New insights into how the galaxy-black hole connection
works
by Kevin Schawinski (ETH Zurich)
Massive galaxies are broadly split into those
forming stars on the main sequence, and those which are quiescent. The physical
processes by which galaxies quench their star formation remain poorly
understood. I analyze the properties of galaxies and track their evolutionary
trajectories as they migrate from the blue cloud of
star forming galaxies to the red sequence of quiescent
galaxies via the `green valley'. I show that there
must be two fundamentally star formation quenching pathways associated with
early- and late-type galaxies which are intricately linked to how hydrogen
gas reservoirs are destroyed or shut off. In the quenching of late-type
galaxies, environment (or halo mass) is a key parameter, while for early-types,
an internal mechanism such as black hole feedback is more likely. I will also
present a new approach to understanding how the black hole feedback mechanism
may work: rapid swings in the Eddington ratio of AGN lead to short term
"flickering" behavior on the ~1e5 year time scale. AGN may swicth back and
forth between radiatively efficient "quasar" mode and radiatively inefficient
modes where kinetic energy is injected in the host galaxy.
