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 (nine 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, we have identified 148 new emission nebulae through their high \sii:\ha ratios, indicating that they are strong SNR candidates. This is over 5 times as many as have previously been identified; yet of the 175 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 nine recorded SNe in \ngal-the first late-time spectrum of SN 2004et, and the first of SN 1980K with high signal-to-noise-adding to the extremely small number of spectra for SNRs only a few decades old. 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 stellar environments that produced the SNe whose remnants we see today.
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