Dissecting the AGN disk-jet system with joint VLBI-Gaia analysis

TL;DR

This study compares Gaia and VLBI positions of over 1000 AGNs, revealing that significant positional offsets are linked to jet and disk emissions, supporting the unified AGN model.

Contribution

It provides a detailed analysis of positional offsets in AGNs, linking them to jet and disk emissions, and introduces methods to distinguish their contributions using redshift and Gaia color.

Findings

Most significant offsets occur along jet directions, confirming astrophysical origins.

Optical jet emission of 20-50pc explains downstream Gaia position offsets.

Upstream offsets are partly due to accretion disk and parsec-scale jet effects.

Abstract

We analyze differences in positions of active galactic nuclei between Gaia data release 2 and VLBI and compare the significant VLBI-to-Gaia offsets in more than 1000 objects with their jet directions. Remarkably at least 3/4 of the significant offsets are confirmed to occur downstream or upstream the jet representing a genuine astrophysical effect. Introducing redshift and Gaia color into analysis can help distinguish between the contribution of the host galaxy, jet, and accretion disk emission. We find that strong optical jet emission at least 20-50pc long is required to explain the Gaia positions located downstream from VLBI ones. Offsets in the upstream direction of up to 2 mas are at least partly due to the dominant impact of the accretion disk on the Gaia coordinates and by the effects of parsec-scale radio jet. The host galaxy was found not to play an important role in the detected offsets. BL Lacertae object and Seyfert 2 galaxies are observationally confirmed to have a relatively weak disk and consequently downstream offsets. The disk emission drives upstream offsets in a significant fraction of quasars and Seyfert 1 galaxies when it dominates over the jet in the optical band. The observed behaviour of the different AGN classes is consistent with the unified scheme assuming varying contribution of the obscuring dusty torus and jet beaming.