Cmb Observations with a Compact Heterogeneous 150 Ghz Interferometer in Chile

We report on the design, first observing season, and analysis of data from a new prototype millimeterwave interferometer, MINT. MINT consists of four 145GHz SIS mixers operating in double-sideband mode in a compact heterogeneous configuration. The signal band is subdivided by a monolithic channelizer, after which the correlations between antennas are performed digitally. The typical receiver sensitivity in a 2GHz band is 1.4mK √ s. The primary beams are 0.55 and 0.37 FWHM, with fringe spacing as low as 0.1. MINT observed the cosmic microwave background (CMB) from Cerro Toco, in the Chilean Altiplano. The site quality at 145GHz is good, with median nighttime atmospheric temperature of 9K at zenith (exclusive of the CMB). Repeated observations of Mars, Jupiter, and a telescope-mounted calibration source establish the phase and magnitude stability of the system. MINT is the first interferometer dedicated to CMB studies to operate above 50GHz. The same type of system can be used to probe the Sunyaev-Zel’dovich effect in galaxy clusters near the SZ null at 217GHz. We give the essential features of MINT and present an analysis of sideband-separated, digitally sampled data recorded by the array. Based on 215 hours of data taken in late 2001, we set an upper limit on the CMB anisotropy in a band of width ∆l = 700 around l = 1550 of δT ≤ 104 μK (95% conf.). Increased sensitivity can be achieved with more integration time, greater bandwidth, and more elements. Subject headings: cosmic microwave background—instrumentation: interferometers