Unveiling the Hidden Universe - from the first galaxies to brown dwarves

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Three of the biggest questions in astronomy are: (1) how do stars form? (2) How did galaxies form? (3) How has the Universe changed over time? It is hard to answer these questions with traditional optical telescopes. First, we now know that the birth of both stars and galaxies is largely hidden from view by cosmic dust, which absorbs the optical light and then reradiates the energy in the far-infrared and submillimetre wavebands. Second, we also know now that the Universe is dominated by dark matter, which does not radiate in any electromagnetic waveband, and 'dark energy', a substance we know even less about than dark matter. UK astronomers are in an excellent position to make substantial progress in answering all of these questions. The installation of the SCUBA-2 submillimetre camera on the James Clerk Maxwell Telescope in 2007 and the launch in 2008 of the Herschel Space Observatory, a telescope which will revolutionize far-infrared and submillimetre astronomy, will make it possible to study the early lives of stars and galaxies by observing the radiation from the dust. Other new facilities will make it possible to infer the properties of the dark matter and energy indirectly, in particular from its gravitational effects. We propose a research programme aimed at answering all of these questions. Building on our strong traditions of submillimetre astronomy (Cardiff is the main UK centre for the Herschel Space Observatory) and computer simulations of star formation, we propose a number of theoretical and observational projects to uncover the early lives of stars, and also to discover how and why they form in the first place. We also propose a project aimed at discovering whether the elliptical galaxies we see around us today are the descendants of the luminous dusty galaxies that filled the Universe ten billion years ago. Finally, we propose two projects to try to answer the third question. The evolution of the Universe depends critically on its dark component. First, we will carry out a project to measure the number of dark galaxies, ones in which contain no stars but only gas and dark matter, in our local neighbourhood. Second, we will use the results from the Planck satellite, which will be launched at the same time as Herschel, to study the properties of distant galaxy clusters, which will allow us to infer the properties of the dark energy.