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

Abstract

We present 0.1" resolution near-infrared integral field spectroscopy of Halpha in a z=1.4781 star forming galaxy, Q2343-BM133. These observations were obtained with OSIRIS (OH Suppressing Infra-Red Imaging Spectrograph) using the W.M. Keck Observatory Laser Guide Star Adaptive Optics system. Halpha emission is resolved over a 0.8" (6.8 kpc) x 0.5" (4.3 kpc) region with a 0.1" spatial resolution. We find a global flux of 4.2+/-0.6x10^{-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 NII/Halpha < 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 Msun yr^{-1}, and a dereddened SFR of 66+/-9 Msun yr^{-1}. Two-dimensional kinematics for Q2343-BM133 fit well with an inclined-disk model, with which we estimate an enclosed mass of 4.3x10^{9} Msun within 5.5 kpc. A possible merger scenario is also presented, and can not be fully ruled out. We derive a virial mass of 1.1x10^{10} Msun 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.