Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-linear violent disc instability with high Toomre's Q in
  high-redshift clumpy disc galaxies   We utilize zoom-in cosmological simulations to study the nature of violent
disc instability (VDI) in clumpy galaxies at high redshift, $z=1$--$5$. Our
simulated galaxies are not in the ideal state assumed in Toomre instability, of
linear fluctuations in an isolated, uniform, rotating disk. There, instability
is characterised by a $Q$ parameter below unity, and lower when the disk is
thick. Instead, the high-redshift discs are highly perturbed. Over long periods
they consist of non-linear perturbations, compact massive clumps and extended
structures, with new clumps forming in inter-clump regions. This is while the
galaxy is subject to frequent external perturbances. We compute the local,
two-component $Q$ parameter for gas and stars, smoothed on a $\sim1~{\rm kpc}$
scale to capture clumps of $10^{8-9}~{\rm M}_\odot$. The $Q<1$ regions are
confined to collapsed clumps due to the high surface density there, while the
inter-clump regions show $Q$ significantly higher than unity. Tracing the
clumps back to their relatively smooth Lagrangian patches, we find that $Q$
prior to clump formation typically ranges from unity to a few. This is unlike
the expectations from standard Toomre instability. We discuss possible
mechanisms for high-$Q$ clump formation, e.g. rapid turbulence decay leading to
small clumps that grow by mergers, non-axisymmetric instability, or clump
formation induced by non-linear perturbations in the disk. Alternatively, the
high-$Q$ non-linear VDI may be stimulated by the external perturbations such as
mergers and counter-rotating streams. The high $Q$ may represent excessive
compressive modes of turbulence, possibly induced by tidal interactions.

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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: econ
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin