The Herschel ATLAS: Dust and galaxy evolution, near and far.

Herschel will be the largest space telescope ever launched. It operates in a largely unexplored part of the spectrum - the far-infrared (FIR) and sub-millimetre (sub-mm), corresponding to light with wavelengths between 0.055 and 0.6 mm. The Earth's atmosphere is not transparent to this radiation (except in a few 'windows') and so, in order to observe the astrophysical processes in this regime, instruments have to be put into space. It has been recognised for more than a decade that this part of the spectrum is of great importance to our understanding of how galaxies and stars form and evolve. This is because galaxies contain dust grains which, due to their small size (0.01 - 0.1 microns), are very effective at absorbing optical and UV radiation emitted by stars. In simple terms, they block around half of all the light from galaxies, creating the dark patches seen in optical images. The dust then re-radiates this 'stolen starlight' at longer wavelengths - from 20 - 1000 microns. Using detectors sensitive to this radiation, astronomers can study the cold dust and gas content of galaxies - the reservoir from which they form their stars. Many galaxies which are undergoing dramatic 'bursts' of star formation contain so much dust that they are almost completely hidden from optical telescopes and are best discovered by observing in the FIR/sub-mm. In fact, in order to have a complete and unbiased picture of galaxy formation and evolution we need to explore this 'hidden Universe' as much as we need to pursue to the more traditional study of the optical light emitted directly by stars. The Herschel ATLAS is a large international project which will map 550 square degrees with Herschel (around 600 times the area of the full moon). This will be the widest area survey Herschel will conduct in its 3 year lifetime and will produce a legacy data-set which will be unsurpassed for decades to come. The primary aim of the survey is to make a census of dust and obscured star formation in ~100,000 galaxies in the local universe. This will create a 'benchmark' for studies of the more distant Universe to compare against and thus deduce how galaxies have evolved. The most detailed studies to date in comparable wavebands consist of only ~200 galaxies pre-selected in other wavebands (and thus being potentially biased) or <60 galaxies selected at the wavelength of interest. Thus the ATLAS will make a quantum leap in our knowledge about the universe in this part of the electromagnetic spectrum. The work we propose to do at Nottingham using ATLAS is split into two main themes. The local universe project will compare the sub-mm maps made by Herschel with optical surveys in order to determine how much optical light is hidden by dust in different types of galaxy. We will be able to learn about how much dust is contained in galaxies and the temperature we measure for the dust will inform us about the radiation environment in that galaxy. This will be very different for a galaxy with a lot of star formation compared to a quiescent galaxy like the Milky Way. The large-scale structure project will look at the how dust is distributed in the largest structures in the Universe - galaxy clusters. We will see if there is a signal from dust which has been 'stripped' from galaxy disks as they move through the intra-cluster gas and interact with other galaxies. We will also look in the regions surrounding massive black holes (quasars and radio galaxies) at in the distant universe to see if these objects are inducing galaxy formation in their immediate environment.