Evolution of Star-formation Properties of High-redshift Cluster Galaxies
  since $z = 2$
  Using a stellar mass limited sample of $\sim 46,600$ galaxies ($M_* >
10^{9.1}\,M_{\odot}$) at $0.5 < z < 2$, we show that the tellar mass, rather
than the environment, is the main parameter controlling quenching of star
formation in galaxies with $M_* > 10^{10}\,M_{\odot}$ out to $z=2$. On the
other hand, the environmental quenching becomes efficient at $z < 1$ regardless
of galaxy mass, and it serves as a main star formation quenching mechanism for
lower mass galaxies. Our result is based on deep optical and near-infrared
imaging data over 2800 arcmin$^2$, enabling us to negate cosmic variance and
identify 46 galaxy cluster candidates with $M \sim 10^{14}\,M_{\odot}$. From
$M_* \sim 10^{9.5}$ to $10^{10.5}\,M_{\odot}$, the fraction of quiescent
galaxies increases by a factor of $\sim 10$ over the entire redshift range, but
the difference between cluster and field environment is negligible. Rapid
evolution in the quiescent fraction is seen from $z=2$ to $z=1.3$ for massive
galaxies suggesting a build-up of massive quiescent galaxies at $z > 1.3$. For
galaxies with $M_* < 10^{10}\,M_{\odot}$ at $z < 1.0$, the quiescent fraction
is found to be as much as a factor of 2 larger in clusters than in field,
showing the importance of environmental quenching in low mass galaxies at low
redshift. Most high mass galaxies are already quenched at $z > 1$, therefore
environmental quenching does not play a significant role for them, although the
environmental quenching efficiency is nearly identical between high and low
mass galaxies.
