VLA and VLBA Observations of the Highest Redshift Radio-Loud QSO   J1427+3312 at z = 6.12
  We present 8.4 GHz VLA A-array and 1.4 GHz VLBA results on the radio continuum emission from the highest redshift radio-loud quasar known to date, the $z=6.12$ QSO J1427+3312. The VLA observations show an unresolved steep spectrum source with a flux density of $250 \pm 20$ uJy at 8.4GHz and a spectral index value of $\alpha^{8.4}_{1.4}=-1.1$. The 1.4 GHz VLBA images reveal several continuum components with a total flux density of $1.778 \pm 0.109$ mJy, which is consistent with the flux density measured with the VLA at 1.4 GHz. Each of these components is resolved with sizes of a few milliarcseconds, and intrinsic brightness temperatures on the order of $10^7$ to $10^8$ K. The physical characteristics as revealed in these observations suggest that this QSO may be a Compact Symmetric Object, with the two dominant components seen with the VLBA, which are separated by 31 mas (174 pc) and have intrinsic sizes of ~22-34 pc, being the two radio lobes that are confined by the dense ISM. If indeed a CSO, then the estimated kinematic age of this radio AGN is only $10^3$ yr. 
E. Momjian, C. L. Carilli, I. D. McGreer