Kavli Affiliate: Huawei Zhang
| First 5 Authors: Haozhu Fu, Haozhu Fu, , ,
| Summary:
Hypervelocity stars (HVSs) are stars with velocities exceeding their local
escape velocities. Searching for HVSs and studying their origins can be an
important way to study the properties of the Milky Way. In this paper, we
utilize precise distances for RR Lyrae stars (RRLs) derived from the
period-absolute magnitude-metallicity (PMZ) relation, along with proper motions
from Gaia DR3, to conduct a large-volume search for HVSs. Our sample consists
of a catalog with 8,172 RRLs with metallicity, distance and radial velocities
estimated from SDSS and LAMOST spectroscopic data, and an extended catalog of
135,873 RRLs with metallicity and distance estimated from Gaia photometry.
After careful quality cuts, 165 hypervelocity RRL candidates were found. We
performed further checks on their light curves, and selected the most reliable
87 hypervelocity RRLs. All of them exceed the Milky Way’s escape velocity in
the tangential component. Among them, 7 stars have tangential velocity over 800
km s^-1. We identified two spatially distinct distributions of hypervelocity
RRLs: one concentrated toward the Galactic Center and another localized around
the Magellanic Clouds, suggesting that their origins are likely associated with
these regions through the Hills or other mechanisms. Furthermore, we detected a
significant number of RRLs associated with dwarf galaxies that exceed the Milky
Way’s escape velocity, likely ejected from their host systems. Future Gaia
releases and spectroscopic follow-up observations will provide further insight
into their ejection origin.
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