XQ-100. X-shooter quasar spectra

We analyse the spectra of 100 quasars with 3.5<z_em_<4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an ~8{sigma} excess in the CIV number density within 10000km/s of the quasar emission redshift with respect to the random occurrence of NALs.

This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000km/s cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10000km/s when weak absorbers (equivalent width <0.2{AA}) are also considered.