C18O Observations of the Dense Cloud Cores and Star Formation in Ophiuchus
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Abstract
In order to reveal the distribution of the dense gas of ≥104 cm3, C18O (J = 1-0) observations have been made toward the molecular clouds in the Ophiuchus region of ~6.4 deg2 with the two 4 m telescopes of Nagoya University. Forty dense cores have been identified, providing the first complete sample of such dense cores in Ophiuchus. The C18O dense cores are distributed not only in the active star-forming region, ρ Oph cloud core, but also in the North region where star formation is less active. The typical core mass, MLTE, radius, R, and average number density, n(H2), of the cores are 90 M☉, 0.24 pc, and 1.7 × 104 cm-3 in the ρ Oph region, respectively, and 14 M☉, 0.19 pc, and 7.6 × 103 cm-3 in the North region, respectively. Nine of the 40 cores are associated with young stellar objects, and most of the C18O cores are starless. An analysis of the physical parameters of the C18O cores show that star-forming cores tend to have larger N(H2) than the rest by a factor of ~3, although there is no significant trend in the other physical parameters between star forming and starless cores.