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
gc_file0['Header'].attrs['Ngroups_Total']
returns 124773
gc_file0['Header'].attrs['Nsubgroups_Total']
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.
hey there! I was poking around the group catalog file headers and saw this:
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.
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.