  To investigate the role of feedback from Active Galactic Nuclei (AGN) in
driving the evolution of their host galaxies, we have carried out a study of
the environments and optical properties of galaxies harboring X-ray luminous
AGN in the Cl1604 supercluster at z~0.9. Making use of Chandra, HST/ACS and
Keck/DEIMOS observations, we examine the integrated colors, morphologies and
spectral properties of nine moderate-luminosity (L_x ~ 10^43 erg s^-1) type 2
Seyferts detected in the Cl1604 complex. We find that the AGN are predominantly
hosted by luminous spheroids and/or bulge dominated galaxies which have colors
that place them in the valley between the blue cloud and red sequence in
color-magnitude space, consistent with predictions that AGN hosts should
constitute a transition population. Half of the hosts have bluer overall colors
as a result of blue resolved cores in otherwise red spheroids and a majority
show signs of recent or pending interactions. We also find a substantial number
exhibit strong Balmer absorption features indicative of post-starburst
galaxies, despite the fact that we detect narrow [OII] emission lines in all of
the host spectra. If the [OII] lines are due in part to AGN emission, as we
suspect, then this result implies that a significant fraction of these galaxies
(44%) have experienced an enhanced level of star formation within the last ~1
Gyr which was rapidly suppressed. Overall we find that the properties of the
nine host galaxies are generally consistent with a scenario in which recent
interactions have triggered both increased levels of nuclear activity and an
enhancement of centrally concentrated star formation, followed by a rapid
truncation of the latter, possibly as a result of feedback from the AGN itself.
[Abridged]
