The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

TL;DR

This study constructs a high signal-to-noise composite spectrum of quasar absorption lines from DESI DR2, revealing over 70 lines and emission features, aiding future research on galaxy environments.

Contribution

It introduces a large, median-combined spectrum of quasar absorption systems with detailed line identification, enhancing analysis of intervening galaxy media.

Findings

Over 70 absorption lines identified

Oxygen and hydrogen emission features detected with high S/N

Atlas of line centroids and equivalent widths provided

Abstract

We present details regarding the construction of a composite spectrum of quasar (QSO) absorption line systems. In this composite spectrum we identify more than 70 absorption lines, and observe oxygen and hydrogen emission features at a higher signal-to-noise ratio than in any previous study. As the light from a distant quasar travels towards an observer, it may interact with the circumgalactic medium environment of an intervening galaxy, forming absorption lines. In order to maximize the signal of these absorption lines, we have selected a sample of 238,838 quasar spectra from the second data release of the Dark Energy Spectroscopic Instrument (DESI), each identified to have absorption lines resulting from such an interaction. By stacking these spectra in the restframe of the absorption, and calculating a median composite spectrum, we are able to isolate and enhance these absorption lines. We provide a full atlas of all detected absorption and emission lines as well as their fit centroids and equivalent width values. This atlas should aid in future studies investigating the compositions and physical conditions of these absorbers.