A Millimeter-wave Galactic Plane Survey with the BICEP Polarimeter

Creators: Bierman, E. M.; Matsumura, T.; Dowell, C. D.; Bock, J. J.; Chiang, H. C.; Culverhouse, T. L.; Hristov, V. V.; Kovac, J. M.; Lange, A. E.; Mason, P. V.; Richter, S.; Rocha, G. M.

Abstract

In order to study inflationary cosmology and the Milky Way Galaxy's composition and magnetic field structure, Stokes I, Q, and U maps of the Galactic plane covering the Galactic longitude range 260° < ℓ < 340° in three atmospheric transmission windows centered on 100, 150, and 220 GHz are presented. The maps sample an optical depth 1 ≾ AV ≾ 30, and are consistent with previous characterizations of the Galactic millimeter-wave frequency spectrum and the large-scale magnetic field structure permeating the interstellar medium. The polarization angles in all three bands are generally perpendicular to those measured by starlight polarimetry as expected and show changes in the structure of the Galactic magnetic field on the scale of 60°. The frequency spectrum of degree-scale Galactic emission is plotted between 23 and 220 GHz (including WMAP data) and is fit to a two-component (synchrotron and dust) model showing that the higher frequency BICEP data are necessary to tightly constrain the amplitude and spectral index of Galactic dust. Polarized emission is detected over the entire region within two degrees of the Galactic plane, indicating the large-scale magnetic field is oriented parallel to the plane of the Galaxy. A trend of decreasing polarization fraction with increasing total intensity is observed, ruling out the simplest model of a constant Galactic magnetic field orientation along the line of sight in the Galactic plane. A generally increasing trend of polarization fraction with electromagnetic frequency is found, varying from 0.5%-1.5% at frequencies below 50 GHz to 2.5%-3.5% above 90 GHz. The effort to extend the capabilities of BICEP by installing 220 GHz band hardware is described along with analysis of the new band.

Additional Information

© 2011 The American Astronomical Society. Received 2011 February 23; accepted 2011 August 3; published 2011 October 20. We especially recognize Andrew Lange whose passing has deeply affected everyone on the team and who never saw the culmination of this project. Without his guidance and friendship this paper would not have been possible. BICEP is supported by NSF Grant OPP-0230438, Caltech Discovery Fund, Caltech President's Fund PF-471, JPL Research and Technology Fund, and the late J. Robinson. We thank our colleagues in the ACBAR, Boomerang, QUaD, Bolocam, POLARBEAR, and SPT collaborations for advice and helpful discussions, Kathy Deniston for logistical and administrative support, and the South Pole Station staff for their support. We gratefully acknowledge support by the NASA Graduate Fellowship program (E.M.B. and H.C.C.), the John B. and Nelly Kilroy Foundation (J.M.K.), the NSF PECASE Award AST-0548262 (B.G.K.), the US DOE contract to SLAC No. DEAC02-76SF00515 (C.L.K. and J.E.T.), KICP (C.P. and C.S.), and the NASA Science Mission Directorate via the US Planck Project (G.R.). We also thank the thorough and comprehensive work of the referee that has tremendously improved the quality of the final version of this paper.

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