Full-sky maps for gravitational lensing of the CMB

TL;DR

This paper presents the creation of detailed full-sky maps of gravitational lensing effects on the CMB using large cosmological simulations, capturing small-scale non-linearities and non-Gaussianities for improved analysis.

Contribution

It introduces a novel map-making method based on ray-tracing through the Millennium Simulation, including large-scale structure contributions, for accurate CMB lensing modeling.

Findings

Angular power spectra match semi-analytic estimates on small scales.

Slight excess of power on small scales indicates non-linear clustering effects.

Method is suitable for studying CMB lensing and cross-correlations with foregrounds.

Abstract

We use the large cosmological Millennium Simulation (MS) to construct the first all-sky maps of the lensing potential and the deflection angle, aiming at gravitational lensing of the CMB, with the goal of properly including small-scale non-linearities and non-Gaussianity. Exploiting the Born approximation, we implement a map-making procedure based on direct ray-tracing through the gravitational potential of the MS. We stack the simulation box in redshift shells up to $z\sim 11$, producing continuous all-sky maps with arcminute angular resolution. A randomization scheme avoids repetition of structures along the line of sight and structures larger than the MS box size are added to supply the missing contribution of large-scale (LS) structures to the lensing signal. The angular power spectra of the projected lensing potential and the deflection-angle modulus agree quite well with semi-analytic estimates on scales down to a few arcminutes, while we find a slight excess of power on small scales, which we interpret as being due to non-linear clustering in the MS. Our map-making procedure, combined with the LS adding technique, is ideally suited for studying lensing of CMB anisotropies, for analyzing cross-correlations with foreground structures, or other secondary CMB anisotropies such as the Rees-Sciama effect.