Fast and precise map-making for massively multi-detector CMB experiments

TL;DR

This paper compares destriping and filtering methods for fast, precise map-making in large-scale CMB experiments, demonstrating destriping's advantages in reducing spurious B-mode signals and improving primordial B-mode detection.

Contribution

It introduces an optimized destriping algorithm for massive multi-detector CMB data, showing its effectiveness over filtering in B-mode power spectrum estimation.

Findings

Destriping outperforms filtering in estimating large-scale E and B-mode spectra.

Filtering introduces spurious B-mode power via EB mixing, affecting detection significance.

Destriping is computationally feasible and integrates well with existing analysis pipelines.

Abstract

Future cosmic microwave background (CMB) polarisation experiments aim to measure an unprecedentedly small signal - the primordial gravity wave component of the polarisation field B-mode. To achieve this, they will analyse huge datasets, involving years worth of time-ordered data (TOD) from massively multi-detector focal planes. This creates the need for fast and precise methods to complement the M-L approach in analysis pipelines. In this paper, we investigate fast map-making methods as applied to long duration, massively multi-detector, ground-based experiments, in the context of the search for B-modes. We focus on two alternative map-making approaches: destriping and TOD filtering, comparing their performance on simulated multi-detector polarisation data. We have written an optimised, parallel destriping code, the DEStriping CARTographer DESCART, that is generalised for massive focal planes, including the potential effect of cross-correlated TOD 1/f noise. We also determine the scaling of computing time for destriping as applied to a simulated full-season data-set for a realistic experiment. We find that destriping can out-perform filtering in estimating both the large-scale E and B-mode angular power spectra. In particular, filtering can produce significant spurious B-mode power via EB mixing. Whilst this can be removed, it contributes to the variance of B-mode bandpower estimates at scales near the primordial B-mode peak. For the experimental configuration we simulate, this has an effect on the possible detection significance for primordial B-modes. Destriping is a viable alternative fast method to the full M-L approach that does not cause the problems associated with filtering, and is flexible enough to fit into both M-L and Monte-Carlo pseudo-Cl pipelines.