Abstract
This chapter discusses the main processes responsible for the observed radiation field in the interstellar medium. The equation of radiative transfer is developed, and an example is given of its solution in the case of the interstellar radiation field.
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Allen, C.W.: Astrophysical Quantities. Athlone, London (1973). Very useful table compilation of physical and astronomical data, constants and unit conversions. Table 2.2 is based on this reference. See also the recent revised version by Cox, A.N. (ed.). 2000. Allen’s Astrophysical Quantities. New York, American Institute of Physics/Springer
Gondhalekar, P.M.: The ultraviolet starlight in the Galaxy. In: Bowyer, S., Leinert, C. (eds.) IAU Symposium 139, p. 49. Kluwer, Dordrecht (1990). Updated discussion on the interstellar radiation field. Figure 2.2 is based on this reference
Kaplan, S.A., Pikelner, S.B.: The Interstellar Medium. Harvard University Press, Cambridge (1970). Referred to in chapter 1. Includes a discussion on the interstellar radiation field
Kolb, E.W., Turner, M.S.: The Early Universe. Addison-Wesley, Reading (1990). A good discussion on the early Universe, the Big Bang and the cosmic microwave background radiation
Lang, K.R.: Astrophysical Formulae. Springer, Berlin (1999). Updated compilation of astrophysical data, including detailed formulae of the principal physical processes mentioned in section 2.2
Mezger, P.G.: In: Setti, G.G., Fazzio, G.G. (eds.) Infrared Astronomy, p. 1. Reidel, Dordrecht (1978). Review article about the interstellar medium. Figure 2.1 is based on this reference
Mihalas, D.: Stellar Atmospheres. Freeman, San Francisco (1978). Accurate discussion on radiative transfer, applied to stellar atmospheres
Pinkau, K. (ed.): The Interstellar Medium. Reidel, Dordrecht (1974). An interesting ensemble of articles by specialists about several aspects of the physics of the interstellar medium
Rybicki, G.B., Lightman, A.P.: Radiative Processes in Astrophysics. Wiley, New York (1979). Very complete discussion on the radiation field concepts and the main radiative processes mentioned in sections 2.2 and 2.6
Schuster, A.: Radiation through a foggy atmosphere. Astrophys J 21, 1 (1905). Discussion of the classical method of the transfer equation solution
Verschuur, G.L., Kellermann, K.I. (eds.): Galactic and Extragalactic Radio Astronomy. Berlin, Springer (1988). Ensemble of basic articles on radio emission applied to the study of galaxies’ structure
Werner, M.W., Salpeter, E.E.: Mon. Grain temperatures in interstellar dust clouds. Notices Roy. Astron. Soc. 145, 249 (1969). Discussion on the interstellar radiation field. Table 2.1 is based on this reference
Witt, A.N., Johnson, M.W.: Astrophys. J. The interstellar radiation density between 1250 and 4250 Angstroms. 181, 363 (1973). An example of the interstellar radiation field calculation in the ultraviolet
Wynn-Williams, G.: The Fullness of Space. Cambridge University Press, Cambridge (1992). Referred to in chapter 1. Includes a qualitative discussion on the interstellar radiation field and images at different wavelengths
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Exercises
Exercises
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2.1
Show that the cosmic microwave background radiation, remnant of the Big Bang, has a maximum given by the peak of curve B from Fig. 2.1. What is the wavelength corresponding to this maximum?
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2.2
The emission measure in the direction of an H II region is 103 pc/cm6 and the column density of hydrogen nuclei in the same direction is 1020 cm−2. Estimate the electron density and the H II region dimensions.
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2.3
Use the radiation field model with four components given in Table 2.1 and equation (2.17) and (a) calculate the energy density U λ in the optical spectrum center, where λ = 5,500 Å. (b) Compare the result with the mean value obtained from the solution of the transfer equation.
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2.4
Use the model obtained from the solution of the transfer equation and estimate the flux, the mean intensity, and the energy density in the rim of the galactic disk for λ = 5,500 Å.
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2.5
(a) Assume that the radiation field at some point in the interstellar medium can be characterized by a blackbody with T = 104 K and dilution factor W = 10−14. What would be the flux at λ = 2,000 Å in erg cm−2 s−1 Å−1? (b) Compare the result with the value predicted by the four component model described in Sect. 2.4. (c) Which of the two above models better follows the observations, taking into account the observational data shown in Fig. 2.2?
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Maciel, W.J. (2013). The Interstellar Radiation Field. In: Astrophysics of the Interstellar Medium. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-3767-3_2
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DOI: https://doi.org/10.1007/978-1-4614-3767-3_2
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