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Published June 10, 2015 | Submitted + Published
Journal Article Open

The Q/U Imaging Experiment: Polarization Measurements of Radio Sources at 43 and 95 GHz


We present polarization measurements of extragalactic radio sources observed during the cosmic microwave background polarization survey of the Q/U Imaging Experiment (QUIET), operating at 43 GHz (Q-band) and 95 GHz (W-band). We examine sources selected at 20 GHz from the public, >40 mJy catalog of the Australia Telescope (AT20G) survey. There are ~480 such sources within QUIET's four low-foreground survey patches, including the nearby radio galaxies Centaurus A and Pictor A. The median error on our polarized flux density measurements is 30–40 mJy per Stokes parameter. At signal-to-noise ratio > 3 significance, we detect linear polarization for seven sources in Q-band and six in W-band; only 1.3 ± 1.1 detections per frequency band are expected by chance. For sources without a detection of polarized emission, we find that half of the sources have polarization amplitudes below 90 mJy (Q-band) and 106 mJy (W-band), at 95% confidence. Finally, we compare our polarization measurements to intensity and polarization measurements of the same sources from the literature. For the four sources with WMAP and Planck intensity measurements >1 Jy, the polarization fractions are above 1% in both QUIET bands. At high significance, we compute polarization fractions as much as 10%–20% for some sources, but the effects of source variability may cut that level in half for contemporaneous comparisons. Our results indicate that simple models—ones that scale a fixed polarization fraction with frequency—are inadequate to model the behavior of these sources and their contributions to polarization maps.

Additional Information

© 2015 The American Astronomical Society. Received 2014 November 24; accepted 2015 April 17; published 2015 June 10. Support for the QUIET instrument and operation was provided through the NSF cooperative agreement AST-0506648. Support was also provided by NSF awards PHY-0855887, PHY-0355328, AST-0448909, AST-1010016, and PHY-0551142; KAKENHI 20244041, 20740158, and 21111002; PRODEX C90284; a KIPAC Enterprise grant; and by the Strategic Alliance for the Implementation of New Technologies (SAINT). This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Some work was performed on the Joint Fermilab-KICP Supercomputing Cluster, supported by grants from Fermilab, the Kavli Institute for Cosmological Physics, and the University of Chicago. Some work was performed on the Abel Cluster, owned and maintained by the University of Oslo and NOTUR (the Norwegian High Performance Computing Consortium), and on the Central Computing System, owned and operated by the Computing Research Center at KEK. Portions of this work were performed at the Jet Propulsion Laboratory (JPL) and California Institute of Technology, operating under a contract with the National Aeronautics and Space Administration. The Q-band modules were developed using funding from the JPL R&TD program. We acknowledge the Northrop Grumman Corporation for collaboration in the development and fabrication of HEMT-based cryogenic temperature-compatible MMICs. C.D. acknowledges an STFC Advanced Fellowship, an EU Marie-Curie IRG grant under the FP7 and an ERC Starting Grant (No. 307209). H. K. E. acknowledges an ERC Starting Grant under FP7. A. D. M. acknowledges a Sloan foundation fellowship. J. Z. gratefully acknowledges a South Africa National Research Foundation Square Kilometre Array Research Fellowship. PWV measurements were provided by the Atacama Pathfinder Experiment (APEX). We thank CONICYT for granting permission to operate within the Chajnantor Scientific Preserve in Chile, and ALMA for providing site infrastructure support. Field operations were based at the Don Esteban facility run by Astro-Norte. We are particularly indebted to the engineers and technician who maintained and operated the telescope: J. Cortés, C. Jara, F. Muñoz, and C. Verdugo. In addition, we would like to acknowledge the following people for their assistance in the instrument design, construction, commissioning, operation, and in data analysis: A. G. Aitken, C. Baines, P. Bannister, H. Barker, M. R. Becker, A. Blein, A. Brizius, L. Bronfman, R. Bustos, A. Campbell, A. Chandra, S. M. Cho, S. Church, J. Cooperrider, M. Crofts, E. Curry, M. Daly, F. Dejongh, J. Didier, G. Dooley, R. Dumoulin, H. Eide, W. Grainger, J. Goh, P. Hamlington, T. Higuchi, S. Hillbrand, B. Hooberman, K. D. Huff, K. Ishidoshiro, N. Jarosik, M. E. Jones, P. Kangaslahti, D. J. Kapner, E. Komatsu, J. Kristiansen, D. Kubik, R. Lai, C. R. Lawrence, D. Leibovitch, K. Lepo, S. Li, M. Limon, M. Malin, M. McCulloch, J. J. McMahon, O. Montes, D. Moore, M. Nagai, H. Nguyen, G. Nixon, I. O'Dwyer, G. Orellana, S. Osborne, S. Padin, T. J. Pearson, F. Pedreros, A. Perko, L. Piccirillo, J. L. Richards, A. Robinson, D. Samtleben, J. Sanders, D. Sanford, Y. Savon, M. Seiffert, M. Shepherd, K. Smith M. Soria, A. Sugarbaker, D. Sutton, K. Vanderlinde, M. Vidal, L. Volkova, R. Williamson, S. Xenos, O. Zapata, and M. Zaskowski. Some of the results in this paper have been derived using the HEALPix package (Górski et al. 2005).

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