Gemini Imaging of the Host Galaxies of Changing-look Quasars

Abstract

Changing-look (CL) quasars are a newly discovered class of luminous active galactic nuclei that undergo rapid (≲10 yr) transitions between Type 1 and Type 1.9/2, with an associated change in their continuum emission. We characterize the host galaxies of four faded CL quasars using broadband optical imaging. We use gri images obtained with the Gemini Multi-Object Spectrograph on Gemini North to characterize the surface brightness profiles of the quasar hosts and search for [O iii ] λ 4959, λ 5007 emission from spatially extended regions, or voorwerpjes, with the goal of using them to examine past luminosity history. Although we do not detect, voorwerpjes surrounding the four quasar host galaxies, we take advantage of the dim nuclear emission to characterize the colors and morphologies of the host galaxies. Three of the four galaxies show morphological evidence of merger activity or tidal features in their residuals. The three galaxies that are not highly distorted are fit with a single Sérsic profile to characterize their overall surface brightness profiles. The single-Sérsic fits give intermediate Sérsic indices between the n  = 1 of disk galaxies and the n  = 4 of ellipticals. On a color–magnitude diagram, our CL quasar host galaxies reside in the blue cloud, with other active galactic nucleus (AGN) host galaxies and star-forming galaxies. On a color-Sérsic index diagram the CL quasar hosts reside with other AGN hosts in the “green valley.” Our analysis suggests that the hosts of CL quasars are predominantly disrupted or merging galaxies that resemble AGN hosts, rather than inactive galaxies.