Uploaded July 2021 | Updated September 2026, 2 days ago
NAM 2021 Plenary
Prof Sandra Faber - 2020 RAS Gold Medal Awardee
A Schematic Model for Black Hole Growth and Galaxy Quenching
Why star formation ends in galaxies is one of the major questions in astronomy. I will describe a semi-empirical model for the linkage between black hole mass, galaxy properties, and dark halo mass. While star-forming, galaxies build their stellar mass at a rate that is set by their dark halo mass but grow BHs at a rate that is set by their central stellar density. When total effective emitted BH energy exceeds 4x halo-gas binding energy, galaxies enter the "green valley" and begin to quench. The crossing point is clearly visible as the slanted boundary between star-forming galaxies and quenched galaxies in mass vs. radius and central stellar density. BH mass data then suggest that BH growth accelerates in the green valley and that greater than 90% of BH growth takes place there. When fully quenched, galaxies stop evolving and come to a halt along the classic MBH ~ σ4 relation, which is offset by about a x10 higher in zero point than the BH scaling law for star-forming galaxies. This simple picture matches many important scaling laws for BHs and galaxies since z ~ 3. It portrays galaxy quenching as a contest between black holes and halos – halos build galaxies, which then build black holes, which then react back and quench their halos.
NAM 2021 Plenary
Prof Sandra Faber - 2020 RAS Gold Medal Awardee
A Schematic Model for Black Hole Growth and Galaxy Quenching
Why star formation ends in galaxies is one of the major questions in astronomy. I will describe a semi-empirical model for the linkage between black hole mass, galaxy properties, and dark halo mass. While star-forming, galaxies build their stellar mass at a rate that is set by their dark halo mass but grow BHs at a rate that is set by their central stellar density. When total effective emitted BH energy exceeds 4x halo-gas binding energy, galaxies enter the "green valley" and begin to quench. The crossing point is clearly visible as the slanted boundary between star-forming galaxies and quenched galaxies in mass vs. radius and central stellar density. BH mass data then suggest that BH growth accelerates in the green valley and that greater than 90% of BH growth takes place there. When fully quenched, galaxies stop evolving and come to a halt along the classic MBH ~ σ4 relation, which is offset by about a x10 higher in zero point than the BH scaling law for star-forming galaxies. This simple picture matches many important scaling laws for BHs and galaxies since z ~ 3. It portrays galaxy quenching as a contest between black holes and halos – halos build galaxies, which then build black holes, which then react back and quench their halos.
