Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Protogalactic evolution and magnetic fields   We show that the relatively strong magnetic fields ($\ge 1 \mu$G) in high
redshift objects can be explained by the combined action of an evolving
protogalactic fluctuation and electrodynamic processes providing the magnetic
seed fields. Three different seed field mechanisms are reviewed and
incorporated into a spherical "top-hat" model and tidal torque theory for the
fate of a forming galaxy in an expanding universe. Very weak fields $10^{-19}
\sim 10^{-23}$G created in an expanding over-dense region are strongly enhanced
due to the dissipative disk formation by a factor $\sim 10^4$, and subsequently
amplified by strong non-axisymmetric flow by a factor $\sim 10^{6-10}$,
depending on the cosmological parameters and the epoch of galaxy formation. The
resulting field strength at $z \sim 0.395$ can be of the order of a few $\mu$G
and be close to this value at $z \sim 2$.

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The categories of this paper are: physics
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The categories of this paper are: math
1
The categories of this paper are: cs
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The categories of this paper are: q-bio
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga