  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.
