Title: MUFASA: The assembly of the red sequence,
Abstract: We examine the growth and evolution of quenched galaxies in the Mufasa
cosmological hydrodynamic simulations that include an evolving halo mass-based
quenching prescription, with galaxy colours computed accounting for
line-of-sight extinction to individual star particles. Mufasa reproduces the
observed present-day red sequence reasonably well, including its slope,
amplitude, and scatter. In Mufasa, the red sequence slope is driven entirely by
the steep stellar mass-stellar metallicity relation, which independently agrees
with observations. High-mass star-forming galaxies blend smoothly onto the red
sequence, indicating the lack of a well-defined green valley at M*>10^10.5 Mo.
The most massive galaxies quench the earliest and then grow very little in mass
via dry merging; they attain their high masses at earlier epochs when cold
inflows more effectively penetrate hot halos. To higher redshifts, the red
sequence becomes increasingly contaminated with massive dusty star-forming
galaxies; UVJ selection subtly but effectively separates these populations. We
then examine the evolution of the mass functions of central and satellite
galaxies split into passive and star-forming via UVJ. Massive quenched systems
show good agreement with observations out to z~2, despite not including a rapid
early quenching mode associated with mergers. However, low-mass quenched
galaxies are far too numerous at z<1 in Mufasa, indicating that Mufasa strongly
over-quenches satellites. A challenge for hydrodynamic simulations is to devise
a quenching model that produces enough early massive quenched galaxies and
keeps them quenched to z=0, while not being so strong as to over-quench
satellites; Mufasa's current scheme fails at the latter.