  The formation mechanism of CO clouds observed with NANTEN2 and Mopra
telescope toward the stellar cluster Westerlund 2 is studied by
three-dimensional magnetohydrodynamic (MHD) simulations taking into account the
interstellar cooling. These molecular clouds show a peculiar shape composing of
an arc-shaped cloud in one side of a TeV-ray source HESS J1023-575 and a linear
distribution of clouds (jet clouds) in another side. We propose that these
clouds are formed by the interaction of a jet with interstellar neutral
hydrogen (HI) clumps. By studying the dependence of the shape of dense cold
clouds formed by shock compression and cooling on the filling factor of HI
clumps, we found that the density distribution of HI clumps determines the
shape of molecular clouds formed by the jet-cloud interaction; arc-clouds are
formed when the filling factor is large. On the other hand, when the filling
factor is small, molecular clouds align with the jet. The jet propagates faster
in models with small filling factors.
