The Supernova Remnant Populations Of The Galaxies Ngc45, Ngc55, Ngc1313, Ngc7793: Luminosity And Excitation Functions

We present a systematic study of the supernova remnant (SNR) populations in the nearby galaxies NGC45, NGC55, NGC1313, and NGC7793 based on deep H alpha and [S II] imaging. We find 42 candidate and 51 possible candidate SNRs based on the [S II]/H alpha>0.4 criterion, 81 of which are new identifications. We derive the H alpha and the joint [S II]-H alpha luminosity functions after accounting for incompleteness effects. We find that the H alpha luminosity function of the overall sample is described with a skewed Gaussian with a mean equal to log(L-H alpha/10(36) erg s(-1)) = 0.07 and sigma(log(L-H alpha/10(36) erg s(-1))) = 0.58. The joint [S II]-H alpha function is parametrized by a skewed Gaussian along the log([S II]/10(36) erg s(-1)) = 0.88 x log(L-H alpha/10(36) erg s(-1)) - 0.06 line and a truncated Gaussian with mu(log(L-[S II]/1036)) = 0.024 and 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 alpha ratios. This function is represented by a truncated Gaussian with a mean at -0.014. We find a sub-linear [S II]-H alpha relation indicating lower excitation for the more luminous objects.