NGC 206, a hole in M31

Abstract

New high resolution 21 cm line observations of M31 show that the interstellar medium of this galaxy contains numerous holes in the H I distribution, some of which are clearly correlated with OB-associations. These holes appear to belong to the same class of objects as the super shells and giant bubbles in the Galaxy and the Magellanic Clouds. NGC 206, a 20-million yr old rich OB-association, coincident with a large 400 x 800 pc hole is studied in detail. Here, 2-million solar masses of H I is missing. This is partly ionized and partly blown away. The observed H-alpha emission is in agreement with the number of OB-stars found