First Measurement of the Submillimeter Sunyaev-Zeldovich Effect

We report the first detection of the Sunyaev-Zeldovich (S-Z) increment on the cosmic microwave background at submillimeter wavelengths in the direction of a cluster of galaxies. It was achieved toward the rich cluster Abell 2163, using the PRONAOS 2 m stratospheric telescope. Together with data from the SuZIE, Diabolo, and ISO-PHT experiments, these measurements, for the first time, give a complete picture of the far-infrared-to-millimeter spectral energy distribution of the diffuse emission toward a cluster of galaxies. It clearly shows the positive and negative parts of the S-Z effect and also a positive signal at short wavelengths that can be attributed to foreground dust in our Galaxy.