The accretion flow and jet of M87: broadband modelling across spatial scales

Abstract: The nearby radio galaxy M87 is an ideal laboratory for studying accretion flows and relativistic jet emission. The EHT collaboration conducted the most comprehensive multi-wavelength observational campaign of M87, in which radio instruments with resolutions ranging from tens of microarcseconds to about an arcsecond sampled different portions of the outflow. We model these data using a radiatively inefficient accretion flow (RIAF) with winds and a new multi-zone jet model, initially magnetically dominated, in which we solve the transport equation for the non-thermal electrons as they are injected, advected, and cooled along the jet. We then compare each radio flux with the jet emission within an effective aperture set by the angular scale of the corresponding observation. The comparison across spatial scales favours a scenario in which the RIAF, rather than the jet, produces the compact $230~{\rm GHz}$ emission, while the jet dominates the lower-frequency radio, optical/UV and X-ray emission, but cannot produce the observed $γ$-rays. The RIAF connects the Bondi-scale gas supply to an accretion rate at the horizon of $1.1\times 10<sup>{-5}$ of the Eddington rate, consistent with EHT polarimetry, and the two jets carry about a quarter of the accretion power, $1.2\times10^{43}~{\rm erg~s}<sup>{-1}$ each. The framework presented in this work provides a simple way to disentangle the accretion-flow and jet contributions to the emission from nearby radio galaxies.