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A Radio and Mid-Infrared Survey of Northern Bright-Rimmed Clouds
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Astronomy Astrophysics manuscript no. 0226 February 2, 2008
(DOI: will be inserted by hand later)
A Radio and Mid-Infrared Survey of Northern Bright-Rimmed
Clouds
L.K. Morgan, M.A. Thompson, J.S. Urquhart, Glenn.J. White J. Miao
Centre for Astrophysics Planetary Science, School of Physical Sciences, University of Kent, Canterbury, Kent
CT2 7NR, UK
e-mail: lkm8@kent.ac.uk
Abstract. We have carried out an archival radio, optical and infrared wavelength imaging survey of 44 Bright-
Rimmed Clouds (BRCs) using the NRAO/VLA Sky Survey (NVSS) archive, images from the Digitised Sky
Survey (DSS) and the Midcourse Space eXperiment (MSX). The data characterise the physical properties of the
Ionised Boundary Layer (IBL) of the BRCs. We have classified the radio detections as: that associated with the
ionised cloud rims; that associated with possible embedded Young Stellar Objects (YSOs); and that unlikely to
be associated with the clouds at all. The stars responsible for ionising each cloud are identified and a comparison
of the expected ionising flux to that measured at the cloud rims is presented. A total of 25 clouds display 20 cm
radio continuum emission that is associated with their bright optical rims. The ionising photon flux illuminating
these clouds, the ionised gas pressure and the electron density of the IBL are determined. We derive internal
molecular pressures for 9 clouds using molecular line data from the literature and compare these pressures to the
IBL pressures to determine the pressure balance of the clouds. We find three clouds in which the pressure exerted
by their IBLs is much greater than that measured in the internal molecular material. A comparison of external
pressures around the remaining clouds to a global mean internal pressure shows that the majority of clouds
can be expected to be in pressure equilibrium with their IBLs and hence are likely to be currently shocked by
photoioni
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