ALMA Observations of N83C in the Early Stage of Star Formation in the Small Magellanic Cloud

We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in the 12CO( ), 13CO( ), C18O( ), 12CO( ), 13CO( ), and CS( ) 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 in 12CO( ) and 13CO( ) 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 ii region. We derived a gas density of cm−3 in molecular clouds associated with YSOs based on the virial mass estimated from the 12CO( ) emission. This high gas density is presumably due to the effect of the ii region under the low-metallicity (and accordingly small-dust content) environment in the SMC; far-UV radiation from the ii region can easily penetrate and photodissociate the outer layer of 12CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in 12CO emission. We obtained the CO-to-H2 conversion factor of 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 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 .