Optically thin CIII absorbers at z~2.5

For logN_CIV_ in [11.7, 14.1], N_CIII_{propto}N_CIV_^1.42+/-0.11^ and <N_CIII}/N_CIV>=1.0+/-0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at logN_HI_ in [12.2, 16.0] and logN_CIV_ in [11.8, 13.8], the gas temperature T_b_ estimated from absorption line widths is well approximated to a Gaussian peaking at logT_b_~4.4+/-0.3 for logT_b_ in [3.5, 5.5], with a negligible non-thermal contribution.

For 32 of 54 tied HI+CIV pairs, also tied with CIII at logN_CIII_ in [11.7, 13.8], we ran both photoionization equilibrium (PIE) and non-PIE (using a fixed temperature T_b_) 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 L_temp_<=20kpc and a total (neutral and ionized) hydrogen volume density logn_H,temp_ in [-4.5, -3.3] and logT_b_ in [3.9, 4.5].