A Limit on the Polarization of the Cosmic Microwave Background Radiation

Author: Cartwright, John Kenneth

Year: 2003

Degree: Dissertation (Ph.D.)

Advisor: Readhead, Anthony C. S.

Committee Members: Phinney, E. Sterl; Lange, Andrew E.; Readhead, Anthony C. S.; Zmuidzinas, Jonas; Padin, Stephen

Option: Astronomy

DOI: 10.7907/D3CT-YV96

Abstract

We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13-element interferometer which operates in the 26-36 GHz band and is located on the Llano de Chajnantor in northern Chile. The array consists of 90 cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single-mode circularly polarized receivers and it samples multipoles from ℓ ~ 400 to ℓ ~ 4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source which was monitored with the VLA. Observations of two deep fields during the 2000 season yielded three limits (95% c.l.) for CℓEE under the assumption that CℓBB = 0: 7.0 µK (ℓ = 603); 12.8 µK (ℓ = 1144); and 25.1 µK (ℓ = 2048). The low-ℓ limit approaches the levels of fluctuations predicted by standard models.

This thesis also entailed the design and implementation of several major components of the CBI signal chain including the downconverter, the noise calibration system, and the low noise HEMT amplifiers. We discuss the design and performance of these critical systems.

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