Program: GN-2021A-Q-222

We propose to develop the first pure, reliable, and reasonably complete sample of supernova remnants (SNRs) in the Magellanic irregular galaxy NGC4449. While samples of SNR populations have been studied in several spiral galaxies in recent years, the Magellanic Clouds are so far the lone samples in a dramatically different galaxy type: ones with low metallicity but high star-formation rate. NGC4449 is the best target to pursue, since it is nearby (4.0 Mpc), relatively unabsorbed, and has a star formation rate of 0.5 M_sun/yr, over twice that of the LMC. The only published census identified 71 SNR candidates in NGC4449 (Leonidaki+ 2013), but this was done using emission-line imaging with a small telescope under mediocre conditions. Although a few of the brightest of their candidates were confirmed spectroscopically, most have not been, furthermore, we know nothing about their sizes or other characteristics. We propose to use emission-line images from GMOS-N to develop a sample of SNR candidates that is both far more sensitive and that has high enough resolution to give size estimates---either directly for ones larger than about 1 arcsec (19 pc), or by enabling unique identification and measurement using archival HST H-alpha images. We will then do follow-up MOS spectroscopy to confirm candidates using dual diagnostics: both the classic [S II]:H-alpha line flux ratio, and our recently demonstrated kinematic criterion---SNRs have velocity widths significantly broader than H II regions. The sample we develop should thus be free from contamination, and we will use it to compare and contrast SNR energetics, chemistry, and evolution with populations in spirals such as M33, M83, and NGC6946, as well as with that in the LMC.