  Dust-obscured galaxies are thought to represent an early evolutionary phase
of massive galaxies in which the active galactic nucleus (AGN) is still deeply
buried in significant amounts of dusty material and its emission is strongly
suppressed. The unprecedented sensitivity of the James Webb Space Telescope
enables us for the first time to detect the rest-frame optical emission of
heavily obscured AGN and unveil the properties of the hidden accreting
super-massive black holes (BHs). In this work, we present the JWST/NIRSpec IFS
data of ALESS073.1, a massive, dusty, star-forming galaxy at $z = 4.76$ hosting
an AGN at its center. The detection of a very broad $H_\alpha$ emission
associated with the Broad Line Region (BLR) confirms the presence of a BH
($\log(M_{BH}/M_\odot)>8.7$) accreting at less than 15\% of its Eddington limit
and classifies the target as a Type 1 AGN. The rest-frame optical emission
lines also reveal a fast ionized gas outflow marginally resolved in the galaxy
center. The high sensitivity of NIRSpec allows us to perform the kinematic
analysis of the narrow H$\alpha$ component which indicates that the warm
ionized gas velocity field is consistent with disk rotation. We also find that,
in the innermost nuclear regions ($< 1.5$ kpc), the intrinsic velocity
dispersion of the disk reaches $\sim 150$ km/s, $\sim 2-3$ times higher than
the velocity dispersion inferred from the [CII] 158$\mu$m line tracing mostly
cold gas. Since, at large radii, the velocity dispersion of the warm and cold
gas are comparable, we conclude that the outflows are injecting turbulence in
the warm ionized gas in the central region, but they are not sufficiently
powerful to disrupt the dense gas and quench star formation. These findings
support the scenario that dust-obscured galaxies represent the evolutionary
stage preceding the unobscured quasar when all gas and dust are removed from
the host.
