Intermediate resolution spectra of quasars with z>2.

Abstract

20 quasars (optically selected) with redshifts in the range 2-2.7 have been observed with a spectral resolution of 7 A, for a statistical study of the properties of the emission lines and also to find interesting candidates for detailed studies. The distribution of the observed equivalent width (EW) of C IV is centered at 95 A and the distribution of the full width at half maximum (FWHM) of C IV, is centered at 5000 km s^-1^ in agreement with previous results obtained from independent data. Modelling of the C IV line with two gaussian components shows the broader component to be blueshifted, the average shift being 11 A or 600 km s^-1^. The ratio of the flux emitted in the two components is approximately 1. In three of the four quasars with the narrowest C IV lines (FWHM in the range 2000-3000 km s^-1^), the emission feature at 1909 A is resolved nicely into the two lines Si III] λ1892 and C III] λ1909 suggesting that in many cases the Fe III UV 34 triplet is not a dominant contributor to this feature. In the fourth one the 1909 A feature is weak and low-contrast. In the quasar 0353-38 which was found by Osmer to have anomalous abundances and in particular a high N/C ratio, we find that the C IV line is narrower than [N III] λ1750. In the gas producing the broadest component of the emission line the ratio N/C is twice as large as previously determined by Osmer, but appears normal in the region emitting the narrow component. Four low ionization absorption line systems are found with z ranging from 0.55 to 1.28, two of these systems being in the same quasar (0254-40).