Subhalo accretion through filaments

TL;DR

This study investigates how filamentary structures influence the accretion and orbital properties of subhalos around galaxy-sized halos, revealing mass-dependent effects on subhalo lifetimes, orbits, and merger behaviors.

Contribution

It provides the first detailed analysis of filamentary accretion effects on subhalo orbits and lifetimes across different host halo masses using cosmological simulations.

Findings

Subhalos from filaments have ~10% shorter lifetimes at low masses.

Filament-accreted subhalos tend to have more radial orbits.

Filamentary accretion enhances satellite association and merger rates.

Abstract

We track subhalo orbits of galaxy and group sized halos in cosmological simulations. We identify filamentary structures around halos and we use these to define a sample of subhalos accreted from filaments as well as a control sample of subhalos accreted from other directions. We use these samples to study differences in satellite orbits produced by filamentary accretion. Our results depend on host halo mass. We find that for low masses, subhalos accreted from filaments show $\sim10\%$ shorter lifetimes compared to the control sample, they show a tendency towards more radial orbits, reach halo central regions earlier, and are more likely to merge with the host. For higher mass halos this lifetime difference dissipates and even reverses for cluster sized halos. This behavior appears to be connected to the fact that more massive hosts are connected to stronger filaments with higher velocity coherence and density, with slightly more radial subhalo orbits. Because subhalos tend to follow the coherent flow of the filament, it is possible that such thick filaments are enough to shield the subhalo from the effect of dynamical friction at least during their first infall. We also identify subhalo pairs/clumps which merge with one another after accretion. They survive as a clump for only a very short time, which is even shorter for higher subhalo masses, suggesting that the Magellanic Clouds and other Local group satellite associations, may have entered the MW virial radius very recently and probably are in their first infall. Filaments boost the accretion of satellite associations.