Thermal and Chemical Evolution of Collapsing Filaments
  Intergalactic filaments form the foundation of the cosmic web that connect
galaxies together, and provide an important reservoir of gas for galaxy growth
and accretion. Here we present very high resolution two-dimensional simulations
of the thermal and chemical evolution of such filaments, making use of a 32
species chemistry network that tracks the evolution of key molecules formed
from hydrogen, oxygen, and carbon. We study the evolution of filaments over a
wide range of parameters including the initial density, initial temperature,
strength of the dissociating UV background, and metallicity. In low-redshift,
$Z \approx 0.1 Z_\odot $ filaments, the evolution is determined completely by
the initial cooling time. If this is sufficiently short, the center of the
filament always collapses to form dense, cold core containing a substantial
fraction of molecules. In high-redshift, $Z=10^{-3} Z_\odot$ filaments, the
collapse proceeds much more slowly. This is due mostly to the lower initial
temperatures, which leads to a much more modest increase in density before the
atomic cooling limit is reached, making subsequent molecular cooling much less
efficient.
  Finally, we study how the gravitational potential from a nearby dwarf galaxy
affects the collapse of the filament and compare this to NGC 5253, a nearby
starbusting dwarf galaxy thought to be fueled by the accretion of filament gas.
In contrast to our fiducial case, a substantial density peak forms at the
center of the potential. This peak evolves faster than the rest of the filament
due to the increased rate at which chemical species form and cooling occur. We
find that we achieve similar accretion rates as NGC 5253 but our
two-dimensional simulations do not recover the formation of the giant molecular
clouds that are seen in radio observations.
