Star formation in the cluster CLG0218.3-0510 at z=1.62 and its
  large-scale environment: the infrared perspective
  The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy
clusters known, with a rich muti-wavelength data set that confirms a mature
galaxy population already in place. Using very deep, wide area (20x20 Mpc)
imaging by Spitzer/MIPS at 24um, in conjunction with Herschel 5-band imaging
from 100-500um, we investigate the dust-obscured, star-formation properties in
the cluster and its associated large scale environment. Our galaxy sample of
693 galaxies at z=1.62 detected at 24um (10 spectroscopic and 683 photo-z)
includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric
radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The
star-formation rates (SFRs) derived from the measured infrared luminosity range
from 18 to 2500 Ms/yr, with a median of 55 Ms/yr, over the entire radial range
(10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy
system, is vigorously forming stars at a rate of 256$\pm$70 Ms/yr, and the
total cluster SFR enclosed in a circle of 1 Mpc is 1161$\pm$96 Ms/yr. We
estimate a dust extinction of about 3 magnitudes by comparing the SFRs derived
from [OII] luminosity with the ones computed from the 24um fluxes. We find that
the in-falling region (1-3 Mpc) is special: there is a significant decrement
(3.5x) of passive relative to star-forming galaxies in this region, and the
total SFR of the galaxies located in this region is lower (130 Ms/yr/Mpc2) than
anywhere in the cluster or field, regardless of their stellar mass. In a
complementary approach we compute the local galaxy density, Sigma5, and find no
trend between SFR and Sigma5. However, we measure an excess of star-forming
galaxies in the cluster relative to the field by a factor 1.7, that lends
support to a reversal of the SF-density relation in CLG0218.
