The possible hierarchical scales of observed clumps in high-redshift disc galaxies. Issue 1 (21st June 2019)

• Record Type: Journal Article
• Authors: Behrendt, M; Schartmann, M; Burkert, A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 488:Issue 1(2019)
• Page Start: 306
• Page End: 323
• Publication Date: 2019-06-21
• Subjects: hydrodynamics -- instabilities -- methods: numerical -- galaxies: irregular -- galaxies: high-redshift -- galaxies: structure; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz1717
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Giant clumps on ∼kpc scales and with masses of $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$ are ubiquitous in observed high-redshift disc galaxies. Recent simulations and observations with high spatial resolution indicate the existence of substructure within these clumps. We perform high-resolution simulations of a massive galaxy to study the substructure formation within the framework of gravitational disc instability. We focus on an isolated and pure gas disc with an isothermal equation of state with T = 10 4 K that allows capturing the effects of self-gravity and hydrodynamics robustly. The main mass of the galaxy resides in rotationally supported clumps which grow by merging to a maximum clump mass of $10^8 \, \mathrm{M_{\odot }}$ with diameter ∼120 pc for the dense gas. They group to clump clusters (CCs) within relatively short times ($\ll 50 \, \mathrm{Myr}$ ), which are present over the whole simulation time. We identify several mass and size scales on which the clusters appear as single objects at the corresponding observational resolution between ${\sim } 10^8 \, \rm{and}\, 10^9 \, \mathrm{M_{\odot }}$ . Most of the clusters emerge as dense groups and for larger beams they are more likely to be open structures represented by a single object. In the high-resolution runs higher densities can be reached, and the initial structures can collapse further and fragment to many clumps smaller than the initial Toomre length. In our low-resolution runs, the clumps directly form on larger scales 0.3–1 kpc with $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$ . Here, the artificial pressure floor which is typically used to prevent spurious fragmentation strongly influences the initial formation of clumps and their properties at very low densities.