Units

Everything is computed in internal units, the dimensionless normalization of Widrow (2000). In internal units, the scale radius and the central potential of the untruncated profile are 1.

The to method of a distribution function, a model or a LosTable presents the result in model units \((G = M_0 = r_0 = 1)\) or, through Astropy, in physical units. Both systems need the concentration \(c\), which defines \(M_0\) as the mass of the untruncated profile inside \(c\,r_0\). The numbers are not recomputed. Observables and particles computed from the presented result are returned in the unit system of the presented result. Some inputs and outputs stay in internal units whatever the model’s unit system: Sampler’s r_sample and r_range, the radii, the v_range and the returned velocities of Sampler.velocities, every argument and value of Differentiable, and the anisotropy theta of likelihood.

Exactly one of the three inputs of a Truncation is given, in these units:

• the truncation energy k_t in internal units;

• a target radius r_t in units of the scale radius;

• a target mass mass_t in units of \(M_0\), together with the concentration that defines \(M_0\).