EVOLUTION OF RADIO QUASARS FROM REDSHIFT 0.6-3.7

This paper presents the results of VLA radio imaging of 58 radio-loud quasars with redshift 2.0 or higher, and which fill the redshift-luminosity plane as evenly as possible. This work completes a survey of ∼250 quasars covering redshifts from 0.6-3.7 and which attempts to sample luminosity and look-back time in a uniform way. Within the constraints of possible selection effects (mentioned in the text) we find the following: The relative population of extended and unresolved sources changes with redshift in a way that suggests that radio quasars may live longer and spend more time as large triple sources in the present epoch than in the earlier universe. There appear to be few low-luminosity radio quasars at high redshift. Ejection of material appears to occur on one side at a time, with usually at least one reversal of direction in the source lifetime. The velocity of ejection appears to be mildly relativistic at high redshift, but of lower velocity in the present epoch. There is also evidence suggestive of changes in the IGM with cosmic time; however the data presented do not show the minimum in density at z∼2 that has been suggested for cluster environments.