The C-Band All Sky Survey (C-BASS) is a radio survey at 5 GHz of the entire sky in total intensity and linear polarization. The northern part of the survey will be completed in 2012 using a cryogenic receiver, optimized for both total intensity and linear polarization, on a 6.1-meter antenna at the Owens Valley Radio Observatory. A parallel southern survey will be conducted in 2012-2013 using a similar receiver on a 7.6-meter antenna in South Africa. This award supports the completion of the northern survey and the publication and interpretation of the results. The C-BASS will be the first all-sky survey of diffuse Galactic emission at a frequency low enough to be dominated by synchrotron radiation but high enough to be uncorrupted by Faraday rotation effects. It will provide new information about the interstellar medium, the Galactic magnetic field, and radiation mechanisms. The C-BASS data are also needed to improve the separation of the polarized cosmic microwave background (CMB) from foreground emission. The CMB polarization is measured by the WMAP and Planck satellites, and by several current and future ground-based and balloon-borne experiments. A major goal for these experiments is to measure the B-mode polarization signal, which is expected to provide information about the epoch of inflation - in particular, the energy scale of inflation - and about physics at grand unification energies. This requires that the CMB is separated from foreground emission with higher accuracy than it is possible with our current understanding of Galactic foregrounds. The C-BASS data will significantly improve the accuracy of foreground subtraction. The survey is conducted in collaboration with groups at the Universities of Oxford and Manchester (UK), Rhodes University and HartRAO (South Africa), and KACST (Saudi Arabia). The receiver for the northern survey has been constructed and deployed at OVRO with support from the NSF and Oxford and Manchester universities. Construction of the southern receiver has been supported by Oxford, Manchester, and KACST. The The C-BASS sky maps will be made freely available soon after completion. Students are involved in the design and construction of the instrumentation as well as the observations and data analysis. Members of the C-BASS team participate in the development and execution of broad outreach programs at The Owens Valley Radio Observatory.
The C-Band All Sky Survey (C-BASS) is a project to image the whole sky at a wavelength of six centimeters (a frequency of 5 GHz), measuring both the brightness and the polarization of the sky. C-BASS employs very sensitive microwave amplifiers, cooled to within a few degrees of absolute zero, and configured to measure tiny differences in temperature and polarization. They are mounted on two separate telescopes — one at the Owens Valley Observatory (OVRO) in California, the other in South Africa. This allows C-BASS to observe both in the northern and southern hemispheres and hence map the whole sky. C-BASS is a collaborative project between the Universities of Oxford and Manchester in the UK, the California Institute of Technology in the USA, the Hartebeesthoek Radio Astronomy Observatory (supported by the Square Kilometer Array project) in South Africa, and the King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia. The southern telescope is a 7.6-m dish donated to the project by Telkom. The northern telescope is a 6.1-m dish donated by the Jet Propulsion Laboratory. The dishes have been outfitted with a novel optical system to minimize pick-up of spurious signals from the ground and terrestrial sources. The all-sky maps produced by this survey will be used to enable accurate subtraction of contaminating signals from the Cosmic Microwave Background (CMB) data collected by specialized telescopes in order that they can reveal the true fluctuations in the microwave background. The polarization is especially important for removing confusing foreground emission in searches for the "B-mode" polarization signal of the inflationary stage of the very early universe. In addition to playing an essential part in the quest for revealing the tiny fluctuations in the CMB and understanding the origin and evolution of our universe, C-BASS will vastly increase our understanding of the physics of the gas between the stars in our own Galaxy, for example by mapping out the magnetic field in the Galaxy. This award supported observations for the northern part of the survey, which have now been completed. The southern part is in progress in South Africa. Preliminary results have been presented at international conferences, and a paper presenting an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane has been published. A Caltech graduate student was awarded a PhD for work on this project, including design, instrument construction, data analysis, and astrophysical studies. Students from the collaborating institutions in the UK have also played a major role and have spent time at OVRO to assist in commissioning. The students received training in radio frequency engineering, digital data acquisition, and data analysis methods, as well as in astronomy and cosmology. The C-BASS project has featured in public outreach events in California, including observatory tours and public lectures.
