The CGM and IGM at z ~ 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 ≤ zem ≤ 6.13) obtained with the ESO Very Large Telescope X-Shooter. We identify 36 C iv and 7 Si iv systems with a ≥ 5σ significance. The highest redshift C iv and Si iv absorbers identified in this work are at z = 5.80738 ± 0.00017 and z = 5.77495 ± 0.00038, respectively. We compute the comoving mass density of Si iv (⁠ΩSiIV⁠) and find that it evolves from ΩSiIV = 4.3+2.1−2.1 ×10−9 at ⟨z⟩ = 5.05 to ΩSiIV = 1.4+0.6−0.4 ×10−9 at ⟨z⟩ = 5.66. We also measure ΩCIV = 1.6+0.4−0.1 ×10−8 at ⟨z⟩ = 4.77 and ΩCIV = 3.4+1.6−1.1 ×10−9 at ⟨z⟩ = 5.66. We classify our C iv absorber population by the presence of associated low- and/or high-ionization systems and compute their velocity width (Δv90). We find that all C iv systems with Δv90 > 200 km s−1 have associated low-ionization 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 multiphase medium where hot and cold gas is mixing at the interface between the circumgalactic medium and intergalactic medium. We further discuss the Mg ii systems presented in a previous work and we identify 5 Si ii, 10 Al ii, 12 Fe ii, 1 C ii, 7 Mg i, and 1 Ca ii associated transitions. We compute the respective comoving mass densities in the redshift range 2–6, as allowed by the wavelength coverage.