A new path to constrain the expansion history of the Universe in future spectroscopic galaxy surveys

Abstract

The current tension between early- and late-Universe measurements of the Hubble constant ($H_0$), along with the still elusive nature of dark matter and dark energy, calls for model-independent probes of the Universe's expansion history. The cosmic chronometers (CC) method offers a unique opportunity to directly measure the Hubble parameter $H(z)$ without relying on any cosmological model assumptions or integrated distance measurements. Despite its potential, this technique remains statistics-limited: no current survey is optimized to detect large samples of CC, restricting the precision on $H(z)$ to $\sim$20% at intermediate redshifts. Here, we investigate the opportunities that a next-generation spectroscopic facility could offer to CC studies, providing an estimate of the accuracy achievable on the reconstruction of the Hubble parameter in redshift. We demonstrate that with such a facility, it will be possible to derive constraints on key cosmological parameters, assessing the impact that such improvements would have on our understanding of the expansion history of the Universe and on current cosmological tensions.

Figures (1)

• Figure 1: Left: Forecasts on the potential $H(z)$ measurements attainable with a WST-like facility. The shaded areas illustrate the 5% (red) or 1% (yellow) precision on the $H(z)$ points. In grey, the collection of $H(z)$ measurements obtained to date with the CC method. Right: Constraints attainable in the $\Omega_m-H_0$ plane with different precisions on the CC dataset. The fit is performed within a flat $w$CDM framework. Corresponding results are in Table \ref{['tab:model_params_opt']}.