Disc-Halo Interactions in {\Lambda}CDM

TL;DR

This paper introduces a new method for embedding stellar discs into cosmological dark matter halos in simulations, allowing for more realistic galaxy formation modeling and analysis of disc-halo interactions.

Contribution

The authors develop a novel approach for inserting and evolving stellar discs in cosmological simulations, improving upon previous methods by dynamically determining disc orientation and structure.

Findings

The presence of a disc makes the halo rounder and more concentrated.

Methods pinning the disc to the halo potential overestimate adiabatic contraction.

The simulated disc develops a realistic bar and disc particles are launched to high latitudes.

Abstract

We present a new method for embedding a stellar disc in a cosmological dark matter halo and provide a worked example from a {\Lambda}CDM zoom-in simulation. The disc is inserted into the halo at a redshift z = 3 as a zero-mass rigid body. Its mass and size are then increased adiabatically while its position, velocity, and orientation are determined from rigid-body dynamics. At z = 1, the rigid disc is replaced by an N-body disc whose particles sample a three-integral distribution function (DF). The simulation then proceeds to z = 0 with live disc and halo particles. By comparison, other methods assume one or more of the following: the centre of the rigid disc during the growth phase is pinned to the minimum of the halo potential, the orientation of the rigid disc is fixed, or the live N-body disc is constructed from a two rather than three-integral DF. In general, the presence of a disc makes the halo rounder, more centrally concentrated, and smoother, especially in the innermost regions. We find that methods in which the disc is pinned to the minimum of the halo potential tend to overestimate the amount of adiabatic contraction. Additionally, the effect of the disc on the subhalo distribution appears to be rather insensitive to the disc insertion method. The live disc in our simulation develops a bar that is consistent with the bars seen in late-type spiral galaxies. In addition, particles from the disc are launched or "kicked up" to high galactic latitudes.