Notice: Illustris[TNG] data and websites will be offline for maintenance Sep 1 (Monday), 2025, from 3am-9am EST.

Get halo ID from subhalo ID

Vinu Vikraman
  • 7 Apr

Hello,

I want to find subhalos belong to halos. I didn't find any 'halo IDs' like 'SubhaloIDs' in the group files. I read that the 'GroupFirstSub' parameter is to find the primary subhalo of the halo. Is 'GroupFirstSub' the halo ID?

Best,
Vinu

Dylan Nelson
  • 7 Apr

For a given halo, the list of its subhalo IDs is given by the numbers from GroupFirstSub to GroupFirstSub + GroupNsubs.

(GroupFirstSub is a subhalo ID, not a halo ID).

Vinu Vikraman

Thank you Dylan.

I have one more doubt.

Halos = il.groupcat.loadHalos(basePath, 99)

I understood that the index of the 'Halos' is the Halo ID.

SubHalos = il.groupcat.loadSubhalos(basePath, 99)

Is Subhalo ID the index of the 'SubHalos' table?

Dylan Nelson
  • 8 Apr

Yes, in both cases, ID means index.

Vinu Vikraman
  • 9 Apr

Thanks Dylan.

  • Page 1 of 1