We present CO (J = 1 → 0 3 → 2 5 → 4 10 → 9) and 1.2
kpc resolution [C II] line observations of the dusty star-forming galaxy
(SFG) HXMM05—carried out with the Karl G. Jansky Very Large Array,
the Combined Array for Research in Millimeter-wave Astronomy, the
Plateau de Bure Interferometer, and the Atacama Large
Millimeter/submillimeter Array, measuring an unambiguous redshift of z =
2.9850 ± 0.0009. We find that HXMM05 is a hyperluminous infrared
galaxy ({L}IR} = (4 ± 1) × 1013 L
⊙) with a total molecular gas mass of (2.1 ± 0.7)
× 1011({α }CO}/0.8) M
⊙. The CO (J = 1 → 0) and [C II] emission are
extended over ∼9 kpc in diameter, and the CO line FWHM exceeds 1100
km s‑1. The [C II] emission shows a monotonic velocity
gradient consistent with a disk, with a maximum rotation velocity of
{v}{{c}} = 616 ± 100 km s‑1 and a
dynamical mass of (7.7 ± 3.1) × 1011 M
⊙. We find a star formation rate of
2900{}-595+750 M ⊙
yr‑1. HXMM05 is thus among the most intensely SFGs
known at high redshift. Photodissociation region modeling suggests
physical conditions similar to nearby SFGs, showing extended star
formation, which is consistent with our finding that the gas emission
and dust emission are cospatial. Its molecular gas excitation resembles
the local major merger Arp 220. The broad CO and [C II] lines and a pair
of compact dust nuclei suggest the presence of a late-stage major merger
at the center of the extended disk, again reminiscent of Arp 220. The
observed gas kinematics and conditions, together with the presence of a
companion and the pair of nuclei, suggest that HXMM05 is experiencing
multiple mergers as a part of the evolution.
This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.3847/1538-4357/aaf860