Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Role of the Parker Instability in Structuring the Interstellar
  Medium   The Parker instability, a Rayleigh-Taylor like instability of thermal gas
supported against gravity by magnetic fields and cosmic rays, is thought to be
dynamically important for galaxy evolution, possibly promoting molecular cloud
formation and the galactic dynamo. In previous work, we examined the effect of
three different cosmic ray transport models on the Parker instability:
decoupled ($\gamma_c = 0$), locked to the thermal gas ($\gamma_c = 4/3$) and
coupled to the gas with streaming by self-confinement. We expand upon that work
here by considering radiative cooling, a smooth gravitational potential, and
simulations into the nonlinear regime. We determine that cosmic ray transport
away from compression points, whether by diffusion or streaming, is the largest
driver of the instability. Heating due to cosmic ray streaming is also
destabilizing and especially affects the nonlinear regime. While cooling
de-pressurizes the dense gas, streaming cosmic rays heat and inflate the
diffuse extraplanar gas, greatly modifying the phase structure of the medium.
In 3D, we find that the fastest growth favors short wavelength modes in the
horizontal direction perpendicular to the background magnetic field; this is
imprinted on Faraday rotation measure maps that may be used to detect the
Parker instability. The modifications to the Parker instability that we observe
in this work have large implications for the structure and evolution of
galaxies, and they highlight the major role that cosmic rays play in shaping
their environments.

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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci