  A sample of 229618 narrow emission-line galaxies is used to establish two new
unambiguous type of evidence for supermassive black holes at the center of
their nuclei: 1) the Seyfert 2 galaxies and LINERs follow the same
characteristic power law relating the luminosity of ionized flux with that of
the continuum; 2) both show the highest concentration of mass at their center,
independent of the morphology of the galaxy, consistent with higher binding
energies. The Full Width at Half Maximum is shown to be related with the mass
concentration, suggesting that the kinetic energy of the gas in AGNs has a
gravitational origin. Within the standard accretion model, the Transition-type
Objects, Seyfert 2 galaxies and LINERs represent AGNs forming supermassive
black holes on different mass-scales, or they could be related through an
evolutionary process, the LINERs representing the end product of this
evolution.
