VLBI observations of VIK J2318-3113, a quasar at z = 6.44
  The nature of jets in active galactic nuclei (AGN) in the early Universe and
their feedback to the host galaxy remain a highly topical question.
Observations of the radio structure of high-redshift AGNs enabled by very long
baseline interferometry (VLBI) provide indispensable input into studies of
their properties and role in the galaxies' evolution. Up to now, only five AGNs
at redshift $z > 6$ have been studied with the VLBI technique. VIKJ2318-3113 is
a recently discovered quasar at z = 6.44 that has not been imaged with VLBI
before the current work. Here we present the first VLBI imaging results of this
high-redshift quasar, with the aim of corroborating its high-resolution
appearance with the physical model of the object. We carried out VLBI
phase-referencing observations of VIKJ2318-3113 using the Very Long Baseline
Array at two frequencies, 1.6 and 4.7 GHz, and obtained the first view at the
radio structure on the milliarcsecond scale. The source was clearly detected at
1.6 GHz. We found that almost all of its radio emission comes from the pc-scale
core region. Our dual-frequency observations constrain the spectral index and
brightness temperature of the radio core. Its properties are similar to those
of other known high-redshift radio-loud AGNs.
