Astrometric evidence for a population of dislodged AGN

TL;DR

This study identifies a subset of AGN that are physically displaced from their host galaxy centers, suggesting a population of dislodged active galactic nuclei based on astrometric data from VLBI and Gaia.

Contribution

It provides the first evidence of a significant population of dislodged AGN using combined radio and optical astrometry, revealing new insights into galaxy and black hole dynamics.

Findings

Over 4% of luminous AGN are displaced from galaxy centers.

Identified 188 high-confidence offset sources with significant positional differences.

Some sources show extended or double structures indicating complex morphology.

Abstract

We investigate a sample of 2293 ICRF2 extragalactic radio-loud sources with accurate positions determined by VLBI, mostly active galactic nuclei (AGN) and quasars, which are cross-matched with optical sources in the first Gaia release (Gaia DR1). The distribution of offsets between the VLBI sources and their optical counterparts is strongly non-Gaussian, with powerful wings extending beyond 1 arcsecond. Limiting our analysis to only high-confidence difference detections, we find (and publish) a list of 188 objects with normalized variances above 12 and offsets below 1 arcsecond. Pan-STARRS stacked and monochromatic images resolve some of these sources indicating the presence of double sources, confusion sources, or pronounced extended structures. Some 89 high-quality objects, however, do not show any perturbations and appear to be star-like single sources, yet displaced by multiples of the expected error from the radio-loud AGN. We conclude that a fraction of luminous AGN (more than 4%) can be physically dislodged from the optical centers of their parent galaxies.