High redshift radio galaxies and divergence from the CMB dipole

Abstract: Previous studies have found our velocity in the rest frame of radio galaxies at high redshift to be substantially larger than that inferred from the CMB temperature dipole anisotropy. We construct a full sky catalogue NVSUMSS, by merging the NVSS and SUMSS catalogues and removing local sources by various means including cross-correlating with the 2MRS catalogue. We take into account both aberration and Doppler boost to deduce our velocity from the hemispherical number count asymmetry, as well as via a 3-dimensional linear estimator. Both the magnitude and direction depend on cuts made to the catalogue, e.g. on the lowest source flux, however these effects are small. With the hemispheric number count asymmetry method we obtain a velocity of 1729 $\pm$ 187 km/s i.e. about 4 times larger than that obtained from the CMB dipole, but close in direction, towards RA=149 $\pm$ 2 degree, DEC = -17 $\pm$ 12 degree. With the 3-dimensional estimator, the derived velocity is 1355 $\pm$ 174 km/s towards RA=141 $\pm$ 11 degree, DEC=-9 $\pm$ 10 degree. We assess the statistical significance of these results by constructing catalogues of random distributions and show that they are at best significant at the $2.81 \sigma$ (99.95% confidence) level.

• The paper reports that velocity measurements from high redshift radio galaxies yield a solar system velocity four times greater than that inferred from the CMB dipole, despite similar directional alignment.
• Using data synthesis and local structure removal, the study measured velocities of 1729 asymp 187 km/s and 1355 asymp 174 km/s from hemispheric asymmetry and a 3D estimator, respectively, with apx 99.75% confidence.
• These findings challenge cosmological models assuming large-scale isotropy and highlight the need for more complete radio surveys and consideration of systematic biases to reconcile the velocity discrepancies.

High Redshift Radio Galaxies and Divergence from the CMB Dipole

The study presented in this paper explores the apparent discrepancy in the velocity measurements obtained from high redshift radio galaxies relative to the cosmic microwave background (CMB) dipole anisotropy. The authors construct a comprehensive all-sky catalog, termed NVSUMSS, by synthesizing data from the NRAO VLA Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS), while meticulously eliminating local structures using cross-correlation with the 2MASS Redshift Survey (2MRS). This approach allows the authors to assess the velocity of our solar system within the radio galaxy rest frame through analyses of hemispheric number count asymmetry and a 3-dimensional linear estimator.

Their findings indicate a velocity magnitude approximately fourfold greater than that inferred from the CMB dipole, yet the directional vectors align closely. Specifically, from hemispheric number count asymmetry, a velocity of $1729 \pm 187$ km/s is reported, directed towards RA = $149\degree \pm 2\degree$, Dec = $-17\degree \pm 12\degree$. Similarly, using the 3-dimensional estimator, a velocity of $1355 \pm 174$ km/s is noted towards RA = $141\degree \pm 11\degree$, Dec = $-9\degree \pm 10\degree$. The robustness of these measurements is reinforced through comparison with random distribution catalogs, establishing a statistical significance of $2.81\sigma$, or 99.75% confidence.

The implications of these results challenge conventional cosmological models that assume isotropy on large scales, specifically questioning the adequacy of gravitational attractions from observed large massive structures such as the Shapley supercluster in explaining the CMB dipole. Enhancing the exposure and completeness of radio surveys, particularly those extending beyond a declination threshold or masking the Galactic plane, is crucial to further reconcile these discrepancies. Additionally, this work highlights the influence large-scale systematic biases, introduced by incomplete survey coverage or local clustering, may exert when identifying dipole signals of purportedly kinematic origin.

Future work should focus on bridging observational gaps between low and high redshift radio sources, ideally utilizing upcoming capabilities from instruments like the Square Kilometer Array (SKA). These efforts will be essential in validating and extending our understanding of cosmological homogeneity and isotropy.

In conclusion, this paper advances the analysis of high redshift radio galaxies, providing substantial data-driven evidence contradicting simple kinematic interpretations of the CMB dipole. It urges reevaluation of cosmological models and proposes methodological refinements to further elucidate the structural nature of our universe on vast scales.