Hgh-precision core-shift measurements for a large sample of ICRF3 sources and systematics of multi-waveband reference frames

The celestial reference frame is a cornerstone of fundamental astronomy, extensively used in astronomy, geodesy, and deep-space navigation. Constructing a fully consistent multi-wavelength celestial reference frame is a primary task in astrometry, while deeply investigating subtle positional differences of ICRF reference sources across various electromagnetic wavebands is crucial to achieving this goal.

Previous studies based on low-frequency VLBI observations of ICRF3 sources have shown a systematic linear alignment of optical and radio positions of ICRF sources along jet directions at sub-milliarcsecond accuracy, with the core-shift effect being one of the primary models explaining this phenomenon. However, a systematic large-sample, high-frequency core-shift study specifically targeting ICRF sources is still lacking. To bridge this gap, this project aims to utilize quasi-simultaneous VLBI observational data at 8 GHz, 24 GHz, and 43 GHz and employ the most advanced high-fidelity and high-resolution imaging algorithms developed by the Event Horizon Telescope (EHT). We propose to obtain high-resolution images of over 400 sources in the third generation of ICRF (ICRF3) and measure their core-shift effects. We expect to achieve the most precise core-shift measurements to date for the largest sample of ICRF3 sources, potentially reaching an accuracy of 0.01 milliarcseconds (mas). Based on the core-shift relationships, we will establish a quantitative link between the optical (Gaia) and radio (VLBI) positions of ICRF3 sources. Furthermore, we propose a novel method for a precise alignment of optical and radio reference frames, grounded in clear astrophysical principles. This interdisciplinary research, bridging astrometry and astrophysics, will provide unprecedented theoretical insights and practical guidance for the construction of the next-generation multi-waveband celestial reference frame.