XMM-Newton observations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass

(Abridged) We present an analysis of the mass and entropy profiles of three poor clusters (A1991, A2717 and MKW9) observed with XMM-Newton. The clusters have similar temperatures (kT=2.65, 2.53 and 2.58 keV), and similar redshifts (0.04 < z < 0.06). We trace the surface brightness, temperature, entropy and integrated mass profiles up to 0.5 (0.35 for MKW9) of the virial radius (r_200). The integrated mass profiles are very similar in physical units and are reasonably well fitted with the NFW mass model with concentration parameters of c_200=4-6 and M_200=1.2-1.6 X 10^14 h_70^-1 \msun. The entropy profiles are similar at large scale, but there is some scatter in the central region (r<50 kpc). None of the clusters has an isentropic core. Including XMM data on A1983 (kT=2.2 keV), and A1413 (kT = 6.5 keV), we discuss the structural and scaling properties of cluster mass and entropy profiles. The scaled mass profiles display <20% dispersion in the 0.05 - 0.5 r_200 radial range. The c_200 parameters of these clusters, and other values from the literature, are fully consistent with the c_200 - M_200 relation derived from simulations. The dispersion in scaled entropy profiles is small, implying self-similarity down to low mass (kT ~2 keV), and is reduced by 30-40% (to ~20%) if we use the empirical relation S \propto T^0.65 instead of the standard self-similar relation, S \propto T. The mean scaled profile is well fitted by a power law for 0.05 < r_200 < 0.5, with a slope slightly lower than expected from pure shock heating (\alpha = 0.94+/-0.14), and a normalisation at 0.1 r_200 consistent with previous studies. The gas history thus likely depends both on gravitational processes and the interplay between cooling and various galaxy feedback mechanisms.Comment: Final refereed version to appear in A&A. Minor changes. 15 pages, 12 figures (Figs 1 & 3 low res

X-ray observations of the mass and entropy distributions in nearby galaxy clusters

I review some important aspects of the structural and statistical properties of the nearby X-ray galaxy cluster population, discussing the new constraints on mass profiles, the mass-temperature relation, and the entropy of the intracluster medium which have become available from recent X-ray observations.Comment: 11 pages, 4 figures. Invited review to appear in the proceedings of the XLIst Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From dark halos to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van. Typos corrected, added reference

Causality Violations in Cascade Models of Nuclear Collisions

Transport models have successfully described many aspects of intermediate energy heavy-ion collision dynamics. As the energies increase in these models to the ultrarelativistic regime, Lorentz covariance and causality are not strictly respected. The standard argument is that such effects are not important to final results; but they have not been seriously considered at high energies. We point out how and why these happen, how serious of a problem they may be and suggest ways of reducing or eliminating the undesirable effects.Comment: RevTeX, 23 pages, 9 (uuencoded) figures; to appear in Phys. Rev

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&

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&

Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku

We present the results from Suzaku observations of the hottest Abell galaxy cluster A2163 at $z=0.2$. To study the physics of gas heating in cluster mergers, we investigated hard X-ray emission from the merging cluster A2163, which hosts the brightest synchrotron radio halo. We analyzed hard X-ray spectra accumulated from two-pointed Suzaku observations. Non-thermal hard X-ray emission should result from the inverse Compton (IC) scattering of relativistic electrons by the CMB photons. To measure this emission, the dominant thermal emission in the hard X-ray band must be modeled in detail. To this end, we analyzed the combined broad-band X-ray data of A2163 collected by Suzaku and XMM-Newton, assuming single- and multi-temperature models for thermal emission and the power-law model for non-thermal emission. From the Suzaku data, we detected significant hard X-ray emission from A2163 in the 12-60 keV band at the $28\sigma$ level (or at the $5.5\sigma$ level if a systematic error is considered). The Suzaku HXD spectrum alone is consistent with the single-T thermal model of gas temperature $kT=14$ keV. From the XMM data, we constructed a multi-T model including a very hot ($kT=18$ keV) component in the NE region. Incorporating the multi-T and the power-law models into a two-component model with a radio-band photon index, the 12-60 keV energy flux of non-thermal emission is constrained within $5.3 \pm 0.9 (\pm 3.8)\times 10^{-12}~{\rm erg\, s^{-1} cm^{-2}}$. The 90% upper limit of detected IC emission is marginal ($< 1.2\times 10^{-11}~{\rm erg\, s^{-1} cm^{-2}}$ in the 12-60 keV). The estimated magnetic field in A2163 is $B > 0.098~{\rm \mu G}$. While the present results represent a three-fold increase in the accuracy of the broad band spectral model of A2163, more sensitive hard X-ray observations are needed to decisively test for the presence of hard X-ray emission due to IC emission.Comment: 7 pages, 7 figures, A&A accepted. Minor correctio

Joint measurement of the galaxy cluster pressure profile with Planck and SPT-SZ

We measured the average Compton profile of 461 clusters detected jointly by the South Pole Telescope (SPT) and Planck. The number of clusters included in this analysis is about one order of magnitude larger than in previous analyses. We propose an innovative method developed in Fourier space to combine optimally the Planck and SPT-SZ data, allowing us to perform a clean deconvolution of the point spread and transfer functions while simultaneously rescaling by the characteristic radial scale $R_{\rm 500}$ with respect to the critical density. The method additionally corrects for the selection bias of SPT clusters in the SPT-SZ data. We undertake a generalised Navarro-Frenk-White (NFW) fit to the profile with only one parameter fixed, allowing us to constrain the other four parameters with excellent precision. The best-fitting profile is in good agreement with the Universal Pressure Profile based on REXCESS in the inner region and with the Planck Intermediate Paper V profile based on Planck and the XMM archive in the outer region. We investigate trends with redshift and mass, finding no indication of redshift evolution but detecting a significant difference in the pressure profile of the low vs. high mass subsamples, in the sense that the low mass subsample has a profile that is more centrally-peaked than that of the high mass subsample. [abridged]Comment: 15 pages, 12 figures, submitted to A&

Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing

We have measured an Ag/Al interface specific resistance, 2AR(Ag/Al)(111) = 1.4 fOhm-m^2, that is twice that predicted for a perfect interface, 50% larger than for a 2 ML 50%-50% alloy, and even larger than our newly predicted 1.3 fOhmm^2 for a 4 ML 50%-50% alloy. Such a large value of 2ARAg/Al(111) confirms a predicted sensitivity to interfacial disorder and suggests an interface greater than or equal to 4 ML thick. From our calculations, a predicted anisotropy ratio, 2AR(Ag/Al)(001)/2AR(Ag/Al)(111), of more then 4 for a perfect interface, should be reduced to less than 2 for a 4 ML interface, making it harder to detect any such anisotropy.Comment: 3 pages, 2 figures, 1 table. In Press: Journal of Applied Physic