A&A 453, 1003-1026 (2006)
DOI: 10.1051/0004-6361:20054383

A SCUBA imaging survey of ultracompact HII regions

The environments of massive star formation

M. A. Thompson^{1, 2}, J. Hatchell³, A. J. Walsh⁴, G. H. Macdonald² and T. J. Millar<sup>5, 6

1</sup>  Centre for Astrophysics Research, Science & Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
    e-mail: mat@star.herts.ac.uk
²  Centre for Astrophysics & Planetary Science, School of Physical Sciences, University of Kent, Canterbury CT2 7NR, UK
³  School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴  School of Physics, University of New South Wales, NSW, 2052, Australia
⁵  Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, PO Box 88, Manchester, M60 1QD, UK
⁶  School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK

(Received 20 October 2005 / Accepted 28 March 2006)

Abstract
We present a SCUBA submillimetre (450 and 850 m) survey of the environment of 105 IRAS point sources, selected from the Wood & Churchwell (1989a) and Kurtz et al. (1994) radio ultracompact (UC) HII region surveys. We detected a total of 155 sub-mm clumps associated with the IRAS point sources and identified three distinct types of object: ultracompact cm-wave sources that are not associated with any sub-mm emission (sub-mm quiet objects), sub-mm clumps that are associated with ultracompact cm-wave sources (radio-loud clumps); and sub-mm clumps that are not associated with any known ultracompact cm-wave sources (radio-quiet clumps). 90% of the sample of IRAS point sources were found to be associated with strong sub-mm emission. We consider the sub-mm colours, morphologies and distance-scaled fluxes of the sample of sub-mm clumps and show that the sub-mm quiet objects are unlikely to represent embedded UC HII regions unless they are located at large heliocentric distances. Many of the 25 SCUBA fields contain more than one sub-mm clump, with an average number of companions (the companion clump fraction) of 0.90. The clumps are more strongly clustered than other candidate HMPOs and the mean clump surface density exhibits a broken power-law distribution with a break at 3 pc. We demonstrate that the sub-mm and cm-wave fluxes of the majority of radio-loud clumps are in excellent agreement with the standard model of ultracompact HII regions. We speculate on the nature of the radio-quiet sub-mm clumps and, whilst we do not yet have sufficient data to conclude that they are in a pre-UC HII region phase, we argue that their characteristics are suggestive of such a stage.

Key words: stars: formation -- ISM: HII regions -- ISM: dust, extinction -- submillimeter -- radio continuum: ISM

© ESO 2006

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