Yellowballs in Milky Way project

In this paper, through a combination of catalog cross-matching and infrared color analysis, we show that yellowballs are a mix of compact star-forming regions, including ultra-compact and compact HII regions, as well as analogous regions for less massive B-type stars.

The resulting MWP yellowball catalog provides a useful complement to the Red MSX Source survey. It similarly highlights regions of massive star formation, but the selection of objects purely on the basis of their infrared morphology and color in Spitzer images identifies a signature of compact star-forming regions shared across a broad range of luminosities and, by inference, masses. We discuss the origin of their striking mid-infrared appearance and suggest that future studies of the yellowball sample will improve our understanding of how massive and intermediate-mass star-forming regions transition from compact to more extended bubble-like structures.