Detecting hydrogen inside IMC's and GMC's

[dougettinger]

I am looking for a brief summary of current hydrogen detection within galaxies.

How are H I and H II detected? Is there a minimum required temperature and/or density ?
How is molecular hydrogen detected? Is this the only form of hydrogen with sufficient density that can become opaque thereby creating Bok globules?

Gas to gas, Doug Ettinger

[mathman]

I can't address the details. However, in general, hydrogen at high temperature has its own characteristic lines in spectra. At low temperature, hydrogen is detected by light shining through it (gas clouds) where the hydrogen lines show up as darkening.

[Drakkith]

This article had some information that might answer some of your questions.
http://en.wikipedia.org/wiki/Molecular_cloud

[dougettinger]

I remember reading that hydrogen cannot be detected by emission lines below 100 degrees Kelvin. So below this temperature how is hydrogen detected ?

Hydrogen is in basically three forms in interstellar space: only one proton, one proton and one neutron, and a hydrogen molecule, H2. Are all these forms equally detectable ? Does each type of isotope prefer a certain temperature range?

Regards, Doug Ettinger