  The fraction of AGN with photoelectric absorption in the X-rays ranging from
NH of 10^{22} up to about 10^{24} cm^{-2} (Compton-thin) appears
observationally to be anticorrelated to their luminosity Lx. This recently
found evidence is used to investigate the location of the absorbing gas. The
molecular torus invoked in the unified picture of AGN, while it can be regarded
as confirmed on several grounds to explain the Compton-thick objects, do not
conform to this new constraint, at least in its physical models as developed so
far. In the frame of observationally based evidence that in Compton-thin
sources the absorbing gas might be located far away from the X-ray source, it
is shown that the gravitational effects of the black hole (BH) on the molecular
gas in a disk, within 25-450 pc (depending on the BH mass, from 10^6 to 10^9
M_solar, leads naturally to the observed anticorrelation, under the assumption
of a statistical correlation between the BH mass and Lx. Its normalization is
also reproduced provided that the surface density, Sigma, of this gas is larger
than about 150-200 M_solar pc^{-2}, and assuming that the bolometric luminosity
is one tenth of the Eddington limit. Interestingly, the required values are
consistent with the value of the 300 pc molecular disk in our own galaxy,
namely 500 M_solar pc^{-2}. In a sample of nearby galaxies from the BIMA SONG
survey, it is found that half of the objects have central Sigma larger than 150
M_solar pc${-2}. Given the simplicity of the proposed model, this finding is
very encouraging, waiting for future higher resolution surveys in CO on more
distant galaxies.
