New generation of galaxy formation simulations on the way

ENGINEERINGNET.BE – Over the last ten years, simulations of galaxies have become much better thanks to the rapid advance of numerical models and the computing power of supercomputers.

Now it can sometimes be almost impossible to distinguish a real galaxy from a simulated galaxy,” says astronomer Evgenii Chaikin from ULeiden.

Chaikin is working on the COLIBRE model, together with colleagues from ULeiden, Great Britain and other European countries. ‘The high spatial resolution of COLIBRE simulations allows you to zoom in on individually simulated galaxies to study the distribution of the gas and stars within them in detail.’

COLIBRE simulations also contain a large number of galaxies with diverse properties and formation histories, which researchers can select, study and compare with observations in several ways.

The art of a good simulation is to adjust the variables in a simulation model in such a way that it generates realistic galaxies. “There are many ingredients and sometimes a small difference in the adjustment of one ingredient can produce a completely different picture,” says Chaikin.

For example, gas mass, the distribution of the gas and the rate of star formation. ‘Stars explode at the end of their lives. The energy released in such an explosion heats the surrounding gas to very high temperatures and pushes the gas out of the galaxy. It is then more difficult for new stars to form, as they need dense and cold gas.’

A major improvement that the team achieved was the realistic transport of cold gas between the stars. ‘Previously it was almost never possible to realistically include dense gas with temperatures below 1000 Kelvin in the models. While in the real universe a large part of it is in molecular gas clouds, in which stars are formed.’

Chaikin mainly focused on realistically including the ingredient supernova explosions. Such a spectacular explosion of a star takes place on a relatively small scale. “Due to the insufficient spatial resolution of the simulations, we cannot simulate this process in detail,” Chaikin said.

‘But a lot of energy is released during such an explosion, so it is very important to include supernova explosions in the model of galaxy formation.’

Chaikin therefore wrote program code and calibrated the strength of energetic feedback from supernova explosions and supermassive black holes in the COLIBRE model. In such a way that the properties of simulated galaxies appear realistic.

Some test simulations showed promising results from his work, but the real test is yet to come. Chaikin, who obtained his PhD with honors on this subject: ‘I have been given a postdoc appointment, in which I will continue to work on the COLIBRE model. The end of the development phase of this model is close.’