The Cosmic Background Imager 2

TL;DR

The paper details an upgrade to the Cosmic Background Imager, enhancing its sensitivity and performance for studying the cosmic microwave background and related phenomena through improved antenna design and calibration.

Contribution

It introduces a novel antenna upgrade with specific design features that improve sensitivity and reduce spillover noise, enabling better cosmic background observations.

Findings

Enhanced sensitivity at small angular scales.

Successful calibration with previous system.

Effective observation of Sunyaev-Zel'dovich effect.

Abstract

We describe an upgrade to the Cosmic Background Imager instrument to increase its surface brightness sensitivity at small angular scales. The upgrade consisted of replacing the thirteen 0.9-m antennas with 1.4-m antennas incorporating a novel combination of design features, which provided excellent sidelobe and spillover performance for low manufacturing cost. Off-the-shelf spun primaries were used, and the secondary mirrors were oversized and shaped relative to a standard Cassegrain in order to provide an optimum compromise between aperture efficiency and low spillover lobes. Low-order distortions in the primary mirrors were compensated for by custom machining of the secondary mirrors. The secondaries were supported on a transparent dielectric foam cone to minimize scattering. The antennas were tested in the complete instrument, and the beam shape and spillover noise contributions were as expected. We demonstrate the performance of the telescope and the inter-calibration with the previous system using observations of the Sunyaev-Zel'dovich effect in the cluster Abell 1689. The enhanced instrument has been used to study the cosmic microwave background, the Sunyaev-Zel'dovich effect and diffuse Galactic emission.