The Impact of Metallicity on the Rate of Type Ia Supernovae
  The metallicity of a star strongly affects both its evolution and the
properties of the stellar remnant that results from its demise. It is generally
accepted that stars with initial masses below ~8 M_sun leave behind white
dwarfs and that some sub-population of these lead to Type Ia supernovae.
However, it is often tacitly assumed that metallicity has no effect on the rate
of SNe Ia. We propose that a consequence of the effects of metallicity is to
significantly increase the SN Ia rate in lower-metallicity galaxies, in
contrast to previous expectations. This is because lower-metallicity stars
leave behind higher-mass white dwarfs, which should be easier to bring to
explosion. We first model SN Ia rates in relation to galaxy masses and ages
alone, finding that the elevation in the rate of SNe Ia in lower-mass galaxies
measured by LOSS is readily explained. However, we then see that models
incorporating this effect of metallicity agree just as well. Using the same
parameters to estimate the cosmic SN Ia rate, we again find good agreement with
data up to z~2. We suggest that this degeneracy warrants more detailed
examination of host galaxy metallicities. We discuss additional implications,
including for hosts of high-z SNe Ia, the SN Ia delay time distribution,
super-Chandrasekhar SNe, and cosmology.
