Probing galaxy-black hole co-evolution across cosmic time: predictions from next-generation observations and simulations

The co-evolution of galaxies and their central super-massive-black-holes (SMBHs) is best understood at low redshifts. Our ability to accurately measure the mass of SMBHs in the local universe through dynamical methods allows us to compare these to their host galaxies properties, leading to our current understanding of how the two co-evolve. However, significant problems remain with our understanding of the driving mechanisms of co-evolution at such low redshifts. In addition, as we move to higher redshifts SMBH mass measurements via dynamical methods become less accurate, leading to a lack of understanding of co-evolution at intermediate to high redshifts. We do not yet understand whether this co-evolution is a function of redshift, what drives this co-evolution and the feedback processes that may cause it.

In the coming months we will use currently available spectroscopic observations of high redshift (z>7) galaxies (Keck Mosfire and VLT X-Shooter) in an attempt to evaluate their properties and potential active galactic nucleus (AGN) activity occurring within them. The results of this will then be compared to current well-established simulations (Illustris, IllustrisTNG and FABLE) to try to better understand the mechanisms driving these properties.

Following this we will attempt to assess the primary driving mechanisms for galaxy quenching. It is now well understood that the probability that a galaxy has been quenched of star-formation (SF) depends primarily on black hole mass. The interesting assessment however is the mechanism that drives this: gas removal via AGN winds, SF efficiency suppression by inter-stellar medium heating or galaxy starvation by the heating of the galactic halo through AGN jets or winds. We will take deep Atacama Large Millimeter Array (ALMA) observations of a selection of quasars, in redshift regimes z>6, z ~ 2.5 and z ~ 1.5, using various emission lines and their ~ 100 GHz continuum to trace atomic, molecular and hot gas in order to probe the presence of either quasar driven outflows, the hot halo or extended cold gas in the circumgalactic medium and how these quenching mechanisms may change in prominence across cosmic time.

We will then compare these results with next generation simulations to piece together the evolution of SMBH feedback across redshifts. These simulations model SMBH feedback, radiation driven outflows, jets and winds allowing us to track changes in SMBH feedback across cosmic time. These simulations will allow us to not only take snapshots of individual galaxies but to observe their evolution from star-forming to quiescent and the changes in their properties that potentially drive such an evolution.