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Published March 2013 | Published
Journal Article Open

H_2O emission in high-z ultra-luminous infrared galaxies


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 2_(02)−1_(11) or 2_(11)−2_(02) H_2O 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 × 10^8 L_⊙, where μ is the lensing magnification factor (3 < μ < 12). These results confirm that H_2O 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 H_2O lines, and implies that high-z galaxies with L_(IR) ≳ 10^(13) L_⊙ tend to be very strong emitters in water vapor, that have no equivalent in the local universe.

Additional Information

© 2013 ESO. Article published by EDP Sciences. Received 28 November 2012. Accepted 7 January 2013. Published online 05 March 2013. Herschel (Pilbratt et al. 2010) is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Based on observations carried out with the IRAM Plateau de Bure interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). The authors are grateful to the IRAM staff for their support. US participants in H-ATLAS acknowledge support from NASA through a contract from JPL. Italian participants in H-ATLAS acknowledge a financial contribution from the agreement ASI-INAF I/009/10/0. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). M. J. Michałowski acknowledges the support of a FWO-Pegasus Marie Curie Fellowship.

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