Toward an independent reconstruction of the expansion history of the Universe

Sep 30, 2022, 12:20 PM
Sestri Levante

Sestri Levante

Grand Hotel dei Castelli, Via Penisola Levante, 26, 16039 Sestri Levante (GE), Italy
Oral contribution Session 9


Nicola Borghi (University of Bologna)


A cosmological-model independent reconstruction of the expansion history of the Universe can help to shed light on the dark sector and the current cosmological tensions. I will discuss past, present, and future efforts to constrain the Hubble parameter $H(z)$ using two optimal astrophysical probes: cosmic chronometers and gravitational waves. Massive and passive galaxies can be used as chronometers to obtain direct measurements of the Hubble parameter without any cosmological model assumptions, $H(z)=-1/(1+z)\,\mathrm{d}z/\mathrm{d}t$ . However, robust $\mathrm{d}t$ estimates require deep spectroscopy to break internal degeneracies between stellar population parameters (e.g., age and chemical content). I present a recent analysis of the stellar ages, $[\text{Z/H}]$, and $[\alpha/\text{Fe}]$ of 140 cosmic chronometers at $z\sim0.7$ from the LEGA-C survey using an optimized set of Lick indices (arXiv:2106.14894). From the age-z relation of this population, a new measurement of $H(z)$ is derived, assessing in detail its robustness and dependence on systematic effects (arXiv:2110.04304). Finally, I will present the synergies betheen cosmic chronometers and gravitational wave cosmology in the context of current and future galaxy surveys and detectors.

Primary author

Nicola Borghi (University of Bologna)

Presentation materials