Mid-infrared Variability-based Active Galactic Nucleus Selection Using the Multiepoch Photometric Data from WISE

Abstract We assess the systematics and efficiency of an active galactic nucleus (AGN) selection method based on mid-infrared (MIR) variability. To this end, we utilize various types of active and inactive galaxies from the Sloan Digital Sky Survey, matching them with multiepoch photometric data from the NEOWISE mission. Using W1 and W2 band light curves with a ∼10 yr baseline, we find that combining the likelihood of deviation from nonvariability with the correlation coefficient between the W1 and W2 bands reliably identifies AGNs. Specifically, this MIR-based method recovers ∼28.2% of optically selected AGNs. Applying the same technique to inactive galaxies, we identify AGN candidates at fractions ranging from 0.4% to 11.8%, indicating that MIR variability allows us to detect AGN candidates even in optically inactive hosts. While some variable sources exhibit transient-like light curves, possibly originating from tidal disruption events or supernovae, their contribution to the total variable population is less than a few percent, indicating a minimal impact on our results. Across all subsamples, the AGN fraction marginally increases with star formation activity, implying coordinated evolution between central black hole growth and star formation. Finally, the AGN fraction inferred from our method drops dramatically in classical LINERs, consistent with their low accretion rates and absence of a dusty torus.