WSRT Detections of HI Absorption in the z=3.4 Damped Lyman $\alpha$ System towards PKS 0201+113
Session 72 -- High Z Line Measurements; Gravitational Microlensing: Distance Determination
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [72.01] WSRT Detections of HI Absorption in the z=3.4 Damped Lyman $\alpha$ System towards PKS 0201+113

S. A. Baum (STScI), A. G. de Bruyn (NFRA), C. P. O'Dea (STScI)

White et al. (1993, ApJ 407, 456) reported the detection of a damped Lyman $\alpha$ system at a redshift of 3.388 in the spectrum of the quasar PKS 0201+113. We have used the Westerbork Synthesis Radio Telescope (WSRT) to conduct an extensive search for HI absorption associated with this high redshift damped Lyman $\alpha$ system. At a redshift of 3.388, the 21 cm line of HI is fortuitously redshifted into the 90cm observing band of WSRT. This coupled with the radio brightness of PKS 0201+113, a powerful, core-dominated, GHz-peaked spectrum radio quasar, allowed us to perform a sensitive search for neutral hydrogen associated with the absorbing system.

Following an extensive search using a variety of bandwidths and velocity resolutions, we have detected two weak absorption lines (at the five sigma confidence level) consistent with the optical redshift of the absorbing system. The two lines have FWHM of $\sim 10$ km sec$^{-1}$, a velocity separation of $\sim 25$ km sec$^{-1}$, and optical depths of $\tau \sim 0.05$. The low optical depth, combined with the high required column density for the damped Lyman $\alpha$ absorption, implies a spin temperature of order 1000K. We discuss the implications of these results for the nature of damped Lyman $\alpha$ absorbers and proto galaxies at high redshifts.