The dipole anisotropy of WISE × SuperCOSMOS number counts

Abstract

We probe the isotropy of the Universe with the largest all-sky photometric redshift data set currently available, namely WISE × 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 cold dark matter-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 data set. 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.