2021MNRAS.507.6020K

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 αand [S II] imaging. We find 42 candidate and 51 possible candidate SNRs based on the [S II]/H α>0.4 criterion, 81 of which are new identifications. We derive the H αand the joint [S II]-H αluminosity functions after accounting for incompleteness effects. We find that the H αluminosity function of the overall sample is described with a skewed Gaussian with a mean equal to log(L_Hα/10³⁶ erg s^–1)=0.07 and σ (log(L_Hα/10³⁶ erg s^–1))=0.58. The joint [S II]-H αfunction is parametrized by a skewed Gaussian along the log([S II]/10³⁶ erg s^–1) = 0.88 ×log(L_Hα/10³⁶ erg s^–1) - 0.06 line and a truncated Gaussian with µ(log(L_[S II]_/10³⁶)) = 0.024 and σ (log(L_[S II]_/10³⁶)) = 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 αratios. This function is represented by a truncated Gaussian with a mean at -0.014. We find a sub-linear [S II]-H αrelation indicating lower excitation for the more luminous objects.