A test of constancy of dark matter halo surface density and radial acceleration relation in relaxed galaxy groups

TL;DR

This study tests the constancy of dark matter halo surface density and the radial acceleration relation in relaxed galaxy groups, finding deviations from scale invariance and larger scatter compared to galaxies and clusters.

Contribution

It extends previous analyses by examining galaxy groups, revealing that halo surface density varies with scale and is not universal, and assessing the radial acceleration relation in this context.

Findings

Halo surface density scales as $ ho_c propto r_c^{-1.35}$ with intrinsic scatter of 27.3%.

Surface density is about four times greater than in galaxies, indicating non-universality.

Residual scatter in the radial acceleration relation is larger than in galaxy clusters.

Abstract

The dark matter halo surface density, given by the product of the dark matter core radius ($r_c$) and core density ($\rho_c$) has been shown to be a constant for a wide range of isolated galaxy systems. Here, we carry out a test of this {\em ansatz} using a sample of 17 relaxed galaxy groups observed using Chandra and XMM-Newton, as an extension of our previous analysis with galaxy clusters. We find that $\rho_c \propto r_c^{-1.35^{+0.16}_{-0.17}}$, with an intrinsic scatter of about 27.3%, which is about 1.5 times larger than that seen for galaxy clusters. Our results thereby indicate that the surface density is discrepant with respect to scale invariance by about 2$\sigma$, and its value is about four times greater than that for galaxies. Therefore, the elevated values of the halo surface density for groups and clusters indicate that the surface density cannot be a universal constant for all dark matter dominated systems. Furthermore, we also implement a test of the radial acceleration relation for this group sample. We find that the residual scatter in the radial acceleration relation is about 0.32 dex and a factor of three larger than that obtained using galaxy clusters. The acceleration scale which we obtain is in-between that seen for galaxies and clusters.