Systematic effects in the radio source proper motion

O. Titov1

1Geoscience Australia, Australia

Oral presentation  

Some models of the expanded Universe predict that the astrometric proper motion of distant radio sources do not vanish as radial distance from observer to the source grows. Systematic effects due to the proper motion can even increase with the distance making possible to measure them with high-precision astrometric techniques like VLBI. We analyzed a large set of geodetic VLBI data spanning from 1979 till 2008 to estimate the dipole and the quadruple harmonics in the expansion of the vector field of the proper motions of quasars in the sky. We estimated the vector spherical harmonics (three - for the dipole and ten - for the quadruple systematic) directly from the VLBI group delays without intermediate calculation of the individual proper motion. The estimates have been obtained separately for different red shift zones to mitigate the effect of intrinsic structure variations of the active galactic nuclei (AGN). It was shown that the dipole harmonic does not vary significantly, whereas the amplitude of the quadruple gradually increases with the red shift. This quadruple pattern can be interpreted either as an anisotropic Hubble expansion, or as an indication of the primordial gravitational waves in the early Universe. However, more prosaic explanation can be also given.