Evolution of the Dependence of Rest-frame Color and Morphology   Distribution on Stellar Mass for Galaxies in the Hubble Deep Field North
  Using the Subaru very deep K'-band imaging and HST WFPC2/NICMOS archival data of the Hubble Deep Field North, we investigate the evolution of the stellar mass, color, morphology of galaxies to z ~ 3. We mainly examine the rest-frame U-V color distribution of galaxies as a function of stellar mass. At 0.3<z<2, galaxies seem to be divided into the two populations at around the stellar mass of ~5x10^9 M_solar. The low-mass galaxies have relatively bluer rest U-V color and their color does not show clear correlation with stellar mass over the range of 10^8-5x10^9 M_solar. On the other hand, at higher mass, the more massive galaxies tend to have the redder U-V color. The average U-V color of the low-mass galaxies becomes bluer gradually with redshift, from U-V ~ 0.2 at z ~ 0.5 to U-V ~ -0.2 at z ~ 2. On the contrary, the correlation between the stellar mass and rest U-V color of the high-mass population does not seem to change significantly between z ~ 0.3 and z ~ 2. At z>2, it is seen that more massive galaxies tend to have redder U-V color over the range of 10^9-10^10 M_solar. These results suggests that the star formation history of galaxies depends on their stellar mass very much. The low-mass population is likely to have relatively long star formation timescale. At the stellar mass larger than ~5x10^9 M_solar, there must be some mechanisms which suppress the star formation in galaxies at 0<z<2. 
Masaru Kajisawa, Toru Yamada (National Astronomical Observatory of   Japan)