The type II supernova rate in z ∼ 0.1 galaxy clusters from the multi-EPOCH nearby cluster survey

We present seven spectroscopically confirmed Type II cluster supernovae (SNeII) discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey targeting 57 low-redshift 0.05 < z < 0.15 galaxy clusters with the Canada-France-Hawaii Telescope. We find the rate of Type II supernovae within R ₂₀₀ of z 0.1 galaxy clusters to be 0.026^+0.085 _{- 0.018}(stat)^+0.003 _{- 0.001}(sys) SNuM. Surprisingly, one SNII is in a red-sequence host galaxy that shows no clear evidence of recent star formation (SF). This is unambiguous evidence in support of ongoing, low-level SF in at least some cluster elliptical galaxies, and illustrates that galaxies that appear to be quiescent cannot be assumed to host only Type Ia SNe. Based on this single SNII we make the first measurement of the SNII rate in red-sequence galaxies, and find it to be 0.007^+0.014 _{- 0.007}(stat)^+0.009 _{- 0.001}(sys) SNuM. We also make the first derivation of cluster specific star formation rates (sSFR) from cluster SNII rates. We find that for all galaxy types the sSFR is 5.1 ^+15.8 _{- 3.1}(stat) ± 0.9(sys) M _o yr ^-1 (10¹² M _o)^-1, and for red-sequence galaxies only it is 2.0^+4.2 _{- 0.9}(stat) ± 0.4(sys) M _o yr^-1 (10¹² M _o)^-1. These values agree with SFRs measured from infrared and ultraviolet photometry, and Hα emission from optical spectroscopy. Additionally, we use the SFR derived from our SNII rate to show that although a small fraction of cluster Type Ia SNe may originate in the young stellar population and experience a short delay time, these results do not preclude the use of cluster SNIa rates to derive the late-time delay time distribution for SNeIa.