Warm and dense molecular gas in the N 159 region:¹²CO J =4-3 and¹³CO J = 3-2 observations with NANTEN2 and ASTE

New ¹²CO J = 4-3 and ¹³CO J = 3-2 observations of the N159 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 ¹²CO 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 ¹²CO J = 1-0, J = 2-1, J = 3-2, and J = 7-6 as well as the isotope transitions of ¹³CO J = 1-0, J = 2-1, / = 3-2, and J = 4-3. The ¹³CO J = 3-2 data were newly taken for the present work. The temperatures and densities were found to be ∼ 70-80 K and ∼3 × 10³cm^-3 in N159 W and N159 E, and ∼30 K and ∼ 1.6 × 10³cm^-3 in N 159 S. These results were compared with the star-formation activity based on data of young stellar clusters and H II regions as well as midinfrared emission obtained with the Spitzer MIPS. The N159 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 N159 E clump is likely to be responsible for a dark lane in a large H II 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 ¹²CO 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 ¹²CO 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 N159 W peak represents a pre-star-cluster core of ∼ 10⁵ M⊙ which deserves further detailed studies. The N159 S clump shows little sign of star formation, as is consistent with the lower temperature, 30 K, and has a somewhat lower density than N159 W and N 159 E. The N159 S clump is also a candidate for future star formation.