Astronomy & Astrophysics Seminar: Extremely Variable and Changing-Look AGNs in SDSS-V

Zoom: https://tau-ac-il.zoom.us/j/81239615480?pwd=qynx9sGBcqWlo2fNUEbZrq1VibGgwM.1

Abstract:

Active galactic nuclei (AGNs) are intrinsically variable across all wavelengths, typically exhibiting stochastic variability of up to a few 10% over days to years. Novel time-domain surveys, however, are revealing much more extreme events on months-to-years timescales. Among the most striking are changing-look AGNs (CLAGNs), in which broad emission lines and quasar-like continuum emission emerge or disappear in their UV/optical spectra. These dramatic changes are thought to be driven by significant changes in the accretion flow or circumnuclear gas, offering novel insights into these physical components. In this talk, I will present a sample of over 100 CLAGNs identified with SDSS-V multi-epoch spectroscopy. I will first highlight several extreme objects from this sample, showing that changing-look events can occur repeatedly and on timescales of only a few months. I will then place these events in the context of normal AGN variability, showing how common they are and how they connect to the broader distribution of AGN variability. I will show that the dominant physical driver is more likely to be changes in the accretion flow than variable obscuration, and that extreme variability is strongly connected to low Eddington ratios, while showing no strong dependence on black hole mass, disfavouring tidal disruption events as the dominant driver. Finally, I will present higher-resolution VLT and Gemini spectroscopy for a subset of dimming CLAGNs, showing that their host galaxies resemble those of typical AGNs and that CLAGNs therefore offer a unique opportunity to study the host galaxies of luminous blue quasars.

Seminar Organizer: Dr. Jonathan Stern