The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

Abstract We present details regarding 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 any previous study. As the light from a distant quasar travels towards an observer, it may interact with the circumgalactic medium of an intervening galaxy, forming absorption lines. In order to maximize the signal of these absorption lines, we have selected a sample of 239,174 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 rest frame 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. We additionally provide analysis of composites constructed using subsamples of absorbers in both redshift and Mg ii equivalent width bins. We find that there is minimal redshift evolution across the considered absorber samples. Additionally, we find that dense gas signatures, such as the presence of Na I absorption, are strongest in the highest equivalent width absorber sample, and that the strengths of the Si IV and C IV absorption lines show a relatively weak correlation with Mg II equivalent width. This atlas should aid in future studies investigating the compositions and physical conditions of these absorbers.

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Publication Details

Journal
The Astronomical Journal
Published
2026-10-07
DOI
https://doi.org/10.3847/1538-3881/aea6da
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
0.00

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article

The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

R. R. Joyce, Abhijeet Anand, Rongpu Zhou, Michael S. Schubnell et al.
The Astronomical Journal
Galaxies: Formation, Evolution, Phenomena
article

The Composite Spectrum of QSO Absorption Line Systems in DESI DR2

R. R. Joyce, Abhijeet Anand, Rongpu Zhou, Michael S. Schubnell, N. Palanque‐Delabrouille, S. Nadathur, H. K. Herrera-Alcantar, Gregory Tarlé, L. Napolitano, Andreu Font-Ribera, Laurent Le Guillou, David Sprayberry, D. Bianchi, David J. Schlegel, Ignasi Pérez-Ràfols, Axel de la Macorra, S. Bailey, Martin Landriau, Marc Manera, Gaston Gutierrez, J. Aguilar, J. Guy, Eusebio Sanchez, Satya Gontcho A Gontcho, S. BenZvi, ENRIQUE GAZTAÑAGA, Andrei Cuceu, Will Percival, Arjun T. Dey, J. E. Forero-Romero, Steven P. Ahlen, Aaron Meisner, Biprateep Dey, John Moustakas, Hu Zou, T. Claybaugh, Graziano Rossi, Benjamin A. Weaver, Peter Doel, Adam D. Myers, Francisco Prada
article en

Abstract

Abstract We present details regarding 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 any previous study. As the light from a distant quasar travels towards an observer, it may interact with the circumgalactic medium of an intervening galaxy, forming absorption lines. In order to maximize the signal of these absorption lines, we have selected a sample of 239,174 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 rest frame 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. We additionally provide analysis of composites constructed using subsamples of absorbers in both redshift and Mg ii equivalent width bins. We find that there is minimal redshift evolution across the considered absorber samples. Additionally, we find that dense gas signatures, such as the presence of Na I absorption, are strongest in the highest equivalent width absorber sample, and that the strengths of the Si IV and C IV absorption lines show a relatively weak correlation with Mg II equivalent width. This atlas should aid in future studies investigating the compositions and physical conditions of these absorbers.

The Astronomical JournalVol. 172(5)
Boston University (US), Institució Catalana de Recerca i Estudis Avançats (ES), Universitat Autònoma de Barcelona (ES), University of Wyoming (US), Fermi National Accelerator Laboratory (US), Consejo Superior de Investigaciones Científicas (ES), Lawrence Berkeley National Laboratory (US), University of Waterloo (CA), Universidad de Los Andes (CO), University of Pittsburgh (US), Perimeter Institute (CA), University of Toronto (CA), Institute for High Energy Physics (ES), University of Milan (IT), Chinese Academy of Sciences (CN), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), University of Michigan (US), CEA Paris-Saclay - Etablissement de Saclay (FR), Institut d'Astrophysique de Paris (FR), Brera Astronomical Observatory (IT), Sejong University (KR), Sorbonne Université (FR), Institut d'Estudis Espacials de Catalunya (ES), Laboratoire de Physique Nucléaire et de Hautes Énergies (FR), CEA Paris-Saclay (FR), NSF NOIRLab (US), Instituto de Astrofísica de Andalucía (ES), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (ES), University College London (GB), University of Virginia (US), University of Rochester (US), University of Portsmouth (GB), National Institute for Astrophysics (IT), Universidad Nacional Autónoma de México (MX), Universitat Politècnica de Catalunya (ES)
National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, Ministerio de Ciencia, Innovación y Universidades, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Agencia Estatal de Investigación, Division of Astronomical Sciences, High Energy Physics
Openalex Percentile: Top 98%
Galaxies: Formation, Evolution, Phenomena
DOIOpen Access PDFOpenAlex
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