Cosmic variance of $H_0$ in light of forthcoming high-redshift surveys

TL;DR

This paper develops a relativistic framework to quantify how large-scale inhomogeneities impact the measurement of the Hubble constant from high-redshift surveys, finding the cosmic variance to be at most 0.1%.

Contribution

It introduces a comprehensive relativistic model for luminosity distance fluctuations, extending previous analyses to high redshifts and including multiple relativistic effects.

Findings

Cosmic variance in H0 measurement is at most 0.1%.

Deep surveys yield more precise H0 estimates than local measurements.

Relativistic effects significantly influence high-redshift Hubble diagrams.

Abstract

Forthcoming surveys will extend the understanding of cosmological large scale structures up to unprecedented redshift. According to this perspective, we present a fully relativistic framework to evaluate the impact of stochastic inhomogeneities on the determination of the Hubble constant. To this aim, we work within linear perturbation theory and relate the fluctuations of the luminosity distance-redshift relation, in the Cosmic Concordance model, to the intrinsic uncertainty associated to the measurement of $H_0$ from high-redshift surveys ($0.15\le z\le3.85$). We first present the detailed derivation of the luminosity distance-redshift relation 2-point correlation function and then provide analytical results for all the involved relativistic effects, such as peculiar velocity, lensing, time delay and (integrated) Sachs-Wolfe, and their angular spectra. Hence, we apply our analytical results to the study of high-redshift Hubble diagram, according to what has been recently claimed in literature. Following the specific of Euclid Deep Survey and LSST, we conclude that the cosmic variance associated with the measurement of the Hubble constant is at most of 0.1 %. Our work extends the analysis already done in literature for closer sources, where only peculiar velocity has been taken into account. We then conclude that deep surveys will provide an estimation of the $H_0$ which will be more precise than the one obtained from local sources, at least in regard of the intrinsic uncertainty related to a stochastic distribution of inhomogeneities.