Browsing by Author "Schwarz, Dominik J."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Constraints on anisotropic cosmic expansion from supernovae
    (Edp Sciences, 2013) Kalus, Benedict; Schwarz, Dominik J.; Seikel, Marina; Wiegand, Alexander
    AIMS. We test the isotropy of the expansion of the Universe by estimating the hemispherical anisotropy of supernova type Ia (SN Ia) Hubble diagrams at low redshifts (z < 0.2). METHODS. We compare the best fit Hubble diagrams in pairs of hemispheres and search for the maximal asymmetric orientation. For an isotropic Universe, we expect only a small asymmetry due to noise and the presence of nearby structures. This test does not depend on the assumed content of the Universe, the assumed model of gravity, or the spatial curvature of the Universe. The expectation for possible fluctuations due to large scale structure is evaluated for the Λ cold dark matter (ΛCDM) model and is compared to the supernova data from the Constitution set for four different light curve fitters, thus allowing a study of the systematic effects. RESULTS. The expected order of magnitude of the hemispherical asymmetry of the Hubble expansion agrees with the observed one. The direction of the Hubble asymmetry is established at 95% confidence level (C.L.) using both, the MLCS2k2 and the SALT II light curve fitter. The highest expansion rate is found towards (ℓ, b) ≈ (−35◦, −19◦), which agrees with directions reported by other studies. Its amplitude is not in contradiction to expectations from the ΛCDM model. The measured Hubble anisotropy is ∆H/H ∼ 0.026. With 95% C.L. the expansion asymmetry is ∆H/H < 0.038.
  • Thumbnail Image
    Item
    Testing foundations of modern cosmology with SKA all-sky surveys
    (Proceedings of Science, 2014) Schwarz, Dominik J.; Bacon, David; Chen, Song; Clarkson, Chris; Huterer, Dragan; Kunz, Martin; Maartens, Roy; Raccanelli, Alvise; Rubart, Matthias; Starck, Jean-Luc
    Continuum and HI surveys with the Square Kilometre Array (SKA) will allow us to probe some of the most fundamental assumptions of modern cosmology, including the Cosmological Principle. SKA all-sky surveys will map an enormous slice of space-time and reveal cosmology at superhorizon scales and redshifts of order unity. We illustrate the potential of these surveys and discuss the prospects to measure the cosmic radio dipole at high fidelity. We outline several potentially transformational tests of cosmology to be carried out by means of SKA all-sky surveys.]