Tomographic redshift dipole: Testing the cosmological principle

The cosmological principle posits that the universe is statistically homogeneous and isotropic on large scales, implying all matter shares the same rest frame. This principle suggests that velocity estimates of our motion from various sources should agree with the cosmic microwave background (CMB) dipole's inferred velocity of 370 km/s. Yet, for over two decades, analyses of radio galaxy and quasar catalogs have found velocities at odds with the CMB dipole, with tensions up to 5σ. In a blind analysis of BOSS and eBOSS spectroscopic data from galaxies and quasars across 0.2 <z<2.2, we applied a novel dipole estimator for a tomographic approach, robustly correcting biases and quantifying uncertainties with realistic mock catalogs. Our findings, indicating a velocity of 353+123−111 km/s, show a 1.4σ agreement with the CMB dipole and a 2-to-3σ tension with previous number count studies. These results support the cosmological principle, emphasizing our motion's consistency with the CMB across vast cosmic distances. Addressing the disparities with earlier number count analyses will be essential for further validating the cosmological principle.