The MUSIC project is a collaboration between UAM, Sapienza and the Leibniz Institute of Astrophysics at Potsdam

The MUSIC project consists of two sets of resimulated clusters extracted from two large volume simulations:

The MareNostrum Universe, a non-radiative SPH simulation with 2 billion particles (10243 gas and dark matter) in a 500 h−1 Mpc cubic box. (Gottlober & Yepes 2007)

The MultiDark Simulation, a dark-matter only N-body simulation with 20483 particles in a 1 Gpc h−1 cubic box.

These two simulations have slightly different cosmologies. The Marenostrum Universe (MU) was made with the cosmological parameters that were compatible with WMAP1 results (ΩM=0.3, Ωb=0.045, ΩΛ=0.7, σ8=0.9, n=1.0, h=0.7) while the MultiDark run was done using the best-fit cosmological parameters to WMAP7 + BAO + SNI ( ΩM=0.27, Ωb=0.0469, ΩΛ=0.73, σ8=0.82, n=0.95, h=0.7).

The procedure to select the interested objects in those two simulations was also different. For the MareNostrum clusters we mainly selected them based on the dynamical state (relaxed
vs bullet-like clusters). For the MultiDark clusters, we made a mass limited selection, taking all clusters with masses above 1015 h−1Mat z=0.

The zooming technique (Klypin et al. 2001) was used to produce the initial conditions of the resimulated objects.  We found all particles within a sphere of 6 Mpc radius around the center of each selected object at z=0 from a low resolution version (2563 particles) of the two simulations. This set of particles was then mapped back onto the initial conditions to find out the lagrangian region corresponding to a 6 h−1Mpc radius sphere centered at the center of mass of the clusters at z=0. The initial conditions of the original simulations were generated in a finer mesh of 20483 (for the MareNostrum) and 40963 (for the MultiDark) sizes. Therefore, we improved the mass resolution of the resimulated objects by a factor of 8 with respect to the original full box simulations. We kept the highest mass-refinement level within the lagrangian region of each cluster, and then cover it with shells of increasing mass particles down to the lower resolution level of 2563.  Thus, for the MultiDark clusters, we have dark matter particles of 5 different mass refinements (from 40963 to 2563) while for the MareNostrum clusters we have 4 different mass species. The gas SPH particles were added only to the highest refinement level.

The SPH particle positions were slightly displaced from their parent dark matter by 0.4 times the mean inter particle distance in the 3 spatial directions, and they were given the same initial velocity as their dark matter counterparts.



 This first subset is composed of 164 resimulated clusters extracted from the MU.  Half of them were selected to be "bullet-like" clusters.  We define a "bullet-like" object when the  physical 2D separation of the two main components:  gas  and dark matter in larger than 200 kpc, as we measure in the real Bullet cluster (see Forero-Romero et al 2011 for details).

In order to have a morphological counterpart to these extremely disturbed systems, we also selected another 82 clusters which exhibit the following relaxed conditions: the displacement between dark and baryonic matter is smaller than 200 kpc and they are composed of a single massive cluster with no big substructures
(i.e. all substructures inside the virial radius must have masses smaller than 10% of the total mass). The relaxed clusters were chosen to have masses similar to those of the bullet systems: in this way every bullet-like cluster has a relaxed companion of the same mass. All the selected clusters were resimulated using the zooming technique and radiative physics, including radiative cooling, heating processes of the gas arisen from a UV background, star formation and supernovae feedback. The particle mass of dark matter was set to mDM=1.03×109h−1Mand the mass of SPH gas particle to mgas=1.82×108h−1M. Due to the relative small size of the computational box of the MU simulation, very few clusters of MUSIC-1 subset have masses  bigger than 1015 h−1M. The cluster masses of MUSIC-1 span from Mvir=2×1015h−1M to  Mvir=1014h−1M.


This  constitutes the largest sample of the MUSIC clusters.  We have selected a mass limited  sample of  cluster-like objects from the low resolution version of the MULTIDARK 1Gpc simulation. In total we simulated 283 differentlagrangian regions corresponding to  spheres of 6/h Mpc radius centred on the 283 most massive clusters  found in the  MULTIDARK simulation.   All these massive clusters were resimulated both with and without radiative physics using the techniques explained above. The mass resolution for these simulations corresponds to mDM = 9.01 × 108h−1 M and to mSPH = 1.9 × 108h−1 M. The gravitational softening was set to 6 h−1 kpc for the SPH and dark matter particles in the high-resolution areas. Several low-mass clusters have been found close to the large ones and not overlapping with them. Thus, the total number of resimulated objects is considerably larger. In total, we obtained 535 clusters with M > 1014h−1 M at z = 0 and more than 2000 group-like objects with masses in the range 1013h−1 M < Mv < 1014h−1 M. All of these resimulations have been done both with NR physics, using the same technique, and with the same resolution as the radiative ones. 



A new sample of  cluster size objects  has been selected from the Multidark simulation. We have extended the mass range towards smaller mass objects. Since the number of objects  grows as power law  towards small masses, we cannot pretend to resimulate a complete  volume sample. Instead, we have  chosen the new set of objects according to two criteria. The mass range of the z=0 central object  must  be between   5x1013h−1 M < Mv < 1015h−1 M and the objects cannot be closer than 12 Mpc  to the already resimulated objects of MUSIC-2 sample.  In this way, the group like objects  will be in rather isolated areas, as compared with similar mass objects found in the zoomed areas of the resimulations of MUSIC-2.    A total of 545 new initial conditions for  the zoomed regions corresponding to 6 /h Mpc spherical radius around the clusters at z=0 have been generated. The radiative runs with  stellar feedbacks are being produced and we expect to run also the same simulations with AGN feedback as well.    The images  of these simulations can be found in the Pictures section of the menu 



In spring 2016 we have started to produce a new set of resimulated clusters  that constitute the 3rd  version of the MUSIC project.  In this case we have used  the MDPL2,  a new MULTIDARK dark matter only simulation box of 1Gpc /h  run with 38403  particles in Planck cosmological parameters. We have selected  more than 300 spherical regions of 15/h Mpc radius centred around the most massive clusters found in this simulation.  This time we used the new GINNUNGAGAP code to generate zoomed initial conditions for these  regions. As always, we have  computed the  lagrangian region of the particles within these spheres and made initial conditions with  the full  3840 resolution within these regions and then  a series of different shells of lower mass resolution particles  of 19203, 9603, 4803 and 2403   respectively.    The complete set of resimulated regions have already been run with the standard Radiative physics model of Springel & Hernquist (2003).  The  images for the different   simulations can be seen in the  Pictures   section by clicking in the MUSIC-PLANCK  button. Also, there is a movie showing the formation of each cluster from z=17 to z=0. Click in Videos and then in MUSIC-PLANCK.

For more information about this database, please take a look at Cui et al 2018 MNRAS paper where we describe in more detail this set of simulations.

Initial conditions for the 300th  clusters are available on demand. If you have got access to them, just click here

For further information on the 300th simulation project please visit the website of the collaboration: