Imaging Systematics and Clustering of DESI Main Targets
  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, $\gamma = 1.98 \pm 0.02$ for LRGs and $r_0 = 5.45 \pm
0.1$ $h^{-1}$Mpc, $\gamma = 1.54 \pm 0.01$ for ELGs. Additionally, from the
angular power spectra, we measure the linear biases and model the scale
dependent biases in the weakly nonlinear 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.
