An energetic high-velocity compact cloud: CO$-$0.31+0.11
  We have discovered an energetic high-velocity compact cloud CO$-$0.31+0.11 in
the central molecular zone of our Galaxy. CO$-$0.31+0.11 is located at a
projected distance of $\sim 45$ pc from the Galactic nucleus Sgr A$^*$. It is
characterized by its compact spatial appearance ($d\simeq4$ pc), extremely
broad velocity width ($\Delta V > 100$ km s$^{-1}$), and high CO
$J$=3$-$2/$J$=1$-$0 intensity ratio. The total gas mass and kinetic energy are
estimated as approximately $10^4$ $M_\odot$ and $10^{51}$ erg, respectively.
Two expanding bubble-like structures are found in our HCN $J$=1$-$0 map
obtained with the Nobeyama Radio Observatory 45 m telescope. In the
longitude--velocity maps, CO$-$0.31+0.11 exhibits an asymmetric V-shape. This
kinematical structure can be well fitted by Keplerian motion on an eccentric
orbit around a point mass of $2\times 10^5$ $M_\odot$. The enhanced CO
$J$=3$-$2/$J$=1$-$0 ratio is possibly attributed to the tidal compression
during the pericenter passage. The model suggests that a huge mass is packed
within a radius of $r < 0.1$ pc. The huge mass, compactness and absence of
luminous stellar counterparts may correspond to a signature of an
intermediate-mass black hole (IMBH) inside. We propose a formation scenario of
CO$-$0.31+0.11 in which a compact cloud has gravitationally interacted with an
IMBH and a bipolar molecular outflow was driven by the past activity of the
putative IMBH.
