As has been previously shown by several authors (e.g.,
Ferland and Netzer 1983;
Stasinska 1984a;
Binette 1985),
as well as by ourselves in a previous work
(Storchi-Bergmann and
Pastoriza 1989),
the emission-line ratios of Seyfert 2's and LINERs can be successfully
reproduced by model nebulae photoionized by a power-law continuum. So
we have calculated the theoretical emission-line ratios using the
photoionization code CLOUDY
(Ferland 1990)
for a constant density
nebula photoionized by a power-law continuum of the form
F
. In
order to reproduce the observations we have varied the slope
"
" of
the ionizing continuum, the gas density, and the abundance of the
elements, as described below. The typical total hydrogen column
densities are in the range 1020-1021 cm-2.
As shock ionization also produces an enhancement of the [N II] /
H ratio
(Dopita 1977),
we have considered, for comparison, the
integrated shock models of
Viegas-Aldrovandi (1988),
which take into
account the contribution of clouds of different velocities (100 < v <
600 km s-1) according to the distribution law f(v)
v-b.