Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z similar to 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 = 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.