Gemini Imaging of the Host Galaxies of Changing-look Quasars

Abstract

Changing-look quasars are a newly-discovered class of luminous active galactic nuclei that undergo rapid ( 10 year) 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 changing-look quasars using broadband optical imaging. We use gri images obtained with the Gemini Multi Object Spectrograph (GMOS) on Gemini North to characterize the surface brightness profiles of the quasar hosts and search for [O III] λ4959, λ5007 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 which 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 changing-look quasar host galaxies reside in the blue cloud, with other AGN host galaxies and star-forming galaxies. On a color-Sérsic index diagram the changing-look quasar hosts reside with other AGN hosts in the "green valley". Our analysis suggests that the hosts of changing-look quasars are predominantly disrupted or merging galaxies that resemble AGN hosts, rather than inactive galaxies.

Changing-look active galactic nuclei: close binaries of supermassive black holes in action

“…First, details of their host morphology should be searched for signatures of disrupted or ripples as may be caused by merged remnants. This is inspired by results reported by Charlton et al (2019), who clearly found such features in Gemini images of four CL-quasars. Second, CL-AGNs could be characterized by profile asymmetries in their broad emission lines.…”

Host galaxy properties of changing-look AGNs revealed in the MaNGA survey

“…The red solid line is the boundary of the starforming main sequence. Charlton et al (2019) used the way of Sérsic indices versus colour diagram to separate galaxies as blue discs, green valley, and red spheroids, and found that all of their faded CL-AGN host galaxies are located in the green valley region. The possible reason is that we defined the star-forming main sequence in different ways.…”

“…The possible reason is that we defined the star-forming main sequence in different ways. We also used SFR versus stellar mass to check the faded CL-AGN host galaxies of Charlton et al (2019). Although there is only one target of Charlton et al (2019) that has been matched with the MPA-JHU catalogue, this galaxy is located in the star-forming main-sequence region.…”

“…The 'turning-off' CL-AGNs provide excellent cases to investigate the host galaxy properties, as the contamination from nuclear radiation is greatly reduced (e.g. LaMassa et al 2015;Yang et al 2018;Charlton et al 2019;Ruan et al 2019). Raimundo et al (2019) used optical and near-infrared integral field unit (IFU) spectroscopy to study the host galaxy properties of Mrk 590, a CL-AGN that has been subject of a 40-yr multiwavelength monitoring campaign.…”

Active galactic nuclei catalog from the AKARI NEP-Wide field

“…Another big question on AGN physics is based on recently discovered changing look (CL) AGNs (e.g., LaMassa et al 2015;Sheng et al 2017;Stern et al 2018;Charlton et al 2019). This type of objects can exhibit transitions between AGN types by the emergence or disappearance of broad emission lines.…”