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High-z massive clusters as a test for dynamical coupled dark energy

Marco Baldi, Valeria Pettorino

TL;DR

The paper tests whether high-redshift massive clusters can distinguish $\Lambda$CDM from dynamical dark energy by considering a scalar field that couples to cold dark matter with coupling $\beta$ and potentials $U(\phi)$ of inverse-power-law or exponential forms. Using a modified version of the N-body code $GADGET$-2, they simulate constant and variable couplings starting from gaussian primordial perturbations consistent with $WMAP7$, and compute cumulative halo mass functions across redshifts. They find that coupling boosts the abundance of massive halos by up to $\sim 10$ for constant coupling and $\sim 3$ for variable coupling around $z \approx 1.5$, and raises $\sigma_8$ today by up to about $0.91$ for the strongest coupling. These results imply that high-$z$ cluster counts can distinguish coupled dark energy from a cosmological constant, offering a potential explanation for the Jee et al. cluster without invoking primordial non-Gaussianity.

Abstract

The recent detection (Jee etal 2009) of the massive cluster XMMU J2235.3-2557 at a redshift z = 1.4, with an estimated mass M = 6.4 +- 1.2 X 10^14 M_sol, has been claimed to be a possible challenge to the standard LCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be 0.005 if a LCDM model with gaussian initial conditions is assumed, resulting in a 3 sigma discrepancy from the standard cosmological model. In this paper we propose to use high redshift clusters as the one detected in Jee etal 2009 to compare the cosmological constant scenario with interacting dark energy models. We show that coupled dark energy models, where an interaction is present between dark energy and cold dark matter, can significantly enhance the probability to observe very massive clusters at high redshift.

High-z massive clusters as a test for dynamical coupled dark energy

TL;DR

The paper tests whether high-redshift massive clusters can distinguish CDM from dynamical dark energy by considering a scalar field that couples to cold dark matter with coupling and potentials of inverse-power-law or exponential forms. Using a modified version of the N-body code -2, they simulate constant and variable couplings starting from gaussian primordial perturbations consistent with , and compute cumulative halo mass functions across redshifts. They find that coupling boosts the abundance of massive halos by up to for constant coupling and for variable coupling around , and raises today by up to about for the strongest coupling. These results imply that high- cluster counts can distinguish coupled dark energy from a cosmological constant, offering a potential explanation for the Jee et al. cluster without invoking primordial non-Gaussianity.

Abstract

The recent detection (Jee etal 2009) of the massive cluster XMMU J2235.3-2557 at a redshift z = 1.4, with an estimated mass M = 6.4 +- 1.2 X 10^14 M_sol, has been claimed to be a possible challenge to the standard LCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be 0.005 if a LCDM model with gaussian initial conditions is assumed, resulting in a 3 sigma discrepancy from the standard cosmological model. In this paper we propose to use high redshift clusters as the one detected in Jee etal 2009 to compare the cosmological constant scenario with interacting dark energy models. We show that coupled dark energy models, where an interaction is present between dark energy and cold dark matter, can significantly enhance the probability to observe very massive clusters at high redshift.

Paper Structure

This paper contains 5 sections, 5 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. coupled dark energy
  3. simulations
  4. Results
  5. Conclusions

Figures (2)

  • Figure 1: Cumulative mass functions for the low-resolution simulations of the coupled DE models with constant (red) and variable (green) couplings, and for the standard $\Lambda$CDM cosmology (black). The four plots correspond to different redshifts and show in the bottom panel the ratio of the halo number density to the $\Lambda$CDM case. The mass functions are based on the groups identified with a FoF algorithm and the masses quoted in the plots are FoF masses. Each plot also reports the mass of the most massive halo found at a given redshift in each simulation, which clearly shows how more massive structures are expected to form at any cosmological epoch in coupled dark energy models as compared with $\Lambda$CDM.
  • Figure 2: Cumulative mass function at $z =1.5$ for the coupled DE model RP of Table \ref{['Simulations_Table']} (orange) compared to $\Lambda$CDM (black) from a high-resolution hydrodynamical simulation in a box of $80~h^{-1}$ comoving Mpc. The enhancement of the mass function in this set of simulations is slightly lower than in pure CDM simulations due to the presence of a fraction of uncoupled baryons. The bottom panel shows the enhancement of halo number density relative to $\Lambda$CDM.