The Landscape of Galaxies Harboring Changing-look Active Galactic Nuclei in the Local Universe

Abstract

Abstract We study the properties of the host galaxies of changing-look active galactic nuclei (CL AGNs) with the aim of understanding the conditions responsible for triggering CL activity. We find that CL AGN hosts primarily reside in the so-called green valley that is located between spiral-like star-forming galaxies and dead ellipticals, implying that CL AGNs are activated during distinct periods of quenching and galaxy transformation processes. CL AGN hosts have low galaxy asymmetry indicators, suggesting that secular evolutionary processes (the influence of bars and spirals, and possibly minor mergers) might be the primary mechanism for transporting gas to the vicinity of the supermassive black hole (SMBH) rather than major mergers. Similar to tidal disruption events and highly variable AGNs, we find that CL AGN hosts are associated with SMBHs residing in high-density pseudo-bulges and appear to overlap most significantly with the population of low-ionization nuclear emission-line region galaxies. As such, CL AGNs are likely fueled by strong episodic bursts of accretion activity, which appear to take place preferentially as the amount of material accessible for star formation and accretion dwindles. We also identify that CL AGN hosts are characterized by either large Sérsic indices or high bulge fractions, which suggests a simple metric for identifying candidates for spectroscopic follow-up observations in forthcoming synoptic surveys.