Astronomy Centre

Galaxy Formation and 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 Sloan Digital Sky Survey is making a five-colour digital map of the sky, and is over half way to measuring the photometric properties of 20 million galaxies and obtaining spectra of one million galaxies. This survey is ideal for measuring the properties of galaxies out to redshift z ~ 0.3. The UKIRT Infrared Deep Sky Survey (UKIDSS), starting April 2005, comprises five near-infrared surveys to various depths. The "Large-Area Survey" is well matched to the depth of the SDSS spectroscopic samples, and by combining UKIDSS near-IR photometry with SDSS optical photometry and redshifts, we will obtain a detailed picture of the distribution of stellar mass in galaxies to redshift z ~ 0.3. We also plan follow-up spectroscopic observations of fainter UKIDSS sources using the AAOmega spectrograph on the Anglo-Australian Telescope. This will enable us to probe galaxy evolution to z ~ 0.8.

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 at https://www.eso.org/public/unitedkingdom/news/eso1633/