Hostname: page-component-cd9895bd7-dzt6s Total loading time: 0 Render date: 2024-12-27T08:29:34.455Z Has data issue: false hasContentIssue false
  • English
  • Français

Diffuse Hα in a Fractal Interstellar Medium

Published online by Cambridge University Press:  05 March 2013

Bruce G. Elmegreen
Bruce G. Elmegreen*
Affiliation:
IBM T. J. Watson Research Center, PO Box 218, Yorktown Hts, NY 10598, USA; [email protected]
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Observations of cloud structure over the last 10 years have led to the conclusion that it is fractal in nature, with a fractal dimension characteristic of turbulence, as found in the laboratory. Such structure has an open texture, with a volume filling factor of nearly 90% for gas that is at low density. Turbulence makes such cavities by clearing away material during convective motions. We propose that most of the low-density intercloud medium is the result of turbulence and not overlapping supernova remnants. This model has important implications for diffuse Hα and ionisation of the halo. Fractal clouds have a gradually decreasing average density with increasing distance, so ionisation zones around these clouds can be very extensive. Fractal clouds are also highly clustered, making the mean free path for ionising photons at least twice as large as in the ‘standard cloud’ model. This long mean free path allows stray ionising photons from midplane H II regions to reach and ionise the halo.

Keywords

turbulenceISM: cloudsISM: structureH II regions
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 15 , Issue 1 , 1998 , pp. 74 - 78
Copyright
Copyright © Astronomical Society of Australia 1998

References

Blaauw, A. 1952, BAN, 11, 405 Google Scholar
Dickey, J. M., Hanson, M. M., & Helou, G. 1990, ApJ, 352, 522 CrossRefGoogle Scholar
Elmegreen, B. G. 1997a, ApJ, 477, 196 (E97a)Google Scholar
Elmegreen, B. G. 1997b, ApJ, 480, 674 CrossRefGoogle Scholar
Elmegreen, B. G., & Efremov, Yu. 1997, ApJ, 480, 235 Google Scholar
Elmegreen, B. G., & Falgarone, E. 1996, ApJ, 471, 816 Google Scholar
Falgarone, E. 1989, in Structure and Dynamics of the Interstellar Medium, ed. G. Tenorio-Tagle, M. Moles & J. Melnick (Berlin: Springer), p. 68 Google Scholar
Ferguson, A. M. N., Wyse, R. F. G., Gallagher, J. S. III., & Hunter, D. A. 1996, AJ, 111, 2265 Google Scholar
Klein, R. I., McKee, C. F., & Colella, P. 1994, ApJ, 420, 213 CrossRefGoogle Scholar
Larson, R. B. 1981, MNRAS, 194, 809 Google Scholar
Lucke, P. B. 1978, A&A, 64, 367 Google Scholar
McKee, C. F., & Ostriker, J. P. 1977, ApJ, 218, 148 CrossRefGoogle Scholar
Mandelbrot, B. B. 1983, The Fractal Geometry of Nature (San Francisco: Freeman)Google Scholar
Meneveau, C., & Sreenivasan, K. R. 1990, Phys. Rev. A, 41, 2246 CrossRefGoogle Scholar
Meyer, D. M., & Blades, J. C. 1996, ApJ, 464, L179 CrossRefGoogle Scholar
Norman, C. A., & Ferrara, A. 1996, ApJ, 467, 280 CrossRefGoogle Scholar
Oey, S., & Clarke, C. 1997, MNRAS, 289, 570 Google Scholar
Passot, T., Vazquez-Semadeni, E., & Pouquet, A. 1995, ApJ, 455, 531 CrossRefGoogle Scholar
Pfenniger, D. 1996, in New Extragalactic Perspectives in the New South Africa, ed. D. L. Block & J. M. Greenberg (Dordrecht: Kluwer), p. 439 Google Scholar
Reynolds, R. J. 1995 in The Physics of the Interstellar Medium and Intergalactic Medium, ASP Conf. Ser. 80, ed. A. Ferrara, C. F. McKee, C. Heiles & P. R. Shapiro (San Francisco: ASP), p. 388 Google Scholar
Scalo, J. M. 1985 in Protostars and Planets II, ed. D. C. Black & M. S. Mathews (Tucson: Univ. Arizona Press), p. 201 Google Scholar
Scalo, J. M. 1990, in Physical Processes in Fragmentation and Star Formation, ed. R. Capuzzo-Dolcetta, C. Chiosi & A. Di Fazio (Dordrecht: Kluwer), p. 151 CrossRefGoogle Scholar
Shelton, R. L., & Cox, D. P. 1994, ApJ, 434, 599 Google Scholar
Vazquez-Semadeni, E., Passot, T., & Pouquet, A. 1995, in Fifth Mex-Tex Meeting in Astrophysics, Gaseous Nebula and Star Formation, ed. M. Peña & S. Kurtz, Rev. Mex. Astron. Ap. Ser. Conf. 3, 61 Google Scholar
Walterbos, R. A. M., & Braun, R. 1994, ApJ, 431, 156 Google Scholar
Watson, J. K., & Meyer, D. M. 1996, ApJ, 473, L127 CrossRefGoogle Scholar
Zimmerman, T., & Stutzki, J. 1993, Fractals, 1, 930 Google Scholar