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

We report rest-frame submillimeter H2O emission line observations of 11 ultra-or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z similar to 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 3(21)-3(12) ortho-H2O lines (E-up/k = 305 K) and nine J = 2 para-H2O lines, either 202-111 (E-up/k = 101 K) or 2(11)-2(02) (E-up/k = 137 K). The apparent luminosities of the H2O emission lines are mu LH2O similar to 6-21 x 10(8) L-circle dot (3 < mu < 15, where mu 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 1 sigma 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 (L-H2O) and infrared (L-IR) that L-H2O similar to L-IR(1.1-1.2), with our new 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 T-warm similar to 45-75 K, H2O column density per unit velocity interval N-H2O/Lambda V >= 0.3 x 10(15) cm(-2) km(-1) s and 100 mu m continuum opacity tau(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-H2O 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.