PATT travel grant support for the Bristol Astrophysics Group

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The Bristol Astrophysics Group works on a number of programmes that require careful observations to be made using the world's largest telescopes. This proposal requests two years of funding for travel to those telescopes, where they cannot be run remotely. In studies of the microwave background radiation, the left-over radiation from the Big Bang, it is important to remove contamination from foreground sources of emission that confuse our measurements of the background itself. These emission sources are radio galaxies and quasars, which may be much brighter than the radiation itself. Thus removal of this contamination requires sensitive observations of the radio environments of our target fields using large radio telescopes in the USA and elsewhere. Many of the effects that we are looking for relate to the 'shadows' cast on the background radiation by the gas in clusters of galaxies. We then also need to study those clusters with optical and infra-red telescopes, to measure the cluster masses, and to gain insights into how clusters form and change over the history of the Universe. Our work on active galaxies, which host supermassive black holes in their nuclei, is principally done using orbiting X-ray telescopes, but to understand the physics of the emission it is essential also to map the galaxies in the radio, infra-red, and optical bands. Here again Group members make extensive use of large ground-based telescopes, particularly the VLA in the USA, the ATCA in Australia, and ESO's large telescopes in Chile. A major aim of this work is to understand how active galaxies pump energy into gas in the Universe, helping to keep the gas between the galaxies hot. Small-scale models of those active galaxies can be found in our own Galaxy, in black hole systems with masses a few times the mass of the Sun. Work on these systems is done in the same way as for the active galaxies, but with the extra need to observe the systems repeatedly to follow their rapid changes in brightness and structure. From such information we can discover how matter behaves near black holes. A unifying thread of our work is the investigation into how the stucture of the Universe forms and changes with time. A large fraction of our observing is therefore dedicated to finding and characterizing the earliest galaxies and clusters, and then seeing how these systems differ from their older counterparts that lie closer to us. Again, we have to use a wide range of ground-based telescopes for this work, from the radio to the optical. Much of the optical work is done with the ESO telescopes in Chile. The corresponding radio work, to detect mm-wave lines from cold gas, often uses the ATCA in Australia, or the GBT in the USA. Nearby galaxies can be studied in more detail than more distant ones, and we also look at the changing populations of galaxies in different environments or at different redshifts. We are particularly interested in galaxies of the lowest mass, which are the most common, but which have properties that are both poorly understood and rather different from galaxies like our own. Finally, we also study our own Galaxy, looking at the gas between the stars, which has been heated by supernovae or young stars, and at the dense lumps of gas that emit coherent (maser) radiation. The gas motions tell us about how processes in the Galaxy continually recycle its gas, and can be used to measure the distances of objects within our Galaxy.