Color Dispersion and Milky Way Reddening Among Type Ia Supernovae
  Past analyses of Type Ia Supernovae (SNe Ia) have identified an irreducible
scatter of 5-10% in distance widely attributed to an intrinsic dispersion in
luminosity. Another, equally valid, source of this scatter is intrinsic
dispersion in color. Misidentification of the true source of this scatter can
bias both the retrieved color-luminosity relation and cosmological parameter
measurements. The size of this bias depends on the magnitude of the intrinsic
color dispersion relative to the distribution of colors that correlate with
distance. We produce a realistic simulation of a misattribution of intrinsic
scatter, and find a negative bias in the recovered color-luminosity relation,
beta, of dbeta -1.0 (~33%) and a positive bias in the equation of state
parameter, w, of dw +0.04 (~4%). We re-analyze current published data sets with
the assumptions that the distance scatter is predominantly the result of color.
Unlike previous analyses, we find that the data are consistent with a Milky Way
reddening law R_V=3.1, and that a Milky Way dust model better predicts the
asymmetric color-luminosity trends than the conventional luminosity scatter
hypothesis. We also determine that accounting for color variation reduces the
correlation between various Host galaxy properties and Hubble residuals by
~20%.
