Proper motion of the radio jets in two blazars at redshift above 3
Máté Krezinger (Konkoly Observatory Hungarian Academy of Sciences, MTA Centre of Excellence, Eötvös Loránd University)
Sándor Frey (MTA Centre of Excellence, Konkoly Observatory Hungarian Academy of Sciences, Eötvös Loránd University)
Krisztina Perger (Konkoly Observatory Hungarian Academy of Sciences, MTA Centre of Excellence)
Krisztina Gabányi (MTA Centre of Excellence, Eötvös Loránd University, Konkoly Observatory Hungarian Academy of Sciences)
Tao An (Chinese Academy of Sciences)
Yingkang Zhang (Chinese Academy of Sciences)
Leonid I. Gurvits (TU Delft - Aerospace Engineering, Joint Institute for VLBI ERIC)
Oleg Titov (Geoscience Australia)
Alexey Melnikov (Institute of Applied Astronomy of the Russian Academy of Sciences)
Zsolt Paragi (Joint Institute for VLBI ERIC)
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Abstract
There is still a limited number of high-redshift (z > 3) active galactic nuclei (AGNs) whose jet kinematics have been studied with very long baseline interferometry (VLBI). Without a dedicated proper motion survey, regularly conducted astrometric VLBI observations of bright radio-emitting AGN with sensitive arrays can be utilized to follow changes in the jets, by means of high-resolution imaging and brightness distribution modelling. Here, we present a first-time VLBI jet kinematic study of NVSS J080518 + 614423 (z = 3.033) and NVSS J165844-073918 (z = 3.742), two flat-spectrum radio quasars that display milliarcsecond-scale jet morphology. Archi v al astrometric observ ations carried out mainly with the Very Long Baseline Array, supplemented by recent data taken with the European VLBI Network, allowed us to monitor changes in their radio structure in the 7.6-8.6 GHz frequency band, covering almost two decades. By identifying individual jet components at each epoch, we were able to determine the apparent proper motion for multiple features in both sources. Apparent superluminal motions range (1-14) c, and are found to be consistent with studies of other high-redshift AGN targets. Using the physical parameters derived from the brightness distribution modelling, we estimate the Doppler-boosting factors (δ≈11.2 and δ≈2.7), the Lorentz factors (Γ ≈7.4 and Γ ≈36.6), and the jet viewing angles (θ≈4.4°and θ≈8.0°), for NVSS J080518 + 614423 and NVSS J165844-073918, respectively. The data revealed a stationary jet component with negligible apparent proper motion in NVSS J165844-073918.
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