Eigenvalues (labeled as EGV above) of for each of the ten frequency bands (represented by different symbol colors), considering CMB, foregrounds (synchrotron and thermal dust) and one noise realization. Eigenvalues from the E-mode (upper panel) and B-mode (lower panel) are shown. The threshold is displayed as a solid black horizontal line. We note that is not strictly positive: the subspace associated to the lowest eigenvalues is dominated by noise, and hence corresponding eigenvalues are centered around zero after the subtraction of the noise covariance from . The eigenvalues, , are shown in absolute value, negative eigenvalues being displayed as red dots.