External tides: an important driver of velocity dispersion in molecular clouds

Abstract

Using the 3D density distribution derived from the 3D dust map of the solar neighborhood, the gravitational potential is obtained by solving the Poisson equation, from which the tidal tensor is computed. In the optimal decomposition, the external tidal tensor follows the same formalism as that of a point mass. The average tidal strength of the clouds, derived from both tidal tensor analysis and pixel-by-pixel computation, shows consistent results. The equivalent velocity dispersion of the clouds, estimated from the average tidal strength, is comparable in magnitude to the velocity dispersion measured from CO (1-0) line emission. This suggests that tidal effects from surrounding material may play a significant role in driving velocity dispersion within the clouds. Future studies should carefully consider these tidal effects in star-forming regions.