The Composite Spectrum of QSO Absorption Line Systems in DESI DR2
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.
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Cite
@article{arxiv.2512.02992,
title = {The Composite Spectrum of QSO Absorption Line Systems in DESI DR2},
author = {Lucas Napolitano and Adam D. Myers and Adam Tedeschi and Abhijeet Anand and Hiram K. Herrera-Alcantar and Jessica Aguilar and Steven Ahlen and Stephen Bailey and Segev BenZvi and Davide Bianchi and David Brooks and Todd Claybaugh and Andrei Cuceu and Axel de la Macorra and Arjun Dey and Biprateep Dey and Peter Doel and Andreu Font-Ribera and Jaime E. Forero-Romero and Enrique Gaztanaga and Satya Gontcho A Gontcho and Gaston Gutierrez and Julien Guy and Dick Joyce and Anthony Kremin and Martin Landriau and Laurent Le Guillou and Marc Manera and Aaron Meisner and Ramon Miquel and John Moustakas and Seshadri Nadathur and Nathalie Palanque-Delabrouille and Will Percival and Francisco Prada and Ignasi Perez-Rafols and Graziano Rossi and Eusebio Sanchez and David Schlegel and Michael Schubnell and Joesph Harry Silber and David Sprayberry and Gregory Tarle and Benjamin Alan Weaver and Rongpu Zhou and Hu Zou},
journal= {arXiv preprint arXiv:2512.02992},
year = {2025}
}
Comments
16 pages, 9 figures