Kinematically Identified Recoiling Supermassive Black Hole Candidates in SDSS QSOs with z $<$ 0.25

TL;DR

This study identifies 26 recoiling supermassive black hole candidates in SDSS quasars with velocities indicating they are moving away from their host galaxy centers, revealing insights into black hole dynamics and galaxy mergers.

Contribution

First spectral decomposition search for recoiling SMBH candidates in SDSS QSOs with detailed velocity and host galaxy analysis.

Findings

26 rSMBH candidates identified with recoil velocities from -76 to -307 km/s.

rSMBH candidates have smaller black hole masses and higher accretion rates than stationary SMBHs.

Estimated spatial offsets range from 0.21 to 1.97 arcseconds, needing high-resolution confirmation.

Abstract

We have performed a spectral decomposition to search for recoiling supermassive black holes (rSMBH) in the SDSS 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 $-76\ \kms$ to $-307\ \kms$ with a mean of $-149\pm58\ \kms$. Most of the rSMBH candidates are hosted by gas-rich LIRGs/ULIRGs, but only 23\% of them shows signs of tidal features suggesting majority of them are advanced mergers. We find that the black hole masses $M_{BH}$ of the rSMBH candidates are on average $\sim$5 times smaller than that of their stationary counterparts and cause a scatter in $M_{BH}-\sigma_*$ relation. The Eddington ratios of all of the rSMBH candidates are larger than 0.1, with mean of 0.52$\pm$0.27, suggesting 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 $-265\ \kms$. Electron density in the narrow line region of the H II rSMBH candidates is about 1/10 of that in AGN rSMBH candidates probably because AGN in the former was more spatially offset than that in the latter. The estimated spatial offsets between the rSMBH candidate and center of host galaxy range from 0.21\as \ to 1.97\as \ and need to be confirmed spatially with high-resolution adaptive optics imaging observations.