Number of groups vs subgroups in file

Jacob Morgan
  • 1
  • 15 Oct '20

hey there! I was poking around the group catalog file headers and saw this:

gc_file0=h5py.File(il.groupcat.gcPath(basepath, 99, 0), 'r') #should select chunk 0 of the group catalog at snapshot 99

returns 124773


returns 118820

to my understanding, the groups/subgroups are the same as halo/subhalo. I am surprised that the number of halos can be greater than the number of subhalos-- I thought every halo had at least 1 subhalo? Does this imply there are large regions where asking for (all subhalos--> all gas in all subhalos) returns nothing, even though the region is within a halo, and therefore should contain a fair amount of gas? Basically, from the perspective of halos being "like clusters" (I know they aren't always), it seems weird that there'd be such a large object with no subgroups.

Dylan Nelson
  • 15 Oct '20

Hi Jacob,

The number of total halos is generally higher than the number of total subhalos as you, because the very smallest halos may not have a bound subhalo.

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