2004AJ....127..587M

We present high-resolution (≤20 mas) observations of the radio continuum emission at 1.4 GHz from three high-redshift quasars: J1053-0016 (z=4.29), J1235-0003 (z=4.69), and J0913+5919 (z=5.11), thereby doubling the number of z>4 radio-loud quasars that have been imaged at milliarcsecond resolution. The observations were carried out with the Very Long Baseline Array (VLBA) of the NRAO. All three sources are unresolved in these observations, with source size limits of a few milliarcseconds. In all cases the flux densities measured by the VLBA are within 10% of those measured with the Very Large Array (VLA), implying that the sources are not highly variable on yearly time scales. We find no indication for multiple images that might be produced by strong gravitational lensing on scales from 20 mas (VLBA) to a few arcseconds (VLA), to dynamic range limits of ∼100.