Apparent cosmic acceleration from Type Ia supernovae

作者：Dam Lawrence H; Heinesen Asta; Wiltshire David L^*

来源：Monthly Notices of the Royal Astronomical Society, 2017, 472(1): 835-851.

DOI：10.1093/mnras/stx1858

• cosmological parameters
• dark energy
• cosmology: observations
• cosmology: theory

Parameters that quantify the acceleration of cosmic expansion are conventionally determined within the standard Friedmann-Lemaiitre-Robertson-Walker (FLRW) model, which fixes spatial curvature to be homogeneous. Generic averages of Einstein's equations in inhomogeneous cosmology lead to models with non-rigidly evolving average spatial curvature, and different parametrizations of apparent cosmic acceleration. The timescape cosmology is a viable example of such a model without dark energy. Using the largest available supernova data set, the JLA catalogue, we find that the timescape model fits the luminosity distance-redshift data with a likelihood that is statistically indistinguishable from the standard spatially flat Lambda cold dark matter cosmology by Bayesian comparison. In the timescape case cosmic acceleration is non-zero but has a marginal amplitude, with best-fitting apparent deceleration parameter, q(0)=-0.043(-0.000)(+0.004). Systematic issues regarding standardization of supernova light curves are analysed. Cuts of data at the statistical homogeneity scale affect light-curve parameter fits independent of cosmology. A cosmological model dependence of empirical changes to the mean colour parameter is also found. Irrespective of which model ultimately fits better, we argue that as a competitive model with a non-FLRW expansion history, the timescape model may prove a useful diagnostic tool for disentangling selection effects and astrophysical systematics from the underlying expansion history.

• 出版日期2017-11