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- Title
CO multi-line imaging of nearby galaxies (COMING). XII. CO-to-H2 conversion factor and dust-to-gas ratio.
- Authors
Yasuda, Atsushi; Kuno, Nario; Sorai, Kazuo; Muraoka, Kazuyuki; Miyamoto, Yusuke; Kaneko, Hiroyuki; Yajima, Yoshiyuki; Tanaka, Takahiro; Morokuma-Matsui, Kana; Takeuchi, Tsutomu T; Kobayashi, Masato I N
- Abstract
We simultaneously measured the spatially resolved CO-to-H2 conversion factor (αCO) and dust-to-gas ratio (DGR) in nearby galaxies on a kiloparsec scale. In this study, we used 12CO(J = 1–0) data obtained by the Nobeyama 45 m radio telescope with H i and dust mass surface densities. We obtained the values of global αCO and DGR in 22 nearby spiral galaxies, with averages of 2.66 ± 1.36 M ⊙ pc−2 (K km s−1)−1 and 0.0052 ± 0.0026, respectively. Furthermore, the radial variations of αCO and DGR in four barred spiral galaxies (IC 342, NGC 3627, NGC 5236, and NGC 6946) were obtained by dividing them into inner and outer regions with a boundary of 0.2 R 25, where R 25 is the isophotal radius at 25 mag arcsec−2 in the B band. The averages of αCO and DGR in the inner region (≤0.2 R 25) are 0.36 ± 0.08 M ⊙ pc−2 (K km s−1)−1 and 0.0199 ± 0.0058, while those in the outer region (>0.2 R 25) are 1.49 ± 0.76 M ⊙ pc−2 (K km s−1)−1 and 0.0084 ± 0.0037, respectively. The value of αCO in the outer region is 2.3 to 5.3 times larger than that of the inner region. When separated into the inner and outer regions, we find that αCO and DGR correlate with the metallicity and the star formation rate surface density. The value of αCO derived in this study tends to be smaller than those obtained in previous studies for the Milky Way and nearby star-forming galaxies. This fact can be attributed to our measurements being biased toward the inner region; we measured αCO at 0.85 and 0.76 times smaller in radius than the previous works for nearby star-forming galaxies and the Milky Way, respectively.
- Subjects
NEW General Catalogue of Nebulae &; Clusters of Stars; MILKY Way; GALAXIES; RADIO telescopes; STAR formation; RADIO galaxies; SPIRAL galaxies
- Publication
Publications of the Astronomical Society of Japan, 2023, Vol 75, Issue 4, p743
- ISSN
0004-6264
- Publication type
Article
- DOI
10.1093/pasj/psad034