for the weaker effects of the DTDs used, the rate does indeed rise more steeply at lower galactic masses than by taking into account age alone. This can be interpreted as a relative change in efficiency, an effect at the factor of $\sim\,$2 level over the mass range of Fig. \[Iarate\] for the $f_{0.85}$ model and slightly less for the $f_{0.70}$ case.

Because galaxy mass is strongly correlated with both age and metallicity, it is inevitable that the models are relatively degenerate and that inferences about the DTD from galaxy populations may err without accounting for metallicity. Our simplified treatment of galactic star formation histories may somewhat underpredict SN Ia rates at intermediate masses. This may be refined through more detailed modeling, although, given the uncertainties in our inputs, we will not attempt to do so here. It is encouraging that such broad agreement with data is already seen using quite general assumptions.

We note here that the normalization of these models can be scaled up or down, although this will directly affect the normalization of the expected cosmic SN Ia rates through the DTD, as we will discuss in the following Section. Note also that care should be taken 