THE LAST EIGHT-BILLION YEARS OF INTERGALACTIC C IV EVOLUTION

Abstract

We surveyed the HST 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 6 likely (G = 2) doublets with rest equivalent widths Wr for both lines detected at ≥ 3σWr. We conducted Monte-Carlo completeness tests to measure the unblocked redshift (∆z) and co-moving pathlength (∆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 dNC IV/dX = 4.2 +0.7 −0.6 for log N(C+3) ≥ 13.2, and dNCIV/dX has not evolved significantly since z = 5. The best-fit power-law to the frequency distribution of column densities f(N(C +3)) ≡ k(N(C +3)/N0) αN has coefficient k = 0.67 +0.12 −0.11 × 10−14 cm 2 and exponent αN = −1.54 +0.11 −0.12, where N0 = 1014 cm−2. Using the power-law fit to f(N(C +3)), we measured the C +3 mass density relative to the critical density: ΩC +3 = (6.07 +1.14 −1.01) × 10−8 for 13 ≤ log N(C +3) ≤ 15. This value is a 2.8 ± 0.5 increase in ΩC +3 compared to the errorweighted mean from several 1 < z < 5 surveys for C IV absorbers. The linear fit to ΩC +3 over the age of the Universe reveals that ΩC +3 has slowly but steadily increased from z = 5 → 0, with dΩC +3/dtage = (0.51 ± 0.16) × 10−8 Gyr −1. Subject headings: intergalactic medium – quasars: absorption lines – techniques: spectroscopic