Cosmic radio dipole from NVSS and WENSS

Rubart M, Schwarz D. Cosmic radio dipole from NVSS and WENSS. Astronomy & Astrophysics. 2013;555: A117.We use linear estimators to determine the magnitude and direction of thecosmic radio dipole from the NRAO VLA Sky Survey (NVSS) and the WesterborkNorthern Sky Survey (WENSS). We show that special attention has to be given tothe issues of bias due to shot noise, incomplete sky coverage and masking ofthe Milky Way. We compare several different estimators and show thatconflicting claims in the literature can be attributed to the use of differentestimators. We find that the NVSS and WENSS estimates of the cosmic radiodipole are consistent with each other and with the direction of the cosmicmicrowave background (CMB) dipole. We find from the NVSS a dipole amplitude of$(1.6 \pm 0.6) \times 10^{-2}$ in direction $(\mathrm{RA}, \mathrm{dec})=(154^\circ \pm 21^\circ, -2^\circ \pm 21^\circ)$. This amplitude exceeds theone expected from the CMB by a factor of about 3 and is inconsistent with theassumption of a pure kinetic origin of the radio dipole at 99.5% CL