I was wondering if anyone came up with a good and fast method to find satellites for massive (> 1.e7 Msun) subhalos? I'm trying to have a list of satellites for each subhalo without it taking too long.

Dylan Nelson

2 Jun '17

Hi Aishwarya,

Subhalos of mass 1.e7 Msun (not sure if you meant stellar or total mass, but regardless) are essentially unresolved in all Illustris simulations. Is this really what you meant?

Our definition of satellites (using the Subfind algorithm) allows you to immediately produce the list, e.g. for FoF halo i the indices of its satellites are simply inds = range(GroupNsubs[i]) + GroupFirstSub[i].

Aishwarya Srivastava

2 Jun '17

Yes, that's pretty much what I was looking for. Thanks! Along the same vein, what does the field "SubhaloGrNr" mean? Is it safe to assume that it corresponds to the parent halo? Also, is the index it refers to 0-based?

Dylan Nelson

2 Jun '17

Hi Aishwarya,

The field SubhaloGrNr is "Index into the Group table of the FOF host/parent of this Subhalo."

If your language is 0-index based, then yes this index is 0-based.

I was wondering if anyone came up with a good and fast method to find satellites for massive (> 1.e7 Msun) subhalos? I'm trying to have a list of satellites for each subhalo without it taking too long.

Hi Aishwarya,

Subhalos of mass 1.e7 Msun (not sure if you meant stellar or total mass, but regardless) are essentially unresolved in all Illustris simulations. Is this really what you meant?

Our definition of satellites (using the Subfind algorithm) allows you to immediately produce the list, e.g. for FoF halo

`i`

the indices of its satellites are simply`inds = range(GroupNsubs[i]) + GroupFirstSub[i]`

.Yes, that's pretty much what I was looking for. Thanks! Along the same vein, what does the field "SubhaloGrNr" mean? Is it safe to assume that it corresponds to the parent halo? Also, is the index it refers to 0-based?

Hi Aishwarya,

The field

`SubhaloGrNr`

is "Index into the Group table of the FOF host/parent of this Subhalo."If your language is 0-index based, then yes this index is 0-based.