Infrared mapping of the galactic plane. III - The large-scale mid-infrared structure of W3, W4, and W5

Infrared mapping of the W3, W4, and W5 complex of giant H II regions and molecular clouds with approximately 9 degree resolution at 11 and 20 microns is presented. A strong emission from W3A, which is embedded within an extended ridge, is the dominant feature. In addition, low surface brightness 11 micron emission is detected which is associated with the extended ratio continuum and molecular emission around W3/W4. The mid-infrared color temperature of this emission is found to be higher than that of compact sources, possibly due in part to radiative transfer effects in objects of high density. It is found, however, that the extended emission high dust temperature is evidence of ongoing star formation throughout virtually the entire W3/W4 molecular cloud. The W5 object shows 11 and 20 micron emissions, and its brighter peaks are directly associated with embedded stars in the molecular clouds encircling the H II region.