How rare is the bullet cluster?
Abstract
The galaxy cluster 1E 0657-56 has a bullet-like subcluster that is moving away from the centre of the main cluster at high speed. Markevitch et al. (2004) recently estimated a relative velocity of Vbullet = 4500+1100-800 kms-1, based on observations of the bow shock in front of the subcluster. The weak lensing analysis of Clowe, Gonzalez & Markevitch (2004) indicates that a substantial secondary mass peak is associated with this subcluster. We estimate the likelihood of such a configuration by examining the distribution of subhalo velocities for clusters in the Millennium Run, a large Λ cold dark matter (ΛCDM) cosmological simulation. We find that the most massive subhalo has a velocity as high as that of the bullet subcluster in only about one out of every 100 cluster-sized haloes. This estimate is strongly dependent on the precise velocity adopted for the bullet. One of the 10 most massive subhaloes has such a high velocity about 40 per cent of the time. We conclude that the velocity of the bullet subcluster is not exceptionally high for a cluster substructure, and can be accommodated within the currently favoured ΛCDM cosmogony.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2006
- DOI:
- 10.1111/j.1745-3933.2006.00184.x
- arXiv:
- arXiv:astro-ph/0604443
- Bibcode:
- 2006MNRAS.370L..38H
- Keywords:
-
- galaxies: clusters: individual: 1E 0657-56: galaxies: formation: dark matter;
- galaxies: clusters: individual: 1E 0657-56;
- galaxies: formation;
- dark matter;
- Astrophysics
- E-Print:
- 5 pages, 3 figures, accepted for publication in MNRAS