Panoramic H-alpha and mid-infrared mapping of star formation in a z=0.8
  cluster
  We present the first wide-field H-alpha imaging survey around the distant
cluster RXJ1716.4+6708 at z=0.81 with a narrow-band filter on MOIRCS/Subaru,
down to SFR(Ha)~1Msun/yr. Combining with a wide-field MIR imaging survey with
AKARI, we compare the unobscured and obscured star formation activities in the
cluster. We find that both H-alpha emitters and MIR galaxies avoid the cluster
centre and their spatial distribution is quite similar. Most of the H-alpha
emitters show blue colours, but we find some H-alpha emitters on the red
sequence. The MIR galaxies tend to be systematically redder than the H-alpha
emitters probably due to heavy dust extinction. Interestingly, the red H-alpha
emitters and the red MIR galaxies (i.e. dusty red galaxies) are most commonly
seen in the medium-density environment such as cluster outskirts, groups and
filaments, where optical colours of galaxies change. We also find that A(Ha)
exceeds ~3 in extreme cases and that such very dusty galaxies are also located
in the medium-density environment. These findings suggest that dusty star
formation is triggered in the in-fall region of the cluster, implying a
probable link between galaxy transition and dusty star formation. We finally
calculate the cluster total SFR and find that the cluster total SFR based on
H-alpha alone can be underestimated more than factor ~2 even after 1 mag
extinction correction. We suggest that the mass-normalized cluster SFR rapidly
declines since z~1 following ~(1+z)^6, although the uncertainty is still large.
