Initial Results from a Systematic Search for Changing-look Active Galactic Nuclei Selected via Mid-infrared Variability

Changing-look active galactic nuclei (CL AGNs) can yield considerable insight into accretion physics as well as the co-evolution of black holes and their host galaxies. A large sample of these CL AGNs is essential to achieve the latter goal. We propose an effective method to select CL candidates from spectroscopic quasar catalogs using the mid-infrared (MIR) variability information derived from ALLWISE/NEOWISE data releases. Our primary selection criteria include both a large amplitude flux variation and a transition of MIR color from an AGN to a normal galaxy. A pilot spectroscopic follow-up of seven candidates among about 300 candidates selected from Sloan Digital Sky Survey low-redshift (z < 0.5) AGN sample results in three new turn-off CL AGNs and three ambiguous objects for suffering low spectral quality. We expect to obtain hundreds of CL AGNs once full spectroscopic follow-up of the sample is carried out.