The Composite Spectrum of QSO Absorption Line Systems in DESI DR2
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.
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Authors: L. Napolitano, Adam D. Myers, Abhijeet Anand, H. K. Herrera-Alcantar, J. Aguilar, Steven P. Ahlen, S. Bailey, S. BenZvi, D. Bianchi, T. Claybaugh, Andrei Cuceu, Axel de la Macorra, Arjun T. Dey, Biprateep Dey, Peter Doel, Andreu Font-Ribera, J. E. Forero-Romero, ENRIQUE GAZTAÑAGA, Satya Gontcho A Gontcho, Gaston Gutierrez, J. Guy, R. R. Joyce, Martin Landriau, Laurent Le Guillou, Marc Manera, Aaron Meisner, John Moustakas, S. Nadathur, N. Palanque‐Delabrouille, Will Percival, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David J. Schlegel, Michael S. Schubnell, David Sprayberry, Gregory Tarlé, Benjamin A. Weaver, Rongpu Zhou, Hu Zou
Institutions: University of Pittsburgh, Universidad Nacional Autónoma de México, University of Rochester, Chinese Academy of Sciences, University of Virginia, University of Michigan, University of Toronto, Boston University, Consejo Superior de Investigaciones Científicas, University College London, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Universitat Autònoma de Barcelona, Sorbonne Université, University of Waterloo, Institució Catalana de Recerca i Estudis Avançats, University of Wyoming, Universitat Politècnica de Catalunya, Université Paris-Saclay, CEA Paris-Saclay, University of Milan, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, University of Portsmouth, Sejong University, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, Institut d'Estudis Espacials de Catalunya, NSF NOIRLab, Institut d'Astrophysique de Paris, Institut de Recherche sur les Lois Fondamentales de l'Univers, Instituto de Astrofísica de Andalucía, National Institute for Astrophysics, Universidad de Los Andes, Brera Astronomical Observatory, Institute for High Energy Physics, Perimeter Institute, CEA Paris-Saclay - Etablissement de Saclay, Laboratoire de Physique Nucléaire et de Hautes Énergies