On Densification of the ICRF Catalog and the Reliability of Its Link to the Gaia Catalog

Two possible sources of random and systematic errors of a new method for determining the parameters of the relative orientation of the catalogs of positions of extragalactic sources implementing the International Celestial Reference System (ICRS) are investigated. This method is based on the median filtering of the differences in the coordinates of common objects in the compared catalogs, distributed over equal cells on the celestial sphere, forming a pixelation grid. The study was based on a comparison of the latest versions of the ICRS implementation in the radio (International Celestial Reference Frame, ICRF) and optical (Gaia-CRF) bands. Based on several computational tests, the dependence of the results of determining the orientation parameters between the ICRF and Gaia-CRF catalogs on the number of cells and on the displacement of the pixelization grid relative to the origin in right ascension was verified. It turned out that the results of calculations obtained in different test cases differ noticeably, but these differences are within the limits of formal errors in determining the orientation parameters. Additional test calculations showed that the main source of these differences is the uneven distribution of the common sources of the compared catalogs over the celestial sphere.