First very long baseline interferometry detection of FornaxA

Abstract

Radio galaxies harbouring jetted active galactic nuclei are a frequent target of very-long-baseline interferometry (VLBI) because they play an essential role in exploring how jets form and propagate. Hence, only few have not been detected with VLBI yet; is one of the most famous examples. Here we present the first detection of the compact core region of with VLBI. At 8.4\,GHz the faint core is consistent with an unresolved point source. We constrained its flux density to be $S_0= and its diameter to be $D_0^ min The high values of the measured brightness temperature ($T_ B K $) imply that the observed radiation is of non-thermal origin, likely associated with the synchrotron emission from the active galactic nucleus. We also investigated the possibility of a second radio source being present within the field of view. Adding a second Gaussian component to the geometrical model-fit does not significantly improve the quality of the fit and we, therefore, conclude that our detection corresponds to the compact core of Analysis of the non-trivial closure phases provides evidence for the detection of more extended flux density, on the angular scale of $ Finally, the fractional circular polarisation of the core is consistent with zero, with a conservative upper limit being $m_ circ