H₂O emission in high-z ultra-luminous infrared galaxies^⋆

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 Purple Mountain Observatory, Nanjing, PR China
⁴ Department of Astronomy, Beijing Normal University, Beijing, PR China
⁵ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin d’ Hères, France
⁶ Univ. Paris-Sud and CNRS, Institut d’Astrophysique Spatiale, UMR8617, 91405 Orsay, France
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, The Netherlands
⁹ Department of Astronomy, Space Science Building, Cornell University, Ithaca, NY, 14853-6801, USA
¹⁰ Centre for Astronomy & Particle Theory, University Park, Nottingham, NG7 2RD, UK
¹¹ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹² Department of Physics and Astronomy, University of Pennsylvania, Philadephia, PA 19104, US
¹³ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, 9000 Gent, Belgium
¹⁴ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019, USA
¹⁵ Argelander Institut fur Astronomie, Universitat Bonn, Auf dem Hugel 71, 53121 Bonn, Germany
¹⁶ Universitat Wien, Institut fur Astronomie, Turkenschanz-strasse 17, 1180 Wien, Austria
¹⁷ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade 5, Cardiff, CF24 3AA, UK
¹⁸ Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
¹⁹ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
²⁰ Max-Plank-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany
²¹ INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, and SISSA, via Bonomea 265, 34136 Trieste, Italy
²² Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²³ Astrophysics Branch, NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035, USA
²⁴ Astrophysics, Department of Physics, Keble Road, Oxford OX1 3RH, UK
²⁵ School of Astronomy, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5746, Tehran, Iran
²⁶ Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, 8140, NZ
²⁷ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
²⁸ California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
²⁹ Jet Propulsion Laboratory, Pasadena, CA 91109, USA
³⁰ University of Colorado, CASA 389-UCB, Boulder, CO 80303, USA
³¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
³² UK Astronomy Technology Centre, The Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
³³ Universidad Catolica de Chile, Departamento de Astronomia y Astrofisica, Casilla 306, Santiago 22, Chile
³⁴ Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
³⁵ Astrophysics Group, Imperial College,Blackett Laboratory, Prince Consort Road, London, SW7 2AZ, UK
³⁶ College of Graduate Studies, University of South Africa, PO Box 392, Unisa, 003, South Africa

Received: 28 November 2012
Accepted: 7 January 2013

Abstract

Using the IRAM Plateau de Bure interferometer (PdBI), we report the detection of water vapor in six new lensed ultra-luminous starburst galaxies at high redshift, discovered in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). The sources are detected either in the 2₀₂−1₁₁ or 2₁₁−2₀₂ H₂O emission lines with integrated line fluxes ranging from 1.8 to 14 Jy km s^-1. The corresponding apparent luminosities are μL_H2O ~ 3−12 × 10⁸ L_⊙, where μ is the lensing magnification factor (3 < μ < 12). These results confirm that H₂O lines are among the strongest molecular lines in high-z ultra-luminous starburst galaxies, with intensities almost comparable to those of the high-J CO lines, and similar profiles and line widths (~200−900 km s^-1). With the current sensitivity of the PdBI, the water lines can therefore easily be detected in high-z lensed galaxies (with F(500 μm) > 100 mJy) discovered in the Herschel surveys. Correcting the luminosities for amplification, using existing lensing models, L_H2O is found to have a strong dependence on the infrared luminosity, varying as ~L_IR^1.2. This relation, which needs to be confirmed with better statistics, may indicate a role of radiative (infrared) excitation of the H₂O lines, and implies that high-z galaxies with L_IR ≳ 10¹³ L_⊙ tend to be very strong emitters in water vapor, that have no equivalent in the local universe.