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

C. Yang, A. Omont, A. Beelen, E. González-Alfonso, R. Neri, Y. Gao, P. van der Werf, A. Weiß, R. Gavazzi, N. Falstad, A. J. Baker, R. S. Bussmann (+12 others)
2016 Astronomy and Astrophysics  
(abridged) We report rest-frame submillimeter H2O emission line observations of 11 HyLIRGs/ULIRGs at z 2-4 selected among the brightest lensed galaxies discovered in the Herschel-ATLAS. Using the IRAM NOEMA, we have detected 14 new H2O emission lines. The apparent luminosities of the H2O emission lines are μ L_H_2O∼ 6-21 × 10^8 L_, 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 30m telescope in seven sources. The
more » ... seven sources. The velocity widths for CO and H2O lines are found to be similar. With almost comparable integrated flux densities to those of the high-J CO line, H2O is found to be among the strongest molecular emitters in high-z Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H2O (L_H_2O) and infrared (L_IR) that L_H_2O∼ L_IR^1.1-1.2, with our new detections. This correlation could be explained by a dominant role of far-infrared (FIR) pumping in the H2O excitation. Modelling reveals the FIR radiation fields have warm dust temperature T_warm 45-75 K, H2O column density per unit velocity interval N_H_2O/Δ V ≳ 0.3 × 10^15 cm^-2 km^-1 s and 100 μm continuum opacity τ_100 > 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 L_H_2O and L_H_2O^+ 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.
doi:10.1051/0004-6361/201628160 fatcat:talyx43lovayhfq5bym6hpphpu