ALMA Images of the Host Cloud of the Intermediate-mass Black Hole
  Candidate CO-0.40-0.22$^* : No Evidence for Cloud-Black Hole Interaction, but
  Evidence for a Cloud-Cloud Collision
  This paper reports a re-analysis of archival ALMA data of the high velocity
(-width) compact cloud (HVCC) CO-0.40-0.22, which has recently been
hypothesized to host an intermediate-mass black Hole (IMBH). If beam-smearing
effects, difference in beam sizes among frequency bands, and Doppler shift due
to the motion of the Earth are considered accurately, none of the features
reported as evidence for an IMBH in previous studies are confirmed in the
re-analyzed ALMA images. Instead, through analysis of the position--velocity
structure of the HCN J=3-2 data cube, we have found kinematics typical of a
cloud-cloud collision (CCC), namely, two distinct velocity components bridged
by broad emission features with elevated temperatures and/or densities. One
velocity component has a straight filamentary shape with approximately constant
centroid velocities along its length but with a steep, V-shaped velocity
gradient across its width. This contradicts the IMBH scenario but is consistent
with a collision between two dissimilar-sized clouds. From a non-LTE analysis
of the multi-transition methanol lines, the volume density of the post-shock
gas has been measured to be $\gtrsim 10^6\ \mathrm{cm}^{-3}$, indicating that
the CCC shock can compress gas in a short timescale to densities typical of
star-forming regions. Evidence for star formation has not been found, possibly
because the cloud is in an early phase of CCC-triggered star formation or
because the collision is non-productive.
