The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

Lucas Napolitano; Adam D. Myers; Adam Tedeschi; Abhijeet Anand; Hiram K. Herrera-Alcantar; Jessica Aguilar; Steven Ahlen; Stephen Bailey; Segev BenZvi; Davide Bianchi; David Brooks; Todd Claybaugh; Andrei Cuceu; Axel de la Macorra; Arjun Dey; Biprateep Dey; Peter Doel; Andreu Font-Ribera; Jaime E. Forero-Romero; Enrique Gaztanaga; Satya Gontcho A Gontcho; Gaston Gutierrez; Julien Guy; Dick Joyce; Anthony Kremin; Martin Landriau; Laurent Le Guillou; Marc Manera; Aaron Meisner; Ramon Miquel; John Moustakas; Seshadri Nadathur; Nathalie Palanque-Delabrouille; Will Percival; Francisco Prada; Ignasi Perez-Rafols; Graziano Rossi; Eusebio Sanchez; David Schlegel; Michael Schubnell; Joesph Harry Silber; David Sprayberry; Gregory Tarle; Benjamin Alan Weaver; Rongpu Zhou; Hu Zou

arXiv · 2512.02992

The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

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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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Lucas Napolitano, Adam D. Myers, Adam Tedeschi, Abhijeet Anand, Hiram K. Herrera-Alcantar, Jessica Aguilar, Steven Ahlen, Stephen Bailey, Segev BenZvi, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Arjun Dey, Biprateep Dey, Peter Doel, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztanaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Julien Guy, Dick Joyce, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Seshadri Nadathur, Nathalie Palanque-Delabrouille, Will Percival, Francisco Prada, Ignasi Perez-Rafols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Joesph Harry Silber, David Sprayberry, Gregory Tarle, Benjamin Alan Weaver, Rongpu Zhou, Hu Zou. 2025-12-02. The Composite Spectrum of QSO Absorption Line Systems in DESI DR2. https://arxiv.org/abs/2512.02992

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