Old, gas-rich galaxies likely had early star formation boom

22 May 2015

The most massive stars (with masses up to a hundred times the mass of our sun) explode as supernovae at the end of their life and release huge amounts of energy and material into their neighbourhoods. These phenomena are so energetic that they can alter the rate of star formation and impact the chemical composition of galaxies since heavy elements are synthesised in the interior of stars via nuclear fusion reactions. Astronomical observations suggest that many supernova explosions adding up can halt the formation of new stars and expel enriched gas out of galaxies. Indirect observations seem also to suggest that a supermassive black hole resides at the centre of virtually all galaxies. We still do not know how these objects formed but we believe that their masses are greater than 1 million solar masses and the energy emitted by gas falling into them could produce outflows at even higher velocity than the supernova driven outflows (thousands of km/s).

In a recent University of Melbourne led paper, Dr Edoardo Tescari and colleagues present the first results of the CAASTRO supported AustraliaN GADGET-3 early Universe Simulations project, or ANGUS for short. The team ran numerical simulations of the Universe in its early stages (up to 13 billion years ago) to study formation and evolution of galaxies and how they interact with their environment. They focused in particular on the so called "feedback" effects associated with the formation of stars and supermassive black holes at the centre of galaxies.

Including the effects of both, supernovae and supermassive black holes, their simulations tested different configurations of feedback (early/late and weak/strong). The researchers found that efficient feedback at early times is needed to reproduce new observations of the global amount of star formation in the "young" Universe. They propose the following theoretical scenario to explain their results: galaxies that formed 13 billion years ago contained a lot of gas that was quickly converted into many stars. The back-reaction of the star formation processes (i.e. feedback) has since suppressed subsequent star formation especially in low mass galaxies.


Publication details:

E. Tescari, A. Katsianis, S. Wyithe, K. Dolag, L. Tornatore, P. Barai, M. Viel, S. Borgani in MNRAS (2014) "Simulated star formation rate functions at z ~ 4 – 7, and the role of feedback in high-z galaxies"