Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar ($z$=6.44)

Abstract

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 $\times 10^{26}$ W Hz${}^{-1}$ at 5 GHz) compared to the optical luminosity (1.8 $\times 10^{24}$ W Hz${}^{-1}$ at 4400 A) makes it the most distant radio-loud quasar observed so far, with a radio loudness R$\sim$70 (R$=L_{5GHz}/L_{4400A}$). Moreover, the high bolometric luminosity of the source (L${}_{\mathrm{bol}}$=7.4 $\times 10^{46}$ erg s${}^{-1}$) suggests the presence of a supermassive black hole with a high mass ($\gtrsim$6 $\times$10${}^8$ M${}_{\odot }$) 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 $\sim$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.

5 pages, 2 figures, 3 tables. Accepted for publication in A&A Letters

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