The evolution of dust-obscured star formation activity in galaxy
  clusters relative to the field over the last 9 billion years
  We compare the star formation (SF) activity in cluster galaxies to the field
from z=0.3-1.5 using $Herschel$ SPIRE 250$\mu$m imaging. We utilize 274
clusters from the IRAC Shallow Cluster Survey (ISCS) selected as rest-frame
near-infrared overdensities over the 9 square degree Bootes field . This
analysis allows us to quantify the evolution of SF in clusters over a long
redshift baseline without bias against active cluster systems. Using a stacking
analysis, we determine the average star formation rates (SFRs) and
specific-SFRs (SSFR=SFR/M$_{\star}$) of stellar mass-limited (M>1.3x10$^{10}$
M$_{\odot}$), statistical samples of cluster and field galaxies, probing both
the star forming and quiescent populations. We find a clear indication that the
average SF in cluster galaxies is evolving more rapidly than in the field, with
field SF levels at z>1.2 in the cluster cores (r<0.5 Mpc), in good agreement
with previous ISCS studies. By quantifying the SF in cluster and field galaxies
as an exponential function of cosmic time, we determine that cluster galaxies
are evolving ~2 times faster than the field. Additionally, we see enhanced SF
above the field level at z~1.4 in the cluster outskirts (r>0.5 Mpc). These
general trends in the cluster cores and outskirts are driven by the lower mass
galaxies in our sample. Blue cluster galaxies have systematically lower SSFRs
than blue field galaxies, but otherwise show no strong differential evolution
with respect to the field over our redshift range. This suggests that the
cluster environment is both suppressing the star formation in blue galaxies on
long time-scales and rapidly transitioning some fraction of blue galaxies to
the quiescent galaxy population on short time-scales. We argue that our results
are consistent with both strangulation and ram pressure stripping acting in
these clusters, with merger activity occurring in the cluster outskirts.
