Polar ring galaxies, where matter is in equilibrium in perpendicularorbits around spiral galaxies, are ideal objects to probe the 3D shapesof dark matter halos. The conditions to constrain the halos are that theperpendicular system does not strongly perturb the host galaxy, or thatit is possible to derive back its initial shape, knowing the formationscenario of the polar ring. The formation mechanisms are reviewed:mergers, tidal accretion, or gas accretion from cosmic filaments.The Tully-Fisher diagram for polar rings reveals that the velocityin the polar plane is higher than in the host plane, which can only be explained if the dark matter is oblate and flattened along the polar plane. Only a few individual systems havebeen studied in details, and 3D shapes of their haloes determinedby several methods. The high frequency of warps could be explainedby spontaneous bending instability, if the disks are sufficientlyself-gravitating, which can put constraints on the dark matter flattening.

The status of kinematic observations in Local Group dwarf spheroidalgalaxies (dSphs) is reviewed. Various approaches to the dynamicalmodelling of these data are discussed and some general features ofdSph dark matter haloes based on simple mass models are presented.

We present interpretations of the line-of-sight velocity distribution of stars in theDraco dwarf spheroidal galaxy in terms of CDM and MOND assuming constant mass-to-light ratioand anisotropy. We estimate the two parameters by fittingthe line-of-sight velocity dispersion and kurtosis profiles for stellar samplesdiffering by a number of stars rejected as interlopers.The results of the fitting procedure for CDM, high mass-to-light ratio(131–141 solar units in the V-band) and weakly tangential orbits, are similar fordifferent samples, but the quality of the fit is much worse when fewer interlopersare removed. For MOND, the derived mass-to-light ratio (21 solar units) is too large to beexplained by the stellar content of the galaxy.

The halo masses of nearby individual elliptical galaxiescan be estimated by using the kinematics of their stars, planetary nebulae, and globularclusters–ideally in combination.With currently improving coverage of galaxies of ordinary luminosities and morphologies,systematic trends may be identified.Bright, boxy ellipticals show strong signatures of dark matter,while faint, disky ones typically do not.The former result is problematic for the MOND theory of gravity, and the latter is a challenge to explain in theΛCDM paradigm of galaxy formation.

We investigate the well-known correlations between the dynamical mass-to-light ratio M/L and other global observables of elliptical (E) and lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates that dark matter in early-type galaxies contributes ~30% of the total mass inside one Re, in agreement with previous studies, with significant variations from galaxy to galaxy. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast rotating galaxies have lower dark matter fractions than the slow rotating and generally more massive ones.

We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fraction, fd = Md/M*, for these systems. We discuss implications about the total star formation efficiency in dark-matter halos and show that the the trend of fd with mass produces virial mass-to-light ratios which are consistent semi-analitical models. Preliminary kurtosis analysis of the quasi-constant M/L galaxies in Romanowsky et al. seems at odd with Dekel et al. simulations.

The kinematical properties of elliptical galaxies formed during the mergersof equal mass, stars+gas+dark matter spiral galaxies are compared to theobserved low velocity dispersions found for planetary nebulae on the outskirts of ellipticals,which have been interpreted as pointing to a lack of dark matter inellipticals (which poses a problem for the standard model of galaxy formation).We find that the velocity dispersion profiles of the stars in thesimulated ellipticalsmatch well the observed ones.The low outer stellar velocity dispersions are mainly caused by the radialorbits of the outermost stars, which, for a given binding energy must havelow angular momentum to reach their large radial distances, usually driven out along tidal tails.

Elements of kinematical and dynamical modeling of elliptical galaxies arepresented.In projection, NFW models resemble Sérsic models, but with a very narrow range of shapes (m = 3±1).The total density profile of ellipticals cannot be NFW-like because the predicted local M/L and aperture velocity dispersion within aneffective radius (Re) are much lower than observed. Stars must then dominate ellipticalsout to a few Re.Fitting an NFW model to the total density profile of Sérsic+NFW (stars+dark matter [DM]) ellipticals results in very high concentration parameters, asfoundby X-ray observers.Kinematical modeling of ellipticals assuming an isotropic NFW DM modelunderestimates M/L at the virial radius by a factor of 1.6 to 2.4, becausedissipationless ΛCDM halos have slightly different density profilesand slightly radial velocity anisotropy. In N-body+gas simulations of ellipticals as merger remnants ofspirals embedded in DM halos,the slope of the DM density profile is steeperwhen the initial spiral galaxies are gas-rich.The Hansen & Moore (2006)relation between anisotropy and the slope of the density profile breaks down for gas and DM, but the stars follow an analogous relation with slightly less radial anisotropies for a given density slope.Using kurtosis (h4) to infer anisotropy in ellipticals is dangerous, as h4 is also sensitive to small levels of rotation.The stationary Jeans equation provides accurate masses out to 8Re.The discrepancy between the modeling of Romanowsky et al. (2003),indicating a dearth of DM in ellipticals,and the simulations analyzed by Dekel et al. (2005), whichmatch thespectroscopic observations of ellipticals, is partly due to radial anisotropy and to observing oblate ellipticals face-on.However,one of the 15 solutions to the orbit modeling of Romanowsky et al. is found to have an amount andconcentration ofDMconsistent withΛCDM predictions.

The serendipitous discovery of a gravitational lens system formedby an elliptical galaxy at z ~ 1 and a post-starburstgalaxy at z ~ 3.8 brings a unique opportunity to study indetail the mass profile of a massive and relaxed object at a lookback time of half the age of the universe. We sketch here a comparisonof different methods to reconstruct the mass of the lens, both parametricallyand non-parametrically, highlighting their advantanges and limitations.

Weak gravitational lensing has become an important tool to study the properties of dark matter halos around galaxies, thanksto the advent of large panoramic cameras on 4 m class telescopes. Thisarea of research has been developing rapidly in the past few years,and in these proceedings we present some results based on theRed-Sequence Cluster Survey, thus highlighting what can be achieved withcurrent data sets. We present results on the measurement of virial masses as afunction of luminosity and the extent of dark matter halos. Muchlarger surveys are underway or planned, which will result in animpressive improvement in the accuracy of the measurements. However,the interpretation of future results will rely more and more oncomparison with numerical simulations, thus providing direct tests ofgalaxy formation models.

Strong gravitational lensing and stellar dynamics provide twocomplementary and orthogonal constraints on the density profiles ofgalaxies. Based on spherically symmetric, scale-free, mass models, itis shown that the combination of both techniques is powerful inbreaking the mass-sheet and mass-anisotropy degeneracies. Second, observational results are presented from the Lenses Structure & Dynamics(LSD) Survey and the Sloan Lens ACS (SLACS) Survey collaborations toillustrate this new methodology in constraining the dark and stellardensity profiles, and mass structure, of early-type galaxies toredshifts of unity.

Cosmological simulations of structure formation predict that galaxiesare dramatically modified by galaxy harassment during the assembly ofgalaxy clusters, losing a substantial fraction of their stellar masswhich today must be in the form of intracluster stars. Simulationspredict non-uniform spatial and radial velocity distributions forthese stars. Intracluster planetary nebulae are the only abundantcomponent of the intracluster light whose kinematics can be measuredat this time. Comparing these velocity distributions with simulationswill provide a unique opportunity to investigate the hierarchicalcluster formation process as it takes place in the nearby universe.

The mass distribution of galaxy clusters can be determined from thestudy of the projected phase-space distribution of cluster galaxies.The main advantage of this method as compared to others, is that itallows determination of cluster mass profiles out to very largeradii. Here I review recent analyses and results on this topic. Inparticular, I briefly describe the Jeans and Caustic methods, and theproblems one has to face in applying these methods to galaxysystems. Then, I summarize the most recent and important results onthe mass distributions of galaxy groups, clusters, and superclusters.Additional covered topics are the relative distributions of the darkand baryonic components, and the orbits of galaxies in clusters.

We present here a study of a sample of 14 nearby clusters of galaxies (0.06 < z < 0.1) observed with the ROSAT/PSPC. We convert the X-ray surface brightness profiles of the clusters into emission measure profiles scaled to the classical scaling relations based on the spherical collapse model. We sort the clusters into different temperature bins and stack the scaled emission measure (ScEM) profiles of clusters belonging to the same bin together. This method enhances the statistics of the profiles – especially in outer regions. The stacked profiles allow us to observe a signal out to radii r > r200.Fitting beta-models to the overall ScEM profiles we find for the different subsamples rc = 0.15-0.18 r200 and β = 0.8, which is higher than the canonical value of β = 2/3 often found. The beta-model is generally a better representation for hotter than for cooler clusters. We see indications for continuous steepening of the profiles with increasing radius: at radii r > 0.8 r200 the profiles are systematically below the beta-model curve with β = 0.8.


Recent X-ray observations have been showing that the old vision ofclusters as peacefully relaxed structures is in most cases absolutelywrong. Coupled with optical and radio observations, these X-ray datashow evidence for violent mechanisms. Results based on XMM-Newton gastemperature maps for four clusters will be presented here.


We revisit the density profile of the galaxies cluster MS 2137-23 bymodelling strong lensing, weak lensing data and the velocity dispersionprofile of the central cD galaxy. Though we are able to model thelensing properties with a NFW density profile, this latter modelcannot explain well the velocity dispersion nor the X-raysproperties. To accommodate all these independent constraints, one needsto go beyond the over-simplistic assumption of spherical symmetry. Thehigher mass and concentration inferred from lensing suggests that thedark matter halo is elongated along the line of sight. Themisalignment between the projected dark matter and stellar componentsalso supports this scenario. Neglecting projection effects leadsto systematic discrepancies between mass estimates. We thus argue thata fully triaxial modelling of haloes is a major concern for precision mass estimates.

Identification of first and second turnaround radii in groups of galaxiesprovide interesting scaling relations and may constrain cosmologicalparameters.

The OSER project (Optical Scintillation by Extraterrestrial Refractors)is proposed to search for scintillation Of extragalactic sourcesthrough the galactic – disk or halo – transparent H2 clouds,the last unknown baryonic structures.This project should allow one to detect column densitystochastic variations in cool Galactic molecular clouds of order of~ 3×10-5 g/cm2 per ~ 10 000 km transverse distance.

The SPI spectrometer aboard of the INTEGRAL satellitehas released a map of the e+e− annihilation emission lineof unprecedented quality, showing that most of the photons arise from aregion coinciding with the stellar bulge of the Milky Way. Theimpressive intensity (≃ 10-3 photon cm-2 s-1) andmorphology (round and wide) of the emission is begging an explanation. Different classes of astrophysical objects could injectpositrons in the interstellar medium of the bulge, but the onlyacceptable ones should inject them at energies low enough to avoidexcessive bremsstrahlung emission in the soft gamma ray regime. Amongthe ~ MeV injectors, none seems generous enough to sustain the highlevel of annihilation observed. Even the most profuse candidate, namelythe β+ radioactivity of 56Co nuclei created and expelled inthe interstellar medium by explosive nucleosynthesis of type Iasupernovae, falls short explaining the phenomenon due to the smallfraction of positrons leaking out from the ejecta (≈3%),together with the low SNIa rate in the bulge (≈0.03 percentury). It is therefore worth exploring alternative solutions, as for instance,the idea that the source of the positrons is the annihilation of lightdark matter (LDM) particles of the kind recently proposed, totally independently, by Bœhm and Fayet. Assuming that LDM is the culprit, crucialconstraints on the characteristics (mass and annihilation cross-section)of the associated particle may be discussed, combining direct gammaray observations and models of the early Universe. In particular,the mass of the LDM particles should be significantly less than 100 MeV, so that the e+ and e− resulting from their annihilations do not radiate exceedingly through bremsstrahlung in the interstellar gas of thegalactic bulge.

Leading candidates for non-baryonic Dark Matter areWeakly Interacting Massive Particles (WIMPs). The principles of WIMP direct detection and different search stategies are introduced. A review of experimental results is presented. The most promising projects for the future are surveyed.