We use the HST ACS imaging of the two GOODS fields during Cycles 11 , 12 , and 13 to derive the Type Ia supernova rate in four redshift intervals in the range 0.2 < z < 1.8 .
Compared to our previous results based on Cycle 11 observations only , we have increased the coverage of the search by a factor 2.7 , making the total area searched equivalent to one square degree .
The sample now consists of 56 Type Ia supernovae .
The rates we derive are consistent with our results based on the Cycle 11 observations .
In particular , the few detected supernovae at z > 1.4 supports our previous result that there is a drop in the Type Ia supernova rate at high redshift , suggesting a long time delay between the formation of the progenitor star and the explosion of the supernova .
If described by a simple one-parameter model , we find a characteristic delay time of 2–3 Gyr .
However , a number of recent results based on e.g. , low redshift supernova samples and supernova host galaxy properties suggest that the supernova delay time distribution is bimodal .
In this model , a major fraction of the Type Ia supernova rate is ’ prompt ’ and follows the star formation rate , while a smaller fraction of the rate has a long delay time , making this channel proportional to mass .
While our results are fully consistent with the bimodal model at low redshifts , the low rate we find at z > 1.4 appears to contradict these results .
Models that corrects for star formation hidden by dust may explain at least part of the differences .
Here we discuss this possibility together with other ways to reconcile data and models .