Study of the H166α Recombination Line in the Southern Milky Way
We review the observations of recombination line emissions with low angular resolution made at the Instituto Argentino de Radioastronomía, and new detections of diffuse ionized gas located in the 3-kpc arm are shown. The observations suggest that the H166α line-emitting gas is associated with Population I material, but it is not always connected to active star formation regions. Around l = 335° the lines show evidence of interarm ionized gas, probably connecting giant complexes of HII regions located in Scutum-Crux and Norma arms. If a non-LTE model is suitable for this ionized gas the analysis of the line emission, along with low frequency continuum observations, suggests a low electron temperature (T e < 500 K) and a low emission measure (E < 200 pc cm-6).
KeywordsEmission Measure Galactic Plane Continuum Emission Recombination Line Fourth Quadrant
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