THE LAST EIGHT-BILLION YEARS OF INTERGALACTIC C IV EVOLUTION

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 >= 3 sigma(Wr). We conducted Monte Carlo completeness tests to measure the unblocked redshift (Delta z) and co-moving path length (Delta X) 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 dN(C) (IV)/dX = 4.1-(+0.7)(0.6) for log N(C(+3)) >= 13.2, and dN(C IV)/dX has not evolved significantly since z = 5. The best-fit power law to the G = 1 frequency distribution of column densities f(N(C(+3))) = k(N(C(+3))/N(0))(alpha N) has coefficient k = 0.67(-0.16)(+ 0.18) x 10(-14) cm(2) and exponent alpha(N) = -1.50(-0.19)(+0.17), where N(0) = 10(14) cm(-2). Using the power-law model of f(N(C(+3))), we measured the C(+3) mass density relative to the critical density: Omega(C+3) = (6.20(-1.52)(+1.82)) x 10(-8) for 13 <= logN(C(+3)) <= 15. This value is a 2.8 +/- 0.7 increase in Omega(C+3) compared to the error-weighted mean from several 1 < z < 5 surveys for C IV absorbers. A simple linear regression to Omega(C+3) over the age of the universe indicates that Omega(C+3) has slowly but steadily increased from z = 5 -> 0, with d Omega(C+3)/dt(age) = (0.42 +/- 0.2) x 10(-8) Gyr(-1).