Direct Comparison of Motions of Neutral and Ionized Hydrogen in the Galaxy


ALTHOUGH it is well known that Population I objects in the galaxy move in approximately circular orbits, the detailed situation is not clear. Anomalies of various types have been found, non-circular components are present on a regional basis, and the relationships between the motions of the various Population I constituents have not yet been completely worked out. Observations of the radio recombination lines of hydrogen provide a new method for measuring velocities of one of the most important constituents, the regions of ionized hydrogen, and furthermore the transparency of the interstellar dust to radio waves makes the method applicable to the whole galaxy. A detailed comparison between the velocities of neutral and ionized hydrogen is of interest in itself, and the comparison has the added advantage that the HII component can be taken as an indicator of the young stars.

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KERR, F., BURKE, B., REIFENSTEIN, E. et al. Direct Comparison of Motions of Neutral and Ionized Hydrogen in the Galaxy. Nature 220, 1210–1211 (1968).

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