on contract to a thin and dense line, while at the same time accreting more gas from the inter-ring region. It is these dense, circular filaments, that subsequently fragment into a large number of clumps. Contrary to what is typically assumed, the clump sizes are therefore not directly determined by the fastest growing wavelength.'
author:
- |
    M.  Behrendt$^{1,2}$[^1], A.  Burkert$^{1,2}$[^2], M.  Schartmann$^{1,2}$\
    $^1$Max Planck Institute for extraterrestrial Physics, PO box 1312, Giessenbachstra${\ss}$e, D-85741 Garching, Germany\
    $^2$University Observatory Munich, Scheinerstraße 1, D-81679 Munich, Germany
bibliography:
- 'mystrings.bib'
- 'mybib.bib'
date: 'Accepted 2015 January 5. Received 2015 January 5; in original form 2014 July 20'
title: |
    Structure formation in gas-rich galactic discs with finite thickness:\
    from discs to rings
---

\[firstpage\]

hydrodynamics – instabilities – methods: numerical – galaxies: evolution – galaxies: high-redshift – galaxies: structure.

Introduction {#sec:introduction}
============

Observations of massive galaxies at high redshift have revealed rotating discs [@2009ApJ...706.1364F] with large gas fractions [@2010ApJ...713..686D] and high velocity dispersion. Their morphology is irregular and often dominated by a few kpc-sized clumps [@2011ApJ...733..101G], seen in the optical [@2007ApJ...658..763E], and also in ionized [@2008ApJ...687...59G] and molecular gas [@2013ApJ...768...74T]. In the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey [CANDELS; @2011ApJS..197...35G; @2011ApJS..197...36K] over 