The Parsec-Scale Morphology of Southern GPS sources

TL;DR

This study uses VLBI imaging to analyze the parsec-scale structures of southern GPS sources, revealing dominant core-jet or compact double morphologies and exploring their spectral and morphological relationships across different redshifts.

Contribution

It provides new VLBI images of four GPS candidates and investigates the morphological diversity and spectral characteristics of southern GPS sources, including high-redshift objects.

Findings

Core-jet and compact double morphologies are prevalent.

A correlation between narrow spectral width and compact double morphology is observed.

High-redshift GPS sources mainly exhibit core-jet morphology.

Abstract

Multi-frequency, multi-epoch ATCA observations of a sample of AGN resulted in the identification of 9 new candidate Giga-hertz Peaked Spectrum (GPS) sources. Here we present Long Baseline Array observations at 4.8 GHz of the four candidates with no previously published VLBI image, and consider these together with previously published VLBI images of the other five sources. We find core-jet or compact double morphologies dominate, with further observations required to distinguish between these two possibilities for some sources. One of the nine candidates, PKS 1831-711, displays appreciable variability, suggesting its GPS spectrum is more ephemeral in nature. We focus in particular on the apparent relationship between a narrow spectral width and "compact double" parsec-scale morphology, finding further examples, but also exceptions to this trend. An examination of the VLBI morphologies high-redshift (z>3) sub-class of GPS sources suggests that core-jet morphologies predominate in this class.