The impact of baryonic physics on the shape and radial alignment of substructures in cosmological dark matter haloes

TL;DR

This study compares dark matter only and gas-inclusive simulations to analyze how baryonic physics influences the shape and radial alignment of subhaloes, revealing that gas physics has minimal impact but that tidal effects drive shape and alignment evolution.

Contribution

It demonstrates that baryonic physics does not significantly alter subhalo shape and alignment, highlighting the role of tidal torquing in their evolution.

Findings

Gas physics has negligible effect on subhalo shape and alignment.

Subhalo shapes become more aspherical near the host center.

Radial alignment weakens in the central regions and strengthens in the outskirts.

Abstract

We use two simulations performed within the Constrained Local UniversE Simulation (CLUES) project to study both the shape and radial alignment of (the dark matter component of) subhaloes; one of the simulations is a dark matter only model while the other run includes all the relevant gas physics and star formation recipes. We find that the involvement of gas physics does not have a statistically significant effect on either property -- at least not for the most massive subhaloes considered in this study. However, we observe in both simulations including and excluding gasdynamics a (pronounced) evolution of the dark matter shapes of subhaloes as well as of the radial alignment signal since infall time. Further, this evolution is different when positioned in the central and outer regions of the host halo today; while subhaloes tend to become more aspherical in the central 50% of their host's virial radius, the radial alignment weakens in the central regime while strengthening in the outer parts. We confirm that this is due to tidal torquing and the fact that subhaloes at pericentre move too fast for the alignment signal to respond.