Publications (15)16.95 Total impact
-
Article: PICACS: a tool for self-consistent modelling of galaxy cluster scaling relations
[show abstract] [hide abstract]
ABSTRACT: In this paper, we introduce PICACS, a physically-motivated, internally consistent model of scaling relations between galaxy cluster masses and their observable properties. This model can be used to constrain simultaneously the form, scatter (including its covariance) and evolution of the scaling relations, as well as the masses of the individual clusters. In this framework, scaling relations between observables (such as that between X-ray luminosity and temperature) are modelled explicitly in terms of the fundamental mass-observable scaling relations, and so are fully constrained without being fit directly. We apply the PICACS model to several observational datasets, and show that it performs as well as traditional regression methods for simply measuring scaling relation parameters, but presents several significant advantages. For clusters with available X-ray hydrostatic masses, PICACS gives a modest improvement of the precision of the mass estimates, while consistently constraining the mass-observable scaling relations. For a sample of clusters without prior mass estimates, we derive self-consistent constraints on the cluster masses and scaling relations, and find a minor improvement in precision on cluster mass estimates compared with a single scaling relation. We are also able to deconstruct the slope of the luminosity-temperature (LT) relation and show that the steepening compared to self-similar expectations is due to contributions from heating and depletion of the gas within the reference radius R500, and not due to a mass dependence of the gas structure within that radius. Finally, we use PICACS to illustrate the dependence of the expected self-similar evolution of the LT relation on the slopes of the mass scaling relations, and show that our self-consistent modelling predicts self-similar evolution significantly weaker than is commonly assumed.12/2012; -
Article: The WARPS Survey. VIII. Evolution of the Galaxy Cluster X-ray Luminosity Function
[show abstract] [hide abstract]
ABSTRACT: 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.10/2012; -
Article: Separating the BL Lac and Cluster X-ray Emissions in Abell 689 with Chandra
[show abstract] [hide abstract]
ABSTRACT: We present the results of a Chandra observation of the galaxy cluster Abell 689 (z=0.279). Abell 689 is one of the most luminous clusters detected in the ROSAT All Sky Survey (RASS), but was flagged as possibly including significant point source contamination. The small PSF of the Chandra telescope allows us to confirm this and separate the point source from the extended cluster X-ray emission. For the cluster we determine a bolometric luminosity of L_{bol}=(3.3+/-0.3)x10^{44} erg s-1 and a temperature of kT=5.1^{+2.2}_{-1.3} keV when including a physically motivated background model. We compare our measured luminosity for A689 to that quoted in the Rosat All Sky Survey (RASS) and find L_{0.1-2.4,keV}=2.8x10^{44} erg s-1, a value \sim10 times lower than the ROSAT measurement. Our analysis of the point source shows evidence for significant pileup, with a pile-up fraction of ~60%. SDSS spectra and HST images lead us to the conclusion that the point source within Abell 689 is a BL Lac object. Using radio and optical observations from the VLA and HST archives, we determine {\alpha}_{ro}=0.50, {\alpha}_{ox}=0.77 and {\alpha}_{rx}=0.58 for the BL Lac, which would classify it as being of 'High-energy peak BL Lac' (HBL) type. Spectra extracted of A689 show a hard X-ray excess at energies above 6 keV that we interpret as inverse Compton emission from aged electrons that may have been transported into the cluster from the BL Lac.12/2011; -
Article: Self-similar scaling and evolution in the galaxy cluster X-ray Luminosity-Temperature relation
[show abstract] [hide abstract]
ABSTRACT: We investigate the form and evolution of the X-ray luminosity-temperature (LT) relation of a sample of 114 galaxy clusters observed with Chandra at 0.1<z<1.3. The clusters were divided into subsamples based on their X-ray morphology or whether they host strong cool cores. We find that when the core regions are excluded, the most relaxed clusters (or those with the strongest cool cores) follow an LT relation with a slope that agrees well with simple self-similar expectations. This is supported by an analysis of the gas density profiles of the systems, which shows self-similar behaviour of the gas profiles of the relaxed clusters outside the core regions. By comparing our data with clusters in the REXCESS sample, which extends to lower masses, we find evidence that the self-similar behaviour of even the most relaxed clusters breaks at around 3.5keV. By contrast, the LT slopes of the subsamples of unrelaxed systems (or those without strong cool cores) are significantly steeper than the self-similar model, with lower mass systems appearing less luminous and higher mass systems appearing more luminous than the self-similar relation. We argue that these results are consistent with a model of non-gravitational energy input in clusters that combines central heating with entropy enhancements from merger shocks. Such enhancements could extend the impact of central energy input to larger radii in unrelaxed clusters, as suggested by our data. We also examine the evolution of the LT relation, and find that while the data appear inconsistent with simple self-similar evolution, the differences can be plausibly explained by selection bias, and thus we find no reason to rule out self-similar evolution. We show that the fraction of cool core clusters in our (non-representative) sample decreases at z>0.5 and discuss the effect of this on measurements of the evolution in the LT relation.08/2011; -
Article: Chandra X-Ray Analysis of the Massive High-Redshift Galaxy Clusters Cl J1113.1–2615 and Cl J0152.7–1357
[show abstract] [hide abstract]
ABSTRACT: We present an analysis of Chandra observations of two high-redshift clusters of galaxies, Cl J1113.1-2615 at z = 0.725 and Cl J0152.7-1357 at z = 0.833. We find Cl J1113.1-2615 to be morphologically relaxed with a temperature of kT = 4.3 keV and a mass (within the virial radius) of 4.3 × 1014 M☉. Cl J0152.7-1357, by contrast, is resolved into a northern and southern subcluster, each massive and X-ray-luminous, in the process of merging. The temperatures of the subclusters are found to be 5.5 and 5.2 keV, respectively, and we estimate their respective masses to be 6.1 × 1014 and 5.2 × 1014 M☉ within the virial radii. A dynamical analysis of the system shows that the subclusters are likely to be gravitationally bound. If the subclusters merge, they will form a system with a mass similar to that of the Coma Cluster. Two-dimensional modeling of the X-ray surface brightness reveals excess emission between the subclusters, suggestive, but not conclusive, evidence of a shock front. We make a first attempt at measuring the cluster M-T relation at z ≈ 0.8 and find no evolution in its normalization, supporting the previous assumption of an unevolving M-T relation when constraining cosmological parameters from cluster evolution studies. A comparison of the cluster properties with those of nearby systems also finds little or no evolution in the L-T relation, the gas fraction-T relation, the β-T relation, or the metallicity. These results suggest that, in at least some massive clusters, the hot gas was in place, and containing its metals, at z ≈ 0.8 and thus that the clusters were assembled at redshifts significantly higher than z = 0.8, as predicted in low-ΩM models. We also highlight the need to correct for the degradation of the Chandra ACIS low-energy quantum efficiency in high-redshift cluster studies when the low-energy absorption is often assumed to be the Galactic value, rather than measured.The Astrophysical Journal 12/2008; 587(2):589. · 6.02 Impact Factor -
Article: XMM-Newton Observes Cl J0152.7–1357: A Massive Galaxy Cluster Forming at Merger Crossroads at z = 0.83
[show abstract] [hide abstract]
ABSTRACT: We present an analysis of a 50 ks XMM-Newton observation of the merging galaxy cluster Cl J0152.7-1357 at z = 0.83. In addition to the two main subclusters and an infalling group detected in an earlier Chandra observation of the system, XMM-Newton detects another group of galaxies possibly associated with the cluster. This group may be connected to the northern subcluster by a filament of cool (1.4 keV) X-ray-emitting gas and lies outside the estimated virial radius of the northern subcluster. The X-ray morphology agrees well with the projected galaxy distribution in new K-band imaging data presented herein. We use detailed spectral and imaging analysis of the X-ray data to probe the dynamics of the system and find evidence that another subcluster or group has recently passed through the northern subcluster. Cl J0152.7-1357 is an extremely dynamically active system, with mergers at different stages occurring along two perpendicular merger axes.The Astrophysical Journal 12/2008; 640(1):219. · 6.02 Impact Factor -
Article: Testing the galaxy cluster mass-observable relations at z = 1 with XMM-Newton and Chandra observations of XLSSJ022403.9-041328
[show abstract] [hide abstract]
ABSTRACT: We present an analysis of deep XMM-Newton and Chandra observations of the z=1.05 galaxy cluster XLSSJ022403.9-041328 (hereafter XLSSC 029), detected in the XMM-Newton large scale structure survey. Density and temperature profiles of the X-ray emitting gas were used to perform a hydrostatic mass analysis of the system. This allowed us to measure the total mass and gas fraction in the cluster and define overdensity radii R500 and R2500. The global properties of XLSSC 029 were measured within these radii and compared with those of the local population. The gas mass fraction was found to be consistent with local clusters. The mean metal abundance was 0.18 +0.17 -0.15 Zsol, with the cluster core regions excluded, consistent with the predicted and observed evolution. The properties of XLSSC 029 were then used to investigate the position of the cluster on the M-kT, YX-M, and LX-M scaling relations. In all cases the observed properties of XLSSC 029 agreed well with the simple self-similar evolution of the scaling relations. This is the first test of the evolution of these relations at z > 1 and supports the use of the scaling relations in cosmological studies with distant galaxy clusters. Comment: 11 pages, 11 figures. Accepted for publication in MNRAS. Revised to include treatment of XMM PSF. Conclusions unchanged09/2007; -
Article: The Lx-Yx Relation: Using Galaxy Cluster X-Ray Luminosity as a Robust, Low Scatter Mass Proxy
[show abstract] [hide abstract]
ABSTRACT: We use a sample of 115 galaxy clusters at 0.1<z<1.3 observed with Chandra ACIS-I to investigate the relation between luminosity and Yx (the product of gas mass and temperature). The scatter in the relation is dominated by cluster cores, and a tight LY relation (11% intrinsic scatter in Lx) is recovered if sufficiently large core regions (0.15R500) are excluded. The intrinsic scatter is well described by a lognormal distribution and the relations are consistent for relaxed and disturbed/merging clusters. We investigate the LY relation in low-quality data (e.g. for clusters detected in X-ray survey data) by estimating Lx from soft band count rates, and find that the scatter increases somewhat to 21%. We confirm the tight correlation between Yx and mass and the self-similar evolution of that scaling relation out to z=0.6 for a subset of clusters in our sample with mass estimates from the literature. This is used to estimate masses for the entire sample and hence measure the LM relation. We find that the scatter in the LM relation is much lower than previous estimates, due to the full removal of cluster cores and more robust mass estimates. For high-redshift clusters the scatter in the LM relation remains low if cluster cores are not excluded. These results suggest that cluster masses can be reliably estimated from simple luminosity measurements in low quality data where direct mass estimates, or measurements of Yx are not possible. This has important applications in the estimation of cosmological parameters from X-ray cluster surveys. Comment: 11 pages, 8 figures. ApJ in press. Replaced to match published version. Added new section testing the Yx-M relation for clusters with masses in literature. Scaling relation parameters are updated to reflect updates to the cluster sample. Conclusions unchanged03/2007; -
Article: Images, structural properties and metal abundances of galaxy clusters observed with Chandra ACIS-I at 0.1<z<1.3
[show abstract] [hide abstract]
ABSTRACT: 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.html03/2007; -
Article: Deep XMM and Chandra observations of ClJ1226.9+3332: A detailed X-ray mass analysis of a z=0.89 galaxy cluster
[show abstract] [hide abstract]
ABSTRACT: 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.09/2006; -
Article: The evolution of the cluster X-ray scaling relations in the WARPS sample at 0.6<z<1.0
[show abstract] [hide abstract]
ABSTRACT: 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 unchangedMonthly Notices of the Royal Astronomical Society 03/2005; · 4.90 Impact Factor -
Article: XMM-Newton observations of the relaxed, high-redshift galaxy cluster ClJ0046.3+8530 at z=0.62
[show abstract] [hide abstract]
ABSTRACT: A detailed analysis of XMM observations of ClJ0046.3+8530 (z=0.624) is presented. The cluster has a moderate temperature (kT=4.1+/-0.3keV) and appears to be relaxed. Emission is detected at >3 sigma significance to a radius of 88% of R200 (the radius enclosing an overdensity of 200 times the critical density at z=0.624) in a surface-brightness profile. A temperature profile (extending to 0.7R200), and hardness-ratio map show no significant departures from the global temperature, within the statistical limits of the data. The cluster's bolometric X-ray luminosity is L=(4.3+/-0.3)*10^44 erg/s, and the total mass derived within R200, assuming isothermality and hydrostatic equilibrium, is M_200=3.0^{+0.6}_{-0.5}*10^14 Msolar. The gas entropy measured at 0.1R200 is compared with a sample of local systems, and found to be consistent with self-similar evolution with redshift. The metallicity, gas density profile slope, and gas mass fraction are all consistent with those found in low-z clusters. Comment: 11 pages, 12 figures. Accepted for publication in MNRAS06/2004; -
Article: An XMM-Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z=0.89
[show abstract] [hide abstract]
ABSTRACT: 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 MNRAS03/2004; -
Article: An XMM and Chandra view of massive clusters of galaxies to z=1
[show abstract] [hide abstract]
ABSTRACT: 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.05/2003; -
Article: Chandra X-ray analysis of the massive high-redshift galaxy clusters ClJ1113.1-2615 and ClJ0152.7-1357
[show abstract] [hide abstract]
ABSTRACT: We present an analysis of Chandra observations of two high-redshift clusters of galaxies, ClJ1113.1-2615 at z=0.725 and ClJ0152.7-1357 at z=0.833. We find ClJ1113 to be relaxed with kT=4.3^{+0.5}_{-0.4}keV and a mass (within the virial radius) of 4.3^{+0.8}_{-0.7}*10^{14}Msol. ClJ0152, by contrast, is resolved into a northern and southern subcluster, each massive and X-ray luminous, in the process of merging. The temperatures of the subclusters are found to be 5.5^{+0.9}_{-0.8}keV and 5.2^{+1.1}_{-0.9}keV respectively, and their respective masses are 6.1^{+1.7}_{-1.5}*10^{14}Msol and 5.2^{+1.8}_{-1.4}*10^{14}Msol within the virial radii. 2D modelling of the X-ray surface brightness reveals excess emission between the subclusters; suggestive, but not conclusive evidence of a shock front. We make a first attempt at measuring the cluster M-T relation at z~0.8, and find no evolution in its normalisation, supporting the previous assumption of an unevolving M-T relation. We also find little or no evolution in the L-T relation, the gas fraction-T relation, the beta-T relation or the metallicity. These results suggest that, in at least some massive clusters, the hot gas was in place, and containing its metals, at z~0.8. We also highlight the need to correct for the degradation of the Chandra ACIS low energy quantum efficiency in high-redshift cluster studies when the low energy absorption is often assumed to be the Galactic value, rather than measured. Comment: 55 pages, 16 figures, Latex. Accepted for publication in Astrophysical Journal. Author address corrected, reference added. Error in Eqn 3 corrected - small changes to gas mass values in text and Fig 15. Conclusions unchanged01/2003;
Top co-authors
Top Journals
Institutions
-
2008
-
Harvard-Smithsonian Center for Astrophysics
Cambridge, MA, USA -
University of Birmingham
- School of Physics and Astronomy
Birmingham, ENG, United Kingdom
-
-
2007
-
University of Bristol
- School of Physics
Bristol, ENG, United Kingdom
-
