CO Multi-line Imaging of Nearby Galaxies (COMING). VI. Radial variations in star formation efficiency

Kazuyuki Muraoka, Kazuo Sorai, Yusuke Miyamoto, Moe Yoda, Kana Morokuma-Matsui, Masato I.N. Kobayashi, Mayu Kuroda, Hiroyuki Kaneko, Nario Kuno, Tsutomu T. Takeuchi, Hiroyuki Nakanishi, Yoshimasa Watanabe, Takahiro Tanaka, Atsushi Yasuda, Yoshiyuki Yajima, Shugo Shibata, Dragan Salak, Daniel Espada, Naoko Matsumoto, Yuto NomaShoichiro Kita, Ryusei Komatsuzaki, Ayumi Kajikawa, Yu Yashima, Hsi An Pan, Nagisa Oi, Masumichi Seta, Naomasa Nakai

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the CO Multi-line Imaging of Nearby Galaxies project (Sorai et al. 2019, PASJ, 71, S14). The radial variations in SFE for individual galaxies are typically a factor of 2-3, which suggests that SFE is nearly constant along the galactocentric radius. We found an averaged SFE in 80 galaxies of (1.69 ± 1.1) × 10-9 yr-1, which is consistent with Leroy et al. (2008, AJ, 136, 2782) if we consider the contribution of helium to the molecular gas mass evaluation and the difference in the assumed initial mass function between the two studies. We compared SFE among different morphological (i.e., SA, SAB, and SB) types, and found that SFE within the inner radii (r/r25 < 0.3, where r25 is the B-band isophotal radius at 25 mag arcsec-2) of SB galaxies is slightly higher than that of SA and SAB galaxies. This trend can be partly explained by the dependence of SFE on global stellar mass, which probably relates to the CO-to-H2 conversion factor through the metallicity. For two representative SB galaxies in our sample, NGC 3367 and NGC 7479, the ellipse of r/r25 = 0.3 seems to cover not only the central region but also the inner part of the disk, mainly the bar. These two galaxies show higher SFE in the bar than in the spiral arms. However, we found an opposite trend in NGC 4303; SFE is lower in the bar than in the spiral arms, which is consistent with earlier studies (e.g., Momose et al. 2010, ApJ, 721, 383). These results suggest a diversity of star formation activities in the bar.

Original languageEnglish
Article numberS15
JournalPublications of the Astronomical Society of Japan
Publication statusPublished - 2019 Dec 1
Externally publishedYes


  • Galaxies: ISM
  • Galaxies: star formation
  • ISM: molecules

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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