MHD accretion-ejection: jets launched by a non-isotropic accretion disk dynamo. I. Validation and application of selected dynamo tensorial components

Abstract

Astrophysical jets are launched from strongly magnetized systems that host an accretion disk surrounding a central object. The origin of the jet launching magnetic field is one of the open questions for modeling the accretion-ejection process. Here we address the question how to generate the accretion disk magnetization and field structure required for jet launching. Applying the PLUTO code, we present the first resistive MHD simulations of jet launching including a non-scalar accretion disk mean-field ${\alpha }^2\Omega$-dynamo in the context of large scale disk-jet simulations. Essentially, we find the ${\alpha }_{\varphi }$-dynamo component determining the amplification of the poloidal magnetic field, which is strictly related to the disk magnetization (and, as a consequence, to the jet speed, mass and collimation), while the ${\alpha }_R$ and ${\alpha }_{\theta }$-dynamo components trigger the formation of multiple, anti-aligned magnetic loops in the disk, with strong consequences on the stability and dynamics of the disk-jet system. In particular, such loops trigger the formation of dynamo inefficient zones, which are characterized by a weak magnetic field, and therefore a lower value of the magnetic diffusivity. The jet mass, speed and collimation are strongly affected by the formation of the dynamo inefficient zones. Moreover, the $\theta$-component of the $\alpha$-dynamo plays a key role when interacting with a non-radial component of the seed magnetic field. We also present correlations between the strength of the disk toy dynamo coefficients and the dynamical parameters of the jet that is launched.

20 pages, 9 figures, Accepted for publication in ApJ

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