Seminario DAS: The Long-Term Time Variability and Triggering of Supermassive Black Hole Growth

Speaker: Dr.  Ezequiel Treister
Affiliation: Associate  Professor, Institute of Astrophysics, Faculty of Physics - PUC

Abstract: It is now well established that the most intense supermassive black hole (SMBH) growth episodes (luminous Active Galactic Nuclei, or AGN) are variable at all time scales, ranging from minutes/hours to billions of years. This has significant implications for our understanding of the cosmic history of SMBH growth and its connection to galaxy evolution. In this talk, I will start by presenting our study of an interesting galaxy population showing large-scale signatures of a powerful AGN, while the small-scale signatures point to a much weaker nuclear source in the recent past. These objects suggest the presence of an AGN that has faded 1-2 dex over a timescale of 10^(4-5) yrs, far beyond what can be observed in a human lifetime. I will present our detailed studies of these sources using spatially-resolved IFU spectroscopy with VLT/MUSE and discuss how these sources fit in our general understanding of the time dependence of the SMBH growth over 13 orders of magnitude in time.

At longer time scales, I will discuss the observational and theoretical evidence for a link between major galaxy mergers and the most rapid SMBH growth episodes.  In this scenario, the more traditional AGN unification paradigm in which orientation is the main parameter only holds at lower luminosities. At the same time, for the more violent accretion events, originated by major mergers, we find evidence for an evolutionary sequence in which the AGN is first heavily obscured (Compton-thick) to reveal an unobscured quasar later. I will present results from our multi-wavelength studies of a sample of nearby confirmed dual AGN (pairs of growing SMBHs with nuclear separation <10 kpc). Specifically, I will focus on our ongoing program combining ALMA and MUSE observations, searching for systems of two or more SMBHs growing simultaneously at very small, <1 kpc, nuclear separations, which have remained hidden until now, and that will be the parent population for the gravitational wave events detectable with LISA in the next decade.