H-Alpha Velocity Fields of H II Regions in Nearby Dwarf Irregular Galaxies
Abstract
We present H-alpha velocity fields of thirteen giant H II regions in four nearby dwarf irregular galaxies, NGC 2366, Holmberg II, IC 2574, and WLM. We classify the velocity features and the morphologies of the H II regions. The H-alpha velocity features are divided into three categories; three H II regions show chaotic feature with a typical scale of variation of a few 100 pc in size and a few 10 km s^{-1} in velocity, one shows expanding-bubble feature, and nine have calm velocity fields. The morphologies are divided into three categories; nine or ten H II regions have circular morphology, one or two show ring shape, and two are filamentary. Based on our classification, we discuss an evolutionary scenario of the H II regions. We measure the bulk motion of the H II regions relative to the ambient H I velocity for the H II regions with calm velocity fields and found a typical velocity difference of about 5 km s^{-1}. Considering the H I characteristics as well as the velocity difference, we suggest that some star-forming regions in dwarf irregulars was generated by the infall of clouds onto the galactic disk.Keywords
All Related Versions
This publication has 0 references indexed in Scilit: