Hostname: page-component-cd9895bd7-gvvz8 Total loading time: 0 Render date: 2024-12-27T11:55:09.806Z Has data issue: false hasContentIssue false
  • English
  • Français

Magnetic fields and the location of the PDR

Published online by Cambridge University Press:  04 October 2008

C. Kramer ,
S. Aalto ,
R. Simon  and
G.J. Ferland
G.J. Ferland*
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA
Get access

Abstract

I review recent studies of the emission-line regions in Orion and M 17. Both have similar geometries, a bubble of hot shocked gas surrounding the central star cluster, with H+, H0, and H2 regions, often referred to as H II regions, PDRs, and molecular clouds, forming successive shells on the surface of a molecular cloud. The magnetic fields in the H0 regions have been measured with 21 cm Zeeman polarization and are found to be 1 – 2 dex stronger than the field in the diffuse ISM. The regions appear to be in rough hydrostatic equilibrium. The H+ region is pushed away from the star cluster by starlight radiation pressure. Since most starlight is in ionizing radiation, most of its outward push will act on the H+ region and then on to the H0 region. The magnetic pressure in the H0 region balances the momentum in starlight and together they set the location of the H0 region. The picture is that, when the star cluster formed, it created a bubble of ionized gas which expanded and compressed surrounding H0 and H2 regions. The magnetic field was amplified until its pressure was able to support the momentum in starlight. This offers a great simplification in understanding the underlying physics that establishes parameters for PDR models.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 31: Far-Infrared Workshop 2007 , 2008 , pp. 53 - 56
Copyright
© EAS, EDP Sciences, 2008

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Abel, N.P., Brogan, C.L., Ferland, G.J., O'Dell, C.R., Shaw, G., & Troland, T.H., 2004, ApJ, 609, 247 CrossRef
Abel, N.P., Ferland, G.J., O'Dell, C.R., Shaw, G., & Troland, T.H., 2006, ApJ, 644, 344 CrossRef
Anish Roshi, D., 2007, ApJ, 658, L48
Baldwin, J., Ferland, G.J., Martin, P.G., Corbin, M., Cota, S., Peterson, B.M., & Slettebak, A., 1991, ApJ, 374, 580 CrossRef
Brogan, C.L., Troland, T.H., Roberts, D.A., & Crutcher, R.M., 1999, ApJ, 515, 304 CrossRef
Ferland, G.J., 2001, PASP, 113, 41 CrossRef
Henney, W.J., Arthur, S.J., Williams, R.J.R., & Ferland, G.J., 2005, ApJ, 621, 328 CrossRef
Henney, W.J., Williams, R., Ferland, G., Shaw, G., & O'Dell, C., 2007, ApJ, 671, L137 CrossRef
Lequeux, J, 2004, The Interstellar Medium (Springer)
Myers, P.C., & Goodman, A.A., 1998, ApJ, 326, L27 CrossRef
Osterbrock, D., & Ferland, G.J., 2006, Astrophysics of gaseous nebulae and active galactic nuclei, 2nd. ed
Pellegrini, E.W., Baldwin, J.A., Brogan, C.L., et al., 2007, ApJ, 658, 1119 (P07) CrossRef
Troland, T.H., Heiles, C., & Goss, W.M., 1989, ApJ, 337, 342 CrossRef