Stacking for Cosmic Magnetism with SKA Surveys

Stacking polarized radio emission in SKA surveys provides statistical information on large samples that is not accessible otherwise due to limitations in sensitivity, source statistics in small fields, and averaging over frequency (including Faraday synthesis). Polarization is a special case because one obvious source of stacking targets is the Stokes I source catalog, possibly in combination with external catalogs, for example an SKA HI survey or a non-radio survey. We point out the significance of stacking sub-samples selected by additional observable parameters to investigate relations that reveal more about the physics of the source. Applications of stacking polarization include, but are not limited to, obtaining in a statistical sense polarization information to the detection limit in total intensity, depolarization as a function of cosmic time at consistent source-frame wavelengths, magnetic field properties in objects with a low radio luminosity such as dwarf and low-surface-brightness galaxies, and investigating potential correlations of observable parameters with the average magnetic field direction in a sample. We also point out the potential use of stacking in validating the polarization calibration of a survey. While stacking is flexible in terms of survey definition, we discuss optimal survey parameters for the science experiments presented, as well as computing and archiving requirements.