Can Coupled Dark Energy Speed Up the Bullet Cluster?

Abstract

It has been recently shown that the observed morphological properties of the Bullet Cluster can be accurately reproduced in hydrodynamical simulations only when the infall pairwise velocity V_{c} of the system exceeds 3000 km/s (or at least possibly 2500 km/s) at the pair separation of 2R_{vir}, where R_{vir} is the virial radius of the main cluster, and that the probability of finding such a bullet-like system is extremely low in the standard LCDM cosmology. We suggest here the fifth-force mediated by a coupled Dark Energy (cDE) scalar field as a possible velocity-enhancing mechanism and conduct a comprehensive investigation of its effect on the infall pairwise velocities of the bullet-like systems identified analyzing the halo catalogs from the CoDECS (COupled Dark Energy Cosmological Simulations) public database. Five different cDE models are considered: three with constant coupling and exponential potential, one with exponential coupling and exponential potential, and one with constant coupling and supergravity potential. For each model, after selecting the bullet-like systems from the clusters of clusters identified at z=0, we determine the probability density distribution of the infall velocities of the bullet-like systems at the pair separations of (2-3)R_{vir}. Approximating each probability density distribution as a Gaussian, we calculate the cumulative probability of finding a bullet-like system with V_{c}>= 3000km/s or V_{c}>= 2500km/s. Our results show that in all of the five cDE models the cumulative probabilities increase compared to the LCDM case and that in the model with exponential coupling P(V_{c}>=2500 km/s) exceeds 10^{-4}. The physical interpretations and cosmological implications of our results are provided.