FOF
The FOFtables contain the halo catalogues which were produced by Stefan Gottlöber using the FriendsofFriends algorithm described in Halos gone MAD: The Halo Finder Comparison Project by Alexander Knebe et al. 2010.
FOF tables exist for different linking lengths, please look up the values in the corresponding table overview for each simulation in the Simulations chapter.
All FOF tables share the same structure as given below. All halos containing at least 20 particles are included.
Column  Type  UCD  Unit  Description 

fofId  bigint  meta.id; meta.main  unique id for FOFgroup usually calculated like this: fofId = (snapnum*10 + level)*10^{8} +(rank in FOFfile) but powers of 10 vary with the simulation to which the FOF catalogue belongs 

snapnum  smallint  time.epoch  number of snapshot; look into redshiftstable to find the corresponding redshift  
level  smallint  level of substructure, indicates the different linking lengths; also see linkLengthtable  
NInFile  int  meta.id  line number of FOFgroup in original catalogue file (= rank in file)  
x  real  pos.cartesian.x  1/h Mpc  comoving position, xcomponent 
y  real  pos.cartesian.y  1/h Mpc  comoving position, ycomponent 
z  real  pos.cartesian.z  1/h Mpc  comoving position, zcomponent 
vx  real  phys.veloc; pos.cartesian.x  km/s  peculiar velocity, xcomponent 
vy  real  phys.veloc; pos.cartesian.y  km/s  peculiar velocity, ycomponent 
vz  real  phys.veloc; pos.cartesian.z  km/s  peculiar velocity, zcomponent 
np  int  meta.number  number of particles inside the FOF group (“halo”)  
mass  real  phys.mass  1/h Msun  total mass of the FOF group 
size  real  phys.size.radius  1/h Mpc  “radius” of the FOF group, if it were a sphere, computed based on the volume 
disp  real  phys.dispMeasure  1/h Mpc  dispersion 
disp_v  real  phys.veloc.dispersion  km/s  velocity dispersion 
delta  real  phys.density  rho_b  overdensity (mass/volume) in terms of mean background density 
spin  real  spin parameter (Gottlöber & Yepes 2007, ApJ 664, 117)  
angMom_x  real  phys.angMomentum; pos.cartesian.x  1/h^{2} Msun Mpc km/s  angular momentum, xcomponent 
angMom_y  real  phys.angMomentum; pos.cartesian.y  1/h^{2} Msun Mpc km/s  angular momentum, ycomponent 
angMom_z  real  phys.angMomentum; pos.cartesian.z  1/h^{2} Msun Mpc km/s  angular momentum, zcomponent 
angMom  real  phys.angMomentum  1/h^{2} Msun Mpc km/s  absolute value of angular momentum 
axis1  real  major axis of the ellipsoidal shape, not normalized  
axis2  real  intermediate axis of the ellipsoidal shape, not normalized  
axis3  real  minor axis of the ellipsoidal shape, not normalized  
axis1_x  real  direction of major axis, unit eigenvector of the inertia tensor, xcomponent  
axis1_y  real  direction of major axis, ycomponent  
axis1_z  real  direction of major axis, zcomponent  
axis2_x  real  direction of intermediate axis, unit eigenvector of the inertia tensor, xcomponent  
axis2_y  real  direction of intermediate axis, ycomponent  
axis2_z  real  direction of intermediate axis, zcomponent  
axis3_x  real  direction of minor axis, unit eigenvector of the inertia tensor, xcomponent  
axis3_y  real  direction of minor axis, ycomponent  
axis3_z  real  direction of minor axis, zcomponent  
ix  int  pos.cartesian.x  spatial index, xdirection  
iy  int  pos.cartesian.y  spatial index, ydirection  
iz  int  pos.cartesian.z  spatial index, zdirection  
phkey  int  PeanoHilbert key 
Example
Get the 10 most massive FOF groups at z=0 from the MDR1database:
SELECT * FROM MDR1.FOF WHERE snapnum = 85 ORDER BY mass DESC LIMIT 10
This query retrieves the first 10 records from the FOFtable for redshift 0 (snapshot number 85) after sorting them by decreasing mass and hence returns the most massive objects.