J2102+6015: a young radio source at z = 4.575

TL;DR

This study presents high-resolution VLBI imaging of the high-redshift AGN J2102+6015, revealing a young, compact symmetric object with stable features over 13 years, providing insights into early Universe black hole activity.

Contribution

First multi-epoch VLBI analysis of a z=4.57 AGN showing its structure and stability, suggesting it is a young, symmetric radio source rather than a blazar.

Findings

Features show flat/inverted spectra.

Separation remains stable over 13 years.

Likely a young, compact symmetric object.

Abstract

Jets of high-redshift active galactic nuclei (AGNs) can be used to directly probe the activity of the black holes in the early Universe. Radio sources with jets misaligned with respect to the line of sight are expected to dominate the high-redshift AGN population. In this paper, we present the high-resolution imaging results of a z=4.57 AGN J2102+6015 by analyzing its multi-epoch dual-frequency very long baseline interferometry (VLBI) data. The 8.4-GHz VLBI images reveal two major features along the east-west direction separated by $\sim$ 10 milli-arcsec (mas). From the spectral index map, both features show flat/inverted spectra. The separation between the two features remains almost unchanged over an observation period of $\sim$ 13 years, placing an upper limit of the separation speed as about 0.04 mas year$^{-1}$. Previous studies have classified the source as a GHz-peaked spectrum quasar. Our results indicate that J2102+6015 is most likely a young, compact symmetric object rather than a blazar-type core-jet source.