A Millimeter/Submillimeter Search for the Sunyaev-Zel’dovich 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) effect towards 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, 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, ∆y ≤ 8.0× 10(2σ). For a spherically symmetric isothermal model, this implies a central Comptonization parameter, yo ≤ 2.0× 10, or a central electron density, no ≤ 5.8× 10cmh50, a result consistent with central densities implied by X-ray brightness measurements and central Comptonization estimates from lower frequency observations of the SZ effect. Laboratory for Astronomy and Solar Physics, NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771 Global Science and Technology, Inc., Laboratory for Astronomy and Solar Physics, NASA/GSFC Code 685, Greenbelt, MD 20771 Hughes STX Corporation, Laboratory for Astronomy and Solar Physics, NASA/GSFC Code 685, Greenbelt, MD 20771 Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Avenue, Chicago IL 60637 Princeton University, Physics Dept., Jadwin Hall, Princeton, NJ 08540 Center for Particle Astrophysics, University of California, Berkeley School of Physics & Astronomy, Tel Aviv University, Tel Aviv, Israel