| Abstract | dc.description.abstract | 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 sub-mm telescopes, respectively. The 12CO J=4–3 distribution
is separated into three clumps, each associated with N159W, N159E and
N159S. 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, J=3–2, and J=4–3. The 13CO J=3–2 data are
newly taken for the present work. The temperatures and densities are determined to
be 70-80K and 3×103 cm−3 in N159W and N159E and 30K and 1.6×103
cm−3 in N159S. Observed 12CO J=2–1 and 12CO J=1–0 intensities toward N159W
and N159E are weaker than expected from calculations of uniform temperature and
density, suggesting that low-excitation foreground gas causes self-absorption. These
results are compared with the star formation activity based on the data of young
stellar clusters and HII regions as well as the mid-infrared emission obtained with the
Spitzer MIPS. The N159E clump is associated with embedded cluster(s) as observed
at 24 μm by the Spitzer MIPS and the derived high temperature, 80K, is explained
as due to the heating by these sources. The N159E clump is likely responsible for
a dark lane in a large HII region by the dust extinction. On the other hand, the
N159W clump is associated with embedded clusters 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 N159W clump exhibits no sign of star formation toward the 12CO J=4–3
peak position and its western region that shows enhanced R4−3/1−0 and R3−2/1−0 ratios.
We therefore suggest that the N159W peak represents a pre-star-cluster core of
105M⊙ which deserves further detailed studies. We note that recent star formation
took place between N159W and N159E as indicated by several star clusters and HII regions, while the natal molecular gas toward the stars have already been dissipated
by the ionization and stellar winds of the OB stars. The N159S clump shows little
sign of star formation as is consistent with the lower temperature, 30K, and somewhat
lower density than N159W and N159E. The N159S clump is also a candidate
for future star formation. | en_US |
