Bullet Cluster: A Challenge to ΛCDM Cosmology
Abstract
To quantify how rare the bulletclusterlike highvelocity merging systems are in the standard Λ cold dark matter (CDM) cosmology, we use a largevolume (27 h ^{3} Gpc^{3}) cosmological Nbody MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall velocity distribution is given at (13)R _{200} of the main cluster (where R _{200} is similar to the virial radius), and thus it gives the distribution of realistic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the noncosmological hydrodynamical simulations of 1E065756 in the literature. The latest parameter search carried out by Mastropietro & Burkert has shown that an initial velocity of 3000 km s^{1} at about 2R _{200} is required to explain the observed shock velocity, Xray brightness ratio of the main and subcluster, Xray morphology of the main cluster, and displacement of the Xray peaks from the mass peaks. We show that such a high infall velocity at 2R _{200} is incompatible with the prediction of a ΛCDM model: the probability of finding 3000 km s^{1} in (23)R _{200} is between 3.3 × 10^{11} and 3.6 × 10^{9}. A lower velocity, 2000 km s^{1} at 2R _{200}, is also rare, and moreover, Mastropietro & Burkert have shown that such a low initial velocity does not reproduce the Xray brightness ratio of the main and subcluster or morphology of the main cluster. Therefore, we conclude that the existence of 1E065756 is incompatible with the prediction of a ΛCDM model, unless a lower infall velocity solution for 1E065756 with lsim1800 km s^{1} at 2R _{200} is found.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 2010
 DOI:
 10.1088/0004637X/718/1/60
 arXiv:
 arXiv:1003.0939
 Bibcode:
 2010ApJ...718...60L
 Keywords:

 cosmology: theory;
 largescale structure of universe;
 methods: statistical;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 accepted for publication in ApJ, lightcone effect discussed, minor typos corrected, 22 pages, 6 figures, 3 tables