High-redshift quasars at $z \geq 3$ -- III. Parsec-scale jet properties from VLBI observations

TL;DR

This study uses VLBI to analyze the parsec-scale jet properties of 86 high-redshift quasars, revealing compact morphologies, slow jet motions, and a high fraction of young sources, shedding light on early AGN evolution.

Contribution

It provides the first detailed VLBI-based analysis of high-redshift quasars' jet structures, highlighting their unique properties and evolutionary implications.

Findings

Majority have compact core or core-jet morphology

Jet proper motions are slower than lower-redshift counterparts

High fraction of young or confined spectrum sources

Abstract

High redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z $\geq$ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35\% unresolved cores, 59\% core-jet structures, and only 6\% core-double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jet proper motions are surprisingly slow compared to lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history.