High Velocity Compact Clouds in the Sagittarius C Region
  We report the detection of extremely broad emission toward two molecular
clumps in the Galactic central molecular zone. We have mapped the Sagittarius C
complex ($-0^\circ.61 < l < -0^\circ.27$, $-0^\circ.29 < b < 0^\circ.04$) in
the HCN $J$ = 4--3, $\mathrm{^{13}CO}$ $J$ = 3--2, and $\mathrm{H^{13}CN}$ $J$
= 1--0 lines with the ASTE 10 m and NRO 45 m telescopes, detecting bright
emission with $80\mbox{--}120$\ $\mathrm{km\,s^{-1}}$ velocity width (in
full-width at zero intensity) toward CO$-0.30$$-0.07$ and CO$-0.40$$-0.22$,
which are high velocity compact clouds (HVCCs) identified with our previous CO
$J$ = 3--2 survey. Our data reveal an interesting internal structure of
CO$-0.30$$-0.07$ comprising a pair of high velocity lobes. The spatial-velocity
structure of CO$-0.40$$-0.22$ can be also understood as multiple velocity
component, or a velocity gradient across the cloud. They are both located on
the rims of two molecular shells of about 10 pc in radius. Kinetic energies of
CO$-0.30$$-0.07$ and CO$-0.40$$-0.22$ are
$\left(0.8\mbox{--}2\right)\times10^{49}$ erg and
$\left(1\mbox{--}4\right)\times10^{49}$ erg, respectively. We propose several
interpretations of their broad emission: collision between clouds associated
with the shells, bipolar outflow, expansion driven by supernovae (SNe), and
rotation around a dark massive object. There scenarios cannot be discriminated
because of the insufficient angular resolution of our data, though the absence
of visible energy sources associated with the HVCCs seems to favor the
cloud--cloud collision scenario. Kinetic energies of the two molecular shells
are $1\times10^{51}$ erg and $0.7\times10^{51}$ erg, which can be furnished by
multiple SN or hypernova explosions in $2\times10^5$ yr. These shells are
candidates of molecular superbubbles created after past active star formation.
