Exploiting non-linear scales in galaxy-galaxy lensing and galaxy clustering: A forecast for the dark energy survey

The combination of g alaxy-g alaxy lensing (GGL) and g alaxy clustering is a powerful probe of low-redshift matter clustering, especially if it is extended to the non-linear regime. To this end, we use an N -body and halo occupation distribution (HOD) emulator method to model the redMaGiC sample of colour-selected passive galaxies in the Dark Energy Surv e y (DES), adding parameters that describe central galaxy incompleteness, galaxy assembly bias, and a scale-independent multiplicative lensing bias A lens . We use this emulator to forecast cosmological constraints attainable from the GGL surface density profile ΔΣ( r p ) and the projected galaxy correlation function w p , gg ( r p ) in the final (Year 6) DES data set o v er scales r p = 0 . 3 -30 . 0 h -1 Mpc . For a 3 per cent prior on A lens we forecast precisions of 1 . 9 per cent , 2 . 0 per cent , and 1 . 9 per cent on Ωm , σ8 , and S 8 ≡σ8 Ω0 . 5 m , marginalized o v er all halo occupation distribution (HOD) parameters as well as A lens . Adding scales r p = 0 . 3 -3 . 0 h -1 Mpc impro v es the S 8 precision by a factor of ∼1.6 relative to a large scale (3 . 0 -30 . 0 h -1 Mpc ) analysis, equi v alent to increasing the surv e y area by a factor of ∼2.6. Sharpening the A lens prior to 1 per cent further impro v es the S 8 precision to 1 . 1 per cent , and it amplifies the gain from including non-linear scales. Our emulator achie ves per cent-le v el accurac y similar to the projected DES statistical uncertainties, demonstrating the feasibility of a fully non-linear analysis. Obtaining precise parameter constraints from multiple galaxy types and from measurements that span linear and non-linear clustering offers many opportunities for internal cross-checks, which can diagnose systematics and demonstrate the robustness of cosmological results.