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

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 h −1 Mpc in both the datasets. We compare these anisotropies with those predicted by the mock catalogues from the N-body simulations of the ΛCDM 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 h −1 Mpc 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.

New Constraints on Anisotropic Expansion from Supernovae Type Ia

“…Quasar polarization directions also appear to be aligned along anomalous directions in the CMB (Hutsemékers et al 2005) and with coherence scales in excess of 500 Mpc (Hutsemékers, D. et al 2014), in potential disagreement with the cosmological principle. Investigating the distribution of galaxies on large scales, Sarkar et al (2019) found however good agreement between the predictions of ΛCDM and the Sloan Digital Sky Survey data, with a transition to isotropy observed beyond a length scale of 200ℎ −1 Mpc (where ℎ is the dimensionless Hubble-Lemaître parameter). More recently, Secrest et al (2020) reported a one-sided 4.9-𝜎 rejection of the hypothesis that the dipole in a sample of 1.3 million quasars is purely due to our motion with respect to the CMB.…”

The angular scale of homogeneity in the local Universe with the SDSS blue galaxies

“…The statistical isotropy of the universe is being tested for many extragalactic objects like Radio sources (Blake & Wall 2002;Ghosh et al 2016), Gamma-ray bursts (Bernui et al 2008a;Tarnopolski 2017;Řípa & Shafiello 2018), galaxy clusters (Bengaly et al 2017a), and galaxy datasets like the WISE (Yoon et al 2014;Bengaly et al 2017b;Novaes et al 2018) and the SDSS catalogues (Sarkar et al 2019), where all these analyses show a good concordance with the isotropy of the universe. The Planck Convergence and Cosmic Microwave Background temperature fluctuations maps have been examined and are also consistent with statistical isotropy at small angular scales (Ade et al 2016;Novaes et al 2016;Marques et al 2018), although some controversy remains at large angles (Bernui 2008b;Gruppuso et al 2013; Polase-mail: felipeavila@on.br tri, Gruppuso & Natoli 2015;Schwarz et al 2016;Aluri, Ralston & Weltman 2017;Rath et al 2017;Bernui et al 2018).…”

Cascaded Gamma-Ray Counterpart of the Icecube Neutrinos

“…In fact, equation A-1 represents a spatially homogeneous and isotropic universe, allowed to expand or contract. Observations have shown us that our universe satisfies these assumptions at scales 200 Mpc, confirming the cosmological principle [181,182].…”