Radio observations of ultracompact HII regions

Abstract

I review recent developments in the field of radio observations of ultracompact H II (UCHII) regions that have appeared in the literature since the last major review (Churchwell 2002). The morphology of UCHII regions continues to be a topic of research and recent studies of individual regions of star formation suggest modifications with respect to the results obtained from galactic plane surveys. I also briefly touch upon the question of the density structure of UCHII regions. Finally, I will also discuss the evidence of time variability in UCHII regions, and present examples of objects that are expanding, varying in flux density, or moving in the sky.