We use the semi-analytic model developed by 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 .