How does an incomplete sky coverage affect the Hubble Constant variance?

TL;DR

This study investigates how incomplete sky coverage influences the observed variance in the Hubble Constant, suggesting that observational limitations may partly explain the tension between local and CMB measurements.

Contribution

It introduces a hemispherical comparison method with simulations to assess the impact of sky coverage on Hubble Constant variance, incorporating real data features.

Findings

Sky coverage affects the H0 tension, reducing it from 4.4σ to 2.7σ.

Increasing data size significantly decreases H0 variance.

Future surveys can clarify if the tension indicates new physics.

Abstract

We address the $\simeq 4.4\sigma$ tension between local and the CMB measurements of the Hubble Constant using simulated Type Ia Supernova (SN) data-sets. We probe its directional dependence by means of a hemispherical comparison through the entire celestial sphere as an estimator of the $H_0$ cosmic variance. We perform Monte Carlo simulations assuming isotropic and non-uniform distributions of data points, the latter coinciding with the real data. This allows us to incorporate observational features, such as the sample incompleteness, in our estimation. We obtain that this tension can be alleviated to $3.4\sigma$ for isotropic realizations, and $2.7\sigma$ for non-uniform ones. We also find that the $H_0$ variance is largely reduced if the data-sets are augmented to 4 and 10 times the current size. Future surveys will be able to tell whether the Hubble Constant tension happens due to unaccounted cosmic variance, or whether it is an actual indication of physics beyond the standard cosmological model.