Speaker
Description
Changing-look active galactic nuclei (CLAGN) are objects that show striking increases or decreases in optical AGN broad line emission over time; e.g., Ricci & Trakhtenbrot, 2023. These events are thought to be mostly the result of dramatic changes in accretion state, and as such provide a laboratory for studying the variation in accretion processes that is known to exist in AGN, but not usually observable on useful timescales or in such grand fashion. The influence of this can be observed across the EM spectrum, from X-rays (e.g., Liu et al., 2022) to mid-infrared (MIR; e.g., Sheng et al., 2017). CLAGN are being discovered in rapidly increasing numbers, due in part to the rise of large spectroscopic surveys like the Dark Energy Spectroscopic Instrument (DESI) - combining this with older SDSS spectroscopy has produced the largest sample of CLAGN to date: ~550 largely previous unknown CLAGN (Guo et al., 2024). With this extensive sample we can show that on a population scale CLAGN are inherently different to comparable non-changing look AGN. In this talk I will demonstrate how we can use longer-term MIR light curves in concert with the two discrete optical spectra to investigate how CLAGN evolve over time. I will discuss how these results can help understand the changes in accretion processes, show that apparent CLAGN can include other accretion events (such as TDEs; e.g., Clark et al., 2025), and that true CLAGN alone are a diverse class of objects.
