2010ApJ...708..868C

We surveyed the Hubble Space Telescope UV spectra of 49 low-redshift quasars for z < 1 C IV candidates, relying solely on the characteristic wavelength separation of the doublet. After consideration of the defining traits of C IV doublets (e.g., consistent line profiles, other associated transitions, etc.), we defined a sample of 38 definite (group G = 1) and five likely (G = 2) doublets with rest equivalent widths W_r for both lines detected at. We conducted Monte Carlo completeness tests to measure the unblocked redshift (Δz) and co-moving path length (ΔX) over which we were sensitive to C IV doublets of a range of equivalent widths and column densities. The absorber line density of (G = 1+2) doublets is for log N(C⁺³) ≥ 13.2, and has not evolved significantly since z = 5. The best-fit power law to the G = 1 frequency distribution of column densities has coefficient k = 0.67^+0.18_–0.16x10^–14 cm2 and exponent α_N= -1.50^+0.17 _–0.19, where N₀= 10¹⁴ cm2. Using the power-law model of f(N(C⁺³)), we measured the C⁺³ mass density relative to the critical density: for 13 ≤ log N(C⁺³) ≤ 15. This value is a 2.8±0.7 increase in compared to the error-weighted mean from several 1 < z < 5 surveys for C IV absorbers. A simple linear regression to over the age of the universe indicates that has slowly but steadily increased from z = 5 -> 0, with.