VLBI observations of VIK J2318-3113, a quasar at z = 6.44

TL;DR

This paper presents the first VLBI imaging of the high-redshift quasar VIK J2318-3113 at z=6.44, revealing its compact radio core and providing insights into early Universe AGN jet properties.

Contribution

First VLBI imaging of VIK J2318-3113 at z=6.44, expanding the limited sample of high-redshift AGNs studied with VLBI techniques.

Findings

Detected the quasar at 1.6 GHz with VLBI.

Radio emission mainly from the pc-scale core.

Core properties similar to other high-redshift radio-loud AGNs.

Abstract

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.