Polarization of active galactic nuclei with significant VLBI-Gaia displacements

TL;DR

This study confirms that active galactic nuclei with VLBI-Gaia displacements aligned with their jets exhibit higher optical polarization, supporting the idea that jet components dominate optical emission and cause positional shifts.

Contribution

It provides new observational evidence linking VLBI-Gaia displacements with optical polarization, supporting the disc-jet dichotomy in AGN and using a larger dataset with multi-band polarization data.

Findings

AGN with downstream VGD have higher optical polarization

Optical polarization distributions are consistent across wavelengths

Results support jet emission dominance in optical polarization

Abstract

Numerous studies have reported significant displacements in the coordinates of active galactic nuclei between measurements using radio interferometry techniques and those obtained by the Gaia space observatory. There is a consensus that these discrepancies do indeed manifest astrometrically resolved sub-components of AGN rather than random measurement noise. Among other evidence, it has been reported that AGN with VLBI-to-Gaia displacements (VGD) pointing downstream their parsec-scale radio jets exhibit higher optical polarization compared to sources with the opposite VGD orientation. We aim to verify this previously reported connection between optical polarization and VGD-jet angle using a larger dataset of polarimetric measurements and updated Gaia DR3 positions. We also seek additional evidence supporting the disc-jet dichotomy as an explanation of such a connection by using mm-wave polarization and multi-band optical polarization measurements. We performed optical polarimetric observations of 152 AGN using three telescopes. We cross-match public astrometric data from VLBI and Gaia experiments, obtain corresponding positional displacements, and join this catalog with the polarimetric and jet directions data. AGN with downstream VGD are confirmed to have significantly higher optical fractional polarization than the upstream sample. At the same time, the mm-wavelength polarization of the two samples demonstrates very similar distributions. Our results support the hypothesis that the VLBI-to-Gaia displacements pointing down the radio jet are likely caused by a component in the jet emitting highly polarized synchrotron radiation and dominating in the overall optical emission. The upstream-oriented VGD are likely to be produced by the low-polarized emission of the central engine sub-components dominating in the optical.