Metal-poor hypervelocity star candidates from the Sloan Digital Sky Survey

TL;DR

This paper identifies 13 metal-poor hypervelocity star candidates from SDSS data, analyzing their origins and suggesting possible ejection mechanisms including Galactic center interactions and dwarf galaxy disruptions.

Contribution

It presents the first set of metal-poor hypervelocity star candidates from SDSS and analyzes their kinematics to infer possible ejection sources.

Findings

Seven stars likely ejected from the Galactic center or disk.

Four stars probably did not originate from the Galactic center or disk.

Some candidates may result from dwarf galaxy disruptions or interactions with black holes in M31 or M32.

Abstract

Hypervelocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this letter, we report 13 metal-poor F-type hypervelocity star candidates selected from 370,000 stars of the data release 7 of the Sloan Digital Sky Survey. With a detailed analysis of the kinematics of these stars, we find that seven of them were likely ejected from the Galactic center (GC) or the Galactic disk, four neither originated from the GC nor the Galactic disk, and the other two were possibly ejected from either the Galactic disk or other regions. Those candidates which unlikely originated from the GC or the Galactic disk, may be explained by other mechanisms, like the tidal disruption of the Milky Way's dwarf galaxies in the Galactic potential, or the gravitational interactions with a massive black hole at the center of M31 or M32.