G09v1.97 CO and H2O datacubes

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+/-0.1kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is {mu}~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_{sun}_. Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities LIR reaching 4x10^12^L_{sun}_, and the total LIR of G09v1.97 is (1.4+/-0.7)x10^13^L_{sun}_.

The approaching southern galaxy (dominating from V=-400 to -150km/s relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of a_s_=0.4kpc, while the receding galaxy (0 to 350km/s) resembles an a_s_=1.2kpc rotating disk. The two galaxies are separated by a projected distance of 1.3kpc, bridged by weak line emission (-150 to 0km/s) 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.