The correlation of spiral arm molecular clouds with cold atomic hydrogen

Abstract

The relationship between molecular clouds and the cold atomic hydrogen gas seen in self-absorption has been examined in the longitude range 36-40 deg. The results confirm what the authors found previously in another region of the Galaxy. By reanalyzing both sets of data, the authors show that those cold clouds which are detected both in H I self-absorption at 21 cm against a hotter background and in CO emission at 2.6 mm are confined to the Sagittarius spiral arm feature in velocity-longitude space. Outside of this arm feature, clouds which show both H I absorption and CO emission are very rare. 14 references.