Spectral measurements of the cosmic microwave background

Technical Report · Sat Apr 01 00:00:00 EST 1989

DOI:https://doi.org/10.2172/6018188· OSTI ID:6018188

Kogut, A J

Three experiments have measured the intensity of the Cosmic Microwave Background (CMB) at wavelengths 4.0, 3.0, and 0.21 cm. The measurement at 4.0 cm used a direct-gain total-power radiometer to measure the difference in power between the zenith sky and a large cryogenic reference target. Foreground signals are measured with the same instrument and subtracted from the zenith signal, leaving the CMB as the residual. The reference target consists of a large open-mouth cryostat with a microwave absorber submerged in liquid helium; thin windows block the radiative heat load and prevent condensation atmospheric gases within the cryostat. The thermodynamic temperature of the CMB at 4.0 cm is 2.59 +- 0.07 K. The measurement at 3.0 cm used a superheterodyne Dicke-switched radiometer with a similar reference target to measure the zenith sky temperature. A rotating mirror allowed one of the antenna beams to be redirected to a series of zenith angles, permitting automated atmospheric measurements without moving the radiometer. A weighted average of 5 years of data provided the thermodynamic temperature of the CMB at 3.0 cm of 2.62 +- 0.06 K. The measurement at 0.21 cm used Very Large Array observations of interstellar ortho-formaldehyde to determine the CMB intensity in molecular clouds toward the giant HII region W51A (G49.5-0.4). Solutions of the radiative transfer problem in the context of a large velocity gradient model provided estimates of the CMB temperature within the foreground clouds. Collisional excitation from neutral hydrogen molecules within the clouds limited the precision of the result. The thermodynamic temperature of the CMB at 0.21 cm is 3.2 +- 0.9 K. 72 refs., 27 figs., 38 tabs.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6018188
• Report Number(s): LBL-27233; ON: DE89014895
• Resource Relation: Other Information: Thesis (Ph.D.). Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
47 OTHER INSTRUMENTATION
BACKGROUND RADIATION
FREQUENCY MEASUREMENT
COSMIC RADIATION
COSMOLOGY
DATA ANALYSIS
EXPERIMENTAL DATA
GHZ RANGE 01-100
HETERODYNE RECEIVERS
MEASURING METHODS
PERFORMANCE TESTING
RADIOMETERS
STANDARD MODEL
DATA
ELECTRONIC EQUIPMENT
EQUIPMENT
FREQUENCY RANGE
GHZ RANGE
INFORMATION
IONIZING RADIATIONS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NUMERICAL DATA
PARTICLE MODELS
RADIATION DETECTORS
RADIATIONS
RADIO EQUIPMENT
TESTING
UNIFIED GAUGE MODELS
640106* - Astrophysics & Cosmology- Cosmology
440300 - Miscellaneous Instruments- (-1989)