QSO cool gaseous haloes

Absorption lines in quasar (QSO) spectra provide a unique tool for probing the gas and dust content of foreground galaxies and of intergalactic medium at almost any redshift. These features are considered to be linked to large gaseous haloes around galaxies extending up to 100 kpc. We investigate the MgII  2800 and CIV 1540 absorption features of the gas in the halo of a foreground QSO  through the absorption imprinting on the spectra of a  background QSO that is closely aligned with the nearest  quasar .  

Despite a number of studies aimed at connecting metal absorption systems (in particular Mg II and C IV) with galaxy properties the origin of the absorbing gas is still unclear. However, in the last decades, it is progressively emerging a scenario in which the stronger absorption lines (rest frame equivalent width EWr∼> 1 A) are linked to winds driven by the star formation activity, while the weaker one are associated with inflows of gas onto the host galaxies.


                gtcdome           esovlt 


 qso pair abs


 qsoabs fig3



qsoabs fig6

At variance  with the case of inactive and less massive galaxies we find that relatively strong (EW  ~ 1 Ang) absorption features  are present out to a radius of 100 kpc. This suggests that a large extended halo is associated with  massive galaxies.  When account is taken for different masses we find no difference between absorptions properties associated with inactive (less massive) and active (more massive) galaxies. Since in the spectra of the foreground QSO there are no signs of MgII absorptions of the same strength seen in the background QSO, we argue that the absorbing gas around the QSO is not homogeneous, as a possible consequence of the non isotropic emission from the QSO.





Figure  Rest frame EW of Mg II(2796) absorption line as a function of projected distance and stellar mass for QSOs and galaxies. Red filled triangles are systems for which the absorption system was detected, while the empty ones are 3 upper limits. Empty blue and filled black circle are data for galaxies from Bar- ton & Cooke (2009) and Chen et al. (2010b), respectively. Black dashed line is the EWr vs. projected distance anti–correlation for galaxies including the scaling relation with stellar mass proposed by Chen et al. (2010b). For the x–axis we have adopted the same projection of Figure 3 in Chen et al. (2010b).








People: Renato Falomo 

Collaboration: E.P. FarinaA. Treves (Insubria University), J. Kotilainen (Tuorla,FIN, FINCA), R. Scarpa (GTC)


  • Farina, E.P., Falomo, R. Decarli, R. Treves, A. Kotilainen J.K., 2012 MNRAS 429 1267  xrXiv:1211.3433  
  • Farina, E.P., Falomo, R. Decarli, R. Treves, A. Kotilainen J.K. 2013 MNRAS, submitted
  • Falomo, R. , Farina, E.P.,  Decarli, R. Treves, A. Kotilainen J.K., 2012 IAU Symp 295 - XXVIII  IAU-GA , Beijing 



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