The brightest 500 μm source in the XMM-LSS field, HXMM01, is a rare merger of luminous starburst galaxies at z = 2.3 with a dust-obscured star formation rate of 2000 M o yr-1. Here we present high-resolution spectroscopic observations of HXMM01 with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect line emission from CO J = 7 → 6, [C i] 3 P 2 → 3 P 1, and p-H2O 211 → 202 and continuum emission at 230 GHz. At a spatial resolution of 0.″2 and a spectral resolution of 40 km s-1, the source is resolved into three distinct components, which are spatially and dynamically associated within a projected radius of 20 kpc and a radial velocity range of 2000 km s-1. For two major components, our Bayesian-based tilted-ring modeling of the ALMA spectral cubes shows almost flat rotation curves peaking at ∼500 km s-1 at galactocentric distances between 2 and 5 kpc. Each of them has a dynamical mass of ∼1011 M o. The combination of the dynamical masses and the archival CO J = 1 → 0 data places strong upper limits on the CO → H2 conversion factor of α CO ≲ 1.4-2.0 M o(K km s-1 pc2)-1. These limits are significantly below the Galactic inner disk α CO value of 4.3 M o(K km s-1 pc2)-1 but are consistent with those of local starbursts. Therefore, the previously estimated short gas depletion timescale of ∼200 Myr remains unchanged.
- galaxies: formation
- galaxies: high-redshift
- galaxies: individual (HERMES J022016.5-060143)
- galaxies: interactions