Recoiling Black Holes in Quasars

TL;DR

This paper investigates the observational signatures of recoiling supermassive black holes in quasars by analyzing emission line shifts, finding no strong evidence for such recoils and setting upper limits on their occurrence.

Contribution

It provides the first systematic search for recoiling black holes in SDSS quasars and constrains their frequency based on emission line velocity shifts.

Findings

No convincing evidence for recoiling black holes with significant accretion disks.

Upper limit of 4% for recoiling black holes with kicks >500 km/s.

Upper limit of 0.35% for kicks >1000 km/s.

Abstract

Recent simulations of merging black holes with spin give recoil velocities from gravitational radiation up to several thousand km/s. A recoiling supermassive black hole can retain the inner part of its accretion disk, providing fuel for a continuing QSO phase lasting millions of years as the hole moves away from the galactic nucleus. One possible observational manifestation of a recoiling accretion disk is in QSO emission lines shifted in velocity from the host galaxy. We have examined QSOs from the Sloan Digital Sky Survey with broad emission lines substantially shifted relative to the narrow lines. We find no convincing evidence for recoiling black holes carrying accretion disks. We place an upper limit on the incidence of recoiling black holes in QSOs of 4% for kicks greater than 500 km/s and 0.35% for kicks greater than 1000 km/s line-of-sight velocity.