  The effect of progenitor metallicity on Type Ia Supernovae (SNe Ia) has
important cosmological implications due to the need for these standardizable
candles to be compared across large spans of cosmic time in which the
progenitor stars might have different properties. Theoretical models have come
to different conclusions as to the wavelength range impacted by metallicity
differences, leading to differing interpretations of the growing sample of UV
observations. Recent work has claimed a correlation between the mid-UV flux of
SNe Ia measured from Swift grism spectra and the gas-phase metallicities
measured for their host galaxies. Here we examine UV photometry for the same
objects. We find no significant correlations between the UV-optical colors (or
UV/optical count rate ratios) of the SNe Ia and the host galaxy properties of
mass or metallicity. The lack of a significant correlation with host galaxy
metallicity implies another physical difference other than progenitor
metallicity dominates the UV flux differences. We are no longer limited by a
lack of UV observations. Rather, understanding the existing observations
requires improved theoretical models and a larger parameter space of physical
differences.
