Probability distributions of v_esc and k_t derived using tangential velocities for a mock data sample drawn from a power-law distribution in the velocity modulus, and convolved with realistic uncertainties. The left panel shows the results based on mock data drawn directly from Eq. (7), and on the right we draw the data from Eq. (12) and then transform the velocities into tangential velocities. The closed contours mark the probability levels at which the probability has dropped to 61%, 14%, and 1% of the maximum a posteriori value (they correspond to the 1, 2, and 3σ levels if the distribution were Gaussian). The coloured markers indicate the highest probability parameter combinations, with the red marker showing the input parameters.