VLBI-Gaia offsets favor parsec-scale jet direction in active galactic nuclei
Petrov, L.; Kovalev, Y. Y.; Plavin, A. V.
Germany, Russia, United States
Abstract
Context. The data release 1 (DR1) of milliarcsecond-scale accurate optical positions of stars and galaxies was recently published by the space mission Gaia.
Aims: We study the offsets of highly accurate absolute radio (very long baseline interferometry, VLBI) and optical positions of active galactic nuclei (AGN) to see whether or not a signature of wavelength-dependent parsec-scale structure can be seen.
Methods: We analyzed VLBI and Gaia positions and determined the direction of jets in 2957 AGNs from their VLBI images.
Results: We find that there is a statistically significant excess of sources with VLBI-to-Gaia position offset in directions along and opposite to the jet. Offsets along the jet vary from 0 to tens of mas. Offsets in the opposite direction do not exceed 3 mas.
Conclusions: The presense of strong, extended parsec-scale optical jet structures in many AGNs is required to explain all observed VLBI-Gaia offsets along the jet direction. The offsets in the opposite direction shorter than 1 mas can be explained either by a non-point-like VLBI jet structure or a "core-shift" effect due to synchrotron opacity.