===== GC IV =====

=== M4 mass modelling challenge: method comparison ===

This is a joint project between many participants, centred around mock data from Douglas Heggie’s N-body simulation of M4. The idea is to fit the M4 mock data with various mass modelling techniques and compare the results obtained with these different methods.

[[:tests:collision:mock_data|M4 mock data can be found here]].

Some preliminary results from GCIII are shown [[:tests:collision:gc3:method_comp|here]]

The current plan is to turn this M4 challenge into one ‘Gaia Challenge' paper (coordinated by Vincent), with contributions from the following people/methods (others welcome too):

  - Jeans modelling (Laura & Antonio - each with their own code)
  - Multi-mass models with full mass function and SSP model (Vincent)
  - Three-component multi-mass models (Mark)
  - Single-mass models (Mark/Alice)
  - Single-mass models with potential escapers (Ian)


The plan is to use combined datasets with increasing level of information:

  - The surface brightness profile and line-of-sight velocity dispersion profile
  - Then additionally consider HST-like proper-motion dispersion profiles
  - Finally, fits including all the previous data and including Gaia-like proper motions and distances

Mock data for steps 1 and 2 are currently available. For step 3, Elena Pancino is working on producing Gaia-like observations of the M4 snapshot (with different simulated backgrounds).

We want to compare how well the different methods recover or fit the following quantities/observables:

  - total cluster mass $M$
  - half-mass radius $r_h$
  - global mass-to-light ratio $M/L$
  - $M/L$ profile 
  - general quality of the fit to the velocity dispersion, surface brightness, and anisotropy profile
  - constraints on the stellar mass function (where applicable)
  - mass in dark remnants (where applicable)

You can put your [[:tests:collision:gc4:method_comp|results and any interesting plots/ideas here]].