Characterization of the Millimeter-wave Polarization of Centaurus a with Quad

Centaurus (Cen) A represents one of the best candidates for an isolated, compact, highly polarized source that is bright at typical cosmic microwave background (CMB) experiment frequencies. We present measurements of the 4× 2 region centered on Cen A with QUaD, a CMB polarimeter whose absolute polarization angle is known to 0.5. Simulations are performed to assess the effect of misestimation of the instrumental parameters on the final measurement, and systematic errors due to the field’s background structure and temporal variability from Cen A’s nuclear region are determined. The total (Q,U) of the inner lobe region is (1.00± 0.07(stat.)± 0.04(sys.),−1.72± 0.06± 0.05)Jy at 100 GHz and (0.80± 0.06± 0.06,−1.40± 0.07± 0.08)Jy at 150 GHz, leading to polarization angles and total errors of −30.0±1.1 and −29.1±1.7. These measurements will allow the use of Cen A as a polarized calibration source for future millimeter experiments. Subject headings: cosmic background radiation – galaxies: individual (Centaurus A) – instrumentation: polarimeters – radio continuum: general