Parsec-scale Properties of eight Fanaroff-Riley Type 0 Radio Galaxies

TL;DR

This study provides high-resolution radio observations of eight Fanaroff-Riley type 0 galaxies, revealing their compact structures, jet morphologies, and proper motions, suggesting they host mildly relativistic jets with lower Lorentz factors.

Contribution

First high-resolution VLBI imaging of a sample of FR 0 galaxies, characterizing their pc-scale structures and jet kinematics, and proposing their jets are mildly relativistic with larger viewing angles.

Findings

Most sources show compact, two-sided jet structures.

Jet proper motions range from -0.08c to 0.51c.

Jets are likely mildly relativistic with lower Lorentz factors.

Abstract

We report the high-resolution radio observations of eight Fanaroff-Riley type 0 radio galaxies (FR 0s), selected from the published FR 0 sample. These observations were carried out with the Very Long Baseline Array (VLBA) and European VLBI Network (EVN) at frequencies of 5 and 8 GHz with a highest resolution of 0.6 mas. All eight sources show compact structures on projected physical sizes of 0.3-10 parsec. Six sources show a two-sided structure and two sources show a one-sided jet structure. J1025+1022 shows an X-shaped jet structure, which could result from a reorientation of the jet axis due to a restart of the central engine or a projection of a highly curved inner jet, but more studies are needed to examine these scenarios. Proper motions for 22 jet components of the eight sources are determined to be between -0.08 c and 0.51 c. Although most of the sources exhibit flat spectra, other observed characteristics, such as, low-amplitude flux density variations, low jet proper motion speeds, and symmetric two-sided jet structures, tend to support that the pc-scale FR 0 jets are mildly relativistic with lower bulk Lorentz factors and larger viewing angles.