Kevin Schawinski (ETH Zürich)

Kevin Schawinski Colloquium: New insights into how the galaxy-black hole connection works

Marsfield Lecture Theatre

Abstract

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.