High-redshift clumpy discs and bulges in cosmological simulations
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 70pc with cooling below 104K. We study three typical star-forming galaxies in haloes of ~5 × 1011Msolar 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 ~45Msolaryr-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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2010
- DOI:
- 10.1111/j.1365-2966.2010.16433.x
- arXiv:
- arXiv:0907.3271
- Bibcode:
- 2010MNRAS.404.2151C
- Keywords:
-
- stars: formation;
- galaxies: evolution;
- galaxies: formation;
- galaxies: kinematics and dynamics;
- galaxies: spiral;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 20 pages, 12 figures, accepted in MNRAS.