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Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-Degree Scales: Is the Universe Isotropic?

Hansen, F. K. and Banday, A. J. and Górski, K. M. and Eriksen, H. K. and Lilje, P. B. (2009) Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-Degree Scales: Is the Universe Isotropic? Astrophysical Journal, 704 (2). pp. 1448-1458. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20091110-185633191

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Abstract

We repeat and extend the analysis of Eriksen et al. and Hansen et al., testing the isotropy of the cosmic microwave background fluctuations. We find that the hemispherical power asymmetry previously reported for the largest scales ℓ = 2-40 extends to much smaller scales. In fact, for the full multipole range ℓ = 2-600, significantly more power is found in the hemisphere centered at (θ = 107° ± 10°, ∅ = 226° ± 10°) in galactic co-latitude and longitude than in the opposite hemisphere, consistent with the previously detected direction of asymmetry for ℓ = 2-40. We adopt a model selection test where the direction and amplitude of asymmetry, as well as the multipole range, are free parameters. A model with an asymmetric distribution of power for ℓ = 2-600 is found to be preferred over the isotropic model at the 0.4% significance level, taking into account the additional parameters required to describe it. A similar direction of asymmetry is found independently in all six subranges of 100 multipoles between ℓ = 2-600. None of our 9800 isotropic simulated maps show a similarly consistent direction of asymmetry over such a large multipole range. No known systematic effects or foregrounds are found to be able to explain the asymmetry.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/704/2/1448DOIUNSPECIFIED
http://www.iop.org/EJ/abstract/0004-637X/704/2/1448PublisherUNSPECIFIED
Additional Information:© 2009 The American Astronomical Society. Received 2008 December 19, accepted for publication 2009 August 28. Published 2009 October 2. We acknowledge the use of the HEALPix (Górski et al. 2005) package. F.K.H. is thankful for an OYI grant from the Research Council of Norway. We acknowledge the use of the NOTUR super computing facilities. 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.
Funders:
Funding AgencyGrant Number
Research Council of Norway OYI grantUNSPECIFIED
NASA Office of Space ScienceUNSPECIFIED
Subject Keywords:cosmic microwave background; cosmology: observations; methods: data analysis; methods: statistical
Issue or Number:2
Record Number:CaltechAUTHORS:20091110-185633191
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20091110-185633191
Official Citation:Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-Degree Scales: Is the Universe Isotropic? F. K. Hansen, A. J. Banday, K. M. Górski, H. K. Eriksen, and P. B. Lilje 2009 ApJ 704 1448-1458 doi: 10.1088/0004-637X/704/2/1448
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16652
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:13 Nov 2009 22:18
Last Modified:03 Oct 2019 01:15

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