Spectroscopy of extended emission-line gas around quasars at Formula

We present long-slit optical spectroscopy for a sample of eight steep-spectrum radio quasars with a range of redshifts from 0.37 to 0.87. All of these quasars display extended oxygen line-emission when corrected for contamination by light spilled over from the nucleus. The pressure of the gas in the extended emission-line regions is determined by comparing the observed [O III]λ5007/[O II]λ3727 intensity ratio with that expected from gas at the observed projected radius photo-ionized by the active nucleus. The pressures are found to be consistent with those of the hot intracluster gas found in groups and clusters of galaxies at the present epoch. We infer that the radio-loud quasars reported on here lie in groups or clusters of galaxies, in agreement with the conclusions reached by Yee & Green, and others, from their direct observations of high galaxy densities surrounding radio-loud quasars of lower mean redshift. The hot intracluster gas confines the gas in the emission-line clouds and is cooling in less than a Hubble time unless its temperature is unusually high $$(\geqslant7\times10^7\enspace\text K)$$. In the best cases, we find pressure profiles indicating that the hot gas is cool enough to respond to the gravitational potential of the host galaxy (i.e. 10⁷ K). The pressures are similar to those around nearby cooling flows where the mass deposition rate is $$\sim 100 \enspace M_\odot \enspace\text{yr}^{-1}$$.