12CO and 13CO observation of the low-metallicity dwarf galaxy DDO 154
Abstract
The conversion factor from carbon monoxide (CO) intensity to molecular gas mass is a source of large uncertainty in understanding gas and its relation to star formation in galaxies. In particular, the conversion factor in low-metallicity environments have remained elusive, as currently only two galaxies have been detected in any CO isotopes in environments with 12 + log (O$/$H) < 8.0. Here we report 12CO (J = 1-0) and 13CO (J = 1-0) observations towards a star-forming region in DDO 154, a low-metallicity dwarf irregular galaxy at 12 + log (O$/$H) = 7.67. This is a re-observation of a previous non-detection at higher angular and velocity resolution. No significant emission was detected. By estimating the molecular gas mass from associated star formation, we find that DDO 154 has a conversion factor of more than 103 times the Milky Way. Alternatively, if we estimate molecular mass using dust continuum emission, the conversion factor is at least 2 orders of magnitude larger than the Milky Way. These estimates signify a large amount of CO-dark molecular gas in this galaxy.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- December 2023
- DOI:
- 10.1093/pasj/psad074
- arXiv:
- arXiv:2311.11495
- Bibcode:
- 2023PASJ...75.1337K
- Keywords:
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- galaxies: dwarf;
- galaxies: ISM;
- ISM: abundances;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 7 pages, 2 figures, published in Publications of the Astronomical Society of Japan (PASJ)