The H II Region Complex G5.48-0.24: Radio Continuum, H I, and CO
Observations
Bon-Chul Koo, Kee-Tae Kim, Ho-Kyu Lee, Min Su Yun, & Paul T. P. Ho
Astrophysical Journal, V.456, p.662 (1996)
Abstract
We have carried out VLA radio continuum (6 and 20cm), VLA HI 21cm line,
and 13CO J = 1 --> 0 line observations of the Galactic H II region
G5.48-0.24. We present the continuum maps at 21 cm with 50" resolution
and at 6 and 20 cm with 5" resolution. The radio continuum maps show
that the H II region is composed of a bright component immersed in a diffuse
emission of 6' (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 & 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.