Evidence for a metal-poor population in the inner Galactic Bulge

TL;DR

This study reveals a previously undetected metal-poor stellar population in the inner Galactic Bulge using APOGEE near-infrared spectroscopic data, indicating complex formation history.

Contribution

First detection of a metal-poor population in the inner Galactic Bulge through high-resolution IR spectroscopy, expanding understanding of bulge composition.

Findings

Identification of a metal-rich population at [M/H] = +0.4 dex

Detection of a metal-poor population at [M/H] = -1.0 dex

Metal-poor stars show enhanced alpha-element abundances

Abstract

The inner Galactic Bulge has, until recently, been avoided in chemical evolution studies due to extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as APOGEE, allow for the first time the measurement of metallicities in the inner region of our Galaxy. We study metallicities of 33 K/M giants situated in the Galactic Center region from observations obtained with the APOGEE survey. We selected K/M giants with reliable stellar parameters from the APOGEE/ASPCAP pipeline. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the inner Galactic Bulge. We find a metal-rich population centered at [M/H] = +0.4 dex, in agreement with earlier studies of other bulge regions, but also a peak at low metallicity around $\rm [M/H] = -1.0\,dex$, suggesting the presence of a metal-poor population which has not previously been detected in the central region. Our results indicate a dominant metal-rich population with a metal-poor component that is enhanced in the $\alpha$-elements. This metal-poor population may be associated with the classical bulge and a fast formation scenario.