The Supernova Remnant Populations of the galaxies NGC 45, NGC 55, NGC
  1313, NGC 7793: Luminosity and Excitation Functions
  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 Ha and
[S II] imaging. We find 42 candidate and 54 possible candidate SNRs based on
the [S II] / Ha > 0.4 criterion, 84 of which are new identifications. We derive
the Ha and the joint [S II]-Ha luminosity functions after accounting for
incompleteness effects. We find that the Ha luminosity function of the overall
sample is described with a skewed Gaussian with a mean equal to log(LHa /
10^(36) erg s^(-1)) = 0.07 and m(log(LHa / 10^(36) erg s^(-1)))) = 0.58. The
joint [S II]-Ha function is parameterized by a skewed Gaussian along the log([S
II] / 10^(36) erg s^(-1)) = 0.88 x log(LHa / 10^(36) erg s^(-1)) - 0.06 line
and a truncated Gaussian with m(log(L[S II] / 10^(36))) = 0.024 and s(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]/Ha ratios. This function is represented by a truncated Gaussian with a mean
at -0.014. We find a sub-linear [S II]-Ha relation indicating lower excitation
for the more luminous objects.
