A comparison of the properties of an unbiased sample of OB associations in the local group galaxies M33 and NGC 6822

The properties of OB associations in the two Local Group galaxies M33 and NGC 6822 are compared Both sets of OB associations were identified using an automated grouping algorithm, with color and brightness cutoffs matched to select the same type of O stars in each galaxy. The mean number of stars, masses and ages of the associations are very similar in the two galaxies, which suggests that the mechanisms which form OB associations are similar in the two galaxies, despite a much lower rate of star formation in NGC 6822 The mean radii of the associations in NGC 6822 are 30% smaller than those of M33; however, unlike other properties such as mass and age, the radii of the OB associations depend very sensitively on the search radius used to identify the associations. The results presented here represent the first completely objective comparison of the OB association properties in two different external galaxies.