The CGM and IGM at z$\sim$5: metal budget and physical connection
  We present further results of a survey for absorption line systems in the
spectra of four high redshift quasars (5.79 $\le$ z$_{\textrm{em}}$ $\le$ 6.13)
obtained with the ESO Very Large Telescope X-Shooter. We identify 36
$\textrm{CIV}$ and 7 $\textrm{SiIV}$ systems with a $\ge$ 5$\sigma$
significance. The highest redshift $\textrm{CIV}$ and $\textrm{SiIV}$ 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 $\textrm{SiIV}$
($\Omega_{\textrm{SiIV}}$) and find that it evolves from
$\Omega_{\textrm{SiIV}}$ = 4.3$^{+2.1}_{-2.1}$ $\times$10$^{-9}$ at <z> = 5.05
to $\Omega_{\textrm{SiIV}}$ = 1.4$^{+0.6}_{-0.4}$ $\times$10$^{-9}$ at <z> =
5.66. We also measure $\Omega_{\textrm{CIV}}$ = 1.6$^{+0.4}_{-0.1}$
$\times$10$^{-8}$ at <z> = 4.77 and $\Omega_{\textrm{CIV}}$ =
3.4$^{+1.6}_{-1.1}$ $\times$10$^{-9}$ at <z> = 5.66. We classify our
$\textrm{CIV}$ absorber population by the presence of associated $\textit{low}$
and/or $\textit{high ionisation}$ systems and compute their velocity width
($\Delta$v$_{90}$). We find that all $\textrm{CIV}$ systems with
$\Delta$v$_{90}$ > 200 kms$^{-1}$ have associated $\textit{low ionisation}$
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 $\textrm{SiII}$, 10 $\textrm{AlII}$, 12 $\textrm{FeII}$, 1
$\textrm{CII}$, 7 $\textrm{MgI}$ and 1 $\textrm{CaII}$ associated transitions.
We compute the respective comoving mass densities in the redshift range 2 to 6,
as allowed by the wavelength coverage.
