The gas dynamics of H II regions. II - Two-dimensional axisymmetric calculations

Abstract

Hydrodynamic numerical calculations of the evolution of H II regions in dense molecular clouds are extended to two space dimensions with axial symmetry. Specific problems are treated which emphasize the behavior of flows that cross a discontinuity between a cloud and the low-density intercloud medium. Calculations are performed for four cases, including two involving 'champagne flows': (1) the edge of the cloud is overrun by a supersonic ionization front; (2) the initial Stromgren sphere surrounding the star lies deep inside the cloud, so that the cloud's edge is ionized by a subsonic ionization front; (3) the ionization front breaks through two opposite faces of the same cloud simultaneously; and (4) the flow encounters an isolated globule with a density of 1000 particles/cu cm shortly after emerging from the molecular cloud. The results are compared with observations of various interstellar clouds.