EXTENDED OPTICAL-EMISSION AROUND RADIO-LOUD QUASARS AT Z APPROXIMATELY 1

We present long-slit optical spectroscopy of a sample of 18 radio-loud quasars, 17 of which have redshifts z > 0.925. They are compared with 3C 281, a quasar at z = 0.599, which has [O II] lambda-3727 and [O III] lambda-5007 emission extending to 70 kpc from the quasar nucleus. Five quasars at z approximately 1 have extended line or continuum emission. The pressure of the extended line-emitting gas around these quasars is shown to exceed 4 x 10(6) cm-3 K within 20 kpc of the quasars. It is argued that the line-emitting gas is in pressure equilibrium with a hot intracluster medium, the short cooling time of which implies that cooled gas is being deposited around the quasars at rates of approximately 1000 M. yr-1. The pressure surrounding more distant (z approximately 1), or equivalently in our sample more luminous, radio-loud quasars is about an order of magnitude greater than that around closer (z approximately 0.3), less luminous quasars. We argue that the pressure of line-emitting gas close to quasars with z approximately 1 cannot be much higher than that inferred here if the pressure is ultimately gravitational in origin. The era of major negative pressure evolution in the intracluster medium is therefore between z approximately 1 and the present time. The typical luminosity of the extended [O II] emission around the quasars is shown to be comparable with that of radio galaxies at similar redshifts.