The HST view of the innermost narrow line region
  We analyze the properties of the innermost narrow line region in a sample of
low-luminosity AGN. We select 33 LINERs (bona fide AGN) and Seyfert galaxies
from the optical spectroscopic Palomar survey observed by HST/STIS. We find
that in LINERs the [NII] and [OI] lines are broader than the [SII] line and
that the [NII]/[SII] flux ratio increases when moving from ground-based to HST
spectra. This effect is more pronounced considering the wings of the lines. Our
interpretation is that, as a result of superior HST spatial resolution, we
isolate a compact region of dense ionized gas in LINERs, located at a typical
distance of about 3 pc and with a gas density of about 10$^4$-10$^5$ cm$^{-3}$,
which we identify with the outer portion of the intermediate line region (ILR).
Instead, we do not observe these kinds of effects in Seyferts; this may be the
result of a stronger dilution from the NLR emission, since the HST slit maps a
larger region in these sources. Alternatively, we argue that the innermost,
higher density component of the ILR is only present in Seyferts, while it is
truncated at larger radii because of the presence of the circumnuclear torus.
The ILR is only visible in its entirety in LINERs because the obscuring torus
is not present in these sources.
