Is there evidence for anomalous dipole anisotropy in the large-scale structure?

TL;DR

This study investigates large-scale structure anisotropy using WISE-2MASS data, finding results consistent with standard cosmological expectations and no evidence for anomalous dipole anisotropy.

Contribution

The paper provides a directional analysis of galaxy counts across the celestial sphere, accounting for systematics, and compares findings with ΛCDM simulations to assess anisotropy.

Findings

Dipole amplitude A = 0.0507 ± 0.0014 in galaxy distribution.

Dipole direction aligned with our proper motion estimates.

Results are consistent with ΛCDM simulations, showing no anomalous anisotropy.

Abstract

We probe the anisotropy of the large-scale structure (LSS) with the WISE-2MASS catalogue. This analysis is performed by a directional comparison of the galaxy number counts through the entire celestial sphere once systematic effects, such as star-galaxy separation and foregrounds contamination, are properly taken into account. We find a maximal hemispherical asymmetry whose dipolar component is $A = 0.0507 \pm 0.0014$ toward the $(l,b) = (323^{\circ},-5^{\circ})$ direction, whose result is consistent with previous estimations of our proper motion in low and intermediate redshifts, as those carried out with Type Ia Supernovae and similar LSS catalogues. Furthermore, this dipole amplitude is statistically consistent ($p$-value = $0.061$) with mock catalogues simulated according to the expected $\Lambda$CDM matter density fluctuations, in addition to observational biases such as the incomplete celestial coverage and anisotropic sky exposure. Our results suggest, therefore, that there is no strong evidence for anomalous anisotropy in the LSS, given the limitations and systematics of current data, in the concordance model scenario.