  The observations of FIR line and continuum spectra throughout the Galactic
centre and in some regions of the disc are analysed in order to determine the
physical conditions (densities, shock velocities, radiation parameters, etc.)
and the relative abundances of some elements (C, N, and O). The models account
for the coupled effect of photoionization and shocks. Consistent model
calculations of the line and continuum spectra show that, although the
radiation from the stars dominates, an active galactic nucleus (AGN) is clearly
present, with a radiation maximum in the Sgr A* region. The flux, similar to
that found for low luminosity AGN (LLAGN), is lower by a factor of about 100
than that of AGN.
