The impact of turbulence on star formation and supermassive black hole growth at high redshift

Physical processes that play a key role in driving galaxy formation and evolution, such as star formation and stellar feedback, and super massive black hole formation, accretion and feedback, take place on extremely small, sub-galactic scales. For this reason, it is a tremendous challenge for numerical hydrodynamics simulations to capture both the environment of galaxies and meaningfully resolve their internal structure to identify the sites where stars form. In particular, the role played by compressible turbulence in shaping galaxy properties has received relatively little attention, even though it has long been known (Larson, 1981) that the cradles of star formation, i.e. molecular clouds, are supersonically turbulent. The aim of the project is therefore to try to bridge this gap and identify the relevant physical processes which drive turbulence in galaxies whilst also quantifying how this turbulence shapes the interstellar medium of galaxies and influences star/black hole formation.

More specifically, this involves running/analysing high-resolution zoom (min 10pc) simulations of individual galaxies in their explicit cosmological context, to address the complex issue of the role played by the environment (large scale gas flows, fly-by encounters, mergers) in driving/triggering turbulence, and explicitly use the partially resolved turbulent cascade of the flow, measured on-the-fly in the simulations, to determine both the loci of star (black hole) formation and the efficiency of the star formation process. These simulations will then be compared to their "twins", i.e. simulations that are identical in every other aspect, except that star formation is determined by the current "standard" sub-grid modelling, i.e. a simple density threshold and a fixed, universal efficiency, empirically calibrated on the observed Kennicutt-Schmidt law (Kennicutt, 1998). Ultimately, the success of the turbulent star formation model will be judged by its capacity to recover the Kennicutt-Schmidt law (which, contrary to the standard model, is not built-in) while at the same time producing galaxies with dark matter to stellar mass ratios in agreement with observed values (Moster et al 2012, Behroozi et al 2013).