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

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

Jan 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...456..662k&link_type=abstract

Astrophysical Journal v.456, p.662

Astronomy and Astrophysics

Astronomy

16

Ism: H Ii Regions, Ism: Individual Alphanumeric: G5.48-0.24, Radio Continuum: Ism, Radio Lines: Ism, Ism: Structure

Scientific paper

We have carried out VLA radio continuum (6 and 20 cm), VLA H I 21 cm 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 O5 ZAMS. If we consider the direct absorption of ionizing stellar photons by dust within H II regions, the bright component alone requires an O5 exciting star.
The brightness of the diffuse continuum emission decreases steeply along its western boundary and gradually at other directions. The VLA H 1 21 cm line maps show that there is an H I cloud in contact with the steep western boundary. 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 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 different dynamical ages (e.g., 4 × 103-2 × 106 yr) may indicate that either the sequential star formation is proceeding, or G5.48-0.24 is a blister-type H II region.

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