12:00–1:00 pm Zoom
Anna-Christina Eilers, MIT, "The Formation and Growth of Supermassive Black Holes"
Observations of high-redshift quasars show that they host supermassive black holes (SMBHs) already less than ~1 Gyr after the Big Bang. It has been argued that in order to grow these SMBHs in such short amounts of cosmic time, they need to accrete matter over timescales comparable to the age of the universe, and thus the lifetime of quasars - the integrated time that galaxies shine as active quasars and during which the black hole growth occurs - is expected to be of order ~10^9 yr at z~6, even if they accrete continuously at the theoretical Eddington limit. I will present a new method to obtain model-independent constraints on the lifetime of high-redshift quasars, based on measurements of the sizes of ionized regions around quasars, known as proximity zones. The sizes of these proximity zones are sensitive to the lifetime of the quasars and therefore act as a "quasar clock", because the intergalactic gas has a finite response time to the quasars’ radiation. Applying this method to a population of high-redshift quasars, we find an average effective lifetime of only about a million years, which is orders of magnitude shorter than expected, posing significant challenges on current black hole formation models. I will show how these new timescale measurements of quasar activity set constraints on the underlying accretion process and discuss several modifications to the current SMBH formation paradigm that might explain our results, e.g. super-critical mass accretion rates, massive initial black hole seeds in excess of stellar remnants, or highly obscured quasar growth phases. In the end I will show how we aim to disentangle the various scenarios by means of on-going and future IFU observations with VLT/MUSE and the James Webb Space Telescope, in order to shed new light onto the formation and growth of the first SMBHs in the universe.