Galactic outflows remove metals and suppress star formation

Galactic winds are thought to be the main mode of transport for metals from star-forming regions to deposit in the surrounding circumgalactic and intergalactic medium. While this sort of energy feedback is important to be accounted for in galaxy evolution simulations, physical and chemical processes are usually not resolved at the scale of cosmological simulations. The current paper (published in MNRAS on 19 February 2013) by Barai and colleagues, including a CAASTRO University of Melbourne member, Dr Edoardo Tescari, presents a hydrodynamic cosmological simulation that includes a kinetic feedback mechanism where supernova energy gives a velocity kick to gas particles at outflow speeds relative to the distance from the galactic centre.

The team tested two different cosmological volumes and four different outflow scenarios. As suggested by results from observational studies, their model also explores the relationship between outflow speed and galaxy mass. The results were found to provide a good match to observational data with regard to dependency of the star formation rate on galaxy stellar mass. In the ‘no wind’ and ‘variable wind dependent on halo mass’ scenarios, the amount of galactic gas was decreased in more massive halos, and there was a higher central concentration of metals originating from star formation. The ‘variable wind independent on halo mass’ scenario produced the clearest galactic disks. All four scenarios indicated that the thermal properties of the intergalactic medium were also affected by different wind conditions: the ‘variable wind independent on halo mass’ case caused a greater heating of the intergalactic medium.

These simulations have confirmed that galactic winds lead to metal-enrichment of the outflowing gas and a suppression of star formation in the galaxy, both of which were strong in the ‘constant wind’ and ‘variable wind independent on halo mass’ scenarios. In addition, they produced interesting features such as pristine gas infall along cosmological filaments that ‘feed’ the galactic centre. Edoardo Tescari's simulations make use of supercomputing facilities at CAASTRO’s partner institution, the National Computational Infrastructure (NCI).


Publication details:

P. Barai, M. Viel, S. Borgani, E. Tescari, L. Tornatore, K. Dolag, M. Killedar, P. Monaco, V. D’Odorico, S. Cristiani in MNRAS 430 “Galactic Winds in Cosmological Simulations of the Circumgalatic Medium