Modeling Star Formation Histories of Changing-Look AGN Host Galaxies with Prospector

TL;DR

This study models the star formation histories of changing-look AGN host galaxies using Prospector, revealing no direct link between galaxy-wide star formation and AGN state transitions, suggesting nuclear or accretion disk effects are responsible.

Contribution

First to apply non-parametric star formation history modeling to CL-AGN hosts, showing their star formation properties are similar to other AGN hosts and not linked to state changes.

Findings

A significant fraction of CL-AGN hosts are star-forming or in the Green Valley.

No significant difference in star formation between turn-on and turn-off CL-AGN.

No evidence of rapid quenching in Green Valley CL-AGN.

Abstract

Changing-look active galactic nuclei, or CL-AGN, are AGN which appear to transition between Seyfert Type 1 and 2 over periods of months to years. Several mechanisms to trigger these transitions have been proposed, but we have yet to conclusively determine their cause. Recent studies suggest CL-AGN are hosted primarily in galaxies which are shutting down star formation (Dodd et al. 2021; Liu et al. 2021, Wang et al. 2023), which may indicate a link between galaxy quenching and changing look events. We use Prospector stellar population synthesis software (Leja et al. 2017; Johnson & Leja 2017; Johnson et al. 2021) to model non-parametric star formation histories for 39 CL-AGN host galaxies. We find that $43^{+13}_{-12}\%$ of our gold sample CL-AGN at z < 0.15 are star forming, while $29^{+13}_{-10}\%$ fall in the Green Valley of the stellar mass-sSFR diagram. At z > 0.15, $57^{+13}_{-18}\%$ of CL-AGN in the gold sample are star-forming and $29^{+19}_{-14}\%$ are in the Green Valley. CL-AGN hosts have similar star formation properties to the host galaxies of Seyfert 1 and 2 AGN at z < 0.15 and to Seyfert 2 AGN at z > 0.15. We find no statistically significant differences in the star formation properties of turn-on and turn-off CL-AGN. We also find no evidence for rapid quenching in the Green Valley CL-AGN. We conclude that CL-AGN state transitions are not associated with the formation history of CL-AGN host galaxies on large spatial scales, implying CL-AGN state transitions may instead result from nuclear-scale or accretion disk effects.