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Foreground subtraction of cosmic microwave background maps using WI-FIT (wavelet-based high-resolution fitting of internal templates)

Hansen, F. K. and Banday, A. J. and Eriksen, H. K. and Górski, K. M. and Lilje, P. B. (2006) Foreground subtraction of cosmic microwave background maps using WI-FIT (wavelet-based high-resolution fitting of internal templates). Astrophysical Journal, 648 (2). pp. 784-796. ISSN 0004-637X. doi:10.1086/506015.

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We present a new approach to foreground removal for CMB maps. Rather than relying on prior knowledge about the foreground components, we first extract the necessary information about them directly from the microwave sky maps by taking differences of temperature maps at different frequencies. These difference maps, which we refer to as internal templates, consist only of linear combinations of Galactic foregrounds and noise, with no CMB component. We obtain the foreground-cleaned maps by fitting these internal templates to, and subsequently subtracting the appropriately scaled contributions of them from, the CMB-dominated channels. The fitting operation is performed in wavelet space, making the analysis feasible at high resolution with only a minor loss of precision. Applying this procedure to the WMAP data, we obtain a power spectrum that matches the spectrum obtained by the WMAP team at the signal-dominated scales. The fact that we obtain basically identical results without using any external templates has considerable relevance for future observations of the CMB polarization, where very little is known about the Galactic foregrounds. Finally, we have revisited previous claims about a north-south power asymmetry on large angular scales and confirm that these remain unchanged with this completely different approach to foreground separation. This also holds when fitting the foreground contribution independently to the northern and southern hemisphere, indicating that the asymmetry is unlikely to have its origin in different foreground properties of the hemispheres. This conclusion is further strengthened by the lack of any observed frequency dependence.

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Additional Information:© 2006 The American Astronomical Society. Received 2006 March 13; accepted 2006 May 18. Print publication: Issue 2 (2006 September 10). We acknowledge the use of the HEALPix (Górski et al. 2005) package. F.K.H. acknowledges support from a European Union Marie Curie reintegration grant. We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science.
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Subject Keywords:cosmic microwave background; cosmology: observations; methods: data analysis; methods: statistical
Issue or Number:2
Record Number:CaltechAUTHORS:HANapj06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13240
Deposited By: Tony Diaz
Deposited On:05 Feb 2009 19:48
Last Modified:08 Nov 2021 22:36

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