Old-Population Hypervelocity Stars from the Galactic Center: Limits from the SDSS

Abstract

We present limits on the ejection of old-population HVS from a sample of over 290,000 stars selected from the SDSS. We derive the speed at the solar circle from the measured positions and radial velocities by assuming a radial orbit and adopting a simple isothermal model of the Galactic halo, which enables us to identify candidate bound and unbound ejectees. We find 4 candidate bound F-stars from this sample, all with negative Galactocentric radial velocity (i.e., returning toward the GC). We additionally find 2 candidate unbound stars (one F and one G), however, existing proper motion measurements make these unlikely to be emerging from the GC. These data place an upper limit on the rate of ejection of old-population stars from the GC of ~45/Myr. Comparing to the rate for more massive B-star ejectees of ~0.5/Myr, our limit on the rate of ejection of old-population HVS shows that the mass function at the GC is not bottom-heavy and is consistent with being normal. Future targeted surveys of old-population HVS could determine if it is indeed top-heavy.

Submitted to ApJ; 14 pages including 2 figures

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• The Velocity Distribution of Hypervelocity Stars
• Predicting the hypervelocity star population in Gaia
• 591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
• Hypervelocity Star Candidates in the SEGUE G & K Dwarf Sample
• Nearby high-speed stars in Gaia DR2
• Gaia DR3 in 6D: The search for fast hypervelocity stars and constraints on the Galactic Centre environment
• Metal-poor hypervelocity star candidates from the Sloan Digital Sky Survey
• The Nearest High-Velocity Stars Revealed by LAMOST Data Release 1
• Supernovae in the Central Parsec: A Mechanism for Producing Spatially Anisotropic Hypervelocity Stars
• New nearby hypervelocity stars and their spatial distribution from Gaia DR2
• SEGUE-2 Limits on Metal-Rich Old-Population Hypervelocity Stars In the Galactic Halo
• The spatial and velocity distributions of hypervelocity stars
• Wandering Stars: an Origin of Escaped Populations
• Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center
• Milky Way archaeology using RR Lyrae and type II Cepheids II. High velocity RR Lyrae stars, and mass of the Milky Way
• Constraints on the Galactic Centre environment from Gaia hypervelocity stars II: The evolved population
• Identifying High Metallicity M Giants at Intragroup Distances with SDSS
• Candidate Hypervelocity Red Clump Stars in the Galactic Bulge Found Using the VVV and Gaia Surveys