Modelling and simulation of large-scale polarized dust emission over the southern Galactic cap using the GASS Hi data

¹ California Institute of Technology, Pasadena, California, USA
e-mail: tghosh@caltech.edu
² Institut d’Astrophysique Spatiale, CNRS (UMR 8617) Université Paris-Sud 11, Bâtiment 121, Orsay, France
³ CITA, University of Toronto, 60 St. George St., Toronto, ON M5S 3H8, Canada
⁴ Laboratoire AIM, IRFU/Service d’Astrophysique – CEA/DSM – CNRS – Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA
⁶ Tartu Observatory, 61602 Tõravere, Tartumaa, Estonia
⁷ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 2 October 2016
Accepted: 24 January 2017

Abstract

The Planck survey has quantified polarized Galactic foregrounds and established that they are a main limiting factor in the quest for the cosmic microwave background B-mode signal induced by primordial gravitational waves during cosmic inflation. Accurate separation of the Galactic foregrounds therefore binds this quest to our understanding of the magnetized interstellar medium. The two most relevant empirical results from analysis of Planck data are line of sight depolarization arising from fluctuations of the Galactic magnetic field orientation and alignment of filamentary dust structures with the magnetic field at high Galactic latitude. Furthermore, Planck and H I emission data in combination indicate that most of the filamentary dust structures are in the cold neutral medium. The goal of this paper is to test whether these salient observational results, taken together, can account fully for the statistical properties of the dust polarization over a selected low column density region comprising 34% of the southern Galactic cap (b ≤ −30°). To do this, we construct a dust model that incorporates H I column density maps as tracers of the dust intensity structures and a phenomenological description of the Galactic magnetic field. By adjusting the parameters of the dust model, we were able to reproduce the Planck dust observations at 353GHz in the selected region. Realistic simulations of the polarized dust emission enabled by such a dust model are useful for testing the accuracy of component separation methods, studying non-Gaussianity, and constraining the amount of decorrelation with frequency.