A Preliminary Detection of Arcminute Scale Cosmic Microwave Background Anisotropy with the BIMA Array

We have used the Berkeley-Illinois-Maryland-Association (BIMA) array outfitted with sensitive cm-wave receivers to expand our search for arcminute scale anisotropy of the Cosmic Microwave Background (CMB). The interferometer was placed in a compact configuration to obtain high brightness sensitivity on arcminute scales over its 6.6 FWHM field of view. The sensitivity of this experiment to flat band power peaks at a multipole of l = 5530 which corresponds to an angular scale of ∼ 2 ′ . We present the analysis of a total of 470 hours of on-source integration time on eleven independent fields which were selected based on their low IR dust contrast and lack of bright radio sources. Applying a Bayesian analysis to the visibility data, we find CMB anisotropy flat-band power Qflat = 6.1 +2.8 −4.8 μK at 68% confidence. The confidence of a non-zero signal is 76% and we find an upper limit of Qflat < 12.4μK at 95% confidence. We have supplemented our BIMA observations with concurrent observations at 4.8 GHz with the VLA to search for and remove point sources. We find that point sources make an insignificant contribution to the observed anisotropy. Subject headings: cosmology: observation – cosmic microwave background Department of Physics, University of California, Berkeley CA 94720 Department of Astronomy and Astrophysics, University of Chicago, Chicago IL 60637 Space Science Laboratory, SD50, NASA Marshall Space Flight Center, Huntsville AL 35812