We present the results of the spectral classiÐcation of the 82 brightest galaxies in a sample of 17 compact groups. We verify that the active galactic nuclei (AGNs) are preferentially located in the most early-type and luminous galaxies of the groups, as is usually observed in the Ðeld. But these AGNs also appear to be systematically concentrated toward the central parts of the groups. Our observations suggest a correlation between activity types, morphologies, and densities of galaxies in the compact groups. This is consistent with a scenario in which galaxies of compact groups evolve by interacting with their environment and are currently in a quiet phase of their activity.

We used optical imaging and spectroscopic data to derive substructure estimates for local Universe (z < 0.11) galaxy clusters from two different samples. The first was selected through the Sunyaev-Zel'dovich (SZ) effect by the Planck satellite and the second is an X-ray selected sample. In agreement to X-ray substructure estimates we found that the SZ systems have a larger fraction of substructure than the X-ray clusters. We have also found evidence that the higher mass regime of the SZ clusters, compared to the X-ray sample, explains the larger fraction of disturbed objects in the Planck data. Although we detect a redshift evolution in the substructure fraction, it is not sufficient to explain the different results between the higher-z SZ sample and the X-ray one. We have also verified a good agreement (∼60%) between the optical and X-ray substructure estimates. However, the best level of agreement is given by the substructure classification given by measures based on the brightest cluster galaxy (BCG), either the BCG−X-ray centroid offset, or the magnitude gap between the first and second BCGs. We advocate the use of those two parameters as the most reliable and cheap way to assess cluster dynamical state. We recommend an offset cut of ∼0.01×R 500 to separate relaxed and disturbed clusters. Regarding the magnitude gap the separation can be done at ∆m 12 = 1.0. The central galaxy paradigm (CGP) may not be valid for ∼20% of relaxed massive clusters. This fraction increases to ∼60% for disturbed systems.

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Many candidate fundamental theories contain scalar fields that can acquire spacetime-varying expectation values in a cosmological context. Such scalars typically obey Lorentz-violating effective dispersion relations. We illustrate this fact within a simple supergravity model that also exhibits the observed late-time cosmological acceleration and implies varying electromagnetic couplings.Comment: 11 pages, 9 figures, 1 tabl

We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD) -designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD<0.05). In this work, we study the gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z < 0.1), 67% of the systems are classified as relaxed, while for the Millennium sample we find 63% (z = 0). We verify that in multimodal groups the average mass of modes in high multiplicity (N 20) systems are significantly larger than in low multiplicity ones (N < 20), suggesting that groups experience a mass growth at an increasing virialization rate towards z=0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g-r, R petro and µ petro ) and the gaussianity of the velocity distribution of the groups. Bright galaxies (M r -20.7) residing in the inner and outer regions of groups, do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7