The special growth history of central galaxies in groups and clusters

TL;DR

This paper uses numerical simulations to analyze the orbital parameters of satellites merging with central galaxies in groups and clusters, revealing distinct differences from cosmological halo-halo mergers and providing data for studying their evolution.

Contribution

It offers new insights into the distribution of merging orbital parameters of satellites accreted by central galaxies, highlighting differences from cosmological mergers and providing useful fits for future studies.

Findings

Satellites' orbits evolve losing energy and angular momentum due to dynamical friction.

Orbits are less bound and less eccentric than in cosmological halo-halo mergers.

Provides fitted distributions of orbital parameters for use in galaxy evolution models.

Abstract

Central galaxies (CGs) in galaxy groups and clusters are believed to form and assemble a good portion of their stellar mass at early times, but they also accrete significant mass at late times via galactic cannibalism, that is merging with companion group or cluster galaxies that experience dynamical friction against the common host dark-matter halo. The effect of these mergers on the structure and kinematics of the CG depends not only on the properties of the accreted satellites, but also on the orbital parameters of the encounters. Here we present the results of numerical simulations aimed at estimating the distribution of merging orbital parameters of satellites cannibalized by the CGs in groups and clusters. As a consequence of dynamical friction, the satellites' orbits evolve losing energy and angular momentum, with no clear trend towards orbit circularization. The distributions of the orbital parameters of the central-satellite encounters are markedly different from the distributions found for halo-halo mergers in cosmological simulations. The orbits of satellites accreted by the CGs are on average less bound and less eccentric than those of cosmological halo-halo encounters. We provide fits to the distributions of the central-satellite merging orbital parameters that can be used to study the merger-driven evolution of the scaling relations of CGs.