3.3.21.2  :  HaloTree

The table stores subhalos from the mini-Millennium-II Simulation in a representation that allows efficient querying for merger histories. For a description of how merger trees were constructed for the mini-Millennium-II Simulation, see Boylan-Kolchin et al. 2009.

See the documentation on merger trees for further details on the structure of merger trees in the database.
columntypeUCDunitdescription
haloId long meta.id;meta.main The identifier of this subhalo in the merger tree, unique within the full simulation. See the documentation on merger trees for further details on the structure of merger trees in the database.
subhaloId long meta.id; The identifier of this subhalo based on its rank within its parent FOF halo. This column is a foreign key ("pointer") to the entry for this subhalo in the SubHalo table.
fofId long meta.id; The id of FOF group this subhalo belongs to.
This column is a foreign key ("pointer") to the entry for this FOF group in the FOF table. That row will have the same value for its fofIId column.
treeRootId long meta.id.parent The haloId of the subhalo at the root of this merger tree. This is especially useful for improving the performance of queries that aim to retrieve descendants of known progenitors. Note that this root halo is not necessarily at z=0, there are some trees in the database that do not extend down to the last snapshot. See the documentation on merger trees for further details on querying merger trees.
descendantId long meta.id.assoc The haloId of the unique descendant of this subhalo in the merger tree. -1 if there is no descendant. This is the case for all halos at z=0, and for some halos at earlier times (see treeRootId).
lastProgenitorId long meta.id.assoc The last progenitor in the subhalo merger tree rooted in this subhalo. All subhalos with haloId between haloId and lastProgenitorId from the merger tree rooted in this subhalo.
mainLeafId long meta.id.assoc The last progenitor along the main branch in the subhalo merger tree for this subhalo. All subhalos with haloId between this halo's haloId and mainLeafId make up the main progenitor branch for this subhalo.
firstProgenitorId long meta.id.assoc The haloId of the main progenitor of this subhalo.
nextProgenitorId long meta.id.assoc The haloId of the "next progenitor" in the subhalo merger trees (the "next progenitor" of a subhalo S is the next most massive subhalo that has the same descendant as subhalo S).
firstHaloInFOFgroupId long meta.id.assoc haloId of the dominant subhalo of the friend-of-friends group to which this subhalo belongs.
nextHaloInFOFgroupId long meta.id.assoc Id of the next most massive halo within the same FOF group.
snapNum int time The snapshot number where this subhalo was identified.
This column corresponds to the snapnum column in the Snapshots table in the Millennium-II database.
redshift float time The redshift of the snapshot to which this subhalo belongs.
np int meta.number Number of simulation particles in this subhalo.
m_crit200 float phys.mass 1010 Msun/h The mass within the radius where the subhalo has an overdensity 200 times the critical density of the simulation.
Note: this value is only defined for subhalos with haloId=firstHaloInFOFgroupId.
m_mean200 float phys.mass 1010 Msun/h The mass within the radius where the subhalo has an overdensity 200 times the mean density of the simulation.
Note: this value is only defined for subhalos with haloId=firstHaloInFOFgroupId.
m_tophat float phys.mass 1010 Msun/h The mass within the radius where the subhalo has an overdensity corresponding to the value at virialisation in the top-hat collapse model for this cosmology.
Note: this value is only defined for subhalos with haloId=firstHaloInFOFgroupId.
x float pos.cartesian.x Mpc/h The X-coordinate of the subhalo's position in comoving coordinates.
y float pos.cartesian.y Mpc/h The Y-coordinate of the subhalo's position in comoving coordinates.
z float pos.cartesian.z Mpc/h The Z-coordinate of the subhalo's position in comoving coordinates.
ix integer pos.cartesian.x Zone index along x-direction, based on 20 bins
See the text on spatial indexes.
iy integer pos.cartesian.x Zone index along y-direction, based on 20 bins
See the text on spatial indexes.
iz integer pos.cartesian.x Zone index along z-direction, based on 20 bins
See the text on spatial indexes.
phKey int The Peano-Hilbert index for the position of this subhalo.
velX float phys.veloc km/sec The X-component of the subhalo's peculiar velocity.
velY float phys.veloc km/sec The Y-component of the subhalo's peculiar velocity.
velZ float phys.veloc km/sec The Z-component of the subhalo's peculiar velocity.
vDisp float phys.veloc.dispersion km/sec The 1-D velocity dispersion of the subhalo, computed from all of the subhalo particles.
vMax float phys.veloc.rotat km/sec Maximum of the circular velocity curve vCirc, where
vCirc2=G M(< r)/r
vMaxRad float Mpc/h The radius at which the circular velocity maximum vMax is attained
spinX float phys.veloc.ang (Mpc/h) (km/sec) The X-component of the spin of the subhalo.
spinY float phys.veloc.ang (Mpc/h) (km/sec) The Y-component of the spin of the subhalo.
spinZ float phys.veloc.ang (Mpc/h) (km/sec) The Z-component of the spin of the subhalo.
mostBoundID long meta.id.assoc The id of the most bound particle of this subhalo.
fileNr int meta.file;meta.id Original file number in which the subhalo was defined. See the documentation on identifiers for its role in defining the haloId.
subhaloIndex int meta.id.assoc Index of this subhalo in the file identified by fileNr.
subhaloFileId long meta.id; This column corresponds to the subhaloFileId in the SubHalo table and gives an alternative way of identifying that halo. This is an older way of identifying that subhalo, it is better to use the subhaloId column instead.
halfmassRadius float phys.size.radius Mpc/h Radius containing half of the mass of the subhalo.
random integer Random number between 0 and 1000000 using java.lang.Math.random().
See the page on random sampling.
treeId long meta.id.parent The unique identifier of the L-Galaxies galaxy formation "tree" to which this subhalo belongs.
See the page on the MPA trees