* Astronomy

Title: The Cold Dark Matter Halos of Local Group Dwarf Spheroidals
Authors: Jorge Penarrubia, Alan McConnachie, Julio F. Navarro (Uvic, Canada)
(Version v2)

We examine the dynamics of stellar systems embedded within cold dark matter (CDM) halos in order to assess observational constraints on the dark matter content of Local Group dwarf spheroidals (dSphs). Our analysis shows that the total mass within the luminous radius is reasonably well constrained and approximately independent of the luminosity of the dwarf, highlighting the poor correspondence between luminosity and halo mass. This result implies that the average density of dark matter is substantially higher in physically small systems such as Draco and Sculptor than in larger systems such as Fornax. For example, our results imply that Draco formed in a halo 5 times more massive than Fornax's despite being roughly 70 times fainter. Stellar velocity dispersion profiles, sigma_p(R), provide further constraints; flat sigma_p(R) profiles imply that stars are deeply embedded within their cold dark matter halos and so quite resilient to tidal disruption. We estimate that halos would need to lose more than 90% of their original mass before tides begin affecting the kinematics of stars.
We estimate that V_max is about 3 times higher than the central velocity dispersion of the stars, which alleviates significantly the CDM ''substructure crisis''.
We use these results to interpret the size differences between the M31 and Milky Way (MW) dSph population. Our modelling indicates that this difference should be reflected in their kinematics, and predicts that M31 dwarfs should have velocity dispersions up to a factor of ~ 2 higher than their MW counterparts. This CDM-motivated prediction may be verified with present observational capabilities.

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Title: Axino warm dark matter and \Omega_b - \Omega_{DM} coincidence
Authors: Osamu Seto, Masahide Yamaguchi
(Version v2)

We show that axinos, which are dominantly generated by the decay of the next-to-lightest supersymmetric particles produced from the leptonic Q-ball (L-ball), become warm dark matter suitable for the solution of the missing satellite problem and the cusp problem. In addition, \Omega_b - \Omega_{DM} coincidence is naturally explained in this scenario.

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-- Edited by Blobrana at 10:34, 2007-06-13

The possibility of detection of extreme ultraviolet or ultraviolet photons from dark matter in our Local Group galaxy cluster progressed in 2006 when NASA decided in October 2006 to upgrade the Hubble UV telescope sensitivity by a factor of 30 in 2008 and Russia announced in June 2006 it will launch an ultraviolet astronomical observatory in 2010 having a 1.7 meter main mirror.

Professor Boris Shustov, Director of Astronomy of the Russian Academy of Sciences, was quoted in 2006 as saying: "One should particularly emphasise the observatory's role in detecting the so-called dark matter of the Universe and unlocking its secrets because such dark matter can only be seen by large ultraviolet telescopes."

Apparently the Russians doubt the primacy of Cold Dark Matter, which doesn't emit EUV or UV photons.

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Title: Measuring the dark matter velocity anisotropy in galaxy clusters
Authors: Steen H. Hansen, Rocco Piffaretti

The Universe contains approximately 6 times more dark matter than normal baryonic matter, and a direct observation of a fundamental difference between dark matter and baryons would both be of significant importance to our understanding of dark matter structures, as well as providing us with information about the basic characteristics of the dark matter particle. We discuss one such distinctive feature of equilibrated dark matter structures, namely the property that a local dark matter temperature may depend on direction. This is in stark contrast to baryonic gases. We use X-ray observations of two nearby relaxed galaxy clusters, under the assumption of hydrostatic equilibrium, to measure this dark matter temperature anisotropy \beta_{dm}, with non-parametric Monte Carlo methods, and we find that \beta_{dm} is larger than the value predicted for baryonic gases, \beta_{gas}=0, at more than 3\sigma confidence. The observed value of the temperature anisotropy is in good agreement with the results of cosmological N-body simulations and shows that the equilibration of the dark matter particles is not governed by local point-like interactions in contrast to baryonic gases.

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