CGCA Seminar – Daniel Palumbo

Spin Signatures in Horizon-Resolved Images of LLAGN

Dr. Daniel Palumbo, Smithsonian Astrophysical Observatory
Harvard University

With the advent of the Event Horizon Telescope (EHT), near-horizon black hole imaging with sub-mm very-long-baseline interferometry (VLBI) is now routine for the two sources for which terrestrial VLBI is sufficient to resolve the black hole shadow: Messier 87* and Sagittarius A*. Since the first images of M87*, the theoretical analysis of these images has advanced a broad class of black hole spin tracers in horizon-resolving observations, all of which have complex interplay with the astrophysical conditions near the horizon. Meanwhile, space VLBI mission concepts such as the Black Hole Explorer aim to drastically improve the angular resolution available via sub-mm VLBI, resolving out the primary accretion disk image to isolate the strongly lensed “photon ring,” which more robustly exposes black hole mass, spin, and viewing inclination to distant observers. In this talk, I will detail many of the spin signatures in both of these angular resolution regimes, and how they work together to build a “robustness ladder” for spin measurement with which the spins of many more low-luminosity AGN will soon become accessible as sub-mm VLBI sensitivity, frequency coverage, angular resolution improves. The resulting local “spin census” will help fill in missing pieces of the history of accretion and merging in the broader AGN population.