Dresden 2013 – scientific programme

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T: Fachverband Teilchenphysik

T 84: Gammaastronomie 4

T 84.1: Talk

Wednesday, March 6, 2013, 16:45–17:00, HSZ-E05

Constraints on anisotropic cosmic expansion from supernovae — •Benedict Kalus¹, Dominik J. Schwarz¹, Marina Seikel^2,3, and Alexander Wiegand⁴ — ¹Bielefeld U., Germany — ²U. of the Western Cape, Cape Town, South Africa — ³U. of Cape Town, Rondebosch, South Africa — ⁴Albert-Einstein-Institut, Potsdam, Germany

We test the isotropy of the expansion of the Universe by estimating the hemispherical anisotropy of SN Ia Hubble diagrams at z<0.2.

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 LCDM model and is compared to the SN data from the Constitution set for four different light curve fitters, thus allowing a study of the systematic effects.

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%CL using both, the MLCS2k2 and the SALT II light curve fitter. The highest expansion rate is found towards (l,b)=(-35,-19) deg, which agrees with directions reported by other studies. Its amplitude is not in contradiction to expectations from the LCDM model. The measured Hubble anisotropy is dH/H=0.026. With 95%CL the expansion asymmetry is dH/H<0.038.