MOIRCS Deep Survey. X. Evolution of Quiescent Galaxies as a Function of Stellar Mass at 0.5 < z < 2.5
We studied the evolution of quiescent galaxies at 0.5 6 by performing a SED fitting of the multi broad-band photometry from the U to Spitzer 5.8 � m bands with the population synthesis model of Bruzual and Charlot (2003, MNRAS, 344, 1000), where exponentially decaying star-formation histories are assumed. The number density of quiescent galaxies increases by a factor of � 3 from 1.0 < z < 1.5 to 0.5 < z < 1.0, and by a factor of � 10 from 1.5 < z < 2.5 to 0.5< z < 1.0, while that of star-forming galaxies with age / �< 4 increases only by factors of � 2a nd� 3 in the same redshift ranges. At 0.5 < z < 2.5, the low-mass slope of the stellar mass function of quiescent galaxies is ˛ � 0–0.6, which is significantly flatter than those of star-forming galaxies (˛ �� 1.3–� 1.5). As a result, the fraction of quiescent galaxies in the overall galaxy population increases with stellar mass in the redshift range. The