Making maps of cosmic microwave background polarization for B-mode studies: the POLARBEAR example

¹ AstroParticule et Cosmologie, Univ. Paris Diderot, CNRS/IN2P3, CEA/Irfu, Obs. de Paris, Sorbonne Paris Cité, 75205 Paris Cedex 13, France
e-mail: dpoletti@apc.univ-paris7.fr
² International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste, Italy
³ INFN, Sezione di Trieste, via Valerio 2, 34127 Trieste, Italy
⁴ Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁵ Department of Physics, University of Wisconsin, Madison WI 53706, USA
⁶ Department of Physics, University of California, Berkeley, CA 94720, USA
⁷ Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
⁸ Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
⁹ Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada
¹⁰ Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, 277-8583 Chiba, Japan
¹¹ Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
¹² Department of Physics, University of California, San Diego, CA 92093-0424, USA
¹³ Sorbonne Universités, Institut Lagrange de Paris (ILP), 98bis boulevard Arago, 75014 Paris, France
¹⁴ LPNHE, CNRS-IN2P3 and Universités Paris 6 & 7, 4 place Jussieu, 75252 Paris Cedex 05, France
¹⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁶ High Energy Accelerator Research Organization (KEK), Tsukuba, 305-0801 Ibaraki, Japan
¹⁷ SOKENDAI (The Graduate University for Advanced Studies), Hayama, Miura District, 240-0115 Kanagawa, Japan
¹⁸ Institute of Physics, Academia Sinica, 128, Sec.2, Academia Road, Nankang, 11529 Taipei, Taiwan
¹⁹ Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
²⁰ School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
²¹ Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
²² Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA

Received: 3 August 2016
Accepted: 18 December 2016

Abstract

Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable.