EVIDENCE FOR ROTATION IN THE GALAXY AT Z=3.15 RESPONSIBLE FOR A DAMPED LYMAN-ALPHA ABSORPTION SYSTEM IN THE SPECTRUM OF Q2233+1310

Proof of the existence of a significant population of normal disk gala xies at redshift z > 2 would have profound implications for theories o f structure formation and evolution. We present evidence based on Keck HIRES spectra that the damped Ly alpha absorber at z = 3.15 toward th e quasar Q2233 + 1310 may well be such an example. Djorgovski et al. h ave recently detected the Ly alpha emission from the absorber, which w e assume is at the systemic redshift of the absorbing galaxy. By exami ning the profiles of the metal absorption lines arising from the absor bing galaxy in relation to its systemic redshift, we find strong kinem atical evidence for rotation. Therefore the absorber is likely to be a disk galaxy. The inferred circular velocity for the galaxy is greater than or equal to 200 km s(-1). With a separation of similar or equal to 17 kpc (q(0) = 0.1, H-0 = 75) between the galaxy and the quasar sig ht line, the implied dynamic mass for the galaxy is greater than or eq ual to 1.6 x 10(11) M.. The metallicity of the galaxy is found to be [ Fe/H] = -1.4, typical of damped Ly alpha galaxies at such redshifts. H owever, in another damped Ly alpha absorber at z = 2.81 toward Q0528-2 505, no kinematical evidence for galactic rotation is evident. In the latter case, the damped Ly alpha absorber occurs near the background q uasar in redshift, so its properties may be influenced by the backgrou nd quasar. These represent the only two cases at present for which the technique used here may be applied. Future applications of the same t echnique to a large sample of damped Ly alpha galaxies may allow us to determine if a significant population of disk galaxies already existe d only a few billion years after the big bang.