Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Radiative Feedback of the First Cosmological Objects   In hierarchical models of structure formation, an early cosmic UV background
(UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before
reionization. The UVB at energies below 13.6eV suppresses the formation of
stars or black holes inside small halos, by photo-dissociating their only
cooling agent, molecular H2. We self-consistently compute the buildup of the
early UVB in Press-Schechter models, coupled with H2 photo-dissociation both in
the intergalactic medium (IGM), and inside virialized halos. We find that the
intergalactic H2 has a negligible effect on the UVB, both because its initial
optical depth is small (tau<0.1), and because it is photo-dissociated at an
early stage. If the UV sources in the first collapsed halos are stars, then
their UV flux suppresses further star-formation inside small halos. This
results in a pause in the buildup of the UVB, and reionization is delayed until
larger halos (T_vir> 10^4 K) collapse. If the small halos host mini-quasars
with hard spectra extending to approximately 1 keV, then their X-rays balance
the effects of the UVB, the negative feedback does not occur, and reionization
can be caused by the small halos.

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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: math-ph