Resolving a merger in a hyper-luminous submillimeter galaxy at z=2.82

Abstract

We present the resolved properties of the $z=2.82$ Hyper Luminous Infrared Galaxy (HyLIRG) HS170850.1, the brightest 850$\mu$m source found in the SCUBA-2 followup to the Keck Baryonic Structure Survey fields (S${}_{850\mu \mathrm{m}}=$19.5 mJy), and amongst the most luminous starbursts known at any redshift. Using the IRAM-NOEMA interferometer in the highest resolution A-configuration, we resolve the source into two components separated by $\sim$8 kpc, visible as blue shifted and red shifted ${}^{12}$CO(5-4) lines, exhibiting the expected kinematic properties of a major merger between two gas-rich galaxies. The combined merger system is traced over 2.3${}^{\prime \prime }$ or 18.3 kpc. Each component of the merger shows ordered gas motions suggestive of a massive, turbulent disk. We measure the masses of the blue and red disks as (1.5 $\pm$ 0.2) $\times 10^{11}$ M${}_{\odot }$ and (0.71 $\pm$ 0.22) $\times 10^{11}$ M${}_{\odot }$ respectively. The more massive disk component shows broad wings in the CO line, offset by $\sim$3 kpc from the disk centroid along the major axis, and extending to velocities $\sim \pm$1000 km ${\mathrm{s}}^{-1}$ from systemic velocity. We interpret this as either a possible bipolar outflowing component, or more likely a warping or tidal structure in the CO disk. Comparing the properties of HS170850.1 to other submillimeter detected galaxies with comparably bright 850$\mu$m luminosities suggests that ongoing gas-rich mergers, or at least a clustered/group environment lead to these most extreme starburst phases.

13 pages, 5 Figures, 2 Tables

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