Galaxies and subhalos

Tommaso Zana
  • 21 Apr '15

Could I assume that every subhalo hosts a single galaxy and, therefore, that I can interpret the 6 entries of the "SubhaloMassType" field as the masses of all types of particles in each single galaxy?

And could I also assume that the first entry of this field is the gas mass and that the other ones follow the GADGET naming convention?

Dylan Nelson
  • 1
  • 22 Apr '15

Hi Tommaso,

This is broadly right, for instance in almost all the figures of the intro papers, "galaxies" does just mean subhalos.

And the "*Type" fields (with 6 entries) are the same numbering as the snapshots (0=gas, 1=dm, 4=stars+wind, 5=bhs).

Two complications you might want to keep in mind:

  • There is a fundamental difference between central and satellite subhalos. For many science questions you may just want to consider one of these groups, although you may want to consider all, regardless.
  • Not every subhalo will host a galaxy (many of the small ones will have zero stellar and/or gas mass, for instance). So you may want to apply some "galaxy criterion" and not just take all subhalos.
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