2021ApJ...916...58K

We constrained the progenitor masses for 169 supernova remnants (SNRs), eight historically observed supernovae (SNe), and the black hole formation candidate in NGC 6946, finding that they are consistent with originating from a standard initial mass function. Additionally, there were 16 remnants that showed no sign of nearby star formation consistent with a core-collapse SN, making them good Type Ia candidates. Using Hubble Space Telescope broadband imaging, we measured the stellar photometry of ACS/WFC fields in the F435W, F555W, F606W, and F814W filters, as well as WFC3/UVIS fields in F438W, F606W, and F814W. We then fitted this photometry with stellar evolutionary models to determine the ages of the young populations present at the positions of the SNRs and SNe. We then inferred a progenitor mass probability distribution from the fitted age distribution. For 37 SNRs, we tested how different filter combinations affected the inferred masses. We find that filters sensitive to Hα, [N II], and [S II] gas emission can bias mass estimates for remnants that rely on our technique. Using a Kolmogorov-Smirnov test analysis on our most reliable measurements, we find that the progenitor mass distribution is well matched by a power-law index of -2.6_–0.6^+0.5, which is consistent with a standard initial mass function.