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Title: Supernova Remnants in the Irregular Galaxy NGC 4449
Abstract

The nearby irregular galaxy NGC 4449 has a star formation rate of ∼0.4M☉yr−1and should host of order 70 supernova remnants (SNRs) younger than 20,000 yr, a typical age for SNRs expanding into an interstellar medium (ISM) with a density of 1 cm−3to reach the radiative phase. We have carried out an optical imaging and spectroscopic survey in an attempt to identify these SNRs. This task is challenging because diffuse gas with elevated ratios of [Sii]:Hαis omnipresent in NGC 4449, causing confusion when using this common diagnostic for SNRs. Using narrowband interference-filter images, we first identified 49 objects that have elevated [Sii]:Hαratios compared to nearby Hiiregions. Using Gemini-N and GMOS, we then obtained high-resolution spectra of 30 of these SNR candidates, 25 of which have [Sii]:Hαratios greater than 0.5. Of these, 15 nebulae are almost certainly SNRs, based on a combination of characteristics: higher [Oi]:Hαratios and broader line widths than observed from Hiiregions. The remainder are good candidates as well, but need additional confirmation. Surprisingly, despite having superior imaging and spectroscopic data sets to examine, we are unable to confirm most of the candidates suggested by Leonidaki et al. While NGC 4449 is likely an extreme case because of the high surface brightness and elevated [Sii]:Hαratio of diffuse gas, it highlights the need for sensitive high-resolution optical spectroscopy, or high spatial resolution radio or X-ray observations that can ensure accurate SNR identifications in external galaxies.

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NSF-PAR ID:
10478205
Author(s) / Creator(s):
; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
959
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 62
Size(s):
["Article No. 62"]
Sponsoring Org:
National Science Foundation
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