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A Millimeter Wave Galactic Plane Survey with the BICEP PolarimeterEvan Bierman (U.C. San Diego) and C. Darren Dowell (JPL, Caltech)

Faculty Advisor: Brian Keating (U.C. San Diego) and NASA Advisor: Ed Wollack (GSFS)BICEP collaboration (Caltech, JPL, UCSD, U.C. Berkeley, U. Wales Cardiff, CEA, IAS)

Abstract: BICEP (the John Robinson Telescope at the South Pole) is a 49-pixel microwave polarimeter that has been observing for 2.5 years in the atmospheric band windows at 100/150/220GHz and beam FWHM's of 0.93/0.63/0.42 degrees respectively. Most observations are of the 2% of the sky with the lowest expected astronomical foreground contamination; however, a fraction are of the galactic plane from l = 265 to 340 degrees. From these observations, high signal to noise maps have been produced within several degrees of the galactic plane, both in temperature and polarization. Our present analysis focuses on the trend of decreasing polarization fraction for objects that have brighter unpolarized intensities, the polarized and unpolarized spectrum of the objects in the galaxy between our bands, and the magnetic field structure of the galaxy on large scales.

CMB Foregrounds, Pasadena CA, July 2008

Observing Strategy from South Pole

A view of the 250mK feedhorn section of the BICEP focal plane looking up to

the 4K section and the sky

220GHz Imaging and Polarimetry

BICEP 100GHz and 150GHz Galactic Plane Maps

Prior to the second year of observation, the focal plane was equipped with two 220GHz feeds to extend the spectral coverage. This greatly enhances BICEP's ability to study polarized dust emission. Contact/

ReferencesContact the authors at: ebierman@ucsd.edu cdd@submm.caltech.edu

[1] K. W. Yoon, et al. 2006, SPIE, 6275, 62751K[2] Planck reference sky model, v1.1, Members of Working Group 2 and available at www.planck.fr/heading79.html [3] R. H. Hildebrand, et al.  1999, ApJ, 516, 834 [4] M.-A. Miville-Deschenes, et al.  2008, arXiv 0802.3345 [5] Finkbeiner, D. P., Davis, M., & Schlegel, D. J. 1999, ApJ, 524, 867[6] NASA/WMAP Science Team http://lambda.gsfc.nasa.gov/product/map

150GHz U Polarization Map

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150GHz Q Polarization MapG

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FDS5/WMAP6 are smoothed and filtered with BICEP beams and observing strategy. WMAP agrees in T for both PSI and NSI objects. WMAP Q maps show less polarization for NSI objects than PSI objects as well, although map noise is currently dominating the direct comparison. FDS has a reasonable PSI pixel prediction at 100 GHz but over-predicts emission at 150 GHz.

Comparison with WMAP W Band and FDS Model 8

The emission from galactic dust grains rises with increasing frequency. Synchrotron and free-free emission decreases with rising frequency. By directly differencing the 100 GHz and 150 GHz maps (smoothed to the same beam resolution), the pixels with strongly increasing or decreasing spectra stand out. The dotted outline on the map to the right indicates the region from which the points on the scatter plots are drawn. Due to current naïve filtering, 1/f atmospheric noise contaminates the maps between 290 to 315 degrees galactic longitude and is excluded in the current analysis.

Microwave Spectrum and Polarization of the Galactic Plane

Blue points are from pixels with a large positive spectral index (PSI): increasing intensity with increasing frequency. Red points have a large negative spectral index (NSI): decreasing intensity with increasing frequency.

Plots of polarization fraction perpendicular (positive Q) or parallel (negative Q) to the galaxy. There is a slight decrease of polarization fraction with increasing intensity, a trend which has been noted and modeled elsewhere3,4. NSI emission is less polarized on average than PSI emission.

(100GHz – 150GHz) Temperature Map (mK)

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150GHz Unpolarized Temperature Map

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100GHz Unpolarized Temperature Map

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100GHz Q Polarization Map

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100GHz U Polarization Map

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220GHz Unpolarized Temperature Map

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BICEP observes at a fixed elevation, scanning in azimuth at 2.8 deg/s. Every hour, the telescope is stepped 0.25 deg, bookended by small scans in elevation to calibrate off the atmosphere. In galactic coordinates, this causes the integration pattern shown on the right.

The BICEP temperature and polarization maps are presented in galactic coordinates and CMB temperature units. Polarization is presented as Stokes parameters: Q = P Cos[2 Ψ] and U = P Sin[2 Ψ], where Ψ is the angle measured counterclockwise from the north galactic pole and P is the total polarized intensity. Processing of the time streams to final maps includes bolometer and filter transfer function deconvolution, bad weather and glitch removal, relative calibration off the atmosphere, 15th order polynomial subtraction with the galaxy masked, variance weighting mapping of T/Q/U, and absolute calibration from WMAP temperature anisotropies and/or a partially polarized rotating dielectric sheet.1

The Planck consortium has begun using these maps, in preliminary form, to compare to the detailed foreground predictions of the Planck Sky Model. Comparisons between maps (with improved analysis) and eventual Planck data in all three of the main HFI science bands should allow powerful cross-checks of the calibrations and methodology of each experiment.2