Constraining cosmic isotropy with type Ia supernovae

TL;DR

This study tests the isotropy of the universe using low-redshift Type Ia supernovae data, finding significant anisotropies in H0 and q0 directions that may be due to local effects or data coverage.

Contribution

It provides a model-independent analysis of cosmic isotropy using supernovae data, revealing anisotropies correlated with local universe motion and data distribution.

Findings

Preferred H0 direction aligns with local bulk flow.

Significant anisotropy detected at 2-3 sigma confidence level.

Anisotropies may be due to local effects or data coverage issues.

Abstract

We investigate the validity of the Cosmological Principle by constraining the cosmological parameters $H_0$ and $q_0$ through the celestial sphere. Our analyses are performed in a low-redshift regime in order to follow a model independent approach, using both Union2.1 and JLA Type Ia Supernovae (SNe) compilations. We find that the preferred direction of the $H_0$ parameter in the sky is consistent with the bulk flow motion of our local Universe in the Union2.1 case, while the $q_0$ directional analysis seem to be anti-correlated with the $H_0$ for both data sets. Furthermore, we test the consistency of these results with Monte Carlo (MC) realisations, finding that the anisotropy on both parameters are significant within $2-3\sigma$ confidence level, albeit we find a significant correlation between the $H_0$ and $q_0$ mapping with the angular distribution of SNe from the JLA compilation. Therefore, we conclude that the detected anisotropies are either of local origin, or induced by the non-uniform celestial coverage of the SNe data set.