N-body lensed CMB maps: lensing extraction and characterization

Abstract

We reconstruct shear maps and angular power spectra from simulated weakly lensed total intensity (TT) and polarised (EB) maps of the Cosmic Microwave Background (CMB) anisotropies, obtained using Born approximated ray-tracing through the N-body simulated Cold Dark Matter (CDM) structures in the Millennium Simulations (MS). We compare the recovered signal with the $Λ$CDM prediction, on the whole interval of angular scales which is allowed by the finite box size, extending from the degree scale to the arcminute, by applying a quadratic estimator in the flat sky limit; we consider PRISM-like instrumental specification for future generation CMB satellites, corresponding to arcminute angular resolution of 3.2' and sensitivity of 2.43 $μ$K-arcmin. -arcmin. The noise bias in the simulations closely follows the estimator prediction, becoming dominated by limits in the angular resolution for the EB signal, at l${\simeq}$1500. The de-biased signal shows no visible departure from predictions of the weak lensing power within uncertainties, when considering TT and EB data singularly. In particular, the reconstruction precision reaches the level of a few percent in bins with $Δ$l ${\simeq}$100 in the angular multiple interval 1000<l<2000 for TT, and about 10$%$ for EB. Within the adopted specifications, polarisation data do represent a significant contribution to the lensing shear, which appear to faithfully trace the underlying N-body structure down to the smallest angular scales achievable with the present setup, validating at the same time the latter with respect to semi-analytical predictions from $Λ$CDM cosmology at the level of CMB lensing statistics. This work demonstrates the feasibility of CMB lensing studies based on large scale simulations of cosmological structure formation in the context of the current and future high resolution and sensitivity CMB experiment.