Tuesday, July 9, 2013

1307.1947 (Rahul Kothari et al.)

Dipole anisotropy in flux density and source count distribution in radio NVSS data    [PDF]

Rahul Kothari, Abhishek Naskar, Prabhakar Tiwari, Sharvari Nadkarni-Ghosh, Pankaj Jain
We study the dipole anisotropy in the number counts and flux density in the NRAO VLA Sky Survey (NVSS) data. The dipole anisotropy is expected due to our local motion with respect to the CMBR rest frame. In agreement with earlier results, we find that the amplitude of anisotropy is significantly larger in comparison to the prediction based on CMBR measurements. The direction, however, is found to be in good agreement. The local speed extracted using flux density is found to be somewhat smaller in comparison to earlier results, but still much larger in comparison to the CMBR expectation. We attribute this partially to the revised formula we use to relate the dipole amplitude to speed in this case. The significance of detection of anisotropy is found to be 3 sigma for flux density and 3.5-5.4 sigma for source counts, depending on the cut on flux density. Furthermore the extracted speed using flux density differs by 2.5 sigma from the speed corresponding to CMBR. The corresponding significance for number counts is 4-5 sigma. We find that the results are relatively insensitive to the lower limit imposed on the flux density. Our results suggest that the Universe is intrinsically anisotropic with the axis of anisotropy axis pointing roughly towards the Virgo cluster.
View original: http://arxiv.org/abs/1307.1947

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