THE H-II REGION COMPLEX G5.48-0.24 - RADIO-CONTINUUM H-I, AND CO OBSERVATIONS

We have carried out VLA radio continuum (6 and 20 cm), VLA H I 21 cm l ine, and (CO)-C-13 J = 1-0 line observations of the Galactic H II regi on G5.48-0.24. We present the continuum maps at 21 cm with similar to 50 '' resolution and at 6 and 20 cm with similar to 5 '' resolution. T he radio continuum maps show that the H II region is composed of a bri ght component immersed in a diffuse emission of similar to 6' (or 21 p c) radius. The bright component has a compact (0.7 pc) core surrounded by an extended (3.4 pc) halo. According to Wood & Churchwell (1989), the compact core has an ultracompact (0.04 pc) subcomponent. The rms e lectron density of the diffuse emission is 7 cm(-3) and it increases r oughly by a factor of 10 from one structure to the next small-scale st ructure. The observed radio continuum flux, half of which is contribut ed by the diffuse emission, requires an ionizing star of O5 ZAMS. If w e consider the direct absorption of ionizing stellar photons by dust w ithin H II regions, the bright component alone requires an O5 exciting star. The brightness of the diffuse continuum emission decreases stee ply along its western boundary and gradually at other directions. The VLA H I 21 cm line maps show that there is an H I cloud in contact wit h the steep western boundary. The (CO)-C-13 line observations show tha t there is a giant molecular cloud associated with the H II region. Th e bright component of the radio continuum emission coincides with the dense core of the molecular cloud. Therefore, G5.48-0.24 appears to be an H II region-molecular cloud complex where the formation of massive stars occurred recently. The radio continuum structures of largely di fferent dynamical ages (e.g., 4 x 10(3)-2 x 10(6) yr) may indicate tha t either the sequential star formation is proceeding, or G5.48-0.24 is a blister-type H II region.