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Published November 10, 2011 | Published
Journal Article Open

First Season QUIET Observations: Measurements of Cosmic Microwave Background Polarization Power Spectra at 43 GHz in the Multipole Range 25 ≤ ℓ ≤ 475


The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43 GHz and 94 GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the cosmic microwave background (CMB). QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, over 10,000 hr of data were collected, first with the 19 element 43 GHz array (3458 hr) and then with the 90 element 94 GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ≈1000 deg^2. This paper reports initial results from the 43 GHz receiver, which has an array sensitivity to CMB fluctuations of 69 μK√s. The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross-correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB, and EB power spectra in the multipole range ℓ = 25-475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3σ significance, the E-mode spectrum is consistent with the ΛCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r = 0.35^(+1.06)_(–0.87). The combination of a new time-stream "double-demodulation" technique, side-fed Dragonian optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r = 0.1.

Additional Information

© 2011 The American Astronomical Society. Received 2010 December 14; accepted 2011 July 12; published 2011 October 25. Support for the QUIET instrument and operation comes through the NSF cooperative agreement AST-0506648. Support was also provided by NSF awards 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). 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 Titan 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 polarimeter modules were developed using funding from the JPL R&TD program. C.D. acknowledges an STFC Advanced Fellowship and an ERC IRG grant under FP7. P.G.F. and J.A.Z. gratefully acknowledge the support of the Beecroft Institute of Particle Astrophysics and Cosmology, the Oxford Martin School, and the Science and Technology Facilities Council. L.B., R.B., and J.M. acknowledge support from CONICYT project Basal PFB-06. R.B. acknowledges support from ALMA-Conicyt 31080022 and 31070015. A.D.M. acknowledges a Sloan foundation 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: José Cortés, Cristobal Jara, Freddy Muñoz, and Carlos Verdugo. In addition, we acknowledge the following people for their assistance in the instrument design, construction, commissioning, operation, and in data analysis: Augusto Gutierrez Aitken, Colin Baines, Phil Bannister, Hannah Barker, Matthew R. Becker, Alex Blein, Mircea Bogdan, April Campbell, Anushya Chandra, Sea Moon Cho, Emma Curry, Maire Daly, Richard Davis, Fritz Dejongh, Joy Didier, Greg Dooley, Hans Eide, Will Grainger, Jonathon Goh, Peter Hamlington, Takeo Higuchi, Seth Hillbrand, Christian Holler, Ben Hooberman, Kathryn D. Huff, William Imbriale, Koji Ishidoshiro, Eiichiro Komatsu, Jostein Kristiansen, Richard Lai, Erik Leitch, Kelly Lepo, Martha Malin, Mark McCulloch, Oliver Montes, David Moore, Makoto Nagai, Ian O'Dwyer, Stephen Osborne, Stephen Padin, Felipe Pedreros, Ashley Perko, Alan Robinson, Jacklyn Sanders, Dale Sanford, Mary Soria, Alex Sugarbaker, David Sutton, Matias Vidal, Liza Volkova, Edward Wollack, Stephanie Xenos, and Mark Zaskowski.

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