Milky Way GCs, we investigated whether RGB star density was correlated with GC metallicity. Isochrone fitting was u…
Albeit radial migration must be a ubiquitous process in disc galaxies, its significance in the evolution of stellar discs is not always reflected through global trends. However, there are other key observables, such as the metallicity distribution function (MDF), that may shed some light in this matter. We argue that the shape of the MDF not only tells us whether the stellar disc experienced radial migration, but it also contains important clues on the structure that triggered it. Specifically, the MDF contains information about the dynamics and morphology of the spiral pattern. To constrain t…
Observations of the Milky Way's low-$α$ disk show that at fixed metallicity, [Fe/H], several element abundance, [X/Fe], correlate with age, with unique slopes and small scatters around the age-[X/Fe] relations. In this study, we turn to simulations to explore the age-[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way-like galaxy, m12i, and understand what physical conditions give rise to the observed age-[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locati…
Using the cosmological zoom simulation VINTERGATAN, we present a new scenario for the onset of star formation at the metal-poor end of the low-[$α$/Fe] sequence in a Milky Way-like galaxy. In this scenario, the galaxy is fueled by two distinct gas flows. One is enriched by outflows from massive galaxies, but not the other. While the former feeds the inner galactic region, the latter fuels an outer gas disk, inclined with respect to the main galactic plane, and with a significantly poorer chemical content. The first passage of the last major merger galaxy triggers tidal compression in the outer…
We develop a high-performance analytical model of Galactic Chemical Evolution, which accounts for delay time distributions and lock-up of stellar yields in a thermal-phased ISM. The model is capable of searching, for the first time, through the high-dimensional parameter space associated with the r-process enrichment of the Milky Way by its possible sources: Neutron Star Mergers and Collapsar events. Their differing formation mechanisms give these two processes different time dependencies, a property which has frequently been used to argue in favour of collapsars as the dominant r-process sour…
Revisiting the Radial Metallicity Gradient-Age Relation in the Milky Way's Thin and Thick Disks
Shanghai Jiao Tong University（上海交通大学）；University of Chinese Academy of Sciences（中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Tianjin Normal University（天津师范大学）
We calculate the ages, orbits and phase-space coordinates for a sample of $\sim$4 million LAMOST and Gaia stars. The ages are crossmatched and compared with values from two other popular age catalogs which derive the ages using different methods. Of these $\sim$4 million stars, we select a sample of 1.3 million stars and investigate their radial metallicity gradients (as determined by orbital radii) as a function of their ages. This analysis is performed on various subsets of the data split by chemistry and orbital parameters. We find that commonly used selections for ``thin disk'' stars (such…
In this letter we examine the evolution of the radial metallicity gradient induced by secular processes, in the disk of an $N$-body Milky Way-like galaxy. We assign a [Fe/H] value to each particle of the simulation according to an initial, cosmologically motivated, radial chemical distribution and let the disk dynamically evolve for 6 Gyr. This direct approach allows us to take into account only the effects of dynamical evolution and to gauge how and to what extent they affect the initial chemical conditions. The initial [Fe/H] distribution increases with R in the inner disk up to R ~ 10 kpc a…
Context. The TOPoS project has the goal to find and analyse Turn-Off (TO) stars of extremely low metallicity. To select the targets for spectroscopic follow-up at high spectral resolution, we have relied on low-resolution spectra from the Sloan Digital Sky Survey. Aims. In this paper we use the metallicity estimates we have obtained from our analysis of the SDSS spectra to construct the metallicity distribution function (MDF) of the Milky Way, with special emphasis on its metal-weak tail. The goal is to provide the underlying distribution out of which the TOPoS sample was extracted. Methods. W…
The Galactic bulge of the Milky Way is made up of stars with a broad range of metallicity, -3.0 < [Fe/H] < 1 dex. The mean of the Metallicity Distribution Function (MDF) decreases as a function of height z from the plane and, more weakly, with galactic radius. The most metal rich stars in the inner Galaxy are concentrated to the plane and the more metal poor stars are found predominantly further from the plane, with an overall vertical gradient in the mean of the MDF of about -0.45 dex/kpc. This vertical gradient is believed to reflect the changing contribution with height of different populat…
The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ([Fe/H] < -3), and currently consists of over 4 million FGK-type stars over a sky area of $\sim 2~500\, \mathrm{deg}^2$. We focus our analysis on a subsample of $\sim 80~000$ main sequence turnoff stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at [Fe/H] = -1.6, and a slope of $Δ$(LogN)/$Δ[Fe/H] = 1.0 \pm 0.1$ in the metallicity range of -3.4…
The disrupted chemical enrichment history of the Milky Way driven by gas accretion
South-Western Institute for Astronomy Research, Yunnan University（西南天文研究所，云南大学）；Yunnan Key Laboratory of Survey Science, Yunnan University（云南省测绘科学重点实验室，云南大学）；Department of Astronomy, Xiamen University（天文学系，厦门大学）；Institute of Astronomy, University of Cambridge（天文学研究所，剑桥大学）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（天文与空间科学学院，中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（国家天文台，中国科学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（天文与天体物理前沿研究院，北京师范大学）；Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences（射电天文与技术重点实验室，中国科学院）
We use N-body chemo-dynamic simulations to study the coupling between morphology, kinematics and metallicity of the bar/bulge region of our Galaxy. We make qualitative comparisons of our results with available observations and find very good agreement. We conclude that this region is complex, since it comprises several stellar components with different properties -- i.e. a boxy/peanut bulge, thin and thick disc components, and, to lesser extents, a disky pseudobulge, a stellar halo and a small classical bulge -- all cohabiting in dynamical equilibrium. Our models show strong links between kine…
We analyze the anisotropy profile of the Milky Way's smooth, diffuse stellar halo using SDSS/SEGUE blue horizontal branch stars and SDSS/SEGUE and LAMOST K giants. These intrinsically luminous stars allow us to probe the halo to approximately 100 kpc from the Galactic center. Line-of-sight velocities, distances, metallicities, and proper motions are available for all stars via SDSS/SEGUE, LAMOST, and Gaia, and we use these data to construct a full 7D set consisting of positions, space motions, and metallicity. We remove substructure from our samples using integrals of motion based on the metho…
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…
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 halo of the Milky-Way circumgalactic gas extends up to the virial radius of the Galaxy, ~250 kpc. The halo properties may be deduced from X-ray spectroscopic observations and from studies of the ram-pressure stripping of satellite dwarf galaxies. The former method is more precise but its results depend crucially on the assumed metallicity of the circumgalactic gas; the latter one does not need these assumptions. Here, the information from both approaches is combined to constrain observationally the gas metallicity and density as functions of the galactocentric distance. It is demonstrated …
The best way to trace back the history of star formation and mass assembly of the Milky Way disc is by combining chemical compositions, ages and phase-space information for a large number of disc stars. With the advent of large surveys of the stellar populations of the Galaxy, such data have become available and can be used to pose constraints on sophisticated models of galaxy formation. We use SDSS-III/APOGEE data to derive the first detailed 3D map of stellar density in the Galactic disc as a function of age, [Fe/H] and $\mathrm{[α/Fe]}$. We discuss the implications of our results for the fo…
We use accurate estimates of aluminium abundance provided as part of the APOGEE Data Release 17 and Gaia Early Data Release 3 astrometry to select a highly pure sample of stars with metallicity $-1.5\lesssim {\rm [Fe/H]}\lesssim 0.5$ born in-situ in the Milky Way proper. We show that the low-metallicity ([Fe/H]$\lesssim -1.3$) in-situ component that we dub Aurora is kinematically hot with an approximately isotropic velocity ellipsoid and a modest net rotation. Aurora stars exhibit large scatter in metallicity and in a number of element abundance ratios. The median tangential velocity of the in…
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 extent to which turbulence mixes gas in the face of recurrent infusions of fresh metals by supernovae (SN) could help provide important constraints on the local star formation conditions. This includes predictions of the metallicity dispersion amongst metal poor stars, which suggests that the interstellar medium was not very well mixed at these early times. The purpose of this {\it Letter} is to help isolate, via a series of numerical experiments, some of the key processes that regulate turbulent mixing of SN elements in galactic disks. We study the gas interactions in small simulated patc…
Using combined asteroseismic and spectroscopic observations of 418 red-giant stars close to the Galactic disc plane (6 kpc $<R_{\rm Gal}\lesssim13$ kpc, $|Z_{\rm Gal}|<0.3$ kpc), we measure the age dependence of the radial metallicity distribution in the Milky Way's thin disc over cosmic time. The slope of the radial iron gradient of the young red-giant population ($-0.058\pm0.008$ [stat.] $\pm0.003$ [syst.] dex/kpc) is consistent with recent Cepheid measurements. For stellar populations with ages of $1-4$ Gyr the gradient is slightly steeper, at a value of $-0.066\pm0.007\pm0.002$ dex/kpc, an…
Two main scenarios for the formation of the Galactic bulge are invoked, the first one through gravitational collapse or hierarchical merging of subclumps, the second through secular evolution of the Galactic disc. We aim to constrain the formation of the Galactic bulge through studies of the correlation between kinematics and metallicities in Baade's Window (l=1, b=-4) and two other fields along the bulge minor axis (l=0, b=-6 and b=-12). We combine the radial velocity and the [Fe/H] measurements obtained with FLAMES/GIRAFFE at the VLT with a spectral resolution of R=20000, plus for the Baade'…
We present a semi-empirical, largely model-independent approach for estimating Galactic birth radii, r_birth, for Milky Way disk stars. The technique relies on the justifiable assumption that a negative radial metallicity gradient in the interstellar medium (ISM) existed for most of the disk lifetime. Stars are projected back to their birth positions according to the observationally derived age and [Fe/H] with no kinematical information required. Applying our approach to the AMBRE:HARPS and HARPS-GTO local samples, we show that we can constrain the ISM metallicity evolution with Galactic radiu…
We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, re-accretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters, which are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in…
While the Milky Way Nuclear star cluster has been studied extensively, how it formed is uncertain. Studies have shown it contains a solar and supersolar metallicity population that may have formed in-situ, along with a subsolar metallicity population that may have formed via mergers of globular clusters and dwarf galaxies. Stellar abundance measurements are critical to differentiate between formation scenarios. We present new measurements of [$M/H$] and $α$-element abundances [$α/Fe$] of two subsolar-metallicity stars in the Galactic Center. These observations were taken with the adaptive-opti…
The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides a powerful constraint on the chemical enrichment and dynamical history of the disk. We present the radial metallicity gradient, Δ[Fe/H]/ΔR, as a function of height above the plane, |Z|, using 7010 main sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 < R < 16 kpc, 0.15 < |Z| < 1.5 kpc. The data reveal th…
Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). II. The age-metallicity relation of Gaia-Sausage-Enceladus globular clusters
Universidade de Vigo（维戈大学）；Universidad de La Laguna（拉古纳大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚天文物理与空间科学研究所）；INAF – Osservatorio Astronomico di Roma（罗马天文台）；INAF – Osservatorio Astronomico di Abruzzo（阿布鲁佐天文台）；INFN - Sezione di Pisa, Universitá di Pisa（比萨大学及意大利国家核物理研究所比萨分部）；Instituto de Astrofísica de Canarias（加那利群岛天体物理学研究所）；Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna（博洛尼亚大学物理与天文学系）；Universidad de Granada（格拉纳达大学）
We report the first star formation history study of the Milky Way's nuclear star cluster (NSC) that includes observational constraints from a large sample of stellar metallicity measurements. These metallicity measurements were obtained from recent surveys from Gemini and VLT of 770 late-type stars within the central 1.5 pc. These metallicity measurements, along with photometry and spectroscopically derived temperatures, are forward modeled with a Bayesian inference approach. Including metallicity measurements improves the overall fit quality, as the low-temperature red giants that were previo…
We investigate here the effect of the selection function on the metallicity distribution function (MDF) and on the vertical metallicity gradient by studying similar lines of sight using four different spectroscopic surveys (APOGEE, LAMOST, RAVE, and Gaia-ESO), which have different targeting strategies and therefore different selection functions. We use common fields between the spectroscopic surveys of APOGEE, LAMOST, RAVE (ALR) and APOGEE, RAVE, Gaia-ESO (AGR) and use two stellar population synthesis models, GALAXIA and TRILEGAL, to create mock fields for each survey. We apply the selection f…
We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW) mass M_vir ~ 10^12.1 M_sun) halos using a suite of 45 zoom-in, dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z=0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M_star ~ 10^8-10^10 M_sun. Halos with more quiescent accretion histories t…
Aims. Using a suite of cosmological chemodynamical disc galaxy simulations, we assess how (a) radial metallicity gradients evolve with scaleheight; (b) the vertical metallicity gradients change through the thick disc; and (c) the vertical gradient of the stellar rotation velocity varies through the disc. We compare with the Milky Way to search for analogous trends. Methods. We analyse five simulated spiral galaxies with masses comparable to the Milky Way. The simulations span a range of star formation and energy feedback strengths and prescriptions, particle- and grid-based hydrodynamical impl…
