Astrometric evidence for a population of dislodged AGN
  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.
