A bright z = 5.2 lensed submillimeter galaxy in the field of Abell 773: HLSJ091828.6+514223

Abstract

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( 3P 2- 3P 1) line we derive a C I/H 2 number abundance of 6 × 10 -5 similar to that in other ULIRGs. The H 2O p(2,0,2-1,1,1) line is strong only in the red velocity component, with an intensity ratio I(H 2O)/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. © 2012 ESO.