Halos with many subhalos that have zero stellar mass

Tara Dacunha
  • 17 Jun '20

We have been looking at simulation data from TNG 300-3 (specifically snapshot 66) and are interested in studying galaxies in clusters/halos. In trying to implement mass cuts on the stellar masses of the subhalos we found that over 50% of all the subhalos in a halo have zero stellar mass. We tried different subhalo fields: SubhaloMassType[:,4], SubhaloMassInRadType[:,4], and SubhaloStellarPhotometricsMassInRad. This was true for even high mass clusters and meant that even a cluster with greater than 10^15 Msun that appeared to have 157 subhalos, only had 65 subhalos with any stellar mass. Is this an expected result? Is this a feature of the redshift/snapshot we are currently analyzing or do clusters in TNG typically not have large numbers of galaxies?
Any insight into this would be appreciated!

Dylan Nelson
  • 18 Jun '20

Hi Tara,

The majority of small subhalos (in both TNG and the real Universe) are thought to be "dark", i.e. contain no stars. As you get to more massive subhalos, the majority should host a luminous galaxy.

Keep in mind the resolution of a given simulation: TNG300-3 has star particles with mass ~ 7x10^8 Msun, which means a 10^9 Msun stellar mass galaxy is represented by only ~two star particles. This is at the extreme edge of numerical resolution (which is to say, TNG300-3 is a very low resolution simulation). Once you have a list of parent host halos of interest, you should check in TNG300-2 and TNG300-1 to get a better sense of the satellite galaxy populations.

Tara Dacunha
  • 2 Jul '20

Ok thank you!

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