Simulating polarized Galactic synchrotron emission at all frequencies

The Hammurabi code

¹ Max Planck Institut für Astrophysik (MPA), Karl-Schwarzschildstr. 1, 85741 Garching, Germany e-mail: waelkens@mpa-garching.mpg.de
² Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Oxford Road, Manchester, M13 9PL, UK

Received: 10 July 2008
Accepted: 15 November 2008

Abstract

Context. Galactic synchrotron emission, rotation measure (RM), and the deflection of ultra-high-energy-cosmic-rays (UHECR) permit detailed studies of the Galactic magnetized inter-stellar-medium (ISM). The synchrotron emission has also to be characterized properly to enable its distinction from other astrophysically interesting signals such as the CMB.

Aims. We present a publicly available code called hammurabi for generating mock, polarized observations of Galactic synchrotron emission with telescopes such as LOFAR, SKA, Planck, and WMAP, based on model inputs for the Galactic magnetic field (GMF), the cosmic-ray density distribution, and the thermal electron density. We also present mock UHECR deflection measure (UDM) maps based on model inputs for the GMF. In future, when UHECR sources are identified, this will allow us to use UDM as a probe of GMF in a way similar to how polarized radio sources enable us to define rotation measures.

Methods. To demonstrate the code's abilities, mock observations are compared with real data. This allows us to constrain the input parameters of our simulations with a focus on large-scale magnetic field properties.

Results. Magnetized ISM models in the literature appear to be unable to reproduce any additional observational data not included in their design.

Conclusions. As expected, attempts to model the synchrotron, UHECR-deflection, and RM input parameters indicate that any additional observational data set significantly increases the constraints on the models. The hammurabi code addresses this by allowing one to perform simulations of several different data sets simultaneously, providing a more reliable constraint of the magnetized ISM.