Non-Gaussianity and direction-dependent systematics in HST Key Project data

Abstract

Two new statistics, namely Δ? and Δ_χ, based on the extreme value theory, were derived by Gupta et al. We use these statistics to study the direction dependence in the HST Key Project data, which provides one of the most precise measurements of the Hubble constant. We also study the non-Gaussianity in this data set using these statistics. Our results for Δ? show that the significance of direction-dependent systematics is restricted to well below the 1σ confidence limit; however, the presence of non-Gaussian features is subtle. On the other hand, the Δ_χ statistic, which is more sensitive to direction dependence, shows direction dependence systematics to be at a slightly higher confidence level, and the presence of non-Gaussian features at a level similar to the Δ? statistic.