On the cool gaseous haloes of quasars

TL;DR

This study investigates the gaseous halos of quasars using optical spectroscopy of QSO pairs, revealing absorption features that suggest extended gaseous regions similar to those around normal galaxies, with some differences in absorption strength and distribution.

Contribution

It provides new observational evidence on the extent and properties of quasar gaseous halos through analysis of MgII and CIV absorption features in QSO pairs.

Findings

Strong absorption systems are present beyond 70 kpc, unlike normal galaxies.

Absence of MgII absorption in the QSO's own gas, but presence of CIV in some cases.

Absorbing gas distribution around QSOs is consistent with that of galaxies when considering galaxy mass.

Abstract

We present optical spectroscopy of projected QSO pairs to investigate the MgII and the CIV absorption features imprinted on the spectrum of the background object by the gaseous halo surrounding the foreground QSO. We observed 13 projected pairs in the redshift range 0.7<z<2.2 spanning projected separations between 60 kpc and 120 kpc. In the spectra of the background QSOs, we identify MgII intervening absorption systems associated to the foreground QSOs in 7 out of 10 pairs, and 1 absorption system out of 3 is found for CIV. The distribution of the equivalent width as a function of the impact parameter shows that, unlike the case of normal galaxies, some strong absorption systems (EWr > 1 Ang) are present also beyond a projected radius of ~70 kpc. If we take into account the mass of the galaxies as an additional parameter that influence the extent of the gaseous haloes, the distribution of the absorptions connected to the QSOs is consistent to that of galaxies. In the spectra of the foreground QSOs we do not detect any MgII absorption lines originated by the gas surrounding the QSO itself, but in 2 cases these features are present for CIV. The 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. Based on observations undertaken at the European Southern Observatory (ESO) Very Large Telescope (VLT) under Programmes 085.B-0210(A) and 086.B-0028(A).