Stephanie LaMassa (Astronomy) - Space Telescope Science Institute
Title: Insights into the Feeding Habits of Supermassive Black Holes from “Changing-Look” AGN
Abstract: Supermassive black holes reside in the centers of galaxies where they grow via the process of accretion, appearing as active galactic nuclei (“AGN”). This activity imprints features in the spectra of AGN that have historically been used to categorize AGN according to the unification model. This paradigm posits that a direct view of the accreting supermassive black hole reveals spectra with broad emission lines, and that AGN with spectra lacking such broad lines are viewed through an obscuring torus of dust and gas. However, some AGN show appearance or disappearance of broad lines in their spectra over timescales of years, accompanied by variability in the AGN continuum. These so-called “changing-look” AGN often can not be physically described by variable obscuration as would be assumed by the unification model. Instead, observations indicate that fluctuations in the accretion flow trigger the change of spectral state. In this talk, I will review the burgeoning sub-field of changing-look AGN, review the evidence that links the observed photometric and spectroscopic variability to changes in the ionizing continuum from the AGN, highlight some theoretical explanations that interpret these observations, and comment on how upcoming surveys like Black Hole Mapper in SDSS-V will advance the field.