High-redshift clumpy discs and bulges in cosmological simulations

Daniel Ceverino*, Avishai Dekel, Frederic Bournaud

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

440 Scopus citations

Abstract

We analyse the first cosmological simulations that recover the fragmentation of high-redshift galactic discs driven by cold streams. The fragmentation is recovered owing to an AMR resolution better than 70 pc with cooling below 104 K. We study three typical star-forming galaxies in haloes of ∼5 × 1011 M at z ≃ 2.3 when they were not undergoing a major merger. The steady gas supply by cold streams leads to gravitationally unstable, turbulent discs, which fragment into giant clumps and transient features on a dynamical time-scale. The disc clumps are not associated with dark-matter haloes. The clumpy discs are self-regulated by gravity in a marginally unstable state. Clump migration and angular-momentum transfer on an orbital time-scale help the growth of a central bulge with a mass comparable to the disc. The continuous gas input keeps the system of clumpy disc and bulge in a near steady state for several Gyr. The average star formation rate, much of which occurs in the clumps, follows the gas accretion rate of ∼45 M yr-1. The simulated galaxies resemble in many ways the observed star-forming galaxies at high redshift. Their properties are consistent with the simple theoretical framework presented in Dekel, Sari & Ceverino. In particular, a two-component analysis reveals that the simulated discs are indeed marginally unstable, and the time evolution confirms the robustness of the clumpy configuration in a cosmological steady state. By z ∼ 1, the simulated systems are stabilized by a dominant stellar spheroid, demonstrating the process of 'morphological quenching' of star formation. We demonstrate that the disc fragmentation is not a numerical artefact once the Jeans length is kept larger than nearly seven resolution elements, i.e. beyond the standard Truelove criterion.

Original languageEnglish
Pages (from-to)2151-2169
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume404
Issue number4
DOIs
StatePublished - Jun 2010

Keywords

  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: kinematics and dynamics
  • Galaxies: spiral
  • Stars: formation

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