Institute of Astronomy

Galaxy Formation

Galaxies are one of the most spectacular astrophysical object and are essential building blocks of the Universe. They are characterised by rich diversity in size, colour and morphology, depending both on their local environment and on their evolutionary past. Thus, galaxies provide us with invaluable clues on the large scale properties of the Universe in which they are embedded. However, equally important they tell us about the physical processes which are responsible for star formation, giving us further insight of how our own galaxy, The Milky Way, was formed.

The figure on the right is showing a beautiful HST picture of the M100 spiral galaxy, very similar to our Milky Way. From the so-called bulge - bright central stellar concentration - spiral arms are unfolding, being the place where the new stars are born. Image credits: D. Hunter (Lowell Observatory) and Z. Levay (Space Telescope Science Institute)/NASA.

During the last decade a wealth of observational evidences (e.g. by Hubble Space Telescope, SDSS Survey, and Spitzer Space Telescope among others) has put the processes of galaxy formation and evolution in a completely new light. It has emerged that variety of physical mechanism, acting from very small scales, where for example the stars are formed, up to the intragalactic distances, where encounters with other galaxies may lead to major merger events, are determining the properties of galaxies and their evolution in time. Henceforth, the study of such complex systems needs to be tackled with highly sophisticated numerical simulations, that take properly into account the cosmological growth of these structures.

Bridging the gap between present day and high redshift galaxies

A group of researchers at IoA are focusing on the so-called "damped Lyman alpha systems" -- galaxies in the process of formation which are not seen directly, but only as absorption when they are in a direct line between us and a yet more distant luminous object. Understanding the nature of these galaxies can ultimately providing a more direct link between them and modern-day galaxies, and thus unveil crucial aspects of galaxy formation. In order to achieve this, some of the most advanced simulations of galaxy formation have been employed and in detail compared with observations.

The figure shows the distribution of the neutral hydrogen responsible for the damped Lyman alpha absorption around a forming galaxy, in the centre.

Figure credits: Andrew Pontzen, based on simulation data run at the Arctic Region Supercomputing Centre; thanks to Fabio Governato and the N-Body Shop at the University of Washington.

Coevolution of galaxies and their central black holes

Remarkable observational evidence is indicating that probably most if not all galactic bulges in their very core contain a supermassive black hole, including our own Milky Way. Moreover, there appears to be a crucial link between the properties of host galaxies and their central black holes, implying that the evolution of galaxies is intimately linked to the evolution of black holes, and vice versa. By employing large scale cosmological simulations, where both the formation and growth of black holes and galaxies is tracked self-consistently, researchers at IoA are trying to understand in which way supermassive black holes are affecting their hosts, and whether indeed their feedback processes lead to the population of galaxies, as we see them today.

The figure is illustrating the relationship between the black hole mass and stellar bulge velocity dispersion obtained from simulations, while the dashed line denotes observational finding.

Figure credits: Debora Sijacki; the simulations were carried out at Computing Centre of Max-Planck Society in Garching, performed with massively parallel TREESPH code GADGET-2 in collaboration with Volker Springel.