Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2–4

Yang, C. and Omont, Alain and Beelen, A. and González-Alfonso, E. and Neri, R. and Gao, Y. and van der Werf, Paul and Weiß, A. and Gavazzi, R. and Falstad, N. and Baker, A.J. and Bussmann, R.S. and Cooray, A. and Cox, P. and Dannerbauer, H. and Dye, S. and Guélin, M. and Ivison, R.J. and Krips, M. and Lehnert, M. and Michałowski, M.J. and Riechers, D.A. and Spaans, M. and Valiante, E. (2016) Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2–4. Astronomy & Astrophysics, 595 . A80/1-A80/23. ISSN 1432-0746

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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.

Item Type: Article
Additional Information: © ESO, 2016
Keywords: Galaxies: high-redshift, Galaxies: ISM, Infrared: galaxies, Submillimeter: galaxies, Radio lines: ISM, ISM: molecules
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Physics and Astronomy
Identification Number: 10.1051/0004-6361/201628160
Depositing User: Eprints, Support
Date Deposited: 27 Apr 2017 10:09
Last Modified: 27 Apr 2017 11:26

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