Cosmology and Astro-particle physics journal club
Testing the large scale isotropy of the Universe with Radio and Infrared surveys, and type 1a SNe
by Dr. Mohamed Rameez (Nield Bohr Institute, Copenhagen)
Tuesday, June 25, 2019 from to (Asia/Kolkata)
The dipolar anisotropy of the CMB is believed to be due to our motion with respect to the CMB rest frame at 369 km/s. This should cause a dipolar modulation in the number counts of distant sources, through special relativistic aberration and Doppler boosting effects. We test this with an all-sky catalogue of ~600000 radio galaxies, by combining the NRAO VLA Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS) catalogues and find a significantly larger dipole than expected, in the same direction but corresponding to a velocity of 1355 +/- 174 km/s, in tension with the kinematic interpretation of the CMB dipole at 2.81σ. We further test this with a sample of galaxies from the Widefield Infrared Survey Explorer (WISE) satellite. After using innovative background rejection strategies to reduce star contamination to <0.1% and rejecting nearby sources, we again find a large dipole in the same direction, consistent with a velocity of 1260 +/- 629 km/s. These and other observations hint at a large bulk flow in the direction of the CMB-dipole. The deceleration parameter q0 derived from local observations is then expected to show a scale-dependent dipolar modulation. From a maximum likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of Type Ia supernovae we do find such a dipole in q0, with the strength and statistical significance depending strongly upon the imposed uncertainty budget of the sample. I will conclude by commenting on the bizarre inconsistencies found in the recent SNe catalogues, and their implications for the cosmological principle.