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Detecting and Characterizing Mg ii Absorption in DESI Survey Validation Quasar Spectra

Napolitano, Lucas; Pandey, Agnesh; Myers, Adam D.; Lan, Ting-Wen; Anand, Abhijeet; Aguilar, Jessica; Ahlen, Steven; Alexander, David M.; Brooks, David; Canning, Rebecca; Circosta, Chiara; De La Macorra, Axel; Doel, Peter; Eftekharzadeh, Sarah; Fawcett, Victoria A.; Font-Ribera, Andreu; Garcia-Bellido, Juan; Gontcho A Gontcho, Satya; Le Guillou, L.; Guy, Julien; Honscheid, Klaus; Juneau, Stephanie; Kisner, T.; Landriau, Martin; Meisner, Aaron M.; Miquel, Ramon; Moustakas, J.; Percival, Will J.; Prochaska, J. Xavier; Schubnell, Michael; Tarlé, Gregory; Weaver, B. A.; Weiner, Benjamin; Zhou, Zhimin; Zou, Hu; Zou, Siwei

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Lucas Napolitano

Agnesh Pandey

Adam D. Myers

Ting-Wen Lan

Abhijeet Anand

Jessica Aguilar

Steven Ahlen

David Brooks

Rebecca Canning

Chiara Circosta

Axel De La Macorra

Peter Doel

Sarah Eftekharzadeh

Victoria A. Fawcett

Andreu Font-Ribera

Juan Garcia-Bellido

Satya Gontcho A Gontcho

L. Le Guillou

Julien Guy

Klaus Honscheid

Stephanie Juneau

T. Kisner

Martin Landriau

Aaron M. Meisner

Ramon Miquel

J. Moustakas

Will J. Percival

J. Xavier Prochaska

Michael Schubnell

Gregory Tarlé

B. A. Weaver

Benjamin Weiner

Zhimin Zhou

Hu Zou

Siwei Zou


We present findings of the detection of Magnesium II (Mg ii, λ = 2796, 2803 Å) absorbers from the early data release of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be at redshifts greater than z > 0.3, such that DESI would be able to observe an associated or intervening Mg ii absorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects these systems through an initial line-fitting process and then confirms the line properties using a Markov Chain Monte Carlo sampler. Based upon a visual inspection of the resulting systems, we estimate that this sample has a purity greater than 99%. We have also investigated the completeness of our sample in regard to both the signal-to-noise properties of the input spectra and the rest-frame equivalent width (W0) of the absorber systems. From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mg ii absorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.8% implies a catalog at the completion of the five-year DESI survey that will contain over eight hundred thousand Mg ii absorbers. The cataloging of these systems will enable significant further research because they carry information regarding circumgalactic medium environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 ≤ z < 2.5.


Napolitano, L., Pandey, A., Myers, A. D., Lan, T., Anand, A., Aguilar, J., …Zou, S. (2023). Detecting and Characterizing Mg ii Absorption in DESI Survey Validation Quasar Spectra. Astronomical Journal, 166(3), Article 99.

Journal Article Type Article
Acceptance Date Jul 9, 2023
Online Publication Date Aug 10, 2023
Publication Date Sep 1, 2023
Deposit Date Nov 1, 2023
Publicly Available Date Nov 1, 2023
Journal The Astronomical Journal
Print ISSN 0004-6256
Electronic ISSN 1538-3881
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 166
Issue 3
Article Number 99
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© 2023. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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