The cosmic radio dipole: Bayesian estimators on new and old radio surveys

Abstract

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 source counts of large radio surveys have shown that though the radio dipole is generally consistent 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 breaking with the assumptions of the cosmological principle, invalidating the most common cosmological models that are built on these assumptions. 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 adapt the Bayesian estimators to take into account systematic effects known to affect such large radio surveys, 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 4.8$\sigma$. This new dipole measurement is made to an unprecedented level of precision for radio sources, which is only matched by recent results using infrared quasars.

14 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics

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• Reassessment of the dipole in the distribution of quasars on the sky
• Tomographic redshift dipole: Testing the cosmological principle
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• Cosmic dipole tensions: confronting the cosmic microwave background with infrared and radio populations of cosmological sources
• An Independent Measure of the Kinematic Dipole from SDSS
• Forty years of the Ellis-Baldwin test
• Clustering properties of the CatWISE2020 quasar catalogue and their impact on the cosmic dipole anomaly
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• Testing General Relativity through the $E_G$ Statistic Using the Weyl Potential and Galaxy Velocities
• Anisotropy in the cosmic acceleration inferred from supernovae
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• Exploring the cosmic microwave background dipole direction using gamma-ray bursts
• Measuring cosmic dipole with the GRB luminosity-time relation
• An effective $\mathbf{\Lambda }$-Szekeres modelling of the local Universe with Cosmicflows-4
• The Ellis and Baldwin test of the Cosmic Dipole: Exploring the impact of multiple flux density cuts