Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effects of a Soft X-ray Background on Structure Formation at High
  Redshift   We use three dimensional hydrodynamic simulations to investigate the effects
of a soft X-ray background, that could have been produced by an early
generation of mini-quasars, on the subsequent cooling and collapse of high
redshift pregalactic clouds. The simulations use an Eulerian adaptive mesh
refinement technique with initial conditions drawn from a flat Lambda-dominated
cold dark matter model cosmology to follow the nonequilibrium chemistry of nine
chemical species in the presence of both a soft ultraviolet Lyman-Werner H_2
photodissociating flux and a soft X-ray background extending to 7.2 keV.
Although we vary the normalization of the X-ray background by two orders of
magnitude, the positive feedback effect of the X-rays on cooling and collapse
of the pregalactic cloud expected due to the increased electron fraction is
quite mild, only weakly affecting the mass threshold for collapse and the
fraction of gas within the cloud that is able to cool. Inside most of the cloud
we find that H_2 is in photodissociation equilibrium with the soft UV flux. The
net buildup of the electron density needed to enhance H_2 formation occurs too
slowly compared to the H_2 photodissociation and dynamical timescales within
the cloud to overcome the negative impact of the soft UV photodissociating flux
on cloud collapse. However, we find that even in the most extreme cases the
first objects to form do rely on molecular hydrogen as coolant and stress that
our results do not justify the neglect of these objects in models of galaxy
formation.

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The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio