Paper detail

Star formation and environment in clusters up to z~2.2

The dependence of galaxy star formation activity on environment - especially in clusters - at high redshift is still poorly understood, as illustrated by the still limited number of z>1.4 clusters on the one hand, and by the still debated star formation-density relation at high redshift on the other hand. The zphot~2.2 JKCS041 cluster allows to probe such environmental dependence of star formation activity at an unprecedented combination of redshifts and environments. Its study permits to enlarge the knowledge of high redshift clusters and to put strong leverage on observational constraints for galaxy evolution models. We analyze deep u\astg'r'i'z'JHKs images from the CFHTLS/WIRDS surveys, which cover JKCS041 cluster field. We first estimate photometric redshifts based on multi-wavelength photometry. We then lead a careful analysis to test the presence of a Butcher-Oemler effect. We work on galaxies within 2\timesr200 and with masses >1.34\times10^11 Msun, and use two comparison clusters at z=0 and z=1 of similar mass. We estimate the radial profiles of the fraction of blue galaxies, taking into account the star aging with decreasing redshift. After confirming the high redshift nature of JKCS041, we find no evidence for a Butcher-Oemler effect between z~2.2 and z~0 for galaxies more massive than 1.34\times10^11 Msun. In the cluster center, a change greater than \Deltafblue/\Deltaz=0.16 between z~0 and z~2.2 would be easily detected. We also find that JKCS041 shows a consistent and systematic increase of the fraction of star-forming galaxies with cluster-centric distance, hence with decreasing density, for both a M>1.34\times10^11 Msun selected sample and a lower mass sample. In particular, very few (less than 15%) star-forming galaxies are found within r200/2 among high mass (M>1.34\times10^11 Msun) galaxies. Our results show that the present-day star formation-density relation is already in place at z~2.2.