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-Zel'dovich (SZ) effecttowards the Coma cluster. This balloon-borne instrument uses a $28\arcmin$ FWHMbeam and a three position chopping pattern with a throw of $\pm40\arcmin$. Withspectral channels at 5.7, 9.3, 16.5, and 22.6~\icm, the observationssimultaneously sample the frequency range where the SZ spectral distortion inthe intensity transitions from a decrement to an increment and where thefractional intensity change is substantially larger than in the Rayleigh-Jeansregion. We set limits on the Comptonization parameter integrated over ourantenna pattern, $\Delta y \leq 8.0 \times 10^{-5}$($2 \sigma$). For aspherically symmetric isothermal model, this implies a central Comptonizationparameter, $y_o \leq 2.0 \times 10^{-4}$, or a central electron density, $n_o\leq 5.8 \times10^{-3}$cm$^{-3}h_{50}$, a result consistent with centraldensities implied by X-ray brightness measurements and central Comptonizationestimates from lower frequency observations of the SZ effect.Comment: 11 pages, LaTeX+aasms4 package, 1 PostScript figure. Submitted to Ap.J Letter