Discovery of a Quasar with Double-Peaked Broad Balmer Emission Lines

TL;DR

This paper reports the discovery of a quasar with double-peaked broad Balmer emission lines, providing evidence for a potential supermassive black hole binary system in an active galactic nucleus.

Contribution

It introduces a new double-peaked broad emission line source and discusses its implications for SMBH binary identification and tidal disruption events.

Findings

Discovery of SDSS J0216 with double-peaked broad emission lines

Identification of five known double-peaked emission line sources

Discussion on SMBH binaries and tidal disruption events

Abstract

Most massive galaxies contain a supermassive black hole (SMBH) at their center. When galaxies merge, their SMBHs sink to the center of the new galaxy where they are thought to eventually merge. During this process an SMBH binary is formed. The presence of two sets of broad emission lines in the optical spectrum of an active galactic nucleus (AGN) has been interpreted as evidence for two broad line regions (BLR), one surrounding each SMBH in a binary. We modeled the broad Balmer emission lines in SDSS spectra of 373 extreme variability AGNs using one broad and several narrow Gaussian components. We report on the discovery of SDSS J021647.53$-$011341.5 (hereafter J0216) as a double-peaked broad emission line source. Among the 373 AGNs there were five sources that are known double-peaked emission line sources. Three of these have been reported as candidate SMBH binaries in previous studies. We present all six objects and their double-peaked broad Balmer emission lines, and discuss the implications for a tidal disruption event (TDE) interpretation of the extreme variability assuming the double-peaked sources are SMBH binaries.