H₂O emission in high-z ultra-luminous infrared galaxies

Omont, A.; Yang, C.; Cox, P.; Neri, R.; Beelen, A.; Bussmann, R. S.; Gavazzi, R.; van der Werf, P.; Riechers, D.; Downes, D.; Krips, M.; Dye, S.; Ivison, R.; Vieira, J. D.; Weiß, A.; Aguirre, J. E.; Baes, M.; Baker, A. J.; Bertoldi, F.; Cooray, A.; Dannerbauer, H.; De Zotti, G.; Eales, S. A.; Fu, H.; Gao, Y.; Guélin, M.; Harris, A. I.; Jarvis, M.; Lehnert, M.; Leeuw, L.; Lupu, R.; Menten, K.; Michałowski, M. J.; Negrello, M.; Serjeant, S.; Temi, P.; Auld, R.; Dariush, A.; Dunne, L.; Fritz, J.; Hopwood, R.; Hoyos, C.; Ibar, E.; Maddox, S.; Smith, M. W. L.; Valiante, E.; Bock, J.; Bradford, C. M.; Glenn, J. and Scott, K. S. (2013). H₂O emission in high-z ultra-luminous infrared galaxies. Astronomy & Astrophysics, 551, article no. A115.

DOI: https://doi.org/10.1051/0004-6361/201220811

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.

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