Confronting Lemaitre–Tolman–Bondi models with observational cosmology

Abstract

The possibility that we live in a special place in the universe, closeto the centre of a large void, seems an appealing alternative to theprevailing interpretation of the acceleration of the universe in terms of aΛCDM model with a dominant dark energy component. In this paper we confront theasymptotically flat Lemaitre–Tolman–Bondi (LTB) models with a series of observations,from type Ia supernovae to cosmic microwave background and baryon acousticoscillations data. We propose two concrete LTB models describing a local void inwhich the only arbitrary functions are the radial dependence of the matter densityΩM and the Hubbleexpansion rate H. We find that all observations can be accommodated within 1 sigma, for ourmodels with four or five independent parameters. The best fit models have aχ2 very close tothat of the ΛCDM model. A general Fortran program for comparing LTB models with cosmologicalobservations, that has been used to make the parameter scan in this paper, has been madepublic, and can be downloaded at http://www.phys.au.dk/∼haugboel/software.shtmltogether with IDL routines for creating the likelihood plots. We perform a simple Bayesiananalysis and show that one cannot exclude the hypothesis that we live within a large localvoid of an otherwise Einstein–de Sitter model.