Heckman (1980)
recognized the class of emission-line galaxies he
called LINERs as low-ionization AGNs. They seem to be objects
photoionized by the same type of hard spectrum, extending to high
energies, as in Seyfert galaxies, but with a lower mean ionization
parameter 
(Ferland and Netzer
1983;
Keel 1983a;
Halpern and Steiner
1983).
This can be due either to a lower-luminosity central source, or
greater mean distance of the ionized gas from the source; probably
both situations appear in nature. A careful study of a well defined
sample of spiral galaxies by
Keel (1983b)
shows that approximately
half of these objects have observed Seyfert (5%) or LINER (50%)
spectra.
Among the LINERS he studied,
Keel (1983a)
found several cases in
which very weak, barely detectable broad
H
emission components are
present in addition to the narrow emission lines. Another example of
this type of object is Mrk 883, whose spectrum was published by
Osterbrock and Dahari
(1983).
In another very interesting study,
Filippenko and Sargent
(1985)
made a special search for such weak broad
H emission components in a
large number of LINERs. This necessitated accurate subtraction of the
galaxy integrated-stellar absorption line spectrum, to detect the
weakest possible emission components. They found that about a
significant fraction of the LINERs analyzed in this way have a
measurable broad H emission
component. Of course these observational
results strongly suggest that all AGNs have some BL gas within them,
whether it is bright enough to be detected in their spectra or not.
Among the LINERS in which
Filippenko and Sargent
(1985)
detected
weak, broad H emission are the
best known elliptical galaxies with
emission lines in their spectra, NGC 1052 and the N1GC 4278. This is
the most convincing evidence known to me to date that the
elliptical-galaxy has LINERs belong to the same general type of AGNs
photoionized by a hard spectrum extending to high energies, as in
spiral-galaxy nuclei.