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 H alpha in a z = 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. H alpha emission is resolved over a 0: 800( 6: 8kpc); 0: 500( 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 similar to 134 km s(-1) across the galaxy and a global velocity dispersion of 73 +/- 9 km s(-1). An upper limit of [N II]/ H alpha less than or similar to 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-circle dot yr(-1) and a dereddened SFR of 66 +/- 9 M-circle dot yr(-1). Two- dimensional kinematics for Q2343 - BM133 fit well with an inclined diskmodel, with which we estimate an enclosed mass of 4: 3; 10(9) M-circle dot 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; 10(10) M-circle dot 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.