A close look at compact triple radio sources

TL;DR

This paper examines the structure of compact triple radio sources, revealing signs of restarted activity and jet reorientation, and discusses the potential for high-resolution VLBI observations to further understand their inner structures.

Contribution

It provides high-resolution imaging evidence of restarted activity and jet reorientation in compact triple radio sources, and identifies candidate quasars for future detailed VLBI studies.

Findings

Inner core structures show signs of restarted activity.

Misalignment between arcsecond and milliarcsecond structures supports jet reorientation.

Two quasars with potential for high-resolution VLBI imaging are identified.

Abstract

We show an archival 1.4-GHz Very Large Array (VLA) image of the core-dominated triple (CDT) radio source J1628+3906, along with a recent high-resolution 5-GHz Very Long Baseline Interferometry (VLBI) image of its core. This core is resolved into two nearly symmetric components at ~10 milli-arcsecond (mas) angular scale. The inner structure is markedly misaligned with respect to the large-scale structure. This morphology can be interpreted as a possible signature of once ceased and then restarted activity of the galactic nucleus, coupled with a rapid repositioning of the central radio jet axis. In a search for compact (<5"), optically identified, and highly redshifted (z>3) quasars in the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) and the Sloan Digital Sky Survey (SDSS) catalogues, we have also found two quasars associated with weaker two-sided radio lobes at ~10" scale. We present archival 1.4-GHz VLA images of these quasars (J1036+1326 and J1353+5725). The compact cores of both of these CDT sources are likely to be detectable at mas scales. Future VLBI observations at the highest resolution could reveal if their inner radio structure is similar to that of the Compact Symmetric Objects (CSOs). The characteristic directions of their arcsecond-scale and mas-scale structures are probably misaligned which could also support the "restarting and rapid repositioning" scenario.