No evidence for anisotropy in galaxy spin directions

Modern cosmology rests on the cosmological principle , that on large enough scales the Universe is both homogeneous and isotropic. A corollary is that galaxies’ spin vectors should be isotropically distributed on the sky. This has been challenged by multiple authors for o v er a decade, with claims to have detected a statistically significant dipole pattern of spins. We collect all publicly available data sets with spin classifications (binary Z-wise/S-wise), and analyse them for large-angle anisotropies ( ≤2). We perform each inference in both a Bayesian and frequentist fashion, the former establishing posterior probabilities on the multipole parameters and the latter calculating p-values for rejection of the null hypothesis of isotropy (i.e. no power at > 0). All analysis indicate consistency with isotropy to within 3 σ. We similarly identify no evidence for a ‘hemisphere anisotropy’ that neglects the angular dependence of the dipole. We isolate the differences with contrary claims in the ad hoc or biased statistics that they employ.