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Session 91 - COBE and the Search for the Cosmic Infrared Background.
Oral session, Friday, January 09
Jefferson,
The Far Infrared Absolute Spectraphotometer (FIRAS) instrument, one of three on NASA's Cosmic Background Explorer (COBE) satellite, was a differential Michelson interferometer, covering a frequency range from 2 to 100 cm^-1 (100 micrometers to 5000 \mum), with a spectral resolution of 0.4 cm^-1. We will present results from our improved, recently delivered, `Pass 4' data products. Careful design and implementation resulted in a successful achievement of the FIRAS primary mission: a detailed measurement of the Cosmic Microwave Background (CMB) spectrum from 2 to 20 cm^-1 that matched a blackbody form, B_\nu(T), T=2.728 K, within 50 parts per million of the peak of the spectrum. The spectrum of the associated dipole signal fit a \partial B_\nu/\partial T spectrum within 1%\ of its peak, consistent with a 370 km s^-1 Doppler signal from the solar system's motion with respect to the CMB defined cosmic rest frame. Correlations of the residual data with the higher order CMB anisotropies, as measured by the COBE / DMR, also showed that they had a similar spectrum as the dipole, confirming the primordial nature of the DMR anisotropies. Besides its primary purpose, the highly accurate measurement of the Cosmic Microwave Background spectrum from 2--20 cm^-1, the COBE / FIRAS instrument measured emission from dust and gas in our galaxy and solar system, and a possible cosmic Far Infrared Background (FIRB), over the band from 12--95 cm-1. If the high galactic latitude, low intensity, galactic foreground has a single spectrum, then FIRAS data alone set a significant lower limit to the FIRB. Possible complications in this simple picture are discussed in the following talk.
