Poster Presentation Astronomical Society of Australia Annual Scientific Meeting including HWWS 2013

New Measurements of the Evolving Growth Rates of Galaxies (#205)

Richard Beare 1 , Michael Brown 1 , Kevin Pimbblet 1
  1. Monash Centre for Astrophysics, Clayton, Victoria, Australia

Using a sample of ~400,000 galaxies in the Bootes field (~10 times larger than previous studies), we have accurately measured the evolving B-band luminosity function of red and blue galaxies at z<1.2.

We find that the comoving space density of red galaxies approximately doubles from z~1.1 to z~0.1, while that of blue galaxies remains relatively unchanged. By contrast the luminosity density of red galaxies changes little over the same redshift range, while that of blue galaxies approximately halves. By comparing our measurements of the luminosity density evolution of red galaxies with those to be expected from passive evolution alone, we deduce that red galaxies have increased in stellar mass by a factor of ~4 from z~1.1 to z~0.1, and we attribute this to the combined effect of mergers and blue galaxies crossing the green valley as they cease to form stars.

We also measure how the rate of growth of massive galaxies evolves with redshift, and find rapid growth at z~1 and far less growth at z~0.4. For massive red galaxies, we compare our observations with those to be expected from passive evolution alone, and deduce that massive red galaxies double in mass from z~1.1 to z~0.5 and then change little in mass from z~0.5 to z~0.1.   As there are insufficient massive blue galaxies at z>0.5 that could cease star formation and become massive red galaxies, we infer that the observed growth in massive red galaxies from z~1.1 to z~0.5 is due almost entirely to mergers.