paper

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

arXiv:1510.07695 · doi:10.1093/mnras/stv2793

Abstract

We utilize zoom-in cosmological simulations to study the nature of violent disc instability (VDI) in clumpy galaxies at high redshift, --. 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 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 parameter for gas and stars, smoothed on a scale to capture clumps of . The regions are confined to collapsed clumps due to the high surface density there, while the inter-clump regions show significantly higher than unity. Tracing the clumps back to their relatively smooth Lagrangian patches, we find that 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- 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- non-linear VDI may be stimulated by the external perturbations such as mergers and counter-rotating streams. The high may represent excessive compressive modes of turbulence, possibly induced by tidal interactions.

Accepted for publication in MNRAS. 20 pages, 21 figures

References in corpus (78)

Cited by in corpus (87)