Program: GN-2015B-Q-91

As the host to more recorded supernovae (nine in the past century) than any other galaxy, NGC 6946 is a unique venue for studying both young and old supernova remnants (SNRs). Using deep emission-line images we obtained from WIYN, we have identified 148 new emission nebulae in NGC 6946 through their high [S II] to H-alpha ratios, indicating that they are strong SNR candidates. This is over 5 times as many as have previously been identified, yet before we began this program, only 6 of the 175 total objects had been spectroscopically confirmed as SNRs. We propose to continue our program of multislit spectroscopy from GMOS-N---begun in 2014B---to include spectra for nearly 75% of the candidates, including ones over the full brightness range and dispersed over the entire galactic disk. Especially interesting are the smallest, hence presumably youngest SNRs, where we have the best chance of sampling fresh products of nucleosynthesis. For the entire SNR population we will use ratios of [N II] and [S II] to H-alpha to map the elemental abundances and their gradient across the face of NGC 6946. Finally, we are using HST images to connect SNRs with the stellar environments from which they sprang. Suitable data already exist in the HST archive for about 1/3 of the galaxy, that will be extended to most of the galactic disk if a joint Chandra-HST program we have proposed is successful.