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Published December 1, 2019 | Accepted Version + Published
Journal Article Open

The Ubiquitous Imprint of Radiative Acceleration in the Mean Absorption Spectrum of Quasar Outflows

Abstract

Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad (> 450 km s⁻¹) absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of C IV, with a separation of ≈497 km s⁻¹, as well as those of other species, appear well resolved in most of our composites. This agrees with broad outflow troughs consisting of the superposition of narrow absorbers. We also report on the ubiquitous detection of the radiative-acceleration signature known as line-locking in all our composite outflow spectra, including one spectrum that was strictly built from broad absorption line (BAL) systems. This is the first line-locking detection in BAL composite spectra. Line-locking is driven by the C IV atomic doublet and is visible on the blue side of most strong absorption transitions. Similar effects from the doublets of O VI, Si IV, or N V, however, seem to not be present. Our results confirm that radiation pressure is a prevalent mechanism for accelerating outflows in quasars.

Additional Information

© 2019 The American Astronomical Society. Received 2018 December 28; revised 2019 September 17; accepted 2019 October 16; published 2019 December 3. The initial inspiration for this work grew out of a stimulating discussion with Paul Martini during a visit supported by the Visitor Program at the Ohio State Center for Cosmology and Astroparticle Physics. We are grateful to him for valuable ideas and comments on our paper, and to the CCAP for their kind hospitality. We thank the anonymous referee for a detailed revision and a constructive report that helped improve our work. We thank Stan Owocki for sharing with us his thoughts and inspiring notes on the dynamics of CIV line-locking. We also thank Ainar Drews, Mattia Mina, Robert Wissing, and Håvard T. Ihle for discussions on line-locking and statistical aspects, and Tzu-Ching Chang, Olivier Doré Phil Berger, Sterl Phinney, Lee Armus, Ski Antonucci, Brice Ménard, Jordi Miralda Escudé Sijing Shen, Johan Fynbo, Joop Schaye, Jason X. Prochaska, Bill Forman, and Christine Jones for enriching conversations and suggestions. We are grateful to Signe Riemer-Sørensen for many useful discussions on quasar continua. L.M.R. is grateful to the UCSB/MPIA ENIGMA group for their kind hospitality, and together with other colleagues at JPL and Caltech, for many inspiring discussions during this work. This research was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

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Published - Mas-Ribas_2019_ApJ_886_151.pdf

Accepted Version - 1902.04085.pdf

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August 22, 2023
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