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Constraining the radio properties of the z = 6.44 QSO VIK J2318-3113


Ighina, L and Leung, JK and Broderick, JW and Drouart, G and Seymour, N and Belladitta, S and Caccianiga, A and Lenc, E and Moretti, A and An, T and Galvin, TJ and Heald, GH and Huynh, MT and McConnell, D and Murphy, T and Pritchard, J and Quici, B and Shabala, SS and Tingay, SJ and Turner, RJ and Wang, Y and White, SV, Constraining the radio properties of the z = 6.44 QSO VIK J2318-3113, Astronomy and Astrophysics, 663 Article 73. ISSN 1432-0746 (2022) [Refereed Article]


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Copyright 2022 ESO Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0)

DOI: doi:10.1051/0004-6361/202142733


The recent detection of the quasi-stellar object (QSO) VIKING J231818.3−311346 (hereafter VIK J2318−3113) at redshift z = 6.44 in the Rapid ASKAP Continuum Survey (RACS) uncovered its radio-loud nature, making it one of the most distant known to date in this class. By using data from several radio surveys of the Galaxy And Mass Assembly 23h field and from a dedicated follow-up, we were able to constrain the radio spectrum of VIK J2318−3113 in the observed range ∼0.110 GHz. At high frequencies (0.8885.5 GHz in the observed frame) the QSO presents a steep spectrum (αr = 1.24, with Sν ∝ ναr), while at lower frequencies (0.40.888 GHz in the observed frame) it is nearly flat. The overall spectrum can be modelled by either a curved function with a rest-frame turnover around 5 GHz, or with a smoothly varying double power law that is flat below a rest-frame break frequency of about 20 GHz and above which it significantly steepens. Based on the model adopted, we estimated that the radio jets of VIK J2318−3113 must be a few hundred years old in the case of a turnover, or less than a few 104 years in the case of a break in the spectrum. Having multiple observations at two frequencies (888 MHz and 5.5 GHz), we further investigated the radio variability previously reported for this source. We found that the marginally significant flux density variations are consistent with the expectations from refractive interstellar scintillation, even though relativistic effects related to the orientation of the source may still play a non-negligible role. Further radio and X-ray observations are required to conclusively discern the nature of this variation.

Item Details

Item Type:Refereed Article
Keywords:galaxies: active, galaxies: high-redshift, quasars: general, quasars: individual: VIKING J231818.3-311346, radio continuum: galaxies, galaxy: abundances
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Cosmology and extragalactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Shabala, SS (Associate Professor Stas Shabala)
UTAS Author:Turner, RJ (Dr Ross Turner)
ID Code:151060
Year Published:2022
Web of Science® Times Cited:2
Deposited By:Physics
Deposited On:2022-07-14
Last Modified:2023-01-10
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