Preliminary clustering properties of the DESI BGS bright targets using DR9 Legacy Imaging Surveys

Abstract

We characterise the selection cuts and clustering properties of a magnitude-limited sample of bright galaxies that is part of the Bright Galaxy Survey (BGS) of the Dark Energy Spectroscopic Instrument (DESI) using the ninth data release of the Legacy Imaging Surveys (DR9). We describe changes in the DR9 selection compared to the DR8 one and we also compare the DR9 selection in three distinct regions: BASS/MzLS in the north Galactic Cap (NGC), DECaLS in the NGC, and DECaLS in the south Galactic Cap (SGC). We investigate the systematics associated with the selection and assess its completeness by matching the BGS targets with the Galaxy and Mass Assembly (GAMA) survey. We measure the angular clustering for the overall bright sample (rmag ≤ 19.5) and as function of apparent magnitude and colour. This enables to determine the clustering strength r0 and slope γ by fitting a power-law model that can be used to generate accurate mock catalogues for this tracer. We use a counts-in-cells technique to explore higher-order statistics and cross-correlations with external spectroscopic data sets in order to check the evolution of the clustering with redshift and the redshift distribution of the BGS targets using clustering-redshifts. While this work validates the properties of the BGS bright targets, the final target selection pipeline and clustering properties of the entire DESI BGS will be fully characterised and validated with the spectroscopic data of Survey Validation.

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

“…By visual inspection, we confirm that Tractor based quality cuts discussed in Ruiz-Macias et al ( 2021) removes a significant number of real galaxies in DR9. Removing these quality cuts increases the BGS target completeness without introducing a significant number of spurious objects (see also Zarrouk et al 2021). We similarly validate the bright limit using visual inspection and confirm that most of the sources excluded by the cut are not galaxies -nearly all are saturated stars.…”

“…In addition to the small differences in the detection limits between DECaLS and BASS, there are also slight differences in their measured magnitudes due to the fact that they were observed using different instruments at different telescopes. Zarrouk et al (2021) quantified this discrepancy in detail using some of the overlapping region between DECaLS and BASS in the NGC over the range 29 < Dec < 35 deg. Overall, the same objects are slightly brighter in the r-band in DECaLS versus BASS.…”

“…We demonstrate that the choices we make for BGS will achieve all of the stated requirements and can be executed in the bright time available over the 5 years of DESI operations. This work presents significant updates and new results from preliminary versions of the BGS target selection presented by Ruiz-Macias et al (2021) and Zarrouk et al (2021). These advancements are based on early spectroscopic observations from the Survey Validation (SV) programs conducted by DESI prior to the main survey.…”

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

“…We demonstrate that the choices we make for BGS will achieve all of the stated requirements and can be executed in the bright time available over the 5 yr of DESI operations. This work presents significant updates and new results from preliminary versions of the BGS target selection presented by Ruiz-Macias et al (2021) and Zarrouk et al (2021). These advancements are based on early spectroscopic observations from the Survey Validation (SV) programs conducted by DESI prior to the main survey.…”

Toward Accurate Measurement of Property-dependent Galaxy Clustering. II. Tests of the Smoothed Density-corrected V max Method

“…Over the last couple of decades, the successful observation of galaxy redshift surveys (e.g., Two Degree Field Galaxy Redshift Survey (2dFGRS) Colless et al 2003; the Sloan Digital Sky Survey (SDSS) York et al 2000; the Baryon Oscillation Spectroscopic Survey (BOSS) Eisenstein et al 2011; the VIMOS Public Extragalactic Redshift Survey (VIPERS) Garilli et al 2012) have enabled significant progress toward our understanding of galaxy formation and evolution (Madgwick et al 2003;Berlind et al 2006;Guo et al 2011Guo et al , 2018Zu et al 2021), the galaxy-halo connection (Jing et al 1998;Yang et al 2003;Vale & Ostriker 2004;Zheng et al 2005;Yang et al 2008;Zheng et al 2009;Yang et al 2012;Wechsler & Tinker 2018;Behroozi et al 2019;Alam et al 2021b), and the nature of gravity and dark energy (Peacock et al 2001;Samushia et al 2013;Weinberg et al 2013;Alam et al 2021a and reference therein). In the coming years, next-generation surveys, such as the Dark Energy Spectroscopic Instrument (DESI; Levi et al 2013;DESI Collaboration et al 2016a, 2016b, the Legacy Survey of Space and Time (LSST; LSST Dark Energy Science Collaboration 2012), the space mission Euclid (Amendola et al 2013), and CSST (Cao et al 2018;Gong et al 2019), will map the 3D galaxy distribution in an unprecedented volume, leading to about an order of magnitude more extragalactic spectroscopic redshifts than those that SDSS, BOSS, and eBOSS have achieved (Zarrouk et al 2022;Yuan et al 2022b;Myers et al 2023;…”