COALA science: cosmology

Chiaki Kobayashi

We are simulating the evolutionary history of the Universe across Cosmic time, from the initial condition inferred from the Cosmic Microwave Background. These large-scale simulations are useful to provide predictions and theoretical interpretations for various observations, and to study the "problems" that are likely to conflict with the standard cosmology with Dark Matter and Dark Energy.

Structure formation and cosmic chemical enrichment

Cosmological simulations.

Using the self-consistent 3D hydrodynamical code in Kobayashi et al. (2007), we simulate the star formation and chemical enrichment history of the Universe. This code is based on the parallel tree-SPH code GADGET-2 by Springel (2005), where the Smoothed Particle Hydrodynamics (SPH) method is adopted for hydrodynamics. To compare with observations, we include detailed physical processes of atomic matter: star formation, supernovae feedback, and chemical enrichment.

Cosmic chemical enrichment

We predict the time evolution of the spatial distributions of elements (Figure 1.1 below), which will be compared with high-redshift observations of Lyman break galaxies and quasar absorption line systems. We also predict the rates of supernovae and gamma-ray bursts, and the properties of the host galaxies, which will be observed with the University’s new SkyMapper telescope. This can automatically tell the origin of elements in the Universe, and possibly the origin of life.

Supernova feedback on galaxy formation

Supernova feedback plays an essential role in solving i) the angular momentum problem (Steinmetz & Navarro 1999); the number and sizes of spiral galaxies in simulations are smaller than those observed, and ii) the missing satellite problem (Moore et al. 1999); the number of satellite galaxies are much larger than those observed. To study these, we will perform large-scale and high resolution simulations, which will also provide a clue to reveal the origin of the galactic morphology; how did spiral and elliptical galaxies form?

Feedback from active-galactic nuclei (AGN)

We will also include the AGN feedback from active-galactic nuclei (AGN), which may be important to explain the observed down-sizing effect (Cowie et al. 1996) that looks to be in conflict with the hierarchical clustering scenario of the standard cosmology.


To study the very high redshift Universe, the re-ionization and the UV background radiation have to be solved consistently with radiative transfer codes, as well as star formation. We encourage young people to do this! This will be one of the most important works at the era of the Square Kilometre Array (SKA) (2020?) that Australia is hoping to host.

Cosmological simulations image panel

Figure 1.1 - the time evolution of our cosmological simulation in a periodic box 10/h mpc on a side. We show the projected stellar v-luminosity (upper panels) and gas metallicity log z/zsun (lower panels). Metals are ejected from stars to intergalactic medium via supernova-driven galactic winds. See movie (MPG 21MB).

Updated:  19 October 2017/Responsible Officer:  RSAA Director/Page Contact:  Webmaster