Groups with Group_M_Crit_200 = 0 in IllustrisTNG 300?

joanne cohn

18 May '22

Hi,
I was looking at higher redshifts (e.g. 5,6,7) and there seem to be a lot of Groups with M_200c = 0 ( >8% of the groups). Are these really diffuse halos or something else? They've got GroupMass>0. Or maybe I've done something weird, or it's all explained somewhere, sorry if it's either of those...
Thanks!

Dylan Nelson

20 May '22

Dear Joanne,

I recall that spherical overdensity quantities are not computed for groups which have no (central) subhalo. So this must only occur for very small groups, where Subfind did not in the end find any gravitationally bound structure with at least 20 particles/cells.

joanne cohn

20 May '22

Thanks a lot! It's a large fraction (8%) but of course the masses are so small at higher redshift (these have median GroupMass 9.13 M_o). Very helpful!

Hi,

I was looking at higher redshifts (e.g. 5,6,7) and there seem to be a lot of Groups with M_200c = 0 ( >8% of the groups). Are these really diffuse halos or something else? They've got GroupMass>0. Or maybe I've done something weird, or it's all explained somewhere, sorry if it's either of those...

Thanks!

Dear Joanne,

I recall that spherical overdensity quantities are not computed for groups which have no (central) subhalo. So this must only occur for very small groups, where Subfind did not in the end find any gravitationally bound structure with at least 20 particles/cells.

Thanks a lot! It's a large fraction (8%) but of course the masses are so small at higher redshift (these have median GroupMass 9.13 M_o). Very helpful!