Type Ia supernovae ( SNe Ia ) occur in both old , passive galaxies and active , star-forming galaxies .
This fact , coupled with the strong dependence of SN Ia rate on star formation rate , suggests that SNe Ia form from stars with a wide range of ages .
Here we show that the rate of SN Ia explosions is about 1 % of the stellar death rate , independent of star formation history .
The dependence of SN Ia rate on star formation rate implies a delay time distribution proportional to t ^ { -0.5 \pm 0.2 } .
The single degenerate channel for SNe Ia can be made to match the observed SN Ia rate – SFR relation , but only if white dwarfs are converted to SNe Ia with uniform efficiency of \sim 1 % , independent of mass .
Since low-mass progenitors are expected to have lower conversion efficiencies than high mass progenitors , we conclude that some other progenitor scenario must be invoked to explain some , or perhaps all , SNe Ia .