The impact of constrained interacting dark energy on the bound-zone velocity profile

Abstract

We numerically study the effects of constrained interacting dark energy (CIDER) on the bound-zone velocity profiles around massive dark matter halos. Analyzing the CIDER simulations performed by Baldi (2023) for three different cases of dark sector coupling (${\hat{I}}^2=0.03$, $0.05$ and $0.08$) as well as for the standard $\hat{I}›$CDM cosmology (${\hat{I}}^2=0$), we determine the mean peculiar velocity profiles in the bound zones around the friends-of-friends halos with masses larger than $M_{\mathrm{cut}}=3\times 10^{13}{h}^{-1}{M}_{\odot }$ at three redshifts, $z=0$, $0.5$ and $1$. It is found that the universal power-law formula proposed by Falco et al. (2024) originally for the $\hat{I}›$CDM case still describes well the bound-zone velocity profiles, $V(r)$, even in the CIDER models. The slope of $V(r)$, turns out to be significantly affected by the CIDER, progressively decreasing as ${\hat{I}}^2$ increases. Meanwhile, the amplitude of $V(r)$ exhibits little dependence on ${\hat{I}}^2$, which is ascribed to the identical Hubble parameters shared by the $\hat{I}›$CDM and CIDER models in the entire redshift range. Our results imply that the bound-zone velocity slope can break a degeneracy even between the $\hat{I}›$CDM and CIDER models with ${\hat{I}}^2\le 0.03$, which the standard cosmological diagnostics fail to distinguish. We devise a simple analytic formula for the bound-zone slope as a function of ${\hat{I}}^2$, and prove its validity at all of the three redshifts. It is concluded that the slope of the mean bound-zone peculiar velocity profile should be in principle a powerful probe of dark sector interaction.

Accepted for publication in JCAP, 8 figures, 1 table