Noise distribution and statistical results. Top: Spatial distribution of the rms noise of the Effelsberg H₂CO (1_1,0–1_1,1) observations at a channel width of 0.5 km s⁻¹ and an HPBW of 3′. Lower left: Power spectrum of the noise image. The very high power pixels in the cross are artifacts that are caused by the Fourier transform of the sharp image (also known as the Gibbs phenomenon). Lower right: Histogram of the rms noise values. The mean and standard deviation values are 0.10 K and 0.01 K, respectively.