Galaxy And Mass Assembly: Deconstructing Bimodality - I. Red ones and
  blue ones
  We measure the mass functions for generically red and blue galaxies, using a
z < 0.12 sample of log M* > 8.7 field galaxies from the Galaxy And Mass
Assembly (GAMA) survey. Our motivation is that, as we show, the dominant
uncertainty in existing measurements stems from how 'red' and 'blue' galaxies
have been selected/defined. Accordingly, we model our data as two naturally
overlapping populations, each with their own mass function and colour-mass
relation, which enables us characterise the two populations without having to
specify a priori which galaxies are 'red' and 'blue'. Our results then provide
the means to derive objective operational definitions for the terms 'red' and
'blue', which are based on the phenomenology of the colour-mass diagrams.
  Informed by this descriptive modelling, we show that: 1.) after accounting
for dust, the stellar colours of 'blue' galaxies do not depend strongly on
mass; 2.) the tight, flat 'dead sequence' does not extend much below log M* ~
10.5; instead, 3.) the stellar colours of 'red' galaxies vary rather strongly
with mass, such that lower mass 'red' galaxies have bluer stellar populations;
4.) below log M* ~ 9.3, the 'red' population dissolves into obscurity, and it
becomes problematic to talk about two distinct populations; as a consequence,
5.) it is hard to meaningfully constrain the shape, including the possibility
of an upturn, of the 'red' galaxy mass function below log M* ~ 9. Points 1-4
provide meaningful targets for models of galaxy formation and evolution to aim
for.
