The nature of nuclear Halpha emission in LINERs
  To get insight in the nature of the ionized gas in the nuclear region of
LINERs we have performed a study of HST Halpha imaging of 32 LINERs. The main
conclusion from this analysis is that for the large majority of LINERs (84%) an
unresolved nuclear source has been identified as well as extended emission with
equivalent sizes ranging from few tens till about hundredths of parsecs. Their
morphologies appear not to be homogeneous being basically grouped into three
classes:nuclear outflow candidates (42%), core-halo morphologies (25%) and
nuclear spiral disks (14%). Clumpy structures reminiscent of young stellar
clusters are not a common property on LINERs. The remaining 5 galaxies are too
dusty to allow a clear view of the ionized gas distribution. A size-luminosity
relation has been found between the equivalent radius of the Halpha emission
and the (2-10 keV) X-ray luminosities. Both ionised gas morphologies and the
size-luminosity relation are indistinguishable from those of low luminosity
Seyferts, suggesting the same origin for the NLR of LINERs and Seyferts. Also a
relation between soft X-rays and ionized gas has been suggested for the first
time in LINERs. From multiwavelength data, only 4 out of the 32 LINERs have no
evidences on an AGN nature of theirnuclear sources from multiwavelength data,
but extremely obscured AGNs cannot be discarded out given the Compton thick
signatures of their X-ray emission. For the confirmed AGN LINERs, their Halpha
imaging favour core-halo and outflow morphologies (65% of the cases). Finally,
their calculated Eddington ratios show that our LINER sources radiate at
sub-Eddington regime, with core-halo systems having on average larger Eddington
ratios than outflow candidates.
