  The clustering of baryons and cold dark matter induced by a single moving
string is analyzed numerically making use of a new three-dimensional Eulerian
cosmological hydro code$^{1)}$ which is based on the PPM method to track the
baryons and the PIC method to evolve the dark matter particles.
  A long straight string moving with a speed comparable to $c$ induces a planar
overdensity (a``wake"). Since the initial perturbation is a velocity kick
towards the plane behind the string and there is no initial Newtonian
gravitational line source, the baryons are trapped in the center of the wake,
leading to an enhanced baryon to dark matter ratio. The cold coherent flow
leads to very low post--shock temperatures of the baryonic fluid.
  In contrast, long strings with a lot of small-scale structure (which can be
described by adding a Newtonian gravitational line source) move slowly and form
filamentary objects. The large central pressure due to the gravitational
potential causes the baryons to be expelled from the central regions and leads
to a relative deficit in the baryon to dark matter ratio. In this case, the
velocity of the baryons is larger, leading to high post-shock temperatures.

Astrophysics