Quenching star formation: insights from the local main sequence
  The so-called star-forming main sequence of galaxies is the apparent tight
relationship between the star formation rate and stellar mass of a galaxy.
Previous studies exclude galaxies which are not strictly 'star forming' from
the main sequence, because they do not lie on the same tight relation. Using
local galaxies in the Sloan Digital Sky Survey we have classified galaxies
according to their emission line ratios, and studied their location on the star
formation rate - stellar mass plane. We find that galaxies form a sequence from
the `blue cloud' galaxies which are actively forming stars, through a
combination of composite, Seyfert, and LINER (Low-ionization nuclear
emission-line region) galaxies, ending as 'red-and-dead' galaxies. The sequence
supports an evolutionary pathway for galaxies in which star formation quenching
by active galactic nuclei (AGN) plays a key role.
