Next generation celestial reference frames from photometry and absolute astrometry of blazars – NGCP2A

The international celestial reference frame (ICRF) is fundamental for both astronomy and geosciences, for both scientific and civilian applications. Nowadays, it is realized with an accuracy of few tenth of milliarcseconds through the positions of thousands to millions of compact extragalactic sources (mainly blazars) observed by very long baseline interferometry (VLBI) at radio wavelengths and by the European satellite Gaia at optical wavelengths. ICRF positions appear to exhibit instabilities and significant optical-radio offsets raising challenging questions about the intrinsic underlying mechanisms and how to get consistent, accurate, and stable multiwaveband ICRF for the need of astronomy and geodesy. The large amount of multiwavelength astrometry and photometry data recently provided by Gaia and VLBI is still expecting to be exploited. The objectives of this project are as follows. First, we propose to investigate in depth the VLBI analysis configurations to minimize the various systematic errors including those arising from the reference frame instability. Second, we propose to unveil the links between absolute astrometric signatures, photometric variability, and other characteristics available in numerous databases, including parsec-scale source structure imaging by using innovative techniques of multivariate analysis and artificial intelligence. We expect to predict subsets/subpopulations of AGN susceptible to better carry a stable and accurate multiwaveband ICRF adapted to current expectations and applications in astronomy and geodesy with and improvement of the alignment and stability by a factor of 2 to 10 following preliminary studies.