column  type  UCD  unit  description 
FoFID 
long 
meta.id;meta.main 

The ID of this FoF group, unique within the full simulation.

NumSubgroups 
int 
meta.number 

Number of subhalos in this FoF group.

FirstSubhaloID 
long 
meta.id.assoc 

The unique ID of the most massive subhalo in this FoF
group. This corresponds to an entry in the Subhalo table.

np 
int 
meta.number 

Number of simulation particles in this FoF group.

SnapNum 
int 
time 

The snapshot number where this FoF group was identified.

Redshift 
float 
time 

The redshift of the snapshot to which this FoF group belongs.

x 
float 
pos.cartesian.x 
1/h Mpc 
xcomponent position

y 
float 
pos.cartesian.y 
1/h Mpc 
ycomponent position

z 
float 
pos.cartesian.z 
1/h Mpc 
zcomponent position

m_Mean200 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the halo has an overdensity 200 times the mean density of the simulation.

m_Crit200 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the halo has an overdensity 200 times the critical density of the simulation.

m_TopHat 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the halo has an overdensity corresponding to the value at virialisation in the tophat collapse model for this cosmology.

r_Mean200 
float 
phys.radius 
Mpc/h 
The radius within which the halo has an overdensity 200 times the mean density of the simulation.

r_Crit200 
float 
phys.radius 
Mpc/h 
The radius within which the halo has an overdensity 200 times the critical density of the simulation.

r_TopHat 
float 
phys.radius 
Mpc/h 
The mass radius within which the halo has an overdensity corresponding to the value at virialisation in the tophat collapse model for this cosmology.

phKey 
integer 


PeanoHilbert key, (bits=8), for position in 500/h Mpc
box. See the text on spatial indexes.

zIndex 
integer 


The "bitinterleaved" or "Zcurve" index, corresponding to this halo's position. Same resolution as phKey.
See the text on spatial indexes.

ix 
integer 
pos.cartesian.x 

Zone index along xdirection, based on 50 bins. See the text on spatial indexes.

iy 
integer 
pos.cartesian.y 

Zone index along ydirection, based on 50 bins. See the text on spatial indexes.

iz 
integer 
pos.cartesian.y 

Zone index along zdirection, based on 50 bins. See the text on spatial indexes.

random 
float 


A random number between 0 and 1000000. See the section on
random sampling.
