How Long do Quasars Shine?

Joe Hennawi
Tuesday, May 22, 2018
4:00 pm
NS2 1201
Luminous quasars are believed to be the progenitors of the supermassive black holes observed ubiquitously at the centers of all massive galaxies. But half a century after their discovery, and decades after tight scaling relations between supermassive black holes and their host galaxies were uncovered, we are still in the dark about how these black holes actually formed. Our ignorance largely results from the long characteristic timescale for supermassive black hole growth, known as the Salpeter time, of 45 million years -- far longer than humans have been conducting astronomical observations. A holy grail would thus be a direct measurement of the lifetimes of luminous quasars, shedding light on the structure of black hole accretion disks, how gas funnels to the centers of galaxies triggering quasar activity, and feedback that might influence galaxy formation.  Analogous to the way O-stars transform their nearby ISM, the enhanced UV radiation field in the vicinity of luminous quasars dramatically alters the physical state of the surrounding intergalactic medium. I will show how observations of diffuse gas in the environs of luminous quasars can be used to chronicle the history of quasar emission on timescales from kiloyears to gigayears. I will also discuss how these same observations can be used to constrain the reionization history of the Universe.
Michael Cooper