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

The id of this FOF group, unique within the full simulation.

snapNum 
int 
time 

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

redshift 
float 
time 

The redshift of the snapshot to which this halo belongs.

np 
int 
meta.number 

Number of simulation particles in this FOF group.

numSubGroups 
int 
meta.number 

The number of sub halos found in this FOF group with the SUBFIND algorithm.
These subhalos are stord in the FofSubHalo table in this same database.

firstSubHaloId 
long 

meta.id.assoc 
The identifier of the most massive subhalo in this FOF group.
NB This is not equivalent to the fofID in MPAGalxies..DeLucia2006a or the firstHaloInFOFGroupId in MPAHalotrees..MHalo! 
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.mass 
Mpc/h 
The (comoving) radius within which the FOF group 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 FOF group has an overdensity 200 times the critical density of the simulation.

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

m_tophat200 
float 
phys.mass 
10^{10} Msun/h 
The mass within the radius where the FOF group has an overdensity corresponding to the value at virialisation in the tophat collapse model for this cosmology.

r_tophat200 
float 
phys.mass 
Mpc/h 
The (comoving) radius within which the FOF group has an overdensity corresponding to the value at virialisation in the tophat collapse model for this cosmology.

x 
float 
pos.cartesian.x 
Mpc/h 
The Xcoordinate of the position in comoving coordinates.

y 
float 
pos.cartesian.y 
Mpc/h 
The Ycoordinate of the position in comoving coordinates.

z 
float 
pos.cartesian.z 
Mpc/h 
The Zcoordinate of the position in comoving coordinates.

phKey 
int 


The PeanoHilbert index for the position of this FOF group.
See the text on spatial indexes.

zIndex 
long 


The "bitinterleaved" or "Zcurve" index, 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.x 

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

iz 
integer 
pos.cartesian.x 

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

random 
integer 


Random number between 0 and 1000000 (using java.lang.Math.random()).
See the page on random sampling.
