3.3.4.3  :  FOF

The table stores all the friend-of-friends (FOF) groups extracted from the raw output from Millennium simulation. These FOF groups form the basis that the SUBFIND algorithm uses to detect the subhalos.

columntypeUCDunitdescription
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 1010 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 1010 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 1010 Msun/h The mass within the radius where the FOF group has an overdensity corresponding to the value at virialisation in the top-hat 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 top-hat collapse model for this cosmology.
x float pos.cartesian.x Mpc/h The X-coordinate of the position in comoving coordinates.
y float pos.cartesian.y Mpc/h The Y-coordinate of the position in comoving coordinates.
z float pos.cartesian.z Mpc/h The Z-coordinate of the position in comoving coordinates.
phKey int The Peano-Hilbert index for the position of this FOF group.
See the text on spatial indexes.
zIndex long The "bit-interleaved" or "Z-curve" index, same resolution as phKey.
See the text on spatial indexes.
ix integer pos.cartesian.x Zone index along x-direction, based on 50 bins
See the text on spatial indexes.
iy integer pos.cartesian.x Zone index along y-direction, based on 50 bins
See the text on spatial indexes.
iz integer pos.cartesian.x Zone index along z-direction, 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.