BDM
BDM tables store the halo catalogues determined using the Bound Density Maximum (BDM) algorithm. Two different versions exist, using either the standard overdensity criterion with 360*ρ_{back} (background density; BDMV
) to define halos, or halos are cutoff at 200*ρ_{crit} (critical density; BDMW
).
Halos are divided into two groups: distinct halos and subhalos (see explanation and illustration at Halo finders).
Distinct halos are those which are not lying inside the virial radius of a larger halo (i.e. halos with
larger virial radius) and the value of their hostFlag
is “1”, subhalos get the bdmId of the parent halo.
NOTE: Subhalos which lie at the opposite side of the (periodic) cosmological box from their host are not marked as subhalos in the current version of BDM halos!
Column  Type  UCD  Unit  Description 

bdmId  bigint  meta.id; meta.main  unique id for bdmhalo, e.g.
bdmId = ( snapnum*10^{8} +(number in BDM catalogue) ) The power of 10 can be different for each simulation database. 

snapnum  smallint  time.epoch  number of snapshot  
NInCat  int  meta.id  number of halo in BDM catalogue file (= “Nhalo”)  
hostFlag  bigint  meta.id  index (flag) indicating if substructure or host; 1 for distinct halo, bdmId of parent halo for subhalos  
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 in halo  
Mvir  real  phys.mass  1/h Msun  halo mass – mass of bound particles within Rvir 
Mtot  real  phys.mass  1/h Msun  halo mass – mass of all particles within Rvir 
Rvir  real  phys.size.radius  1/h Mpc; for MDPL: 1/h kpc 
virial radius NOTE: For a small fraction of distinct halos the ‘virial’ radius is smaller than the formal virial radius. This is due to overlapping of distinct halos. If radii of two halos overlap, then the smaller halo has its radius reduced. This affects about 2% of halos. 
Vrms  real  phys.veloc.dispMeasure  km/s  root mean square proper velocities of bound dark matter particles 
Vcir  real  phys.veloc  km/s  maximum circular velocity in the halo 
conc  real  phys.size; arith.ratio  concentration of the halo as found from Vcirc / sqrt(G Mvir / Rvir) assuming a NFW profile


Xoff  real  phys.size; arith.ratio  offset parameter = ratio of (distance from the halo center to the center of mass) to (the virial radius)  
virialRatio  real  arith.ratio  virial ratio = 2 K/Epot  1 , K = kinetic energy, Epot = potential energy


spin  real  spin parameter with K used instead of Etot . Use virialRatio for the definition of Etot .


Rrms  real  phys.size.radius  1/h Mpc; for MDPL: 1/h kpc 
root mean square distance of halo particles Rrms = sqrt(sum(r_i**2))

axisratio_2_1  real  ratio of intermediate to major axis (as estimated in a spherical region via the modified inertia tensor)  
axisratio_3_1  real  ratio of minor to major axis  
axis1_x  real  xcomponent of major axis (eigenvector with largest eigenvalue, from inertia tensor)  
axis1_y  real  ycomponent of major axis  
axis1_z  real  zcomponent of major axis  
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  PeanoHilbertkey, i.e. index along the PeanoHilbert curve 
Example
Get the 10 most massive BDM halos at z=0:
SELECT * FROM MDR1.BDMV WHERE snapnum = 85 ORDER BY Mvir DESC LIMIT 10
This query retrieves the first ten records from the BDMVtable for redshift 0 (snapshot number 85) after sorting them by decreasing mass and hence returns the ten most massive objects.