A study of optical observing techniques for extra-galactic supernova remnants: Case of NGC300

We present the results of a study of observational and identification techniques used for surveys and spectroscopy of candidate supernova remnants (SNRs) in the Sculptor Group galaxy NGC300. The goal of this study was to investigate the reliability of using [Sii]:Hα ≥ 0.4 in optical SNR surveys and spectra as an identifying feature of extra-galactic SNRs (egSNRs), and also to investigate the effectiveness of the observing techniques (which are hampered by seeing conditions and telescope pointing errors) using this criterion in egSNR surveys and spectrographs. This study is based on original observations of these objects and archival data obtained from the Hubble Space Telescope which contained images of some of the candidate SNRs in NGC300. We found that the reliability of spectral techniques may be questionable and very high-resolution images may be needed to confirm a valid identification of some egSNRs.