The COS-legacy survey of C IV absorbers: properties and origins of the intervening systems

Abstract

We present here results from a survey of intervening C IV absorbers at z < 0.16 conducted using 223 sightlines from the Hubble Spectroscopic Legacy Archive. Most systems (83%) out of the total sample of 69 have simple kinematics with 1 or 2 C IV components. In the 22 C IV systems with well constrained H I column densities, the temperatures from the b-values imply predominantly photoionized plasma (T ≤ 10⁵ K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C IV line density of $\mathrm{ d}\mathcal {N}/\mathrm{ d}X = 5.1\pm 1.0$ for $\log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})]\ge 12.9$, and $\Omega _{\rm {C}\, \rm {\rm {iv}}}=(8.01\pm 1.62) \times 10^{-8}$ for $12.9 \le \log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})] \le 15.0$. The C IV bearing diffuse gas in the z < 0.16 Universe has a metallicity of (2.07 ± 0.43) × 10^-3 Z_⊙, an order of magnitude more than the metal abundances in the IGM at high redshifts (z ≳ 5), and consistent with the slow build-up of metals in the diffuse circum/intergalactic space with cosmic time. For z < 0.015 (complete above L > 0.01L^⋆), the Sloan Digital Sky Survey provides a tentative evidence of declining covering fraction for strong C IV (N > 10^13.5 cm^-2) with ρ (impact parameter) and ρ/R_vir. However, the increase at high separations suggests that strong systems are not necessarily coincident with such galaxies. We also find that strong C IV absorption at z < 0.051 is not coincident with galaxy overdense regions complete for L > 0.13L^⋆.