Galaxy formation

In our cosmic surroundings, a great diversity of structures is observed: from tiny dwarf galaxies barely visible by modern telescopes, to large disk galaxies like our own Milky Way, to giant elliptical systems situated in the centers of supermassive clusters. 

Today, astronomical observations have mapped, in great detail, the constituents, ages and kinematics along this sequence of diverse morphologies. Despite the wealth of available data, our theoretical understanding of galaxy formation is still incomplete.

Observations of the minute features in the cosmic microwave background radiation, via COBE, WMAP and recently PLANCK, have revealed details of what kind of Universe we live in; the cosmic energy content is dominated by dark matter and dark energy, two unknown entities that are believe to be crucial for reconciliation with observations. Dark matter is five times more abundant than normal baryonic matter, and is predicted to gravitationally cluster into extended "haloes" - the birth places of galaxies. Details of galaxy assembly is complicated, involving gravity, hydrodynamics, gas cooling and heating mechanisms, energetic processes from stars and black holes etc., all within a cosmological framework of an expanding Universe. Despite this complexity, galaxies are observed to follow a large number of fairly simple scaling relations, relating e.g. rotational velocities and intrinsic luminosity of spiral galaxies, the rate of star formation and content of heavy elements to the total mass of stars, the mass of the central black hole to the velocity dispersion of bulge stars etc.

Numerical simulations have historically been successful in explaining the large scale features of cosmic structures, i.e. the cosmic web. However, numerical simulations struggle with reproducing thin extended disk galaxies such as our own Milky Way galaxy. Most attempts produce very compact, too massive systems and feature disks that are too small in comparison to observations, warranting a considerable effort in improving our understanding how the formation of stars within galaxies, and their related feedback processes operate.

Using state-of-the-art numerical methods, our group aims to improve upon our knowledge of galaxy formation, answering salient question such as: How did our Galaxy form? What is the origin of galactic morphology – the Hubble sequence? How do galaxies acquire their baryons? Why does the star-formation history of the Universe decline from redshift two? Can we reconcile the mass function of dark matter haloes with the observed luminosity function of galaxies? Why do clusters of galaxies contain so many more satellite galaxies than the Milky Way? What drives galactic outflows?

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Astrophysics Research Group
University of Surrey