Component separation methods for the PLANCK mission

¹ SISSA - ISAS, Astrophysics Sector, via Beirut 4, 34014 Trieste, Italy e-mail: leach@sissa.it
² INFN, Sezione di Trieste, via Valerio 2, 34014 Trieste, Italy
³ CNRS & Université Paris 7, Laboratoire APC, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France
⁴ Laboratoire de Traitement et Communication de l'Information (CNRS and Telecom ParisTech), 46, rue Barrault, 75634 Paris, France
⁵ Instituto de Física de Cantabria (CSIC-UC), Avda. de los Castros s/n, 39005 Santander, Spain
⁶ 
CEA - Saclay, SEDI/Service d'Astrophysique, 91191 Gif-Sur-Yvette, France
⁷ 
INAF - Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁸ 
Dipartimento di Astronomia, vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁹ 
Infrared Processing and Analysis Center, California Institute of Technology, M/S 220-6, 1200 E. California Blvd, Pasadena, 91125, USA
¹⁰ 
Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
¹¹ 
Centre of Mathematics for Applications, University of Oslo, PO Box 1053 Blindern, 0316 Oslo, Norway
¹² 
Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
¹³ 
DSM/Irfu/SPP, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
¹⁴ 
Institut d'Astrophysique Spatiale, Bâtiment 121, 91405 Orsay, France
¹⁵ 
Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France
¹⁶ 
Space Sciences Laboratory, University of California Berkeley, Computational Cosmology Center, Lawrence Berkeley National Laboratory, CA 94720, USA
¹⁷ 
Istituto di Scienza e Technologie dell'Informazione, CNR, Area della ricerca di Pisa, via G. Moruzzi 1, 56124 Pisa, Italy

Received: 2 May 2008
Accepted: 17 September 2008

Abstract

Context. The planck satellite will map the full sky at nine frequencies from 30 to 857 GHz. The CMB intensity and polarization that are its prime targets are contaminated by foreground emission.

Aims. The goal of this paper is to compare proposed methods for separating CMB from foregrounds based on their different spectral and spatial characteristics, and to separate the foregrounds into “components” with different physical origins (Galactic synchrotron, free-free and dust emissions; extra-galactic and far-IR point sources; Sunyaev-Zeldovich effect, etc.).

Methods. A component separation challenge has been organised, based on a set of realistically complex simulations of sky emission. Several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested.

Results. Different methods proved to be effective in cleaning the CMB maps of foreground contamination, in reconstructing maps of diffuse Galactic emissions, and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power spectrum of the residuals is, on the largest scales, four orders of magnitude lower than the input Galaxy power spectrum at the foreground minimum. The CMB power spectrum was accurately recovered up to the sixth acoustic peak. The point source detection limit reaches 100 mJy, and about 2300 clusters are detected via the thermal SZ effect on two thirds of the sky. We have found that no single method performs best for all scientific objectives.

Conclusions. We foresee that the final component separation pipeline for planck will involve a combination of methods and iterations between processing steps targeted at different objectives such as diffuse component separation, spectral estimation, and compact source extraction.