CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we report high angular-resolution observations of the redshift z？？=？3.63 galaxy H-ATLAS J083051.0+013224 (G09v1.97), one of the most luminous strongly lensed galaxies discovered by the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). We present resolution images of the rest-frame 188 and 419？μm dust continuum and the CO(6–5), H_{2O(211？202), and Jup？=？2？H2O^{+ line emission. We also report the detection of H2O(211？202) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO(6–5), H2O(211？202), and Jup？=？2？H2O+ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H2O, and H2O+ line emission at sub-kiloparsec scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7？±？0.1 kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is μ？～？10？11, the magnification of the line emission varies from 5 to 22 across different velocity components. The line emission of CO(6–5), H2O(211？202), and H2O+ have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase, with a total molecular gas mass of ～1011？M⊙. Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities LIR reaching ？4？×？1012？L⊙, and the total LIR of G09v1.97 is (1.4？±？0.7)×1013？L⊙. The approaching southern galaxy (dominating from V？=？？400 to ？150 km s？1 relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of as？=？0.4 kpc, while the receding galaxy (0 to 350 km s？1) resembles an as？=？1.2 kpc rotating disk. The two galaxies are separated}}