The Bulge Metallicity Distribution from the APOGEE Survey

Abstract

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on homogeneous measurements from the SDSS Data Release 12 for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple-Gaussian decompositions, to be distributed in several components indicative of the presence of various stellar populations such as the bar, or the thin and the thick disk. A super-solar ([Fe/H]=+0.32) and a solar ([Fe/H]=+0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be the major contributors near the midplane. The solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] =-0.46), tentatively associated with the thick disk, and which becomes the dominant component far from the midplane ($|Z| > +0.75 kpc). Varying contributions from these different components produce a transition region at +0.5 kpc < |Z| < +1.0 kpc characterized by a significant vertical metallicity gradient.

15 pages, 11 figures

References in corpus (21)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Structure of the Milky Way's Bar Outside the Bulge
• Radial mixing and the transition between the thick and thin Galactic discs
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
• Constraining the thick disc formation scenario of the Milky Way
• The GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields
• New H-band Stellar Spectral Libraries for the SDSS-III/APOGEE survey
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• ARGOS II: The Galactic Bulge Survey
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Kinematics at the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
• Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution
• Kinematics of the local disk from the RAVE survey and the Gaia first data release
• The origin of pseudobulges in cosmological simulations of galaxy formation
• Mapping a stellar disk into a boxy bulge: The outside-in part of the Milky Way bulge formation
• Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge
• Chemical abundances in Galactic planetary nebulae with Spitzer spectra
• Baade's window with APOGEE: Metallicities, ages and chemical abundances
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics

Cited by in corpus (19)

• The Poor Old Heart of the Milky Way
• The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way
• The inner two degrees of the Milky Way. Evidence of a chemical difference between the Galactic Center and the surrounding inner bulge stellar populations
• Exploring the stellar age distribution of the Milky Way Bulge using APOGEE
• The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14
• The Star Formation History of the Milky Way's Nuclear Star Cluster
• The Three-Phase Evolution of the Milky Way
• Abundances of disk and Bulge giants from high-resolution optical spectra III. Sc, V, Cr, Mn, Co, Ni
• CAPOS: The bulge Cluster APOgee Survey I. Overview and initial ASPCAP results
• The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution
• Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results
• Mapping the Interstellar Reddening and Extinction towards Baade's Window Using Minimum Light Colors of ab-type RR Lyrae Stars. Revelations from the De-reddened Color-Magnitude Diagrams
• HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis
• Radial velocities in the outermost disk toward the anticenter
• CO line observations of OH/IR stars in the inner Galactic Bulge: Characteristics of stars at the tip of the AGB
• Understanding the velocity distribution of the Galactic Bulge with APOGEE and Gaia
• The multi-zone chemical evolution of the Galactic bulge: predicting abundances for different radial zones
• The Spheroidal Bulge of the Milky Way: Chemodynamically Distinct from the Inner-Thick Disc and Bar
• The COMBS Survey -- III. The Chemodynamical Origins of Metal-Poor Bulge Stars