AGN jets under the microscope: A divide?

TL;DR

This study compares the jet kinematics of BL Lac objects and flat-spectrum radio quasars, revealing significant differences that suggest the presence of helically structured jets in active galactic nuclei.

Contribution

It provides the first comprehensive comparison of jet kinematics between BL Lacs and quasars, supporting the hypothesis of helical jet structures.

Findings

BL Lacs have more bent and wider jets.

BL Lacs exhibit slower jet component motions.

Significant kinematic differences support helical jet models.

Abstract

A new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry. In this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant non-radial motions. This paper presents results from our kinematic investigation of the jets of a statistically complete sample of radio-loud flat-spectrum active galaxies, focusing on the comparison between the jet kinematic properties of BL Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis, compared to flat-spectrum radio-quasars. This is interpreted as evidence for helically structured jets.