What is Inside the Double-Double Structure of the Radio Galaxy J0028+0035?

TL;DR

This study investigates the complex radio structure of galaxy J0028+0035, aiming to identify multiple episodes of activity through high-resolution VLBI observations, but finds only a single core with no evidence of a third inner double.

Contribution

The paper provides high-resolution VLBI imaging of J0028+0035, offering detailed insights into its core structure and clarifying the nature of nearby sources, contributing to understanding of double-double radio galaxy structures.

Findings

No third innermost double detected in high-res images

Background source 5BZU J0028+0035 is a weak, resolved radio source

The galaxy shows a compact core with no evidence of multiple activity episodes

Abstract

The radio source J0028+0035 is a recently discovered double--double radio galaxy at redshift z=0.398. Its relic outer lobes are separated by about 3' in the sky, corresponding to ~1 Mpc projected linear size. Inside this large-scale structure, the inner pair of collinear lobes span about 100 kpc. In the arcsec-resolution radio images of J0028+0035, there is a central radio feature that offers the intriguing possibility of being resolved into a pc-scale, third pair of innermost lobes. This would make this radio galaxy a rare triple-double source where traces of three distinct episodes of radio activity could be observed. To reveal the compact radio structure of the central component, we conducted observation with the European Very Long Baseline Interferometer Network and the enhanced Multi Element Remotely Linked Interferometer Network. Our 1.66 GHz image with high (~5 milliarcsec) resolution shows a compact central radio core with no indication of a third, innermost double feature. The observation performed in multi-phase-centre mode also revealed that the physically unrelated but in projection closely separated background source 5BZU J0028+0035 has a single weak, somewhat resolved radio feature, at odds with its blazar classification.