Effects of Coupled Dark Energy on the Milky Way and its Satellites

TL;DR

This study uses high-resolution simulations to explore how coupled dark energy influences galaxy and satellite structures, revealing lower halo concentrations and fewer substructures, which could address small-scale issues in cosmology.

Contribution

First numerical simulations of coupled dark energy effects on galactic scales, showing impacts on halo concentration and substructure abundance with potential to resolve small-scale cosmological problems.

Findings

Coupled dark energy reduces halo concentrations and substructure numbers.

Lower concentrations are linked to gravitational dynamics, not formation time.

Coupled dark energy may help reconcile observed and simulated galaxy rotation curves.

Abstract

We present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and sub-galactic scales. We choose two constant couplings and a time-varying coupling function and we run simulations of three Milky-Way-size halos ($\sim$10$^{12}$M$_{\odot}$), a lower mass halo (6$\times$10$^{11}$M$_{\odot}$) and a dwarf galaxy halo (5$\times$10$^{9}$M$_{\odot}$). We resolve each halo with several millions dark matter particles. On all scales the coupling causes lower halo concentrations and a reduced number of substructures with respect to LCDM. We show that the reduced concentrations are not due to different formation times, but they are related to the extra terms that appear in the equations describing the gravitational dynamics. On the scale of the Milky Way satellites, we show that the lower concentrations can help in reconciling observed and simulated rotation curves, but the coupling values necessary to have a significant difference from LCDM are outside the current observational constraints. On the other hand, if other modifications to the standard model allowing a higher coupling (e.g. massive neutrinos) are considered, coupled dark energy can become an interesting scenario to alleviate the small-scale issues of the LCDM model.