  Most of the stars today reside in galactic spheroids, whose properties are
tightly tied to the supermassive black holes (MBHs) at their centers, implying
that the accretion activity onto MBHs leaves a lasting imprint on the evolution
of their host galaxies. Despite the importance of this so-called MBH-galaxy
co-evolution, the physical mechanisms responsible for driving this relationship
- such as the dominant mode of energetic feedback from active galactic nuclei
(AGN) - remain a poorly understand aspect of galaxy assembly. A key challenge
for identifying and characterizing AGN during the peak epoch of galaxy assembly
and beyond is the presence of large columns of gas and dust, which fuels the
growth of their MBHs but effectively obscures them from view in optical and
X-ray studies. The high sensitivity of the ngVLA will capture emission from AGN
in an extinction-free manner out to $z \sim 6$ and beyond. At lower-redshifts
($z \sim 2$), the high angular resolution of the ngVLA will enable
spatially-resolved studies capable of localizing the sites of actively growing
MBHs within their host galaxies during the peak epoch of cosmic assembly.
