Resolution of the incongruency of dipole asymmetries within various large radio surveys -- implications for the Cosmological Principle

Abstract

We investigate dipole asymmetries in four large radio surveys, each spanning more than 80\% of the sky. Two of them, the Very Large Array Sky Survey (VLASS) and the Rapid ASKAP Continuum Survey (RACS), have recently yielded dipoles that appear incongruent with each other as well as seem inconsistent with previous radio survey dipoles and the Cosmic Microwave Background (CMB) dipole. Because these radio surveys have large overlaps in sky coverage, comprising hence large majority of common radio sources, one would not expect significant differences between their radio dipoles, irrespective of their underlying source of origin. We examine here in detail these radio dipoles, to ascertain the source of incongruency amongst them. We find the VLASS and RACS data to be containing some declination-dependent systematics, seemingly in the vicinity of the declination limit of each survey. We show that the effects of such systematics can be mitigated by restricting the declination limits of the respective survey during the dipole determination. A weighted mean of the sky coordinates of thus derived dipoles from the four radio surveys lies within $1.2\sigma$ of the CMB dipole direction. However, the amplitude appears significantly larger, $3.7\pm 0.6$ times or more than the CMB dipole. This puts in doubt not only the conventional wisdom that the genesis of all these dipoles, including that of the CMB dipole, is due to the Solar peculiar motion, it also raises uncomfortable questions about the Cosmological Principle (CP), the basis of the standard $\Lambda$CDM cosmological model.

15 pages, 8 figures, 7 tables, accepted in MNRAS

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Cited by in corpus (6)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Reassessment of the dipole in the distribution of quasars on the sky
• Cosmic dipoles of active galactic nuclei at optical and radio wavelengths display much larger amplitudes than the cosmic microwave background dipole
• 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
• Solar peculiar motion inferred from dipole anisotropy in redshift distribution of quasars appears to lie along the Galactic Centre direction