arXiv subjects

Ben Morton

Publications and source records attributed to Ben Morton.

3 recordsLinked to original sources

arXiv2026

Impact of subhalo dynamical friction heating on the formation of the first structures in the universe

We present a model for gas heating, driven by dynamical friction from orbiting subhalos within dark matter halos. Using data from the TNG50 simulation, we derive the subhalo mass function and calculate the dynamical friction heating rate for a wide range of halo masses and redshifts from $z = 15$ to 0. Our results show that, by converting gravitational potential energy into thermal energy, dynamical friction is an important mechanism for galaxy quenching in massive halos at low redshifts, consistent with previous studies. Additionally, we find that in the early universe at $z \sim 15$, heating rates can be comparable to the molecular hydrogen cooling rates in metal-free minihalos. This can suppress gas cooling and fragmentation and does increase the critical molecular fraction for Pop III star formation by up to one order of magnitude, thereby making Pop III star formation more difficult. In combination with the Lyman-Werner background, the dynamical friction heating mechanism favors the formation of direct-collapse black hole (DCBH) seeds in atomic cooling halos, even when the average H$_2$ fraction is $\sim 10^{-5}$ during the minihalo progenitor phase. Dynamical friction heating at a fixed host halo mass can vary by two orders of magnitude due to the scatter in the number of subhalos. To capture dynamical friction heating in simulations, it is necessary to resolve subhalos with a subhalo to host halo mass ratio $\psi \gtrsim 0.05$.

astro-ph.GA↗

arXiv2022

A New Residual Distribution Hydrodynamics Solver for Astrophysical Simulations

Many astrophysical systems can only be accurately modelled when the behaviour of their baryonic gas components is well understood. The residual distribution (RD) family of partial differential equation (PDE) solvers produce approximate solutions to the corresponding fluid equations. We present a new implementation of the RD method. The solver efficiently calculates the evolution of the fluid, with up to second order accuracy in both time and space, across an unstructured triangulation, in both 2D and 3D. We implement a novel variable time stepping routine, which applies a drifting mechanism to greatly improve the computational efficiency of the method. We conduct extensive testing of the new implementation, demonstrating its innate ability to resolve complex fluid structures, even at very low resolution. We can resolve complex structures with as few as 3-5 resolution elements, demonstrated by Kelvin-Helmholtz and Sedov blast tests. We also note that we find cold cloud destruction time scales consistent with those predicted by a typical PPE solver, albeit the exact evolution shows small differences. The code includes three residual calculation modes, the LDA, N and blended schemes, tailored for scenarios from smooth flows (LDA), to extreme shocks (N), and both (blended). We compare our RD solver results to state-of-the-art solvers used in other astrophysical codes, demonstrating the competitiveness of the new approach, particularly at low resolution. This is of particular interest in large scale astrophysical simulations, where important structures, such as star forming gas clouds, are often resolved by small numbers of fluid elements.

astro-ph.IM↗

arXiv2021

Gaseous Dynamical Friction: a Numerical Study of Extended Perturbers

The process of momentum and energy transfer between a massive body and a background medium it is moving through is known as dynamical friction (DF). It is key to our understanding of many astrophysical systems. We present a series of high-resolution simulations of gaseous DF using Lagrangian meshless finite mass hydrodynamics solver, the moving-mesh MUSCL scheme, and the piecewise parabolic method (PPM) solver. We use a set of simulations of massive bodies, modelled as Plummer spheres, moving with Mach $0.2 \leq \mathcal{M} \leq 3$. We investigate at which radial distances from the perturber these solvers recover the linear point mass solution for gaseous DF. We analyse the drag force and the structure and time evolution of the wake. The different solvers agree closely. Numerical convergence is reached when the initial spatial resolution is $0.2r_s$, where $r_s$ is the softening scale of the Plummer sphere. We find that the wake structure and drag force are recovered, at the $5\%$ level, when compared beyond $4r_\mathrm{s}$. Our results predict that models using the standard linear point mass DF solution will overestimate the drag force on extended perturbers by as much as 25\%, for Mach$\sim$1. Finally, we consider DF in the context of galaxy clusters, where dark matter subhaloes move through circumgalactic media. We show that DF is typically in the linear regime for most subhaloes in hosting haloes $<10^{11}$ M$_{\odot}$ but non-linear in more massive host haloes.

astro-ph.GA↗