one of galactic [*metallicity*]{}. To do this, we convert between galactic mass and median metallicity using the relation derived from SDSS data in @Gallazzi:2005df, as shown by the upper axis of Fig. \[Iarate\]. This technique effectively averages over a large representative galaxy population similar to that sampled by LOSS.

Since there is a delay from stellar birth to SN Ia explosion, a galaxy’s SN Ia rate depends upon the age of its white dwarf population. This is typically quantified by an empirical or theoretical delay-time distribution (DTD), which results in a SN Ia rate that can be simply written as $$\dot{N}_{\rm Ia}(t) = \int_{t_0}^{t} dt^\prime \, \phi(t-t^\prime) \,  \dot{\rho}_*(t^\prime),
    \label{eq:rate}$$ where $t_0$ is the age of the universe when SN Ia progenitor stars first formed and $\phi(t-t^\prime)$ is the DTD, which maps between the rate of star formation at time $t^\prime$, $\dot{\rho}_*(t^\prime)$, and the SN Ia rate at a later time $t=t^\prime+\Delta t$. Eq. (\[eq:rate\]) can be used to calculate the expected SN Ia rate of an individual galaxy or the universe as a whole, given a properly normalized $\dot{\rho}_*(t)$ (for the cosmic SN Ia rate, we will use the star formation rate density). Recent studies have suggested that $\phi$ 