Supernova Remnants in the Irregular Galaxy NGC 4449
The nearby irregular galaxy NGC 4449 has a star formation rate of ∼0.4 M _☉ yr ^−1 and 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 ^−3 to reach the radiative phase. We have carried...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad0237 |
| _version_ | 1797403207198048256 |
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| author | P. Frank Winkler Knox S. Long William P. Blair |
| author_facet | P. Frank Winkler Knox S. Long William P. Blair |
| author_sort | P. Frank Winkler |
| collection | DOAJ |
| description | The nearby irregular galaxy NGC 4449 has a star formation rate of ∼0.4 M _☉ yr ^−1 and 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 ^−3 to 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 [S ii ]:H α is 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 [S ii ]:H α ratios compared to nearby H ii regions. Using Gemini-N and GMOS, we then obtained high-resolution spectra of 30 of these SNR candidates, 25 of which have [S ii ]:H α ratios greater than 0.5. Of these, 15 nebulae are almost certainly SNRs, based on a combination of characteristics: higher [O i ]:H α ratios and broader line widths than observed from H ii regions. 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 [S ii ]:H α ratio 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. |
| first_indexed | 2024-03-09T02:35:12Z |
| format | Article |
| id | doaj.art-275d074a0e5c44849a5dd3946a795178 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-09T02:35:12Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-275d074a0e5c44849a5dd3946a7951782023-12-06T09:22:53ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195916210.3847/1538-4357/ad0237Supernova Remnants in the Irregular Galaxy NGC 4449P. Frank Winkler0https://orcid.org/0000-0001-6311-277XKnox S. Long1https://orcid.org/0000-0002-4134-864XWilliam P. Blair2https://orcid.org/0000-0003-2379-6518Department of Physics, Middlebury College , Middlebury, VT 05753, USA ; winkler@middlebury.edu; Visiting astronomer, Kitt Peak National Observatory , part of NSF's NOIRLab, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, USAVisiting astronomer, Kitt Peak National Observatory , part of NSF's NOIRLab, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, USA; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore MD 21218, USA ; long@stsci.edu; Eureka Scientific, Inc. 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017, USAVisiting astronomer, Kitt Peak National Observatory , part of NSF's NOIRLab, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, USA; The William H. Miller III Department of Physics and Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD, 21218, USA ; wblair@jhu.eduThe nearby irregular galaxy NGC 4449 has a star formation rate of ∼0.4 M _☉ yr ^−1 and 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 ^−3 to 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 [S ii ]:H α is 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 [S ii ]:H α ratios compared to nearby H ii regions. Using Gemini-N and GMOS, we then obtained high-resolution spectra of 30 of these SNR candidates, 25 of which have [S ii ]:H α ratios greater than 0.5. Of these, 15 nebulae are almost certainly SNRs, based on a combination of characteristics: higher [O i ]:H α ratios and broader line widths than observed from H ii regions. 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 [S ii ]:H α ratio 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.https://doi.org/10.3847/1538-4357/ad0237Supernova remnants |
| spellingShingle | P. Frank Winkler Knox S. Long William P. Blair Supernova Remnants in the Irregular Galaxy NGC 4449 The Astrophysical Journal Supernova remnants |
| title | Supernova Remnants in the Irregular Galaxy NGC 4449 |
| title_full | Supernova Remnants in the Irregular Galaxy NGC 4449 |
| title_fullStr | Supernova Remnants in the Irregular Galaxy NGC 4449 |
| title_full_unstemmed | Supernova Remnants in the Irregular Galaxy NGC 4449 |
| title_short | Supernova Remnants in the Irregular Galaxy NGC 4449 |
| title_sort | supernova remnants in the irregular galaxy ngc 4449 |
| topic | Supernova remnants |
| url | https://doi.org/10.3847/1538-4357/ad0237 |
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