Introduce triaxiality into cluster satellite distributions

[aphearin]

I have recently finished implementing an overhaul to the spatial distributions of satellite galaxies in cosmoDC2, with the primary goal of supporting efforts within the cluster working group to study biases that can result from cluster projection effects. In the new modeling approach, satellites will be distributed according to an ellipsoidal NFW profile, as opposed to the current approach that directly uses subhalo-based positions taken from UniverseMachine. In order to implement this new approach, it was necessary to develop an analytical model for the shapes of host halos, since halo shape information is not available in the version of the Outer Rim halo catalogs used in cosmoDC2. The plots below demonstrate the fidelity with which the model recovers halo shapes in the Bolshoi-Planck simulation. The code implementing this model is located here.

Comments welcome from anyone with science targets that are influenced by satellite distributions. After further input, particularly and hopefully from the cluster WG, the ellipsoidal NFW model is the model we will use to generate the 5000 deg**2 catalog.

CC @erykoff @j-dr @evevkovacs @katrinheitmann @hywu @abmantz @yymao