The Lx-T Relation and Intracluster Gas Fractions of X-ray Clusters

We re-examine the X-ray luminosity-temperature relation using a nearly homogeneous data set of 24 clusters selected for statistically accurate temperature measurements and absence of strong cooling flows. The data exhibit a remarkably tight power-law relation between bolometric luminosity and temperature with a slope 2.88 \pm 0.15. With reasonable assumptions regarding cluster structure, we infer an upper limit on fractional variations in the intracluster gas fraction <(\delta\fgas/\fgas)^2)^1/2 \le 15%. Imaging data from the literature are employed to determine absolute values of fgas within spheres encompassing density contrast 500 and 200 with respect to the critical density. Comparing binding mass estimates based on the virial theorem (VT) and the hydrostatic, betamodel (BM), we find a temperature-dependent discrepancy in fgas between the two methods caused by sytematic variation of the outer slope parameter beta with temperature. There is evidence that cool clusters have a lower mean gas fraction that hot clusters, but it is not possible to assess the statistical significance of this effect in the present dataset. The temperature dependance of the ICM density structure, coupled with the increase of the gas fraction with T in the VT aproach, explains the steepening of the Lx-T relation. The small variation about the mean gas fraction within this majority sub-population of clusters presents an important constraint for theories of galaxy formation and supports arguments against an Einstein-deSitter universe based on the population mean gas fraction and primordial nucleosynthesis. The apparent trend of lower gas fractions and more extended atmospheres in low T systems are consistent with expectations of models incorporating the effects of galactic winds on the ICM. ABRIDGEDComment: 11 pages, 4 figures, uses mn.sty and epsf.sty, accepted for publication in MNRAS; minor modifications: discussion added on CF LX (Sec. 3.1);comparison with Allen & Fabian L-T results (Sec.3.1 & Sec.4.4); statistics precised (3.1), discussion clarified (Sec. 2.2,Sec. 4.4); slight mistake in the r-T and M-T relation calibration corrected and thus fgas in Fig.3, Fig 4, Tab 2 slightly change

Benchmark Models for Air Conditioned Residential Buildings in Hot Humid Climate

peer reviewedThis study reports the results of a recent field survey for residential apartment buildings in Egypt. The aim of the survey is to create representative building energy models. Two building performance simulation models are created reflecting the average energy consumption characteristics of air-conditioned residential apartments in Alexandria, Cairo and Asyut. Aiming for future evaluation of the cost and energy affects of the new Egyptian energy standard this study established two detailed models describing the energy use profiles for air-conditioners, lighting, DHW and appliances in respect to buildings layout and construction. Using EnergyPlus simulation tool the collected surveyed data was used as input for two building simulation models. The simulation models were verified against the apartment characteristic found in the survey. This paper presents details of the building models including the energy use patterns and profiles created for this study

Self-similarity of clusters of galaxies and the L_X-T relation

In this paper based on ROSAT/PSPC data we investigate the emission measure profiles of a sample of hot clusters of galaxies (kT>3.5keV) in order to explain the differences between observed and theoretically predicted L_X-T relation. Looking at the form of the emission measure profiles as well as their normalizations we find clear indication that indeed the profiles have similar shapes once scaled to the virial radius, however, the normalization of the profiles shows a strong temperature dependence. We introduce a M_gas-T relation with the dependence M_gas propto T^1.94. This relationship explains the observed L_X-T relation and reduces the scatter in the scaled profiles by a factor of 2 when compared to the classical scaling. We interpret this finding as strong indication that the M_gas-T relation in clusters deviates from classical scaling.Comment: 4 pages including 4 figures, accepted for publication in A&A Letter

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

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En avril 2016, une Semaine de la construction en terre crue fût organisée par la faculté Loci. Mêlant conférences, ateliers et séminaire, elle avait pour ambition de croiser les trois missions de la faculté - l’enseignement, la recherche et le service à la société – autour de la terre crue. Cet article en propose un bref compte-rendu

High redshift X-ray galaxy clusters. II. The L_X-T relationship revisited

In this paper we re-visit the observational relation between X-ray luminosity and temperature for high-z galaxy clusters and compare it with the local L_X-T and with theoretical models. To these ends we use a sample of 17 clusters extracted from the Chandra archive supplemented with additional clusters from the literature, either observed by Chandra or XMM-Newton, to form a final sample of 39 high redshift (0.25 < z < 1.3) objects. Different statistical approaches are adopted to analyze the L_X-T relation. The slope of the L_X-T relation of high redshift clusters is steeper than expected from the self-similar model predictions and steeper, even though still compatible within the errors, than the local L_X-T slope. The distant cluster L_X-T relation shows a significant evolution with respect to the local Universe: high-z clusters are more luminous than the local ones by a factor ~2 at any given temperature. The evolution with redshift of the L_X-T relation cannot be described by a single power law nor by the evolution predicted by the self-similar model. We find a strong evolution, similar or stronger than the self-similar model, from z = 0 to z <0.3 followed by a much weaker, if any, evolution at higher redshift. The weaker evolution is compatible with non-gravitational models of structure formation. According to us a statistically significant sample of nearby clusters (z < 0.25) should be observed with the current available X-ray telescopes to completely exclude observational effects due to different generation detectors and to understand this novel result.Comment: 14 pages, 10 postscript figures. Accepted for publication in Astronomy & Astrophysics. Corrected typo

Effects of Selection and Covariance on X-ray Scaling Relations of Galaxy Clusters

We explore how the behavior of galaxy cluster scaling relations are affected by flux-limited selection biases and intrinsic covariance among observable properties. Our models presume log-normal covariance between luminosity (L) and temperature (T) at fixed mass (M), centered on evolving, power-law mean relations as a function of host halo mass. Selection can mimic evolution; the \lm and \lt relations from shallow X-ray flux-limited samples will deviate from mass-limited expectations at nearly all scales while the relations from deep surveys (10^{-14} \cgsflux) become complete, and therefore unbiased, at masses above \sims 2 \times 10^{14} \hinv \msol. We derive expressions for low-order moments of the luminosity distribution at fixed temperature, and show that the slope and scatter of the \lt relation observed in flux-limited samples is sensitive to the assumed \lt correlation coefficient. In addition, \lt covariance affects the redshift behavior of halo counts and mean luminosity in a manner that is nearly degenerate with intrinsic population evolution.Comment: 5pages, 4 Figures, Submitted to MNRA

Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983

An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044, is presented. Gas density and temperature profiles are calculated for the inner 500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness profile are well described with a beta model with beta=0.74, but the central regions require the introduction of a second component. The temperature profile is flat at the exterior with a slight dip towards the centre. The total mass profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B ratio profile shows that, at large scale, light traces mass to a reasonable extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with mass observed in the optical. The M_Fe/L_B ratio is about two times less than that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties of the emission measure profile are consistent with the empirical relation \mgas \propto \Tx^{1.94}, and not with the self-similar relation \mgas \propto \Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot cluster A1413 shows that the profiles are well scaled using the empirically determined relation S \propto \Tx^{0.65}, suggesting that the slope of the S-T relation is shallower than in the self-similar model. The form of the entropy profiles is remarkably similar, and there is no sign of a larger isentropic core in the cooler cluster. These data provide powerful agruments against preheating models. In turn, there is now increasing observational support for a trend of f_gas with system mass, which may go some way towards explaining the observed scaling behaviour. (Abridged.)Comment: Final refereed version to appear in A&A; Figs 2, 7, 11 and 12 are low re

Mass distribution in the most X-ray-luminous galaxy cluster RX J1347.5-1145 studied with XMM-Newton

We report on the analysis of XMM-Newton observations of RX J1347.5-1145 (z=0.451), the most X-ray-luminous galaxy cluster. We present a detailed total and gas mass determination up to large distances (~1.7 Mpc), study the scaling properties of the cluster, and explore the role of AGN heating in the cluster cool core. By means of spatially resolved spectroscopy we derive density, temperature, entropy, and cooling time profiles of the intra-cluster medium. We compute the total mass profile of the cluster in the assumption of hydrostatic equilibrium. If the disturbed south-east region of the cluster is excluded from the analysis, our results on shape, normalization, scaling properties of density, temperature, entropy, and cooling time profiles are fully consistent with those of relaxed, cool core clusters. We compare our total and gas mass estimates with previous X-ray, lensing, dynamical, and SZ studies. We find good agreement with other X-ray results, dynamical mass measurements, weak lensing masses and SZ results. We confirm a discrepancy of a factor ~2 between strong lensing and X-ray mass determinations and find a gross mismatch between our total mass estimate and the mass reconstructed through the combination of both strong and weak lensing. We explore the effervescent heating scenario in the core of RX J1347.5-1145 and find support to the picture that AGN outflows and heat conduction are able to quenching radiative cooling.Comment: 12 pages, 6 figures, accepted for publication in A&

The distant galaxy cluster CL0016+16: X-ray analysis up to R200R_{200}

To study the mass distribution of galaxy clusters up to their Virial radius, CL0016+16 seems to be a good candidate,since it is a bright massive cluster, previously considered as being dynamically relaxed. Using XMM-Newton observations of CL0016+16, we performed a careful X-ray background analysis, and we detected convincingly its X-ray emission up to $R_{200}$. We then studied its dynamical state with a detailed 2D temperature and surface brightness analysis of the inner part of the cluster. Using the assumption of both spherical symmetry and hydrostatic equilibrium (HE) we can determine the main cluster parameters: total mass, temperature profile, surface brightness profile and $\beta$-parameter. We also build a temperature map which clearly exhibits departure from spherical symmetry in the centre. To estimate the influence of these perturbations onto our total mass estimate, we also compute the total mass in the framework of the HE approach, but this time with various temperature profiles obtained in different directions. These various total mass estimates are consistent with each other. The temperature perturbations are clear signatures of ongoing merger activity. We also find significant residuals after subtracting the emissivity map by a 2D $\beta$-model fit. We conclude that, although CL0016+16 shows clear signs of merger activity and departure from spherical symmetry in the centre, its X-ray emissivity can be detected up to $R_{200}$ and the corresponding mass $M_{200}$ can be computed directly. It is therefore a good candidate to study cosmological scaling laws as predicted by the theory.Comment: 11 pages, 17 figures, Accepted for publication in A&