Fast jet proper motion discovered in a blazar at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si18.svg"><mml:mrow><mml:mi>z</mml:mi><mml:mo linebreak="goodbreak" linebreakstyle="after">=</mml:mo><mml:mn>4.72</mml:mn></mml:mrow></mml:math>

Zhang, Yingkang; An, Tao; Frey, Sándor

doi:10.1016/j.scib.2020.01.008

Cited by 20 publications

(24 citation statements)

References 58 publications

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“…For VIK J2318−3113 we find that δ 5, which would constrain the Doppler factor to values normally observed in radio QSOs whose jets are closely aligned to our line of sight, such as blazars (e.g. Hovatta et al 2009;Zhang et al 2020;Homan et al 2021). This indicates that relativistic beaming might play an important role in the observed radio emission of VIK J2318−3113.…”

Section: Intrinsic Variabilitysupporting

confidence: 64%

Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113

Ighina,

Leung,

Broderick

et al. 2022

Preprint

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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 23 h field and from dedicated follow-up, we were able to constrain the radio spectrum of VIK J2318−3113 in the observed range ∼0.1-10 GHz. At high frequencies (0.888-5.5 GHz in the observed frame) the QSO presents a steep spectrum (α r =1.24, with S ν ∝ ν −αr ), while at lower frequencies (0.4-0.888 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 which significantly steepens above it. 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 few×10 4 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.

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Section: Intrinsic Variabilitysupporting

confidence: 64%

Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113

Ighina,

Leung,

Broderick

et al. 2022

Preprint

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“…These place strong observational constraints on the modeling of the spectral energy distribution (SED) of the jet (Sbarrato et al 2022). Current detections of jet proper motions of high-redshift (z  4) AGNs are limited to a few sources (Veres et al 2010;Frey et al 2015;Perger et al 2018;An et al 2020b;Zhang et al 2020). All these are blazars, with apparent superluminal speeds distributed in a wide range from 2c to about 20c, where c denotes the speed of light.…”

Section: Introductionmentioning

confidence: 99%

Radio Jet Proper-motion Analysis of Nine Distant Quasars above Redshift 3.5

Zhang

Frey

et al. 2022

ApJ

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Up to now, jet kinematic studies of radio quasars have barely reached beyond the redshift range z > 3.5. This significantly limits our knowledge of high-redshift jets, which can provide key information for understanding the jet nature and the growth of black holes in the early universe. In this paper, we selected nine radio-loud quasars at z > 3.5 which display milliarcsecond-scale jet morphology. We provided evidence of the source nature by presenting high-resolution very long baseline interferometry (VLBI) images of the sample at 8.4 GHz frequency and making spectral index maps. We also consider Gaia optical positions that are available for seven out of the nine quasars for better identification of the jet components within the radio structures. We find that six sources can be classified as core–jet blazars. The remaining three objects are more likely young jetted radio sources, compact symmetric objects. By including multiepoch archival VLBI data, we also obtained jet component proper motions of the sample and estimated the jet kinematic and geometric parameters (Doppler factor, Lorentz factor, and viewing angle). Our results show that at z > 3.5, the jet’s apparent transverse speeds do not exceed 20 times the speed of light (c). This is consistent with earlier high-redshift quasar measurements in the literature and the tendency derived from low-redshift blazars that fast jet speeds (>40c) only occur at low redshifts. The results from this paper contribute to the understanding of the cosmological evolution of radio active galactic nuclei.

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“…Hence, a significant offset between the radio and optical positions could be related to the misaligned nature of the jet, while for blazars, no large positional difference is expected. Long-term VLBI monitoring of resolved radio jets can be used to measure the components' proper motion and to determine their physical and geometric properties (e.g., Frey et al 2015;Perger et al 2018;Zhang et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Radio-loud Quasars above Redshift 4: Very Long Baseline Interferometry (VLBI) Imaging of an Extended Sample

Krezinger

Perger

Gabányi

et al. 2022

ApJS

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High-redshift radio sources provide plentiful opportunities for studying the formation and evolution of early galaxies and supermassive black holes. However, the number of known radio-loud active galactic nuclei (AGN) above redshift 4 is rather limited. At high redshifts, it appears that blazars, with relativistically beamed jets pointing toward the observer, are in the majority compared to the radio-loud sources with jets misaligned with respect to the line of sight. To find more of these misaligned AGN, milliarcsecond-scale imaging studies carried out with very long baseline interferometry (VLBI) are needed, as they allow us to distinguish between compact-core–jet radio sources and those with more extended emission. Previous high-resolution VLBI studies revealed that some of the radio sources among blazar candidates in fact show unbeamed radio emission on milliarcsecond scales. The most accurate optical coordinates determined with the Gaia astrometric space mission are also useful in the classification process. Here, we report on dual-frequency imaging observations of 13 high-redshift (4 < z < 4.5) quasars at 1.7 and 5 GHz with the European VLBI Network. This sample increases the number of z > 4 radio sources for which VLBI observations are available by about a quarter. Using structural and physical properties, such as radio morphology, spectral index, variability, brightness temperature, as well as optical coordinates, we identified six blazars and six misaligned radio AGNs, with the remaining one tentatively identified as blazar.

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Fast jet proper motion discovered in a blazar at z=4.72

Cited by 20 publications

References 58 publications

Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113

Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113

Radio Jet Proper-motion Analysis of Nine Distant Quasars above Redshift 3.5

Radio-loud Quasars above Redshift 4: Very Long Baseline Interferometry (VLBI) Imaging of an Extended Sample

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