2005ApJ...618...91K

Using very deep Subaru K'-band imaging and archival Hubble Space TelescopeWFPC2/NICMOS data of the Hubble Deep Field-North, we investigate the evolution of the stellar mass, color, and 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 ∼5x10⁹ M_☉. The low-mass galaxies have relatively bluer rest-frame U-V color, and their color does not show a clear correlation with stellar mass over the range 10⁸ to 5x10⁹ M_☉. On the other hand, at higher mass, the more massive galaxies tend to have redder U-V color. The average U-V color of the low-mass galaxies gradually becomes bluer with redshift, from U-V∼0.2 at z∼0.5 to U-V~-0.2 at z∼2. However, the correlation between the stellar mass and rest-frame U-V color of the high-mass population does not seem to change significantly between z∼0.3 and z∼2. The morphological distribution shows that at z≲1, the low-mass population is dominated by disk galaxies, while the fraction of early-type galaxies is larger in the high-mass population. At 1<z<2, although the fraction of irregular galaxies increases, a similar trend is observed. At z>2, it is seen that more massive galaxies tend to have redder U-V color over the range 10⁹-10¹⁰ M_☉, although we can only sample galaxies with stellar mass larger than ∼1x10⁹ M_☉. These results suggest that the star formation history of galaxies depends greatly on their stellar mass. The low-mass population is likely to have a relatively long star formation timescale, and under the assumption of a constant star formation rate, their formation redshifts do not seem to be much higher than z∼2. At stellar masses larger than ∼5x10⁹ M_☉, there must be some mechanism that suppresses star formation in galaxies at 0<z<2.