The Multi-Epoch Nearby Cluster Survey: Type Ia supernova rate measurement in z 0.1 clusters and the late-time delay time distribution

We describe the Multi-Epoch Nearby Cluster Survey, designed to measure the cluster Type Ia supernova (SN Ia) rate in a sample of 57 X-ray selected galaxy clusters, with redshifts of 0.05 < z < 0.15. Utilizing our real-time analysis pipeline, we spectroscopically confirmed twenty-three cluster SNe Ia, four of which were intracluster events. Using our deep Canada-France-Hawaii Telescope/MegaCam imaging, we measured total stellar luminosities in each of our galaxy clusters, and we performed detailed supernova (SN) detection efficiency simulations. Bringing these ingredients together, we measure an overall cluster SN Ia rate within R₂₀₀ (1Mpc) of 0.042^+0.012 _-0.010 ^+0.010_-0.008 SNuM (0.049 ^+0.016_-0.014 ^+0.005_-0.004 SNuM) and an SN Ia rate within red-sequence galaxies of 0.041^+0.015 _-0.015 ^+0.005_-0.010 SNuM (0.041 ^+0.019_-0.015 ^+0.005_-0.004 SNuM). The red-sequence SN Ia rate is consistent with published rates in early-type/elliptical galaxies in the "field." Using our red-sequence SN Ia rate, and other cluster SN measurements in early-type galaxies up to z 1, we derive the late-time (>2Gyr) delay time distribution (DTD) of SN Ia assuming a cluster early-type galaxy star formation epoch of z_f = 3. Assuming a power-law form for the DTD, Ψ(t)t^s , we find s = -1.62 0.54. This result is consistent with predictions for the double degenerate SN Ia progenitor scenario (s ∼ -1) and is also in line with recent calculations for the double detonation explosion mechanism (s ∼ -2). The most recent calculations of the single degenerate scenario DTD predicts an order-of-magnitude drop-off in SN Ia rate ∼6-7Gyr after stellar formation, and the observed cluster rates cannot rule this out.