On the Orbits of Infalling Satellite Halos

TL;DR

This paper investigates the initial orbital parameters of infalling satellite halos using cosmological simulations, revealing their dependence on host mass and redshift, and providing formulas for these dependencies.

Contribution

It offers new insights into how satellite orbital properties depend on mass and redshift, with detailed fitting formulas for orbital circularity and pericenter.

Findings

Satellite orbits are more radial at higher host masses and redshifts.

Satellites infall with less angular momentum than the host virial value.

Most satellites are 'hotter' than the host virial velocity.

Abstract

The orbital properties of infalling satellite halos set the initial conditions which control the subsequent evolution of subhalos and the galaxies that they host, with implications for mass stripping, star formation quenching, and merging. Using a high-resolution, cosmological N-body simulation, I examine the orbital parameters of satellite halos as they merge with larger host halos, focusing primarily on orbital circularity and pericenter. I explore in detail how these orbital parameters depend on mass and redshift. Satellite orbits become more radial and plunge deeper into their host halo at higher host halo mass, but they do not significantly depend on satellite halo mass. Additionally, satellite orbits become more radial and plunge deeper into their host halos at higher redshift. I also examine satellite velocities, finding that most satellites infall with less specific angular momentum than the host halo virial value, but that satellites are `hotter' than the host virial velocity. I discuss the implications of these results to the processes of galaxy formation and evolution, and I provide fitting formulas to the mass and redshift dependence of satellite orbital circularity and pericenter.