Millimeter/Submillimeter Search for the Sunyaev-Zeldovich Effect in the Coma Cluster

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM1-92) are analyzed to search for the Sunyaev-Zeldovich (SZ) effect toward the Coma cluster. This balloon-borne instrument uses a 28' FWHM beam and a three-position chopping pattern with a throw of ±40'. With spectral channels at 5.7, 9.3, 16.5, and 22.6 cm^-1, the observations simultaneously sample the frequency range where the SZ spectral distortion in the intensity transitions from a decrement to an increment and where the fractional intensity change is substantially larger than in the Rayleigh-Jeans region. We set limits on the Comptonization parameter integrated over our antenna pattern, Δy ≤ 8.0 × 10^-5 (2 σ). For a spherically symmetric isothermal model, this implies a central Comptonization parameter y₀ ≤ 2.0 × 10^-4 or a central electron density n₀ ≤ 5.8 × 10^-3 cm^-3 h₅₀, a result consistent with central densities implied by X-ray brightness measurements and central Comptonization estimates from lower frequency observations of the SZ effect.