An analytical dynamo solution for large-scale magnetic fields of galaxies

TL;DR

This paper develops an analytical asymptotic solution for the large-scale magnetic fields in galaxies, combining local dynamo solutions to predict observable magnetic signatures in a computationally efficient way.

Contribution

It introduces a global analytical galactic dynamo solution that integrates local solutions with non-linear effects, providing a new tool for modeling galactic magnetic fields.

Findings

The analytical solution agrees reasonably with numerical models.

It can be used to generate synthetic observational data.

The solution's dependence on parameters is systematically analyzed.

Abstract

We present an effectively global analytical asymptotic galactic dynamo solution for the regular magnetic field of an axisymmetric thin disc in the saturated state. This solution is constructed by combining two well-known types of local galactic dynamo solution, parameterized by the disc radius. Namely, the critical (zero growth) solution obtained by treating the dynamo equation as a perturbed diffusion equation is normalized using a non-linear solution that makes use of the `no-$z$' approximation and the dynamical $\alpha$-quenching non-linearity. This overall solution is found to be reasonably accurate when compared with detailed numerical solutions. It is thus potentially useful as a tool for predicting observational signatures of magnetic fields of galaxies. In particular, such solutions could be painted onto galaxies in cosmological simulations to enable the construction of synthetic polarized synchrotron and Faraday rotation measure (RM) datasets. Further, we explore the properties of our numerical solutions, and their dependence on certain parameter values. We illustrate and assess the degree to which numerical solutions based on various levels of approximation, common in the dynamo literature, agree with one another.