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

Abstract Changing-look active galactic nuclei (CL-AGNs), are AGNs that 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-AGNs are hosted primarily in galaxies that are shutting down star formation (S. A. Dodd et al. 2021; W.-J. Liu et al. 2021; J. Wang et al. 2023), which may indicate a link between galaxy quenching and changing-look events. We use Prospector stellar population synthesis software (B. Johnson J. Leja et al. 2017; B. D. Johnson et al. 2021) to model nonparametric star formation histories for 39 CL-AGN host galaxies. We find that 4 3 − 12 + 13 % of our gold sample CL-AGNs at z 2 9 − 10 + 13 % fall in the Green Valley of the stellar mass–specific star formation rate diagram. At z > 0.15, 5 7 − 18 + 13 % of CL-AGNs in the gold sample are star-forming and 2 9 − 14 + 19 % are in the Green Valley. CL-AGN hosts have similar star formation properties to the host galaxies of Seyfert 1 and 2 AGNs at z 0.15. We find no statistically significant differences in the star formation properties of turn-on and turn-off CL-AGNs. We also find no evidence for rapid quenching in the Green Valley CL-AGNs. 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.