Hostname: page-component-78c5997874-t5tsf Total loading time: 0 Render date: 2024-11-14T17:39:14.219Z Has data issue: false hasContentIssue false
  • English
  • Français

The Phase Structure of the ISM in Galaxies

Published online by Cambridge University Press:  21 October 2010

Mark G. Wolfire
Mark G. Wolfire*
Affiliation:
Astronomy Department, University of Maryland, College Park, MD 20742, USA email: mwolfire@astro.umd.edu
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.

Diffuse gas in the Galaxy is observed to exist as cold (T ~ 100 K) neutral atomic gas (CNM) and warm neutral atomic (T ~ 8000 K) gas (WNM). In addition to these “thermal” phases, gas can also exist as warm (T ~ 8000 K) ionized gas, cold (T ~ 10 K) molecular gas and in warm (T ~ 100 - 500 K) interface regions or Photodissociation Regions (PDRs) on the surfaces of molecular clouds. The same chemical and thermal processes that dominate in the PDRs associated with molecular clouds are also at work in the diffuse neutral gas. Two additional “phases” are gas associated with GMCs that has H2 but no or little CO, and short lived or transient phases such as shocks, shears, and turbulence. I will first review the different gas phases in the Galaxy, their physical conditions and their dominant cooling lines. I will also discuss the observations and theoretical modeling in support of turbulence versus thermal instability as the driving force in producing the “thermal” gas phase distributions. Rough estimates for the distribution of phases in the Galaxy and the origin of the dominant emission lines has been conducted by previous telescopes (e.g., COBE, BICE) but with low velocity and low spectral resolution. The distribution and mass of the various gas phases is important for sorting out the role of SN in setting ISM pressures and in driving ISM turbulence. In addition, understanding the Galactic phase distribution is important in interpreting observations of extragalactic systems in which beams encompass several emission components. I will review the potential for future observations by e.g., STO, SOFIA, and Herschel to detect and separate phases in Galactic and extragalactic systems.

Keywords

ISM: cloudsISM: generalISM: HII regionsgalaxies: ISM
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Highlights H15: Highlights of Astronomy , November 2009 , pp. 409 - 410
Copyright
Copyright © International Astronomical Union 2010

References

Gazol, A., Vázquez-Semadeni, E., & Kim, J. 2005, ApJ, 630, 911CrossRefGoogle Scholar
Gazol, A., Vázquez-Semadeni, E., Sánchez-Salcedo, F. J., & Scalo, J. 2001, ApJL, 557, L121CrossRefGoogle Scholar
Heiles, C. & Troland, T. H. 2003, ApJ, 586, 1067CrossRefGoogle Scholar
Koyama, H. & Ostriker, E. C. 2009, ApJ, 693, 1316CrossRefGoogle Scholar
Kulkarni, S. R. & Heiles, C. 1987, Interstellar Processes, 134, 87CrossRefGoogle Scholar
Vázquez-Semadeni, E. 2009, in: de Avillez, M. (ed.), The Role of Disk-Halo Interaction in Galaxy Evolution, EAS Publication Series (Paris: EDP), 2009 in pressGoogle Scholar
Wolfire, M. G., McKee, C. F., Hollenbach, D., & Tielens, A. G. G. M. 2003, ApJ 587, 278CrossRefGoogle Scholar