New candidate hypervelocity red clump stars in the inner Galactic bulge

TL;DR

This study identifies 69 candidate hypervelocity stars in the inner Galactic bulge using combined Gaia and infrared data, providing new insights into stellar ejection mechanisms near the Galaxy's center.

Contribution

The paper introduces a novel method combining Gaia DR3 and infrared data to detect candidate hypervelocity stars in the inner Galactic bulge, expanding the search for HVSs.

Findings

Detected 69 candidate HVSs with velocities exceeding local escape velocity.

Identified 4 prime candidate HVSs with motions consistent with Galactic center ejection.

Found 65 additional candidates with proper motions pointing away from the Galactic center.

Abstract

We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and NIR proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which 4 are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity.