Emulating galaxy clustering and galaxygalaxy lensing into the deeply nonlinear regime: methodology, information, and forecasts
Abstract
The combination of galaxygalaxy lensing (GGL) with galaxy clustering is one of the most promising routes to determining the amplitude of matter clustering at low redshifts. We show that extending clustering+GGL analyses from the linear regime down to {∼ } 0.5 h^{1} Mpc scales increases their constraining power considerably, even after marginalizing over a flexible model of nonlinear galaxy bias. Using a grid of cosmological Nbody simulations, we construct a Taylorexpansion emulator that predicts the galaxy autocorrelation ξ_{gg}(r) and galaxymatter crosscorrelation ξ_{gm}(r) as a function of σ_{8}, Ω_{m}, and halo occupation distribution (HOD) parameters, which are allowed to vary with largescale environment to represent possible effects of galaxy assembly bias. We present forecasts for a fiducial case that corresponds to BOSS LOWZ galaxy clustering and SDSSdepth weak lensing (effective source density ∼0.3 arcmin^{2}). Using tangential shear and projected correlation function measurements over 0.5 ≤ r_ p ≤ 30 h^{1} Mpc yields a 2 per cent constraint on the parameter combination σ _8Ω _ m^{0.6}, a factor of two better than a constraint that excludes nonlinear scales (r_ p > 2 h^{1} Mpc, 4 h^{1} Mpc for γ_{t}, w_{p}). Much of this improvement comes from the nonlinear clustering information, which breaks degeneracies among HOD parameters. Increasing the effective source density to 3 arcmin^{2} sharpens the constraint on σ _8Ω _ m^{0.6} by a further factor of two. With robust modelling into the nonlinear regime, lowredshift measurements of matter clustering at the 1per cent level with clustering+GGL alone are well within reach of current data sets such as those provided by the Dark Energy Survey.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 March 2019
 DOI:
 10.1093/mnras/sty2258
 arXiv:
 arXiv:1709.07099
 Bibcode:
 2019MNRAS.484..989W
 Keywords:

 gravitational lensing: weak;
 cosmological parameters;
 argescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 23 pages, 7 figures