An Infrared Study of the Velocity Structure of the Cometary Compact H II Region G29.96-0.02

Abstract

We have mapped the velocity structure of the cometary compact H II region G29.96-0.02 using long-slit echelle spectra of the Brγ line. This technique detects line emission over a much wider area at the necessary spatial resolution compared to radio recombination line observations. Significant structure in both the velocity centroids and the line widths is seen over the entire nebula. Large line widths are seen ahead of the bow and in the tail, which may be due to turbulent motions in shocked and interface regions, respectively. We construct analytic models of the density and velocity structure in order to attempt to distinguish between the bow shock and champagne flow models that have been put forward to explain the cometary morphology of many compact H II regions. The bow shock model is unable to explain the large velocity gradient that we see right across the tail of the cometary region, which can be explained only by the streaming motions toward low-density regions in the champagne model. However, our approximation to the champagne model is also not able to fit all of the features of the data. More realistic versions of this model that include the effects of stellar winds and density gradients may be able to provide a better match to these data.