What defines a compact symmetric object? A carefully vetted sample of CSOs

TL;DR

This paper refines the classification criteria for Compact Symmetric Objects (CSOs) by adding variability and velocity criteria to distinguish them from other compact radio sources, aiming to improve the accuracy of CSO identification.

Contribution

The authors propose new criteria, including slow variability and low apparent velocity, to better identify genuine CSOs and reduce misclassification in radio source samples.

Findings

Proposed five criteria for CSO classification.

Compiled a catalog of CSOs using these criteria.

Reduced misclassification of CSOs in radio samples.

Abstract

Compact Symmetric Objects (CSOs), young jetted-AGN of overall projected size <1 kpc, are of great interest due to their youth and evolution. The classification was introduced to distinguish between ~95% of powerful compact extragalactic radio sources in flux density limited samples that are dominated by asymmetric emission due to relativistic beaming from jets aligned close to the line of sight, and ~5% of objects that are not. The original classification criteria were: (i) overall projected diameter smaller than ~1 kpc, (ii) identified center of activity, and (iii) symmetric jet structure about the center. There is confusion and erosion of the value of the CSO classification due to misclassifications. Many jets contain compact bright features outside core, resulting in a GPS total spectrum and a "compact double" appearance, and some objects with jet axes aligned close to the line of sight appear symmetric because the approaching jet is projected on both sides of the core. To eliminate the confusion, we propose adding (iv) slow radio variability and (v) low apparent velocity of bright features moving along the jets to the above CSO criteria. We are compiling a catalog of CSOs using these five criteria to eliminate the confusion of Doppler boosting.