Maps of optical depth at wavelengths of 154 μm (top left), 160 μm (top right), 214 μm (bottom left), and 850 μm (bottom right). The contour lines mark 10, 20, 30, 40, 50, 60, 70, 80, and 90 % of the maximum optical depth for each wavelength. The white asterisk symbols mark known stellar sources (Chini et al. 1997). The beam size of 18.2″ (band E) is indicated on the lower-right of each figure.