Non-linear violent disc instability with high Toomre's Q in high-redshift clumpy disc galaxies

Shigeki Inoue*, Avishai Dekel, Nir Mandelker, Daniel Ceverino, Frédéric Bournaud, Joel Primack

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

80 Scopus citations


We utilize zoom-in cosmological simulations to study the nature of violent disc instability 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 disc. There, instability is characterized by a Q parameter below unity, and lower when the disc 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 interclump 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 ~1 kpc scale to capture clumps of 108-9M. The Q < 1 regions are confined to collapsed clumps due to the high surface density there, while the interclump 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 disc. 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.

Original languageAmerican English
Pages (from-to)2052-2069
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 2016

Bibliographical note

Publisher Copyright:
© 2015 The Authors. Published by Oxford University Press.


  • Galaxies: formation
  • Galaxies: kinematics and dynamics
  • Instabilities
  • Methods: numerical


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