The rise of the C IV mass density at z<2.5

TL;DR

This study measures the evolution of C IV metal density in the intergalactic medium from redshift 1.5 to 4, revealing a significant increase at lower redshifts, which challenges previous assumptions of constancy.

Contribution

It provides a new, extensive measurement of Omega_CIV over a broad redshift range, more than doubling previous data coverage at z<2.5, and shows a rising trend contrary to earlier beliefs.

Findings

Omega_CIV increases towards lower redshifts

Sample includes over 1500 C IV lines

Contradicts previous constant behavior assumption

Abstract

The cosmic evolution of the metal content of the intergalactic medium puts stringent constraints on the properties of galactic outflows and on the nature of UV background. In this paper, we present a new measure of the redshift evolution of the mass density of C IV, Omega_CIV, in the interval 1.5 < z < 4 based on a sample of more than 1500 C IV lines with column densities 10^{12} < N(CIV) < 10^{15} cm^{-2}. This sample more than doubles the absorption redshift path covered in the range z<2.5 by previous samples. The result shows a significant increase of Omega_CIV towards the lower redshifts at variance with the previously pictured constant behaviour.