Landing page for project ES116

The 8% difference between the value of H0 measured from local and early Universe probes has become known in the last years has the "Hubble tension". This discrepancy can be attributed either to unknown systematics or to new physics. Therefore, independent methods are crucial today to confirm (rule out) the tension. Using time-varying AGN strongly lensed by galaxy clusters represents a novel and complementary technique that remains largely unexploited. We propose to observe the cluster-scale lensed AGN SDSSJ1029+2623 with the EVN+e-MERLIN at L- and C- bands. This is a unique object, with clear predictions for time delays and a rich multi-wavelength dataset. These will be the first VLBI observations of this system and the final piece of a broadband characterization of this source. In particular these observations will i) test possible systematics from optical observations; ii) reveal the milliarcsecond structure of the AGN multiple images, giving extra-precise constraints to the lens mass model; iii) determine the presence of variability at 5 GHz. These observations will set the requirements for future dedicated VLBI monitoring to precisely measure for the first time radio time delays, providing a new independent method to test the Hubble tension.

This data is part of the archive of VLBI data maintained by JIVE on behalf of the EVN, a network of radio telescopes located primarily in Europe and Asia, with additional antennas in South Africa. The EVN archive itself has the DOI https://doi.org/10.17616/R3Z197