Browsing by Subject "Red shift"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Open Access
    Constraining scalar-tensor quintessence by cosmic clocks
    (2007) Capozziello, S; Dunsby, P K S; Piedipalumbo, E; Rubano, C
    Aims. We study scalar tensor theories of gravity with power law scalar field potentials as cosmological models for accelerating universe, using cosmic clocks. Methods. Scalar-tensor quintessence models can be constrained by identifying suitable cosmic clocks which allow one to select confidence regions for cosmological parameters. In particular, we constrain the characterizing parameters of non-minimally coupled scalar-tensor cosmological models which admit exact solutions of the Einstein field equations. Lookback time to galaxy clusters at low intermediate, and high redshifts is considered. The high redshift time-scale problem is also discussed in order to select other cosmic clocks such as quasars. Results. The presented models seem to work in all the regimes considered: the main feature of this approach is the fact that cosmic clocks are completely independent of each other, so that, in principle, it is possible to avoid bias due to primary, secondary and so on indicators in the cosmic distance ladder. Conclusions. We have used different methods to test cosmological models at low, intermediate and high redshift by different indicators: this seems to confirm independently these proposed dark energy models.
  • Thumbnail Image
    Item
    Open Access
    Extragalactic large-scale structures behind the southern Milky Way: IV. Redshifts obtained with MEFOS
    (2004) Woudt, P A; Kraan-Korteweg, R C; Cayatte, V; Balkowski, C; Felenbok, P
    Abbreviated: As part of our efforts to unveil extragalactic large-scale structures behind the southern Milky Way, we here present redshifts for 764 galaxies in the Hydra/Antlia, Crux and Great Attractor region (266deg < l < 338deg, < 10deg), obtained with the Meudon-ESO Fibre Object Spectrograph (MEFOS) at the 3.6-m telescope of ESO. The observations are part of a redshift survey of partially obscured galaxies recorded in the course of a deep optical galaxy search behind the southern Milky Way. A total of 947 galaxies have been observed, a small percentage of the spectra (N=109, 11.5%) were contaminated by foreground stars, and 74 galaxies (7.8%) were too faint to allow a reliable redshift determination. With MEFOS we obtained spectra down to the faintest galaxies of our optical galaxy survey, and hence probe large-scale structures out to larger distances (v <~ 30000 km/s) than our other redshift follow-ups. The most distinct large-scale structures revealed in the southern Zone of Avoidance are discussed in context to known structures adjacent to the Milky Way.
  • Thumbnail Image
    Item
    Open Access
    Unveiling the nature of INTEGRAL objects through optical spectroscopy: III. Observations of seven southern sources
    (2006) Masetti, N; Pretorius, M L; Palazzi, E; Bassani, L; Bazzano, A; Bird, A J; Charles, P A; Dean, A J; Malizia, A; Nkundabakura, P; Stephen, J B; Ubertini, P
    . The detection, thanks to the