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