On the cool gaseous haloes of quasars

We present the optical spectroscopy of projected quasar (QSO) pairs in order to investigate the Mg ii and C iv absorption features imprinted on the spectrum of the background object by the gaseous halo surrounding the foreground QSO. We have observed 13 projected pairs in the redshift range 0.7 z F 2.2, spanning projected separations between 60 and 120 kpc. In the spectra of the background QSOs, we have identified Mg ii intervening absorption systems associated with the foreground QSOs in seven out of 10 pairs, and one absorption system out of three is found for C iv. The distribution of the equivalent width (EW) as a function of the impact parameter shows that, unlike the case of normal galaxies, some strong absorption systems (EWr > 1 Å) are also present beyond a projected radius of ∼70 kpc. If we take into account the mass of the galaxies as an additional parameter that influences the extent of the gaseous haloes, the distribution of the absorptions connected to the QSOs is consistent with that of galaxies. In the spectra of the foreground QSOs, we do not detect any Mg ii absorption lines originated by the gas surrounding the QSO itself, but in two cases, these features are present for C iv. A comparison between the absorption features observed in the transverse direction and those along the line of sight allows us to comment on the distribution of the absorbing gas and on the emission properties of the QSOs.