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

TL;DR

This paper characterizes the clustering and selection properties of bright galaxy targets in DESI's BGS using DR9 data, comparing regions, assessing systematics, and measuring clustering to aid in mock catalog creation.

Contribution

It provides a detailed analysis of the DR9 selection, clustering measurements, and systematics for the DESI BGS bright targets, improving the understanding of their properties for future surveys.

Findings

Clustering strength and slope are measured and modeled.

Selection systematics and completeness are assessed.

Higher-order statistics and cross-correlations are explored.

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 as explored in Ruiz-Macias et al. (2021). 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 (r $\leq$ 19.5) and as function of apparent magnitude and colour. This enables to determine the clustering strength and slope 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.