BigMDPL with Rockstar released

The simulation BigMDPL was recently added and comes now with the full Rockstar table, a halo catalog with merger tree information for 80 snapshots. The Rockstar table has the same format as for the other simulations. If you use it for your scientific work, please cite this dataset as doi:10.17876/cosmosim/bigmdpl/001.

Here is a slice at snapshot number 79 (redshift 0) for z ~ 1786 Mpc/h, where the most massive halo lies. It shows a density-colored plot of dark matter halo positions (scaled with their size and made half transparent) extracted from the Rockstar table.

Since the Rockstar table contains also the links between halos and their progenitors and the depthFirstIds, you can retrieve all progenitors of a dark matter halo with just one SQL query. Here’s an example for the most massive halo at redshift 0 in that simulation:

Get progenitors of a halo

SELECT p.rockstarId, p.snapnum, p.x, p.y, p.z, p.Mvir, p.Rvir 
FROM BigMDPL.Rockstar AS p, 
  (SELECT depthFirstId, lastProg_depthFirstId 
   FROM BigMDPL.Rockstar WHERE rockstarId=14568342049) AS r 
WHERE p.depthFirstId BETWEEN r.depthFirstId AND r.lastProg_depthFirstId 
ORDER BY p.snapnum

This query makes use of the properties of depthFirstIds: all halos with ids between the current halos id and its last progenitor id (lastProg_depthFirstId) must be progenitors.

Here’s a picture of the 3D distribution of these progenitors, colored by snapshot number. See how the halos merged at the final timestep into one big object?

If you want to track back the halo’s main progenitors only (e.g. for checking the accretion of mass, evolution of spin etc.), you can use the mainLeaf_depthFirstId instead.

Get the main branch

SELECT p.* FROM BigMDPL.Rockstar AS p, 
  (SELECT depthFirstId, mainLeaf_depthFirstId 
   FROM BigMDPL.Rockstar WHERE rockstarId=14568342049) AS r
WHERE p.depthFirstId BETWEEN r.depthFirstId AND r.mainLeaf_depthFirstId 
ORDER BY p.snapnum

This uses the mainLeaf_depthFirstId which is the depthFirstId of the last leaf on the main branch, i.e. it’s the earliest found main progenitor (with mmp-flag = 1).

Check out the documentation page on merger trees to learn more about the structure of merger trees in the database.

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