The H II Region Complex G5.48-0.24: Radio Continuum, H I, and CO Observations

摘要

We have carried out VLA radio continuum (6 and 20cm), VLA HI 21cm line, and 13CO J = 1 --\u3e 0 line observations of the Galactic H II region G5.48-0.24. We present the continuum maps at 21 cm with 50\u22 resolution and at 6 and 20 cm with 5\u22 resolution. The radio continuum maps show that the H II region is composed of a bright component immersed in a diffuse emission of 6\u27 (or 21 pc) radius. The bright component has a compact (0.7 pc) core surrounded by an extended (3.4 pc) halo. According to Wood \u26 Churchwell (1989), the compact core has an ultracompact (0.04 pc) subcomponent. The rms electron density of the diffuse emission is 7 cm^-3 and it increases roughly by a factor of 10 from one structure to the next small-scale structure. The observed radio continuum flux, half of which is contributed by the diffuse emission, requires an ionizing star of 05 ZAMS. If we consider the direct absorption of ionizing stellar photons by dust within H II regions, the bright component alone requires an 05 exciting star. The brightness of the diffuse continuum emission decreases steeply 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 with the steep western bounday. The 13CO line observations show that there is a giant molecular cloud associated with the H II region. The bright component of the radio continuum emission coincides with teh 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 different dynamical ages (e.g. 4 x 10^3 to 2 x 10^6 yr) may indicate that either the sequential star formation is proceeding or G5.48-0.24 is a blister-type H II region.