A study has been made of the intensities and radial velocities of faint galactic Ha and [N II] A6584 emission lines not associated with any known bright H ii regions. Although some ( 10 percent) of the observed radiation may be scattered galactic light from bright H ii regions in the galactic plane, most of the radiation appears to be produced by an ionized component of the interstellar gas which is distributed throughout the interstellar medium within the three nearby galactic spiral arms. In the local Orion arm the emitting gas has a temperature between 3000 and 8000' K and mean square electron density n,2 0.05 cm -6 in the galactic plane, while in the Perseus and Sagittarius arms n,2> 0.1 and 0.9 cm -6, respectively. Subject heading: interstellar matter
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Reynolds et al. (1973) studied this question.