WSRT DETECTION OF HI ABSORPTION IN THE Z=3.4 DAMPED LY-ALPHA SYSTEM IN PKS-0201+113

We report the detection of a faint narrow HI absorption line at a reds hift of 3.38 against the quasar PKS 0201+113 which itself has an emiss ion redshift of 3.61. The absorption line redshift agrees, to within t he errors, with that of a damped Ly alpha line. The line has a halfwid th of about 9 km s(-1). Comparing the line equivalent width with the H I column density of the neutral gas we deduce a spin temperature for t he gas of about 1100 K. In view of the fact that the spin temperature is remarkably similar to that derived for other high redshift absorpti on systems we consider it unlikely that it is due to different lines-o f-sight for the ultraviolet continuum and the compact radio source. Th e high spin temperature may reflect a high kinetic temperature in most of the intervening HI. The HI in high redshift damped Ly alpha absorb ers may therefore contain relatively more warm gas than our own and ne arby galaxies. The damped Ly alpha system in PKS 0201+113 is currently the most distant system detected through the 21 cm line of atomic hyd rogen. Its properties appear to be remarkably similar to those of syst ems at redshifts around 1. If damped Ly alpha systems are due to proto disks and/or disks of spiral galaxies, then galaxies similar to those of present day spiral galaxies were already forming at a redshift of 3 .4. Following Wolfe ct al. (1976) we use the agreement between the red shifts of the 21 cm line and the optical resonance lines to constrain the possible variation, over the lookback time to the absorber, of the product of the fine structure constant, nuclear g factor for the prot on, and the masses of the electron and proton. We obtain a 3 sigma upp er limit of 5 x 10(-4) on the change in the ratio alpha(2)g(p)m(e)/m(p ) at a redshift of z = 3.4. The corresponding 3 sigma upper limit to t he rate of change of this ratio is 6 x 10(-14) yr(-1).