Disentangling star formation and merger growth in the evolution of
  Luminous Red Galaxies
  We introduce a novel technique for empirically understanding galaxy
evolution. We use empirically determined stellar evolution models to predict
the past evolution of the Sloan Digital Sky Survey (SDSS-II) Luminous Red
Galaxy (LRG) sample without any a-priori assumption about galaxy evolution. By
carefully contrasting the evolution of the predicted and observed number and
luminosity densities we test the passive evolution scenario for galaxies of
different luminosity, and determine minimum merger rates. We find that the LRG
population is not purely coeval, with some of galaxies targeted at z<0.23 and
at z>0.34 showing different dynamical growth than galaxies targeted throughout
the sample. Our results show that the LRG population is dynamically growing,
and that this growth must be dominated by the faint end. For the most luminous
galaxies, we find lower minimum merger rates than required by previous studies
that assume passive stellar evolution, suggesting that some of the dynamical
evolution measured previously was actually due to galaxies with non-passive
stellar evolution being incorrectly modelled. Our methodology can be used to
identify and match coeval populations of galaxies across cosmic times, over one
or more surveys.
