Projected distances to host galaxy reduce SNIa dispersion
  We use multi-band imagery data from the Sloan Digital Sky Survey (SDSS) to
measure projected distances of 302 supernova type Ia (SNIa) from the centre of
their host galaxies, normalized to the galaxy's brightness scale length, with a
Bayesian approach. We test the hypothesis that SNIas further away from the
centre of their host galaxy are less subject to dust contamination (as the dust
column density in their environment is smaller) and/or come from a more
homogeneous environment. Using the Mann-Whitney U test, we find a statistically
significant difference in the observed colour correction distribution between
SNIas that are near and those that are far from the centre of their host. The
local p-value is 3 x 10^{-3}, which is significant at the 5 per cent level
after look-elsewhere effect correction. We estimate the residual scatter of the
two subgroups to be 0.073 +/- 0.018 for the far SNIas, compared to 0.114 +/-
0.009 for the near SNIas -- an improvement of 30 per cent, albeit with a low
statistical significance of 2sigma. This confirms the importance of host galaxy
properties in correctly interpreting SNIa observations for cosmological
inference.
