Speaker
Description
The cosmic radio dipole is an anisotropy in the number counts of radio
sources, analogous to the dipole seen in the cosmic microwave background
(CMB). Measurements of the radio dipole with large radio surveys have
shown that though the radio dipole is aligned in direction with the CMB
dipole, the amplitudes are in tension. These observations present an
intriguing puzzle as to the cause of this discrepancy, with a true
anisotropy having large repercussions for cosmology as a whole. We
present a novel set of Bayesian estimators to determine the cosmic radio
dipole and compare the results with commonly used methods on the Rapid
ASKAP Continuum Survey (RACS) and the NRAO VLA Sky Survey (NVSS) radio
surveys. In addition, we enhanced the Baysian estimators in various ways
to take into account systematic effects known to affect such large radio
surveys, i.e. folding information such as the local noise floor or array
configuration directly into the parameter estimation. The enhancement of
these estimators allows us to greatly increase the amount of sources
used in the parameter estimation, yielding tighter constraints on the
cosmic radio dipole estimation than previously achieved with NVSS and
RACS. We extend the estimators further to work on multiple catalogues
simultaneously, leading to a combined parameter estimation using both
NVSS and RACS. The result is a dipole estimate that perfectly aligns
with the CMB dipole in terms of direction but with an amplitude that is
three times as large, and a significance of 4.8σ. This new dipole
measurement is made to an unprecedented level of precision for radio
sources, which is only matched by recent results using infrared AGN.
