Testing isotropy in the Universe using photometric and spectroscopic data from the SDSS

TL;DR

This study tests the isotropy of the local Universe using SDSS galaxy data, finding anisotropy on small scales that diminishes with scale and aligns with Lambda CDM predictions, indicating a transition to isotropy beyond 200 Mpc/h.

Contribution

It provides the first detailed analysis of galaxy distribution anisotropy across multiple scales using information entropy and compares observations with Lambda CDM simulations.

Findings

Anisotropy is high on small scales and decreases with scale.

Observed anisotropy agrees well with Lambda CDM mock catalogues.

No preferred direction found in galaxy distribution.

Abstract

We analyze two volume limited galaxy samples from the SDSS photometric and spectroscopic data to test the isotropy in the local Universe. We use information entropy to quantify the global anisotropy in the galaxy distribution at different length scales and find that the galaxy distribution is highly anisotropic on small scales. The observed anisotropy diminishes with increasing length scales and nearly plateaus out beyond a length scale of 200 Mpc/h in both the datasets. We compare these anisotropies with those predicted by the mock catalogues from the N-body simulations of the Lambda CDM model and find a fairly good agreement with the observations. We find a small residual anisotropy on large scales which decays in a way that is consistent with the linear perturbation theory. The slopes of the observed anisotropy converge to the slopes predicted by the linear theory beyond a length scale of ~ 200 Mpc/h indicating a transition to isotropy. We separately compare the anisotropies observed across the different parts of the sky and find no evidence for a preferred direction in the galaxy distribution.