  We study the relation between obscuration and supermassive black hole (SMBH)
growth using a large sample of hard X-ray selected Active Galactic Nuclei
(AGN). We find a strong decrease in the fraction of obscured sources above the
Eddington limit for dusty gas ($\log \lambda_{\rm Edd}\gtrsim -2$) confirming
earlier results, and consistent with the radiation-regulated unification model.
This also explains the difference in the Eddington ratio distribution functions
(ERDFs) of type 1 and type 2 AGN obtained by a recent study. The break in the
ERDF of nearby AGN is at $\log \lambda_{\rm Edd}^{*}=-1.34\pm0.07$. This
corresponds to the $\lambda_{\rm Edd}$ where AGN transition from having most of
their sky covered by obscuring material to being mostly devoid of absorbing
material. A similar trend is observed for the luminosity function, which
implies that most of the SMBH growth in the local Universe happens when the AGN
is covered by a large reservoir of gas and dust. These results could be
explained with a radiation-regulated growth model, in which AGN move in the
$N_{\rm H}-\lambda_{\rm Edd}$ plane during their life cycle. The growth episode
starts with the AGN mostly unobscured and accreting at low $\lambda_{\rm Edd}$.
As the SMBH is further fueled, $\lambda_{\rm Edd}$, $N_{\rm H}$ and covering
factor increase, leading AGN to be preferentially observed as obscured. Once
$\lambda_{\rm Edd}$ reaches the Eddington limit for dusty gas, the covering
factor and $N_{\rm H}$ rapidly decrease, leading the AGN to be typically
observed as unobscured. As the remaining fuel is depleted, the SMBH goes back
into a quiescent phase.
