Model Of Cluster Formation Research Articles

TheLX‐TandLX‐σ Relationships for Galaxy Clusters Revisited

The relationships between the X-ray-determined bolometric luminosity, LX, the temperature, T, of the intracluster gas, and the optical measured velocity dispersion, σ, of the cluster galaxies are updated for galaxy clusters using the largest sample of 256 clusters drawn from literature. The newly established relationships, based on the doubly weighted orthogonal distance regression (ODR) method, are justified by both their self-consistency and co-consistency, which can then be used to test the theoretical models of cluster formation and evolution. The observationally determined LX-T and LX-σ relationships, LX ∝ T2.72±0.05 ∝ σ5.24±0.29, are marginally consistent with those predicted by the scenario in which both intracluster gas and galaxies are in isothermal and hydrostatic equilibrium with the underlying gravitational potential of clusters. A comparison between these observed and predicted LX-T relationships also suggests that the mean cluster baryon fraction, fb, remains approximately constant among different clusters, fb ≈ 0.17, which gives rise to a low mass density universe of Ωm ≈ 0.3.

Cluster renormalization in the Becker-Döring equations

We apply ideas from renormalization theory to models of cluster formation in nucleation and growth processes. We study a simple case of the Becker-Doring system of equations and show how a novel coarse-graining procedure applied to the cluster aggregation space affects the coagulation and fragmentation rate coefficients. A dynamical renormalization structure is found to underlie the Becker-Doring equations, nine archetypal systems are identified, and their behaviour is analysed in detail. These architypal systems divide into three distinct groups: coagulation-dominated systems, fragmentation-dominated systems and those systems where the two processes are balanced. The dynamical behaviour obtained for these is found to be in agreement with certain fine-grained solutions previously obtained by asymptotic methods. This work opens the way for the application of renormalization ideas to a wide range of non-equilibrium physicochemical processes, some of which we have previously modelled on the basis of the Becker-Doring equations.

Effect of I− impurity on the efficiency of silver cluster formation on AgBr microcrystal surfaces

Computer simulation is used to study the effect of iodide impurity on silver cluster formation on AgBr microcrystals. The simulation is based on a nucleation-and-growth model of silver cluster formation in competition with recombination of electrons and holes. The efficiency of silver cluster formation is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. This behavior is due to a partitioning of the hole between free and trapped states which favors the free side as size increases. As a result, recombination decreases and efficiency increases at large microcrystal size. Iodide impurity decreases efficiency relatively more at larger sizes because it introduces an internal recombination pathway not present in the control simulation. Because of their larger volume-to-surface-area ratios, the larger microcrystals are affected more by this additional recombination pathway than smaller microcrystals.

Cosmological Implications of the Fundamental Relations of X-Ray Clusters

Based on the two-parameter family nature of X-ray clusters of galaxies obtained in a separate paper, we discuss the formation history of clusters and cosmological parameters of the universe. Utilizing the spherical collapse model of cluster formation, and assuming that the cluster X-ray core radius is proportional to the virial radius at the time of the cluster collapse, the observed relations among the density, radius, and temperature of clusters imply that cluster formation occurs in a wide range of redshift. The observed relations favor the low-density universe. Moreover, we find that the model of $n\sim -1$ is preferable.

Molecular Interpretation of Different Morphologies of KCl Microcrystals Growing From Aqueous Solutions

Experimental data on the morphology of KCl microcrystals are interpreted from estimations of the possibility of growth of the (100) and (111)2 faces. Ion attachment energy and water adsorption energy for five different growth sites on the (100) face were calculated for different solution concentrations c and temperature T = 298.15 K using the molecular interaction model of cluster formation applied to large cubic KCl clusters with specified growth site in the centre of one of the (100) face. The results show that, above the equilibrium concentration c0 = 4.17 mol/dm3, attachment of ions is possible only for dislocation originated kink sites where the ion attachment energy is positive. For c > 5.3 mol/dm3, ions can also join a step producing new kink sites, thus increasing the growth velocity of (100) face. Further increase in the growth velocity is predicted to occur in solutions with c > 5.7 mol/dm3 when formation of growth islands is possible.

Clusters of galaxies: magnetic fields and nonthermal emission

The nonthermal particle content of galaxy clusters should in part have a cosmological component generated during the early starburst phase of the member galaxies. This is reviewed in the framework of a simple cluster formation model suggested previously. It implies a nonthermal energy fraction of about 10 percent for the Intracluster gas. We also propose a mechanism for the early generation of Intracluster magnetic fields in terms of Galactic Winds. It results in typical field strenghts of 10 −7 G. Such comparatively weak fields are consistent with an inverse Compton origin of the excess EUV and hard X-ray emission of the Coma cluster, given the radio synchrotron emission. The required relativistic electrons must have been accelerated rather recently, less than a few billion years ago, presumably in cluster accretion shocks. This is in contrast to the hadronic nonthermal component which accumulates on cosmological time scales, and whose π 0-decay TeV γ-ray emission is expected to be larger, or of the same order as the inverse Compton TeV emission. This γ-radiation characterizes the energetic history of cluster formation and should be observable with future arrays of imaging atmospheric Cherenkov telescopes.

Study of the geometry of KCl clusters nucleating from vapour and in aqueous solutions

The molecular interaction model of cluster formation was used to compute the formation energy of KCl clusters having ions from 4 to ca 10000, taking into consideration repulsion forces between ions. Four types of cluster geometries were analysed: spherical, cube-shaped (perfect cubes or cuboids with steps on one of their {1 0 0} faces) and octahedral with {1 1 1} and {1 1 1} 2 faces. It was found that cube-shaped clusters forming from the vapour phase are always preferential (more abundant) due to Coulomb interactions. In aqueous solutions, the subcritical clusters, both spherical and cube-shaped, can be preferential. Larger KCl clusters should have the cubic geometry due to the small values of the average adsorption energy of water molecules on their surface. Spherical and octahedral {1 1 1} 2 clusters adsorb water molecules more strongly, which leads to their significantly lower growth.

Proto–Globular Cluster Candidates in NGC 1275

The discovery, with HST imaging, of proto–globular cluster candidates in NGC 1275 (Holtzman et al. 1992) was regarded by many as a major success of the merger model for globular cluster formation (e.g. Ashman & Zepf 1992) and has been cited in support of the idea that elliptical galaxies form from the merger of two or more spiral galaxies. A prediction of the Ashman & Zepf model was that newly-formed clusters should be observable in currently or recently merging systems. The NGC 1275 clusters constitute an important test of globular cluster formation models. NGC 1275 is the peculiar cD galaxy at the center of the Perseus cluster. It shows evidence for a merger history and may indeed be undergoing a merger at present. It also has one of the largest known cooling flows.

Star Formation in Cluster Galaxies at 0.2 < [CLC][ITAL]z[/ITAL][/CLC] < 0.55

The rest-frame equivalent width of the [OII] λ3727 emission line, W0(O II), has been measured for cluster and field galaxies in the Canadian Network for Observational Cosmology redshift survey of rich clusters at 0.2 10 A, as expected in a model of cluster formation in which star formation is truncated on infall. Evidence of suppressed star formation relative to the field is present in the whole cluster sample, out to 2R200, so the mechanism responsible for the differential evolution must be acting at a large distance from the cluster center and not just in the core. The mean star formation rate in the cluster galaxies with the strongest emission corresponds to an increase in the total stellar mass of less than about 4% if the star formation is due to a secondary burst lasting 0.1 Gyr.

Star Clusters Driven to Form by Strong Collisions Between Gas Clouds in High-Velocity Random Motion

view Abstract Citations (46) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Star Clusters Driven to Form by Strong Collisions Between Gas Clouds in High-Velocity Random Motion Fujimoto, Mistuaki ; Kumai, Yasuki Abstract Two topics are discussed about the globular and populous star clusters, based on an idea that they were/are driven to form through strong collisions between massive gas clouds in high-velocity random motion. The first is a global trial to reproduce the approximately-constant specific frequency of globular clusters among normal elliptical galaxies: The ratio of the total number of globular clusters to the luminosity of their host galaxy is obtained to be approximately constant by counting the number of collisions between gas clouds in virialized motion in the gravitational potential of the protogalaxy. The second is presenting a local dynamical model for the formation of binary star clusters such as detected numerously in the Magellanic Clouds. It is stressed that the oblique cloud-cloud collisions occur more frequently than the head-on collisions, and the former collisions yield shear and rotation to the compressed gaseous slab, which works to split a local Jeans gas clump into two objects revolving around each other (fission). In order to examine this dynamical model for the binary star cluster formation, we determine numerical values of the split objects, such as their mass, diameter of revolution, frequency of occurrence, etc., to be compared with those measured in the Large Magellanic Cloud. Publication: The Astronomical Journal Pub Date: January 1997 DOI: 10.1086/118249 Bibcode: 1997AJ....113..249F Keywords: ISM: KINEMATICS AND DYNAMICS; ISM: CLOUDS; GALAXIES: STAR CLUSTERS full text sources ADS | data products SIMBAD (39) NED (1)

STM study on one-dimensional cluster formation processes of Y@C 82 and C 60 molecules

Using scanning tunneling microscopy (STM), we have studied cluster formation processes of fullerene molecules adsorbed on the Cu(111) 1 × 1 surface. We used two endohedral metallofullerenes; Y@C 82 and Gd@C 82, and pristine C 60. All adsorbed molecules are observed at step edges of the surface, and thus their processes can be treated with a model of one-dimensional cluster formation. When small amounts of molecules are deposited on the surface, we found that the dimer is most abundant among the clusters of Y@C 82 while monomers are dominant in the cases of Gd@C 82 and C 82. Since Y@C 82 has an electronic spin while the others do not, we speculated that the preferred dimer formation of Y@C 82 is owing to an interaction of the spin. Interaction energies among fullerene molecules were estimated based on a statistical analysis of the STM data.

Onset of fragment formation in periodic expanding systems.

The problem of the time evolution of the process of fragment formation is investigated in the framework of expanding periodic systems. We focus on the fragmentation of small (100 constituents) systems. We use a molecular-dynamics method that simulates the behavior of condensed matter under homogeneous adiabatic expansion. Fragment formation is studied using a generalized version of the early cluster formation model (GECFM) which searches for the most bound density fluctuations in phase space. We show that the asymptotic fragment spectra is early realized in phase space not only for the total multiplicity but also for the populations of different mass ranges. In order to map the evolution of the system on the phase diagram of the small cell periodic one, its equation of state is calculated. It is shown that the fragmentation of the system cannot be unambiguously related to spinodal decomposition or nucleation processes. \textcopyright{} 1996 The American Physical Society.

Hierarchical clustering and the Butcher–Oemler effect

We show that the rapid evolution in the fraction of blue, star-forming galaxies seen in clusters as a function of redshift (the Butcher-Oemler effect) can be explained very simply if structure formation in the universe proceeeds hierarchically. We show that a rich cluster observed at high redshift has had a significantly different evolutionary history to a cluster of the same richness observed today. High redshift clusters take longer to assemble and thus under- go more merging at small lookback times. We have investigated two models of star formation in cluster galaxies: 1) a model in which star formation is induced by galaxy-galaxy mergers and interactions and 2) a model in which star formation is regulated by the infall of galaxies onto larger systems such as groups and clusters. Both models produce trends consistent with the Butcher- Oemler effect. Our models of cluster formation and evolution allow us to make predictions about trends in the observed properties of clusters with redshift. We find that there should be a correlation between the mass of the cluster or group and the strength of the observed Butcher-Oemler effect, with more massive systems exhibiting more evolution than less massive systems. We also predict that both the blue galaxy fraction and the incidence of interacting galaxies in rich clusters should rise continuously with redshift. Finally, we have explored the influence of cosmological parameters on our predictions for cluster evolution. We find that models in which structure formation occurs at very early epochs, such as low $\Omega$ models, predict rather little recent star formation and merging activity in clusters at redshifts of around 0.4.

On the Formation of Globular Clusters. II. Early Dynamical Evolution

view Abstract Citations (67) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Formation of Globular Clusters. II. Early Dynamical Evolution Brown, J. H. ; Burkert, A. ; Truran, J. W. Abstract A consistent model of globular cluster formation is presented. We investigate the dynamical evolution of a supershell that is created and chemically enriched by supernovae at the center of a primordial cloud, embedded in a hot protogalactic environment. It is shown that such an expanding supershell can be decelerated sufficiently by the pressure of the hot medium to ensure that the second-generation stars (i.e., those forming in the supershell) can form a bound cluster. When we assume that only the most tightly bound systems survive, we can make detailed predictions concerning the masses, radii, and binding energies of resulting clusters which agree well with those of observed globular clusters. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175304 Bibcode: 1995ApJ...440..666B Keywords: GALAXY: GLOBULAR CLUSTERS: GENERAL; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; STARS: EVOLUTION full text sources ADS |

The fundamental plane correlations for globular clusters

In the parameter space whose axes include a radius (core, or half-light), a surface brightness (central, or average within the half-light radius), and the central projected velocity dispersion, globular clusters lie on a two-dimensional surface (a plane, if the logarithmic quantities are used). This is analogous to the 'fundamental plane' of elliptical galaxies. The implied bivariate correlations are the best now known for globular clusters. The derived scaling laws for the core properties imply that cluster cores are fully virialized, homologous systems, with a constant (M/L) ratio. The corresponding scaling laws on the half-light scale are differrent, but are nearly identical to those derived from the 'fundamental plane' of ellipticals. This may be due to the range of cluster concentrations, which are correlated with other parameters. A similar explanation for elliptical galaxies may be viable. These correlations provide new empirical constraints for models of globular cluster formation and evolution, and may also be usable as rough distance-indicator relations for globular clusters.

Anomalous rotational dynamics of NH4 ions in the paraelectric phase of K1-x(NH4)xH2PO4 mixed crystals

A study of the rotational dynamics of NH4 ions in the paraelectric phase of mixed crystals of K1-x(NH4)xH2PO4 by quasielectric neutron scattering is reported. For high NH4 concentrations (x=0.9) no anomalous behaviour was found and the model of NH4 ion jumps between equivalent orientations in the crystal gave a good description of the experimental data. In contrast the crystal with x=0.6, which forms a protonic dipolar glass state at low temperatures, revealed an unusual temperature dependence of the elastic incoherent structure factor far above the glass formation boundary. This temperature dependence is analysed in the framework of the model of dynamical cluster formation in the paraelectric phase. The order parameter for the gradually condensing NH4 groups is obtained. The results are compared with data obtained by other methods on related compounds.

The galactic globular cluster system

We explore correlations between various properties of Galactic globular clusters, using a database on 143 objects. Our goal is identify correlations and trends which can be used to test and constrain theoretical models of cluster formation and evolution. We use a set of 13 cluster parameters, 9 of which are independently measured. Several arguments suggest that the number of clusters still missing in the obscured regions of the Galaxy is of the order of 10, and thus the selection effects are probably not severe for our sample. Known clusters follow a power-law density distribution with a slope approximately -3.5 to -4, and an apparent core with a core radius approximately 1 kpc. Clusters show a large dynamical range in many of their properties, more so for the core parameters (which are presumably more affected by dynamical evolution) than for the half-light parameters. There are no good correlations with luminosity, although more luminous clusters tend to be more concentrated. When data are binned in luminosity, several trends emerge: more luminous clusters tend to have smaller and denser cores. We interpret this as a differential survival effect, with more massive clusters surviving longer and reaching more evolved dynamical states. Cluster core parameters and concentrations also correlate with the position in the Galaxy, with clusters closer to the Galactic center or plane being more concentrated and having smaller and denser cores. These trends are more pronounced for the fainter (less massive) clusters. This is in agreement with a picture where tidal shocks form disk or bulge passages accelerate dynamical evolution of clusters. Cluster metallicities do not correlate with any other parameter, including luminosity and velocity dispersion; the only detectable trend is with the position in the Galaxy, probably reflecting Zinn's disk-halo dichotomy. This suggests that globular clusters were not self-enriched systems. Velocity dispersions show excellent correlations with luminosity and surface brightness. Their origin is not well understood, but they may well reflect initial conditions of cluster formation, and perhaps even be used to probe the initial density perturbation spectrum on a approximately 10(exp 6) solar mass scale. Core radii and concentrations play a role of a 'second parameter' in these correlations. While a global manifold of cluster properties has a high statistical dimensionality (D greater than 4), a subset of structural, photometric, and dynamical parameters forms a statistically three-dimensional family, as expected from objects following King models; we propose to call this set of quantities the King Manifold. Some of the observed correlations may be usable as distance indicator relations for globular clusters.

A Merger Model and Globular Cluster Formation

We propose a self-consistent model for globular cluster formation in, but not limited to, our Galaxy, based on the merger model of Mathews & Schramm (1993). Stars and star clusters form in bursts at the merging interfaces as protogalactic clouds collide. We describe the formation of those star clusters with a simple schematic Ansatz which takes into account the thermal and Kelvin-Helmholtz instabilities. It is shown that this model is consistent with many observational properties such as the age and metallicity distributions of globular clusters, the overall number of globular clusters, and the near constancy of the numbers of globular clusters in different size host galaxies. Most of the features of this merger model are insensitive to choices of parameters. However, the model does not produce as many high-metallicity clusters as observed. Possible explanations for this are presented.

A model for cluster formation from the inner track in the PDMS-process

Negative ion-spectra desorbed by 252Cf-fission fragments, called plasma desorption mass spectra (PDMS), of hydrocarbon substances show a strange mass distribution. They are rather similar for all studied substances such as small alkanes, benzene as well as big molecules like β-carotene and even for fullerene where hydrogen may be present only as a rest gas in the apparatus or adsorbed on the surface. This leads to the assumption that the ions found in the low mass region of these spectra are ions formed by a process by which the primary chemical structure information is lost. We present a model which describes by a differential equation network the formation of hydrocarbon clusters out of an expanding atomic gas formed in the inner track of the primary fast heavy ion.

Ge cluster formation with monolayer and submonolayer coverages on the GaAs(110) surface

We examine the deposition process of Ge adatoms on the GaAs(110) surface. We use total energy calculations based on ab initio pseudopotentials constructed within the local density approximation. The equilibrium morpholoies for the adatoms, and the growth pattern determined for monolayer and submonolayer coverages, are calculated. Also, the binding energy of different sites, vibrational frequencies of adatoms on these sites, and the migration energy barrier along the [11̄0] direction are presented. Our theoretical model for Ge cluster formation and morphology on the GaAs surface is consistent with recent scanning tunnelling microscopy measurements for this surface.