Letters to the Editor

Observation of H₂O in a strongly lensed Herschel-ATLAS source at z = 2.3^⋆

¹ UPMC Univ Paris 06, UMR7095, Institut d’Astrophysique de Paris, 75014 Paris, France
e-mail: omont@iap.fr
² CNRS, UMR7095, Institut d’Astrophysique de Paris, 75014 Paris, France
³ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
⁴ Department of Physics and Astronomy, University of Pennsylvania, Philadephia, PA 19104, USA
⁵ Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, The Netherlands
⁶ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
⁷ Univ Paris-Sud and CNRS, Institut d’Astrophysique Spatiale, UMR8617, 91405 Orsay, France
⁸ Argelander Institut fur Astronomie, Universit Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁹ Astrophysics Group, Physics Department, Blackett Lab, Imperial College London, Prince Consort Road, London SW7, UK
¹⁰ Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
¹¹ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
¹² Laboratoire Astrophysique, Instrumentation et Modélisation Paris Saclay, Commissariat à l’Énergie Atomique (CEA)/Direction des Sciences de la Matière (DSM) – CNRS – Université Paris Diderot, Institut de recherche sur les lois fondamentales de l’Univers (Irfu)/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
¹³ INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy ; SISSA, via Bonomea 265, 34136 Trieste, Italy
¹⁴ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK
¹⁵ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51 y 216, 72000 Puebla, Mexico
¹⁶ UK Astronomy Technology Center, Royal Observatory Edinburgh, Edinburgh, EH9 3HJ, UK
¹⁷ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹⁸ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁹ SETI Institute, 515 North Whisman Avenue, Mountain View CA, 94043, USA
²⁰ Astrophysics Branch, NASAAmes Research Center, MS 245-6, Moffett Field, CA 94035, USA
²¹ Oxford Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
²² Max-Plank-Institut fïr Radioastronomie, Auf dem Hïgel 69, 53121 Bonn, Germany
²³ National Radio Astronomy Observatory Post Office Box 2, Green Bank, WV 24944, USA
²⁴ INAF-IASF Milano, via E. Bassini 15, 20133, Italy
²⁵ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²⁶ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
²⁷ School of Astronomy, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5746, Tehran, Iran
²⁸ California Institute of Technology, Pasadena, CA 91125, USA
²⁹ Jet Propulsion Laboratory, Pasadena, CA 91109, USA
³⁰ University of Colorado, CASA 389-UCB, Boulder, CO 80303, USA
³¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, 9000 Gent, Belgium
³² Departamento de Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
³³ Department of Physics, McGill University, Ernest Rutherford Building, 3600 Rue University, Montréal, Québec, H3A 2T8, Canada
³⁴ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019, USA
³⁵ Centre for Astrophysics, Science & Technology Research Institute, University of Hertfordshire, Hatfield, Herts, AL10 9AB, UK
³⁶ Department of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA, UK

Received: 18 March 2011
Accepted: 11 April 2011

Abstract

The Herschel survey, H-ATLAS, with its large areal coverage, has recently discovered a number of bright, strongly lensed high-z submillimeter galaxies. The strong magnification makes it possible to study molecular species other than CO, which are otherwise difficult to observe in high-z galaxies. Among the lensed galaxies already identified by H-ATLAS, the source J090302.9-014127B (SDP.17b) at z = 2.305 is remarkable because of its excitation conditions and a tentative detection of the H₂O 2₀₂-1₁₁ emission line (Lupu et al. 2010, ApJ, submitted). We report observations of this line in SDP.17b using the IRAM interferometer equipped with its new 277–371 GHz receivers. The H₂O line is detected at a redshift of z = 2.3049 ± 0.0006, with a flux of 7.8 ± 0.5 Jy km s^-1 and a FWHM of 250 ± 60   km   s^-1. The new flux is 2.4 times weaker than the previous tentative detection, although both remain marginally consistent within 1.6σ. The intrinsic line luminosity and ratio of H₂O(2₀₂ − 1₁₁)/CO(8 − 7) are comparable with those of the nearby starburst/enshrouded-AGN Mrk 231, and the ratio I(H₂O)/L_FIR is even higher, suggesting that SDP.17b could also host a luminous AGN. The detection of a strong H₂O 2₀₂ − 1₁₁ line in SDP.17b implies an efficient excitation mechanism of the water levels that must occur in very dense and warm interstellar gas probably similar to Mrk 231.