  Measurements of Zn and Cr abundances in damped Lyman alpha systems at
absorption redshifts between 0.692 and 3.390 show that metals and dust are much
less abundant in high redshift galaxies than in the Milky Way today. We
conclude that the overall degree of metal enrichment of DLA galaxies
approximately 13.5 Gyr ago is 1/15 solar. The depletion of Cr is approximately
2, significantly less than in local interstellar clouds. We propose this
reflects an overall lower abundance of dust, and deduce a typical dust-to-gas
ratio of 1/30 of the Milky Way value, still sufficient to explain the weakness
of Lyman alpha emission from star-forming regions. We show that, despite claims
to the contrary, these conclusions are not inconsistent with recent high
resolution observations of DLAs with the Keck Telescope.

Astrophysics