Chandra Discovery of the Intracluster Medium around UM 425 at a Redshift of 1.47

Abstract

We report on the discovery of a candidate cluster of galaxies at redshift z = 1.47 based on Chandra observations in the field of quasars UM 425A and UM 425B. We detect with high significance diffuse emission due to the intracluster hot gas around the quasar pair. This is the second highest redshift cluster candidate after 3C 294 at z = 1.786. The diffuse emission is elliptical in shape with about 17'' extent. If indeed at z = 1.47, this corresponds to a physical size of 140 h kpc and 2-10 keV luminosity of ~3 × 1043 ergs s-1. The cluster is unlikely to be the long-sought gravitational lens invoked to explain the unusual brightness of UM 425A and the close quasar pair. Coexistence of the quasars with the cluster suggests a link of activity to cluster environment. The unusually high luminosity of UM 425A may then be due to a higher accretion rate. We also comment briefly on the X-ray spectra of UM 425A and UM 425B, both of which exhibit broad absorption line optical spectra. The present evidence suggests that the quasars are just a pair and not lensed images of the same quasar.