The collision of clouds with a galactic disk

The gas-dynamical effects produced by the collision of low, intermediate, and/or high velocity clouds with a galactic disk are studied. From an analytical formulation, confident limits are established for the various possible solutions (i.e. coalescence or re-expansion of the colliding components), and a test to see whether or not the collisions could lead to the formation of stars is also performed. The analytical limits and the various assumptions used are later confirmed and justified with the results obtained through a series of one-dimensional hydrodynamic numerical calculations. The results imply that the collisions of clouds with a galactic disk provide a large source of energy for the interstellar medium. Also, they are responsible for some large-scale structural peculiarities inside and outside galactic disks, e.g. giant rings, coronal gas, loop structures, and giant H II regions. (25 refs).