X-RAY-EMISSION FROM THE HOST CLUSTERS OF POWERFUL AGN

We report the detection of X-ray emission from the host cluster of the unusual radio-quiet quasar H 1821+643 using the ROSAT HRI, and the no n-detection of X-ray emission from the host cluster of the radio-loud quasar 3C 206 (3 sigma upper limit of 1.63x10(44) ergs s(-1)) using th e EINSTEIN HRI. The host cluster of H 1821+643 is one of the most X-ra y luminous clusters known, with a rest-frame 0.1-2.4 keV luminosity of 3.74+/-0.57h(50)(-2)X10(45) ergs s(-1), 38% of which is from a barely resolved cooling flow component. The cluster emission complicates int erpretation of previous X-ray spectra of this field. In particular, th e observed Fe K alpha emission can probably be attributed entirely to the cluster and either the quasar is relatively X-ray quiet for its op tical luminosity or the cluster has a relatively low temperature for i ts luminosity. We combine these data with the recent detection of X-ra y emission from the host cluster of the ''buried'' radio-quiet quasar IRAS 09104+4109 [Fabian & Crawford, MNRAS, 274, L63 (1995)], our previ ous upper limits for the host clusters of two z similar to 0.7 radio-l oud quasars, and literature data on FR II radio galaxies. We compare t his dataset to the predictions of three models for the presence and ev olution of powerful AGN in clusters: the low-velocity-dispersion model , the low-ICM-density model, and the cooling flow model. Neither the l ow-ICM-density model nor the cooling flow model can explain all the ob servations. We suggest that strong interactions with gas-containing ga laxies mag. be the only mechanism needed to explain the presence and e volution of powerful AGN in clusters, a scenario consistent with the f ar-IR and optical properties of the host galaxies studied here, all of which show some evidence for past interactions. However, the cooling flow model cannot be ruled out for at least some objects, and it is li kely that both processes are at work in creating and fueling powerful AGN in clusters. Each scenario makes testable predictions for future X -ray and optical observations which can test the relative importance o f each process. (C) 1997 American Astronomical Society.