Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Scattered Lyman-alpha Radiation Around Sources Before Cosmological
  Reionization   The spectra of the first galaxies and quasars in the Universe should be
strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by
neutral hydrogen (HI) in the intervening intergalactic medium. However, the
Lyman-alpha line photons emitted by these sources are not eliminated but rather
scatter until they redshift out of resonance and escape due to the Hubble
expansion of the surrounding intergalactic HI. We calculate the resulting
brightness distribution and the spectral shape of the diffuse Lyman-alpha line
emission around high redshift sources, before the intergalactic medium was
reionized. Typically, the Lyman-alpha photons emitted by a source at z=10
scatter over a characteristic angular radius of order 15 arcseconds around the
source and compose a line which is broadened and redshifted by about a thousand
km/s relative to the source. The scattered photons are highly polarized.
Detection of the diffuse Lyman-alpha halos around high redshift sources would
provide a unique tool for probing the neutral intergalactic medium before the
epoch of reionization. On sufficiently large scales where the Hubble flow is
smooth and the gas is neutral, the Lyman-alpha brightness distribution can be
used to determine the cosmological mass densities of baryons and matter.

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The categories of this paper are: stat
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: math
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The categories of this paper are: alg-geom