Imaging systematics and clustering of DESI main targets

Abstract

We evaluate the impact of imaging systematics on the clustering of luminous red galaxies (LRG), emission-line galaxies (ELG), and quasars (QSO) targeted for the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. Using Data Release 7 of the DECam Legacy Survey, we study the effects of astrophysical foregrounds, stellar contamination, differences between north galactic cap and south galactic cap measurements, and variations in imaging depth, stellar density, galactic extinction, seeing, airmass, sky brightness, and exposure time before presenting survey masks and weights to mitigate these effects. With our sanitized samples in hand, we conduct a preliminary analysis of the clustering amplitude and evolution of the DESI main targets. From measurements of the angular correlation functions, we determine power law fits $r_0 = 7.78 \pm 0.26\, h^{-1}$Mpc, γ = 1.98 ± 0.02 for LRGs and $r_0 = 5.45 \pm 0.1\, h^{-1}$Mpc, γ = 1.54 ± 0.01 for ELGs. Additionally, from the angular power spectra, we measure the linear biases and model the scale-dependent biases in the weakly non-linear regime. Both sets of clustering measurements show good agreement with survey requirements for LRGs and ELGs, attesting that these samples will enable DESI to achieve precise cosmological constraints. We also present clustering as a function of magnitude, use cross-correlations with external spectroscopy to infer dN/dz and measure clustering as a function of luminosity, and probe higher order clustering statistics through counts-in-cells moments.

Cross-correlation of Planck CMB lensing with DESI-like LRGs

“…We find that the linear biases are unaffected by the choice of ℓ max and that the cross bias g is consistently lower than the galaxy bias Lower: The difference between the two measurements as a fraction of the theoretical prediction, with three bands illustrating 1%, 5% and 10%. gg , with the latter agreeing well with DESI survey expectations and the findings of Kitanidis et al 2020. The lower-than-expected g could arise from choosing an incorrect fiducial cosmology (e.g.…”

“…Myers et al 2006, Crocce et al 2011, Ross et al 2011, Suchyta et al 2016, Crocce et al 2016, Leistedt et al 2016, Elvin-Poole et al 2018, Ross et al 2020, Weaverdyck & Huterer 2020 for studies of imaging systematics in the context of other surveys). A full analysis of the effect of imaging systematics on the clustering of DESI main targets using data from DECaLS DR7 is presented in Kitanidis et al 2020. Here, we briefly perform tests of the LRG density dependence on these potential systematics using DR8 data and target selection.…”

“…The survey properties we look at are stellar density, galactic extinction, airmass, seeing, sky background, and exposure time. For full descriptions of these survey properties, how they are calculated, and why they are included in the analysis, see Section 6 of Kitanidis et al 2020.…”

“…Since clustering-based redshift estimation presents an attractive alternative to photometric redshift methods, it has experienced a recent resurgence in popularity. Over the last decade or so, a number of clustering / estimators have been presented and analyzed (Matthews & Newman 2010, Schulz 2010, Matthews & Newman 2012, McQuinn & White 2013) and tested on real or simulated data (Schmidt et al 2013, Scottez et al 2016, Hildebrandt et al 2017, Scottez et al 2018, Davis et al 2018, Gatti et al 2018, Chiang et al 2018, Krolewski et al 2019, Kitanidis et al 2020.…”

Characterizing the target selection pipeline for the Dark Energy Spectroscopic Instrument Bright Galaxy Survey

“…Our aim is to provide a reliable input galaxy catalogue for the DESI BGS and to characterize its properties, such as the surface density of galaxies and their clustering. A complementary study by Kitanidis et al (2020) examined the impact of imaging systematics on the selection and clustering of targets in the LRG, ELG, and quasi-stellar object (QSO) DESI surveys, using an earlier release of the LS imaging data (Dey et al 2019).…”