The origin of magnetic fields in galaxies: observational tests with the Square Kilometre Array

The all-sky survey of Faraday rotation, a Key Science Project of the planned Square Kilometre Array, will accumulate tens of millions of rotation measure measurements toward background radio sources and will provide a unique database for characterizing the overall magnetic geometry of magnetic fields in galaxies and in the intergalactic medium. Deep imaging of the polarized synchrotron emission from a large number of nearby galaxies, combined with Faraday rotation data, will allow us to test primordial, gas flow, and dynamo models for field origin and amplification. The SKA will find the first magnetic fields in young galaxies and determine the timescale for building up small-scale turbulent and large-scale coherent fields. The spectrum of dynamo modes, if existing, will be resolved. The present-day coherent field may keep memory of the direction of the seed field which can be used for mapping the structure of the seed field before galaxy formation.