Raising the bar: new constraints on the Hubble parameter with cosmic chronometers at z  ∼ 2

Abstract One of the most compelling tasks of modern cosmology is to constrain the expansion history of the Universe, since this measurement can give insights on the nature of dark energy and help to estimate cosmological parameters. In this letter are presented two new measurements of the Hubble parameter H(z) obtained with the cosmic chronometer method up to z ∼ 2. Taking advantage of near-infrared spectroscopy of the few very massive and passive galaxies observed at z > 1.4 available in literature, the differential evolution of this population is estimated and calibrated with different stellar population synthesis models to constrain H(z), including in the final error budget all possible sources of…