Reconciling Volumetric and Individual Galaxy Type Ia Supernova Rates
  Significant observational effort has been devoted to determining volumetric
type Ia supernova rates at high redshifts, leading to clues about the nature of
Ia supernova progenitors and constraints on the iron production in the
universe. A complementary approach is to investigate type Ia supernova rates in
individual, more nearby, galaxies. The popular A+B model for the specific
supernova rate, while reliable for a wide range of galaxy properties, diverges
for large specific star formation rates. Applying it outside its range of
validity could lead to the prediction of excessive type Ia supernova rates.
Moreover, the A+B model it is not directly derived from a delay time
distribution. We here introduce a new model which is explicitly motivated by a
simple delay time distribution composed of a prompt and a delayed component.
The model is in remarkably good agreement with current observational
constraints. It yields a prompt fraction of $f_{p}= 0.11^{+0.10}_{-0.06}$ in
agreement with results based on volumetric rates of type Ia supernovae at high
redshift (Rodney et al. 2014). The model is tested against realistic star
formation rates from the Illustris-1 simulation and is found to be self
consistent in the asymptotic limits. An analytic function that encapsulates the
features of the new model is shown to be in excellent agreement with the data.
In terms of goodness of fit, the new model is strongly preferred over the A+B
model. At $\log{({\rm sSFR})} \gtrsim -9$ there are no constraints from
observations. Observations in this regime will further constrain the delay time
distribution of type Ia supernovae at short delay times.
