The DESI Bright Galaxy Survey: Final Target Selection, Design, and Validation

Abstract

Over the next 5 yr, the Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on the 4 m Mayall Telescope at Kitt Peak National Observatory to conduct the first Stage IV dark energy galaxy survey. At z < 0.6, the DESI Bright Galaxy Survey (BGS) will produce the most detailed map of the universe during the dark-energy-dominated epoch with redshifts of >10 million galaxies spanning 14,000 deg2. In this work, we present and validate the final BGS target selection and survey design. From the Legacy Surveys, BGS will target an r < 19.5 mag limited sample (BGS Bright), a fainter 19.5 < r < 20.175 color-selected sample (BGS Faint), and a smaller low-z quasar sample. BGS will observe these targets using exposure times scaled to achieve homogeneous completeness and cover the footprint three times. We use observations from the Survey Validation programs conducted prior to the main survey along with simulations to show that BGS can complete its strategy and make optimal use of “bright” time. BGS targets have stellar contamination <1%, and their densities do not depend strongly on imaging properties. BGS Bright will achieve >80% fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve >95% redshift success over any observing condition. BGS meets the requirements for an extensive range of scientific applications. BGS will yield the most precise baryon acoustic oscillation and redshift-space distortion measurements at z < 0.4. It presents opportunities for new methods that require highly complete and dense samples (e.g., N-point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter.

The DESI One-Percent Survey: Constructing Galaxy–Halo Connections for ELGs and LRGs Using Auto and Cross Correlations

“…Raichoor et al (2023, in preparation), andSchlafly et al (2023). The target selections and SVs of DESI can be found in a series of papers (Allende Prieto et al 2020;Raichoor et al 2020;Ruiz-Macias et al 2020;Yèche et al 2020;Zhou et al 2020;Alexander et al 2023;Chaussidon et al 2023;Cooper et al 2023;Hahn et al 2023;Lan et al 2023;Raichoor et al 2023;Zhou et al 2023). The parent catalog used for DESI target selections is constructed from Data Release 9 of the DESI Legacy Imaging Surveys (Zou et al 2017;Dey et al 2019;D.…”

The Hitchhiker’s Guide to the Galaxy Catalog Approach for Dark Siren Gravitational-wave Cosmology

“…In this section, we describe how to build the probability, p CBC (z), of a CBC occurring at redshift z, under the assumption that CBCs occur in galaxies and so will trace the distribution of galaxies in the universe in some fashion. As described above, we will also implicitly assume that the number density of CBCs (constrained to be 18-44 Gpc −3 yr −1 by ground-based observations to date; Abbott et al 2023a) is much smaller than the number density of galaxies (bright galaxies have a local comoving density of ∼10 8 h −3 Gpc −3 ; Hahn et al 2023) and so each CBC can be treated as an independent draw from the redshift distribution inferred from the galaxy catalog. Note that in this section (and for the rest of the paper) we will discuss the distribution of galaxies purely as a function of redshift, and thus neglect their spatial distribution in R.A. and decl.…”

Outlier Detection in the DESI Bright Galaxy Survey

“…For BGS, we only use spectra observed with functioning fiber positioners and with reliable redshift measurements as defined in Hahn et al (2023). We only keep spectra classified as galaxy spectra by Redrock (i.e., SPECTYPE == ''GALAXY'') with redshifts z ä [0, 0.8] (cutting off a very minor high-redshift tail) and having no Redrock warning flags ZWARN.…”

“…In this work, we search for outliers in the Early Data Release (EDR; DESI Collaboration et al 2023a) of the DESI Bright Galaxy Survey (BGS; Hahn et al 2023), which we briefly describe in Section 2. We employ the spectrum autoencoder (AE) architecture SPENDER introduced by Melchior et al (2023).…”