Galactic dynamo action in presence of stochastic α and shear

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 time-scale 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 similar to 0.01 of the equipartition field B-eq for dynamo numbers vertical bar D vertical bar similar to 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 disc galaxies.