Distribution Of Substructures Research Articles

The spatial distribution of the Milky Way and Andromeda satellite galaxies

There are two fundamentally different physical origins of faint satellite galaxies: cosmological sub-structures that contain shining baryons and the fragmentation of gas-rich tidal arms thrown out from interacting galaxies during hierarchical structure formation. The latter tidal-dwarf galaxies (TDG) may form populations with correlated orbital angular momenta about their host galaxies. The existence of TDGs is a stringent necessity because they arise as a result of fundamental physical principals. We determine the significance of the apparent disc-like distribution of Milky Way (MW) satellite galaxies. The distribution of the MW satellites is found to be inconsistent with an isotropic or prolate DM sub-structure distribution at a 99.5 per cent level including the recently discovered UMa and CVn dwarf spheroidal galaxies. The distribution is extremely oblate and inclined by about $88\degr$ with respect to the the MW disc. We also apply the methods to Andromeda's (M31) satellite galaxies using two recently published data-sets. It can not be excluded that the whole population of M31 companions is drawn randomly from an isotropic parent distribution. However, two subsamples of Andromeda satellites are identified which have disc-like features. [abbreviated]

Dynamical flows through dark matter haloes: inner perturbative dynamics, secular evolution and applications

We investigate statistically the dynamical consequences of cosmological fluxes of matter and related moments on progenitors of today's dark matter haloes. These haloes are described as open collisionless systems which do not undergo strong interactions anymore. Their dynamics is described via canonical perturbation theory which accounts for two types of perturbations: the tidal field corresponding to flybys and accretion of dark matter through the outer boundary of the halo. The non-linear evolution of both the entering flux and the particles of the halo is followed perturbatively. The dynamical equations are solved linearly, order by order, projecting on a bi-orthogonal basis to consistently satisfy the field equation. Since our perturbative solution of the Boltzmann–Poisson is explicit, we obtain, as a result, expressions for the N-point correlation function of the response of the halo to the perturbative environment. It allows statistical predictions for the ensemble distribution of the inner dynamical features of haloes. We demonstrate the feasibility of the implementation via a simple example in Appendix B. We argue that the fluid description accounts for the dynamical drag and the tidal stripping of incoming structures. We discuss the realm of non-linear problems which could be addressed statistically by such a theory, such as differential dynamical friction, tidal stripping and the self-gravity of objects within the virial sphere. The secular evolution of open galactic haloes is investigated: we derive the kinetic equation which governs the quasi-linear evolution of dark matter profile induced by infall and its corresponding gravitational correlations. This yields a Fokker–Planck-like equation for the angle-averaged underlying distribution function. This equation has an explicit source term accounting for the net infall through the virial sphere. Under the assumption of ergodicity we then relate the corresponding source, drift and diffusion coefficients for the ensemble-average distribution to the underlying cosmic two-point statistics of the infall and discuss possible applications. The internal dynamics of substructures within galactic haloes (distortion, clumps as traced by Xray emissivity, weak lensing, dark matter annihilation, tidal streams, etc.), and the implication for the disc (spiral structure, warp, etc.) are then briefly discussed. We show how this theory could be used to (i) observationally constrain the statistical nature of the infall, (ii) predict the observed distribution and correlations of substructures in upcoming surveys, (iii) predict the past evolution of the observed distribution of clumps and finally (iv) weight the relative importance of the intrinsic (via the unperturbed distribution function) and external (tidal and/or infall) influence of the environment in determining the fate of galaxies. We stress that our theory describes the perturbed distribution function (mean profile removed) directly in phase space.

Proportioning Whole-Genome Single-Nucleotide–Polymorphism Diversity for the Identification of Geographic Population Structure and Genetic Ancestry

The identification of geographic population structure and genetic ancestry on the basis of a minimal set of genetic markers is desirable for a wide range of applications in medical and forensic sciences. However, the absence of sharp discontinuities in the neutral genetic diversity among human populations implies that, in practice, a large number of neutral markers will be required to identify the genetic ancestry of one individual. We showed that it is possible to reduce the amount of markers required for detecting continental population structure to only 10 single-nucleotide polymorphisms (SNPs), by applying a newly developed ascertainment algorithm to Affymetrix GeneChip Mapping 10K SNP array data that we obtained from samples of globally dispersed human individuals (the Y Chromosome Consortium panel). Furthermore, this set of SNPs was able to recover the genetic ancestry of individuals from all four continents represented in the original data set when applied to an independent, much larger, worldwide population data set (Centre d'Etude du Polymorphisme Humain-Human Genome Diversity Project Cell Line Panel). Finally, we provide evidence that the unusual patterns of genetic variation we observed at the respective genomic regions surrounding the five most informative SNPs is in agreement with local positive selection being the explanation for the striking SNP allele-frequency differences we found between continental groups of human populations.

The effect of low-mass substructures on the cusp lensing relation

It has been argued that the flux anomalies detected in gravitationally lensed QSOs are evidence for substructures in the foreground lensing haloes. In this paper we investigate this issue in greater detail focusing on the Cusp relation which corresponds to images of a source located to the cusp of the inner caustic curve. We use numerical simulations combined with a Monte Carlo approach to study the effects of the expected power law distribution of substructures within LCDM haloes on the multiple images. Generally, the high number of anomalous flux ratios in the cusp configurations is unlikely explained by 'simple' perturbers (subhaloes) inside the lensing galaxy, either modeled by point masses or extended NFW subhaloes. We considered in our analysis a mass range of 10^5-10^7 Msun for the subhaloes. We also demonstrate that including the effects of the surrounding mass distribution, such as other galaxies close to the primary lens, does not change the results. We conclude that triple images of lensed QSOs do not show any direct evidence for dark dwarf galaxies such as cold dark matter substructure.

Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution CDM hydrodynamical simulations

We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N-body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray-shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N-body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars.

The Triaxial Spatial Distribution of CDM Subhalos

I review recent results on the angular distribution of substructure in CDM halos. I show that the subhalo distribution is anisotropic and generally prolate with a long axis that is closely aligned with the long axis of the total mass distribution of the host halo. I show that the correlation between the subhalo distribution and the long axis of the host halo is strong both in dissipationless and dissipational gasdynamical simulations. More massive subhalos tend to be more strongly clustered along the major axis of the host halo reflecting filamentary accretion. The anisotropy of subhalos has potential implications for the interpretation of several observations. For example, I show that while the mean projected mass fraction in substructure in the central regions of CDM halos is f sub ≈ 0.4%, f sub is a strong function of projection angle and is ~6 times higher for projections nearly collinear with the major axis of the host.

Effects of dynamical evolution on the distribution of substructures

We develop a semi-analytical model that determines the evolution of the mass, position and internal structure of dark matter substructures orbiting in dark matter haloes. We apply this model to the case of the Milky Way. We focus in particular on the effects of mass loss, dynamical friction and substructure--substructure interactions, the last of which has previously been ignored in analytic models of substructure evolution. Our semi-analytical treatment reproduces both the spatial distribution of substructures and their mass function as obtained from the most recent N-body cosmological calculations of Gao et al. (2004). We find that, if mass loss is taken into account, the present distribution of substructures is practically insensitive to dynamical friction and scatterings from other substructures. Implementing these phenomena leads to a slight increase (~5%) in the number of substructures at r<0.35 r_vir, whereas their effects on the mass function are negligible. We find that mass loss processes lead to the disruption of substructures before dynamical friction and gravitational scattering can significantly alter their orbits. Our results suggest that the present substructure distribution at r>0.35 r_vir reflects the orbital properties at infall and is, therefore, purely determined by the dark matter environment around the host halo and has not been altered by dynamical evolution.

Development of Nonuniform Substructure and Microstrain Distribution by Texture Formation in Metal Materials

The substructure nonuniformity of metal materials with developed deformation texture was studied by use of the X-ray method of Generalized Pole Figures. Main regularities of substructure nonuniformity were revealed for the first time. Substructure conditions of grains in rolled material form an extremely wide spectrum and vary by passing from texture maxima to texture minima, where residual deformation effects are most significant. The distribution of residual elastic microstrains in the orientational space of rolled material shows the distinct cross-wise system, consisting in alternation of quadrants with predominant microstrains of opposite signs.

Are great disks defined by satellite galaxies in Milky-Way type halos rare in ΛCDM?

We study the spatial distribution of satellite galaxies by assuming that they follow the dark matter distribution. This assumption is supported by semi- analytical studies based on high- resolution numerical simulations. We find that for a Milky- Way type halo, if only a dozen satellite galaxies are observed, then they can lie on a disk with an rms height of about 40 kpc. The normal to the plane is roughly isotropic on the sky. These results are consistent with the observed properties of the satellite galaxies in the Milky Way. If, however, the satellite galaxies follow the distribution of substructure selected by the present mass, then great disks similar to the one in the Milky Way will be rare and difficult to reproduce, in agreement with the conclusion reached by Kroupa et al. ( 2004).

Local rigidity of a protein molecule

Distribution of soft and rigid substructures within a protein molecule has been implicated in several occasions and most recently from the imaging and indentation experiments using an atomic force microscope. In this paper, previously reported result of mechanical extension experiments on the recombinant bovine carbonic anhydrase II, Q253C, is re-analyzed to estimate the distribution of Young's modulus, Y, in this protein. The force vs. extension curve of the enzymatically active, type I conformer gave an estimate of Y increasing from 40 to 220 MPa as the polypeptide chain was extended from 10 to 75 nm indicating the presence of a rigid core structure. The enzymatically inactive type II, in contrast, gave an almost constant modulus of 55 ± 15 MPa in the same extension range in agreement with the previous proposal that it lacked a core structure.

A realistic model for spatial and mass distributions of dark halo substructures: An analytic approach

We construct a realistic model for the dark halo substructures, and derive analytically their spatial, mass, and velocity distributions. Basically, our model is a modification of the Press-Schechter theory to account for the dominant dynamical processes that mark the evolution of dark halo substructures such as the tidal stripping and dynamical friction. Our analytic model successfully reproduces all the well known behaviors of the substructure distributions that have been found in recent numerical simulations: the weak dependence of the mass distributions on the host halo mass; the anti-bias of the spatial distribution relative to the dark matter particle components; the nearly power-law shapes of the mass and velocity distributions. We compare our analytic results with recent high-resolution N-body simulation data and find that they are in excellent agreement with each other.

Linking star formation and environment in supercluster galaxies

We present a unique multiwavelength dataset of the Abell 901/902 supercluster at $z=0.16$ . The environment of the structure is well characterized by weak lensing analysis, galaxy dynamics, and X-ray imaging, and we examine how galaxy properties correlate with these measures of environment. We examine the star-formation–density relation and find a surface mass density threshold above which star-formation in supercluster galaxies is truncated, and that this transformation affects primarily the faint end of the star-forming galaxy population (down to $M^*+6$ ). In addition, we present a preliminary dynamical analysis of the spectroscopic sample ( $n\sim 300$ galaxies), revealing a bimodal distribution of galaxy velocities and significant substructure. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The genomic distribution of population substructure in four populations using 8,525 autosomal SNPs

Understanding the nature of evolutionary relationships among persons and populations is important for the efficient application of genome science to biomedical research. We have analysed 8,525 autosomal single nucleotide polymorphisms (SNPs) in 84 individuals from four populations: African-American, European-American, Chinese and Japanese. Individual relationships were reconstructed using the allele sharing distance and the neighbour-joining tree making method. Trees show clear clustering according to population, with the root branching from the African-American clade. The African-American cluster is much less star-like than European-American and East Asian clusters, primarily because of admixture. Furthermore, on the East Asian branch, all ten Chinese individuals cluster together and all ten Japanese individuals cluster together. Using positional information, we demonstrate strong correlations between inter-marker distance and both locus-specific FST (the proportion of total variation due to differentiation) levels and branch lengths. Chromosomal maps of the distribution of locus-specific branch lengths were constructed by combining these data with other published SNP markers (total of 33,704 SNPs). These maps clearly illustrate a non-uniform distribution of human genetic substructure, an instructional and useful paradigm for education and research.

Distribution of substructures in clusters of galaxies

Wavelet analysis has been applied to the positional data of galaxies in the 117 Abell clusters. The calculations used allowed us to obtain coordinates of the centres substructures detected and to estimate the number of galaxies belonging to them. This study has shown that substructures are present in 45 clusters. Moreover, the analysis of the distribution of substructures within clusters shows that small substructures have a higher projected density than large substructures do and, for each applied wavelet scale a, the number of substructures increases towards the cluster centre.

Substructures in cold dark matter haloes

We analyse the properties of substructures within dark matter haloes (subhaloes) using a set of high-resolution numerical simulations of the formation of structure in a ACDM universe. Our simulation set includes 11 high-resolution simulations of massive clusters as well as a region of mean density, allowing us to study the spatial and mass distribution of substructures down to a mass resolution limit of 10 9 h -1 M ○. . We also investigate how the properties of substructures vary as a function of the mass of the 'parent' halo in which they are located. We find that the substructure mass function depends at most weakly on the mass of the parent halo and is well described by a power law. The radial number density profiles of substructures are steeper in low mass haloes than in high-mass haloes. More massive substructures tend to avoid the centres of haloes and are preferentially located in the external regions of their parent haloes. We also study the mass accretion and merging histories of substructures, which we find to be largely independent of environment. We find that a significant fraction of the substructures residing in clusters at the present day were accreted at redshifts z < 1. This implies that a significant fraction of present-day 'passive' cluster galaxies were still outside the cluster progenitor and were more active at z ∼ 1.

Cancellation of vorticity in steady-state non-isentropic flows of complex fluids

In steady-state non-isentropic flows of perfect fluids there is always thermodynamic generation of vorticity when the difference between the product of the temperature with the gradient of the entropy and the gradient of total enthalpy is different from zero. We note that this property does not hold in general for complex fluids for which the prominent influence of the material substructure on the gross motion may cancel the thermodynamic vorticity. We indicate the explicit condition for this cancellation (topological transition from vortex sheet to shear flow) for general complex fluids described by coarse-grained order parameters and extended forms of Ginzburg-Landau energies. As a prominent sample case we treat first Korteweg's fluid, used commonly as a model of capillary motion or phase transitions characterized by diffused interfaces. Then we discuss general complex fluids. We show also that, when the entropy and the total enthalpy are constant throughout the flow, vorticity may be generated by the inhomogeneous character of the distribution of material substructures, and indicate the explicit condition for such a generation. We discuss also some aspects of unsteady motion and show that in two-dimensional flows of incompressible perfect complex fluids the vorticity is in general not conserved, due to a mechanism of transfer of energy between different levels.

Spectral gamma-ray signatures of cosmological dark matter annihilations.

We propose a new signature for weakly interacting massive particle (WIMP) dark matter, a spectral feature in the diffuse extragalactic gamma-ray radiation. This feature, a sudden drop of the gamma-ray intensity at an energy corresponding to the WIMP mass, comes from the asymmetric distortion of the line due to WIMP annihilation into two gamma rays caused by the cosmological redshift. Unlike other proposed searches for a line signal, this method is not very sensitive to the exact dark matter density distribution in halos and subhalos.

Substructure: Clues to the Formation of Clusters of Galaxies

We have examined the spatial distribution of substructure in clusters of galaxies using Einstein X-ray observations. Subclusters are found to have a markedly anisotropic distribution that reflects the surrounding matter distribution on supercluster scales. Our results suggest a picture in which cluster formation proceeds by mergers of subclusters along large-scale filaments. The implications of such an anisotropic formation process for the shapes, orientations, and kinematics of clusters are discussed briefly.

Structured fluid theory: Kinematics of substructure redistribution

A complete theory of structured fluids is formulated. The substructure distribution, velocity profile and apparent viscosity are calculated for parallel flow between two parallel plates.