Upper panel: radial profile of y in a set of circular annuli centred on Coma. The blue curve is the best fitting simple model to the profile over the radial range from 85 arcmin to 300 arcmin. The model consists of a power law plus a constant y_off. The best fitting value of y_off is shown with the dashed horizontal line. Two vertical lines indicate the range of radii used for fitting. Lower panel: the probability of finding an observed value of y > y_Coma in a given annulus. The probability was estimated by measuring y in a set of annuli with random centres in any part of the image outside 5 × R₅₀₀, where R₅₀₀ = 47   arcmin.