Extremely Energetic Outflow and Decelerated Expansion in W49N
  W49N is a mini-starburst in the Milky Way and thus an ideal laboratory for
high-mass star formation studies. Due to its large distance
(11.1$_{-0.7}^{+0.9}$ kpc), the kinematics inside and between the dense
molecular clumps in W49N are far from well understood. The SMA observations
resolved the continuum emission into two clumps. The molecular line observation
of SO$_{2}$ (28$_{4,24}$-28$_{3,25}$) suggests that the two clumps have a
velocity difference of $\sim$7 km~s$^{-1}$. The eastern clump is very close to
two radio sources "G1" and "G2", and the western clump coincides with a radio
source "B". The HCN (3-2) line reveals an extremely energetic outflow, which is
among the most energetic molecular outflows in the Milky Way. This is the first
report of high-velocity molecular outflow detection in W49N. The outflow jet
might be in precession, which could account for the distribution, velocity and
rotation of water maser spots. Three absorption systems are identified in
HCO$^{+}$ (3-2) spectra. The absorption features are blueshifted with respect
to the emission of SO$_{2}$ (28$_{4,24}$-28$_{3,25}$) lines, indicating that a
cold layer is expanding in front of the warm gas. Further analysis indicates
that the expansion is decelerated from the geometric expansion centers.
