Constraints on interacting dark energy models from galaxy Rotation Curves

TL;DR

The paper investigates whether a class of interacting Dark Energy models with a rapidly growing coupling to Dark Matter can be constrained by the rotation curves of luminous spiral galaxies. It combines high-resolution N-body simulations predicting significant halo concentration enhancements with detailed mass modelling of galaxy RCs to compare against the Universal Rotation Curve, testing the viability of the models. The results rule out the most extreme coupling-growth scenario (EXP015a3) due to its failure to reproduce observed RCs, while a milder model (EXP010a2) remains marginally acceptable, highlighting the potential of small-scale dynamics to constrain DE interactions. Overall, the study demonstrates a direct link between nonlinear DE–DM coupling and observable galactic dynamics, underscoring the value of galaxy rotation curves as a probe of Dark Energy physics beyond background cosmology.

Abstract

[Abridged] High-resolution N-body simulations have recently shown that the structural properties of highly nonlinear cosmic structures, as e.g. their average concentration at a given mass, could be significantly modified in the presence of an interaction between Dark Energy and Dark Matter. While a constant interaction strength leads to less concentrated density profiles, a steep growth in time of the coupling function has been shown to determine a large increase of halo concentrations over a wide range of masses, including the typical halos hosting luminous spiral galaxies. This determines a substantial worsening of the "cusp-core" tension arising in the standard $Λ$CDM model and provides a direct way to constrain the form of the Dark Energy interaction. In the present paper we make use of the outcomes of some high-resolution N-body simulations of a specific class of interacting Dark Energy models to compare the predicted rotation curves of luminous spiral galaxies forming in these cosmologies against real observational data. Our results show how some specific interacting Dark Energy scenarios featuring a steep growth in time of the coupling function -- which are virtually indistinguishable from LCDM in the background -- cannot fit the observed rotation curves of luminous spiral galaxies and can therefore be ruled out only on the basis of dynamical properties of small-scale structures. Our study is a pilot investigation of the effects of a Dark Energy interaction at small scales, and demonstrates how the dynamical properties of visible galaxies can in some cases provide direct constraints on the nature of Dark Energy.

Figures (3)

• Figure 1: The ratio of the halo concentration in cDE models with respect to the standard $\Lambda$CDM scenario as a function of the halo virial mass $M_{200}$, as obtained from the N-body simulations of Baldi_2011a. The curves represent the Mean (solid) and the Median (dashed) concentration within each of the four logarithmic mass bins in which the sample has been subdivided.
• Figure 2: Circular rotation velocity for the case of a standard $\Lambda$CDM concentration vs. Mass relation (black solid line) and for the two cDE models under investigation, EXP010a2 (red solid line) and EXP015a3 (green solid line), compared to the URC at $M_{I} = -23$ (black points with error bars).
• Figure 3: Values of $\chi _{\rm red}^{2}$of the best-fit mass models for different assumptions on the concentration parameter $c/c_{\Lambda }$. Standard NFW models correspond to $c/c_{\Lambda}=1$. The $\chi _{\rm red}^{2}$ values for the two cDE models discussed in the present work are shown by a red (EXP010a2) and a green (EXP015a3) dot. The latter model provides a very poor fit to the data, as shown by the large $\chi _{\rm red}^{2}$ value.