Chemical evolution of the inner 2 degrees of the Milky Way bulge: [alpha/Fe] trends and metallicity gradients

Abstract

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 spectral synthesis of 2 micron spectra observed with VLT/CRIRES of 28 M-giants, lying along the Southern minor axis at (l,b)=(0,0), (0,-1), and (0,-2). VLT/ISAAC spectra are used to determine the effective temperature of the stars. We present the first connection between the Galactic Center and the Bulge using similar stars, high spectral resolution, and analysis techniques. The [alpha/Fe] trends in all our 3 fields show a large similarity among each other and with trends further out in the Bulge, with a lack of an [α/Fe] gradient all the way into the centre. This suggests a homogeneous Bulge when it comes to the enrichment process and star-formation history. We find a large range of metallicities (-1.2<[Fe/H]<+0.3), with a lower dispersion in the Galactic center: -0.2<[Fe/H]<+0.3. The derived metallicities get in the mean, progressively higher the closer to the Galactic plane they lie. We could interpret this as a continuation of the metallicity gradient established further out in the Bulge, but due to the low number of stars and possible selection effects, more data of the same sort as presented here is necessary to conclude on the inner metallicity gradient from our data alone. Our results firmly argues for the center being in the context of the Bulge rather than very distinct.

Accepted for publication in AJ

References in corpus (20)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Galactic chemical evolution: Carbon through Zinc
• The rapid formation a large rotating disk galaxy three billion years after the Big Bang
• Star Formation in the Central 400 pc of the Milky Way: Evidence for a Population of Massive YSOs
• Chemical similarities between Galactic bulge and local thick disk red giant stars
• The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• The First Detailed Abundances for M giants in the inner Bulge from Infrared Spectroscopy
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• Cool luminous stars: the hybrid nature of their infrared spectra -- Carbon, oxygen, and their isotopic abundances in 23 K - M giant stars
• Abundances in bulge stars from high-resolution, near-IR spectra I. The CNO elements observed during the science verification of CRIRES at VLT
• Interstellar Extinction and Long-Period Variables in the Galactic Center
• Chemical Abundances of M giants in the Galactic Center: a Single Metal-Rich Population with Low [alpha/Fe]
• Chemical evolution of the Galactic Center
• Chemical and kinematical properties of Galactic bulge stars surrounding the stellar system Terzan 5
• Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy
• Observing with a space-borne gamma-ray telescope: selected results from INTEGRAL

Cited by in corpus (33)

• De Re Metallica: The cosmic chemical evolution of galaxies
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• Chemodynamical history of the Galactic Bulge
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
• High-precision stellar abundances of the elements - methods and applications
• The origin of diverse $\alpha$-element abundances in galaxy discs
• KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars
• The age of the young bulge-like population in the stellar system Terzan5: linking the Galactic bulge to the high-z Universe
• High Eccentricities and High Masses Characterize Gravitational-wave Captures in Galactic Nuclei as Seen by Earth-based Detectors
• The disc origin of the Milky Way bulge
• The Chemical Composition of the Galactic Bulge and Implications for its Evolution
• 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 inner two degrees of the Milky Way. Evidence of a chemical difference between the Galactic Center and the surrounding inner bulge stellar populations
• Detailed abundances in the Galactic center: Evidence of a metal-rich alpha-enhanced stellar population
• Abundances of disk and bulge giants from hi-res optical spectra: II. O, Mg, Ca, and Ti in the bulge sample
• Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results
• Evidence against anomalous compositions for giants in the Galactic Nuclear Star Cluster
• Detailed abundance analysis of a metal-poor giant in the Galactic Center
• Chemical Characterization of the Inner Galactic bulge:North-South Symmetry
• FeI lines in 0.91-1.33 $\mu$m spectra of red giants for measuring the microturbulence and metallicities
• HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis
• Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid
• Temperatures and metallicities of M giants in the galactic Bulge from low-resolution K-band spectra
• Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations
• Detailed $\alpha$ abundance trends in the inner Galactic bulge
• The population of planetary nebulae near the Galactic centre: chemical abundances
• Probing the physical properties of the intergalactic medium using gamma-ray bursts
• New Fe I Level Energies and Line Identifications from Stellar Spectra. III. Initial Results from UV, Optical, and Infrared Spectra
• The multi-zone chemical evolution of the Galactic bulge: predicting abundances for different radial zones
• Modelling the chemical evolution of the Milky Way
• Detailed near-IR stellar abundances of red giants in the Inner Bulge and Galactic Center