Opening Remarks

Extract

The following papers formed a Joint Discussion sponsored by Commissions 40, 44, 47 and 48 of the International Astronomical Union. The topic was Cosmic Backgrounds. The plural “backgrounds” is important. Speakers considered electromagnetic radiation fields ranging from radio wavelengths to X-rays. Because other sessions at this General Assembly treated higher energy backgrounds, in particular the X-ray region, emphasis in this Joint Discussion was on radio and infrared backgrounds. In addition to the wide range of wavelengths covered, the session also dealt with a wide range of models for various backgrounds. For instance, at some wavelengths (e.g., λ ~ 1 cm) the background is truly a background, generated at very high redshifts—in this case a thermal radiation field at ~ 3 K. At other wavelengths (e.g., in the X-ray region) the “background” may consist in whole or in part of the summed emission from many unresolved or subliminal sources.