Precious Metals in SDSS Quasar Spectra I: Tracking the Evolution of Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of Systems

TL;DR

This study analyzes thousands of CIV quasar absorption systems from SDSS data to track the evolution of metal-enriched gas in the universe from redshift 4.5 to 1.5, revealing a steady increase in cosmic metal enrichment over 12 billion years.

Contribution

It provides the largest intermediate-redshift CIV absorber sample to date and models the equivalent width distribution with an exponential, offering new insights into the evolution of cosmic metal enrichment.

Findings

CIV absorber frequency distribution is well modeled by an exponential.

The co-moving line density of CIV increases by a factor of ~2.4 from z=4.55 to 1.96.

There is an approximately 10-fold increase in CIV line density from z~6 to 0.

Abstract

We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release 7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6 \AA. We analyzed the sample as a whole and in ten small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift, increasing by a factor of 2.37+/-0.09 from z = 4.55 to 1.96, then plateauing at dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1 (ultraviolet) and z > 5 (infrared) surveys, we see an approximately 10-fold increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12 Gyr lifetime of the universe.