We measure the intracluster medium temperature distributions for 62 galaxy clusters in the HIFLUGCS, an X-ray flux-limited sample, with available X-ray data from XMM-Newton. We search for correlations between the width of the temperature distributions and other cluster properties, including median cluster temperature, luminosity, size, presence of a cool core, AGN activity, and dynamical state. We use a Markov Chain Monte Carlo analysis which models the ICM as a collection of X-ray emitting smoothed particles of plasma. Each smoothed particle is given its own set of parameters, including temperature, spatial position, redshift, size, and emission measure. This allows us to measure the width of the temperature distribution, median temperature, and total emission measure of each cluster. We find that none of the clusters have a temperature width, \sigma_kT, consistent with isothermality. Counterintuitively, we also find that the temperature distribution widths of disturbed, non-cool-core, and AGN-free clusters tend to be wider than in other clusters. A linear fit to \sigma_kT - kT_med finds \sigma_kT ~ 0.20kT_med + 1.08, with an estimated intrinsic scatter of ~ 0.55 keV, demonstrating a large range in ICM thermal histories.

The galaxy cluster SPT-CL J0205−5829 currently has the highest spectroscopically confirmed redshift, z = 1.322, in the South Pole Telescope Sunyaev–Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a core-excluded temperature of TX = 8.7+1.0−0.8 keV producing a mass estimate that is consistent with the Sunyaev–Zel'dovich-derived mass. The combined SZ and X-ray mass estimate of M500 = (4.8 ± 0.8) × 1014h−170 M☉ makes it the most massive known SZ-selected galaxy cluster at z > 1.2 and the second most massive at z > 1. Using optical and infrared observations, we find that the brightest galaxies in SPT-CL J0205−5829 are already well evolved by the time the universe was <5 Gyr old, with stellar population ages ≳3 Gyr, and low rates of star formation (<0.5 M☉ yr−1). We find that, despite the high redshift and mass, the existence of SPT-CL J0205−5829 is not surprising given a flat ΛCDM cosmology with Gaussian initial perturbations. The a priori chance of finding a cluster of similar rarity (or rarer) in a survey the size of the 2500 deg2 SPT-SZ survey is 69%.

We present a catalog of galaxy cluster candidates, selected through their Sunyaev-Zel'dovich (SZ) effect signature in the first 720 deg(2) of the South Pole Telescope (SPT) survey. This area was mapped with the SPT in the 2008 and 2009 austral winters to a depth of similar to 18 mu K-CMB-arcmin at 150 GHz; 550 deg(2) of it was also mapped to similar to 44 mu K-CMB-arcmin at 95 GHz. Based on optical imaging of all 224 candidates and near-infrared imaging of the majority of candidates, we have found optical and/or infrared counterparts for 158, which we then classify as confirmed galaxy clusters. Of these 158 clusters, 135 were first identified as clusters in SPT data, including 117 new discoveries reported in this work. This catalog triples the number of confirmed galaxy clusters discovered through the SZ effect. We report photometrically derived (and in some cases spectroscopic) redshifts for confirmed clusters and redshift lower limits for the remaining candidates. The catalog extends to high redshift with a median redshift of z = 0.55 and maximum confirmed redshift of z = 1.37. Forty-five of the clusters have counterparts in the ROSAT bright or faint source catalogs from which we estimate X-ray fluxes. Based on simulations, we expect the catalog to be nearly 100% complete above M-500 approximate to 5 x 10(14) M-circle dot h(70)(-1) at z greater than or similar to 0.6. There are 121 candidates detected at signal-to-noise ratio greater than five, at which the catalog purity is measured to be 95%. From this high-purity subsample, we exclude the z < 0.3 clusters and use the remaining 100 candidates to improve cosmological constraints following the method presented by Benson et al. Adding the cluster data to CMB + BAO + H-0 data leads to a preference for non-zero neutrino masses while only slightly reducing the upper limit on the sum of neutrino masses to Sigma m(nu) < 0.38 eV (95% CL). For a spatially flat wCDM cosmological model, the addition of this catalog to the CMB + BAO + H-0 + SNe results yields sigma(8) = 0.807 +/- 0.027 and w = -1.010 +/- 0.058, improving the constraints on these parameters by a factor of 1.4 and 1.3, respectively. The larger cluster catalog presented in this work leads to slight improvements in cosmological constraints from those presented by Benson et al. These cosmological constraints are currently limited by uncertainty in the cluster mass calibration, not the size or quality of the cluster catalog. A multi-wavelength observation program to improve the cluster mass calibration will make it possible to realize the full potential of the final 2500 deg(2) SPT cluster catalog to constrain cosmology.

We usemeasurements from the South Pole Telescope (SPT) Sunyaev-Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg(2) of the 2500 deg(2) SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat Lambda CDM cosmological model, we find the SPT cluster sample constrains sigma(8)(Omega(m)/0.25)(0.30) = 0.785 +/- 0.037. In combination with measurements of the cosmic microwave background (CMB) power spectrum from the SPT and the seven-year Wilkinson Microwave Anisotropy Probe data, the SPT cluster sample constrains sigma(8) = 0.795 +/- 0.016 and Omega(m) = 0.255 +/- 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the Lambda CDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Sigma m(nu)), the effective number of relativistic species (N-eff), and a primordial non-Gaussianity (f(NL)). We find that adding the SPT cluster data significantly improves the constraints on w and Sigma m(nu) beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = -0.973 +/- 0.063 and the sum of neutrino masses Sigma m(nu) < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a Lambda CDM model with a free N-eff and Sigma m(nu), we measure N-eff = 3.91 +/- 0.42 and constrain Sigma m(nu) < 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain f(NL) = -220 +/- 317, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg(2) SPT-SZ survey. The survey has detected similar to 500 clusters with a median redshift of similar to 0.5 and a median mass of similar to 2.3 x 10(14) M-circle dot h(-1) and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w.

We use measurements from the South Pole Telescope (SPT) Sunyaev Zel’dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg of the 2500 deg SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat ΛCDM cosmological model, we find the SPT cluster sample constrains σ8(Ωm/0.25) 0.30 = 0.785 ± 0.037. In combination with measurements of the CMB power spectrum from the SPT and the seven-year WMAP data, the SPT cluster sample constrains σ8 = 0.795± 0.016 and Ωm = 0.255±0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the ΛCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Σmν), the effective number of relativistic species (Neff), and a primordial non-Gaussianity (fNL). We find that adding the SPT cluster data significantly improves the constraints on w and Σmν beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = −0.973± 0.063 and the sum of neutrino masses Σmν< 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a ΛCDM model with a free Neff and Σmν , we measure Neff= 3.91 ± 0.42 and constrain Σmν< 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain fNL= −192 ± 310, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg SPT-SZ survey. The survey has detected ∼500 clusters with a median redshift of ∼ 0.5 and a median mass of ∼ 2.3 × 10M /h and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w. Subject headings: galaxies: clusters: individual, cosmology: observations Electronic address: bbenson@kicp.uchicago.edu 1 Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 2 Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 3 Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada 4 Department of Physics, University of California, Berkeley, CA 94720 5 University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 6 Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany 7 MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 8 National Center for Supercomputing Applications, University of Illinois, 1205 West Clark Street, Urbana, IL 61801 9 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 10 Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138 11 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany 12 Department of Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 13 Department of Physics, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 14 Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 15 Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, ar X iv :1 11 2. 54 35 v1 [ as tr oph .C O ] 2 2 D ec 2 01 1

We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background (CMB) from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky surveyed by the South Pole Telescope. Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the intracluster medium (ICM) within r_500 for each cluster. From these, we calculate Y_X=M_g T_X and estimate the total cluster mass using a M_500-Y_X scaling relation measured from previous X-ray studies. The integrated Comptonization, Y_SZ, is derived from the SZ measurements, using additional information from the X-ray measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables, and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y_SZ-Y_X relation and find a normalization of 0.82 +- 0.07, marginally consistent with the predicted ratio of Y_SZ/Y_X=0.91+-0.01 that would be expected from the density and temperature models used in this work. Using the Y_X derived mass estimates, we fit a Y_SZ-M_500 relation and find a slope consistent with the self-similar expectation of Y_SZ ~ M^5/3 with a normalization consistent with predictions from other X-ray studies. We compare the X-ray mass estimates to previously published SZ mass estimates derived from cosmological simulations of the SPT survey. We find that the SZ mass estimates are lower by a factor of 0.89+-0.06, which is within the ~15% systematic uncertainty quoted for the simulation-based SZ masses.

The South Pole Telescope (SPT) is currently surveying 2500 deg^2 of the southern sky to detect massive galaxy clusters out to the epoch of their formation using the Sunyaev-Zel'dovich (SZ) effect. This paper presents a catalog of the 26 most significant SZ cluster detections in the full survey region. The catalog includes 14 clusters which have been previously identified and 12 that are new discoveries. These clusters were identified in fields observed to two differing noise depths: 1500 deg^2 at the final SPT survey depth of 18 uK-arcmin at 150 GHz, and 1000 deg^2 at a depth of 54 uK-arcmin. Clusters were selected on the basis of their SZ signal-to-noise ratio (S/N) in SPT maps, a quantity which has been demonstrated to correlate tightly with cluster mass. The S/N thresholds were chosen to achieve a comparable mass selection across survey fields of both depths. Cluster redshifts were obtained with optical and infrared imaging and spectroscopy from a variety of ground- and space-based facilities. The redshifts range from 0.098 \leq z \leq 1.132 with a median of z_med = 0.40. The measured SZ S/N and redshifts lead to unbiased mass estimates ranging from 9.8 \times 10^14 M_sun/h_70 \leq M_200(rho_mean) \leq 3.1 \times 10^15 M_sun/h_70. Based on the SZ mass estimates, we find that none of the clusters are individually in significant tension with the LambdaCDM cosmological model. We also test for evidence of non-Gaussianity based on the cluster sample and find the data show no preference for non-Gaussian perturbations.

We present a study of the galaxy populations in massive galaxy clusters selected by their Sunyaev–Zel’dovich Effect (SZE) signatures. Selection via the SZE is approximately mass- limited where the mass limit varies only slightly with redshift, making it an ideal selection method for studying the evolution of the galaxy content of clusters. We begin by introducing the SZE, the South Pole Telescope (SPT), and the larger research project in which this Thesis is embedded. We then present the core galaxy population studies of this Thesis. In Chapter 3, we present the first large-scale follow-up of an SZE-selected galaxy cluster sample. Of 224 galaxy cluster candidates in the sample, we optically confirm 158 clusters and measure their photometric redshifts. We find a redshift range of 0.1

We present South Pole Telescope (SPT) observations of the five galaxy cluster candidates in the southern hemisphere which were reported as unconfirmed in the Planck Early Sunyaev-Zel'dovich (ESZ) sample. One cluster candidate, PLCKESZ G255.62-46.16, is located in the 2500-square-degree SPT SZ survey region and was reported previously as SPT-CL J0411-4819. For the remaining four candidates, which are located outside of the SPT SZ survey region, we performed short, dedicated SPT observations. Each of these four candidates was strongly detected in maps made from these observations, with signal-to-noise ratios ranging from 6.3 to 13.8. We have observed these four candidates on the Magellan-Baade telescope and used these data to estimate cluster redshifts from the red sequence. Resulting redshifts range from 0.24 to 0.46. We report measurements of Y_0.75', the integrated Comptonization within a 0.75' radius, for all five candidates. We also report X-ray luminosities calculated from ROSAT All-Sky Survey catalog counts, as well as optical and improved SZ coordinates for each candidate. The combination of SPT SZ measurements, optical red-sequence measurements, and X-ray luminosity estimates demonstrates that these five Planck ESZ cluster candidates do indeed correspond to real galaxy clusters with redshifts and observable properties consistent with the rest of the ESZ sample.

Using the South Pole Telescope (SPT), we have discovered the most massive known galaxy cluster at z > 1, SPT-CL J2106-5844. In addition to producing a strong Sunyaev-Zel'dovich effect signal, this system is a luminous X-ray source and its numerous constituent galaxies display spatial and color clustering, all indicating the presence of a massive galaxy cluster. VLT and Magellan spectroscopy of 18 member galaxies shows that the cluster is at z = 1.132^+0.002_-0.003. Chandra observations obtained through a combined HRC-ACIS GTO program reveal an X-ray spectrum with an Fe K line redshifted by z = 1.18 +/- 0.03. These redshifts are consistent with galaxy colors in extensive optical, near-infrared, and mid-infrared imaging. SPT-CL J2106-5844 displays extreme X-ray properties for a cluster, having a core-excluded temperature of kT = 11.0^+2.6_-1.9 keV and a luminosity (within r_500) of L_X (0.5 - 2.0 keV) = (13.9 +/- 1.0) x 10^44 erg/s. The combined mass estimate from measurements of the Sunyaev-Zel'dovich effect and X-ray data is M_200 = (1.27 +/- 0.21) x 10^15 M_sun. The discovery of such a massive gravitationally collapsed system at high redshift provides an interesting laboratory for galaxy formation and evolution, and is a powerful probe of extreme perturbations of the primordial matter density field. We discuss the latter, determining that, under the assumption of LambdaCDM cosmology with only Gaussian perturbations, there is only a 7% chance of finding a galaxy cluster similar to SPT-CL J2106-5844 in the 2500 deg^2 SPT survey region, and that only one such galaxy cluster is expected in the entire sky.

We report the spectroscopic confirmation of SPT-CL J0546-5345 at = 1.067. To date this is the most distant cluster to be spectroscopically confirmed from the 2008 South Pole Telescope (SPT) catalog, and indeed the first z > 1 cluster discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which are quiescent, early-type galaxies. From these quiescent galaxies we obtain a velocity dispersion of 1179^{+232}_{-167} km/s, ranking SPT-CL J0546-5345 as the most dynamically massive cluster yet discovered at z > 1. Assuming that SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M_200 = 1.0^{+0.6}_{-0.4} x 10^{15} Msun, in agreement with the X-ray and SZE mass measurements. Combining masses from several independent measures leads to a best-estimate mass of M_200 = (7.95 +/- 0.92) x 10^{14} Msun. The spectroscopic confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected SPT cluster survey, marks the onset of the high redshift SZE-selected galaxy cluster era.

We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPT-CL J2342-5411, in X-rays. These clusters were also independently detected through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and in the optical band by the Southern Cosmology Survey. They are thus the first clusters detected under survey conditions by all major cluster search approaches. The X-ray detection is made within the frame of the XMM-BCS cluster survey utilizing a novel XMM-Newton mosaic-mode of observations. The present study makes the first scientific use of this operation mode. We estimate the X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z = 0.32) to be T = 9.3(-1.9)(+3.3) keV, implying a high mass, M(500) = 8.8 +/- 3.8 x 10(14) M(circle dot). For SPT-CL J2342-5411, at z = 1.08, the available X-ray data do not allow us to directly estimate the temperature with good confidence. However, using our measured luminosity and scaling relations we estimate that T = 4.5 +/- 1.3 keV and M(500) = 1.9 +/- 0.8 x 10(14) M(circle dot). We find a good agreement between the X-ray masses and those estimated from the Sunyaev-Zel'dovich effect.

We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background (CMB) from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky surveyed by the South Pole Telescope. Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the intracluster medium (ICM) within r_500 for each cluster. From these, we calculate Y_X=M_g T_X and estimate the total cluster mass using a M_500-Y_X scaling relation measured from previous X-ray studies. The integrated Comptonization, Y_SZ, is derived from the SZ measurements, using additional information from the X-ray measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables, and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y_SZ-Y_X relation and find a normalization of 0.82 +- 0.07, marginally consistent with the predicted ratio of Y_SZ/Y_X=0.91+-0.01 that would be expected from the density and temperature models used in this work. Using the Y_X derived mass estimates, we fit a Y_SZ-M_500 relation and find a slope consistent with the self-similar expectation of Y_SZ ~ M^5/3 with a normalization consistent with predictions from other X-ray studies. We compare the X-ray mass estimates to previously published SZ mass estimates derived from cosmological simulations of the SPT survey. We find that the SZ mass estimates are lower by a factor of 0.89+-0.06, which is within the ~15% systematic uncertainty quoted for the simulation-based SZ masses.

We report the application of the new Monte Carlo method, smoothed particle inference (SPI, described in a pair of companion papers), toward analysis and interpretation of X-ray observations of clusters of galaxies with the XMM-Newton satellite. Our sample consists of publicly available well exposed observations of clusters at redshifts z > 0.069, totaling 101 objects. We determine the luminosity and temperature structure of the X-ray emitting gas, with the goal to quantify the scatter and the evolution of the LX–T relation, as well as to investigate the dependence on cluster substructure with redshift. This work is important for the establishment of the potential robustness of mass estimates from X-ray data which in turn is essential toward the use of clusters for measurements of cosmological parameters. We use the luminosity and temperature maps derived via the SPI technique to determine the presence of cooling cores, via measurements of luminosity and temperature contrast. The LX–T relation is investigated, and we confirm that LX ∝ T3. We find a weak redshift dependence (), in contrast to some Chandra results. The level of dynamical activity is established using the "power ratio" method, and we compare our results to previous application of this method to Chandra data for clusters. We find signs of evolution in the P3/P0 power ratio. A new method, the "temperature two-point correlation function," is proposed. This method is used to determine the "power spectrum" of temperature fluctuations in the X-ray emitting gas as a function of spatial scale. We show how this method can be fruitfully used to identify cooling core clusters as well as those with disturbed structures, presumably due to ongoing or recent merger activity.

We present a new mass estimate of a well studied gravitational lensing cluster, Abell 1689, from deep Chandra observations with a total exposure of 200 ks. Within r = 200 h(-1) kpc, the X-ray mass estimate is systematically lower than that of lensing by 30%-50%. At r > 200 h(-1) kpc, the mass density profiles from X-ray and weak lensing methods give consistent results. The most recent weak lensing work suggests a steeper profile than what is found from the X- ray analysis, while still in agreement with the mass at large radii. Fitting the total mass profile to a Navarro-Frenk-White model, we find M(200) = (1.16(-0.27)(+ 0.45)) x 10(15) h(-1) M(circle dot) with a concentration, c(200) = 5.3(-1.2)(+1.3), using nonparametric mass modeling. With parametric profile modeling, we find M(200) = (0.94(-0.06)(+0.11)) x 10(15) h(-1) M(circle dot) and c(200) = 6.6(-0.4)(+0.4). This is much lower compared to masses deduced from the combined strong and weak lensing analysis. Previous studies have suggested that cooler small-scale structures can bias X- ray temperature measurements or that the northern part of the cluster is disturbed. We find these scenarios unlikely to resolve the central mass discrepancy since the former requires 70%-90% of the space to be occupied by these cool structures, and excluding the northern substructure does not significantly affect the total mass profiles. A more plausible explanation is a projection effect. Assuming that the gas temperature and density profiles have a prolate symmetry, we can bring the X- ray mass estimate into a closer agreement with that of lensing. We also find that the previously reported high hard-band to broadband temperature ratio in A1689, and many other clusters observed with Chandra, may be resulting from the instrumental absorption that decreases 10%-15% of the effective area at similar to 1.75 keV. Caution must be taken when analyzing multiple spectral components under this calibration uncertainty.

We propose a new Monte Carlo method to study extended X-ray sources with the European Photon Imaging Camera (EPIC) aboard XMM-Newton. The smoothed particle inference (SPI) technique, described in a companion paper, is applied here to the EPIC data for the clusters of galaxies Abell 1689, Centaurus, and RX J0658-55 (the "bullet cluster"). We aim to show the advantages of this method of simultaneous spectral and spatial modeling over traditional X-ray spectral analysis. In Abell 1689 we confirm our earlier findings about structure in the temperature distribution and produce a high-resolution temperature map. We also find a hint of velocity structure within the gas, consistent with previous findings. In the bullet cluster, RX J0658-55, we produce the highest resolution temperature map ever to be published of this cluster, allowing us to trace what looks like the trail of the motion of the bullet in the cluster. We even detect a south-to-north temperature gradient within the bullet itself. In the Centaurus cluster we detect, by dividing up the luminosity of the cluster in bands of gas temperatures, a striking feature to the northeast of the cluster core. We hypothesize that this feature is caused by a subcluster left over from a substantial merger that slightly displaced the core. We conclude that our method is very powerful in determining the spatial distributions of plasma temperatures and very useful for systematic studies in cluster structure.

We propose an ambitious new method that models the intracluster medium in clusters of galaxies as a set of X-ray-emitting smoothed particles of plasma. Each smoothed particle is described by a handful of parameters including temperature, location, size, and elemental abundances. Hundreds to thousands of these particles are used to construct a model cluster of galaxies, with the appropriate complexity estimated from the data quality. This model is then compared iteratively with X-ray data in the form of adaptively binned photon lists via a two-sample likelihood statistic and iterated via Markov chain Monte Carlo. The complex cluster model is propagated through the X-ray instrument response using direct sampling Monte Carlo methods. With this approach, the method can reproduce many of the features observed in the X- ray emission in a less assumption-dependent way than traditional analyses, and it allows for a more detailed characterization of the density, temperature, and metal abundance structure of clusters. Multi-instrument X- ray analyses and simultaneous X- ray, Sunyaev-Zeldovich ( SZ), and lensing analyses are a straightforward extension of this methodology. Significant challenges still exist in understanding the degeneracy in these models and the statistical noise induced by the complexity of the models.

We report results from XMM-Newton observations of 13 X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample (SSS). The survey was designed to look for evidence of departures of the X-ray spectra from a simple power-law shape (i.e., curvature and/or line features) and to find objects worthy of deeper study. Our data are generally well fit by power-law models, with three cases having hard (Γ < 2; dN/dE ∝ E-Γ) spectra that indicate synchrotron peaks at E ≳ 5 keV. Previous data had suggested a presence of absorption features in the X-ray spectra of some BL Lac objects. In contrast, none of these spectra show convincing examples of line features in either absorption or emission, suggesting that such features are rare among BL Lac objects, or, more likely, are artifacts caused by instrumental effects. We find significant evidence for intrinsic curvature [steepening by dΓ/d(log E) = 0.4 ± 0.15] in 14 of the 17 X-ray spectra. This cannot be explained satisfactorily via excess absorption, since the curvature is essentially constant from 0.5-6 keV, an observation that is inconsistent with the modest amounts of absorption that would be required. We use the XMM-Newton Optical Monitor data with concurrent radio monitoring to derive broadband spectral energy distributions and peak frequency estimates. From these, we examine models of synchrotron emission and model the spectral curvature we see as the result of episodic particle acceleration.