No Evidence of Quasar-Mode Feedback in a Four-Way Group Merger at z~0.84
  We report on the results of a Chandra search for evidence of triggered
nuclear activity within the Cl0023+0423 four-way group merger at z ~ 0.84. The
system consists of four interacting galaxy groups in the early stages of
hierarchical cluster formation and, as such, provides a unique look at the
level of processing and evolution already under way in the group environment
prior to cluster assembly. We present the number counts of X-ray point sources
detected in a field covering the entire Cl0023 structure, as well as a
cross-correlation of these sources with our extensive spectroscopic database.
Both the redshift distribution and cumulative number counts of X-ray sources
reveal little evidence to suggest that the system contains X-ray luminous
active galactic nuclei (AGNs) in excess to what is observed in the field
population. If preprocessing is under way in the Cl0023 system, our
observations suggest that powerful nuclear activity is not the predominant
mechanism quenching star formation and driving the evolution of Cl0023
galaxies. We speculate that this is due to a lack of sufficiently massive
nuclear black holes required to power such activity, as previous observations
have found a high late-type fraction among the Cl0023 population. It may be
that disruptive AGN-driven outflows become an important factor in the
preprocessing of galaxy populations only during a later stage in the evolution
of such groups and structures when sufficiently massive galaxies (and central
black holes) have built up, but prior to hydrodynamical processes stripping
them of their gas reservoirs.
