Geometrical tests of cosmological models. III. The Cosmology-evolution diagram at z = 1
Résumé
The rotational velocity of distant galaxies, when interpreted as a size (luminosity) indicator, may be used as a tool to select high redshift standard rods (candles) and probe world models and galaxy evolution via the classical angular diameter-redshift or Hubble diagram tests. We implement the proposed testing strategy using a sample of 30 rotators spanning the redshift range 0.2 < z < 1 with high resolution spectra and images obtained by the VIMOS/VLT Deep Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs). We show that by applying at the same time the angular diameter-redshift and Hubble diagrams to the same sample of objects (i.e. velocity selected galactic discs) one can derive a characteristic chart, the cosmology-evolution diagram, mapping the relation between global cosmological parameters and local structural parameters of discs such as size and luminosity. This chart allows to put constraints on cosmological parameters when general prior information about discs evolution is available. In particular, by assuming that equally rotating large discs cannot be less luminous at z = 1 than at present (M(z=1) ≲ M(0)), we find that a flat matter dominated cosmology (Ω_m=1) is excluded at a confidence level of 2 σ and an open cosmology with low mass density (Ωm ˜ 0.3) and no dark energy contribution (ΩΛ) is excluded at a confidence level greater than 1 σ. Inversely, by assuming prior knowledge about the cosmological model, the cosmology-evolution diagram can be used to gain useful insights about the redshift evolution of baryonic discs hosted in dark matter halos of nearly equal masses. In particular, in a Λ CDM cosmology, we find evidence for a bimodal evolution where the low-mass discs have undergone significant surface brightness evolution over the last 8.5 Gyr, while more massive systems have not. We suggest that this dichotomy can be explained by the epochs at which these two different populations last assembled.