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 ( 20 \times 20 Mpc ) imaging by Spitzer MIPS at 24 \mu m , in conjunction with Herschel 5-band imaging from 100–500 \mu m , 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 \sim 1.62 detected at 24 \mu m ( 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 M _ { \odot } /yr , with a median of 55 M _ { \odot } /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 M _ { \odot } /yr , and the total cluster SFR enclosed in a circle of 1 Mpc is 1161 \pm 96 M _ { \odot } /yr .
We estimate a dust extinction of \sim 3 magnitudes by comparing the SFRs derived from [ OII ] luminosity with the ones computed from the 24 \mu m fluxes .
We find that the in-falling region ( 1–3 Mpc ) is special : there is a significant decrement ( 3.5 \times ) of passive relative to star-forming galaxies in this region , and the total SFR of the galaxies located in this region is lower ( \sim 130 M _ { \odot } /yr/Mpc ^ { 2 } ) than anywhere in the cluster or field , regardless of their stellar mass .
In a complementary approach we compute the local galaxy density , \Sigma _ { 5 } , and find no trend between SFR and \Sigma _ { 5 } .
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 SF–density relation in CLG0218 .