From the following excerpt of the Data Specifications:
If zero, this subhalo should generally be excluded, and is not thought to be of cosmological origin.
...
If one, this subhalo should be considered a 'galaxy' or 'satellite' of cosmological origin.
(Note: always true for centrals).
Am I correct in interpreting this as: "SubhaloFlag" is always equal to 1 for central/primary subhalos?
And therefore subhalos whose indices are returned by "GroupFirstSub" (which are central/primary?) should have 1 as their "SubhaloFlag"?
Using the indices given by "GroupFirstSub", I find some instances where "SubhaloFlag" is 0.
I am using TNG300-1 and I give one example below.
Yes you are correct, this does seem strange. I cannot remember immediately how this could happen.
What snapshot of TNG300-1? For snapshot 99, I see GroupFirstSub[841] = 648064.
Rui Lan Zhang
4 Jul '22
Sorry, I forgot to mention the snapshot. It's snapshot 43.
Dylan Nelson
6 Jul '22
Hi Rui,
You're right, there are a small number of central subhalos with SubhaloFlag==1.
The actual definition of this field is:
# construct SubhaloFlag (i.e. define)
# flag == True if satisfies all three conditions, otherwise False
SubhaloFlag = data['isSat_atForm'] * \
(data['rad_rvir_atForm'] < 1.0) * \
(data['dmFrac_atForm'] < 0.8)
SubhaloFlag = np.invert( SubhaloFlag.astype('bool') ) # 0=bad, 1=good
In particular, a subhalo can be flagged bad so long as it is a satellite subhalo at its 'time of formation'. I suspect, then, that any central subhalos which are flagged were previously satellites, i.e. these are backsplash-like galaxies (and/or structures which were then ejected out of the halo due to gravitational dynamics).
From the following excerpt of the Data Specifications:
Am I correct in interpreting this as:
"SubhaloFlag"is always equal to1for central/primary subhalos?And therefore subhalos whose indices are returned by
"GroupFirstSub"(which are central/primary?) should have1as their"SubhaloFlag"?Using the indices given by
"GroupFirstSub", I find some instances where"SubhaloFlag"is0.I am using TNG300-1 and I give one example below.
Yes you are correct, this does seem strange. I cannot remember immediately how this could happen.
What snapshot of TNG300-1? For snapshot 99, I see
GroupFirstSub[841] = 648064.Sorry, I forgot to mention the snapshot. It's snapshot 43.
Hi Rui,
You're right, there are a small number of central subhalos with
SubhaloFlag==1.The actual definition of this field is:
In particular, a subhalo can be flagged bad so long as it is a satellite subhalo at its 'time of formation'. I suspect, then, that any central subhalos which are flagged were previously satellites, i.e. these are backsplash-like galaxies (and/or structures which were then ejected out of the halo due to gravitational dynamics).
Ah I see. Thank you for looking into this for me!