Volume 647, March 2021
|Number of page(s)||5|
|Section||Letters to the Editor|
|Published online||22 March 2021|
Letter to the Editor
Radio detection of VIK J2318−3113, the most distant radio-loud quasar (z = 6.44)
INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milan, Italy
2 DiSAT – Università degli Studi dell’ Insubria, Via Valleggio 11, 22100 Como, Italy
3 International Centre for Radio Astronomy Research, Curtin University, 1 Turner Avenue, Bentley, WA 6102, Australia
Accepted: 1 March 2021
We report the 888 MHz radio detection in the Rapid ASKAP Continuum Survey (RACS) of VIK J2318−3113, a z = 6.44 quasar. Its radio luminosity (1.2 × 1026 W Hz−1 at 5 GHz) compared to the optical luminosity (1.8 × 1024 W Hz−1 at 4400 Å) makes it the most distant radio-loud quasar observed so far, with a radio loudness R ∼ 70 (R = L5 GHz/L4400 Å). Moreover, the high bolometric luminosity of the source (Lbol = 7.4 × 1046 erg s−1) suggests the presence of a supermassive black hole with a high mass (≳6 × 108 M⊙) at a time when the Universe was younger than a billion years. Combining the new radio data from RACS with previous ASKAP observations at the same frequency, we found that the flux density of the source may have varied by a factor of ∼2, which could suggest the presence of a relativistic jet oriented towards the line of sight, that is, a blazar nature. However, currently available radio data do not allow us to firmly characterise the orientation of the source. Further radio and X-ray observations are needed.
Key words: galaxies: active / galaxies: high-redshift / galaxies: jets / quasars: general / quasars: individual: VIK J231818.3–311346
© ESO 2021
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