2012MNRAS.423.3652G

We present the results of an extended narrow-band Hα study of the massive galaxy cluster XMMU J2235.3-2557 at z= 1.39. This paper represents a follow-up study to our previous investigation of star formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph on Gemini North Telescope we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of Hα at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-infrared colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20 per cent are excess line emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFRs) of excess emitters outside this cluster quenching radius, R_Q ∼ 200kpc , are on average = 2.7±1.0 M_☉/yr, but do not show evidence of increasing SFRs towards the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M_☉/yr. Massive galaxies (log M*/M_☉ > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of ∼4.5 Gyr) the suppression of star formation is an effect of the cluster environment which persists at fixed galaxy stellar mass.