On the radiative and thermodynamic properties of the cosmic radiations
  using COBE FIRAS instrument data: III. Galactic far-infrared radiation
  Using the three-component spectral model describing the FIRAS average
continuum spectra, the analytical expressions for the temperature dependence of
the thermodynamic and radiative functions of the galactic far-infrared
radiation are obtained. The COBE FIRAS instrument data in the 0.15 - 2.88 THz
frequency interval at the mean temperatures T = 17.72 K, T = 14 K, and T =6.73
K are used for calculating the radiative and thermodynamic functions, such as
the total radiation power per unit area, total energy density, total
emissivity, number density of photons, Helmholtz free energy density, entropy
density, heat capacity at constant volume and pressure for the warm,
intermediate-temperature and very cold components of the Galactic continuum
spectra. The generalized Stefan-Boltzmann laws for the warm,
intermediate-temperature and very cold components are constructed. This result
is important when we construct the cosmological models of radiative transfer in
the inner Galaxy. Within the framework of the three- component spectral model,
the total number of photons in our Galaxy and the total radiation power (total
luminosity) emitted from the surface of the Galaxy are calculated. Other
radiative and thermodynamic properties of the galactic far-infrared radiation
(photon gas) for the Galaxy are presented. The expressions for astrophysical
parameters, such as the entropy density/Boltzmann constant, and number density
of the galactic far-infrared photons are obtained. We assume that the obtained
analytical expressions for thermodynamic and radiative functions may be useful
for describing the continuum spectra of the far-infrared radiation for outer
galaxies.
