The supernova remnant populations of the galaxies NGC 45, NGC 55, NGC 1313, NGC 7793: luminosity and excitation functions

ABSTRACT We present a systematic study of the supernova remnant (SNR) populations in the nearby galaxies NGC 45, NGC 55, NGC 1313, and NGC 7793 based on deep H $\rm {\alpha }$ and [S ii] imaging. We find 42 candidate and 51 possible candidate SNRs based on the [S ii]/H $\rm {\alpha }$>0.4 criterion, 81 of which are new identifications. We derive the H $\rm {\alpha }$ and the joint [S ii]–H $\rm {\alpha }$ luminosity functions after accounting for incompleteness effects. We find that the H $\rm {\alpha }$ luminosity function of the overall sample is described with a skewed Gaussian with a mean equal to $\rm \log (L_{H\alpha }/10^{36}\, erg\, s^{-1})=0.07$ and $\rm \sigma (\log (L_{H\alpha }/10^{36}\, erg\, s^{-1}))=0.58$. The joint [S ii]–H $\rm {\alpha }$ function is parametrized by a skewed Gaussian along the log([S ii]$\rm /10^{36}\, erg\, s^{-1}) = 0.88 \times \log (L_{H\alpha }/10^{36}\, erg\, s^{-1}) - 0.06$ line and a truncated Gaussian with $\rm \mu (\log (L_{[S\, II]}/10^{36})) = 0.024$ and $\rm \sigma (\log (L_{[S\, II]}/10^{36})) = 0.14$, on its vertical direction. We also define the excitation function as the number density of SNRs as a function of their [S ii]/H $\rm {\alpha }$ ratios. This function is represented by a truncated Gaussian with a mean at −0.014. We find a sub-linear [S ii]–H $\rm {\alpha }$ relation indicating lower excitation for the more luminous objects.