Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers

TL;DR

This paper introduces a new method using spectral features of early type galaxies to measure the Universe's expansion rate, reducing systematic errors and providing consistent estimates of Hubble constant and dark energy parameters.

Contribution

The paper presents a novel spectral analysis technique based on the 4000Å break in ETGs, improving cosmic chronometer measurements and minimizing systematic uncertainties.

Findings

Derived H_0 = 72.6 ± 2.8 (stat) ± 2.3 (syst) km/s/Mpc

Estimated dark energy equation of state w = -1 ± 0.2 (stat) ± 0.3 (syst)

Demonstrated method's potential with low-redshift SDSS data

Abstract

We present a new methodology to determine the expansion history of the Universe analyzing the spectral properties of early type galaxies (ETG). We found that for these galaxies the 4000\AA break is a spectral feature that correlates with the relative ages of ETGs. In this paper we describe the method, explore its robustness using theoretical synthetic stellar population models, and apply it using a SDSS sample of $\sim$14 000 ETGs. Our motivation to look for a new technique has been to minimise the dependence of the cosmic chronometer method on systematic errors. In particular, as a test of our method, we derive the value of the Hubble constant $H_0 = 72.6 \pm 2.8$ (stat) $\pm2.3$ (syst) (68% confidence), which is not only fully compatible with the value derived from the Hubble key project, but also with a comparable error budget. Using the SDSS, we also derive, assuming w=constant, a value for the dark energy equation of state parameter $w = -1 \pm 0.2$ (stat) $\pm0.3$ (syst). Given the fact that the SDSS ETG sample only reaches $z \sim 0.3$, this result shows the potential of the method. In future papers we will present results using the high-redshift universe, to yield a determination of H(z) up to $z \sim 1$.