PI: P. Frank Winkler, Middlebury College, firstname.lastname@example.org
Address: Department of Physics, Bicentennial Hall, Middlebury, VT 05753, USA
CoI: Knox S. Long, STScI
CoI: William P. Blair, The Johns Hopkins University
Title: Supernova Remnants in the Most Fertile Galaxy: NGC 6946
Abstract: As the host to more recorded supernovae (9 in the past century) than any other galaxy, \ngal is a unique venue for studying young (and old) supernova remnants (SNRs). Using deep emission-line images of \ngal we obtained from WIYN in June 2011, we have identified 108 new emission nebulae through their high \sii:\ha ratios, indicating that they are strong SNR candidates. This is 4 times as many as have previously been identified; of the 135 total objects, only 6 have been spectroscopically confirmed. We propose multislit spectroscopy from GMOS-N to study the majority of those with no spectra to date. Some 26 are essentially unresolved in our images (diameters \lesssim 1\arcsec (=27 pc at \ngal) and hence probably are relatively young. Several are also coincident with soft X-ray sources (a further indicator of youthful vigor) and have strong \oiii emission. Some may be rare, ejecta- dominated core-collapse SNRs akin to Cas A where ``fresh" nucleosynthesis products can be seen. Only spectroscopy, to look for \em broad emission lines from fast-moving ejecta, can confirm this. We will include spectra of two of the 9 recorded SNe in \ngal-the first late-time spectrum of SN 2004et, and the first of SN 1980K with high signal-to-noise. Very few SNRs only a few decades old are known; these spectra will provide a window into the transition from SN to SNR. Finally we will use the \nii:\ha ratio in a large number of ISM- dominated SNRs to map the N abundance and its gradient across the disk of \ngal, and we will use archival \em HST images to identify the environments which produced the SNe whose remnants we see today.
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