Testing the Cosmological Principle with CatWISE Quasars: A Bayesian Analysis of the Number-Count Dipole

Abstract

The Cosmological Principle, that the Universe is homogeneous and isotropic on sufficiently large scales, underpins the standard model of cosmology. However, a recent analysis of 1.36 million infrared-selected quasars has identified a significant tension in the amplitude of the number-count dipole compared to that derived from the CMB, thus challenging the Cosmological Principle. Here we present a Bayesian analysis of the same quasar sample, testing various hypotheses using the Bayesian evidence. We find unambiguous evidence for the presence of a dipole in the distribution of quasars with a direction that is consistent with the dipole identified in the CMB. However, the amplitude of the dipole is found to be 2.7 times larger than that expected from the conventional kinematic explanation of the CMB dipole, with a statistical significance of $5.7\sigma$. To compare these results with theoretical expectations, we sharpen the $\Lambda$CDM predictions for the probability distribution of the amplitude, taking into account a number of observational and theoretical systematics. In particular, we show that the presence of the Galactic plane mask causes a considerable loss of dipole signal due to a leakage of power into higher multipoles, exacerbating the discrepancy in the amplitude. By contrast, we show using probabilistic arguments that the source evolution of quasars improves the discrepancy, but only mildly so. These results support the original findings of an anomalously large quasar dipole, independent of the statistical methodology used.

15 pages, 7 figures; accepted for publication in MNRAS

References in corpus (12)

• Array Programming with NumPy
• Initial Performance of the NEOWISE Reactivation Mission
• New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects
• The CatWISE2020 Catalog
• The Rapid ASKAP Continuum Survey I: Design and First Results
• Is the Observable Universe Consistent with the Cosmological Principle?
• Dipoles in the Sky
• Spectral estimation on a sphere in geophysics and cosmology
• A new way to test the Cosmological Principle: measuring our peculiar velocity and the large scale anisotropy independently
• The cosmic radio dipole: Bayesian estimators on new and old radio surveys
• The kinematic dipole in galaxy redshift surveys
• The effects of lensing by local structures on the dipole of radio source counts

Cited by in corpus (35)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Quaia, the Gaia-unWISE Quasar Catalog: An All-Sky Spectroscopic Quasar Sample
• A simultaneous solution to the Hubble tension and observed bulk flow within 250 $h^{-1}$ Mpc
• The Cosmic Dipole in the Quaia Sample of Quasars: A Bayesian Analysis
• The expected kinematic matter dipole is robust against source evolution
• Testing cosmic anisotropy with Pade approximation and Pantheon+ sample
• Anisotropy in Pantheon+ supernovae
• Testing anisotropic Hubble expansion
• Measuring kinematic anisotropies with pulsar timing arrays
• Reassessment of the dipole in the distribution of quasars on the sky
• Tomographic redshift dipole: Testing the cosmological principle
• The kinematic contribution to the cosmic number count dipole
• Cosmic dipoles of active galactic nuclei at optical and radio wavelengths display much larger amplitudes than the cosmic microwave background dipole
• Tracking the validity of the quasi-static and sub-horizon approximations in modified gravity
• Cosmic dipole tensions: confronting the cosmic microwave background with infrared and radio populations of cosmological sources
• Spatially Homogeneous Universes with Late-Time Anisotropy
• An Independent Measure of the Kinematic Dipole from SDSS
• Testing inhomogeneous cosmography in our cosmic neighborhood using CosmicFlows-4
• Clustering properties of the CatWISE2020 quasar catalogue and their impact on the cosmic dipole anomaly
• Special Issue on Modified Gravity Approaches to the Tensions of $\Lambda$CDM: Goals and Highlights
• Redshift drift in a universe with structure III: Numerical relativity
• No evidence for anisotropy in galaxy spin directions
• Measuring our peculiar velocity from spectroscopic redshift surveys
• No evidence for local $H_0$ anisotropy from Tully--Fisher or supernova distances
• Fast and spurious: a robust determination of our peculiar velocity with future galaxy surveys
• Homology reveals significant anisotropy in the cosmic microwave background
• Measuring cosmic dipole with the GRB luminosity-time relation
• Numerical evolution of Maxwell's equations for wavefronts propagating through a spherical gravitational potential
• Constraints on the gravitational potential from DESI DR2 BAO and its implications for the local void scenario
• Testing the cosmological principle on gigaparsec scales
• Addressing Dipole Tension via Clustering in $\Lambda$CDM and beyond
• An effective $\mathbf{\Lambda }$-Szekeres modelling of the local Universe with Cosmicflows-4
• The Cosmological Dipole in Tilted Anisotropic Universes
• The Ellis and Baldwin test of the Cosmic Dipole: Exploring the impact of multiple flux density cuts
• Testing the cosmological principle with quasars