Mass-dependent Color Evolution of Field Galaxies Back to z~3 Over the   Wide Range of Stellar Mass
  We use deep multi-band optical and near-infrared data for four general fields, GOODS-South, HDF North/South, and IRAC UDF in GOODS-North to investigate the evolution of the observed rest-frame U-V color of field galaxies as a function of the stellar mass. In these four fields, the U-V color distributions of the galaxies at each mass and redshift interval are very similar. At 0.3<z<2.7, we found that more massive galaxies always tend to have a redder U-V color. High- and low-mass galaxies exhibit quite different color evolutions. As seen in our previous study in HDF-N, the color distribution of low-mass (M_stellar < 3x10^9M_solar) galaxies becomes significantly bluer with an increase in the redshift. This evolution of the average color can be explained by a constant star formation rate model with z_form~4. On the other hand, the average color of high-mass galaxies (M_stellar > 3x10^10M_solar) evolves more strongly at a high redshift. Such mass-dependent color distribution and its evolution indicate that galaxies with a larger stellar mass appear to have shorter star-formation timescales, and on an average, they form the larger fraction of their stars in the earlier epoch. 
Masaru Kajisawa, Toru Yamada