SILC: a newPlanckinternal linear combination CMB temperature map using directional wavelets

Keir K Rogers,Andrew Pontzen,Boris Leistedt,Jason D Mcewen,Hiranya V Peiris

doi:10.1093/mnras/stw1121

Abstract

We present new clean maps of the CMB temperature anisotropies (as measured by Planck) constructed with a novel internal linear combination (ILC) algorithm using directional, scale-discretised wavelets --- Scale-discretised, directional wavelet ILC or SILC. Directional wavelets, when convolved with signals on the sphere, can separate the anisotropic filamentary structures which are characteristic of both the CMB and foregrounds. Extending previous component separation methods, which use the frequency, spatial and harmonic signatures of foregrounds to separate them from the cosmological background signal, SILC can additionally use morphological information in the foregrounds and CMB to better localise the cleaning algorithm. We test the method on Planck data and simulations, demonstrating consistency with existing component separation algorithms, and discuss how to optimise the use of morphological information by varying the number of directional wavelets as a function of spatial scale. We find that combining the use of directional and axisymmetric wavelets depending on scale could yield higher quality CMB temperature maps. Our results set the stage for the application of SILC to polarisation anisotropies through an extension to spin wavelets.

Highlights

Accurate measurements of the cosmic microwave background (CMB) arguably form the bedrock of modern precision cosmology
Remazeilles & Delabrouille (2010) calculated the consequence of a first-order error in ac on a multiplicative correction to the CMB term in equation (20). They showed that even a small error in calibration can lead to a significant negative multiplicative bias in the CMB term, when the signal-to-noise ratio is large. (Here, the noise in this ratio includes foreground signal.) They consider the implications for using an internal linear combination (ILC) on Planck data, where the signalto-noise ratio is larger than for Wilkinson Microwave Anisotropy Probe (WMAP) data
We have shown that the axisymmetric limit of SILC gives comparable performance to NILC and SMICA

Summary

Introduction

Accurate measurements of the cosmic microwave background (CMB) arguably form the bedrock of modern precision cosmology. The full-sky multifrequency CMB maps provided by three generations of satellite experiments – COBE (Mather et al 1990; Boggess et al 1992), Wilkinson Microwave Anisotropy Probe (WMAP; Bennett et al 2003a) and Planck (Planck Collaboration I 2011) – represent milestones in our understanding of the cosmological model. To obtain a full-sky map of the CMB requires removing instrumental noise and signals due to astrophysical foregrounds (primarily in the Milky Way). There are numerous methods to perform foreground component separation. They broadly fall into two categories: blind methods which make minimal physical assumptions about the contributing signals and the so-called mixing matrix

Methods

Findings

Discussion

Conclusion