A Search for Radio Supernova Remnants in Four Irregular Galaxies

TL;DR

This study surveys four irregular galaxies using high-resolution radio data to identify and classify supernova remnants, finding 43 candidates and analyzing their luminosity and distribution.

Contribution

It provides a detailed catalog of radio supernova remnants in four irregular galaxies using multi-frequency radio observations and spectral analysis.

Findings

Identified 43 SNR candidates across four galaxies.

Most SNRs are less luminous than Cas A at 20 cm.

A significant fraction of thermal flux is in diffuse or low-luminosity H II regions.

Abstract

We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1 sigma ~ 20 microJy), high resolution (~20 pc) VLA continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and H alpha images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, 7 in NGC 4214, 5 in NGC 2366, and 8 in NGC 4449. Only one SNR--the well-studied object J1228+441 in NGC 4449--is more luminous at 20 cm than Cas A. By comparing the total thermal flux density in each galaxy to that localized in H II regions, we conclude that a significant fraction must be in a diffuse component or in low-luminosity H II regions.