Shape of the Galactic Orbits in the CNOC1 Clusters

We present an analysis of the orbital properties in 9 intermediate-redshifts cluster of the CNOC1 survey and we compare them to a control sample of 12 nearby clusters. Similar to the nearby elliptical galaxies, the bulge-dominated galaxies in clusters at redshifts ~0.1-0.4 present orbits that are more eccentric than those for disk-dominated galaxies. However, the orbital segregation is less significant than that found for elliptical and spiral galaxies in nearby cluster. When galaxies are separated by colors - red galaxies with colors in the rest frame (U-V)_o > 1.4, and blue galaxies with (U-V)_o =< 1.4 - the strongest orbital segregation is found. Therefore, the segregation we found seems to modify more efficiently the star formation activity than the internal shape of the galaxies. When we compare the orbits of early-type galaxies at intermediate-redshift with those for z=0, they seem to develop significant changes getting much more eccentric. A different behavior is observed in the late-type galaxies, which present no-significant evolution in their orbit shapes.Comment: Accepted for publication in ApJ, April 2000. Latex with aaspp4.sty, 20 pages, 4 tables, 6 eps figure

On the DM interpretation of the origin of non-thermal phenomena in galaxy clusters

(Abridged) We study the predictions of various annihilating Dark Matter (DM) models in order to interpret the origin of non-thermal phenomena in galaxy clusters. We consider three neutralino DM models with light (9 GeV), intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created by neutralino annihilation produce a multi-frequency Spectral Energy Distribution (SED), as well as heating of the intracluster gas, that are tested against the observations available for the Coma cluster. The DM produced SEDs are normalized to the Coma radio halo spectrum. We find that it is not possible to interpret all non-thermal phenomena observed in Coma in terms of DM annihilation. The DM model with 9 GeV mass produces too small power at all frequencies, while the DM model with 500 GeV produces a large excess power at all frequencies. The DM model with 60 GeV and $\tau^{\pm}$ composition is consistent with the HXR and gamma-ray data but fails to reproduce the EUV and soft X-ray data. The DM model with 60 GeV and $b{\bar b}$ composition is always below the observed fluxes. The radio halo spectrum of Coma is well fitted only in the $b{\bar b}$ or light and intermediate mass DM models. The heating produced by DM annihilation in the center of Coma is always larger than the intracluster gas cooling rate for an NFW DM density profile and it is substantially smaller than the cooling rate only for a cored DM density profile in DM model with 9 GeV. We conclude that the possibility of interpreting the origin of non-thermal phenomena in galaxy clusters with DM annihilation models requires a low neutralino mass and a cored DM density profile. If we then consider the multimessenger constraints to the neutralino annihilation cross-section, it turns out that such scenario would also be excluded unless we introduce a substantial boost factor due to the presence of DM substructures.Comment: 9 pages, 6 figures, 2 Tables. Submitted to A&