Parsec-scale radio structure of 14 Fanaroff-Riley type 0 radio galaxies

TL;DR

This study investigates the parsec-scale radio structures of 14 FR 0 radio galaxies using VLBI imaging, revealing diverse properties including relativistic beaming, jet motions, and variability, which suggest FR 0s are a heterogeneous population with potential links to FR I galaxies.

Contribution

First VLBI imaging study of 14 FR 0 radio galaxies, providing detailed insights into their compact structures, jet dynamics, and variability, highlighting their heterogeneity and potential connection to FR I sources.

Findings

All sources show compact structures.

Four sources exhibit relativistic beaming with Doppler factors 1.7 to 6.

Jet proper motions between 0.23 c and 0.49 c in two sources.

Abstract

Recently a population of compact radio galaxies were classified as Fanaroff-Riley type 0 radio galaxies (FR 0s). The physical nature of FR 0s and the connection with the classical FR I and II galaxies are not currently well understood. Here, we report the radio properties of fourteen FR 0s on parsec (pc) scales derived from their very long baseline interferometry (VLBI) imaging observations. All sources show compact structures. Four sources show relativistic beaming with Doppler boosting factors ranging from 1.7 to 6. The brightness temperatures of the other ten are below the equilibrium limit. Jet proper motions are determined in two sources which have multiple epoch data, between 0.23 c and 0.49 c, implying mildly relativistic jet flow. Low-amplitude flux density variation is found in J0943+3614 over a time period of 10 years. No significant variability are detected in three other sources over time scales of a few years. The radio properties of the FR 0s inferred from the VLBI data resemble GHz-peaked spectrum or compact steep-spectrum sources. Moreover, the diversity of their relativistic beaming indicators (brightness temperature, variability, jet proper motion) also imply that FR 0s might not be a homogeneous population of radio sources. Detailed studies of the low-power FR 0 sources in the local Universe additionally offer a promising opportunity to understand their connection to the FR Is.