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 54 possible candidate SNRs based on the [S ii]/H$\rm {\alpha }$>0.4 criterion, 84 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 parameterized 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.

Optical emission-line Luminosity Function models for populations of Supernova Remnants

“…In Figure 2 (blue histogram) we show the derived H𝛼 LF, for an SNR sample with an age and ambient ISM density distribution as described in § 2.1, magnetic parameters from 1 to 3 𝜇𝐺 𝑐𝑚 3/2 , and filling factor 𝑓 = 1. Its shape is very similar to the observed luminosity function of SNRs in nearby galaxies (red line; Kopsacheili et al 2021). However, the peak of the theoretical H𝛼 LF is at luminosities ∼0.3 dex higher than expected from the observations.…”

“…red points in Figure 4) where the SNR distribution on the H𝛼 -[S ] plane presents a sub-linearity (Fig. 8 and 10 in Kopsacheili et al 2021). In the data this trend is magnified since SNRs in denser environments are more likely to be embedded in H regions.…”

“…In Figure 3 and in the right-hand panels of Figure 4, we compare the theoretical luminosity functions with those measured in 4 nearby galaxies (red line; Kopsacheili et al 2021). We see that there is a very good agreement between the theoretical and observational luminosity functions more or less for all the magnetic parameters.…”

“…In some of these cases, and especially for the joint LF (figures 4 and 6) we see that the theoretical luminosities have a broader luminosity range than the data, extending to lower luminosities. This happens because the observed population of candidate SNRs presented in this study (Kopsacheili et al 2021) were selected such as their H𝛼 luminosity is 3𝜎 above the background and their [S ] /H𝛼 ratio 3𝜎 above the 0.4 threshold. These limits exclude especially sources with lower luminosity.…”

“…★ E-mail: mariakop@physics.uoc.gr Despite the growing number of known SNRs and SNR populations in other galaxies, we still lack a framework that can describe the SNR populations in terms of their observational characteristics but also in the context of expectations from theoretical models for their evolution. A first step in this direction was made in Kopsacheili et al (2021), who presented a method for the calculation of luminosity functions of SNRs free of selection effects, and introduced the joint H𝛼 -[S ] luminosity function (LF), as well as, their excitation function (i.e. the offset of an SNR from the L [S II] = 0.4L H𝛼 relation).…”