Dust-obscured star formation in the outskirts of XMMU J2235.3−2557, a massive galaxy cluster at z = 1.4

Star formation (SF) in the galaxy populations of local massive clusters is reduced with respect to field galaxies, and tends to be suppressed in the core region. Indications of a reversal of the SF–density relation have been observed in a few z > 1.4 clusters. Using deep imaging from 100–500 μm from Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, we investigate infrared properties of spectroscopic and photo-z cluster members, and of Hα emitters in XMMU J2235.3−2557, one of the most massive, distant, X-ray selected clusters known. Our analysis is based mostly on fitting of the galaxies spectral energy distribution (SED) in the rest-frame 8–1000 μm. We measure total IR luminosity, deriving star formation rates (SFRs) ranging from 89 to 463 M⊙ yr−1 for 13 galaxies individually detected by Herschel, all located beyond the core region (r >250 kpc). We perform a stacking analysis of nine star-forming members not detected by PACS, yielding a detection with SFR = 48 ± 16 M⊙ yr−1. Using a colour criterion based on a star-forming galaxy SED at the cluster redshift, we select 41 PACS sources as candidate star-forming cluster members. We characterize a population of highly obscured SF galaxies in the outskirts of XMMU J2235.3−2557. We do not find evidence for a reversal of the SF–density relation in this massive, distant cluster.