The dipole anisotropy of WISE x SuperCOSMOS number counts

TL;DR

This study investigates the large-scale isotropy of the universe using WISE x SuperCOSMOS galaxy counts, finding general consistency with isotropy except at the lowest redshifts where anomalies persist.

Contribution

It provides the largest all-sky photometric redshift analysis of galaxy counts for anisotropy, highlighting persistent low-redshift anisotropy not explained by current models.

Findings

Dipole directions align with previous studies.

Dipole amplitudes match ΛCDM mock expectations at higher redshifts.

Persistent anisotropy observed at z<0.15.

Abstract

We probe the isotropy of the Universe with the largest all-sky photometric redshift dataset currently available, namely WISE~$\times$~SuperCOSMOS. We search for dipole anisotropy of galaxy number counts in multiple redshift shells within the $0.10 < z < 0.35$ range, for two subsamples drawn from the same parent catalogue. Our results show that the dipole directions are in good agreement with most of the previous analyses in the literature, and in most redshift bins the dipole amplitudes are well consistent with $\Lambda$CDM-based mocks in the cleanest sample of this catalogue. In the $z<0.15$ range, however, we obtain a persistently large anisotropy in both subsamples of our dataset. Overall, we report no significant evidence against the isotropy assumption in this catalogue except for the lowest redshift ranges. The origin of the latter discrepancy is unclear, and improved data may be needed to explain it.