The delay-time distribution of type-Ia supernovae from Sloan II

We derive the delay-time distribution (DTD) of type-Ia supernovae (SNe Ia) using a sample of 132 SNe Ia, discovered by the Sloan Digital Sky Survey II (SDSS2) among 66,000 galaxies with spectral-based star-formation histories (SFHs). To recover the best-fit DTD, the SFH of every individual galaxy is compared, using Poisson statistics, to the number of SNe that it hosted (zero or one), based on the method introduced in Maoz et al. (2011). This SN sample differs from the SDSS2 SN Ia sample analyzed by Brandt et al. (2010), using a related, but different, DTD recovery method. Furthermore, we use a simulation-based SN detection-efficiency function, and we apply a number of important corrections to the galaxy SFHs and SN Ia visibility times. The DTD that we find has 4-sigma detections in all three of its time bins: prompt (t < 420 Myr), intermediate (0.4 < t < 2.4 Gyr), and delayed (t > 2.4 Gyr), indicating a continuous DTD, and it is among the most accurate and precise among recent DTD reconstructions. The best-fit power-law form to the recovered DTD is t^(-1.12+/-0.08), consistent with generic ~t^-1 predictions of SN Ia progenitor models based on the gravitational-wave induced mergers of binary white dwarfs. The time integrated number of SNe Ia per formed stellar mass is N_SN/M = 0.00130 +/- 0.00015 Msun^-1, or about 4% of the stars formed with initial masses in the 3-8 Msun range. This is lower than, but largely consistent with, several recent DTD estimates based on SN rates in galaxy clusters and in local-volume galaxies, and is higher than, but consistent with N_SN/M estimated by comparing volumetric SN Ia rates to cosmic SFH.