The database MPAHalotrees contains various tables storing sub-halo merging trees
in a representation that allows efficient
querying for merger histories. For a description how these merger trees were constructed see
Springel2005a
and DeLucia2006b.
For a description of how the merger trees are stored in these tables to allow efficient querying of
their structure and example queries, see the discussion on
this page.
There are currently 5 tables stored in this database, all of them with the same structure documented in the table below.
The tables MR, MRII, MR7 store the subhalos extracted from the Millennium, Millennium-II and Millennium-WMAP7 simulations.
(See here for the description of the simulations).
The tables MRscWMAP7 and MRIIscWMAP7 contain the merger trees from MR and MRII respectively,
but scaled to WMAP 7 cosmology according to the algorithm presented in
Angulo & White (2010).
Note, before the update to the database from 2013-02-26, the table currently named MR was represented by
a table named MHalo. This table is not exactly the same as the current version, but for backwards compatibility
we make MR available also as MHalo. Similarly, for the time being we left the original version of the Millennium-II merger trees in the
table MillenniumII..HaloTree.
For queries aiming to retrieve halos at a particular snapshot one should use the snapnum column to select
the precise snapshot. That column is always used in table indexes
Note that the relation between the snapnum and redshift values varies between the different tables.
See the tables in the Snapshots database
for tables with the different snaphot lists for the precise relations.
| column | type | UCD | unit | description |
| haloId |
long |
meta.id;meta.main |
|
The primary key of this sub-halo 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.
|
| subhaloFileId |
long |
meta.id; |
|
Column identifying the counterpart of this subhalo in the original SUBFIND result files.
For the tables MR and MRscWMAP7 this is a
foreign key identifying
the subhaloId column in the
MField..FOFSubHalo table.
For MRII and MRIIscWMAP7 this is a
foreign key identifying
the subhaloFileId column in the
MillenniumII..SubHalo table.
For MR7 there is as yet no counterpart table in the database for this foreign key.
|
| treeRootId |
long |
meta.id.parent |
|
Foreign key identifying the subhalo
at the root of the merger tree containing this halo. This column 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 |
|
Foreign key identifying 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 |
|
Foreign key identifying
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.
See the documentation on merger trees for further
details on the structure of merger trees in the database. |
| mainLeafId |
long |
meta.id.assoc |
|
Foreign key identifying
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.
See the documentation on merger trees for further
details on the structure of merger trees in the database. |
| firstProgenitorId |
long |
meta.id.assoc |
|
Foreign key identifying the main progenitor of this subhalo.
See this page and
this page for more details on the definition
of this column.
|
| nextProgenitorId |
long |
meta.id.assoc |
|
Foreign key identifying 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).
See this page for more details on the definition
of this column.
|
| firstHaloInFOFgroupId |
long |
meta.id.assoc |
|
Foreign key identifying the dominant subhalo of the friend-of-friends group to which this subhalo belongs.
See this page for more details on the definition
of this column.
|
| nextHaloInFOFgroupId |
long |
meta.id.assoc |
|
Foreign key identifying the next most massive halo within the same FOF group.
|
| snapNum |
int |
time |
|
The snapshot number where this subhalo was identified.
This column is a
foreign key to the snapnum column in the
table
in the Snapshots database
with the same name as the current HaloTrees table.
I.e. Snapshots..MR,Snapshots..MRII,Snapshots..MR7, Snapshots..MRscWMAP7 or Snapshots..MRIIscWMAP7
|
| 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 |
This column has two different usages depending on whether the current halo is at the center of its FOF group or not.
A halo is a memer of its FOF group iff haloId=firstHaloInFOFgroupId.
In that case this column represents the mass within the radius where the subhalo has an overdensity 200 times the critical density of the simulation.
In case the halos is not a center, i.e. if it is a satellite halo, this column stores the m_crit200 value of the
progenitor subhalo on the main branch that was for the last time at the center of ots FOF group.
For more information about this definition see this page.
In the rare case where there is no main-progenitor that was a center of its FOF group (i.e. if the subhalo was born as satellite halo), the value of this column is set to 0.
|
| m_mean200 |
float |
phys.mass |
1010 Msun/h |
For halos at the center of their FOF group, this column stores the mass
within the radius where the subhalo has an overdensity 200 times the mean density of the simulation.
For satellite halos it stores the m_mean200 value of the last main-progenitor that was a center of its subhalo (see also the description of the m_crit200 column).
If the halo never was a center the value is set to 0.
|
| m_tophat |
float |
phys.mass |
1010 Msun/h |
For halos at the center of their FOF group, this column stores 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.
For satellite halos it stores the m_tophat value of the last main-progenitor that was a center of its subhalo
(see also the description of the m_crit200 column).
If the halo never was a center the value is set to 0.
|
| 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.
|
| phKey |
int |
|
|
The Peano-Hilbert index based on a 2563 grid for the position of this subhalo.
See this page for more information.
For the MR simulation, this column together with the snapnum column is a
foreign key identifying the cell
in the density field in the MField..MField table.
|
| 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
The maximum is determined from the expression calculated for each particles in the halo,
i.e. from: maxi(G*(i-1)*mp/ri) |
| 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 |
REAL |
phys.size.radius |
Mpc/h |
Radius containing half of the mass of the subhalo.
|
| lastCentralId |
BIGINT |
meta.id; |
|
Foreign key identifying the most recent progenitor subhalo on the main branch that was at the center of its friends-of-friends group.
I.e. if the current subhalo is a center, this value will equal its own haloId.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case this column has the value -1.
The m_crit200, m_mean200, m_tophat columns store the corresponding mass of this identified halo, whether it is
the halo itself or a progenito. |
| lastCentralSnap |
INTEGER |
TBD |
|
The snapnum of the most recent progenitor subhalo on the main branch that was at the center of its friends-of-friends group.
I.e. if the current subhalo is a center, this value will equal its own snapnum.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is also set at the non-physical value of -1. |
| lastCentralVmax |
REAL |
TBD |
|
The vMax of the most recent progenitor subhalo on the main branch that was at the center of its friends-of-friends group.
I.e. if the current subhalo is a center, this value will equal its own vMax.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is set to 0. |
| peakMassId |
BIGINT |
meta.id; |
|
Foreign key identifying the progenitor subhalo on the main branch that was a central subhalo of its FOF group and has the largest value of m_crit200.
I.e. if the current subhalo is a center and the most massive of all such halos on the main branch "above"
this halo, this value will equal its own haloId.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is also set to -1. |
| peakMassSnap |
INTEGER |
TBD |
|
The snapnum of the halo identified by the peakMassId column.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is also set to -1. |
| peakMassMcrit |
REAL |
TBD |
|
The m_crit200 value of the halo identified by the peakMassId column.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is set to 0. |
| peakMassVmax |
REAL |
TBD |
|
The vMax value of the halo identified by peakMassId column, i.e. of the most massive progenitor.
IMPORTANT there are rare cases where a subhalo was never at the center of a FOF group, in that case the lastCentralId column
has the value -1, and the current column's value is set to 0. |
| treeId |
BIGINT |
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 for a description of these "trees".
The value of this column is related to the haloId. For MR, MR7 and MRscWMAP7 the relation is
treeId=floor(haloid/100000000)
For MRII and MRIIscWMAP7 the relation is
treeId=floor(haloid/1000000000)
|
