Comparison of VLBI radio source catalogs

Abstract

Aims. I checked the consistency of recent astrometric radio source catalogs obtained by geodetic very long baseline radio interferometry (VLBI) with the second realization of the International Celestial Reference Frame (ICRF2), released in 2009, which is the most accurate astrometric catalog currently available.Methods. The catalogs were compared to the ICRF2 in terms of radio source coordinates, global second-degree deformations, and error distribution.Results. All catalogs were found to be consistent with the ICRF2 within 20 μ as. At high observational rates, the formal error is likely limited to the level of ~10 μ as by correlated-noise errors. The comparison of offsets to ICRF2 against formal errors raised noise floors of the differences between 50 μ as and 100 μ as, and hence no improvement with respect to the ICRF2.Conclusions. The inconsistencies between catalogs result in differences significantly larger than the accuracy expected for the future realizations of the celestial reference frame. These inconsistencies have to be clarified in the near future in view of the next ICRF realization and accurate linking to reference frames at other frequencies.