The magnetic filling in magnetically arrested accretion disk simulations and its impact on the jet in M87

TL;DR

This study investigates how the initial magnetic field extent in MAD simulations influences jet energetics, polarization, and brightness in M87*, providing insights into magnetic flux effects on black hole jets.

Contribution

It introduces the magnetic filling factor as a key parameter in MAD simulations and explores its effects on jet properties and observational signatures in M87*.

Findings

Elevated magnetic filling factors increase electromagnetic energy and angular momentum transport.

High magnetic fillings lead to higher linear polarization fractions, matching observations.

Jets with higher magnetic fillings are brighter downstream and better match observed jet widths.

Abstract

Magnetically arrested accretion disks (MADs) in black hole jet launching simulations are very successful in modelling low-luminosity active galactic nuclei (AGN) like M87*. The Fishbone-Moncrief torus is well established for this purpose in numerical astrophysics. The extent of the magnetic vector potential inside the torus that we coin the filling factor has not been studied before in the case of MAD simulations. We employ five 3D general relativistic magneto-hydrodynamics (GRMHD) simulations initialized with large-scale tori, that are immersed in weak, poloidal magnetic fields. To study the impact of the spatial extent of the initial magnetic field, hence the magnetic energy content in the torus, we scale it with the filling factor w.r.t. the poloidal geometric area of the mass density distribution. A common choice of the filling factor is complimented and investigated in terms of altered energetics and angular momentum transport. Further, we investigate the polarized, radiative imprints of synchrotron emission on M87 at 86 GHz, comparing them with VLBI observations. Our simulations show that elevated filling factors significantly increase the electromagnetic energy contributions and outward angular momentum transport in the jet, due to the initially increased magnetic energy-content in the torus. High magnetic fillings exhibit increased linear polarization fractions, agreeing with the observed 15$\%$ in M87*. We find the jet morphology more prone to disk-vertical flux tubes generated by MAD events. We show, that GRMHD simulations bracket the jet width measurements at the jet base in M87*. Increased magnetic filling of the torus produces jets that are noticeably brighter downstream compared to our reference models, hence, we find high fillings well suited for extended GRMHD jet models of other low-luminosity AGN, as well.