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

Abstract

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.

The Jiao Tong University Spectroscopic Telescope Project

“…The spectroscopically confirmed satellite galaxies will enable mass estimates of individual haloes through the velocity dispersion [49][50][51] and caustic boundary [52][53][54] , improving the calibration of the cluster mass-observable relation beyond the optical richness [55] . Meanwhile, JUST will probe the properties of the intracluster medium, particularly the circumgalactic medium of cluster galaxies, by measuring metal absorption lines recorded in the DESI spectra of background quasars in the cluster fields [56][57][58][59][60] .…”

DESI Survey Validation Data in the COSMOS/Hyper Suprime-Cam Field: Cool Gas Trace Main-sequence Star-forming Galaxies at the Cosmic Noon

“…Target selection and samples of quasars, bright galaxies, emission-line galaxies, and luminous red galaxies from the SV data can be found in Yèche et al (2020), Chaussidon et al (2023), Lan et al (2023), Raichoor et al (2023), Yang et al (2023), andZhou et al (2023). The full Mg II absorber catalog of the DESI EDR data is presented in Napolitano et al (2023).…”