KINEMATICALLY IDENTIFIED RECOILING SUPERMASSIVE BLACK HOLE CANDIDATES IN SDSS QSOs WITH z 0.25

摘要

We have performed a spectral decomposition to search for recoiling supermassive black holes (rSMBHs) in Sloan Digital Sky Survey (SDSS) quasi-stellar objects (QSOs) with z 0.25. Out of 1271 QSOs, we have identified 26 rSMBH candidates that are recoiling toward us. The projected recoil velocities range from ?76 to ?307 km s?1 with a mean of ?149 ± 58 km s?1. Most of the rSMBH candidates are hosted by gas-rich luminous infrared galaxies (LIRGs)/ultra-luminous infrared galaxies (ULIRGs), but only 23% of them show signs of tidal features, which suggests that a majority of them are advanced mergers. We find that the black hole masses M BH of the rSMBH candidates are on average ~5 times smaller than those of their stationary counterparts and cause a scatter in the relation. The Eddington ratios of all of the rSMBH candidates are larger than 0.1, with a mean of 0.52 ± 0.27, suggesting that they are actively accreting mass. Velocity shifts in high-excitation coronal lines suggest that the rSMBH candidates are recoiling with an average velocity of about ?265 km s?1. The electron density in the narrow line region of the H ii rSMBH candidates is about 1/10 of that in active galactic nucleus (AGN) rSMBH candidates, probably because the AGN in the former was more spatially offset than that in the latter. The estimated spatial offsets between the rSMBH candidate and the center of the host galaxy range from 021 to 197 and need to be confirmed spatially with high-resolution adaptive optics imaging observations.