206 research outputs found

    Survival of Substructure within Dark Matter Haloes

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    Using high resolution cosmological N-body simulations, we investigate the survival of dark matter satellites falling into larger haloes. Satellites preserve their identity for some time after merging. We compute their loss of mass, energy and angular momentum as dynamical friction, tidal forces and collisions with other satellites dissolve them. We also analyse the evolution of their internal structure. Satellites with less than a few per cent the mass of the main halo may survive for several billion years, whereas larger satellites rapidly sink into the center of the main halo potential well and lose their identity. Penetrating encounters between satellites are frequent and may lead to significant mass loss and disruption. Only a minor fraction of cluster mass (10 per cent on average) is bound to substructure at most redshifts of interest. We discuss the application of these results to the survival and extent of dark matter haloes associated with cluster galaxies, and to interactions between galaxies in clusters. We find that 35-40 per cent of galaxy dark matter haloes are disrupted by the present time. The fraction of satellites undergoing close encounters is similar to the fraction of interacting or merging galaxies in clusters at moderate redshift.Comment: 16 pages, Latex, 14 Postscript figures. Submitted to MNRAS. Postscript version also available at http://www.mpa-garching.mpg.de/~bep

    Non-gaussian CMB temperature fluctuations from peculiar velocities of clusters

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    We use numerical simulations of a (480 Mpc/h)^3 volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev-Zeldovich effects will be highly non-Gaussian, and very different from the peak height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak height distributions. At fixed optical depth, the distribution of peak heights due to the kinematic effect is Gaussian, with a width which is approximately proportional to optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass, and the distribution of halo speeds is Gaussian, with a dispersion which is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter.Comment: Revised, citation added. To appear in MNRA

    How the Scalar Field of Unified Dark Matter Models Can Cluster

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    We use scalar-field Lagrangians with a non-canonical kinetic term to obtain unified dark matter models where both the dark matter and the dark energy, the latter mimicking a cosmological constant, are described by the scalar field itself. In this framework, we propose a technique to reconstruct models where the effective speed of sound is small enough that the scalar field can cluster. These models avoid the strong time evolution of the gravitational potential and the large Integrated Sachs-Wolfe effect which have been a serious drawback of previously considered models. Moreover, these unified dark matter scalar field models can be easily generalized to behave as dark matter plus a dark energy component behaving like any type of quintessence fluid.Comment: 26 pages, 1 figur
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