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Title: A 6% measurement of the Hubble parameter at z~0.45: direct evidence of the epoch of cosmic re-acceleration
Author: Moresco, Michele
Pozzetti, Lucia
Cimatti, Andrea
Jiménez, Raúl (Jiménez Tellado)
Maraston, Claudia
Verde, Licia
Thomas, Daniel
Citro, Annalisa
Tojeiro, Rita
Wilkinson, David
Keywords: Cosmologia
Issue Date: May-2016
Publisher: Institute of Physics (IOP)
Abstract: Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H(z) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ~11-16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H(z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring zt = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond and including the ΛCDM model.
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It is part of: Journal of Cosmology and Astroparticle Physics, 2016, vol. 5, num. 014
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ISSN: 1475-7516
Appears in Collections:Publicacions de projectes de recerca finançats per la UE
Articles publicats en revistes (Institut de Ciències del Cosmos (ICCUB))

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