ASTE CO (3-2) observations of the barred spiral galaxy M 83: I. Correlation between CO (3-2)/CO (1-0) ratios and star formation efficiencies

Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Takeshi Okuda, Seiichi Sakamoto, Akira Endo, Bunyo Hatsukade, Kazuhisa Kamegai, Kunihiko Tanaka, Juan Cortes, Hajime Ezawa, Nobuyuki Yamaguchi, Takeshi Sakai, Ryohei Kawabe

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47 Citations (Scopus)


We present CO(J = 3-2) emission observations with the ASTE toward the 5′ × 5′ (or 6.6 kpc × 6.6 kpc at the distance D = 4.5 Mpc) region of the nearby barred spiral galaxy M 83. We successfully resolved the major structures, i.e., the nuclear starburst region, bar, and inner spiral arms at a resolution of 22″ (480 pc), showing a good spatial coincidence between CO and 6 cm continuum emissions. We found a global luminosity, L′CO(3-2), of 5.1 × 108 K km s-1 pc2 within the observed region. We also found L′ CO(3-2) in a disk region (0.5 < r < 3.5 kpc) of 4.2 × 108 K km s-1 pc2, indicating that (J = 3-2) emission in the disk region significantly contributes to the global L′CO(3-2). From a comparison of CO (J = 3-2) data with CO (J = 1-0) intensities measured with the Nobeyama 45-m telescope, we found that the radial profile of the CO (J = 3-2)/CO (J = 1-0) integrated intensity ratio, R3-2/1-0, is almost unity in the central region (r < 0.25 kpc), whereas it drops to a constant value, 0.6-0.7, in the disk region. The radial profile of star formation efficiencies (SFEs), determined from 6 cm radio continuum and CO (J = 1-0) emission, shows the same trend as that of R 3-2/1-0. At the bar-end (r ∼ 2.4 kpc), the amounts of molecular gas and the massive stars are enhanced when compared with other disk regions, whereas there is no excess of R3-2/1-0 and SFE in that region. This means that a simple summation of the star-forming regions at the bar-end and the disk cannot reproduce the nuclear starburst of M 83, implying that the spatial variation of the dense gas fraction traced by R3-2/1-0 governs the spatial variation of SFE in M 83.

Original languageEnglish
Pages (from-to)43-54
Number of pages12
JournalPublications of the Astronomical Society of Japan
Issue number1
Publication statusPublished - 2007
Externally publishedYes


  • Galaxies: ISM
  • Galaxies: individual (M 83 = NGC 5236)
  • Galaxies: starburst

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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