Using rotation measure grids to detect cosmological magnetic fields: A Bayesian approach

¹ INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
² Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
³ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto ON, M5S 3H8, Canada
⁴ Ludwig-Maximilians – Universität München, Geschwister-Scholl-Platz 1, 80539 München, Germany
⁵ CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France
⁶ Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
⁷ IBM Deutschland Research and Development GmbH Schönaicher Straße 220, 71032 Böblingen, Germany
⁸ Argelander-Institut für Astronomie, Auf dem Hügel 71, 52121 Bonn, Germany
⁹ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁰ INAF–Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
¹¹ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
¹² National Radio Astronomy Observatory, PO Box 0, Socorro, NM 87801, USA
¹³ Jansky Fellow of the National Radio Astronomy Observatory  
¹⁴ Department of Earth and Space Sciences, Chalmers University of Technology, OSO, 439 92 Onsala, Sweden
¹⁵ Department of Physics, UNIST, 689-798 Ulsan, Korea
¹⁶ School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, 6014 Wellington, New Zealand
¹⁷ ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
¹⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁹ Kumamoto University, 2-39-1, Kurokami, 860-8555 Kumamoto, Japan

Received: 1 September 2015
Accepted: 25 March 2016

Abstract

Determining magnetic field properties in different environments of the cosmic large-scale structure as well as their evolution over redshift is a fundamental step toward uncovering the origin of cosmic magnetic fields. Radio observations permit the study of extragalactic magnetic fields via measurements of the Faraday depth of extragalactic radio sources. Our aim is to investigate how much different extragalactic environments contribute to the Faraday depth variance of these sources. We develop a Bayesian algorithm to distinguish statistically Faraday depth variance contributions intrinsic to the source from those due to the medium between the source and the observer. In our algorithm the Galactic foreground and measurement noise are taken into account as the uncertainty correlations of the Galactic model. Additionally, our algorithm allows for the investigation of possible redshift evolution of the extragalactic contribution. This work presents the derivation of the algorithm and tests performed on mock observations. Because cosmic magnetism is one of the key science projects of the new generation of radio interferometers, we have predicted the performance of our algorithm on mock data collected with these instruments. According to our tests, high-quality catalogs of a few thousands of sources should already enable us to investigate magnetic fields in the cosmic structure.