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

TL;DR

This study used high-resolution radio interferometry to confirm the blazar nature of a high-redshift candidate, revealing its compact structure and comparing its properties with similar AGN to understand relativistic boosting.

Contribution

First high-resolution VLBI observations of a high-redshift blazar candidate confirming its blazar nature and analyzing its radio properties at milliarcsecond scales.

Findings

Detected a compact radio feature at both frequencies with a flat spectrum.

Confirmed blazar nature based on radio properties and brightness temperature.

Found diverse relativistic boosting characteristics among similar AGN.

Abstract

Active galactic nuclei (AGN) have been observed as far as redshift z~7. They are crucial in investigating the early Universe as well as the growth of supermassive black holes at their centres. Radio-loud AGN with their jets seen at a small viewing angle are called blazars and show relativistic boosting of their emission. Thus, their apparently brighter jets are easier to detect in the high-redshift Universe. DES J014132.4-542749.9 is a radio-luminous but X-ray weak blazar candidate at z = 5. We conducted high-resolution radio interferometric observations of this source with the Australian Long Baseline Array at 1.7 and 8.5 GHz. A single, compact radio emitting feature was detected at both frequencies with a flat radio spectrum. We derived the milliarcsecond-level accurate position of the object. The frequency dependence of its brightness temperature is similar to that of blazar sources observed at lower redshifts. Based on our observations, we can confirm its blazar nature. We compared its radio properties with those of two other similarly X-ray-weak and radio-bright AGN, and found that they show very different relativistic boosting characteristics.