SDSS-III finds a large population of massive galaxies making stars 5 billion years ago

Building on the legacy of the Sloan Digital Sky Survey (SDSS), the SDSS-III’s Baryon Oscillation Spectroscopic Survey (BOSS) is currently mapping the spatial distribution of the most massive galaxies in the Universe. SDSS-III astronomers have been using the galaxy spectra obtained by these experiments to infer important physical information about the stars and the gas in these systems, which illuminate how galaxies formed and evolved over the history of the Universe.
In a recent paper, BOSS scientists from the University of Wisconsin, the Max Planck Institute for Astrophysics, Johns Hopkins University, along with other members of the SDSS-III team, studied the masses and ages of around 300,000 massive galaxies at redshifts ranging from 0.45 to 0.7, corresponding to a time when the Universe was 60 percent of its present age of 13.7 billion years. These galaxies all have stellar masses larger than 100 billion times that mass of our Sun (10^11 Msun), making this the largest sample of massive galaxies with spectra to have been analyzed thus far.
“Evolution of the Most Massive Galaxies to z=0.6: I. A New Method for Physical Parameter Estimation”
Yan-Mei Chen et al.
http://arxiv.org/abs/1108.4719

The above figure from the paper shows the fraction of ...