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 ∼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 H0=72.6±2.8 (stat) ±2.3 (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±0.2 (stat) ±0.3 (syst). Given the fact that the SDSS ETG sample only reaches z∼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∼1.
@article{arxiv.1010.0831,
title = {Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers},
author = {Michele Moresco and Raul Jimenez and Andrea Cimatti and Lucia Pozzetti},
journal= {arXiv preprint arXiv:1010.0831},
year = {2015}
}