Exploring KSZ velocity reconstruction with N-body simulations and the halo model

Abstract

KSZ velocity reconstruction is a recently proposed method for mappingthe largest-scale modes of the universe, by applying a quadratic estimatorv̂ r to the small-scale CMB and a galaxy catalog.We implement kSZ velocity reconstruction in an N-body simulationpipeline and explore its properties.We find that the reconstruction noise can be larger than the analyticprediction which is usually assumed.We revisit the analytic prediction and find additional noise terms which explain the discrepancy.The new terms are obtained from a six-point halo model calculation,and are analogous to the N (1) and N (3/2) biasesin CMB lensing.We implement an MCMC pipeline which estimates fNL fromN-body kSZ simulations, and showthat it recovers unbiased estimates of fNL , with statisticalerrors consistent with a Fisher matrix forecast.Overall, these results confirm that kSZ velocity reconstruction will bea powerful probe of cosmology in the near future, but new termsshould be included in the noise power spectrum.