**3.1.3. FIELDINTENSITIES**

This module contains routines that give the spectral energy densities
(in erg/cm^{3}/Hz)
of some particular radiation fields taken from the literature. The
routines take as input
the wavelength in Å at which the field is to be evaluated (as well
as some additional
parameters required by each particular model) and interpolates linearly
the table of points using routine LINTERPOL.

The radiation fields currently available are:

- FGAL: this function returns the radiation field of the Galaxy, as
given by Gondhalekar
et al. [5];
- FUVB: this function returns the UV background radiation field of all
QSOs, as given by
Madau et al. [6].
It also takes as input the redshift at which the radiation field is
to be evaluated Z and a flag MODEL. MODEL = 1 corresponds to a
cosmological model with
*q*_{0}= 0, MODEL = 2 to one with*q*_{0}= 0.5 and MODEL = 3 corresponds to*q*_{0}= 0.5 as revised by [6], - FHOTHALO: this function returns the radiation field of the hot halo model proposed by Viegas and Friaça [7] to explain the source of ionization of Lyman Limit QSO absorbtion line systems. It takes as input two flags: R and T. R is the distance from the center of the galaxy at which the radiation field is to be evaluated, R = 1 corresponds to 10 kpc, R = 2 to 30 kpc and R = 3 to 100 kpc. T is the age of the galaxy, T = 1 corresponds to 0.206 Gyr and T = 2 to 0.3644 Gyr.