The CGM and IGM at z$\sim$5: metal budget and physical connection

Abstract

We present further results of a survey for absorption line systems in the spectra of four high redshift quasars (5.79 $\le$ z${}_{\text{em}}$ $\le$ 6.13) obtained with the ESO Very Large Telescope X-Shooter. We identify 36 $\text{CIV}$ and 7 $\text{SiIV}$ systems with a $\ge$ 5$\ddot{I}ƒ$ significance. The highest redshift $\text{CIV}$ and $\text{SiIV}$ absorbers identified in this work are at z = 5.80738 $\pm$ 0.00017 and z = 5.77495 $\pm$ 0.00038, respectively. We compute the comoving mass density of $\text{SiIV}$ ($\hat{I}{\text{c◯}}_{\text{SiIV}}$) and find that it evolves from $\hat{I}{\text{c◯}}_{\text{SiIV}}$ = 4.3${}_{-2.1}^{+2.1}$ $\times$10${}^{-9}$ at <z> = 5.05 to $\hat{I}{\text{c◯}}_{\text{SiIV}}$ = 1.4${}_{-0.4}^{+0.6}$ $\times$10${}^{-9}$ at <z> = 5.66. We also measure $\hat{I}{\text{c◯}}_{\text{CIV}}$ = 1.6${}_{-0.1}^{+0.4}$ $\times$10${}^{-8}$ at <z> = 4.77 and $\hat{I}{\text{c◯}}_{\text{CIV}}$ = 3.4${}_{-1.1}^{+1.6}$ $\times$10${}^{-9}$ at <z> = 5.66. We classify our $\text{CIV}$ absorber population by the presence of associated $\text{low}$ and/or $\text{high ionisation}$ systems and compute their velocity width ($\hat{I}”$v${}_{90}$). We find that all $\text{CIV}$ systems with $\hat{I}”$v${}_{90}$ > 200 kms${}^{-1}$ have associated $\text{low ionisation}$ systems. We investigate two such systems, separated by 550 physical kpc along a line of sight, and find it likely that they are both tracing a multi-phase medium where hot and cold gas is mixing at the interface between the CGM and IGM. We further discuss the \textrm{MgII} systems presented in a previous work and we identify 5 $\text{SiII}$, 10 $\text{AlII}$, 12 $\text{FeII}$, 1 $\text{CII}$, 7 $\text{MgI}$ and 1 $\text{CaII}$ associated transitions. We compute the respective comoving mass densities in the redshift range 2 to 6, as allowed by the wavelength coverage.

Accepted for publication in MNRAS 22 pages, 19 figures, 6 tables