Concept information
Preferred term
Diffuse molecular clouds
Definition
- A type of molecular cloud in which the interstellar radiation field is sufficiently attenuated, so that the local fraction of molecular hydrogen becomes substantial (> 0.1). However, enough interstellar radiation is still present to photoionize any atomic carbon, or to photodissociate carbon monoxide (CO) such that carbon is predominantly still in the form of C+ (> 0.5). In steady state, diffuse molecular clouds must necessarily be surrounded by diffuse atomic gas, in order to provide the shielding of radiation. This means that most sightlines that cross a diffuse molecular cloud will also cross diffuse atomic gas. (en)
Broader concept
- Molecular clouds (en)
URI
http://astrothesaurus.org/uat/381
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