A bright z = 5.2 lensed submillimeter galaxy in the field of Abell 773

HLSJ091828.6+514223

¹ Observatoire de Paris, LERMA, CNRS, 61 Av. de l’Observatoire, 75014 Paris, France
e-mail: francoise.combes@obspm.fr
² Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721, USA
³ Université de Toulouse, UPS-OMP, CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁴ Institute for Computational Cosmology, Durham University, South Road, Durham, DH1 3LE, UK
⁵ CRAL, Université Lyon-1, 9 Av. Charles André, 69561 St Genis Laval, France
⁶ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr, Honolulu, HI 96822, USA
⁹ Institut d’Astrophysique de Paris, UPMC and CNRS, 98bis Bd. Arago, 75014 Paris, France
¹⁰ ASTRON, PO Box 2, 2990 AA Dwingeloo, The Netherlands
¹¹ Geneva Observatory, Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland
¹² LAM, CNRS – Université Aix-Marseille, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
¹³ Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), PO Box 23-141, 10617 Taipei, Taiwan
¹⁴ Dep. de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁵ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 28 December 2011
Accepted: 16 January 2012

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 × 10¹⁴/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-H₂ conversion ratio, the H₂  mass is 5.8 × 10¹¹/μ M_⊙, of which one third is in a cool component. From the C I(³P₂-³P₁) line we derive a C I/H₂  number abundance of 6 × 10^-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]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.