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 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 components. In the 22 C systems with well constrained H column densities, the temperatures from the 𝑏-values imply predominantly photoionized plasma (𝑇 ≤ 10 5 K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C line density of 𝑑N /𝑑𝑋 = 5.1±1.0 for log[𝑁 (C ) (cm −2 )] ≥ 12.9, and Ω C = (8.01±1.62) ×10 −8 for 12.9 ≤ log[𝑁 (C ) (cm −2 )] ≤ 15.0. The C 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 (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 absorption at 𝑧 < 0.051 is not coincident with galaxy over-dense regions complete for 𝐿 > 0.13𝐿 ★ .