SN Ia rate (rate per unit mass) versus galaxy mass as measured by LOSS [@Li:2010iii]. One is first struck by the steep dependence of this specific rate on galaxy mass. This variation of over an order of magnitude demands a physical explanation. The cause should be distinct from the origin of a similar pattern seen in the specific core-collapse supernova rate by LOSS, which likely arises mainly from the dependence of the specific star formation rate on galaxy mass [@Li:2010iii].

![The specific rate of Type Ia supernovae versus host galaxy mass. Shown are data from LOSS for galaxies grouped by Hubble type [@Li:2010iii]. Our models are also displayed, which assume either a $\Delta t^{-1}$ delay time distribution alone ([*solid line*]{}) or an additional dependence on stellar metallicity ([*dashed, dotted lines*]{}; see text).\
\[Iarate\]](Iarate){width="3.38in"}

Importantly, we also see that at a fixed mass the SN Ia rate does not vary greatly between galaxies of different Hubble type. This suggests that by examining a large set of galaxies one can arrive at the global behavior of SNe Ia. We proceed by translating the LOSS measured specific SN Ia rates in galaxies of various Hubble types from a function of galactic mass into 