1994A&A...291..737G

We present the results of a continuing study of the milliarcsecond structure of extremely high-redshift radio sources aimed at investigating possible cosmological evolutionary effects in quasars and their use in testing cosmological models. We present VLBI maps of four quasars at redshifts z≥3: 0336-017 (z=3.197), 0636+680 (z=3.174), 1442+101 (z=3.531), and 2048+312 (z=3.185). All four sources are resolved. Two, 0636+680 and 1442+101, show well defined jets, while the other two are slightly extended and may contain jets. A means of estimating the cosmological deceleration parameter q_o using these and earlier data (Gurvits et al. 1992) is shown.