Tidal Stripping and Post-Merger Relaxation of Dark Matter Halos: Causes and Consequences of Mass Loss

TL;DR

This paper investigates the causes and effects of mass loss in dark matter halos, focusing on post-merger relaxation and tidal stripping, revealing how these processes alter halo properties and their evolution.

Contribution

It provides a detailed analysis of the mechanisms behind halo mass loss and their impact on halo shape, spin, and concentration using cosmological simulation data.

Findings

Major mergers cause temporary mass loss and shape changes.

Tidal stripping reduces halo mass and alters halo morphology.

Low mass halos are more affected by both processes.

Abstract

We study the properties of distinct dark matter halos (i.e., those that are not subhalos) that have a final virial mass $M_{\mathrm{vir}}$ at $z = 0$ less than their peak mass ($M_{\mathrm{peak}}$) in the Bolshoi-Planck cosmological simulation. We identify two primary causes of halo mass loss: relaxation after a major merger and tidal stripping by a massive neighbouring halo. Major mergers initially boost $M_{\mathrm{vir}}$ and typically cause the final halo to become more prolate and less relaxed and to have higher spin and lower NFW concentration. As the halo relaxes, high energy material from the recent merger gradually escapes beyond the virial radius, temporarily resulting in a net negative accretion rate that reduces the halo mass by $5-15\%$ on average. Halos that experience a major merger around $z = 0.4$ typically reach a minimum mass near $z = 0$. Tidal stripping mainly occurs in dense regions, and it causes halos to become less prolate and have lower spins and higher NFW concentrations. Tidally stripped halos often lose a large fraction of their peak mass ($> 20\%$) and most never recover (or even reattain a positive accretion rate). Low mass halos can be strongly affected by both post-merger mass loss and tidal stripping, while high mass halos are predominantly influenced by post-merger mass loss and show few signs of significant tidal stripping.