A Survey of Metal Lines at High-redshift (I) : SDSS Absorption Line Studies - The Methodology and First Search Results for OVI

TL;DR

This paper presents a systematic search for OVI metal line absorbers in SDSS quasar spectra, introducing a new detection method, and reports a significant increase in known high-redshift OVI absorbers, aiding understanding of the intergalactic medium.

Contribution

It introduces a novel search algorithm for OVI absorbers in SDSS data and provides a large, refined sample of high-redshift OVI candidates, enhancing previous surveys.

Findings

Identified 145 secure OVI absorber candidates at high redshift.

Discovered many new OVI absorbers beyond z > 2.7.

Most candidates are previously undetected by automated methods.

Abstract

We report the results of a systematic search for signatures of metal lines in quasar spectra of the Sloan Digital Sky Survey (SDSS) Data Release 3(DR3), focusing on finding intervening absorbers via detection of their OVI doublet. Here we present the search algorithm, and criteria for distinguishing candidates from spurious Lyman $\alpha${} forest lines. In addition, we compare our findings with simulations of the Lyman $\alpha${} forest in order to estimate the detectability of OVI doublets over various redshift intervals. We have obtained a sample of 1756 OVI doublet candidates with rest-frame equivalent width > 0.05 \AA{} in 855 AGN spectra (out of 3702 objects with redshifts in the accessible range for OVI detection). This sample is further subdivided into 3 groups according to the likelihood of being real and the potential for follow-up observation of the candidate. The group with the cleanest and most secure candidates is comprised of 145 candidates. 69 of these reside at a velocity separation > 5000 km/s from the QSO, and can therefore be classified tentatively as intervening absorbers. Most of these absorbers have not been picked up by earlier, automated QSO absorption line detection algorithms. This sample increases the number of known OVI absorbers at redshifts beyond z$_{abs} > 2.7 substantially.