Galaxy Formation and Evolution

Galaxy evolution

It is believed that the seeds of galaxy formation are small fluctuations in the density of the Universe at redshifts z ~ 1000, left behind after a period of inflation (see Physics of the Early Universe). However, the simplest models produce far too many faint galaxies, suggesting the need for strong feedback of energy from supernovae, or large amounts of merging. Numerical simulations of structure formation are now starting to reach sufficient resolution that they can predict the morphologies, colours and star-formation histories of galaxies. At Sussex we have access to a large number of state-of-the-art galaxy surveys which provide an incomparable wealth of observational detail for galaxies at a range of redshifts that can be used to test our models.

The Sussex Astronomy Centre is involved in several major projects that will revolutionise our understanding of galaxy formation and evolution.

The Galaxy and Mass Assembly survey (GAMA) has recently compiled a panchromatic and spectroscopic survey to r-band magnitude limit of r = 19.8 over 180 square degrees (~375,000 galaxies with redshift z < 0.5).  The GAMA survey provides a valuable resource with which to study galaxy evolution in detail, including its dependence on intrinsic galaxy properties such as stellar mass, as well as environment, since redshift z ~ 0.5, covering a lookback time of 5 Gyr, about one third of the age of the Universe.  GAMA has already provided definitive measurements of the galaxy luminosity and stellar mass functions, and will soon be determining the halo mass function, thus completing the link between galaxies and their host dark matter halos.

 We have recently joined the 4-metre Multi-Object Spectroscopic Telescope (4MOST) project.  4MOST will be the premier wide-field spectroscopic facility in the southern hemisphere for at least the next decade and will carry out large surveys of Milky Way stars, galaxies, AGN and quasars. Sussex has leading involvement in the Wide Area Vista Extragalactic Survey (WAVES) and the Cosmology survey. 

We also have two co-Is (Loveday & Romer) in the Large Synoptic Survey Telescope (LSST).  This new 8.4-m telescope will produce the deepest and widest image of the Universe, and will impact on all areas of astronomy, from the Solar System, stars and galaxies, to distant supernovae. 

At higher redshifts, most galaxies contain large amounts of dust. The ultra-violet radiation generated by star formation in these young galaxies is absorbed by the dust and re-emitted at mid-far infrared wavelengths. We have a strong involvement in several space-based infrared surveys: the recently started Spitzer Wide-Area Infra-Red Extragalactic (SWIRE) Survey, and the Akari all-sky infrared survey and Herschel Space Observatory. These infrared surveys will measure the evolution of galaxies out to redshifts z ~ 3, ie. beyond the epoch of peak star formation activity at z ~ 2.

The Astronomy Centre - working with an international team - have observed the Hubble Ultra Deep Field - our deepest view of the Universe.  A new telescope, the Atacama Large Millimetre Array (ALMA), has been used to measure the light which is missed by the Hubble Space Telescope and thereby gain a full picture of the galaxies.  The ALMA observations are significantly deeper and sharper than anything seen before.  More information can be found on the European Southern Observatory website