Program: GN-2005B-Q-60

The nature of high redshift damped Lya (DLA) galaxies remains a controversial issue: are they massive disks, as inferred from absorption kinematics, or dwarf galaxies, as suggested by their chemical abundances? The determination of spin temperatures (T_s) by the combination of Ly alpha and 21 cm absorption observations provides a discriminant between these two scenarios: spiral galaxies typically have T_s of a few hundred K, whereas in metal-poor dwarf galaxies T_s > 1000 K. Initial observations indicate that no high z DLA out of the seven studied so far has a low T_s, in contrast to some 30% of z<2 systems. However, the statistics at z>2 are still very poor. We propose a survey towards radio-loud quasars aimed at finding DLAs suitable for 21 cm follow-up. Our survey will triple the number of T_s measurements at z>2, and will allow us to establish whether the spin temperatures are consistent with disks or dwarfs.