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Star Formation in the Galaxy and the Fluctuating UV Radiation FieldWe examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this Field on the star-forming interstellar medium. Following previous researchers such as Habing (1968), we calculate the average interstellar radiation field at the Solar Circle of the Galaxy. However, our new calculations follow more closely the time dependence of the field at any point. We show that there is a significant difference between the mean field and the median field, and that there are substantial fluctuations of the field (on timescales of order 100 million years) at a given point. Far Ultraviolet Radiation (FUV, photon energies of 6 eV - 13.6 eV) has been recognized as the main source of heating of the neutral interstellar gas. Given the pressure of the interstellar medium (ISM) the FUV field determines whether the thermal balance of the neutral gas results in cold (T approximately 50 - 100 K) clouds (CNM), warm (T about 10,000 K) (WNM), for a combination of the two (the two phase ISM) We present results for the time history of the FUV field for points in the local ISM of the Milky Way Galaxy. The presence of this fluctuating heating rate converts CNM to WNM and vice versa. We show how to calculate the average fractions of the gas in the CNM and WNM when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties (i.e. mean density and composition) and on the FUV-sources (i.e. the star formation rate, or the IMF, or the size distribution of associations) is a basic step in building any detailed model of the large scale behavior of the ISM and the mutual relation between the ISM and the SFR.
Document ID
20010084722
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Hollenbach, David
(NASA Ames Research Center Moffett Field, CA United States)
Parravano, A.
(NASA Ames Research Center Moffett Field, CA United States)
McKee, C.
(NASA Ames Research Center Moffett Field, CA United States)
DeVincenzi, Donald L.
Date Acquired
August 20, 2013
Publication Date
January 9, 2000
Subject Category
Astrophysics
Meeting Information
Meeting: High-Mass Star Formation: An Origin in Clusters
Location: Volterra
Country: Italy
Start Date: May 24, 2000
End Date: June 4, 2000
Funding Number(s)
PROJECT: RTOP 344-04-10-02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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