DOI

https://doi.org/10.48717/n085-4g93

Project

ET036

Title

High-Z Astrometry S/X

Abstract

The programme operated by the International VLBI Service (IVS) produces high-accuracy positions of radio sources in a wide range of redshifts, with the high end of redshift distribution exceeding z=3. The estimated source positions are affected by the intrinsic source structures and their proper motion. We investigated the ways of mitigating the source morphology effects on the astrometric accuracy based on the so-called scaling factor. This factor theoretically is equal to unity and free of influence of source morphologies. However, we found that this factor, as a function of a proper motion, demonstrates a subtle dipole effect. Moreover, our preliminary analysis of available IVS data for a dozen of quasars at z>3 hints on a possible deviation of the scaling factor from unity. The available IVS data on these sources are inconclusive due to the sensitivity limitations of the IVS network. With this proposal we aim to investigate the unexpected effect deeper by observing a sample of twenty radio sources at z>3 with a more sensitive EVN array.