Abstract. We investigate temperature and entropy profiles of 13 nearby cooling flow clusters observed with the EPIC cameras of XMM-Newton. When normalized and scaled by the virial radius the temperature profiles turn out to be remarkably similar. At large radii the temperature profiles show a clear decline starting from a break radius at ∼0.1 r vir . The temperature decreases by ∼30% between 0.1 r vir and 0.5 r vir . As expected for systems where non-gravitational processes are of great importance, the scale length characterizing the central temperature drop is not found to be proportional to the virial radius of the system. The entropy of the plasma increases monotonically moving outwards almost proportional to the radius and the central entropy level is tightly correlated with the core radius of the X-ray emission. The dispersion in the entropy profiles is smaller if the empirical relation S ∝ T 0.65 is used instead of the standard self-similar relation S ∝ T and, as expected for cooling flow clusters, no entropy cores are observed.

We analyse the colour gradients (CGs) of ∼ 50 000 nearby Sloan Digital Sky Survey galaxies estimated by their photometrical parameters (Sérsic index, total magnitude and effective radius). From synthetic spectral models based on a simplified star formation recipe, we derive the mean spectral properties and explain the observed radial trends of the colour as gradients of the stellar population age and metallicity. CGs have been correlated with colour, luminosity, size, velocity dispersion and stellar mass. Distinct behaviours are found for early‐ and late‐type galaxies (ETGs and LTGs), pointing to slightly different physical processes at work in different morphological types and at different mass scales. In particular, the most massive ETGs (M*≳ 1011  M⊙) have shallow (even flat) CGs in correspondence of shallow (negative) metallicity gradients. In the stellar mass range (1010.3− 1010.5) ≲M*≲ 1011  M⊙, the metallicity gradients reach their minimum of ∼ − 0.5   dex−1. At M*∼ 1010.3− 1010.5  M⊙, colour and metallicity gradient slopes suddenly change. They turn out to anticorrelate with the mass, becoming highly positive at the very low masses, the transition from negative to positive occurring at M*∼ 109−9.5  M⊙. These correlations are mirrored by similar trends of CGs with the effective radius and the velocity dispersion. We have also found that age gradients anticorrelate with metallicity gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have colour and metallicity gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and supernovae feedback scenarios. Metallicity is found to be the main driver of the trend of CGs, especially for LTGs, but age gradients are not negligible and seem to play a significant role too. Owing to the large data set, we have been able to highlight that older galaxies have systematically shallower age and metallicity gradients than younger ones. The emerging picture is qualitatively consistent with the predictions from hydrodynamical and chemodynamical simulations. In particular, our results for high‐mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and supernovae feedback.

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Dark matter or modifications of the Newtonian inverse‐square law in the Solar system are studied with accurate planetary astrometric data. From extraperihelion precession and possible changes in the third Kepler's law, we get an upper limit on the local dark matter density, ρDM≲ 3 × 10−16 kg m−3 at the 2σ confidence level. Variations in the 1/r2 behaviour are considered in the form of either a possible Yukawa‐like interaction or a modification of gravity of Milgrom's modified Newtonian dynamics (MOND) type. Up to scales of 1011 m, scale‐dependent deviations in the gravitational acceleration are really small. We examined the MOND interpolating function μ in the regime of strong gravity. Gradually varying μ suggested by fits of rotation curves are excluded, whereas the standard form μ(x) =x/(1 +x2)1/2 is still compatible with data. In combination with constraints from galactic rotation curves and theoretical considerations on the external field effect, the absence of any significant deviation from inverse square attraction in the Solar system makes the range of acceptable interpolating functions significantly narrow. Future radio ranging observations of outer planets with an accuracy of few tenths of a metre could either give positive evidence of dark matter or disprove modifications of gravity.

LISA might detect gravitational waves from mergers of massive black hole binaries strongly lensed by intervening galaxies (Sereno et al. 2010). The detection of multiple gravitational lensing events would provide a new tool for cosmography. Constraints on cosmological parameters could be placed by exploiting either lensing statistics of strongly lensed sources or time delay measurements of lensed gravitational wave signals. These lensing methods do not need the measurement of the redshifts of the sources and the identification of their electromagnetic counterparts. They would extend cosmological probes to redshift z <= 10 and are then complementary to other lower or higher redshift tests, such as type Ia supernovae or cosmic microwave background. The accuracy of lensing tests strongly depends on the formation history of the merging binaries, and the related number of total detectable multiple images. Lensing amplification might also help to find the host galaxies. Any measurement of the source redshifts would allow to exploit the distance-redshift test in combination with lensing methods. Time-delay analyses might measure the Hubble parameter H_0 with accuracy of >= 10 km s^{-1}Mpc^{-1}. With prior knowledge of H_0, lensing statistics and time delays might constrain the dark matter density (delta Omega_M >= 0.08, due to parameter degeneracy). Inclusion of our methods with other available orthogonal techniques might significantly reduce the uncertainty contours for Omega_M and the dark energy equation of state