Distribution of the PDM around two point masses (zero external field assumed) with various mass ratios indicated above each column. The mass of M₁ is 10¹¹ M_⊙ and the two point masses are 200 kpc apart. The mass ratio is the same for each column. The top row shows the whole system, in the bottom row we can see magnified the region of the negative PDM. Note that the vertical ranges of the plots in the bottom row are different for each plot. In each plot, the r and z axes have the same scale.