Galactic HII regions velocity gradients

We craft HII region simulations that include bipolar outflows or solid body rotational motions to explain the observed velocity gradients. The simulations favor solid body rotation since, unlike the bipolar outflow kinematic models, they are able to produce both the large, >40m/s/arcsec, velocity gradients and also the RRL width structure that we observe in some sources. The bipolar outflow model, however, cannot be ruled out as a possible explanation for the observed velocity gradients for many sources in our sample.

We nevertheless suggest that most HII region complexes are rotating and may have inherited angular momentum from their parent molecular clouds.