We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15

During our Herschel Lensing Survey (HLS) of massive galaxy clusters, we have discovered an exceptionally bright source behind the z = 0.22 cluster Abell 773, which appears to be a strongly lensed submillimeter galaxy (SMG) at z = 5.2429. This source is unusual compared to most other lensed sources discovered by Herschel so far, because of its higher submm flux (∼200 mJy at 500 μm) and its high redshift. The dominant lens is a foreground z = 0.63 galaxy, not the cluster itself. The source has a far-infrared (FIR) luminosity of L FIR = 1.1 × 10 14 /μ L , where μ is the magnification factor, likely ∼11. We report here the redshift identification through CO lines with the IRAM-30 m, and the analysis of the gas excitation, based on CO(7-6), CO(6-5), CO(5-4) detected at IRAM and the CO(2-1) at the EVLA. All lines decompose into a wide and strong red component, and a narrower and weaker blue component, 540 km s −1 apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H 2 conversion ratio, the H 2 mass is 5.8 × 10 11 /μ M , of which one third is in a cool component. From the C I( 3 P 2 − 3 P 1 ) line we derive a C I/H 2 number abundance of 6 × 10 −5 similar to that in other ULIRGs. The H 2 O p (2, 0, 2−1, 1, 1) line is strong only in the red velocity component, with an intensity ratio I(H 2 O)/I(CO) ∼ 0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the [NII]205 μm line for the first time at high-z. It shows comparable blue and red components, with a strikingly broad blue one, suggesting strong ionized gas flows.

We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.153 M ⊙ yr −1 , of the form f SF ∝(1 + z) 7.6±1.1 . We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ∼3× decline in the mean specific-SFRs of star-forming cluster galaxies since z∼0.3 with a ∼1.5× decrease in number density. Two-thirds of this reduction in the specific-SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific-SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star-formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intra-cluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z∼0.4 likely reflects the increased susceptability of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear star-burst episodes.