Evidence for chemical evolution in the spectra of high redshift galaxies^*

¹ Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
² Universitätssternwarte München, Scheinerstraße 1, 81679 München, Germany
³ Universitäts-Sternwarte Göttingen, Geismarlandstraße 11, 37083 Göttingen, Germany

Corresponding author: D. Mehlert, dmehlert@lsw.uni-heidelberg.de

Received: 14 June 2002
Accepted: 1 July 2002

Abstract

Using a sample of 57 VLT FORS spectra in the redshift range (selected mainly from the FORS Deep Field survey) and a comparison sample with 36 IUE spectra of local () starburst galaxies we derive C iv and Si iv equivalent width values and estimate metallicities of starburst galaxies as a function of redshift. Assuming that a calibration of the C iv equivalent widths in terms of the metallicity based on the local sample of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about at the cosmic epoch corresponding to to about at . A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the local starburst galaxies our high-redshift objects tend to be overluminous for a fixed metallicity. Our observational results are in good agreement with published observational data by other authors and with theoretical predictions of the cosmic chemical evolution.