Letter to the Editor

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

¹ SKA Regional Centre Joint Lab, Shanghai Astronomical Observatory, CAS, Nandan Road 80, Shanghai 200030, PR China
e-mail: ykzhang@shao.ac.cn, antao@shao.ac.cn
² SKA Regional Centre Joint Lab, Peng Cheng Lab, Shenzhen 518066, PR China
³ College of Astronomy and Space Sciences, University of Chinese Academy of Sciences, 19A Yuquanlu, Beijing 100049, PR China
⁴ Konkoly Observatory, ELKH Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
⁵ Institute of Physics, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁶ Joint Institute for VLBI ERIC, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁷ Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
⁸ Department of Astronomy, Institute of Geography and Earth Sciences, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁹ ELKH-ELTE Extragalactic Astrophysics Research Group, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary

Received: 14 April 2022
Accepted: 6 May 2022

Abstract

Context. The nature of jets in active galactic nuclei (AGNs) in the early Universe and their feedback to the host galaxy remains 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. To date, only five AGNs at redshift z > 6 have been studied with the VLBI technique.

Aims. VIK J2318−3113 is a recently discovered quasar at z = 6.44 that had 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.

Methods. We carried out VLBI phase-referencing observations of VIK J2318−3113 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.

Results. The source was clearly detected at 1.6 GHz. We found that almost all of its radio emission comes from the parsec-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.