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.
