Discovery of new changing-look quasar 3C 332 and constraints for a double-peaked emission line scenario

Abstract

Abstract Recently, a new class of quasars, called changing-look quasars (CLQs), has been reported. CLQs exhibit significant changes in optical and mid-infrared luminosity, accompanied by the appearance or disappearance of broad emission lines. We performed spectroscopic observations at the Nishi-Harima Astronomical Observatory in 2018 May to identify objects that show long-term (∼10 yr) continuous optical luminosity variations as candidates for CLQs. We discovered significant fluctuations in the Hβ emission line of 3C 332. This source has previously been reported to have a characteristic double-peaked Hα emission line. To explain the shape of the emission lines, a ring disk model has been proposed, and the possibility of a binary black hole has also been suggested. To further investigate the characteristics of 3C 332, we performed nine spectroscopic observations at Okayama Observatory (Kyoto University) from 2020 February to June. Based on the change in the velocity offset of the emission lines and the negative correlation between the line intensity and the velocity difference between the two peaks, we conclude that the double-peaked origin of this source is consistent with the ring disk model. In addition, the timescale of the changing look (of the optical and mid-infrared luminosities) is consistent with the thermal timescale or the propagation timescale of the heating/cooling front.