The Masses of Supernova Remnant Progenitors in NGC 6946

TL;DR

This study estimates progenitor masses for supernova remnants in NGC 6946, finding they align with a standard initial mass function and identifying potential Type Ia candidates using Hubble imaging and stellar population analysis.

Contribution

It provides the first comprehensive progenitor mass distribution for a large sample of remnants in NGC 6946, incorporating effects of different filter combinations and biases.

Findings

Progenitor masses are consistent with a standard initial mass function.

16 remnants are likely Type Ia supernovae.

Filter choices can bias progenitor mass estimates.

Abstract

We constrained the progenitor masses for 169 supernova remnants, 8 historically observed supernovae, 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 supernova, making them good Type Ia candidates. Using $Hubble$ $Space$ $Telescope$ broadband imaging, we measured stellar photometry of ACS/WFC fields in 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 infer 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 H$\alpha$, [N II], and [S II] gas emission can bias mass estimates for remnants that rely on our technique. Using a KS-test analysis on our most reliable measurements, we find the progenitor mass distribution is well-matched by a power-law index of $-2.6^{+0.5}_{-0.6}$, which is consistent with a standard initial mass function.