CO multi-line imaging of nearby galaxies (COMING). XII. CO-to-H2 conversion factor and dust-to-gas ratio

Author:

Yasuda Atsushi1ORCID,Kuno Nario123ORCID,Sorai Kazuo1245ORCID,Muraoka Kazuyuki6ORCID,Miyamoto Yusuke7ORCID,Kaneko Hiroyuki8910ORCID,Yajima Yoshiyuki5ORCID,Tanaka Takahiro1,Morokuma-Matsui Kana1112ORCID,Takeuchi Tsutomu T1314ORCID,Kobayashi Masato I N1516ORCID

Affiliation:

1. Graduate School of Pure and Applied Sciences, University of Tsukuba , 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan

2. Tomonaga Center for the History of the Universe, University of Tsukuba , 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan

3. Department of Physics, School of Science and Technology, Kwansei Gakuin University , 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan

4. Department of Physics, Faculty of Science, Hokkaido University , Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan

5. Department of Cosmosciences, Graduate School of Science, Hokkaido University , Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan

6. Department of Physics, Graduate School of Science, Osaka Metropolitan University , 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan

7. Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Fukui University of Technology , 3-6-1 Gakuen, Fukui, Fukui 910-8505, Japan

8. National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

9. Graduate School of Education, Joetsu University of Education, 1 , Yamayashiki-machi, Joetsu, Niigata 943-8512, Japan

10. Center for Astronomy, Ibaraki University , 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan

11. Institute of Astronomy, Graduate School of Science, The University of Tokyo , 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

12. Center for Computational Sciences, University of Tsukuba , Ten-nodai, 1-1-1 Tsukuba, Ibaraki 305-8577, Japan

13. Division of Particle and Astrophysical Science, Nagoya University , Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan

14. The Research Center for Statistical Machine Learning, the Institute of Statistical Mathematics , 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan

15. Division of Science, National Astronomical Observatory of Japan , Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan

16. I. Physikalisches Institut, Universität zu Köln , Zülpicher Str. 77, D-50937 Cologne, Germany

Abstract

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 R25, where R25 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 R25) 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 R25) 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.

Funder

Japan Society for the Promotion of Science

MEXT

Jet Propulsion Laboratory

California Institute of Technology

National Aeronautics and Space Administration

NRAO

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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