2000ApJ...543...24V

Zinc is a good indicator of metallicity in damped Lyα (DLA) systems because it is almost unaffected by dust depletion. However, the use of zinc as a tracer of metallicity evolution has been hampered by the difficulty of detecting the Zn II resonance lines at high redshift. The measurement of zinc abundance in a DLA system at z_abs>3 obtained by means of the UVES spectrograph at the VLT prompted us to reanalyze the full sample of zinc abundances present in the literature to search for a metallicity-redshift relation in DLA systems. A study of the metallicities of individual systems shows evidence for an anticorrelation between [Zn/H] and redshift, supported by different types of statistical tools. The zinc metallicity decreases by -0.3±0.1 dex per unit redshift interval in the range 0.5≲z_abs≲3.5. This rate is in good agreement with that found by Savaglio, Panagia, & Stiavelli in their recent study of DLA abundances corrected for dust depletion. The present result does not require a knowledge of the dust depletion pattern(s) in DLA systems. On the other hand, analysis of the column-density-weighted metallicity of the sample, Z, does not show a clear evidence for redshift evolution, consistent with previous studies of zinc abundances. We propose that the apparent lack of evolution of Z is due to the combination of selection bias effects together with the extreme sensitivity of Z to low-number statistics.