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.

M4 mock data can be found here.

Some preliminary results from GCIII are shown 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):

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

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

1. The surface brightness profile and line-of-sight velocity dispersion profile
2. Then additionally consider HST-like proper-motion dispersion profiles
3. 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:

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

You can put your results and any interesting plots/ideas here.