The Way of Water: ALMA Resolves H2O Emission Lines in a Strongly Lensed Dusty Star-forming Galaxy at z similar to 3.1

We report Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution (less than or similar to 0.3 '') observations of water emission lines p-H2O(2(02) - 1(11)), o-H2O(3(21) - 3(12)), p-H2O(4(22) - 4(13)), in the strongly lensed galaxy HATLASJ113526.2-01460 at redshift z similar to 3.1. From the lensing-reconstructed maps of water emission and line profiles, we infer the general physical properties of the interstellar medium (ISM) in the molecular clouds where the lines arise. We find that the water vapor lines o-H2O(3(21) - 3(12)), p-H2O(4(22) - 4(13)) are mainly excited by far-infrared (FIR) pumping from dust radiation in a warm and dense environment, with dust temperatures ranging from 70 to similar to 100 K, as suggested by the line ratios. The p-H2O(2(02) - 1(11)) line, instead, is excited by a complex interplay between FIR pumping and collisional excitation in the dense core of the star-forming region. This scenario is also supported by the detection of the medium-level excitation of CO resulting in the line emission CO (J = 8-7). Thanks to the unprecedented high resolution offered by the combination of ALMA capabilities and gravitational lensing, we discern the different phases of the ISM and locate the hot molecular clouds into a physical scale of similar to 500 pc. We discuss the possibility of J1135 hosting an active galactic nucleus in its accretion phase. Finally, we determine the relation between the water emission lines and the total IR luminosity of J1135, as well as the star formation rate as a function of water emission intensities, comparing the outcomes to local and high-z galactic samples from the literature.