Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hydrogen Clouds before Reionization: a Lognormal Model Approach   We study the baryonic gas clouds (the IGM) in the universe before the
reionization with the lognormal model which is shown to be dynamcially
legitimate in describing the fluctuation evolution in quasilinear as well as
nonlinear regimes in recent years. The probability distribution function of the
mass field in the LN model is long tailed and so plays an important role in
rare events, such as the formation of the first generation of baryonic objects.
We calculate density and velocity distributions of the IGM at very high spatial
resolutions, and simulate the distributions at resolution of 0.15 kpc from z=7
to 15 in the LCDM cosmological model. We performed a statistics of the hydrogen
clouds including column densities, clumping factors, sizes, masses, and spatial
number density etc. One of our goals is to identify which hydrogen clouds are
going to collapse. By inspecting the mass density profile and the velocity
profile of clouds, we found that the velocity outflow significantly postpones
the collapsing process in less massive clouds, in spite of their masses are
larger than the Jeans mass. Consequently, only massive (> 10^5 M_sun) clouds
can form objects at higher redshift, and less massive (10^4-10^5) collapsed
objects are formed later. For example, although the mass fraction in clouds
with sizes larger than the Jeans length is already larger than 1 at z=15, there
is only a tiny fraction of mass (10^{-8}) in the clouds which are collapsed at
that time. If all the ionizing photons, and the 10^{-2} metallicity observed at
low redshift are produced by the first 1% mass of collapsed baryonic clouds,
the majority of those first generation objects would not happen until z=10.

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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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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: hep-ph
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th