Surface density of GCs vs. the colour for three different radial bins. The vertical dashed lines in the left panel indicate the colour of the models of Marigo et al. (2008) for 11.2 Gyr old clusters and for the metallicities Z = 0.001 ([Fe/H] = −2.3; B − R = 0.99) and Z = 0.04 ([Fe/H] = +0.3; B − R = 1.78). The rightmost panel is the background. The distinct bimodal appearance remains visible at all radii.
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