EDP Sciences
Free access
Volume 415, Number 2, February IV 2004
Page(s) 627 - 642
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20031681

A&A 415, 627-642 (2004)
DOI: 10.1051/0004-6361:20031681

A Compact Array imaging survey of southern bright-rimmed clouds

M. A. Thompson, J. S. Urquhart and G. J. White

Centre for Astrophysics & Planetary Science, School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NR, UK

(Received 5 August 2003 / Accepted 30 October 2003)

We have carried out a radio-wavelength imaging survey of 45 bright-rimmed clouds (BRCs), using the Australia Telescope Compact Array to characterise the physical properties in their ionised boundary layers. We detected radio emission from a total of 25 clouds and using a combination of Digitised Sky Survey and mid-infrared MSX 8  $\mu$m images classified the emission into that associated with the ionised cloud rims, that associated with embedded possible massive YSOs and that unlikely to be associated with the clouds at all. A total of 18 clouds display radio emission clearly associated with the cloud rim and we determine the ionising photon flux illuminating these clouds and the electron density and pressure of their ionised boundary layers. Using a global estimate for the interior molecular pressure of these clouds we show that the majority are likely to be in pressure equilibrium and hence are currently being shocked by photoionisation-induced shocks. We identify those clouds where the predicted ionising photon flux is inconsistent with that derived from the observations and show that either the spectral types of the stars illuminating the BRCs are earlier than previously thought or that there must be additional ionising sources within the HII regions. Finally, we identify the radio sources embedded within the clouds with infrared stellar clusters and show that they contain late O and early B-type stars, demonstrating that a number of BRCs are intimately involved with high to intermediate-mass star formation.

Key words: stars: formation -- ISM: HII regions -- ISM: clouds -- radio continuum: ISM

Offprint request: M. A. Thompson, m.a.thompson@kent.ac.uk

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