Abstract
Quasars are among the most luminous objects in the Universe, and therefore they can be detected and investigated in detail even at very high redshifts, up to z > 6 (Fan et al. 2001, 2003, 2004). The prominent emission line spectrum of high redshift quasars contains important information on the enrichment history of the gas and, therefore, provide constraints on the star formation history in their host galaxies (Hamann & Ferland 1999). We investigate the metallicity of the Broad Line Region (BLR) in a sample of 27 quasars in the redshift range at 4 < z ≤ 6.4, by using near-IR and optical spectra. We focus on the ratio of the broad emission lines (SiIV λ 1398+OIV λ 1402)/CIV λ 1549, which is a good metallicity tracer of the BLR. Here, we present measurements of the (SiIV+OIV)/CIV ratio with the goal of better investigating the metallicity evolution of quasars in the early Universe.
