Runaway M Dwarf Candidates from the Sloan Digital Sky Survey

We present a sample of 20 runaway M dwarf candidates (RdMs) within 1 kpc of the Sun whose Galactocentric (GC) velocities exceed 400 km s. The candidates were selected from the Sloan Digital Sky Survey (SDSS) DR7 M Dwarf Catalog of West et al. Our RdMs have SDSS+USNO-B proper motions that are consistent with those recorded in the PPMXL, LSPM, and combined Wide-field Infrared Survey Explorer+SDSS+Two-micron All-sky Survey catalogs. Sixteen RdMs are classified as dwarfs, while the remaining four RdMs are subdwarfs. We model the Galactic potential using a bulge-disk-halo profile. Our fastest RdM, with a GC velocity of 658.5 ± 236.9 km s, is a possible hypervelocity candidate, as it is unbound in 77% of our simulations. About half of our RdMs have kinematics that are consistent with ejection from the Galactic center. Seven of our RdMs have kinematics consistent with an ejection scenario from M31 or M32 to within 2σ, although our distance-limited survey makes such a realization unlikely. No more than four of our RdMs may have originated from the Leo stream. We propose that to within measurement errors, most of our bound RdMs are likely disk runaways or halo objects, and may have been accelerated through a series of multi-body interactions within the Galactic disk or possibly supernovae explosions.