My question concerns the half mass radius's given. Are these half mass radii defined by their specific component? In other words, is the half mass radius for dm literally the radial extent to which half the dark matter is distributed? This would be as opposed to the half light radius. Thanks for all your help.
I would like to compare the average half mass densities of gas, dm and stars. I am currently doing this by taking massinhalfradius / volume . So for example, to find average half mass dm density of a given cluster I would take dm mass inhalf radius and divide it by 4/3pi (half_mass_radius_dm)^3 .
It is as you describe it, the radius enclosing half of the total mass of particles of that type. Note that 'total mass' means the sum of masses of all particles (of that type) which belong to the subhalo.
There aren't any half light radii in the catalogs, although you could compute them using e.g. SubhaloStellarPhotometrics.
Great, thanks Dr. Nelson.