A multi-wavelength study of Supernova Remnants in six nearby galaxies. II. New optically selected Supernova Remnants

TL;DR

This study identifies and characterizes approximately 400 optically emitting supernova remnants across six nearby galaxies using deep imaging and spectroscopy, revealing their properties, environmental influences, and relation to star formation.

Contribution

It provides a comprehensive catalog of optically selected SNRs in multiple galaxies and analyzes their properties and correlations with X-ray data, highlighting environmental effects and metallicity influences.

Findings

Approximately 400 SNRs detected down to a specific flux limit.

Spectroscopic confirmation of 56 shock-excited SNRs.

No correlation found between optical and X-ray luminosities.

Abstract

We present results from a study of optically emitting Supernova Remnants (SNRs) in six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4395, NGC 4449 and NGC 5204) based on deep narrow band H{\alpha} and [SII] images as well as spectroscopic observations. The SNR classification was based on the detected sources that fulfill the well-established emission line flux criterion of [SII]/H{\alpha} > 0.4. This study revealed ~400 photometric SNRs down to a limiting H{\alpha} flux of 10^(-15) erg sec^(-1) cm^(-2). Spectroscopic observations confirmed the shock-excited nature of 56 out of the 96 sources with ([SII]/H{\alpha})$_{phot}$> 0.3 (our limit for an SNR classification) for which we obtained spectra. 11 more sources were spectroscopically identified as SNRs although their photometric [SII]/H{\alpha} ratio was below 0.3. We discuss the properties of the optically-detected SNRs in our sample for different types of galaxies and hence different environments, in order to address their connection with the surrounding interstellar medium. We find that there is a difference in [NII]/H{\alpha} line ratios of the SNR populations between different types of galaxies which indicates that this happens due to metallicity. We cross-correlate parameters of the optically detected SNRs ([SII]/H{\alpha} ratio, luminosity) with parameters of coincident X- ray emitting SNRs, resulted from our previous studies in the same sample of galaxies, in order to understand their evolution and investigate possible selection effects. We do not find a correlation between their H{\alpha} and X-ray luminosities, which we attribute to the presence of material in a wide range of temperatures. We also find evidence for a linear relation between the number of luminous optical SNRs (10^(37) erg sec^(-1)) and SFR in our sample of galaxies.