column  type  UCD  unit  description 
fofId 
long 
meta.id; 

The id of this FOF group.

snapNum 
int 
time 

The snapshot number where this FOF group was identified.
This column corresponds to the snapnum column in
the Snapshots table in the MillenniumII database.

redshift 
float 
time 

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

np 
int 
meta.number 

Number of simulation particles in this FOF group.

mass 
float 
phys.mass 
10^{10} Msun/h 
The mass of the halo, calculated as np times the mass per particle.

x 
float 
pos.cartesian.x 
Mpc/h 
The Xcoordinate of this FOF group's position in comoving coordinates (1).

y 
float 
pos.cartesian.y 
Mpc/h 
The Ycoordinate of this FOF group's position in comoving coordinates (1).

z 
float 
pos.cartesian.z 
Mpc/h 
The Zcoordinate of this FOF group's position in comoving coordinates (1).

ix 
integer 
pos.cartesian.x 

Zone index along xdirection, based on 20 bins (2)
See the text on spatial indexes.

iy 
integer 
pos.cartesian.x 

Zone index along ydirection, based on 20 bins (2)
See the text on spatial indexes.

iz 
integer 
pos.cartesian.x 

Zone index along zdirection, based on 20 bins (2)
See the text on spatial indexes.

phKey 
int 


The PeanoHilbert index for the position of this halo.

cmx 
float 
pos.cartesian.x 
Mpc/h 
The Xcoordinate of this FOF group's center of mass in comoving coordinates.

cmy 
float 
pos.cartesian.y 
Mpc/h 
The Ycoordinate of this FOF group's center of mass in comoving coordinates.

cmz 
float 
pos.cartesian.z 
Mpc/h 
The Zcoordinate of this FOF group's center of mass in comoving coordinates.

cvx 
float 
phys.veloc 
km/sec 
The Xcomponent of the peculiar centerofmass velocity of this FOF group.

cvy 
float 
phys.veloc 
km/sec 
The Ycomponent of the peculiar centerofmass velocity of this FOF group.

cvz 
float 
phys.veloc 
km/sec 
The Zcomponent of the peculiar centerofmass velocity of this FOF group.

m_crit200 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the FOF group has an overdensity 200 times the critical density of the simulation.

r_crit200 
float 
phys.radius 
Mpc/h 
The radius within which the FOF group has an overdensity 200 times the critical density of the simulation.

m_mean200 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the FOF group has an overdensity 200 times the mean density of the simulation.

r_mean200 
float 
phys.radius 
Mpc/h 
The radius within which the FOF group has an overdensity 200 times the mean density of the simulation.

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

r_tophat 
float 
phys.radius 
Mpc/h 
The radius within which the FOF group has an overdensity corresponding to the value at virialization in the
tophat collapse model for this cosmology.

numSubs 
integer 


Number of subhalos in this FOF halo. Note that the dominant subhalo counts as a subhalo.

firstSubhaloId 



subhaloId of the dominant subhalo within this FOF group (1 if numSubs=0, i.e. if there are no bound substructures in the FOF group). 