Impediments to the cosmic growth of galaxies: The outflow budget from Star Formation and Active Galactic Nuclei

Abstract

The gas reservoir of galaxies can be altered by outflows that are driven by star formation and luminous active galactic nuclei. Jets heating the surroundings of host galaxies can also prevent the gas from cooling and prevent inflows. Spectacular examples for these three mass-displacement channels have been observed, but their importance in transforming the galaxy population depends on the occurrence rates of the outflow triggers. We investigate the absolute and relative importance of these three channels. In an observation-driven approach, we combined distribution functions and scaling relations to empirically compare average outflow rates across the total stellar mass spectrum of the galaxy and across cosmic time. This hinges on local outflow studies, which should be extended to systematic, large, and diverse samples, and we did not consider a halo-heating effect by radiation-driven outflows so far. Independent of simulations, our results show the dominance of star formation-driven outflows in low-mass galaxies. Massive galaxies today are predominately prevented from growing further by jet heating, while at z = 1 − 3, all three processes are approximately similarly important. Over the full mass spectrum and cosmic history, outflows driven by the radiation from active galactic nuclei are never the dominant process.