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Scaling Relations (scaling + relation)

Distribution by Scientific Domains

Physics and Astronomy	83%
Chemistry	12%

Distribution within Physics and Astronomy

Astronomy & Astrophysics	80%
Solid State Physics	10%
General & Introductory Physics	7%

Selected Abstracts

A Universal Scaling Relation in High-Temperature Superconductors.

CHEMINFORM, Issue 40 2004
C. C. Homes
No abstract is available for this article. [source]

Probing cosmology and galaxy cluster structure with the Sunyaev,Zel'dovich decrement versus X-ray temperature scaling relation

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
Cien Shang
ABSTRACT Scaling relations among galaxy cluster observables, which will become available in large future samples of galaxy clusters, could be used to constrain not only cluster structure, but also cosmology. We study the utility of this approach, employing a physically motivated parametric model to describe cluster structure and applying it to the expected relation between the Sunyaev,Zel'dovich decrement (S,) and the emission-weighted X-ray temperature (Tew). The slope and normalization of the entropy profile, the concentration of the dark matter potential, the pressure at the virial radius and the level of non-thermal pressure support as well as the mass and redshift dependence of these quantities are described by free parameters. With a suitable choice of fiducial parameter values, the cluster model satisfies several existing observational constraints. We employ a Fisher matrix approach to estimate the joint errors on cosmological and cluster structure parameters from a measurement of S, versus Tew in a future survey. We find that different cosmological parameters affect the scaling relation differently: predominantly through the baryon fraction (,m and ,b), the virial overdensity (w0 and wa for low- z clusters) and the angular diameter distance (w0 and wa for high- z clusters; ,DE and h). We find that the cosmology constraints from the scaling relation are comparable to those expected from the number counts (dN/dz) of the same clusters. The scaling-relation approach is relatively insensitive to selection effects and it offers a valuable consistency check; combining the information from the scaling relation and dN/dz is also useful to break parameter degeneracies and help disentangle cluster physics from cosmology. Our work suggests that scaling relations should be a useful component in extracting cosmological information from large future cluster surveys. [source]

Multilevel structure of reinforcing silica and carbon

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000
D.W. Schaefer
Using small-angle x-ray (SAXS), neutron (SANS), x-ray diffraction and light scattering, we study the structure of colloidal silica and carbon on length scales from 4 Å < q,1 < 107 Å where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 Å, aggregated into micron-sized aggregates that in turn are agglomerated into 100 µ agglomerates. The diffraction data show that the primary particles in precipitated silica are composed of highly defective amorphous silica with little intermediate-range order (order on the scale of several bond distances). On the next level of morphology, primary particles arise by a complex nucleation process in which primordial nuclei briefly aggregate into rough particles that subsequently smooth out to become the seeds for the primaries. The primaries aggregate to strongly bonded clusters by a complex process involving kinetic growth, mechanical disintegration and restructuring. Finally, the small-angle scattering (SAS) data lead us to postulate that the aggregates cluster into porous, rough-surfaced, non-mass-fractal agglomerates that can be broken down to the more strongly bonded aggregates by application of shear. We find similar structure in pelletized carbon blacks. In this case we show a linear scaling relation between the primary and aggregate sizes. We attribute the scaling to mechanical processing that deforms the fractal aggregates down to the maximum size able to withstand the compaction stress. Finally, we rationalize the observed structure based on empirical optimization by filler suppliers and some recent theoretical ideas due to Witten, Rubenstein and Colby. [source]

Constraints on modified gravity from the observed X-ray luminosity function of galaxy clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
David Rapetti
ABSTRACT We use measurements of the growth of cosmic structure, as inferred from the observed evolution of the X-ray luminosity function (XLF) of galaxy clusters, to constrain departures from general relativity (GR) on cosmological scales. We employ the popular growth rate parameterization, ,m(z),, for which GR predicts a growth index ,, 0.55. We use observations of the cosmic microwave background (CMB), type Ia supernovae (SNIa) and X-ray cluster gas mass fractions (fgas), to simultaneously constrain the expansion history and energy content of the Universe, as described by the background model parameters: ,m, w and ,k, i.e. the mean matter density, the dark energy equation of state parameter and the mean curvature, respectively. Using conservative allowances for systematic uncertainties, in particular for the evolution of the mass,luminosity scaling relation in the XLF analysis, we find ,= 0.51+0.16,0.15 and ,m= 0.27 ± 0.02 (68.3 per cent confidence limits), for a flat cosmological constant, cold dark matter (,CDM) background model. Allowing w to be a free parameter, we find ,= 0.44+0.17,0.15. Relaxing the flatness prior in the ,CDM model, we obtain ,= 0.51+0.19,0.16. When in addition to the XLF data we use the CMB data to constrain , through the ISW effect, we obtain a combined constraint of ,= 0.45+0.14,0.12 for the flat ,CDM model. Our analysis provides the tightest constraints to date on the growth index. We find no evidence for departures from GR on cosmological scales. [source]

Probing cosmology and galaxy cluster structure with the Sunyaev,Zel'dovich decrement versus X-ray temperature scaling relation

The impact of mergers on relaxed X-ray clusters , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
Effects on compact cool cores
ABSTRACT We use the simulations presented in Poole et al. to examine the effects of mergers on the properties of cool cores in X-ray clusters. Motivated by recent Chandra and XMM,Newton observations, we propose a scheme for classifying the morphology of clusters based on their surface brightness and entropy profiles. Three dominant morphologies emerge: two hosting compact cores and central temperatures which are cool [CCC (compact cool core) systems] or warm [CWC (compact warm core) systems] and one hosting extended cores which are warm [EWC (extended warm core) systems]. In the cases we have studied, CCC states are disrupted only after direct collisions with merging cluster cores. This can happen in head-on collisions or during second pericentric passage in off-axis mergers. By the time they are relaxed, our remnant cores have generally been heated to warm core (CWC or EWC) states but subsequently recover CCC states by the end of the simulation. The only case resulting in a long-lived EWC state is a slightly off-axis 3:1 merger for which the majority of shock heating occurs during the accretion of a low-entropy stream formed from the disruption of the secondary's cool core. Since tdyn,tcool for all our relaxing merger remnant cores, compression prevents their core temperatures from falling until after they relax to the compact states allowed by their remnant central entropies. This naturally explains the population of relaxed CWC systems observed in recent Chandra and XMM,Newton observations with no need to invoke active galactic nuclei feedback. The morphological segregation in the Lx,Tx scaling relation noted by McCarthy et al. is qualitatively reflected in the results of our mergers as well. However, none of the cases we have studied produces systems with sufficiently high central entropies to account for the most underluminous EWC systems observed. Lastly, mergers do not efficiently mix the intracluster medium in our simulations. As a result, merging systems which initially host central metallicity gradients do not yield merger remnants with flat metallicity profiles. Taken together, these results suggest that once formed, compact core systems are remarkably stable against disruption from mergers. It remains to be demonstrated exactly how the sizable observed population of extended core systems was formed. [source]

Mergers between elliptical galaxies and the thickening of the Fundamental Plane

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
A. C. González-García
ABSTRACT We have carried out computer simulations to study the effect of merging on the Fundamental Plane (FP) relation. Initially, systems are spherical Jaffe models following a simple scaling relation (M/R2e= constant). They have been put on the FP by imposing different M/L values. Various orbital characteristics have been considered. Our results show that the merger remnants lie very close to the FP of the progenitors. Although non-homology is introduced by the merging process, mergers among homologous galaxies leave a pre-existing FP-relation intact. As a side result we find that variations in the point of view lead to non-negligible scatter about the FP. [source]

Growth model on (1 + 1) dimensions with local relaxation and discrete number of orientations

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2004
W. L. Cavalcanti
Abstract We introduced in this work a simple model for studying the texture formation during the electrodeposition process. Monte Carlo simulations were used to describe the formation of the deposits, and scaling concepts were also employed to characterize their growth and roughness properties. Particles are randomly deposited on a substrate, and their main axis can be aligned in a discrete set of possible directions. The final orientation of the deposited particle is determined by the interaction energy with its first neighboring particles and substrate temperature. Particle interactions are chosen according to the q -state ferromagnetic Potts model hamiltonian. Simulations were performed on (1 + 1) dimensions, for different values of temperature and substrate size. We have found different behaviors at low and high temperatures. Only at zero temperature the system reaches an absorbing state with all the layers occupied by particles oriented in the same direction. At this temperature we found the dynamic, roughness and growth exponents of the model, which satisfies the well known Family,Vicsek scaling relation for the self-affine interfaces. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Homes relation in the attractive Hubbard model in d = ,

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
M. Bak
Abstract Lack of the recognized theory of high-temperature superconductivity (HTS) has led to an intense experimental and theoretical search for some universal relationships, which might unravel the physics behind the HTS. One of the most known is so called Uemura relation, ,s(0) , Tc, where ,s is superfluid density and Tc is the superconducting transition temperature. Recently Homes et al. [Nature 430, 539 (2004)] reported a new universal scaling relation, ,s , ,dc(Tc) · Tc, where ,dc(T ) is dc conductivity. In the present paper Homes relation is investigated theoretically in the limit of infinite dimensions in the second order perturbation theory. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Modelling the light induced metastable effects in amorphous silicon

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008
G. Munyeme
Abstract We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which act as efficient charge trapping and recombination centres. The increase in dangling bond states causes a decrease in the performance of amorphous silicon solar cells. To show this effect, a modelling approach has been developed which uses the density of localised states with exponentially increasing band-tails and dangling bond defect states distribution chosen according to the defect pool model. The calculation of the evolution of dangling bond state density during illumination has been achieved through a dynamic scaling relation derived from a defect creation model. The approach considers the amphoteric nature of the dangling bond state and thus accounts for the contributions of the different charge states of the dangling bond during the degradation process. This paper attempts to describe the simulation approach which calculates the defect density as a function of energy, position in the solar cell and illumination time. In excellent agreement with other workers, our simulation results show that the increase in the density of neutral dangling bond states during illumination is higher than of the charged states. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Towards a classification of icosahedral viruses in terms of indexed polyhedra

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2006
A. Janner
The standard Caspar & Klug classification of icosahedral viruses by means of triangulation numbers and the more recent novel characterization of Twarock leading to a Penrose-like tessellation of the capsid of viruses not obeying the Caspar,Klug rules can be obtained as a special case in a new approach to the morphology of icosahedral viruses. Considered are polyhedra with icosahedral symmetry and rational indices. The law of rational indices, fundamental for crystals, implies vertices at points of a lattice (here icosahedral). In the present approach, in addition to the rotations of the icosahedral group 235, crystallographic scalings play an important rôle. Crystallographic means that the scalings leave the icosahedral lattice invariant or transform it to a sublattice (or to a superlattice). The combination of the rotations with these scalings (linear, planar and radial) permits edge, face and vertex decoration of the polyhedra. In the last case, satellite polyhedra are attached to the vertices of a central polyhedron, the whole being generated by the icosahedral group from a finite set of points with integer indices. Three viruses with a polyhedral enclosing form given by an icosahedron, a dodecahedron and a triacontahedron, respectively, are presented as illustration. Their cores share the same polyhedron as the capsid, both being in a crystallographic scaling relation. [source]

Scaling law and critical exponent for ,0 at the 3D Anderson transition

ANNALEN DER PHYSIK, Issue 12 2009
L.J. Vasquez
Abstract We use high-precision, large system-size wave function data to analyse the scaling properties of the multifractal spectra around the disorder-induced three-dimensional Anderson transition in order to extract the critical exponents of the transition. Using a previously suggested scaling law, we find that the critical exponent , is significantly larger than suggested by previous results. We speculate that this discrepancy is due to the use of an oversimplified scaling relation. [source]

Double Excited High-n Spin Dependent Atomic Structure Scaling Laws for He I: Application to Radiative Properties for Edge Plasma Conditions

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006
E. H. Guedda
Abstract We present our numerical calculations of dielectronic recombination rate coefficients which are spin dependent (2lnl , -1snl1L, 1snl3L ) and develop scaling relations which are converging for all spin (S), angular (L) and main (n) quantum numbers. The influence of atomic data inaccuracies, spin dependent channelling of dielectronic recombination rates and collisions on the atomic/ionic fractions is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Allometric growth, life-history invariants and population energetics

ECOLOGY LETTERS, Issue 4 2005
Evan P. Economo
Abstract Population and community level processes must be at least partially determined by variation in the body sizes of constituent individuals, implying quantitative scaling relations can be extended to account for variation in those processes. Here we integrate allometric growth and life-history invariant theories, and use this approach to develop theory describing the energetics of stationary populations. Our predictions approximate, with no free parameters, the scaling of production/biomass and assimilation/biomass ratios in mammalian populations and work partially for fish populations. This approach appears to be a promising direction and suggests the need for further development of the growth and life-history models, and extensions of those theories. [source]

The effect of mixer properties and fill level on granular flow in a bladed mixer

AICHE JOURNAL, Issue 2 2010
Brenda Remy
Abstract The discrete element method was used to study the effect of mixer properties and fill level on the granular flow of monodisperse, cohesionless spheres in a bladed mixer. For fill levels just covering the span of the blades, a three-dimensional (3-D) recirculation zone develops in front of the blades, which promotes vertical and radial mixing. Increasing fill level reduces the size of the recirculation zone, decreases bed dilation and hinders particle diffusivities. However, above a critical fill level, the behavior of the particles within the span of the blade is found to be invariant of fill level. At low-fill levels, the pressure within the particle bed varies linearly with bed height and can be approximated by hydrostatics. At higher fill levels, a constant pressure region develops within the span of the blades due to the angled pitch of the blades. Cylinder wall friction is shown to significantly influence granular behavior in bladed mixers. At low-wall friction, the 3-D recirculation zone observed for high-wall friction conditions does not develop. High-wall friction leads to an increase in convective and diffusive particle mixing. Shear stresses are shown to be a function of wall friction. Blade position along the vertical axis is shown to influence flow patterns, granular temperature and stress. The effect of increasing the mixer diameter at a constant particle diameter was also studied. When the mixer diameter is larger than a critical size such that wall effects are minimized, the observed granular behavior follows simple scaling relations. Particle velocities and diffusivities scale linearly with mixer size and blade speed. Normal and shear stress profiles are found to scale linearly with the total weight of the particle bed. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Radiative transfer in disc galaxies , IV.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
The effects of dust attenuation on bulge, disc structural parameters
ABSTRACT Combining Monte Carlo radiative transfer simulations and accurate 2D bulge/disc decompositions, we present a new study to investigate the effects of dust attenuation on the apparent structural properties of the disc and bulge of spiral galaxies. We find that dust affects the results from such decompositions in ways which cannot be identified when one studies dust effects on bulge and disc components separately. In particular, the effects of dust in galaxies hosting pseudo-bulges might be different from those in galaxies hosting classical bulges, even if their dust content is identical. Confirming previous results, we find that disc scalelengths are overestimated when dust effects are important. In addition, we also find that bulge effective radii and Sérsic indices are underestimated. Furthermore, the apparent attenuation of the integrated disc light is underestimated, whereas the corresponding attenuation of bulge light is overestimated. Dust effects are more significant for the bulge parameters, and, combined, they lead to a strong underestimation of the bulge-to-disc ratio, which can reach a factor of 2 in the V band, even at relatively low galaxy inclinations and dust opacities. Nevertheless, it never reaches factors larger than about 3, which corresponds to a factor of 2 in bulge-to-total ratio. Such effect can have an impact on studies of the black hole/bulge scaling relations. [source]

X-ray groups and clusters of galaxies in the Subaru,XMM Deep Field

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
A. Finoguenov
Abstract We present the results of a search for galaxy clusters in the Subaru,XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5,2 keV band of 2 × 10,15 erg cm,2 s,1 over one of the widest XMM,Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) , log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance ,8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed. [source]

Cosmology and cluster halo scaling relations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009
Pablo A. Araya-Melo
ABSTRACT We explore the effects of dark matter and dark energy on the dynamical scaling properties of galaxy clusters. We investigate the cluster Faber,Jackson (FJ), Kormendy and Fundamental Plane (FP) relations between the mass, radius and velocity dispersion of cluster-sized haloes in cosmological N -body simulations. The simulations span a wide range of cosmological parameters, representing open, flat and closed Universes. Independently of the cosmology, we find that the simulated clusters are close to a perfect virial state and do indeed define an FP. The fitted parameters of the FJ, Kormendy and FP relationships do not show any significant dependence on ,m and/or ,,. One outstanding effect is the influence of ,m on the thickness of the FP. Following the time evolution of our models, we find slight changes of FJ and Kormendy parameters in high-,m universe, along with a slight decrease of FP fitting parameters. We also see an initial increase of the FP thickness followed by a convergence to a nearly constant value. The epoch of convergence is later for higher values of ,m, while the thickness remains constant in the low- ,m , models. We also find a continuous increase of the FP thickness in the standard cold dark matter cosmology. There is no evidence that these differences are due to the different power spectrum slopes at cluster scales. From the point of view of the FP, there is little difference between clusters that quietly accreted their mass and those that underwent massive mergers. The principal effect of strong mergers is to significantly change the ratio of the half-mass radius rhalf to the harmonic mean radius rh. [source]

Probing cosmology and galaxy cluster structure with the Sunyaev,Zel'dovich decrement versus X-ray temperature scaling relation

Evolution in the discs and bulges of group galaxies since z= 0.4

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008
Sean L. McGee
ABSTRACT We present quantitative morphology measurements of a sample of optically selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and the gim2d surface brightness fitting software package. The group sample is derived from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) and follow-up Magellan spectroscopy. We compare these measurements to a similarly selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z < 0.12. We find that, at both epochs, the group and field fractional bulge luminosity (B/T) distributions differ significantly, with the dominant difference being a deficit of disc-dominated (B/T < 0.2) galaxies in the group samples. At fixed luminosity, z= 0.4 groups have ,5.5 ± 2 per cent fewer disc-dominated galaxies than the field, while by z= 0.1 this difference has increased to ,19 ± 6 per cent. Despite the morphological evolution we see no evidence that the group environment is actively perturbing or otherwise affecting the entire existing disc population. At both redshifts, the discs of group galaxies have similar scaling relations and show similar median asymmetries as the discs of field galaxies. We do find evidence that the fraction of highly asymmetric, bulge-dominated galaxies is 6 ± 3 per cent higher in groups than in the field, suggesting there may be enhanced merging in group environments. We replicate our group samples at z= 0.4 and 0 using the semi-analytic galaxy catalogues of Bower et al. This model accurately reproduces the B/T distributions of the group and field at z= 0.1. However, the model does not reproduce our finding that the deficit of discs in groups has increased significantly since z= 0.4. [source]

Photometric properties and scaling relations of early-type Brightest Cluster Galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
F. S. Liu
ABSTRACT We investigate the photometric properties of the early-type Brightest Cluster Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4 cluster catalogue with a redshift of less than 0.1. We perform accurate background subtractions and surface photometry for these BCGs to 25 mag arcsec,2 in the Sloan r band. By quantitatively analysing the gradient of the Petrosian profiles of BCGs, we find that a large fraction of BCGs have extended stellar envelopes in their outskirts; more luminous BCGs tend to have more extended stellar haloes that are likely to be connected with mergers. A comparison sample of elliptical galaxies was chosen with similar apparent magnitude and redshift ranges, for which the same photometric analysis procedure is applied. We find that BCGs have steeper size,luminosity (R,L,) and Faber,Jackson (L,,,) relations than the bulk of early-type galaxies. Furthermore, the power-law indices (, and ,) in these relations increase as the isophotal limits become deeper. For isophotal limits from 22 to 25 mag arcsec,2, BCGs are usually larger than the bulk of early-type galaxies, and a large fraction (,49 per cent) of BCGs have discy isophotal shapes. The differences in the scaling relations are consistent with a scenario where the dynamical structure and formation route of BCGs may be different from the bulk of early-type galaxies; in particular dry (dissipationless) mergers may play a more important role in their formation. We highlight several possible dry merger candidates in our sample. [source]

Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
J. Thomas
ABSTRACT Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB=,18.79 and ,22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1,4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10,50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss,Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations. [source]

New scaling relations in cluster radio haloes and the re-acceleration model

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
R. Cassano
ABSTRACT In this paper we derive new expected scaling relations for clusters with giant radio haloes in the framework of the re-acceleration scenario in a simplified, but physically motivated, form, namely: radio power (PR) versus size of the radio emitting region (RH), and PR versus total cluster mass (MH) contained in the emitting region and cluster velocity dispersion (,H) in this region. We search for these correlations by analysing the most recent radio and X-ray data available in the literature for a well-known sample of clusters with giant radio haloes. In particular we find a good correlation between PR and RH and a very tight ,geometrical' scaling between MH and RH. From these correlations PR is also expected to scale with MH and ,H and this is confirmed by our analysis. We show that all the observed trends can be well reconciled with expectations in the case of a slight variation of the mean magnetic field strength in the radio halo volume with MH. A byproduct correlation between RH and ,H is also found, and can be further tested by optical studies. In addition, we find that observationally RH scales non-linearly with the virial radius of the host cluster, and this immediately means that the fraction of the cluster volume which is radio emitting increases with cluster mass and thus that the non-thermal component in clusters is not self-similar. [source]

The evolution of the cluster X-ray scaling relations in the Wide Angle ROSAT Pointed Survey sample at 0.6 < z < 1.0

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
B. J. Maughan
ABSTRACT The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1.0) clusters observed with Chandra and/or XMM,Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L,T, M,T, Mg,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. 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 virialized 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= 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B= 2. This suggests that the same non-gravitational processes are responsible for steepening the local and high- z relations, possibly occurring universally at z, 1 or in the early stages of the cluster formation, prior to their observation. The properties of the intracluster 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(z) and R200(z) are 0.069 ± 0.012 and 0.11 ± 0.02, respectively, and the mean metallicity of the sample is 0.28 ± 0.11 Z,. [source]

Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosity

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
D. Pierini
ABSTRACT We investigate whether dust emission in the far-infrared (far-IR) continuum provides a robust estimate of the star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40,1000 ,m luminosity (Ldust) to the far-ultraviolet (far-UV) (0.165 ,m) luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 ,m limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K -band (2.2 ,m) luminosity, morphology and inclination (i). This sample shows that the ratio of Ldust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K -band luminosity. We find that Ldust/LFUV, eLK0.62, where LFUV and LK are the unattenuated stellar luminosities in far-UV and K, respectively, and , is the ratio of the attenuation optical depths at 0.165 ,m (,FUV) and 2.2 ,m (,K). This relation is to zeroth order independent of i and morphology. It may be further expressed as Ldust/LFUV,L,K, where ,= 0.61 , 0.02,, under the observationally motivated assumption that, for an average inclination, e,L,0.02K. We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle-averaged values of ,. We find that , is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. The far-IR luminosity systematically overestimates SFR in more luminous, earlier-type spirals, owing to the increased fractional contribution to dust heating of optical/near-IR photons in these objects. Conversely, it systematically underestimates SFR in fainter, later-type galaxies, the ,FUV of which is reduced. The limited statistics and the uncertainty affecting the previous scaling relations do not allow us to establish quantitative conclusions, but an analogous analysis making use of larger data sets, available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), and of more advanced models will allow a quantitative test of our conclusions. [source]

The effect of stellar rotation on colour,magnitude diagrams: on the apparent presence of multiple populations in intermediate age stellar clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009
N. Bastian
ABSTRACT A significant number of intermediate age clusters (1,2 Gyr) in the Magellanic Clouds appear to have multiple stellar populations within them, derived from bimodal or extended main-sequence turn-offs. If this is interpreted as an age spread, the multiple populations are separated by a few hundred million years, which would call into question the long-held notion that clusters are simple stellar populations. Here, we show that stellar rotation in stars with masses between 1.2 and 1.7 M, can mimic the effect of a double or multiple population, whereas in actuality only a single population exists. The two main causes of the spread near the turn-off are the effects of stellar rotation on the structure of the star and the inclination angle of the star relative to the observer. Both effects change the observed effective temperature, hence colour, and flux of the star. In order to match observations, the required rotation rates are 20,50 per cent of the critical rotation, which are consistent with observed rotation rates of similar mass stars in the Galaxy. We provide scaling relations which can be applied to non-rotating isochrones in order to mimic the effects of rotation. Finally, we note that rotation is unlikely to be the cause of the multiple stellar populations observed in old globular clusters, as low-mass stars (<1 M,) are not expected to be rapid rotators. [source]

Local group dwarf galaxies in the ,CDM paradigm

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008
J. Peñarrubia
Abstract We report the results of two theoretical studies that examine the dynamics of stellar systems embedded within cold dark matter (CDM) halos in order to assess observational constraints on the dark matter content of Local Group dwarf spheroidals (dSphs). (i) Firstly, approximating the stellar and dark components by King and NFW models, respectively, we calculate the parameters of dark halos consistent with the kinematics and spatial distribution of stars in dSphs as well as with cosmological N-body simulations. (ii) Subsequently, N-body realization of these models are constructed to study the evolution of dwarf spheroidal galaxies (dSphs) driven by galactic tides. The analytical estimates highlight the poor correspondence between luminosity and halo mass. In systems where data exist, the stellar velocity dispersion profiles remains flat almost to the nominal "tidal" radius, implying that stars are deeply embedded within the dwarf halos and are therefore quite resilient to tidal disruption. This is confirmed by our N-body experiments: halos need to lose more than 90% of their original mass before stars can be stripped. As tidal mass loss proceeds, the stellar luminosity, L, velocity dispersion, ,0, central surface brightness, ,0, and core radius, Rc, decrease monotonically. Remarkably, the evolution of these parameters is solely controlled by the total amount of mass lost from within the luminous radius, which permit us to derive a tidal evolutionary track for each of them. This information is used to examine whether the newly-discovered ultra-faintMilkyWay dwarfs are tidally-stripped versions of the "classical", bright dwarfs. Although dSph tidal evolutionary tracks parallel the observed scaling relations in the luminosity-radius plane, they predict too steep a change in velocity dispersion compared with the observational estimates. The ultra-faint dwarfs are thus unlikely to be the tidal remnants of systems like Fornax, Draco, or Sagittarius. Despite spanning four decades in luminosity, dSphs appear to inhabit halos of comparable peak circular velocity, lending support to scenarios that envision dwarf spheroidals as able to form only in halos above a certain mass threshold. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]