Galactic dynamo action in presence of stochastic alpha and shear

TL;DR

This study investigates how stochastic alpha effects combined with shear can drive galactic dynamos, potentially overcoming quenching issues and amplifying magnetic fields in galaxy centers.

Contribution

It introduces a one-dimensional stochastic alpha-omega dynamo model for galaxies, highlighting how randomness in alpha can aid magnetic field growth and reduce quenching.

Findings

Stochastic alpha can help sustain dynamo action.

Final magnetic fields can reach about 1% of equipartition strength.

Field amplification depends on dynamo number and alpha fluctuations.

Abstract

Using a one-dimensional $\alpha\omega$-dynamo model appropriate to galaxies, we study the possibility of dynamo action driven by a stochastic alpha effect and shear. To determine the field evolution, one needs to examine a large number of different realizations of the stochastic component of $\alpha$. The net growth or decay of the field depends not only on the dynamo parameters but also on the particular realization, the correlation time of the stochastic $\alpha$ compared to turbulent diffusion timescale and the time over which the system is evolved. For dynamos where both a coherent and fluctuating $\alpha$ are present, the stochasticity of $\alpha$ can help alleviate catastrophic dynamo quenching, even in the absence of helicity fluxes. One can obtain final field strengths up to a fraction $\sim 0.01$ of the equipartition field $ B_{eq}$ for dynamo numbers $| D| \sim 40$, while fields comparable to $ B_{eq}$ require much larger degree of $\alpha$ fluctuations or shear. This type of dynamo may be particularly useful for amplifying fields in the central regions of disk galaxies.