Galaxy And Mass Assembly: Deconstructing Bimodality - I. Red ones and blue ones

Understand

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.