A Radio Search for High Redshift HI Absorption

The rare damped Ly α systems seen in absorption against the UV continuum of high redshift QSOs nonetheless dominate the observed neutral gas at high redshift. HI 21cm absorption studies of these systems are challenging and only a handful of have been detected hitherto (Carilli et al., these proceedings). HI 21cm observations are however of great value because they potentially yield physical information (velocity dispersion, spin temperature, size), that cannot be obtained by other means.