# The density distribution of accreting cosmic filaments as shaped by Kelvin-Helmholtz instability

## TL;DR

This study uses high-resolution hydrodynamical simulations to investigate how Kelvin-Helmholtz instability influences the density distribution of cold gas in cosmic filaments, revealing broad, skewed distributions and turbulence effects relevant to galaxy evolution.

## Contribution

It demonstrates the impact of Kelvin-Helmholtz instability on filament density distributions and turbulence, providing new insights into gas accretion processes in the circumgalactic medium.

## Key findings

- Density distribution is skewed log-normal with a high-density tail at high Mach numbers.
- Maximum densities correlate with accretion velocity, consistent with turbulence models.
- Cosmological accretion can induce turbulence and broad density distributions in the CGM.

## Abstract

Cosmic filaments play a crucial role in galaxy evolution transporting gas from the intergalactic medium into galaxies. However, little is known about the efficiency of this process and whether the gas is accreted in a homogenous or clumpy way. Recent observations suggest the presence of broad gas density distributions in the circumgalactic medium which could be related to the accretion of filaments. By means of high-resolution hydrodynamical simulations, we explore here the evolution of cold accreting filaments flowing through the hot circumgalactic medium (CGM) of high-z galaxies. In particular, we examine the nonlinear effects of Kelvin-Helmholtz instability (KHI) on the development of broad gas density distributions and on the formation of cold, dense clumps. We explore a large parameter space in filament and perturbation properties, such as, filament Mach number, initial perturbation wavelength, and thickness of the interface between the filament and the halo. We find that the time averaged density distribution of the cold gas is qualitatively consistent with a skewed log-normal probability distribution function (PDF) plus an additional component in form of a high density tail for high Mach-numbers. Our results suggest a tight correlation between the accreting velocity and the maximum densities developing in the filament which is consistent with the variance-Mach number relation for turbulence. Therefore, cosmological accretion could be a viable mechanism to produce turbulence and broad gas density distributions within the CGM.