X-ray Surface Brightness Profiles Research Articles

Cluster geometry and inclinations from deprojection uncertainties

{The determination of cluster masses is a complex problem that would be aided by information about the cluster shape and orientation (along the line-of-sight).} {It is in this context, that we have developed a scheme for identifying the intrinsic morphology and inclination of a cluster, by looking for the signature of the true cluster characteristics in the inter-comparison of the different deprojected emissivity profiles (that all project to the same X-ray brightness distribution) and by using SZe data when available.} {We deproject the cluster X-ray surface brightness profile under the assumptions of four different geometry and inclination configurations for the observed system; these 4 configurations correspond to four extreme geometry+inclination scenarios. The deprojection in question is performed by the non-parametric algorithm DOPING. The formalism is tested with model systems and then is applied to a sample of 24 clusters. While the shape determination is possible by implementing the X-ray brightness alone, the estimation of the inclination is usually markedly improved by the usage of SZe data that is available for the considered sample.}{We spot 8 prolate systems, 1 oblate and 15 of the clusters in our sample as triaxial. In fact, for systems identified as triaxial, we are able to discern how the three semi-axes lengths compare with each other. This, when compounded by the information about the line-of-sight extent, allows us to constrain the inclination quite tightly and offers the two intrinsic axial ratios of the triaxial systems.}{}

Why Do Only Some Galaxy Clusters Have Cool Cores?

Flux-limited X-ray samples indicate that about half of rich galaxy clusters have cool cores. Why do only some clusters have cool cores while others do not? In this paper, cosmological N-body + Eulerian hydrodynamic simulations, including radiative cooling and heating, are used to address this question as we examine the formation and evolution of cool core (CC) and noncool core (NCC) clusters. These adaptive mesh refinement simulations produce both CC and NCC clusters in the same volume. They have a peak resolution of 15.6 h−1 kpc within a (256 h−1 Mpc)3 box. Our simulations suggest that there are important evolutionary differences between CC clusters and their NCC counterparts. Many of the numerical CC clusters accreted mass more slowly over time and grew enhanced CCs via hierarchical mergers; when late major mergers occurred, the CCs survived the collisions. By contrast, NCC clusters experienced major mergers early in their evolution that destroyed embryonic CCs and produced conditions that prevented CC reformation. As a result, our simulations predict observationally testable distinctions in the properties of CC and NCC beyond the core regions in clusters. In particular, we find differences between CC versus NCC clusters in the shapes of X-ray surface brightness profiles, between the temperatures and hardness ratios beyond the cores, between the distribution of masses, and between their supercluster environs. It also appears that CC clusters are no closer to hydrostatic equilibrium than NCC clusters, an issue important for precision cosmology measurements.

Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17

We present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 per square arcmin) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly-lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17 obtained in such a way is remarkable. It reveals a ringlike dark matter substructure at r~75 surrounding a soft, dense core at r~50. We interpret this peculiar sub-structure as the result of a high-speed line-of-sight collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated by the cluster velocity distribution. Our numerical simulation with purely collisionless particles demonstrates that such density ripples can arise by radially expanding, decelerating particles that originally comprised the pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56, but viewed $along$ the collision axis at a much later epoch. In addition, we show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and lensing can be resolved by treating the cluster X-ray emission as coming from a superposition of two X-ray systems. The cluster's unusual X-ray surface brightness profile that requires a two isothermal sphere description supports this hypothesis.

The β‐Model Problem: The Incompatibility of X‐Ray and Sunyaev‐Zeldovich Effect Model Fitting for Galaxy Clusters

We have analyzed a large sample of numerically simulated clusters to demonstrate the adverse effects resulting from the use of X-ray-fitted β-model parameters with Sunyaev-Zeldovich effect (SZE) data. There is a fundamental incompatibility between β-model fits to X-ray surface brightness profiles and those done with SZE profiles. Since observational SZE radial profiles are in short supply, the X-ray parameters are often used in SZE analysis. We show that this leads to biased estimates of the integrated Compton y-parameter inside r500 calculated from clusters. We suggest a simple correction of the method, using a nonisothermal β-model modified by a universal temperature profile, which brings these calculated quantities into closer agreement with the true values.

Simulated X-ray galaxy clusters at the virial radius: Slopes of the gas density, temperature and surface brightness profiles

Using a set of hydrodynamical simulations of nine galaxy clusters with masses in the range 1.5 x 10 14 < M vir < 3.4 x 10 15 M ⊙ , we have studied the density, temperature and X-ray surface brightness profiles of the intracluster medium in the regions around the virial radius. We have analysed the profiles in the radial range well above the cluster core, the physics of which are still unclear and matter of tension between simulated and observed properties, and up to the virial radius and beyond, where present observations are unable to provide any constraints. We have modelled the radial profiles between 0.3R 200 and 3R 200 with power laws with one index, two indexes and a rolling index. The simulated temperature and [0.5-2] keV surface brightness profiles well reproduce the observed behaviours outside the core. The shape of all these profiles in the radial range considered depends mainly on the activity of the gravitational collapse, with no significant difference among models including extraphysics. The profiles steepen in the outskirts, with the slope of the power-law fit that changes from -2.5 to -3.4 in the gas density, from -0.5 to -1.8 in the gas temperature and from -3.5 to -5.0 in the X-ray soft surface brightness. We predict that the gas density, temperature and [0.5-2] keV surface brightness values at R 200 are, on average, 0.05, 0.60, 0.008 times the measured values at 0.3R 200 . At 2R 200 , these values decrease by an order of magnitude in the gas density and surface brightness, by a factor of 2 in the temperature, putting stringent limits on the detectable properties of the intracluster-medium (ICM) in the virial regions.

Probing the Mass Distributions in NGC 1407 and Its Associated Group with the X‐Ray Imaging Spectroscopic and Optical Photometric and Line‐Strength Indices Data

We present a study of the mass distributions in the bright E0 galaxy NGC 1407 and its associated group by analyzing the high quality Chandra and ROSAT X-ray spectroscopic data. In order to probe the stellar mass distribution we calculated the B-band mass-to-light ratio profile by comparing the observed line-strength indices and multi-color photometric data with different stellar synthesis model predictions. We find that the gas is single-phase with a temperature of ~0.7 keV within 1Re. Outside 1Re the gas temperature increases quickly outwards to >1 keV, indicating its group origin. We reveal that the X-ray surface brightness profile shows a central excess in the innermost region, and on both the total mass and dark matter profiles there is a flattened feature at about 1Re is dominated by dark matter. At the virial radius r200=572\pm118 kpc, the inferred mass and mass-to-light ratio are M200=2.20\pm0.42E13 solarM and Mvir/LB=311\pm60 solarM/solarL,respectively, showing that the NGC 1407 group is an extremely dark system even comparable to many clusters of galaxies. Since the obtained total mass is lower than those given in the earlier galaxy kinematic works, we speculate that NGC 1400 is not a virialized member in the group's gravitational potential well.

An improved deprojection and PSF-deconvolution technique for galaxy-cluster X-ray surface-brightness profiles

We have developed a regularisation procedure for the direct deprojection and PSF-deconvolution of X-ray surface brightness profiles of clusters of galaxies. This procedure allows us to obtain accurate density profiles in a straightforward manner from X-ray observations (in particular data from XMM-Newton, where the PSF correction is important), while retaining information about substructure in the gas distribution, in contrast to analytic modelling of the profiles. In addition to describing our procedure, we present here a detailed investigation of the accuracy of the method and its error calculations over a wide range of input profile characteristics and data quality using Monte Carlo simulations. We also make comparisons with gas density profiles obtained from Chandra observations, where the PSF correction is small, and with profiles obtained using analytic modelling, which demonstrate that our procedure is a useful improvement over standard techniques. This type of method will be especially valuable in the ongoing analysis of unbiased and complete samples of X-ray clusters, both local and distant, helping to improve the quality of their results.

The Sunyaev‐Zel’dovich Effect in a Sample of 31 Clusters: A Comparison between the X‐Ray Predicted andWMAPObserved Cosmic Microwave Background Temperature Decrement

The WMAP Q-, V-, and W-band radial profiles of temperature deviation of the cosmic microwave background (CMB) were constructed for a sample of 31 randomly selected nearby clusters of galaxies in directions of Galactic latitude > 30°. The profiles were compared in detail with the expected CMB Sunyaev-Zel'dovich effect (SZE) caused by these clusters, with the hot gas properties of each cluster inferred observationally by applying gas temperatures as measured by ASCA to isothermal β-models of the ROSAT X-ray surface brightness profiles, with the WMAP point-spread function fully taken into consideration. After co-adding the 31 cluster fields to significantly reduce the systematic and random uncertainties, it appears that WMAP detected the SZE in all three bands. Quantitatively, however, the observed SZE only accounts for about 1/4 of the expected decrement. The discrepancy represents too much unexplained extra flux: in the W band, the detected SZE corresponds on average to 5.6 times less X-ray gas mass within a 10' radius than the mass value given by the ROSAT β-model. We critically examined how the X-ray prediction of the SZE may depend on our uncertainties in the density and temperature of the hot intracluster plasma, and emission by cluster radio sources. Although our comparison between the detected and expected SZE levels is subject to a margin of error, the fact remains that the average observed SZE depth and profile are consistent with those of the primary CMB anisotropy, i.e., the overall WMAP temperature decrement among the 31 rich clusters is too shallow to necessitate an interpretation in terms of an additional effect like the SZE. A unique aspect of this SZE investigation is that because all the data being analyzed are in the public domain, our work is readily open to scrutiny by others.

Weak‐lensing Detection atz∼ 1.3: Measurement of the Two Lynx Clusters with the Advanced Camera for Surveys

We present a Hubble Space Telescope Advanced Camera for Surveys (ACS) weak-lensing study of RX J0849+4452 and RX J0848+4453, the two most distant (at z = 1.26 and 1.27, respectively) clusters yet measured with weak lensing. The two clusters are separated by ~4' from each other and appear to form a supercluster in the Lynx field. Using our deep ACS i775 and z850 imaging, we detected weak-lensing signals around both clusters at ~4 σ levels. The mass distribution indicated by the reconstruction map is in good spatial agreement with the cluster galaxies. From the singular isothermal sphere (SIS) fitting, we determined that RX J0849+4452 and RX J0848+4453 have similar projected masses of (2.0 ± 0.6) × 1014 and (2.1 ± 0.7) × 1014 M☉, respectively, within a 0.5 Mpc (~60'') aperture radius. In order to compare the weak-lensing measurements with the X-ray results calibrated by the most recent low-energy quantum efficiency determination and time-dependent gain correction, we also reanalyzed the archival Chandra data and obtained TX = 3.8 and 1.7 keV for RX J0849+4452 and RX J0848+4453, respectively. Combined with the X-ray surface brightness profile measurement under the assumption of an isothermal β-model, the temperature of RX J0849+4452 predicts that the projected mass of the cluster within r = 0.5 Mpc is 2.3 × 1014 M☉, consistent with the weak-lensing analysis. On the other hand, for RX J0848+4453 we find that the mass derived from this X-ray analysis is much smaller (6.3 × 1013 M☉) than the weak-lensing measurement.

ChandraReveals Galaxy Cluster with the Most Massive Nearby Cooling Core: RXC J1504.1−0248

A Chandra follow-up observation of an X-ray-luminous galaxy cluster with a compact appearance, RXC J1504.1-0248, discovered in our REFLEX Cluster Survey, reveals an object with one of the most prominent cluster cooling cores. A β-model fit to the X-ray surface brightness profile gives a core radius of ~30 h kpc, which is much smaller than the cooling radius with ~140 kpc. As a consequence, more than 70% of the high X-ray luminosity of Lbol = 4.3 × 1045 h ergs s-1 of this cluster is radiated inside the cooling radius. A simple modeling of the X-ray morphology of the cluster leads to a formal mass deposition rate within the classical cooling flow model of 1500-1900 M☉ yr-1 (for h100 = 0.7; 2300-3000 M☉ yr-1 for h100 = 0.5). The center of the cluster is marked by a giant elliptical galaxy, which is also a known radio source. Thus, it is very likely that we are observing one of the interaction systems where the central cluster active galactic nucleus (AGN) is heating the cooling core region in a self-regulated way to prevent a massive cooling of the gas, similar to several such cases studied in detail in more nearby clusters. The interest raised by this system is then due to the high power recycled in RXC J1504-0248 over cooling timescales, which is about 1 order of magnitude higher than what occurs in the studied, nearby cooling core clusters. The assumption that cooling is exactly balanced by the AGN heating implies a central black hole mass growth rate of the order of 0.5 M☉ yr-1. This cluster is therefore a prime target for the study of AGN-intracluster medium interaction at very extreme conditions. Further features common to cooling cores found in this cluster are a strong temperature drop toward the center and narrow, low-ionization emission lines in the central cluster galaxy. The cluster is also found to be very massive, with a global X-ray temperature of about 10.5 keV and a total mass of about 1.7 × 1015 h M☉ inside 3 h Mpc.

ChandraObservation of the Cluster of Galaxies MS 0839.9+2938 atz= 0.194: The Central Excess Iron and Type Ia Supernova Enrichment

We present the Chandra study of the intermediate-redshift (z = 0.194) cluster of galaxies MS 0839.9+2938. By performing both projected and deprojected spectral analyses, we find that the gas temperature is approximately constant at about 4 keV within 130-444 h kpc. In the inner regions, the gas temperature decreases toward the center, reaching ≲3 keV in the central 37 h kpc. This implies that the lower and upper limits of the mass deposit rate are 9-34 and 96-126 M☉ yr-1, respectively, within 74 h kpc, where the gas is significantly colder. Along with the temperature drop, we detect a significant inward iron abundance increase from about 0.4 Z☉ in the outer regions to ≃1 Z☉ within the central 37 h kpc. Thus, MS 0839.9+2938 is the cluster showing the most significant central iron excess at z ≳ 0.2. We argue that most of the excess iron should have been contributed by SNe Ia. Using the observed SN Ia rate and stellar mass loss rate, we estimate that the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr, which is similar to those found for nearby clusters. Coinciding with the optical extension of the cD galaxy (up to about 30 h kpc), the observed X-ray surface brightness profile exhibits an excess beyond the distribution expected by either the β model or the Navarro-Frenk-White (NFW) model and can be well fitted with an empirical two-β model that leads to a relatively flatter mass profile in the innermost region.

Tracing the X-ray emitting intra-cluster medium of clusters of galaxies beyondr$\mathsf{_{200}}$

(Abridged) We present in this paper a sample of 14 nearby clusters of galaxies observed with the ROSAT/PSPC. We only select clusters with low galactic nH in order to trace the X-ray emitting intra-cluster medium (ICM) out to large radii. 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 together. The stacked profiles allow us to observe out to radii r>r_200. In the center we find that the ScEM profiles deviate from predicted scaling laws. This result is in very good agreement with current studies on the L_X-T relation and the entropy - temperature relation (S \propto T^0.65) found recently. At radii r>0.4r_200 we find that the ScEM profiles agree well within the error bars, suggesting self-similarity. Fitting beta-models to the overall ScEM profiles we find for the different sub samples r_c=0.15-0.18 r_200 and beta=0.8, which is higher than beta=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>0.8r_200 the profiles are systematically below the beta-model curve with beta=0.8. We discuss our results with respect to the observed X-ray luminosity L_X-T relation, the gas mass M_gas-T relation and the total mass M-T relation. We also address implications on the origin of the observed S-T relation. Furthermore we discuss the observed steepness of the X-ray profiles, which falls off more rapidly than predicted from the NFW-profile for cold dark matter halos.

ChandraObservations of Diffuse Gas and Luminous X‐Ray Sources around the X‐Ray–bright Elliptical Galaxy NGC 1600

We observed the X-ray-bright E3 galaxy NGC 1600 and nearby members of the NGC 1600 group with the Chandra X-Ray Observatory ACIS-S3 to study their X-ray properties. Unresolved emission dominates the observation; however, we resolved some of the emission into 71 sources, most of which are low-mass X-ray binaries associated with NGC 1600. Twenty-one of the sources have LX > 2 ? 1039 ergs s-1 (0.3-10.0 keV; assuming they are at the distance of NGC 1600), marking them as ultraluminous X-ray point source (ULX) candidates; we expect that only 11 ? 2 are unrelated foreground/background sources. NGC 1600 may have the largest number of ULX candidates in an early-type galaxy to date; however, cosmic variance in the number of background active galactic nuclei cannot be ruled out. The spectrum and luminosity function (LF) of the resolved sources are more consistent with sources found in other early-type galaxies than with sources found in star-forming regions of galaxies. The source LF and the spectrum of the unresolved emission both indicate that there are a large number of unresolved point sources. We propose that these sources are associated with globular clusters (GCs) and that NGC 1600 has a large GC specific frequency. Observations of the GC population in NGC 1600 would be very useful for testing this prediction. Approximately 50%-75% of the unresolved flux comes from diffuse gaseous emission. The spectral fits, hardness ratios, and X-ray surface brightness profile all point to two gas components. We interpret the soft inner component (a 25'', kT ~ 0.85 keV) as the interstellar medium of NGC 1600 and the hotter outer component (a 25'', kT ~ 1.5 keV) as the intragroup medium of the NGC 1600 group. The X-ray image shows several interesting structures. First, there is a central region of excess emission that is roughly cospatial with H? and dust filaments immediately west of the center of NGC 1600. There appear to be holes in the X-ray emission to the north and south of the galaxy center that are roughly coincident with the lobes of the NGC 1600 radio source. On larger scales, there is excess emission to the northeast, which we suggest may indicate the center of the group potential. The group galaxy NGC 1603 shows a tail of X-ray emission to its west that is probably due to ram pressure stripping.

The Distribution of Two‐dimensional Eccentricity of Sunyaev‐Zel'dovich Effect and X‐Ray Surface Brightness Profiles

With the triaxial density profile of dark matter halos and the corresponding equilibrium gas distribution, we derive two-dimensional Sunyaev-Zel'dovich (SZ) effect and X-ray surface brightness profiles for clusters of galaxies. It is found that the contour map of these observables can be well approximated by a series of concentric ellipses with scale-dependent eccentricities. The statistical distribution of their eccentricities (or, equivalently, axial ratios) is analyzed by taking into account the orientation of clusters with respect to the line of sight and the distribution of the axial ratios and the concentration parameters of dark matter halos. For clusters of mass 1013 h-1 M☉ at redshift z = 0, the axial ratio is peaked at η ~ 0.9 for both SZ and X-ray profiles. For larger clusters, the deviation from circular distributions is more apparent, with η peaked at η ~ 0.85 for M = 1015 h-1 M☉. To be closer to observations, we further study the axial-ratio distribution for mass-limited cluster samples with the number distribution of clusters at different redshifts described by a modified Press-Schechter model. For a mass limit of value Mlim = 1014 h-1 M☉, the average axial ratio is η ~ 0.84, with a tail extended to η ~ 0.6. With the fast advance of high-quality imaging observations of both SZ effect and X-ray emissions, our analyses provide a useful way to probe cluster halo profiles and therefore to test theoretical halo formation models.

A multiband study of Hercules A - I.ROSATobservations of the intracluster medium

We have made ROSAT PSPC and HRI X-ray observations to study the intracluster gas surrounding the powerful radio source Hercules A. The cluster is luminous in X-rays (Lbol = 4.8 × 10 37 W), although apparently poor in optical galaxies, and the host of the radio source is the central dominating galaxy of the cluster. The azimuthally-averaged X-ray surface brightness profile is well fitted by a modified King (�) model, with core radius rc = 121 ± 10 kpc and � = 0.74 ± 0.03, but the cluster is elongated parallel to the radio source, especially on the scale of the radio lobes, and fits to individual quadrants give a core radius 50 per cent larger along the radio axis. Part of this elongation appears to be associated with enhanced X-ray emission superimposed on the outer radio lobes, which extend to just over 2rc. There are no obvious depressions in the X-ray emission coincident with the radio lobes, as expected if the relativistic plasma displaces the ICM. However, we show that these depressions may be quite weak, essentially because the main part of the lobes are outside the cluster core. From the surface brightness profile for the PSPC data the X-ray emission extends out to � 2.2 Mpc radius. In the absence of the powerful jets (which must be a transient phenomenon on cosmological timescales), we would expect a cooling flow at the centre of the cluster; but currently it must be substantially disturbed by the expansion of the radio lobes. The PSPC spectrum reveals a cool component of the ICM with 0.5 <kT <1 keV in addition to the � 4 keV component detected by ASCA and BeppoSAX. The central cooling time could be as low as 2 Gyr if the cool component is centrally concentrated, otherwise it is around 6 Gyr. Cooling is significant on a Hubble time to a radius of about 90 kpc. The modelled central electron density of n0 = 1.0 × 10 4 m 3 is typical for modest cooling flows. Finally, we have detected faint X-ray emission from a compact central source, with size < 15 kpc and luminosity � 2 × 10 36 W.

Constraints on the Cluster Mass‐Temperature Relation Imposed by the Diffuse X‐Ray Background

We show the constraints on the dynamical properties of groups and clusters of galaxies imposed by the diffuse X-ray background (XRB) emission. We first estimate the total integrated diffuse X-ray emission associated with groups and clusters of galaxies using the X-ray luminosity function derived from the Press-Schechter mass function and the mass-temperature (M-T) and X-ray luminosity-temperature relations of the galaxy groups and clusters. We have applied different cosmological models and M-T relations in estimating the integrated emission. For most of the models associated with the M-T relations derived from X-ray mass estimates, we find that the integrated emission significantly exceeds the unresolved diffuse XRB emission. We suggest that using the X-ray surface brightness profiles as a cluster mass estimator may significantly underestimate the real mass of galaxy clusters. Our methods provide strong constraints on the distribution and the dynamical evolution models of the galaxy clusters.

High-redshift X-ray properties of the haloes of simulated disc galaxies

X-ray luminosities and surface brightness profiles of the hot gas haloes of simulated disc galaxies at redshifts z = 0 2 are presented. The galaxies are extracted from fully cosmological simulations and correspond in mass to the Milky Way. We find that the bolometric X-ray luminosities of the haloes decrease by a factor 4 10 from z � 1 to z � 0, reflecting the decrease in the rate at which hot halo gas cools out on to the disc. At all redshifts, most of the emission is found to originate within 10–15 kpc of the disc. When combined with models in which the evolution of disc X-ray luminosity is dominated by X-ray binaries, the predicted halo luminosities at z � 1 show good agreement with constraints from spiral galaxies in Chandra Deep Field data. There is an indication that haloes with a metal abundance of 0.3Z⊙ overpredict observed Xray luminosities at z � 1, suggesting that halo metallicities are lower than this value. Prospects for direct detection of the haloes of Milky Way–sized galaxies with current and future X-ray instrumentation are discussed. It is found that XEUS should be able to single out the halo emission of highly inclined Milky Way–sized disc galaxies out to z � 0.3. For such galaxies in this redshift interval, we estimate a lower limit to the surface density of detectable haloes on the sky of � 10 deg −2 . More generally, owing to their luminosity evolution, the optimum redshifts at which to observe such haloes could be 0.5 < z < 1, depending on their assembly history.

Joint X-Ray and Optical Measurements of the Mass Distribution of the Distant Galaxy Cluster Cl J0152.7-1357

We present joint X-ray and optical observations of the high redshift (z~0.83) lensing cluster CLJ0152.7-1357 made with the Chandra X-ray Observatory and the Keck telescope. We confirm the existence of significant substructure at both X-ray and optical wavelengths in the form of two distinct clumps, whose temperatures are 6.6(-1.5,+2.4) keV and 5.7(-1.6,+2.9) keV, respectively. The X-ray surface brightness profiles of the two clumps can be fitted by either a single beta-model or an NFW-like profile; the latter giving better fits to the central regions. We find that the X-ray derived mass of this cluster is in good agreement with independent lensing measurements. While its appearance indicates that the cluster has not reached a dynamical equilibrium state, its X-ray luminosity L_x, temperature T and dynamical mass M are consistent with the well-defined L_x-T and M-T relations for low-redshift galaxy clusters, which suggests that the dynamical properties of the clusters have remained almost unchanged since z~0.8.

ChandraAnalysis and Mass Estimation of the Lensing Cluster of Galaxies Cl 0024+17

We present a detailed analysis of Chandra X-ray observations of the lensing cluster of galaxies CL0024+17 at z = 0.395. We found that the radial temperature profile is consistent with being isothermal out to ∼ 600 kpc and that the average X-ray temperature is 4.47 +0.83 −0.54 keV. The X-ray surface brightness profile is represented by the sum of extended emission centered at the central bright elliptical galaxy with a small core of 50 kpc and more extended emission which can be well described by a spherical β-model with a core radius of about 210 kpc. Assuming the X-ray emitting gas to be in hydrostatic equilibrium, we estimated the X-ray mass within the arc radius and found it is significantly smaller than the strong lensing mass by a factor of about 2–3. We detected a strong redshifted iron K line in the X-ray spectrum from the cluster for the first time and find the metal abundance to be 0.76 +0.37 −0.31 solar. Subject headings: galaxies: clusters: individual (CL0024+17) — X-rays: galaxies — gravitational lensing — dark matter

A study of dark matter halos and gas properties in clusters of galaxies from ROSAT data

Self-gravitating systems such as elliptical galaxies appear to have a constant integrated specific entropy and obey a scaling law relating their potential energy to their mass. These properties can be interpreted as due to the physical processes involved in the formation and evolution of these structures. Dark matter halos obtained through numerical simulations have also been found to obey a scaling law relating their potential energy to their mass with the same slope as for ellipticals, and very close to the expected value predicted by theory. Since the X- ray gas in clusters is weakly dissipative, we test here the hypothesis that it verifies similar properties. Comparable properties for the dark matter component are also investigated. With this aim, we have analyzed ROSAT-PSPC images of 24 clusters, and fit a Sersic law to their X-ray surface brightness profiles. We found that: 1) the Sersic law parameters (intensity, shape and scale) describing the X-ray gas emission are correlated two by two, with a strong correlation between the shape and scale parameters; 2) the hot gas in all these clusters roughly has the same integrated specific entropy, although a second order correlation between this integrated specific entropy and both the gas mass and the dynamical mass is observed; 3) a scaling law links the cluster potential energy to its total mass, with the same slope as that derived for elliptical galaxies and for dark matter halo simulations. Comparable relations are obtained for the dark matter component. All these correlations are probably the consequence of the formation and evolution processes undergone by clusters of galaxies.