Medium-resolution spectroscopy of galaxies with redshifts 2.3 $< z <$ 3.5

Abstract

Using FORS2 at the ESO VLT we obtained medium-resolution ($R \approx 2000$) spectra of 12 galaxies with $2.37 \leq z \leq 3.40$ in the FORS Deep Field. Two individual spectra with good S/N and a composite of all 12 spectra were used to derive properties of the stellar and interstellar absorption lines of galaxies in this redshift range. Systematic differences between the individual spectra were found for the strength and profiles of the intrinsic interstellar lines. For eight spectra with sufficient S/N , we measured the “1370” and “1425” metallicity indices, from which we find for our sample that galaxies at $ z > 3$ have lower mean metallicity than galaxies at $2.3 < z < 3$. However uncertainties remain concerning the absolute calibration of the metallicity tracers in use for high-redshift galaxies. Additional modeling will be needed to resolve these uncertainties.