Towards Unveiling the Origins of the Milky Way Bulge through Multi-band-Messenger Sky Surveys

TL;DR

This study combines multi-band and multi-messenger sky survey data to analyze the structure, kinematics, and chemical properties of the Milky Way's bulge, revealing distinct populations and supporting a pseudo-bulge formation scenario.

Contribution

It introduces a comprehensive analysis integrating RR Lyrae, giant star data, and chemical distributions to elucidate the bulge's origins and morphology.

Findings

Identification of three bulge populations with distinct kinematics.

Confirmation of a bimodal chemical distribution indicating different formation pathways.

Support for a pseudo-bulge origin through disk instability.

Abstract

We analyze the structure and chemo-dynamical properties of the Galactic bulge using ab-type RR Lyrae stars (RRabs) from OGLE-IV and giant stars from APOGEE and Gaia. Orbital integration of 1,879 RRab variables reveals three populations: central bulge, inner bulge, and halo/disk contaminants. Inner bulge RRabs display bar-like kinematics, whereas central bulge stars show slower rotation and lower dispersion. APOGEE data for 28,188 stars confirm these kinematic trends and reveal a bimodal chemical distribution, indicating distinct formation pathways. Our results support a pseudo-bulge origin of the inner bulge through disk instability, with the overall morphology better described as boxy rather than X-shaped. Through the integration of multi-messenger, multi-band data, our collaboration aims to provide deeper insights into the physical properties and evolutionary history of the Galactic bulge.