Galaxy Evolution in 3D: Mass, Dissipation, and Truncation

To zeroth order, early type galaxies form a one-dimensional family in
which their observed properties (color, metallicity, environment,
central black hole masses) all scale with their mass. This makes it
difficult to disentangle the critical properties that determine their
evolutionary history because everything correlates with everything
else. Examining where this 1D sequence breaks down can provide
essential clues to galaxy evolution.  I present observational evidence
that galaxy star formation histories form a multi-dimensional family,
such that galaxies of the same mass today start out with similar star
formation histories but shut down star formation ("quench") at
different times.  A parallel study using semi-analytic models of
galaxy evolution suggests that these differences are due to their
underlying halo mass assembly histories. Indeed, the observed family
of galaxy star formation histories seems to be a generic result of a
mass-threshold for quenching, given a standard LCDM paradigm that
includes mass-dependent evolution and stochastic hierarchical
assembly.