A search for radio supernova remnants in four irregular galaxies

Abstract

We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1σ ∼ 20 μJy), high-resolution (∼20 pc) Very Large Array continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and Hα images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, seven in NGC 4214, five in NGC 2366, and eight 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 with 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. © 2009. The American Astronomical Society. All rights reserved.