Kinematics of Ultracompact H<scp>ii</scp>Regions Revealed: High Spatial and Spectral Resolution Mapping of the 12.8 Micron [Ne<scp>ii</scp>] Line in Monoceros R2

Abstract

We present the first results of a study of the kinematics and morphology of ultracompact HII regions using a new observational technique. We used very high spatial (1.5") and spectral (3.4 km/s)resolution observations of the [NeII] line at 12.8 microns to study the ionized gas in Monoceros R2. The [NeII] emission shows an HII region with highest emission measure in a ~24" shell. Line widths are as narrow as 8 km/s at some positions. In places where the lines are complex and broader, the additional width is most likely due to overlap of narrower features along the line of sight. The global kinematics suggest that the 24" shell is expanding at ~10 km/s. However, the spectral profiles toward the southeast side of the shell are not consistent with a simple expansion picture.