The evolution of the cluster X-ray scaling relations in the WARPS sample at 0.6<z<1.0

The X-ray properties of a sample of 11 high-redshift (0.6<z<1.0) clusters observed with Chandra and/or XMM are used to investigate the evolution of the cluster scaling relations. The observed evolution of the L-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the universe at their redshift of observation. When the systematic effect of assuming isothermality on the derived masses of the high-redshift clusters is taken into account, the high-redshift M-T and Mgas-T relations are also consistent with self-similar evolution. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having formed at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high-redshift (B=3.29+/-0.38) is consistent with the local relation, and significantly steeper then the self-similar prediction of B=2. This suggests that the non-gravitational processes causing the steepening occurred at z>1 or in the early stages of the clusters' formation, prior to their observation. The properties of the intra-cluster medium at high-redshift are found to be similar to those in the local universe. The mean surface-brightness profile slope for the sample is 0.66+/-0.05, the mean gas mass fractions within R2500 and R200 are 0.073+/-0.010 and 0.12+/-0.02 respectively, and the mean metallicity of the sample is 0.28+/-0.16 solar.Comment: 23 pages, 17 figures. Accepted for publication in MNRAS. Revised to match accepted version: reanalysed data with latest calibrations, several minor changes. Conclusions unchange

Stability of gel wax based optical scattering phantoms

Phantoms with tuneable optical scattering properties are essential in the development and refinement of optical based imaging techniques. Mineral oil based ‘gel wax’ phantoms are the subject of increasing interest due to their ease and speed of manufacture, non-toxic nature, ability to cast into anatomically realistic shapes, as well as their cost-effective nature of production. The addition of scatterers such as titanium dioxide powder and monodisperse silica microspheres to the gel wax allows for the creation of phantoms with a controllable optical scattering coefficient. To enable repeated use of such phantoms, the stability of the scattering properties must be determined–a property which has yet to be investigated. We present an analysis of the stability of the reduced scattering coefficient (µ’sµs’) of such phantoms over time. We conclude that due to the measurable reduction in scattering coefficient over time, gel wax phantoms embedded with silica spheres may not be suitable for repeated use over time, however gel wax-TiO2 phantoms are much more temporally stable

Images, structural properties and metal abundances of galaxy clusters observed with Chandra ACIS-I at 0.1<z<1.3

We have assembled a sample of 115 galaxy clusters at 0.1<z<1.3 with archived Chandra ACIS-I observations. We present X-ray images of the clusters and make available region files containing contours of the smoothed X-ray emission. The structural properties of the clusters were investigated and we found a significant absence of relaxed clusters (as determined by centroid shift measurements) at z>0.5. The slope of the surface brightness profiles at large radii were steeper on average by 15% than the slope obtained by fitting a simple beta-model to the emission. This slope was also found to be correlated with cluster temperature, with some indication that the correlation is weaker for the clusters at z>0.5. We measured the mean metal abundance of the cluster gas as a function of redshift and found significant evolution, with the abundances dropping by 50% between z=0.1 and z~1. This evolution was still present (although less significant) when the cluster cores were excluded from the abundance measurements, indicating that the evolution is not solely due to the disappearance of relaxed, cool core clusters (which are known to have enhanced core metal abundances) from the population at z>0.5.Comment: 23 pages, 12 figures. Accepted for publication in ApJS. Updated to match published version. Redshifts of two clusters (RXJ1701 and CL0848) corrected and two observations of MACSJ0744.8 have been combined into one. Conclusions unchanged. A version with images of all of the clusters is available at http://hea-www.harvard.edu/~bmaughan/clusters.htm

The WARPS Survey. VIII. Evolution of the Galaxy Cluster X-ray Luminosity Function

We present measurements of the galaxy cluster X-ray Luminosity Function (XLF) from the Wide Angle ROSAT Pointed Survey (WARPS) and quantify its evolution. WARPS is a serendipitous survey of the central region of ROSAT pointed observations and was carried out in two phases (WARPS-I and WARPS-II). The results here are based on a final sample of 124 clusters, complete above a flux limit of 6.5 10E-15 erg/s/cm2, with members out to redshift z ~ 1.05, and a sky coverage of 70.9 deg2. We find significant evidence for negative evolution of the XLF, which complements the majority of X-ray cluster surveys. To quantify the suggested evolution, we perform a maximum likelihood analysis and conclude that the evolution is driven by a decreasing number density of high luminosity clusters with redshift, while the bulk of the cluster population remains nearly unchanged out to redshift z ~ 1.1, as expected in a low density Universe. The results are found to be insensitive to a variety of sources of systematic uncertainty that affect the measurement of the XLF and determination of the survey selection function. We perform a Bayesian analysis of the XLF to fully account for uncertainties in the local XLF on the measured evolution, and find that the detected evolution remains significant at the 95% level. We observe a significant excess of clusters in the WARPS at 0.1 < z < 0.3 and LX ~ 2 10E42 erg/s compared with the reference low-redshift XLF, or our Bayesian fit to the WARPS data. We find that the excess cannot be explained by sample variance, or Eddington bias, and is unlikely to be due to problems with the survey selection function.Comment: 13 pages, 12 figures, accepted for publication in MNRA

Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: The Luminosity-Mass Relation

We present the results of work involving a statistically complete sample of 34 galaxy clusters, in the redshift range 0.15$\le$z$\le$0.3 observed with $Chandra$. We investigate the luminosity-mass ($LM$) relation for the cluster sample, with the masses obtained via a full hydrostatic mass analysis. We utilise a method to fully account for selection biases when modeling the $LM$ relation, and find that the $LM$ relation is significantly different than the relation modelled when not account for selection effects. We find that the luminosity of our clusters is 2.2$\pm$0.4 times higher (when accounting for selection effects) than the average for a given mass, its mass is 30% lower than the population average for a given luminosity. Equivalently, using the $LM$ relation measured from this sample without correcting for selection biases would lead to the underestimation by 40% of the average mass of a cluster with a given luminosity. Comparing the hydrostatic masses to mass estimates determined from the $Y_{X}$ parameter, we find that they are entirely consistent, irrespective of the dynamical state of the cluster.Comment: 31 pages, 43 figures, accepted for publication in MNRA

An XMM-Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z=0.89

A detailed X-ray analysis of an XMM-Newton observation of the high-redshift (z=0.89) galaxy cluster ClJ1226.9+3332 is presented. The X-ray temperature is found to be 11.5{+1.1}{-0.9}keV, the highest X-ray temperature of any cluster at z>0.6. In contrast to MS1054-0321, the only other very hot cluster currently known at z>0.8, ClJ1226.9+3332 features a relaxed X-ray morphology, and its high overall gas temperature is not caused by one or several hot spots. The system thus constitutes a unique example of a high redshift, high temperature, relaxed cluster, for which the usual hydrostatic equilibrium assumption, and the X-ray mass is most reliable. A temperature profile is constructed (for the first time at this redshift) and is consistent with the cluster being isothermal out to 45% of the virial radius. Within the virial radius (corresponding to a measured overdensity of a factor of 200), a total mass of (1.4+/-0.5)*10^15 M_solar is derived, with a gas mass fraction of 12+/-5%. The bolometric X-ray luminosity is (5.3+/-0.2)*10^45 erg/s. The probabilities of finding a cluster of this mass within the volume of the discovery X-ray survey are 8*10^{-5} for Omega_M=1 and 0.64 for Omega_M=0.3, making Omega_M=1 highly unlikely. The entropy profile suggests that entropy evolution is being observed. The metal abundance (of Z=0.33{+0.14}{-0.10} Z_solar), gas mass fraction, and gas distribution are consistent with those of local clusters; thus the bulk of the metals were in place by z=0.89.Comment: 13 pages, 8 figures. Accepted for publication in MNRA

Rapid and flexible high-resolution scanning enabled by cycloidal computed tomography and convolutional neural network (CNN) based data recovery

We have combined a recently developed imaging concept (“cycloidal computed tomography”) with convolutional neural network (CNN) based data recovery. The imaging concept is enabled by exploiting, in synergy, the benefits of probing the sample with a structured x-ray beam and applying a cycloidal acquisition scheme by which the sample is simultaneously rotated and laterally translated. The beam structuring provides a means of increasing the in-slice spatial resolution in tomographic images irrespective of the blur imposed by the x-ray source and detector, while the “roto-translation” sampling allows for rapid scanning. Data recovery based on the recently proposed Mixed-Scale Dense (MSD) CNN architecture enables an efficient reconstruction of high-quality, high-resolution images despite the fact that cycloidal computed tomography data are highly incomplete. In the following, we review the basic principles underpinning cycloidal computed tomography, introduce the CNN based data recovery method and discuss the benefit of combining both

Cycloidal CT with CNN-based sinogram completion and in-scan generation of training data

In x-ray computed tomography (CT), the achievable image resolution is typically limited by several pre-fixed characteristics of the x-ray source and detector. Structuring the x-ray beam using a mask with alternating opaque and transmitting septa can overcome this limit. However, the use of a mask imposes an undersampling problem: to obtain complete datasets, significant lateral sample stepping is needed in addition to the sample rotation, resulting in high x-ray doses and long acquisition times. Cycloidal CT, an alternative scanning scheme by which the sample is rotated and translated simultaneously, can provide high aperture-driven resolution without sample stepping, resulting in a lower radiation dose and faster scans. However, cycloidal sinograms are incomplete and must be restored before tomographic images can be computed. In this work, we demonstrate that high-quality images can be reconstructed by applying the recently proposed Mixed Scale Dense (MS-D) convolutional neural network (CNN) to this task. We also propose a novel training approach by which training data are acquired as part of each scan, thus removing the need for large sets of pre-existing reference data, the acquisition of which is often not practicable or possible. We present results for both simulated datasets and real-world data, showing that the combination of cycloidal CT and machine learning-based data recovery can lead to accurate high-resolution images at a limited dose

Deep XMM and Chandra observations of ClJ1226.9+3332: A detailed X-ray mass analysis of a z=0.89 galaxy cluster

Deep XMM and Chandra observations of ClJ1226.9+3332 at z=0.89 have enabled the most detailed X-ray mass analysis of any such high-redshift galaxy cluster. The XMM temperature profile of the system shows no sign of central cooling, with a hot core and a radially declining profile. A temperature map shows asymmetry with a hot region that appears to be associated with a subclump of galaxies at the cluster redshift, but is not visible in the X-ray surface brightness. This is likely to be result of a merger event in the cluster, but does not appear to significantly affect the overall temperature profile. The XMM temperature profile, and combined Chandra and XMM emissivity profile allowed precise measurements of the global properties of ClJ1226.9+3332; we find kT=10.4+/-0.6keV, Z=0.16+/-0.05\Zsol, and M=5.2^{+1.0}_{-0.8}x10^{14}Msol. We obtain profiles of the metallicity, entropy, cooling time and gas fraction, and find a high concentration parameter for the total density profile of the system. The global properties are compared with the local LT and MT relations, and we are able to make the first observational test of the predicted evolution of the YM relation. We find that departures from these scaling relations are most likely caused by an underestimate of the total mass by ~30% in the X-ray hydrostatic mass analysis due to the apparent recent or ongoing merger activity.Comment: 14 pages, 19 figures. To be submitted to Ap

An XMM and Chandra view of massive clusters of galaxies to z=1

The X-ray properties of a sample of high redshift (z>0.6), massive clusters observed with XMM-Newton and Chandra are described, including two exceptional systems. One, at z=0.89, has an X-ray temperature of T=11.5 (+1.1, -0.9) keV (the highest temperature of any cluster known at z>0.6), an estimated mass of (1.4+/-0.2)x10^15 solar masses and appears relaxed. The other, at z=0.83, has at least three sub-clumps, probably in the process of merging, and may also show signs of faint filamentary structure at large radii,observed in X-rays. In general there is a mix of X-ray morphologies, from those clusters which appear relaxed and containing little substructure to some highly non-virialized and probably merging systems. The X-ray gas metallicities and gas mass fractions of the relaxed systems are similar to those of low redshift clusters of the same temperature, suggesting that the gas was in place, and containing its metals, by z=0.8. The evolution of the mass-temperature relation may be consistent with no evolution or with the ``late formation'' assumption. The effect of point source contamination in the ROSAT survey from which these clusters were selected is estimated, and the implications for the ROSAT X-ray luminosity function discussed.Comment: 9 pages, in Carnegie Observatories Astrophysics Series, Vol. 3: Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution, ed. J. S. Mulchaey, A. Dressler, and A. Oemler. See http://www.ociw.edu/ociw/symposia/series/symposium3/proceedings.html for a full-resolution versio