  We analyze the internal structures of clusters A1689 and A2218 by applying a
recent development of the method of wavelet analysis, which uses the complete
information obtained from optical data, i.e. galaxy positions and redshifts. We
find that both clusters show the presence of structures superimposed along the
line of sight with different mean redshifts and smaller velocity dispersions
than that of the system as a whole, suggesting that the clusters could be cases
of the on-going merging of clumps. In the case of A2218 we find an acceptable
agreement between our estimate of optical virial mass and X-ray and
gravitational lensing masses. On the contrary, in the case of A1689 we find
that our mass estimates are smaller than X-ray and gravitational lensing ones
at both small and large radii. In any case, at variance with earlier claims,
there is no evidence that X-ray mass estimates are underestimated.

Astrophysics