ZINC AND CHROMIUM ABUNDANCES IN A 3RD DAMPED LYMAN-ALPHA SYSTEM AT INTERMEDIATE REDSHIFT

We have determined the metallicity of the z(abs) = 1.0093 damped Lyman alpha system in the bright QSO EX 0302-223; this is only the third su ch measurement at redshifts z less than or similar to 1. Unlike the pr evious two cases, we find that the abundance of Zn is only a factor of similar to 2 lower than in the Galactic interstellar medium today and is entirely compatible with the typical metallicity of stars in the M ilky Way disk at a look-back time of 9.5 Gyrs. Although the galaxy res ponsible for producing the absorption system has yet to be positively identified, our observations show that galaxies on a chemical evolutio n path similar to that of the Milky Way do contribute to the damped Ly man alpha population at intermediate redshifts. Cr is 2.5 times less a bundant than Zn, presumably because of depletion onto dust; however, t he degree of depletion is less severe than in diffuse interstellar clo uds in the disk of our Galaxy and in the Magellanic Clouds. Evidently, the interstellar environment in damped Lyman alpha galaxies is less c onducive to the formation and survival of dust grains (and molecular h ydrogen), but the physical processes at the root of this effect have y et to be clarified.