High-resolution simulations of clusters of galaxies

As a starting point, we used the LCDM-GIF simulation, carried out by the Virgo consortium. The following panel shows a slice through the simulation box, centered by Volker Springel on the richest cluster that has formed in the periodic simulation volume. Using GADGET together with Bepi' Tormens zooming initial conditions generator ZIC, we have resimulated this object of mass ~10e15 Msun/h several times, with ever increasing numerical resolution. In the last step, we reached a mass resolution of 4.7e7 Msun/h, with about 20 million particles ending up in the virial radius of the final cluster.

The following two pictures compare the original cluster in the GIF simulation with one of our resimulations. In the latter, the resolution gradually decreases with increasing distance from the center. You may be able to see residuals of the spherical grid structure used in this multi-mass technique towards the edges of the right picture.  However, in the the region of the cluster itself, glass-like initial conditions are used and the resolution is much higher than in the original parent simulation.
The vast increase of resolution makes rich substructure in the cluster visible. Dark matter halos in CDM universes are far from being smooth objects - they exhibit a large number of subhalos. As we've done in picture on the top, we now enlarge the region in the white square still further, thereby zooming in onto the cluster itself....
Here are a few more examples of substructure in our clusters. The blue picture at the bottom shows the cluster in our highest resolution simulation. At the final time at redshift zero, our subhalo identification algorithms are able to identify almost 5000 gravitationally bound subhalos in this object.


If you like, you may download a transparency showing the dark matter substructure in one of our cluster simulations.

Last modified: Jan 20, 2000  vspringel@cfa.harvard.edu