A Massive Disk Galaxy at z=1.34

Abstract

We report the discovery of a rapidly rotating disk in a K-selected galaxy at z=1.34. Spatially resolved kinematics are determined from deep, moderate resolution Keck spectroscopy covering the redshifted [OII] 3727 line. A conservative estimate of the maximum rotation velocity V_max = 290 +- 20 km/s, placing the galaxy among the most rapid rotators known. An HST WFPC2 image taken in the F814W filter (rest-frame U) shows that the [OII] emission originates in a ring of star forming regions ~3'' (~20 kpc) across. In the K-band the galaxy is compact, and its position coincides with the center of the star forming ring seen in the rest-frame near-UV. The galaxy has M_V = -22.4 +- 0.2 (~3 L*) in the rest-frame, and its spectral energy distribution is very well fitted by that of a redshifted Sb/c galaxy. The observed kinematics, morphology, and spectral energy distribution are consistent with a massive bulge-disk system at z=1.34. The lower limit on V_max gives an upper limit on the offset from the present-day Tully-Fisher relation. The galaxy is overluminous by less than 0.7 +- 0.4 magnitudes in rest-frame V, consistent with previous studies of disk galaxies at lower redshift. Taken together, these results suggest that some of the most luminous spiral galaxies in the nearby Universe were already in place ~10^10 yr ago, placing a constraint on models for their formation.