X-ray reflection features observed from the innermost regions of accretion disks in Active Galactic Nuclei ( AGNs ) allow important tests of accretion theory .
In recent years it has been possible to use the Fe K \alpha line and reflection continuum to parametrize the ionization state of the irradiated inner accretion disk .
Here , we collect 10 measurements of \xi , the disk ionization parameter , from 8 AGNs with strong evidence for reflection from the inner accretion disk and good black hole mass estimates .
We find strong statistical evidence ( 98.56 % confidence ) for a nearly linear correlation between \xi and the AGN Eddington ratio .
Moreover , such a correlation is predicted by a simple application of \alpha -disk accretion theory , albeit with a stronger dependence on the Eddington ratio .
The theory shows that there will be intrinsic scatter to any correlation as a result of different black hole spins and radii of reflection .
There are several possibilities to soften the predicted dependence on the Eddington ratio to allow a closer agreement with the observed correlation , but the current data does not allow for an unique explanation .
The correlation can be used to estimate that MCG–6-30-15 should have a highly ionized inner accretion disk , which would imply a black hole spin of \sim 0.8 .
Additional measurements of \xi from a larger sample of AGNs are needed to confirm the existence of this correlation , and will allow investigation of the accretion disk/corona interaction in the inner regions of accretion disks .