Effects of expanding compact H II regions upon molecular clouds: Molecular dissociation waves, shock waves, and carbon ionization

Journal Article · Sun Oct 15 00:00:00 EDT 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156501· OSTI ID:6627761

Hill, J K; Hollenbach, D J

The effect of young expanding compact H II regions upon their molecular environments are studied, emphasizing the simultaneous evolution of the molecular hydrogen dissociation front and the shocked shell of gas surrounding the nebula. For H II regions powered by 05 stars embedded in molecular clouds of ambient density 10/sup 3/-10/sup 4/ cm/sup -3/ the dissociation wave initially travels outward much more rapidly than the shock, but later decelerates and is swept up by the shock about 10/sup 5/ yr after the expansion begins. The 21 cm line of atomic hydrogen will be optically thick in both the preshock and postshock gas for most of this period. The most important coolant transitions are the (O I) 63 ..mu..m line and, for t> or approx. =10/sup 5/ yr, the rotational transitions of H/sub 2/ and/or the rotational transitions of CO. The vibrational transitions of H/sub 2/ are excited predominantly by ultraviolet pumping. We estimate the preshock and postshock carbon recombination-line emission measures.

• Research Organization: National Radio Astronomy Observatory, Green Bank, West Virginia
• OSTI ID: 6627761
• Journal Information: Astrophys. J.; (United States), Vol. 225:2
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
H2 REGIONS
EXPANSION
INTERSTELLAR SPACE
MOLECULES
CARBON
COSMIC DUST
COSMIC GASES
COSMIC RADIO SOURCES
DISSOCIATION
ENERGY-LEVEL TRANSITIONS
IONIZATION
NEBULAE
SHOCK WAVES
DUSTS
ELEMENTS
FLUIDS
GASES
NONMETALS
SPACE
640105* - Astrophysics & Cosmology- Galaxies