Abstract / Description of output
The Bullet Cluster has provided some of the best evidence for the
Λ cold dark matter (ΛCDM) model via direct empirical proof
of the existence of collisionless dark matter, while posing a serious
challenge owing to the unusually high inferred pairwise velocities of
its progenitor clusters. Here, we investigate the probability of finding
such a high-velocity pair in large-volume N-body simulations,
particularly focusing on differences between halo-finding algorithms. We
find that algorithms that do not account for the kinematics of infalling
groups yield vastly different statistics and probabilities. When
employing the ROCKSTAR halo finder that considers particle velocities,
we find numerous Bullet-like pair candidates that closely match not only
the high pairwise velocity, but also the mass, mass ratio, separation
distance, and collision angle of the initial conditions that have been
shown to produce the Bullet Cluster in non-cosmological hydrodynamic
simulations. The probability of finding a high pairwise velocity pair
among haloes with Mhalo ≥ 1014
M⊙ is 4.6 × 10-4 using ROCKSTAR, while
it is ≈34 × lower using a friends-of-friends (FoF)-based
approach as in previous studies. This is because the typical spatial
extent of Bullet progenitors is such that FoF tends to group them into a
single halo despite clearly distinct kinematics. Further requiring an
appropriately high average mass among the two progenitors, we find the
comoving number density of potential Bullet-like candidates to be of the
order of ≈10-10 Mpc-3. Our findings suggest
that ΛCDM straightforwardly produces massive, high relative
velocity halo pairs analogous to Bullet Cluster progenitors, and hence
the Bullet Cluster does not present a challenge to the ΛCDM
model.
Original language | English |
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Pages (from-to) | 3030-3037 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 452 |
Issue number | 3 |
DOIs | |
Publication status | Published - 29 Jul 2015 |
Keywords / Materials (for Non-textual outputs)
- methods: numerical
- galaxies: clusters: general
- galaxies: evolution
- galaxies: clusters: individual: The Bullet Cluster
- cosmology: theory
- dark matter