Moritz Haslbauer
  • 26 Apr '18

Dear Dylan, I am a little bit confused with the mass resolution of the Illustris-1 simulation. On your homepage the mgas (minimal mass of one gas particle) is 1.26*10^6 Msun ( and here m{baryon} is 1.610^6 Msun ( Shouldn't it be 1.2610^6? In the Illustris-1 simulation, I also found subhalos with a stellar mass below this particle resolution (not the cell resolution). Therefore, I am now confused about the resolution of stellar particles? I am correct, that m_baryons=1.26*10^6 is not valid for the stellar particles? Many thanks in advance!

Dylan Nelson
  • 1
  • 27 Apr '18

Hi Moritz,

For the gas, these are both approximations - there is no "constant" gas cell mass, since gas cells can exchange mass. The result is a continuous spectrum of resolution. A nice view of this is from the Pillepich et al. TNG methods paper:


One of these numbers is likely the mean cell mass at z=0, the other possibly the mean or median at the initial conditions. In any case, if you need a precise measure, you can load the Masses field of PartType0 and work with it directly.

For stars, they inherit the gas mass from which they form, so they also have variable mass resolution. They also then continuously decrease in mass due to stellar evolution.

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