19,892 research outputs found

    Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies

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    We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco (2004) and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as ALMA. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable soon. Nonetheless, we conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is a promising way of constraining the dark distribution in dSphs, especially if the particles are light.Comment: 10 pages, 5 figures, MNRAS, in pres

    Transonic flow

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    The main original contributions of this thesis are presented in Chapters II, III and IV, each of which is largely self-contained, but which are all directed at particular aspects of the same problem, the prediction of the pressure on an airfoil in symmetrical transonic flow. Chapter I sets this problem in its relation to transonic aerodynamics and provides accounts of various studies which are used in subsequent chapters with only limited explanation. Chapters II and III are devoted to extending the theory of Cole and Royce for transonic flow past an axisymmetric body, first to two-dimensional transonic flow past a thin airfoil, and then to flow past a thin planar delta wing. Chapter IV examines a different type of approximation which has received considerable attention, the parabolic equation approximation. It is shown how to remove certain deficiencies of methods based on this approximation, but one of the consequences is to cast doubt on the reliability of the method which appeared to give closest agreement with experiment
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