2016MNRAS.456.3509K

We present the Voigt profile analysis of 132 intervening Civ+Ciii components associated with optically thin HI absorbers at 2.1 < z < 3.4 in the 19 high-quality UVES/VLT and HIRES/Keck QSO spectra. For logN_C IV ∈[11.7, 14.1], N_C III ∝N_C IV^1.42±0.11 and <¡N_C III/N_C IV¡>   = 1.0±0.3 with a negligible redshift evolution. For 54 Civ components tied (aligned) with HI at logN_H I ∈[12.2, 16.0] and logN_C IV ∈[11.8, 13.8], the gas temperature Tb estimated from absorption line widths is well approximated to a Gaussian peaking at logTb ∼ 4.4±0.3 for logTb ∈ [3.5, 5.5], with a negligible non-thermal contribution. For 32 of 54 tied Hi+Civ pairs, also tied with Ciii at logN_C III ∈[11.7, 13.8], we ran both photoionization equilibrium (PIE) and non-PIE (using a fixed temperature Tb) cloudy models for the Haardt-Madau QSOs+galaxies 2012 UV background. We find evidence of bimodality in observed and derived physical properties. High-metallicity branch absorbers have a carbon abundance [C/H]temp ≥ -1.0, a line-of-sight length Ltemp ≤ 20kpc and a total (neutral and ionized) hydrogen volume density lognH,temp ∈ [-4.5, -3.3] and logTb ∈ [3.9, 4.5]. Low-metallicity branch absorbers have [C/H]temp ≤ -1.0, Ltemp ∈ [20, 480]kpc and lognH,temp ∈ [-5.2, -4.3] and logTb ∼ 4.5. High-metallicity branch absorbers seem to be originated from extended discs, inner haloes or outflowing gas of intervening galaxies, while low-metallicity absorbers are produced by galactic haloes or the surrounding intergalactic medium filament.