This research project will produce the most sensitive maps yet of Cosmic Microwave Background (CMB) polarization by extending observations with the Q and U Imaging ExperimenT (QUIET) through 2010. With prior NSF and other support, the QUIET collaboration has constructed and deployed two large receiver arrays of correlation polarimeters, one for 44 GHz (Q band) and one for 95 GHz (W band), and has completed a successful nine month campaign of Q band observations producing outstanding results. The project team are now observing with the W-band receiver, which is the largest, most sensitive polarimeter array of any experiment to date.
Observations of the CMB, in particular the temperature anisotropies, are a cornerstone of precision cosmology, providing a wealth of information about the structure of the Universe and conditions at early times. CMB polarization observations add qualitatively distinct information, but only recently have reached the level of sensitivity to provide meaningful constraints on cosmological models. With more precise measurements of the angular power spectrum, QUIET will continue to test the standard cosmological model, further limiting proposed variants. This research will tighten the limits on CMB B-mode polarization signals generated either by foreground gravitational lensing or by primordial gravitational waves. These new deep observations will study polarized foregrounds, particularly synchrotron, at levels approaching those needed to extract cosmological information about primordial B-mode signals. In addition to their intrinsic interest, these foreground studies will enhance the interpretation of results from other contemporaneous CMB experiments and influence the design of future experiments.
Cosmology continues to captivate the public imagination. QUIET will contribute to understanding by disseminating the results and their context to a broad range of audiences. This research collaboration continues a strong tradition of training students through research, providing both technical and collaborative experiences as a foundation for future achievements. Because the observations are from a Chilean site, there is a special interest in academic and scientific cooperation with institutions there. The outreach program allows Chilean school science classes to design and carry out their own radio astronomy observations. QUIET is a global collaboration, with strong ties among US universities, federal research centers, and institutions outside the US.
The Cosmic Microwave Background (CMB) provides a direct image of the early Universe. The strength and characteristic angular scales of the faint intensity and polarization patterns in the CMB encode a wealth of information about the structure of the Universe and conditions at early times. CMB polarization and intensity observations are complementary, providing qualitatively distinct information. The Q and U Imaging Experiment (QUIET) measured the faint polarization patterns in the Cosmic Microwave Background at two frequencies, 43 GHz and 95 GHz. Observations were made for 2.5 years from the high altitude Chajnantor plateau in northern Chile, the best site in the world with year round access for millimeter wavelength radio astronomy. The observing efficiency was very high; about 76% of the elapsed time provided useful data. QUIET observations have demonstrated the successful use of large focal plane arrays of cryogenically cooled, compact polarimeters based on monolithic microwave integrated circuit amplifiers made with indium phosphide for CMB polarization measurements. At their observing frequencies, the QUIET receivers are the most sensitive deployed so far. The 43 GHz observations confirm the only previous detection of the first acoustic peak in the angular power spectrum of the curl free (EE) polarization patterns. Although analysis of the data is still underway, the 95 GHz observations are expected to surpass the lower frequency results, measuring several peaks in the EE spectrum and providing an important constraint on the curly (BB) component of the polarization pattern. These results add further support to the the consensus (ΛCDM) cosmology model and limit the proposed variants. Over twenty students and ten postdoctoral scholars were involved in QUIET. They were central to the experiment, participating in all phases of instrument construction, integration, testing, and deployment followed by the CMB observations and the data analysis. Seven students based their doctoral theses on the experiment. QUIET was a global collaboration, including institutions from six other counties in addition to universities and federal research centers in the United States.
