Impact of beam deconvolution on noise properties in CMB measurements: Application to Planck LFI

¹ Department of Physics, Gustaf Hällströminkatu 2University of Helsinki, 00014 Helsinki, Finland
e-mail: elina.keihanen@helsinki.fi
² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
e-mail: martin@mpa-garching.mpg.de
³ Helsinki Institute of Physics, Gustaf Hällströminkatu 2, University of Helsinki, 00014 Helsinki, Finland

Received: 29 June 2015
Accepted: 11 December 2015

Abstract

We present an analysis of the effects of beam deconvolution on noise properties in CMB measurements. The analysis is built around the artDeco beam deconvolver code. We derive a low-resolution noise covariance matrix that describes the residual noise in deconvolution products, both in harmonic and pixel space. The matrix models the residual correlated noise that remains in time-ordered data after destriping, and the effect of deconvolution on this noise. To validate the results, we generate noise simulations that mimic the data from the Planck LFI instrument. A χ² test for the full 70 GHz covariance in multipole range ℓ = 0 − 50 yields a mean reduced χ² of 1.0037. We compare two destriping options, full and independent destriping, when deconvolving subsets of available data. Full destriping leaves substantially less residual noise, but leaves data sets intercorrelated. We also derive a white noise covariance matrix that provides an approximation of the full noise at high multipoles, and study the properties on high-resolution noise in pixel space through simulations.