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 d N/dX = 5.1± 1.0 for log [N(Civ)(cm-2)] ≥ 12.9, and ΩCiv=(8.01± 1.62) × 10-8 for 12.9 ≤ log [N(Civ)(cm-2)] ≤ 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 > 1013.5 cm-2) with ρ (impact parameter) and ρ/Rvir. 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∗.