Dynamical State Of Cluster Research Articles

LoCuSS: the connection between brightest cluster galaxy activity, gas cooling and dynamical disturbance of X-ray cluster cores

We study the distribution of projected offsets between the cluster X-ray centroid and the brightest cluster galaxy (BCG) for 65 X-ray selected clusters from the Local Cluster Substructure Survey (LoCuSS), with a median redshift of z=0.23. We find a clear correlation between X-ray/BCG projected offset and the logarithmic slope of the cluster gas density profile at 0.04r500 (alpha), implying that more dynamically disturbed clusters have weaker cool cores. Furthermore, there is a close correspondence between the activity of the BCG, in terms of detected H_alpha and radio emission, and the X-ray/BCG offset, with the line emitting galaxies all residing in clusters with X-ray/BCG offsets of <~15 kpc. Of the BCGs with alpha < -0.85 and an offset < 0.02r500, 96 per cent (23/24) have optical emission and 88 per cent (21/24) are radio active, while none has optical emission outside these criteria. We also study the cluster gas fraction (fgas) within r500 and find a significant correlation with X-ray/BCG projected offset. The mean fgas of the `small offset' clusters (< 0.02r500) is 0.106+/-0.005 (sigma=0.03) compared to 0.145+/-0.009 (sigma=0.04) for those with an offset > 0.02r500, indicating that the total mass may be systematically underestimated in clusters with larger X-ray/BCG offsets. Our results imply a link between cool core strength and cluster dynamical state consistent with the view that cluster mergers can significantly perturb cool cores, and set new constraints on models of the evolution of the intracluster medium.

Exploring the magnetized cosmic web through low-frequency radio emission

Recent improvements in the capabilities of low frequency radio telescopes provide a unique opportunity to study thermal and non-thermal properties of the cosmic web. We argue that the diffuse, polarized emission from giant radio relics traces structure formation shock waves and illuminates the large-scale magnetic field. To show this, we model the population of shock-accelerated relativistic electrons in high-resolution cosmological simulations of galaxy clusters and calculate the resulting radio synchrotron emission. We find that individual shock waves correspond to localized peaks in the radio surface brightness map which enables us to measure Mach numbers for these shocks. We show that the luminosities and number counts of the relics strongly depend on the magnetic field properties, the cluster mass and dynamical state. By suitably combining different cluster data, including Faraday rotation measures, we are able to constrain some macroscopic parameters of the plasma at the structure formation shocks, such as models of turbulence. We also predict upper limits for the properties of the warm-hot intergalactic medium, such as its temperature and density. We predict that the current generation of radio telescopes (LOFAR, GMRT, MWA, LWA) have the potential to discover a substantially larger sample of radio relics, with multiple relics expected for each violently merging cluster. Future experiments (SKA) should enable us to further probe the macroscopic parameters of plasma physics in clusters.

Richness dependence of the recent evolution of clusters of galaxies

We revisit the issue of the recent dynamical evolution of clusters of galaxies using a sample of Abell, Corwin & Olowin (ACO) clusters with z < 0.14, which has been selected such that it does not contain clusters with multiple velocity components nor strongly merging or interacting clusters, as revealed in X-rays. We use as proxies of the cluster dynamical state the projected cluster ellipticity, velocity dispersion and X-ray luminosity. We find indications for a recent dynamical evolution of this cluster population, which however strongly depends on the cluster richness. Poor clusters appear to be undergoing their primary phase of virialization, with their ellipticity increasing with redshift with a rate de/dz ≃ 2.5 ± 0.4, while the richest clusters show an ellipticity evolution in the opposite direction (with de/d z ≃ -1.2 ± 0.1), which could be due to secondary infall. When taking into account sampling effects due to the magnitude-limited nature of the ACO cluster catalogue we find no significant evolution of the cluster X-ray luminosity, while the velocity dispersion increases with decreasing redshift, independent of the cluster richness, at a rate dσ v /d z ≃ -1700 ± 400 km s -1 .

Galaxy-cluster gas-density distributions of the representativeXMM-Newtoncluster structure survey (REXCESS)

We present a study of the structural and scaling properties of the gas distributions in the intracluster medium (ICM) of 31 nearby (z < 0.2) clusters observed with XMM-Newton, which together comprise the Representative XMM-Newton Cluster Structure Survey (REXCESS). In contrast to previous studies, this sample is unbiased with respect to cluster dynamical state, and it fully samples the cluster X-ray luminosity function. The clusters cover a temperature range of 2.0 -- 8.5 keV and possess a variety of morphologies. The sampling strategy allows us to compare clusters with a wide range of central cooling times on an equal footing. We present non-parametric gas-density profiles out to distances ranging between 0.8 R_500 and 1.5 R_500. The central gas densities differ greatly from system to system, with no clear correlation with system temperature. At intermediate radii the scaled density profiles show much less scatter, with a clear dependence on system temperature, consistent with the presence of an entropy excess as suggested in previous literature. However, at large scaled radii this dependence becomes weaker: clusters with kT > 3 keV scale self-similarly, with no temperature dependence of gas-density normalisation. We find some evidence of a correlation between dynamical state and outer gas density slope, and between dynamical state and both central gas normalisation and cooling time. We find no evidence of a significant bimodality in the distributions of central density, density gradient, or cooling time. Finally, we present the gas mass-temperature relation for the REXCESS sample, which is consistent with the expectation of self-similar scaling modified by the presence of an entropy excess in the inner regions of the cluster, and has a logarithmic intrinsic scatter of ~10%.

Simulating cosmic rays in clusters of galaxies - I. Effects on the Sunyaev-Zel'dovich effect and the X-ray emission

We performed high-resolution simulations of a sample of 14 galaxy clusters that span a mass range from 5 × 10 13 to 2 × 10 15 h −1 Mto study the effects of cosmic rays (CRs) on thermal cluster observables such as X-ray emission and the Sunyaev-Zel'dovich effect. We analyse the CR effects on the intra-cluster medium while simultaneously taking into account the cluster's dynamical state as well as the mass of the cluster. The modelling of the CR physics includes adiabatic CR transport processes, injection by supernovae and cosmological structure formation shocks, as well as CR thermalization by the Coulomb interaction and catastrophic losses by hadronic interactions. While the relative pressure contained in CRs within the virial radius is of the order of 2 per cent in our non-radiative simulations, their contribution rises to 32 per cent in our simulations with dissipative gas physics including radiative cooling, star formation and supernova feedback. The relative CR pressure rises towards the outer regions due to a combination of the following effects: CR acceleration is more efficient at the peripheral strong accretion shocks compared to weak central flow shocks, adiabatic compression of a composite of CRs and thermal gas disfavours the CR pressure relative to the thermal pressure due to the softer equation of state of CRs and CR loss processes are more important at the dense centres. Interestingly, in the radiative simulations the relative CR pressure reaches high values of the order of equipartition with the thermal gas in each cluster galaxy due to the fast thermal cooling of gas which diminishes the thermal pressure support relative to that in CRs. This also leads to a lower effective adiabatic index of the composite gas that increases the compressibility of the intra-cluster medium. This effect slightly increases the central density, thermal pressure and the gas fraction. While the X-ray luminosity in low-mass cool core clusters is boosted by up to 40 per cent, the integrated Sunyaev-Zel'dovich effect appears to be remarkably robust and the total flux decrement only slightly reduced by typically 2 per cent. The resolved Sunyaev-Zel'dovich maps, however, show a larger variation with an increased central flux decrement.

Testing X‐Ray Measurements of Galaxy Clusters with Cosmological Simulations

X-ray observations of galaxy clusters potentially provide powerful cosmological probes if systematics due to our incomplete knowledge of the ICM physics is understood and controlled. In this paper we present mock Chandra analyses of cosmological cluster simulations and assess X-ray measurements of galaxy cluster properties using a model and procedure essentially identical to that used in real data analysis. We show that reconstruction of three-dimensional ICM density and temperature profiles is excellent for relaxed clusters, but still reasonably accurate for unrelaxed systems. The total ICM mass is measured quite accurately (6%) in all clusters, while the hydrostatic estimate of the gravitationally bound mass is biased low by about 5%-20% through the virial region, primarily due to additional pressure support provided by subsonic bulk motions in the ICM, ubiquitous in our simulations even in relaxed systems. Gas fraction determinations are therefore biased high; the bias increases toward cluster outskirts and depends sensitively on its dynamical state, but we do not observe significant trends of the bias with cluster mass or redshift. We also find that different average ICM temperatures, such as the X-ray spectroscopic Tspec and gas-mass-weighted Tmg, are related to each other by a constant factor with a relatively small object-to-object scatter and no systematic trend with mass, redshift, or the dynamical state of clusters. We briefly discuss direct applications of our results for different cluster-based cosmological tests.

First Results on Shear‐selected Clusters from the Deep Lens Survey: Optical Imaging, Spectroscopy, and X‐Ray Follow‐up

We present the first sample of galaxy clusters selected on the basis of their weak gravitational lensing shear. The shear induced by a cluster is a function of its mass profile and its redshift relative to the background galaxies being sheared; in contrast to more traditional methods of selecting clusters, shear selection does not depend on the cluster's star formation history, baryon content, or dynamical state. Because mass is the property of clusters which provides constraints on cosmological parameters, the dependence on these other parameters could induce potentially important biases in traditionally-selected samples. Comparison of a shear-selected sample with optically and X-ray selected samples is therefore of great importance. Here we present the first step toward a new shear-selected sample: the selection of cluster candidates from the first 8.6 deg$^2$ of the 20 deg$^2$ Deep Lens Survey (DLS), and tabulation of their basic properties such as redshifts and optical and X-ray counterparts.

The Evolution of Structure in X‐Ray Clusters of Galaxies

Using Chandra archival data, we quantify the evolution of cluster morphology with redshift. Clusters form and grow through mergers with other clusters and groups, and the amount of substructure in clusters in the present epoch and how quickly it evolves with redshift depend on the underlying cosmology. Our sample includes 40 X-ray-selected, luminous clusters from the Chandra archive, and we quantify cluster morphology using the power ratio method of Buote & Tsai. The power ratios are constructed from the moments of the X-ray surface brightness and are related to a cluster's dynamical state. We find that, as expected qualitatively from hierarchical models of structure formation, high-redshift clusters have more substructure and are dynamically more active than low-redshift clusters. Specifically, the clusters with z > 0.5 have significantly higher average third- and fourth-order power ratios than the lower redshift clusters. Of the power ratios, P3/P0 is the most unambiguous indicator of an asymmetric cluster structure, and the difference in P3/P0 between the two samples remains significant even when the effects of noise and other systematics are considered. After correcting for noise, we apply a linear fit to P3/P0 versus redshift and find that the slope is greater than zero at better than 99% confidence. This observation of structure evolution indicates that dynamical state may be an important systematic effect in cluster studies seeking to constrain cosmology, and when calibrated against numerical simulations, structure evolution will itself provide interesting bounds on cosmological models.

Galaxy Alignments as a Probe of the Dynamical State of Clusters

We present indications, based on a sample of 303 Abell clusters, for a relation between the dynamical state of clusters and the alignments of galaxy members with their parent cluster major-axis orientation as well as with the large-scale environment within which the clusters are embedded. The statistical results are complemented with a deep, wide-field case study of galaxy alignments in the cluster A521, which is characterized by multiple merging events (Maurogrdato et al.; Ferrari et al.) and whose galaxy members show a strong alignment signal out to ~5 h-1 Mpc. Our results show that galaxy alignments appear to be stronger the more dynamically young the cluster is, especially when found in high-density environments. This relation complements the recently found cluster substructure-alignment connection (Plionis & Basilakos) by which dynamically young clusters, found in high-density environments, show stronger cluster-cluster alignments.

Dwarf Galaxies in Clusters

Dwarf and Low Surface Brightness (LSB) galaxies are the most numerous type of galaxies in the local Universe. However ubiquitous they are, their properties remain widely unexplored. Dwarf galaxies range from Ultra Compact Objects (UCO), Dwarf Ellipticals (dE), Dwarf Spheroidals (dSph) to Dwarf Irregulars (dIrr) and are generally of low surface brightness. In this paper we focus on the relation between these objects and galaxy clusters. The discussion is centered on three main issues, the faint end of the cluster luminosity function, segregation of dwarfs in clusters and the dwarf galaxy – cluster dynamical state connection. A further analysis of the population and clustering properties of dwarf galaxies in clusters require better statistics. While concluding, we present, as well, future prospects on how to measure distances to dwarfs using the surface brightness fluctuation method so as to increase the number of confirmed dwarf member galaxies in more distant clusters.

Effective desynchronization with bipolar double-pulse stimulation.

This paper is devoted to the desynchronizing effects of bipolar stimuli on a synchronized cluster of globally coupled phase oscillators. The bipolar pulses considered here are symmetrical and consist of a positive and a negative monopolar pulse. A bipolar single pulse with the right intensity and duration desynchronizes a synchronized cluster provided the stimulus is administered at a vulnerable initial phase of the cluster's order parameter. A considerably more effective desynchronization is achieved with a bipolar double pulse consisting of two qualitatively different bipolar pulses. The first bipolar pulse is stronger and resets the cluster, so that the second bipolar pulse, which follows after a constant delay, hits the cluster in a vulnerable state and desynchronizes it. A bipolar double pulse desynchronizes the cluster independently of the cluster's dynamical state at the beginning of the stimulation. The dynamics of the order parameter during a bipolar single pulse or a bipolar double pulse is different from the dynamics during a monopolar single pulse or a monopolar double pulse. Nevertheless, concerning their desynchronizing effects the monopolar and the bipolar stimuli are comparable, respectively. This is significant for applications where bipolar stimulation is required. For example, in medicine and physiology charge-balanced stimulation is typically necessary in order to avoid tissue damage. Based on the results presented here, demand-controlled bipolar double-pulse stimulation is suggested as a milder and more efficient therapy compared to the standard permanent high-frequency deep brain stimulation in neurological patients.

Substructure in Clusters Containing Wide-Angle–Tailed Radio Galaxies. I. New Redshifts

We present new redshifts and positions for 635 galaxies in nine rich clusters containing wide-angle tailed (WAT) radio galaxies. Combined with existing data, we now have a sample of 18 WAT-containing clusters with more than 10 redshifts. This sample contains a substantial portion of the WAT clusters in the VLA 20 cm survey of Abell clusters, including 75% of WAT clusters in the complete survey (z ≤ 0.09), and 20% of WAT clusters with z > 0.09. It is a representative sample, which should not contain biases other than selection by radio morphology. We graphically present the new data using histograms and sky maps. A semiautomated procedure is used to search for emission lines in the spectra in order to add and verify galaxy redshifts. We find that the average apparent fraction of emission-line galaxies is about 9% in both the clusters and the field. We investigate the magnitude completeness of our redshift surveys with CCD data for a test case, Abell 690. This case indicates that our galaxy target lists are deeper than the detection limit of a typical MX exposure, and they are 82% complete down to R = 19.0. The importance of the uniformity of the placement of fibers on targets is posited, and we evaluate this in our data sets. We find some cases of nonuniformities which may influence dynamical analyses. A second paper will use this database to look for correlations between the WAT radio morphology and the cluster's dynamical state.

CCD photometry of Large Magellanic Cloud clusters. III - The unique, remote cluster ESO 121-SC03

view Abstract Citations (72) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Photometry of Large Magellanic Cloud Clusters. III. The Unique, Remote Cluster ESO 121-SC03 Mateo, Mario ; Hodge, Paul ; Schommer, R. A. Abstract Johnson B and V CCD photometry of stars in the extremely remote LMC cluster ESO 121-SC03 are analyzed, and the data are used to construct a C-M diagram of the cluster to V of roughly 23. The age and metallicity of the cluster are estimated, and it is argued that the C-M diagram implies that the cluster is a unique object among LMC clusters for which sufficiently deep photometry is available. Digital aperture photometry of the cluster has been performed, and the results are compared with King profiles to deduce some of the structural parameters of the cluster. Finally, the cluster's dynamical state is discussed. Publication: The Astrophysical Journal Pub Date: December 1986 DOI: 10.1086/164757 Bibcode: 1986ApJ...311..113M Keywords: Astronomical Photometry; Magellanic Clouds; Star Clusters; Charge Coupled Devices; Color-Magnitude Diagram; Error Analysis; Interstellar Extinction; Metallicity; Astrophysics; CLUSTERS: OPEN; GALAXIES: MAGELLANIC CLOUDS; PHOTOMETRY; STARS: ABUNDANCES; STARS: EVOLUTION full text sources ADS | data products SIMBAD (2) NED (1) Related Materials (2) Part 1: 1985PASP...97..753M Part 2: 1986ApJS...60..893M