Warm and Dense Molecular Gas in the N 159 Region: ^(12)CO J = 4–3 and ^(13)CO J = 3–2 Observations with NANTEN2 and ASTE

Abstract

New ^(12)CO J = 4–3 and ^(13)CO J = 3–2 observations of the N 159 region, an active site of massive star formation in the Large Magellanic Cloud, have been made with the NANTEN2 and ASTE submillimeter telescopes, respectively. The ^(12)CO J = 4–3 distribution is separated into three clumps, each associated with N 159 W, N 159 E, and N 159 S. These new measurements toward the three clumps are used in coupled calculations of molecular rotational excitation and line radiation transfer, along with other transitions of the ^(12)CO J = 1–0, J = 2–1, J = 3–2, and J = 7–6 as well as the isotope transitions of ^(13)CO J = 1–0, J = 2–1, J = 3–2, and J = 4–3. The ^(13)CO J = 3–2 data were newly taken for the present work. The temperatures and densities were found to be ~70–80 K and ~3 × 10^3 cm^(-3) in N 159 W and N 159 E, and ~30 K and ~1.6 × 10^3 cm^(-3) in N 159 S. These results were compared with the star-formation activity based on data of young stellar clusters and HII regions as well as midinfrared emission obtained with the Spitzer MIPS. The N 159 E clump is associated with cluster(s) embedded, as observed at 24 μm by the Spitzer MIPS, and the derived high temperature, 80 K, is interpreted as being heated by these sources. The N 159 E clump is likely to be responsible for a dark lane in a large HII region by dust extinction. On the other hand, the N 159 W clump is associated with clusters embedded mainly toward the eastern edge of the clump only. These clusters show offsets of 20"–40" from the ^(12)CO J = 4–3 peak, and are probably responsible for heating indicated by the derived high temperature, 70 K. The N 159 W clump exhibits no sign of star formation toward the ^(12)CO J = 4–3 peak position and its western region that shows enhanced R_(4-3/1-0) and R_(3-2/1-0) ratios. We therefore suggest that the N 159 W peak represents a pre-star-cluster core of ~10^5 M_☉ which deserves further detailed studies. The N 159 S clump shows little sign of star formation, as is consistent with the lower temperature, 30 K, and has a somewhat lower density than N 159 W and N 159 E. The N 159 S clump is also a candidate for future star formation.

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