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

Lucas Napolitano, Agnesh Pandey, Adam D. Myers, Ting Wen Lan, Abhijeet Anand, Jessica Aguilar, Steven Ahlen, David M. Alexander, 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 GuyKlaus 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

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


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 (W 0) 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.

Original languageEnglish (US)
Article number99
JournalAstronomical Journal
Issue number3
StatePublished - Sep 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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