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tokens: offering a realistic quantification of the effect, we resort to a simulation of an isolated halo of mass . The simulation is similar to those used by Nusser ( 2018 ) to study the effect of dynamical friction of the population of the star clusters in NGC 1052-DF2 . The simulation contains 2.4 × 10 5 particles of equal mass distributed according to the Einasto mass profile. The particles were advanced forward for 10 Gyr using the publicly available treecode by Barnes Hut ( 1986 ). Further details can be found in Nusser ( 2018 ). We select those particles found at distances of less than a trimming radius r tr = 10 kpc from the halo centre in all 50 snapshots covering the last 5 Gyr of the simulation. We assume that those particles were never at a farther distance and we identify them as composing the halo surviving a tidal stripping process. We then project the particle velocities along a single axis (the l.o.s) and compute the corresponding velocity dispersion, σ u , at a 3D distance r from the centre. We compare this with the velocity dispersion computed from all original particles (i.e. including pre-trimming particles passing by from distances beyond 10 kpc). The red and blue solid curves in the top panel of Fig. 2 plot square velocity dispersions versus r for the trimmed (tidally stripped) and the untrimmed haloes. The l.o.s velocity variance is represented by the solid curves. As r approaches the trimming radius of 10 kpc, of the trimmed halo (red solid curve) falls substantially below the untrimmed halo (blue solid). The ratio of between the two curves approaches unity only at r 2 kpc. The dotted curves represent the variance, , of the radial (from the halo centre) velocity component. The red dotted curve actually drops to zero at 10 kpc, since there are no particles moving beyond that radius. The dashed curves are the tangential velocity variance divided by 2, . Trimming also reduces the tangential dispersion but the reduction in the is mainly due to the lowered dispersion in the radial direction. Note that the velocity dispersion ellipsoid in the original halo is skewed to the tangential direction with an anisotropy parameter for 2 ≲ r ≲ 10 kpc. The reduction in σ u clearly depends on the parameter β of the original halo. We emphasize that the numerical experiment presented here is simply for illustration purposes. In fact, haloes in simulations with generic initial conditions based on the ΛCDM model have a marked tendency at large radii towards a positive β (e.g. Colín, Klypin Kravtsov 2000 ; Mamon Łokas 2005 ; Ascasibar Gottlöber 2008 ; Mamon, Biviano Murante 2010 ; Lemze et al. 2012 ; Sparre Hansen 2012 ). This implies both a more significant reduction in σ u and also a more isotropic velocity ellipsoid in the trimmed halo at r r tr . Figure 2. Top: The variance of velocity, versus the 3D radius, of particles inside a radius of r tr = 10 kpc in a simulated halo of . The blue curve is the variance from particles in the pre-trimmed