Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39

Details Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39 Subarcsecond Submillimeter Imaging of the Ultracompact HII Region G5.89-0.39

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.8928h&link_type=abstract

American Astronomical Society, AAS Meeting #211, #89.28; Bulletin of the American Astronomical Society, Vol. 39, p.882

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the first sub-arcsecond submillimeter images of the enigmatic ultracompact radio source G5.89-0.39 (W28A2) observed in the extended configuration of the Submillimeter Array (SMA). For comparison, we have generated a comprehensive set of continuum images from the VLA archive at the same angular resolution, from 5 GHz to 43 GHz. The 342 GHz continuum emission exhibits a shell-like morphology analogous to that seen in the 15 GHz to 43 GHz VLA images. After removing the free-free component from the 342 GHz image, we find residual sources of dust emission, two adjacent to the shell and three outside of it. Images of 18 spectral lines in the dataset are also presented. The molecular line emission is restricted to locations on and outside the shell. Our observations support the previously proposed picture of a dust-free cavity located inside a shell-like ultracompact HII (UCHII) region with warm, high-density gas tracing its periphery. On the northeast and southwest borders of the shell, most of the molecular gas tracers (SO, SO2, HCCCN, C17O) form ridges which may be restricting the expansion of the UCHII. In contrast, there is little molecular gas on the southeast side of the shell, perhaps allowing the ionized nebula to expand more easily in that direction. We find a partial secondary shell of dust and molecular gas emission located south of the main shell, which may mark an expansion front of lower density ionized gas. The two spots of dust emission (SMA1 and SMA2) adjacent to the main UCHII shell also exhibit compact spatial peaks in one or more of the optically thin tracers (33SO, 34SO2, and C17O). We interpret these objects as possible embedded protostars, one of which (SMA1) corresponds to the brightest source in the TIMMI mid-infrared image.

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