2012A&A...538L...4C

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 (∼200mJy at 500µm) 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=1.1x10¹⁴/µ*L_☉, where µ is the magnification factor, likely ∼11. We report here the redshift identification through CO lines with the IRAM-30m, 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, 540km/s apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H₂ conversion ratio, the H₂ mass is 5.8x10¹¹/µ*M_☉, of which one third is in a cool component. From the CI(³P₂-³P₁) line we derive a CI/H₂ number abundance of 6x10^–5 similar to that in other ULIRGs. The H₂O_p(2,0,2-1,1,1) line is strong only in the red velocity component, with an intensity ratio I(H₂O)/I(CO)∼0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the [NII]205µm 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.