A Test of the Cosmological Principle with Quasars

Nathan J Secrest,Mohamed Rameez,Subir Sarkar,Roya Mohayaee,Jacques Colin,Sebastian Von Hausegger

doi:10.3847/2041-8213/abdd40

Abstract

Abstract We study the large-scale anisotropy of the universe by measuring the dipole in the angular distribution of a flux-limited, all-sky sample of 1.36 million quasars observed by the Wide-field Infrared Survey Explorer (WISE). This sample is derived from the new CatWISE2020 catalog, which contains deep photometric measurements at 3.4 and 4.6 μm from the cryogenic, post-cryogenic, and reactivation phases of the WISE mission. While the direction of the dipole in the quasar sky is similar to that of the cosmic microwave background (CMB), its amplitude is over twice as large as expected, rejecting the canonical, exclusively kinematic interpretation of the CMB dipole with a p-value of 5 × 10−7 (4.9σ for a normal distribution, one-sided), the highest significance achieved to date in such studies. Our results are in conflict with the cosmological principle, a foundational assumption of the concordance ΛCDM model.

Highlights

The standard Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology is based on the “cosmological principle,” which posits that the universe is homogeneous and isotropic on large scales
The unique statistical power of our study has allowed us to confirm the anomalously large matter dipole suggested in previous work, which used objects selected at a different wavelength, using surveys completely independent of Wide-field Infrared Survey Explorer (WISE), namely NRAO VLA Sky Survey (NVSS), WENNS, SUMMS, and TIFR GMRT Sky Survey (TGSS)
The ecliptic scanning pattern of WISE has no relationship with the cosmic microwave background (CMB) dipole, so there is no reason to suspect that the dipole we measure in the CatWISE quasar sample is an artifact of the survey

Summary

Introduction

The standard Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology is based on the “cosmological principle,” which posits that the universe is homogeneous and isotropic on large scales. This assumption is supported by the smoothness of the CMB, which has temperature fluctuations of only ∼1 part in 100,000 on small angular scales. According to the most recent measurements, the inferred velocity is 369.82 ± 0.11 km s−1 toward l, b = 264°.021, 48°.253 (Planck Collaboration et al 2020) This motion is usually attributed to the gravitational effect of the inhomogeneous distribution of matter on local scales, originally dubbed the “Great Attractor” (see, e.g., Dressler 1991)

Methods

Results

Conclusion