Satellite Galaxies and Fossil Groups in the Millennium Simulation

TL;DR

This study uses the Millennium Simulation to analyze satellite galaxy systems around isolated primaries, revealing their distribution, kinematics, and the presence of fossil groups, with implications for understanding dark matter halos in LCDM cosmology.

Contribution

It provides a detailed characterization of satellite systems in LCDM, including their spatial and velocity distributions, and examines fossil groups and scaling relations.

Findings

Satellite distribution follows an NFW profile with mild anisotropy.

Fossil groups are present and match observational constraints.

The L_{host} t_{sat}^3 relation is recovered for isolated primaries.

Abstract

We use a semianalytic galaxy catalogue constructed from the Millennium Simulation to study the satellites of isolated galaxies in the LCDM cosmogony. This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites) allows the characterization, with minimal statistical uncertainty, of the dynamical properties of satellite/primary galaxy systems in a LCDM universe. We find that, overall, the satellite population traces the dark matter rather well: its spatial distribution and kinematics may be approximated by an NFW profile with a mildly anisotropic velocity distribution. Their spatial distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg'' effect that reflects the misalignment between the major axis and angular momentum of the host halo. The isolation criteria for our primaries picks not only galaxies in sparse environments, but also a number of primaries at the centre of ''fossil'' groups. We find that the abundance and luminosity function of these unusual systems are in reasonable agreement with the few available observational constraints. We recover the expected L_{host} \sigma_{sat}^3 relation for LCDM models for truly-isolated primaries. Less strict primary selection, however, leads to substantial modification of the scaling relation. Our analysis also highlights a number of difficulties afflicting studies that rely on blind stacking of satellite systems to constrain the mean halo mass of the primary galaxies.