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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 beenhypothesized to host an intermediate-mass black Hole (IMBH). If beam-smearingeffects, difference in beam sizes among frequency bands, and Doppler shift dueto the motion of the Earth are considered accurately, none of the featuresreported as evidence for an IMBH in previous studies are confirmed in there-analyzed ALMA images. Instead, through analysis of the position--velocitystructure of the HCN J=3-2 data cube, we have found kinematics typical of acloud-cloud collision (CCC), namely, two distinct velocity components bridgedby broad emission features with elevated temperatures and/or densities. Onevelocity component has a straight filamentary shape with approximately constantcentroid velocities along its length but with a steep, V-shaped velocitygradient across its width. This contradicts the IMBH scenario but is consistentwith a collision between two dissimilar-sized clouds. From a non-LTE analysisof the multi-transition methanol lines, the volume density of the post-shockgas has been measured to be $\gtrsim 10^6\ \mathrm{cm}^{-3}$, indicating thatthe CCC shock can compress gas in a short timescale to densities typical ofstar-forming regions. Evidence for star formation has not been found, possiblybecause the cloud is in an early phase of CCC-triggered star formation orbecause the collision is non-productive.

astrophysical journal/the astrophysical journal

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