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

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.

High-resolution Imaging of Two Radio Quasars at the End of the Reionization Epoch

“…This constrains the spectral index of the pc-scale feature to < −1.2, which is consistent with the value found for the kpc-scale radio emission [8]. These findings imply that the radio emission originates from a recently formed young quasar jet in the early Universe [19].…”

“…The source was detected as a compact 'core' at 1.6 GHz with a flux density of 550 Jy, while no compact component brighter than 130 Jy (i.e. 5 image noise) was detected at 4.7 GHz [19]. This constrains the spectral index of the pc-scale feature to < −1.2, which is consistent with the value found for the kpc-scale radio emission [8].…”

“…The amplitude and phase self-calibration, imaging, and model fitting were carried out with program [16]. A detailed description of the observations, calibrations, and model fitting is given in the original paper describing the project [19].…”

Very long baseline interferometry observations of the high-redshift blazar candidate J0141–5427

“…Hovatta et al (2014) studied 190 blazar jets of the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE, Lister et al 2019) survey, and showed that in sources at higher redshifts e the derived core parameters are more likely contaminated by a neighbouring jet component due to the lower effective linear resolution. Interestingly, high brightness temperature values, close to the equipartition limit are rarely observed in other z > 5 blazars (Coppejans et al 2016;Zhang et al 2022), with the notable exception of J0906+6930 (An et al 2020).…”

“…However, such low brightness temperatures can also be measured in blazars due to insufficient resolution, when the core and a close jet component cannot be resolved and thus the fitted size is larger, resulting in lower T b value. Hovatta et al (2014) Interestingly, high brightness temperature values, close to the equipartition limit are rarely observed in other z > 5 blazars (Coppejans et al 2016;Zhang et al 2022), with the notable exception of J0906+6930 (An et al 2020).…”