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

TL;DR

This survey of low-redshift C IV absorbers reveals their properties, metallicity, and origins, showing they are predominantly photoionized, metal-enriched, and not always associated with galaxy overdensities, informing our understanding of circumgalactic and intergalactic media.

Contribution

First comprehensive low-redshift C IV absorber survey using Hubble data, characterizing their properties, metallicities, and relationship with galaxies, advancing knowledge of cosmic metal distribution.

Findings

Most C IV systems have simple kinematics with 1-2 components.

C IV systems are predominantly photoionized with solar or higher metallicities.

Metallicity of C IV-bearing gas is an order of magnitude higher than high-redshift IGM.

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 ($T\leq 10^5$ K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C IV line density of $d\mathcal{N}/dX = 5.1\pm 1.0$ for $\log [N(C~IV)~(cm^{-2})]\geq12.9$, and $\Omega_{C~IV}=(8.01\pm 1.62) \times 10^{-8}$ for $12.9 \leq \log [N(C~IV)~(cm^{-2})] \leq 15.0$. The C IV bearing diffuse gas in the $z < 0.16$ Universe has a metallicity of $(2.07~{\pm}~0.43)~\times~10^{-3}$ Z$_{\odot}$, an order of magnitude more than the metal abundances in the IGM at high redshifts ($z \gtrsim 5$), and consistent with the slow build-up of metals in the diffuse circum/intergalactic space with cosmic time. For $z<0.015$ (complete above $L>0.01L^\star$), the Sloan Digital Sky Survey provides a tentative evidence of declining covering fraction for strong C IV ($N>10^{13.5}~cm^{-2}$) with $\rho$ (impact parameter) and $\rho/R_\mathrm{vir}$. 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 over-dense regions complete for $L>0.13L^\star$