Integral Field Spectroscopy of a Candidate Disk Galaxy at z ~ 1.5 Using Laser Guide Star Adaptive Optics

We present 0.1'' resolution near-infrared integral field spectroscopy of Hα in a z = 1.4781 star-forming galaxy, Q2343-BM133. These observations were obtained with the OH Suppressing Infra-Red Imaging Spectrograph (OSIRIS) using the W. M. Keck Observatory laser guide star adaptive optics (LGS AO) system. Hα emission is resolved over a 0.8′′(6.8 kpc) × 0.5′′(4.3 kpc) region with a 0.1'' spatial resolution. We find a global flux of 4.2 ± 0.6 × 10-16 ergs s-1 cm-2, and detect a spatially resolved velocity gradient of ~134 km s-1 across the galaxy and a global velocity dispersion of 73 ± 9 km s-1. An upper limit of [N ]/Hα ≲ 0.12 is inferred, which implies that this galaxy is not dominated by an active galactic nucleus and has a metallicity at or below 1/2 solar metallicity. We derive a star formation rate (SFR) of 47 ± 6 M☉ yr-1 and a dereddened SFR of 66 ± 9 M☉ yr-1. Two-dimensional kinematics for Q2343-BM133 fit well with an inclined disk model, with which we estimate an enclosed mass of 4.3 × 109 M☉ within 5.5 kpc. A possible merger scenario is also presented, and cannot be fully ruled out. We derive a virial mass of 1.1 × 1010 M☉ for a disk geometry, using the observed velocity dispersion. We propose that Q2343-BM133 is currently at an early stage of disk formation at a look-back time of 9.3 Gyr.