Exploring the intergalactic magnetic field by means of Faraday tomography

Abstract

Unveiling the intergalactic magnetic field (IGMF) in filaments of galaxies is a very important and challenging subject in modern astronomy. In order to probe the IGMF from rotation measures (RMs) of extragalactic radio sources, we need to separate RMs due to other origins such as the source, intervening galaxies, and our Galaxy. In this paper, we discuss observational strategies for the separation by means of Faraday tomography (Faraday RM synthesis). We consider an observation of a single radio source such as a radio galaxy or a quasar viewed through the Galaxy and the cosmic web. We then compare the observation with another observation of a neighboring source with a small angular separation. Our simulations with simple models of the sources suggest that it would be not easy to detect the RM due to an IGMF of order ∼ 1 rad m-2, an expected value for the IGMF through a single filament. Contrary to this, we find that an RM of at least ∼ 10 rad m-2 could be detected with the Square Kilometre Array or its pathfinders/precursors, if we achieve selection of ideal sources. These results would be improved if we incorporated decomposition techniques such as RMCLEAN and QU-fitting. We discuss the feasibility of the strategies for cases with complex Galactic emissions as well as with effects of observational noise and radio frequency interferences.