The combination of galaxy–galaxy lensing (GGL) and galaxy clustering is a powerful probe of lowredshift matter clustering, especially if it is extended to the nonlinear regime. To this end, we use an Nbody and halo occupation distribution (HOD) emulator method to model the redMaGiC sample of colourselected passive galaxies in the Dark Energy Survey (DES), adding parameters that describe central galaxy incompleteness, galaxy assembly bias, and a scaleindependent multiplicative lensing bias Alens. We use this emulator to forecast cosmological constraints attainable from the GGL surface density profile ΔΣ(rp) and the projected galaxy correlation function wp, gg(rp) in the final (Year 6) DES data set over scales $r_p=0.3\!\!30.0\, h^{1} \, \mathrm{Mpc}$. For a $3{{\ \rm per\ cent}}$ prior on Alens we forecast precisions of $1.9{{\ \rm per\ cent}}$, $2.0{{\ \rm per\ cent}}$, and $1.9{{\ \rm per\ cent}}$ on Ωm, σ8, and $S_8 \equiv \sigma _8\Omega _m^{0.5}$, marginalized over all halo occupation distribution (HOD) parameters as well as Alens. Adding scales $r_p=0.3\!\!3.0\, h^{1} \, \mathrm{Mpc}$ improves the S8 precision by a factor of ∼1.6 relative to a large scale ($3.0\!\!30.0\, h^{1} \, \mathrm{Mpc}$) analysis, equivalent to increasing the survey area by a factor of ∼2.6. Sharpening the Alens prior to $1{{\ \rm per\ cent}}$ further improves the S8 precision to $1.1{{\ \rm per\ cent}}$, and it amplifies the gain from including nonlinear scales. Our emulator achieves per centlevel accuracy similar to the projected DES statistical uncertainties, demonstrating the feasibility of a fully nonlinear analysis. Obtaining precise parameter constraints from multiple galaxy types and from measurements that span linear and nonlinear clustering offers many opportunities for internal crosschecks, which can diagnose systematics and demonstrate the robustness of cosmological results.
We present a novel simulationbased hybrid emulator approach that maximally derives cosmological and Halo Occupation Distribution (HOD) information from nonlinear galaxy clustering, with sufficient precision for DESI Year 1 (Y1) analysis. Our hybrid approach first samples the HOD space on a fixed cosmological simulation grid to constrain the highlikelihood region of cosmology + HOD parameter space, and then constructs the emulator within this constrained region. This approach significantly reduces the parameter volume emulated over, thus achieving much smaller emulator errors with fixed number of training points. We demonstrate that this combined with stateoftheart simulations result in tight emulator errors comparable to expected DESI Y1 LRG sample variance. We leverage the new abacussummit simulations and apply our hybrid approach to CMASS nonlinear galaxy clustering data. We infer constraints on σ8 = 0.762 ± 0.024 and fσ8(zeff = 0.52) = 0.444 ± 0.016, the tightest among contemporary galaxy clustering studies. We also demonstrate that our fσ8 constraint is robust against secondary biases and other HOD model choices, a critical first step towards showcasing the robust cosmology information accessible in nonlinear scales. We speculate that the additional statistical power of DESI Y1 should tighten the growth rate constraints by at least another 50–60 ${{\ \rm per\ cent}}$, significantly elucidating any potential tension with Planck. We also address the ‘lensing is low’ tension, which we find to be in the same direction as a potential tension in fσ8. We show that the combined effect of a lower fσ8 and environmentbased bias accounts for approximately $50{{\ \rm per\ cent}}$ of the discrepancy.
more » « less NSFPAR ID:
 10427694
 Publisher / Repository:
 Oxford University Press
 Date Published:
 Journal Name:
 Monthly Notices of the Royal Astronomical Society
 Volume:
 515
 Issue:
 1
 ISSN:
 00358711
 Page Range / eLocation ID:
 p. 871896
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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