Measuring the alpha-abundance of subsolar-metallicity stars in the Milky Way's central half-parsec: testing globular cluster and dwarf galaxy infall scenarios

Abstract

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 $\alpha$-element abundances [$\alpha /Fe$] of two subsolar-metallicity stars in the Galactic Center. These observations were taken with the adaptive-optics assisted high-resolution (R=24,000) spectrograph NIRSPEC in the K-band (1.8 - 2.6 micron). These are the first $\alpha$-element abundance measurements of sub-solar metallicity stars in the Milky Way nuclear star cluster. We measure [$M/H$]=$-0.59\pm 0.11$, [$\alpha /Fe$]=$0.05\pm 0.15$ and [$M/H$]= $-0.81\pm 0.12$, [$\alpha /Fe$]= $0.15\pm 0.16$ for the two stars at the Galactic center; the uncertainties are dominated by systematic uncertainties in the spectral templates. The stars have an [$\alpha /Fe$] in-between the [$\alpha /Fe$] of globular clusters and dwarf galaxies at similar [$M/H$] values. Their abundances are very different than the bulk of the stars in the nuclear star cluster. These results indicate that the sub-solar metallicity population in the Milky Way nuclear star cluster likely originated from infalling dwarf galaxies or globular clusters and are unlikely to have formed in-situ.

arXiv commentAccepted by ApJ

References in corpus (62)

• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• Multimodal nested sampling: an efficient and robust alternative to MCMC methods for astronomical data analysis
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole
• Abundances, Stellar Parameters, and Spectra From the SDSS-III/APOGEE Survey
• The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze
• A Comparison of Elemental Abundance Ratios in Globular Clusters, Field Stars, and Dwarf Spheroidal Galaxies
• A high resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• Chemodynamics of the Milky Way. I. The first year of APOGEE data
• Surface Brightness Profile of the Milky Way's Nuclear Star Cluster
• The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy
• Dissipationless Formation and Evolution of the Milky Way Nuclear Star Cluster
• Origin and growth of nuclear star clusters around massive black holes
• The Ital-FLAMES survey of the Sagittarius dwarf Spheroidal galaxy. I. Chemical abundances of bright RGB stars
• On the Origin of Nuclear Star Clusters in Late Type Spiral Galaxies
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?
• Calibrations of Atmospheric Parameters Obtained from the First Year of SDSS-III APOGEE Observations
• A New Stellar Atmosphere Grid and Comparisons with HST/STIS Calspec Flux Distributions
• The First Stellar Abundance Measurements in the Galactic Center: the M Supergiant IRS 7
• Really Cool Stars and the Star Formation History at the Galactic Center
• Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way
• The Sgr dSph hosts a metal-rich population
• VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy
• Stellar Iron Abundances at the Galactic Center
• The nuclear cluster of the Milky Way: Our primary testbed for the interaction of a dense star cluster with a massive black hole
• KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars
• Discovery of low-metallicity stars in the central parsec of the Milky Way
• Recurrent gas accretion by massive star clusters, multiple stellar populations and mass thresholds for spherical stellar systems
• The chemical abundances in the Galactic Centre from the atmospheres of Red Supergiants
• VLT-FLAMES Analysis of 8 giants in the Bulge Metal-poor Globular Cluster NGC 6522: Oldest Cluster in the Galaxy?
• APOGEE DR14/DR15 Abundances in the Inner Milky Way
• High-resolution abundance analysis of red giants in the globular cluster NGC 6522
• Age and mass segregation of multiple stellar populations in galactic nuclei and their observational signatures
• Chemodynamics of newly identified giants with globular cluster like abundance patterns in the bulge, disk, and halo of the Milky Way
• Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
• Super-Solar Metallicity Stars in the Galactic Center Nuclear Star Cluster: Unusual Sc, V, and Y Abundances
• The Populations of Carina. II. Chemical Enrichment
• SPISEA: A Python-Based Simple Stellar Population Synthesis Code for Star Clusters
• Discovery of RR Lyrae Stars in the Nuclear Bulge of the Milky Way
• The Infrared Telescope Facility (IRTF) spectral library: spectral diagnostics for cool stars
• Detailed abundances in the Galactic center: Evidence of a metal-rich alpha-enhanced stellar population
• Aluminum Enhanced Metal-Poor Stars buried in the Inner Galaxy
• Asymmetric spatial distribution of sub-solar metallicity stars in the Milky Way nuclear star cluster
• On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster
• Revealing the Formation of the Milky Way Nuclear Star Cluster via Chemo-Dynamical Modeling
• Evidence for a metal-poor population in the inner Galactic Bulge
• Cool stars in the Galactic Center as seen by APOGEE: M giants, AGB stars and supergiant stars/candidates
• Detailed abundance analysis of a metal-poor giant in the Galactic Center
• Can a Satellite Galaxy Merger Explain the Active Past of the Galactic Center?
• Abundance sensitive points of line profiles in the stellar spectra

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