Journal Article

Influence of the Local Void on measurements of the clustering dipole

Maciej Bilicki and Michał J. Chodorowski

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 2, pages 1358-1363
Published in print August 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16771.x
Influence of the Local Void on measurements of the clustering dipole

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In measurements of the clustering dipole from all-sky surveys, an important problem is the lack of information about galaxy distribution in the so-called zone of avoidance (ZoA). The existence of the Local Void (LV) has a systematic effect on these measurements. If the ZoA is randomly filled with mock galaxies, then the calculated acceleration of the Local Group (LG) of galaxies has a spurious component, resulting from the lack of real galaxies in the intersection of the LV with the ZoA. This component affects both the misalignment angle between the clustering dipole and the CMB dipole, and the inferred value of mean matter density Ωm. We calculate the amplitude of the spurious acceleration acting on the LG due to the LV. Its value depends on the geometry and size of the LV, as well as on its density contrast. However, under the simplest assumption of the LV being spherical and completely empty, within the linear theory this amplitude amounts only to about 45 km s−1 in units of velocity. The resulting change in the misalignment angle is smaller than 1°, and the fractional change in the deduced value of Ωm is about 5 per cent. Accounting for observationally indicated elongation of the LV and maintaining the maximizing assumption of a complete lack of galaxies inside increases these numbers only moderately. Specifically, the amplitude of the spurious acceleration rises to about 60 km s−1, the misalignment angle remains still smaller than 1° and the fractional change in the deduced value of Ωm is enhanced to about 7 per cent. Thus, despite the overall importance of the LV for the motion of the LG, the influence of the intersection of the LV with the ZoA on measurements of the clustering dipole is found to be only a minor systematic effect.

Keywords: methods: analytical; Local Group; cosmological parameters; cosmology: observations; large-scale structure of Universe

Journal Article.  4625 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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