Probing the dark matter profile of hot clusters and the M-T relation with XMM-Newton

We present results based on XMM-Newton observations of a small sample of hot galaxy clusters. Making a full use of XMM-Newton's spectro-imaging capabilities, we have extracted the radial temperature profile and gas density profile, and with this information, calculated the total mass profile of each cluster (under the assumption of hydrostatic equilibrium and spherical symmetry). Comparing the individual scaled total mass profiles, we have probed the Universality of rich cluster mass profiles over a wide range of radii (from 0.01 to 0.7 the virial radius). We have also tested the shape of cluster mass profiles by comparing with the predicted profiles from numerical simulations of hierarchical structure formation. We also derived the local mass-temperature (M-T) scaling relation over a range of temperature going from 4 to 9 keV, that we compare with theoretical predictions.Comment: 7 pages, 2 figures, Advances in Space Research in press (proceedings of the COSPAR 2004 Assembly, Paris

Distances and Cosmology From Galaxy Cluster CMB Data

The measurement of angular diameter distance to galaxy clusters, through combined Sunyaev-Zel'dovich (SZ) effect data with X-ray emission observations, is now a well-known probe of cosmology. Using a combination of SZ data and a map of the lensed CMB anisotropies by the galaxy cluster potential, we propose an alternative geometric technique to measure distance information primarily through cluster related multi-frequency CMB measurements. We discuss necessary requirements to implement this measurement, potential errors including systematic biases, and the extent to which cosmological parameters can be extracted. While individual cluster distances are not likely to be precise, with upcoming subarcminute resolution wide-area CMB observations, useful information on certain cosmological parameters, such as the equation of state of dark energy, can be obtained from a large sample of galaxy clusters.Comment: 4 pages, 2 figure

Decaying dark matter: a stacking analysis of galaxy clusters to improve on current limits

We show that a stacking approach to galaxy clusters can improve current limits on decaying dark matter by a factor $\gtrsim 5-100$, with respect to a single source analysis, for all-sky instruments such as Fermi-LAT. Based on the largest sample of X-ray-selected galaxy clusters available to date (the MCXC meta-catalogue), we provide all the astrophysical information, in particular the astrophysical term for decaying dark matter, required to perform an analysis with current instruments.Comment: 6 pages, 3 figures, supplementary file available on demand, accepted for publication in PR

Calibration of the galaxy cluster M_500-Y_X relation with XMM-Newton

The quantity Y_ X, the product of the X-ray temperature T_ X and gas mass M_ g, has recently been proposed as a robust low-scatter mass indicator for galaxy clusters. Using precise measurements from XMM-Newton data of a sample of 10 relaxed nearby clusters, spanning a Y_ X range of 10^13 -10^15 M_sun keV, we investigate the M_500-Y_ X relation. The M_500 - Y_ X data exhibit a power law relation with slope alpha=0.548 \pm 0.027, close to the self-similar value (3/5) and independent of the mass range considered. However, the normalisation is \sim 20% below the prediction from numerical simulations including cooling and galaxy feedback. We discuss two effects that could contribute to the normalisation offset: an underestimate of the true mass due to the HE assumption used in X-ray mass estimates, and an underestimate of the hot gas mass fraction in the simulations. A comparison of the functional form and scatter of the relations between various observables and the mass suggest that Y_ X may indeed be a better mass proxy than T_ X or M_g,500.Comment: 4 pages, 2 figures, accepted for publication in A&

Scaling relations for galaxy clusters: properties and evolution

Well-calibrated scaling relations between the observable properties and the total masses of clusters of galaxies are important for understanding the physical processes that give rise to these relations. They are also a critical ingredient for studies that aim to constrain cosmological parameters using galaxy clusters. For this reason much effort has been spent during the last decade to better understand and interpret relations of the properties of the intra-cluster medium. Improved X-ray data have expanded the mass range down to galaxy groups, whereas SZ surveys have openened a new observational window on the intracluster medium. In addition,continued progress in the performance of cosmological simulations has allowed a better understanding of the physical processes and selection effects affecting the observed scaling relations. Here we review the recent literature on various scaling relations, focussing on the latest observational measurements and the progress in our understanding of the deviations from self similarity.Comment: 38 pages. Review paper. Accepted for publication in Space Science Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done by an international team at the International Space Science Institute (ISSI) in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and Lensing View

The hot gas content of fossil galaxy clusters

We investigate the properties of the hot gas in four fossil galaxy systems detected at high significance in the Planck Sunyaev-Zeldovich (SZ) survey. XMM-Newton observations reveal overall temperatures of kT ~ 5-6 keV and yield hydrostatic masses M500,HE > 3.5 x 10e14 Msun, confirming their nature as bona fide massive clusters. We measure the thermodynamic properties of the hot gas in X-rays (out to beyond R500 in three cases) and derive their individual pressure profiles out to R ~ 2.5 R500 with the SZ data. We combine the X-ray and SZ data to measure hydrostatic mass profiles and to examine the hot gas content and its radial distribution. The average Navarro-Frenk-White (NFW) concentration parameter, c500 = 3.2 +/- 0.4, is the same as that of relaxed `normal' clusters. The gas mass fraction profiles exhibit striking variation in the inner regions, but converge to approximately the cosmic baryon fraction (corrected for depletion) at R500. Beyond R500 the gas mass fraction profiles again diverge, which we interpret as being due to a difference in gas clumping and/or a breakdown of hydrostatic equilibrium in the external regions. Overall our observations point to considerable radial variation in the hot gas content and in the gas clumping and/or hydrostatic equilibrium properties in these fossil clusters, at odds with the interpretation of their being old, evolved and undisturbed. At least some fossil objects appear to be dynamically young.Comment: 4 pages, 2 figures. Accepted for publication in A&

Weak Lensing of Galaxy Clusters in MOND

We study weak gravitational lensing of galaxy clusters in terms of the MOND (MOdified Newtonian Dynamics) theory. We calculate shears and convergences of background galaxies for three clusters (A1689, CL0024+1654, CL1358+6245) and the mean profile of 42 SDSS (Sloan Digital Sky Survey) clusters and compare them with observational data. The mass profile is modeled as a sum of X-ray gas, galaxies and dark halo. For the shear as a function of the angular radius, MOND predicts a shallower slope than the data irrespective of the critical acceleration parameter $g_0$. The dark halo is necessary to explain the data for any $g_0$ and for three interpolation functions. If the dark halo is composed of massive neutrinos, its mass should be heavier than 2 eV. However the constraint still depends on the dark halo model and there are systematic uncertainties, and hence the more careful study is necessary to put a stringent constraint.Comment: 12 pages, 7 figures, references added, minor changes, accepted for publication in Ap

The structural and scaling properties of nearby galaxy clusters - II. The M-T relation

Using a sample of ten nearby (z< 0.15), relaxed galaxy clusters in the temperature range [2-9] keV, we have investigated the scaling relation between the mass at various density contrasts (delta=2500,1000,500,200) and the cluster temperature. The masses are derived from NFW-type model fits to mass profiles, obtained under the hydrostatic assumption using precise measurements, with XMM, at least down to delta=1000. The logarithmic slope of the M-T relation is well constrained and is the same at all delta, reflecting the self-similarity of the mass profiles. At delta=500, the slope of the relation for the sub-sample of hot clusters (kT>3.5 keV) is consistent with the standard self-similar expectation: alpha= 1.49\pm0.15. The relation steepens when the whole sample is considered: alpha=1.71\pm0.09. The normalisation of the relation is discrepant (by ~ 30%), at all density contrasts, with the prediction from purely gravitation based models. Models that take into account radiative cooling and galaxy feedback are generally in better agreement with our data. We argue that remaining discrepancies, in particular at low delta, are more likely due to problems with models of the ICM thermal structure rather than to an incorrect estimate of the mass from X-ray data.Comment: 11 pages, 4 figures, A&A in press, updated to match the accepted version (19/08/2005). Minor text clarifications, more detailed analysis of the M-T relations in Sect 3.2, corrected typo in Table 1 (redshift) and on cluster markers in Fig 1 legen

Structural and scaling properties of galaxy clusters: probing the physics of structure formation

We present XMM-Newton studies of the total mass, gas density, temperature and entropy profiles in nearby hot and cool clusters, together with follow-up observations of distant clusters from the SHARC Survey. The observed structural and scaling properties are compared with the predictions of the self-similar model of cluster formation. These data indicate that clusters do form a self-similar population down to low mass and up to high redshift, and give support to the standard picture of structure formation for the dark matter component. However, deviations from the standard scaling laws confirm that the specific physics of the gas component is still insufficiently understood.Comment: 9 pages, 8 figures; to be published in Memorie della Societa' Astronomica Italiana, the Proceedings of the EPIC Consortium (held on Oct 14-16, 2003 in Palermo