COALA science: galactic chemo-dynamics

Chiaki Kobayashi, Ralph Sutherland

How galaxies did form and evolution? - to answer this unsolved problem, we are simulating the formation and evolutionary history of galaxies in the Universe, including star formation, supernovae feedback, and chemical enrichment. Comparing the spacial distribution of elements within galaxies with observations, we will examine fundamental physical processes that drive galaxy formation.

Chemical and dynamical evolution of galaxies

Chemo-dynamical simulations of galaxies

Using the chemodynamical model in Kobayashi (2004)Kobayashi (2005), we simulate the formation and evolution of individual galaxies. For hydrodynamics, Smoothed Particle Hydrodynamics (SPH) method is adopted, and for gravity, the direct summation with the GRAPE system or tree method is applied. The relevant physical processes such as radiative cooling, star formation, supernovae feedback, and chemical enrichment are all included. Among supernovae, both core-collapse supernovae of massive stars and thermonuclear supernovae from low-mass binary stars are included, which produce different elements with different timescales. Now it is possible to predict the time/redshift evolution of the spacial distribution of elements from Lithium to Zinc (A=30), and will be extended up to Uranium (A=92) with the collaboration with the stellar astrophysics group.

Supernovae feedback drive galactic winds

Supernovae eject not only thermal energy to suppress star formation, but also produce heavy elements to enhance star formation. Therefore, those processes have to be solved simultaneously. In less-massive galaxies, supernova feedback drive galactic winds (Fig. 2.1), and heavy elements are ejected from galaxies into intergalactic medium.

Disk galaxy simulation

FIGURE 2.1 - THE TIME EVOLUTION OF THE FORMATION OF AN ISOLATED DISK GALAXY IN A HALO OF MASS OF 10^10/H MSUN. THE BLACK POINTS SHOW STAR PARTICLES, WHILE THE GAS PARTICLES ARE COLOUR-CODED ACCORDING TO THEIR TEMPERATURE. EACH PANEL IS 20 KPC ON A SIDE. THE UPPER ROW SHOWS FACE-ON PROJECTIONS, THE LOWER ROW GIVES EDGE-ON VIEWS. SEE MOVIE (MPG 8,6MB).

How did our Milky Way Galaxy form?

We will perform high-resolution simulations of the Milky Way Galaxy (Figure 2.2). Comparing the observed kinematics and elemental abundances of stars, we will untangle the formation and evolutionary history of the Milky Way Galaxy (the Galactic Archaeology). This will provide predictions and theoretical interpretations for the next generation of Australian instrument, the multi-object spectrograph HERMES (2012), being developed by the AAO.

Simulated Milky Way-type galaxy

FIGURE 2.2 - B-BAND LUMINOSITY MAP OF OUR SIMULATED MILKY WAY-TYPE GALAXY AT PRESENT FOR THE FACE-ON (LEFT PANEL) AND EDGE-ON PROJECTIONS. EACH PANEL IS 20 KPC ON A SIDE.

Galactic morphology and environmental effect.

We will simulate various types of galaxies in different environment: our Milky Way Galaxy, elliptical galaxies, spiral galaxies, and clusters of galaxies. From the comparison with the observed chemical abundances in nearby and distant galaxies, we would like to construct a consistent scenario when and how galaxies form and evolve ("g"alactic archaeology). This will also provide a clue to reveal the origin of the galactic morphology; how did spiral and elliptical galaxies form?

Mapping the kinematics and stellar populations within galaxies.

Internal structures are one of the most stringent constraints. With chemodynamical simulations, we can predict those, and will compare with the observations with the University's integral-field spectrograph WiFeS and the Giant Magellan Telescope (GMT) (2020) in which Australia is participating.

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