A High-Resolution Survey for Low-Redshift CIV Absorbers

Abstract

We present results from a survey for low-redshift CIV absorbers in the sight lines to nine QSOs. Using echelle spectra obtained with the Space Telescope Imaging Spectrograph (STIS) at 7 km s^-1 resolution, we robustly identify six CIV systems. All systems show at least the CIV doublet and HI Lyα; Si III, CIII, O VI, and higher Lyman series lines are also detected in several of these absorbers in the STIS data and complementary Far Ultraviolet Spectroscopic Explorer (FUSE) spectra. We calculate the number of CIV systems per unit redshift (dN/dz) and the cosmological mass density of the CIV ions (Ω_CIV) We find dN/dz = 5.2 ± 2.7 for absorbers with a rest-frame equivalent width greater than 38 mÅ. Comparison of our estimate of Ω_CIV at z > 0.1 to analogous measurements at z < 2 provides a preliminary indication that the metallicity of the IGM is increasing with time. These results may have implications for understanding the effectiveness of observed galactic-scale outflows at high-z at enriching the IGM.