An improved map of the Galactic Faraday sky

¹ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
e-mail: niels@mpa-garching.mpg.de
² Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
³ Australia Telescope National Facility, CSIRO Astronomy & Space Science, PO Box 76, Epping, NSW 1710, Australia
⁴ Department of Physics & Astronomy, University of Calgary, AB T2N 1N4, Canada
⁵ Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, USA
⁶ Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia
⁷ ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁸ School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
⁹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Department of Physics, University of Toronto, 60 St. George Street, Toronto ON M5S 1A7, Canada
¹¹ Los Alamos National Laboratory, M.S. B283, Los Alamos, NM 87545, USA
¹² Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
¹³ Dominion Radio Astrophysical Observatory, HIA-NRC, 717 White Lake Road, PO Box 248, Penticton, BC, V2A 6J9, Canada
¹⁴ National Centre for Radio Astrophysics, TIFR, Pune University Campus, Post Bag 3, Ganeshkhind, Pune 411007, India
¹⁵ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁶ Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
¹⁷ School of Physics, University of New South Wales, Sydney NSW 2052, Australia

Received: 26 November 2011
Accepted: 23 March 2012

Abstract

We aim to summarize the current state of knowledge regarding Galactic Faraday rotation in an all-sky map of the Galactic Faraday depth. For this we have assembled the most extensive catalog of Faraday rotation data of compact extragalactic polarized radio sources to date. In the map-making procedure we used a recently developed algorithm that reconstructs the map and the power spectrum of a statistically isotropic and homogeneous field while taking into account uncertainties in the noise statistics. This procedure is able to identify some rotation angles that are offset by an integer multiple of π. The resulting map can be seen as an improved version of earlier such maps and is made publicly available, along with a map of its uncertainty. For the angular power spectrum we find a power law behavior C_ℓ ∝ ℓ^-2.17 for a Faraday sky where an overall variance profile as a function of Galactic latitude has been removed, in agreement with earlier work. We show that this is in accordance with a 3D Fourier power spectrum P(k) ∝ k^-2.17 of the underlying field n_eB_r under simplifying geometrical and statistical assumptions.