Environmental dependence of polycyclic aromatic hydrocarbon emission at
  z~0.8. Investigation by observing the RX J0152.7-1357 with AKARI
  We study the environmental dependence of the strength of polycyclic aromatic
hydrocarbon (PAH) emission by AKARI observations of RX J0152.7-1357, a galaxy
cluster at z=0.84. PAH emission reflects the physical conditions of galaxies
and dominates 8 um luminosity (L8), which can directly be measured with the L15
band of AKARI. L8 to infrared luminosity (LIR) ratio is used as a tracer of the
PAH strength. Both photometric and spectroscopic redshifts are applied to
identify the cluster members. The L15-band-detected galaxies tend to reside in
the outskirt of the cluster and have optically green colour, R-z'~ 1.2. We find
no clear difference of the L8/LIR behaviour of galaxies in field and cluster
environment. The L8/LIR of cluster galaxies decreases with
specific-star-formation rate divided by that of main-sequence galaxies, and
with LIR, consistent with the results for field galaxies. The relation between
L8/LIR and LIR is between those at z=0 and z=2 in the literature. Our data also
shows that starburst galaxies, which have lower L8/LIR than main-sequence, are
located only in the outskirt of the cluster. All these findings extend previous
studies, indicating that environment affects only the fraction of galaxy types
and does not affect the L8/LIR behaviour of star-forming galaxies.
