Dipole anisotropy in sky brightness and source count distribution in radio NVSS data

TY - JOUR

T1 - Dipole anisotropy in sky brightness and source count distribution in radio NVSS data

AU - Tiwari, Prabhakar

AU - Kothari, Rahul

AU - Naskar, Abhishek

AU - Nadkarni-Ghosh, Sharvari

AU - Jain, Pankaj

PY - 2015/2

Y1 - 2015/2

N2 - We study the dipole anisotropy in number counts and flux density weighted number counts or sky brightness 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. We analyse data with an improved fit to the number density, n(S), as a function of the flux density S, which allows deviation from a pure power law behaviour. We also impose more stringent cuts to remove the contribution due to clustering dipole. 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 extracted speed is found to be roughly 3 times the speed corresponding to CMBR. The significance of deviation is smaller, roughly 2σ, in comparison to earlier estimates. For the cut, S>30 mJy, the speed is found to be 1110±370 km/s using the source count analysis. The direction of the dipole anisotropy is found to be approximately in agreement with CMBR. We find that the results are relatively insensitive to the lower as well as upper limit imposed on the flux density. Our results suggest that the Universe is intrinsically anisotropic with the axis of anisotropy pointing roughly towards the CMBR dipole direction. Finally we present a method which may allow an independent extraction of the local speed and an intrinsic dipole anisotropy, provided a larger data set becomes available in future.

AB - We study the dipole anisotropy in number counts and flux density weighted number counts or sky brightness 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. We analyse data with an improved fit to the number density, n(S), as a function of the flux density S, which allows deviation from a pure power law behaviour. We also impose more stringent cuts to remove the contribution due to clustering dipole. 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 extracted speed is found to be roughly 3 times the speed corresponding to CMBR. The significance of deviation is smaller, roughly 2σ, in comparison to earlier estimates. For the cut, S>30 mJy, the speed is found to be 1110±370 km/s using the source count analysis. The direction of the dipole anisotropy is found to be approximately in agreement with CMBR. We find that the results are relatively insensitive to the lower as well as upper limit imposed on the flux density. Our results suggest that the Universe is intrinsically anisotropic with the axis of anisotropy pointing roughly towards the CMBR dipole direction. Finally we present a method which may allow an independent extraction of the local speed and an intrinsic dipole anisotropy, provided a larger data set becomes available in future.

KW - CMBR dipole

KW - Galaxies: active

KW - Radio galaxies: high-redshift

UR - http://www.scopus.com/inward/record.url?scp=84903973431&partnerID=8YFLogxK

U2 - 10.1016/j.astropartphys.2014.06.004

DO - 10.1016/j.astropartphys.2014.06.004

M3 - 文章

AN - SCOPUS:84903973431

SN - 0927-6505

VL - 61

SP - 1

EP - 11

JO - Astroparticle Physics

JF - Astroparticle Physics

ER -