Alice Pasetto, IRyA
Host: The magnetic field configuration of AGN jets, how far from the central engine it maintains its configuration and how it evolves during its journey along the jet, are still a matters of debate. In the talk I will present unprecedented high fidelity radio images of the M87 jet. Jansky Very Large Array (VLA) broadband, full polarization, radio data from 4 to 18 GHz, taken at A configuration, allow the study of the emission of the jet up to kpc scales. The high sensitivity and resolution of our data allow to resolve the jet width. The double-helix morphology of the jet material between $\sim$300 pc and $\sim$1 kpc has been confirmed. A gradient of the polarization degree with a minimum at the projected axis and maxima at the jet edges, and a gradient in the Faraday depth with opposite signs at the jet edges have been detected. The 3D configuration of the magnetic field of the jet M87 is finally mapped. The behavior of the polarization properties along the wide range of frequencies is consistent with internal Faraday depolarization. All these characteristics strongly support the presence of a helical magnetic field in the M87 jet up to 1 kpc from the central black hole although the jet is most likely particle dominated at these large scales. A plausible scenario I will show is that the helical configuration of the magnetic field is maintained to large scales thanks to the presence of Kelvin-Helmholtz instabilities. This work is paving the way for future investigations on this matter which will be easily addressed with the upcoming ngVLA.