Redshift Evolution and Covariances for Joint Lensing and Clustering Studies with DESI Y1

Galaxy-galaxy lensing (GGL) and clustering measurements from the Dark EnergySpectroscopic Instrument Year 1 (DESI Y1) dataset promise to yieldunprecedented combined-probe tests of cosmology and the galaxy-halo connection.In such analyses, it is essential to identify and characterise all relevantstatistical and systematic errors. In this paper, we forecast the covariancesof DESI Y1 GGL+clustering measurements and characterise the systematic bias dueto redshift evolution in the lens samples. Focusing on the projected clusteringand galaxy-galaxy lensing correlations, we compute a Gaussian analyticalcovariance, using a suite of N-body and log-normal simulations to characterisethe effect of the survey footprint. Using the DESI One Percent Survey data, wemeasure the evolution of galaxy bias parameters for the DESI Luminous RedGalaxy (LRG) and Bright Galaxy Survey (BGS) samples. We find mild evolution inthe LRGs in 0.4 < z < 0.8, subdominant compared to the expected statisticalerrors. For BGS, we find less evolution effects for brighter absolute magnitudecuts, at the cost of reduced sample size. We find that with a fiducial redshiftbin width delta z = 0.1, evolution effects on GGL is negligible across allscales, all fiducial selection cuts, all fiducial redshift bins, given DESI Y1sample size. Galaxy clustering is more sensitive to evolution due to the biassquared scaling. Nevertheless the redshift evolution effect is insignificantfor clustering above the 1-halo scale of 0.1Mpc/h. For studies that wish toreliably access smaller scales, additional treatment of redshift evolution islikely needed. This study serves as a reference for GGL and clustering studiesusing the DESI Y1 sample