High-excitation CS and C34S towards ultracompact H II regions

Details High-excitation CS and C34S towards ultracompact H II regions High-excitation CS and C34S towards ultracompact H II regions

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...352..266o&link_type=abstract

Astronomy and Astrophysics, v.352, p.266-276 (1999)

Astronomy and Astrophysics

Astrophysics

24

Ism: H {+/-C Ii} Regions, Ism: Molecules, Stars: Formation, Radio Lines: Ism

Scientific paper

We have used the JCMT telescope to observe the J=5-4 and J=7-6 rotational transitions of CS and C32SI towards 19 ultracompact Hii regions. The main goal was to extend the survey of Cesaroni et al. (\cite{bib:cesa91}) to a larger sample of sources and to higher energy transitions sensitive to the densest, hottest molecular gas. In all cases we find gas with n_H_2 ~= 105-106 cm-3 associated with the ultracompact Hii regions, thus confirming that massive stars are born inside dense molecular clumps. In particular, the observed line intensities can be satisfactorily reproduced with a single density model, without the contribution of a radiative field. A comparison between the profiles of different transitions suggests that the regions traced by the CS molecule could be collapsing. Also, higher energy lines seem to trace more turbulent environments: it is shown that turbulence can be an efficient mechanism to confine the expansion of ultracompact Hii regions, as proposed by Xie et al. (\cite{bib:xie96}), although confinement by thermal pressure cannot be excluded on the basis of our data. For one of the sources, G10.47+0.03, we present a map in the CS(7-6) transition: this shows that the diameter of the emitting region is comparable to that measured in the lower excitation lines observed by Cesaroni et al. (\cite{bib:cesa91}).

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