  There are several key open questions as to the nature and origin of AGN
including: 1) what initiates the active phase, 2) the duration of the active
phase, and 3) the effect of the AGN on the host galaxy. Critical new insights
to these can be achieved by probing the central regions of AGN with sub-mas
angular resolution at UV/optical wavelengths. In particular, such observations
would enable us to constrain the energetics of the AGN "feedback" mechanism,
which is critical for understanding the role of AGN in galaxy formation and
evolution. These observations can only be obtained by long-baseline
interferometers or sparse aperture telescopes in space, since the aperture
diameters required are in excess of 500 m - a regime in which monolithic or
segmented designs are not and will not be feasible and because these
observations require the detection of faint emission near the bright unresolved
continuum source, which is impossible from the ground, even with adaptive
optics. Two mission concepts which could provide these invaluable observations
are NASA's Stellar Imager (SI; Carpenter et al. 2008 &
http://hires.gsfc.nasa.gov/si/) interferometer and ESA's Luciola (Labeyrie
2008) sparse aperture hypertelescope.
