The Diversity of Growth Histories of Milky Way-mass Galaxies

TL;DR

This study uses a semi-analytic model to investigate the diverse star formation histories of Milky Way-mass galaxies, highlighting the role of quenching, black hole mass, and active galactic nuclei in shaping galaxy evolution.

Contribution

It demonstrates that quenching driven by black hole activity explains the diversity in galaxy growth histories and the flattening of the stellar mass-halo mass relation.

Findings

Quiescent galaxies show more diverse growth histories than star-forming ones.

Quenching correlates strongly with black hole mass and AGN heating.

The emergence of quiescent galaxies flattens the stellar mass-halo mass relation.

Abstract

We use the semi-analytic model developed by Henriques et al. (2015) to explore the origin of star formation history diversity for galaxies that lie at the centre of their dark matter haloes and have present-day stellar masses in the range 5-8 $\times$ 10$^{10}$ M$_{\odot}$, similar to that of the Milky Way. In this model, quenching is the dominant physical mechanism for introducing scatter in the growth histories of these galaxies. We find that present-day quiescent galaxies have a larger variety of growth histories than star-formers since they underwent 'staggered quenching' - a term describing the correlation between the time of quenching and present-day halo mass. While halo mass correlates broadly with quiescence, we find that quiescence is primarily a function of black hole mass, where galaxies quench when heating from their active galactic nuclei becomes sufficient to offset the redshift-dependent cooling rate. In this model, the emergence of a prominent quiescent population is the main process that flattens the stellar mass-halo mass relation at mass scales at or above that of the Milky Way.