Based on a simple model of the chemical evolution of the Milky Way disk, we investigate the disk oxygen abundance gradient and its time evolution. Two star formation rates (SFRs) are considered, one is the classical Kennicutt-Schmidt law ($ Ψ= 0.25 Σ_{\rm{gas}}^{1.4}$, hereafter C-KS law), another is the modified Kennicutt law ($Ψ= αΣ_{\rm{gas}}^{1.4} ({V/r})$, hereafter M-KS law). In both cases, the model can produce some amount of abundance gradient, and the gradient is steeper in the early epoch of disk evolution. However, we find that when C-KS law is adopted, the classical chemical evolution model, which assumes a radial dependent infall time scale, cannot produce a sufficiently steep present-day abundance gradient. This problem disappears if we introduce a disk formation time scale, which means that at early times, infalling gas cools down onto the inner disk only, while the outer disk forms later. This kind of model, however, will predict a very steep gradient in the past. When the M-KS law is adopted, the model can properly predict both the current abundance gradient and its time evolution, matching recent observations from planetary nebulae and open clusters along the Milky Way disk. Our best model also predicts that outer disk (artificially defined as the disk with $R_g \ge 8kpc$) has a steeper gradient than the inner disk. The observed outer disk gradients from Cepheids, open clusters and young stars show quite controversial results. There are also some hints from Cepheids that the outer disk abundance gradient may have a bimodal distribution. More data is needed in order to clarify the outer disk gradient problem. Our model calculations show that for an individual Milky Way-type galaxy, a better description of the local star formation is the modified KS law.
We introduce a novel abundance matching technique that produces a more accurate estimate of the pre-infall halo mass, $M_{200}$, for satellite galaxies. To achieve this, we abundance match with the mean star formation rate, averaged over the time when a galaxy was forming stars, $\langle {\rm SFR}\rangle$, instead of the stellar mass, $M_*$. Using data from the Sloan Digital Sky Survey, the GAMA survey and the Bolshoi simulation, we obtain a statistical $\langle {\rm SFR}\rangle-{\rm M}_{200}$ relation in $Λ{\rm CDM}$. We then compare the pre-infall halo mass, $M^{\rm abund}_{200}$, derived fr…
We review the state of our chemical evolution models for spiral and low mass galaxies. We analyze the consequences of using different stellar yields, infall rate laws and star formation prescriptions in the time/redshift evolution of the radial distributions of abundances, and other quantities as star formation rate or gas densities, in the Milky Way Galaxy; In particular we will study the evolution of the Oxygen abundance radial gradient analyzing its relation with the ratio SFR/infall. We also compare the results with our old chemical evolution models, cosmological simulations and with the e…
Carbon enhanced metal poor (CEMP) stars with low abundances of neutron capture elements (CEMP-no stars) are ubiquitous among metal poor stars in the Milky Way. Recent observations have uncovered their two subgroups that differ in the carbon to magnesium ([C/Mg]) abundance ratio. Here we demonstrate that similar abundance patterns are also present in Milky Way-like galaxies in the EAGLE cosmological hydrodynamical simulation, where these patterns originate from the fact that stars may form from gas enriched predominantly by asymptotic giant branch (AGB) stars or by type-II supernovae. This occu…
A major goal in the field of galaxy formation is to understand the formation of the Milky Way's disk. The first step toward doing this is to empirically describe its present state. We use the new high-dimensional dataset of 19 abundances from 27,135 red clump APOGEE stars to examine the distribution of clusters defined using abundances. We explore different dimensionality reduction techniques and implement a non-parametric agglomerate hierarchical clustering method. We see that groups defined using abundances are spatially separated, as a function of age. Furthermore, the abundance groups repr…
I would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic …
On small scales there have been a number of claims of discrepancies between the standard Cold Dark Matter (CDM) model and observations. The 'missing satellites problem' infamously describes the overabundance of subhalos from CDM simulations compared to the number of satellites observed in the Milky Way. A variety of solutions to this discrepancy have been proposed; however, the impact of the specific properties of the Milky Way halo relative to the typical halo of its mass have yet to be explored. Motivated by recent studies that identified ways in which the Milky Way is atypical (e.g., Licqui…
The four main findings about the age and abundance structure of the Milky Way bulge based on microlensed dwarf and subgiant stars are: (1) a wide metallicity distribution with distinct peaks at [Fe/H]=-1.09, -0.63, -0.20, +0.12, +0.41; (2) a high fraction of intermediate-age to young stars where at [Fe/H]>0 more than 35 % are younger than 8 Gyr, (3) several episodes of significant star formation in the bulge 3, 6, 8, and 11 Gyr ago; (4) the `knee' in the alpha-element abundance trends of the sub-solar metallicity bulge appears to be located at a slightly higher [Fe/H] (about 0.05 to 0.1 dex) t…
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 extend the Ultra-Diffuse Galaxy (UDG) abundance relation, $N_{UDG}-M_{200}$, to lower halo mass hosts $(M_{200}\sim10^{11.6-12.2}M_{\odot})$. We select UDG satellites from published catalogs of dwarf satellite galaxies around Milky Way analogs, namely the Exploration of Local Volume Satellites (ELVES) survey, Satellite Around Galactic Analogs (SAGA) survey, and a survey of Milky Way-like systems conducted using the Hyper-Suprime Cam. Of the 516 satellites around a total of 75 Milky Way-like hosts, we find 41 satellites around 33 hosts satisfy the UDG criteria. The distributions of host halo…
Studies of the ages, abundances, and motions of individual stars in the Milky Way provide one of the best ways to study the evolution of disk galaxies over cosmic time. The formation of the Milky Way's barred inner region in particular is a crucial piece of the puzzle of disk galaxy evolution. Using data from APOGEE and Gaia, we present maps of the kinematics, elemental abundances, and age of the Milky Way bulge and disk that show the barred structure of the inner Milky Way in unprecedented detail. The kinematic maps allow a direct, purely kinematic determination of the bar's pattern speed of …
We determine the radial abundance gradient of Cl in the Milky Way from HII regions spectra. For the first time, the Cl/H ratios are computed by simply adding ionic abundances and not using an ionization correction factor (ICF). We use a collection of published very deep spectra of Galactic HII regions. We have re-calculated the physical conditions, ionic and total abundances of Cl and O using the same methodology and updated atomic data for all the objects. We find that the slopes of the radial gradients of Cl and O are identical within the uncertainties: -0.043 dex/kpc. This is consistent wit…
We study the role of radial motions of stars and gas on the evolution of abundance profiles in the Milky Way disk. We investigate, in a parametrized way, the impact of radial flows of gas and radial migration of stars induced mainly by the Galactic bar and its iteraction with the spiral arms. We use a model with several new or up-dated ingredients (atomic and molecular gas phases, star formation depending on molecular gas, recent sets of metallicity-dependent stellar yields from H to Ni, observationally inferred SNIa rates), which reproduces well most global and local observables of the Milky …
The concordance $Λ$CDM cosmology predicts tens of satellite galaxies distributed in the inner region ($<40\ \lkpc$) of the Milky Way (MW), yet at most $12$ were discovered at present day, including 3 discovered very recently by Dark Energy Survey (DES) and 5 from other surveys (e.g. PanSTARRS, MagLiteS). We use $5$ ultra-high resolution simulations of MW sized dark matter haloes from the $\aqua$ project, combined with $\galf$ semi-analytical galaxy formation model, to investigate properties of the model satellite galaxy population inside $40\ \lkpc$ of MW sized haloes. On average, in each halo…
We investigate the presence and importance of dark matter discs in a sample of 24 simulated Milky Way galaxies in the APOSTLE project, part of the EAGLE programme of hydrodynamic simulations in Lambda-CDM cosmology. It has been suggested that a dark disc in the Milky Way may boost the dark matter density and modify the velocity modulus relative to a smooth halo at the position of the Sun, with ramifications for direct detection experiments. From a kinematic decomposition of the dark matter and a real space analysis of all 24 halos, we find that only one of the simulated Milky Way analogues has…
This paper explores the integrated-light characteristics of the Milky Way (MW) bulge and to what extent they match those of elliptical galaxies in the local universe. We model composite stellar populations with realistic abundance distribution functions (ADFs), tracking the trends of individual elements as a function of overall heavy element abundance as actually observed in MW bulge stars. The resultant predictions for absorption feature strengths from the MW bulge mimic elliptical galaxies better than solar neighborhood stars do, but the MW bulge does not match elliptical galaxies, either. C…
Measuring Detailed Chemical Abundances From Co-added Medium Resolution Spectra I. Tests using Milky Way dwarf spheroidal galaxies and globular clusters
Milky Way-mass galaxies in the FIRE-2 simulations demonstrate two main modes of star formation. At high redshifts star formation occurs in a series of short and intense bursts, while at low redshifts star formation proceeds at a steady rate with a transition from one mode to another at times ranging from 3 to 7 Gyr ago for different galaxies. We analyse how the mode of star formation affects iron and alpha-element abundance. We find that the early bursty regime imprints a measurable pattern in stellar elemental abundances in the form of a "sideways chevron" shape on the [Fe/H] - [O/Fe] plane a…
We present preliminary results of the O, Ne, S and Cl abundance gradients of the Milky Way. We analyze in a homogenous way the physical conditions and chemical abundances of a sample of 35 H II regions with deep spectra observed mainly with the GTC and VLT telescopes. The sample covers a range in Galactocentric distances from 5 to 17 kpc. We reanalyze the O abundance gradient, obtaining a similar complex shape than previously reported in the literature. We calculate the Cl abundance gradient including a significantly larger number of objects than in previous works. Our results show a gradient …
We present an overview of the distributions of 11 elemental abundances in the Milky Way's inner regions, as traced by APOGEE stars released as part of SDSS Data Release 14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na, Al, and K. This sample spans ~4000 stars with R_GC<4 kpc, enabling the most comprehensive study to date of these abundances and their variations within the innermost few kiloparsecs of the Milky Way. We describe the observed abundance patterns ([X/Fe]-[Fe/H]), compare to previous literature results and to patterns in stars at the solar Galactic radius, and discuss …
The recent Gaia Third Data Release contains a homogeneous analysis of millions of high-quality Radial Velocity Spectrometer (RVS) stellar spectra by the GSP-Spec module. This led to the estimation of millions of individual chemical abundances and allows us to chemically map the Milky Way. Among the published GSP-Spec abundances, three heavy-elements produced by neutron-captures in stellar interiors can be found: Ce, Zr and Nd. We use a sample of about 30,000 LTE Ce abundances, selected after applying different combinations of GSP-Spec flags. Thanks to the Gaia DR3 astrometric data and radial v…
Large stellar surveys are revealing the chemodynamical structure of the Galaxy across a vast spatial extent. However, the many millions of low-resolution spectra observed to date are yet to be fully exploited. We employ The Cannon, a data-driven approach to estimating abundances, to obtain detailed abundances from low-resolution (R = 1800) LAMOST spectra, using the GALAH survey as our reference. We deliver five (for dwarfs) or six (for giants) estimated abundances representing five different nucleosynthetic channels, for 3.9 million stars, to a precision of 0.05 - 0.23 dex. Using wide binary p…
We present a reassessment of the radial abundance gradients of He, C, N, O, Ne, S, Cl, and Ar in the Milky Way using the deep optical spectra of 42 HII regions presented in Arellano-Córdova et al. (2020, 2021) and Méndez-Delgado et al. (2020) exploring the impact of: (1) new distance determinations based on Gaia EDR3 parallaxes and (2) the use of Peimbert's temperature fluctuations paradigm ($t ^ 2> 0$) for deriving ionic abundances. We find that distances based on Gaia EDR3 data are more consistent with kinematic ones based on Galactic rotation curves calibrated with radio parallaxes, which g…
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…
To understand the formation of the Milky Way's prominent bar it is important to know whether stars in the bar differ in the chemical element composition of their birth material as compared to disk stars. This requires stellar abundance measurements for large samples across the Milky Way's body. Such samples, e.g. luminous red giant stars observed by SDSS's Apogee survey, will inevitably span a range of stellar parameters; as a consequence, both modelling imperfections and stellar evolution may preclude consistent and precise estimates of their chemical composition at a level of purported bar s…
Chemical abundances of stars in the Milky Way disk are empirical tracers of its enrichment history. However, they capture joint-information that is valuable to disentangle. In this work, we seek to quantify how individual abundances evolve across the present-day radius of the disk, at fixed supernovae contribution ([Fe/H], [Mg/Fe]). We use 18,135 APOGEE DR17 red clump stars and 7,943 GALAH DR3 main sequence stars to compare the abundance distributions conditioned on ([Fe/H], [Mg/Fe]) across $3-13$ kpc and $6.5-9.5$ kpc, respectively. In total we examine 15 elements: C, N, Al, K (light), O, Si,…
The evolution of the metal content of the universe can be tracked through rest-frame UV spectroscopy of damped Ly-$α$ systems (DLAs). Gas-phase abundances in DLAs must be corrected for dust depletion effects, which can be accomplished by calibrating the relation between abundance ratios such as [Zn/Fe] and depletions (the fraction of metals in gas, as opposed to dust). Using samples of gas-phase abundances and depletions in the Milky Way (MW), LMC, and SMC, we demonstrate that the relation between [Zn/Fe] and other abundance ratios does not change significantly between these local galaxies and…
We investigate the influence of stellar migration caused by minor mergers (mass ratio from 1:70 to 1:8) on the radial distribution of chemical abundances in the disks of Milky Way-like galaxies during the last four Gyr. A GPU-based pure N-body tree-code model without hydrodynamics and star formation was used. We computed a large set of mergers with different initial satellite masses, positions, and orbital velocities. We find that there is no significant metallicity change at any radius of the primary galaxy in the case of accretion of a low-mass satellite of 10$^9$ M$_{\odot}$ (mass ratio 1:7…
We present the discovery of a very hot gas phase of the Milky Way circumgalactic medium (CGM) at T $\approx 10^7$ K, using deep XMM-Newton RGS observations of 1ES 1553+113. The hot gas, coexisting with a warm-hot phase at T $\approx 10^6$ K is $α-$enhanced, with [O/Fe] = 0.9$^{+0.7}_{-0.3}$, indicating core-collapse supernovae enrichment. Additionally we find [Ne/O] and [N/O] = $0.7^{+1.6}_{-0.2}$, such that N/Ne is consistent with solar. Along with the enrichment by AGB stars and core-collapse supernovae, this indicates that some oxygen has depleted onto dust and/or transited to cooler gas ph…
Milky Way Mapper decoded abundances -- II: From patterns to paths
Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）；Department of Astronomy, Columbia University（哥伦比亚大学天文学系）；Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado（科罗拉多大学天体物理学与行星科学系天体物理学与空间天文中心）；Department of Physics & Astronomy, University of Utah（犹他大学物理与天文学系）；Department of Physics and Astronomy, Vanderbilt University（范德堡大学物理与天文学系）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；School of Physics and Astronomy, Monash University（莫纳什大学物理与天文学院）；Department of Astronomy, The Ohio State University（俄亥俄州立大学天文学系）；Center for Cosmology and Astroparticle Physics (CCAPP), The Ohio State University（俄亥俄州立大学宇宙学与高能粒子物理中心）
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…
(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…
Milky Way Mapper decoded abundances -- I. Shared disc enrichment patterns
Australian National University（澳大利亚国立大学）；Columbia University（哥伦比亚大学）；University of Colorado（科罗拉多大学）；University of Utah（犹他大学）；Vanderbilt University（范德堡大学）；Flatiron Institute（平顿研究所）；Monash University（莫纳什大学）；The Ohio State University（俄亥俄州立大学）；New York University（纽约大学）
We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 $\text{H}\thinspace \text{II}$ regions and ring nebulae surrounding massive O stars. We revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He$^{+}$ in a homogeneous way, using between 3 and 10 $\text{He}\thinspace \text{I}$ recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slo…
We develop a new method to account for the finite lifetimes of stars and trace individual abundances within a semi-analytic model of galaxy formation. At variance with previous methods, based on the storage of the (binned) past star formation history of model galaxies, our method projects the information about the metals produced by each simple stellar population (SSP) in the future. Using this approach, an accurate accounting of the timings and properties of the individual SSPs composing model galaxies is possible. We analyse the dependence of our chemical model on various ingredients, and ap…
We revisited barium abundance in a sample of giant stars in the dwarf spheroidal Fornax galaxy. Non-local thermodynamic equilibrium (NLTE) synthesis was used to derive the barium abundance from two Ba II lines. Our new NLTE result for barium shows that in the range of metallicities from -1 to -0.5 the abundance of this element is almost the same as in the stars of the Milky Way. We conclude that the evolution of barium abundance in the dSph Fornax galaxy resembles that of the Milky Way at the epoch of the corresponding metallicity level.
