Galaxy Evolution
What is Galaxy Evolution?
Schematic illustration of galaxy evolution,
using images from the Hubble Ultra Deep Field,
and the Nearby Field Galaxy Catalogue
Galaxies, like our own Milky Way galaxy, are comprised of hundreds of billions of stars. Galaxies come in many shapes, sizes and colours. In the nearby universe (bottom of image to the left), galaxies have shapes classified broadly as spirals, ellipticals, or irregulars, but the further away we look (middle, top of image), corresponding to looking further into our universe's past, the more irregular galaxies appear to be. Trying to understand this evolution in the appearance of galaxies is one aspect of galaxy evolution research. Another aspect is in trying to understand how galaxies accumulate their mass. Galaxies turn gas mass into stellar mass through star formation, but galaxies also interact with each other, sometimes colliding and coalescing, and understanding the role and significance of galaxy star formation histories and galaxy interactions are further aspects of this research. The environment that galaxies inhabit also seems to play a role in their evolution, with galaxies inhabiting dense, cluster environments seeming to evolve more quickly in general than those in lower density environments. The impact on this evolution caused by the presence of a massive black hole in a galaxy's nucleus (see Active Galaxies) is also of particular current research interest.
Current research areas
Galaxy morphology evolution
The aim of this research is to understand how galaxies evolved from small, mostly irregularly shaped objects at early times to the well-ordered spirals and ellipticals that dominate the light we observe in the nearby universe. By using new software tools to quantify galaxy morphologies, taking into account their appearance over a range of wavelengths, and to map the distribution of star formation within galaxies and its history, a connection between star formation properties of galaxies and the development of their morphologies can be explored.
Galaxy mass distribution
A new survey called GAMA (Galaxy And Mass Assembly) is currently underway, to probe constraints on Cold Dark Matter models of the mass assembly and evolution of dark matter halos and the galaxies inhabiting them. This survey will measure the dark halo mass function down to 1012 Msun and its evolution to z=0.4. It will also measure the galaxy stellar mass function to extremely low mass limits, 107 Msun, building up a large sample of these very low mass galaxies in order to quantify their significance and role in galaxy evolution.
Galaxy and cosmic star formation histories
Accurately measuring the global star formation history of the universe provides strong constraints on all models of galaxy evolution. This area of research has matured over the past decade, and is now being explored as a function of galaxy mass. This will allow us to determine when, and over how long, galaxies of high and low mass formed the majority of their stars, and what other factors or processes regulate this aspect of galaxy evolution. In particular, very sensitive radio surveys provide large samples of star forming galaxies spanning a broad range of redshift with which to pursue this exploration. Among such surveys, with which Andrew Hopkins is involved, are the Phoenix Deep Survey, the ATLAS Survey, and the 1hr and 13hr deep fields led by Nick Seymour and researchers at Southampton. The use of sensitive radio surveys also provides large numbers of distant AGN systems, and exploring their evolution (see Active Galaxies), and their connection with broader aspects of galaxy evolution, is a closely related research area.
For more information on all the research described above contact Andrew Hopkins
Formation and evolution of the Local Group
This research (entitled Near Field Cosmology) aims to place the nearest galaxies, members of the Local Group, within a cosmological context. A physical model is being developed describing the formation and evolution of the Local Group, with attention to radiative and gaseous processes, combining radiative hydrodynamics code with multiwavelength data.
For more information contact Joss Bland-Hawthorn