Daily Image

Click here or on the picture for a full size image.

Today's Colloquium: Radioastrometry in post-Gaia epoch

Submitter: Leonid Petrov
Description: It is not an exaggeration to say that the date September 15, 2016 split astrometry into two epochs: before and after Gaia.

I will provide the overview of VLBI absolute astrometry programs in the last 3 years and describe the main result: the Radio Fundamental Catalogue (RFC) of 14,768 sources. Comparison of the RFC against Gaia DR1 showed a striking peculiarity: the directions of offsets of Gaia and VLBI positions of matching active galactic nuclei shows a strong anisotropy with a concentration along parsec-scale radio jet directions.

I argue that the most probable explanation of such an anisotropy is the presence of optical structure at scales 1-200 mas, i.e. below the Gaia resolution.

This discovery has a number of interesting observational consequences and has a profound impact on future VLBI astrometry programs. In some cases we will be able to reveal milliarcsecond-scale optical structure that cannot be studied directly with optical telescopes. We will be in a position to pinpoint in which area the optical flares occur: in the accretion disk, at the jet base (core) or at the hot spot on the extended jet.
Future observational programs will be outlined.
Copyright: Leonid Petrov
  Follow us on Twitter
Please feel free to submit an image using the Submit page.