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 0.″2−0.″4 resolution images of the rest-frame 188 and 419 μ m dust continuum and the CO(6–5), H 2 O(2 11 −2 02 ), and J up = 2 H 2 O + line emission. We also report the detection of H 2 O(2 11 −2 02 ) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ∼1. ″ 5 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), H 2 O(2 11 −2 02 ), and J up = 2 H 2 O + lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H 2 O, and H 2 O + 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), H 2 O(2 11 −2 02 ), and H 2 O + 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 ∼10 11 M ⊙ . Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities L IR reaching ≳4 × 10 12 L ⊙ , and the total L IR of G09v1.97 is (1.4 ± 0.7)×10 13 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 a s = 0.4 kpc, while the receding galaxy (0 to 350 km s −1 ) resembles an a s = 1.2 kpc rotating disk. The two galaxies are separated by a projected distance of 1.3 kpc, bridged by weak line emission (−150 to 0 km s −1 ) that is co-spatially located with the cold dust emission peak, suggesting a large amount of cold interstellar medium (ISM) in the interacting region. As one of the most luminous star-forming dusty high-redshift galaxies, G09v1.97 is an exceptional source for understanding the ISM in gas-rich starbursting major merging systems at high redshift.