ALMA observations of N83C in the early stage of star formation in the small Magellanic cloud

Kazuyuki Muraoka, Aya Homma, Toshikazu Onishi, Kazuki Tokuda, Ryohei Harada, Yuuki Morioka, Sarolta Zahorecz, Kazuya Saigo, Akiko Kawamura, Norikazu Mizuno, Tetsuhiro Minamidani, Erik Muller, Yasuo Fukui, Margaret Meixner, Remy Indebetouw, Marta Sewiło, Alberto Bolatto

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19 Citations (Scopus)


We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in the12CO(J = 2 - 1),13CO(J = 2 - 1), C18O(J = 2 - 1),12CO(J = 3 - 2),13CO(J = 3 - 2), and CS(J = 7 - 6) lines toward the active star-forming region N83C in the Small Magellanic Cloud (SMC), whose metallicity is about one-fifth of the Milky Way (MW). The ALMA observations first reveal subparsec-scale molecular structures in12CO(J = 2 - 1) and13CO(J = 2 - 1) emissions. We found strong CO peaks associated with young stellar objects (YSOs) identified by the Spitzer Space Telescope, and we also found that overall molecular gas is distributed along the edge of the neighboring H II region. We derived a gas density of ~104 cm−3 in molecular clouds associated with YSOs based on the virial mass estimated from the12CO(J = 2 - 1) emission. This high gas density is presumably due to the effect of the H II region under the low-metallicity (and accordingly small-dust content) environment in the SMC; far-UV radiation from the H II region can easily penetrate and photodissociate the outer layer of12CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in12CO emission. We obtained the CO-to-H2 conversion factor XCO of 7.5 ´ 1020 cm−2 (K km s−1)−1 in N83C based on virial masses and CO luminosities, and it is four times larger than that in the MW, 2 1020 cm−2 (K km s−1)−1. We also discuss the difference in the nature between two high-mass YSOs, each of which is associated with a molecular clump with a mass of about a few 103 M.

Original languageEnglish
Article number98
JournalAstrophysical Journal
Issue number2
Publication statusPublished - Aug 1 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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