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Overdispersed Radio Source Counts and Excess Radio Dipole Detection

Lukas Böhme1,*, Dominik J. Schwarz1, Prabhakar Tiwari2, Morteza Pashapour-Ahmadabadi1, Benedict Bahr-Kalus3,4,5, Maciej Bilicki6, Catherine L. Hale7, Caroline S. Heneka8, and Thilo M. Siewert1,9

  • *Contact author: Lboehme@physik.uni-bielefeld.de
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Phys. Rev. Lett. 135, 201001 – Published 10 November, 2025

DOI: https://doi.org/10.1103/6z32-3zf4

Abstract

The source count dipole from wide-area radio continuum surveys allows us to test the cosmological standard model. Many radio sources have multiple components, which can cause an overdispersion of the source counts distribution. We account for this effect via a new Bayesian estimator, based on the negative binomial distribution. Combining the two best understood wide-area surveys, NVSS and RACS-low, and the deepest wide-area survey, LoTSS-DR2, we find that the source count dipole exceeds its expected value as the kinematic dipole amplitude from standard cosmology by a factor of 3.67±0.49—a 5.4σ discrepancy.

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Phys. Rev. Lett. 135, 201001– Published 10 November, 2025
  • Received 3 March 2025
  • Revised 2 July 2025
  • Accepted 19 September 2025
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