  As a pilot study to investigate the distribution of matter in the fields of
powerful AGN, we present weak lensing observations of deep fields centered on
the radio-quiet quasar E1821 + 643, the radio galaxy 3C295, and the two
radio-loud quasars, 3C334 and 3C254. The host clusters of E1821 + 643 and 3C295
are comfortably detected via their weak lensing signal, and we report the
detection of a cluster-sized mass concentration in the field of the z=0.734
quasar 3C254. The data for the 3C334 field are so far inconclusive. We find
that the clusters are massive and have smooth mass distributions, although one
shows some evidence of past merger activity. The mass-to-light ratios are found
to be moderately high. We discuss the results in light of the cooling flow and
the merger/interaction scenarios for triggering and fuelling AGN in clusters,
but find that the data do not point unambiguously to neither of the two.
Instead, we speculate that sub-cluster mergers may be responsible for
generating close encounters or mergers of galaxies with the central cluster
member, which could trigger the AGN.
