2017MNRAS.468.1953P

We use information entropy to test the isotropy in the nearby galaxydistribution mapped by the Two Micron All-Sky redshift survey (2MRS). We find that the galaxy distribution is highly anisotropic on small scales. The radial anisotropy gradually decreases with increasing length-scales and the observed anisotropy is consistent with that expected for an isotropic Poisson distribution beyond a length-scale of 90 h^–1 Mpc. Using mock catalogues from N-body simulations, we find that the galaxy distribution in the 2MRS exhibits a degree of anisotropy compatible with that of the Λ cold dark matter (ΛCDM) model after accounting for the clustering bias of the 2MRS galaxies. We also quantify the polar and azimuthal anisotropies and identify two directions (l, b) = (150°, -15°), (l, b) = (310°, -15°) that are significantly anisotropic compared to the other directions in the sky. We suggest that their preferential orientations in the sky may indicate a possible alignment of the Local Group with two nearby large-scale structures. Despite the differences in the degree of anisotropy on small scales, we find that the galaxy distributions in both the 2MRS and the ΛCDM model are isotropic on a scale of 90 h^–1 Mpc.