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Clumpy galaxies at z~2

Galaxies at high redshift tend to have higher star-formation rates than galaxies of the same mass in the local Universe. At redshift z=2, when the Universe was roughly 3.5 billion years old, galaxies were forming stars at rates of tens to hundreds of solar masses per year. Star-forming galaxies at that time had very irregular morphologies, and their images are sometimes dominated by several prominent “clumps”.

To understand the formation of such galaxies, I have been running cosmological simulations with a version of the Gadget-2 Code (Springel et al. 2005, Oppenheimer et al. 2008), which solves the gravitational N-body equations with a tree method, and the Euler hydrodynamical equations with the smoothed particle hydrodynamics (SPH) method. In these simulations, I include a “sub-grid” recipe for strong galactic outflows.

In the simulations, large star-forming clumps form as a result of gravitational instability in the disk, in accordance with the theory of Toomre (1964). However, they do not survive for long, as a result of the implemented wind model, i.e. the high rate of mass that flows out of them to the intergalactic medium.

Comparisons of the galaxies that form in these simulations to real observed galaxies shows good agreement, indicating that the simulations may be reproducing the mechanisms by which these galaxies form and evolve in nature.