Improving the S/X Celestial Reference Frame in the South: A Status Update

Paper in proceeding, 2021

Catalogues of positions of compact extragalactic radio sources, including the ICRF-3, are generally weaker in the south by factors of 2 or more in both density and precision. In 2018 we started a campaign to improve the S/X celestial reference frame in the south by upgrading existing IVS astrometric observing programmes. Our efforts were mainly focused on the Celestial Reference Frame (CRF) and Celestial Reference Frame Deep South (CRDS) sessions, which are dedicated astrometric observing programmes of sources at mid- and southern declinations. In particular, the data rate of the CRF and CRDS sessions were increased from 256 Mbps to 1 Gbps and the pool of sources were increased by a factor of two. The scheduling was also optimised to allow for simultaneous astrometric and imaging observations, and the CRF network was revised for improved uv-coverage. We provide details of our efforts, to date, to improve both the density and precision of the southern celestial reference frame, as well as our efforts to map and monitor the sources to quantify non-point-like structure and measure jet directions. We also discuss planned changes and upgrades, noting that the Australian 12-m telescopes are transitioning to broadband and may not be available for S/X astrometric observing in future. We also present the ideas and role of the newly-established IVS-CRF committee to improve the celestial reference frame in the south.