Search for Non-Gaussian Signals in the BOOMERANG Maps: Pixel-Space Analysis

We search the BOOMERANG (Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics) maps of the anisotropy of the cosmic microwave background (CMB) for deviations from Gaussianity. In this Letter, we focus on analysis techniques in pixel space and compute skewness, kurtosis, and Minkowski functionals for the BOOMERANG maps and for Gaussian simulations of the CMB sky. We do not find any significant deviation from Gaussianity in the high galactic latitude section of the 150 GHz map. We do find deviations from Gaussianity at lower latitudes and at 410 GHz, and we ascribe them to Galactic dust contamination. Using non-Gaussian simulations of instrumental systematic effects, of foregrounds, and of sample non-Gaussian cosmological models, we set upper limits to the non-Gaussian component of the temperature field in the BOOMERANG maps. For fluctuations distributed as a 1 degree of freedom χ2 mixed to the main Gaussian component, our upper limits are in the few percentile range.