Radio-loud high-redshift quasars ( HRQs ) , although only a few of them are known to date , are crucial for the studies of the growth of supermassive black holes ( SMBHs ) and the evolution of active galactic nuclei ( AGN ) at early cosmological epochs .
Radio jets offer direct evidence of SMBHs , and their radio structures can be studied with the highest angular resolution using Very Long Baseline Interferometry ( VLBI ) .
Here we report on the observations of three HRQs ( J0131 - 0321 , J0906 + 6930 , J1026 + 2542 ) at z > 5 using the Korean VLBI Network and VLBI Exploration of Radio Astrometry Arrays ( together known as KaVA ) with the purpose of studying their pc-scale jet properties .
The observations were carried out at 22 and 43 GHz in 2016 January among the first-batch open-use experiments of KaVA .
The quasar J0906 + 6930 was detected at 22 GHz but not at 43 GHz .
The other two sources were not detected and upper limits to their compact radio emission are given .
Archival VLBI imaging data and single-dish 15-GHz monitoring light curve of J0906 + 6930 were also acquired as complementary information .
J0906 + 6930 shows a moderate-level variability at 15 GHz .
The radio image is characterized by a core–jet structure with a total detectable size of \sim 5 pc in projection .
The brightness temperature , \gtrsim 1.9 \times 10 ^ { 11 } K , indicates relativistic beaming of the jet .
The radio properties of J0906 + 6930 are consistent with a blazar .
Follow-up VLBI observations will be helpful for determining its structural variation .