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

Abstract

Two new statistics, namely Δ and Δχ, 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 Δχ 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.

High-z Type Ia supernova data: non-Gaussianity and direction dependence

“…• Using HST key project data McClure & Dyer (2007) showed that a statistically significant variation of at least 9 km/s/Mpc exists in the observed value of H0 with a directional uncertainty of about 10-20%. Gupta, Saini (2011) also found directional dependence in the HST key project data.…”

Measurement of Hubble constant: non-Gaussian errors in HST Key Project data

“…The variation does not appear to be an artifact of the Galactic dust; and the overall structure in the map is not consistent with the distribution of dust in the Cosmic Background Explorer (COBE) map [4]. Using techniques based on extreme value theory [5], [6] have reported that the errors in HST key project data are non-Gaussian.…”