Physical Contact between the +20 km/s Cloud and the Galactic
  Circumnuclear Disk
  This paper reports the discovery of evidence for physical contact between the
Galactic circumnuclear disk (CND) and an exterior giant molecular cloud. The
central 10 pc of our Galaxy has been imaged in the HCN J=1-0, HCO+ J=1-0, CS
J=2-1, H13CN J=1-0, SiO J=2-1, SO N_J=2_3-1_2, and HC3N J=11-10 lines using the
Nobeyama Radio Observatory 45 m radio telescope. Based on our examination of
the position-velocity maps of several high-density probe lines, we have found
that an emission "bridge" may be connecting the +20 km/s cloud (M-0.13-0.08)
and the negative-longitude extension of the CND. Analyses of line intensity
ratios imply that the chemical property of the bridge is located between the
+20 km/s cloud and the CND. We introduce a new interpretation that a part of
the CND may be colliding with the 20 km/s cloud and the collision may be
responsible for the formation of the bridge. Such collisional events could
promote mass accretion onto the CND or into the inner ionized cavity, which may
be further tested by proper motion studies.
