Volume 595, November 2016
|Number of page(s)||23|
|Published online||03 November 2016|
Submillimeter H2O and H2O+emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2–4 ⋆,⋆⋆
1 Purple Mountain Observatory/Key Lab of Radio Astronomy, Chinese Academy of Sciences, 210008 Nanjing, PR China
2 Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 121, 91405 Orsay Cedex, France
3 Graduate University of the Chinese Academy of Sciences, 19A Yuquan Road, Shijingshan District, 10049 Beijing, PR China
4 CNRS, UMR 7095, Institut d'Astrophysique de Paris, 75014 Paris, France
5 UPMC Univ. Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
6 Universidad de Alcalá, Departamento de Fisica y Matemáticas, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
7 Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d’ Hères, France
8 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
9 Max Planck Institut für Radioastronomie, Auf dem Hgel 69, 53121 Bonn, Germany
10 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
11 Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019, USA
12 Astronomy Department, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA
13 Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697, USA
14 Joint ALMA Observatory, 3107 Alonso de Córdova, Vitacura, Santiago, Chile
15 Universitat Wien, Institut für Astrophysik, Türkenschanzstrasse 17, 1180 Wien, Austria
16 School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
17 Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
18 European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
19 Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen, The Netherlands
20 School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
Received: 19 January 2016
Accepted: 20 July 2016
We report rest-frame submillimeter H2O emission line observations of 11 ultra- or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z ~ 2–4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H2O emission lines. These include five 321–312ortho-H2O lines (Eup/k = 305 K) and nine J = 2 para-H2O lines, either 202–111(Eup/k = 101 K) or 211–202(Eup/k = 137 K). The apparent luminosities of the H2O emission lines are μLH2O ~ 6–21 × 108 L⊙ (3 <μ< 15, where μ is the lens magnification factor), with velocity-integrated line fluxes ranging from 4–15 Jy km s-1. We have also observed CO emission lines using EMIR on the IRAM 30 m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H2O lines are found to be similar, generally within 1σ errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H2O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H2O (LH2O) and infrared (LIR) that LH2O ~ LIR1.1–1.2, with ournew detections. This correlation could be explained by a dominant role of far-infrared pumping in the H2O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature Twarm ~ 45–75 K, H2O column density per unit velocity interval NH2O /ΔV ≳ 0.3 × 1015 cm-2 km-1 s and 100 μm continuum opacity τ100> 1 (optically thick), indicating that H2O is likely to trace highly obscured warm dense gas. However, further observations of J ≥ 4 H2O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H2O+ emission in three sources. A tight correlation between LH2O and LH2O+ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H2O+ and H2O suggests that cosmic rays generated by strong star formation are possibly driving the H2O+ formation.
Key words: galaxies: high-redshift / galaxies: ISM / infrared: galaxies / submillimeter: galaxies / radio lines: ISM / ISM: molecules
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
The reduced spectra as FITS files are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A80
© ESO, 2016
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