Cluster-Supercluster Alignments

We study correlations in spatial orientation between galaxy clusters and their host superclusters using a Hubble Volume N-body realization of a concordance cosmology and an analytic model for tidally-induced alignments. We derive an analytic form for distributions of the alignment angle as functions of halo mass (M), ellipticity (epsilon), distance (r) and velocity (v) and show that the model, after tuning of three parameters, provides a good fit to the numerical results. The parameters indicate a high degree of alignment along anisotropic, collapsed filaments. The degree of alignment increases with M and epsilon while it decreases with r and is independent of v. We note the possibility of using the cluster-supercluster alignment effect as a cosmological probe to constrain the slope of the initial power spectrum.Comment: accepted by ApJ, revised version, new analysis using those superclusters with more than 5 clusters include

The Asymptotic Form of Cosmic Structure: Small Scale Power and Accretion History

We explore the effects of small scale structure on the formation and equilibrium of dark matter halos in a universe dominated by vacuum energy. We present the results of a suite of four N-body simulations, two with a LCDM initial power spectrum and two with WDM-like spectra that suppress the early formation of small structures. All simulations are run into to far future when the universe is 64Gyr/h old, long enough for halos to essentially reach dynamical equilibrium. We quantify the importance of hierarchical merging on the halo mass accretion history, the substructure population, and the equilibrium density profile. We modify the mass accretion history function of Wechsler et al. (2002) by introducing a parameter, \gamma, that controls the rate of mass accretion, dln(M) / dln(a) ~ a^(-\gamma), and find that this form characterizes both hierarchical and monolithic formation. Subhalo decay rates are exponential in time with a much shorter time scale for WDM halos. At the end of the simulations, we find truncated Hernquist density profiles for halos in both the CDM and WDM cosmologies. There is a systematic shift to lower concentration for WDM halos, but both cosmologies lie on the same locus relating concentration and formation epoch. Because the form of the density profile remains unchanged, our results indicate that the equilibrium halo density profile is set independently of the halo formation process.Comment: 17 pages, submitted to ApJ. Full resolution version avaliable at http://www-personal.umich.edu/~mbusha/Papers/AccretionHistory.pd

COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems

We describe a new hybrid N-body/hydrodynamical code based on the particle-mesh (PM) method and the piecewise-parabolic method (PPM) for use in solving problems related to the evolution of large-scale structure, galaxy clusters, and individual galaxies. The code, named COSMOS, possesses several new features which distinguish it from other PM-PPM codes. In particular, to solve the Poisson equation we have written a new multigrid solver which can determine the gravitational potential of isolated matter distributions and which properly takes into account the finite-volume discretization required by PPM. All components of the code are constructed to work with a nonuniform mesh, preserving second-order spatial differences. The PPM code uses vacuum boundary conditions for isolated problems, preventing inflows when appropriate. The PM code uses a second-order variable-timestep time integration scheme. Radiative cooling and cosmological expansion terms are included. COSMOS has been implemented for parallel computers using the Parallel Virtual Machine (PVM) library, and it features a modular design which simplifies the addition of new physics and the configuration of the code for different types of problems. We discuss the equations solved by COSMOS and describe the algorithms used, with emphasis on these features. We also discuss the results of tests we have performed to establish that COSMOS works and to determine its range of validity.Comment: 43 pages, 14 figures, submitted to ApJS and revised according to referee's comment

The Role of Gas in the Merging of Massive Black Holes in Galactic Nuclei. I. Black Hole Merging in a Spherical Gas Cloud

Using high-resolution SPH numerical simulations, we investigate the effects of gas on the inspiral and merger of a massive black hole binary. This study is motivated by both observational and theoretical work that indicate the presence of large amounts of gas in the central regions of merging galaxies. N-body simulations have shown that the coalescence of a massive black hole binary eventually stalls in a stellar background. However, our simulations suggest that the massive black hole binary will finally merge if it is embedded in a gaseous background. Here we present results in which the gas is assumed to be initially spherical with a relatively smooth distribution. In the early evolution of the binary, the separation dimishes due to the gravitational drag exerted by the background gas. In the later stages, when the binary dominates the gravitational potential in its vicinity, the medium responds by forming an ellipsoidal density enhancement whose axis lags behind the binary axis, and this offset produces a torque on the binary that causes continuing loss of angular momentum and is able to reduce the binary separation to distances where gravitational radiation is efficient. Assuming typical parameters from observations of Ultra Luminous Infrared Galaxies, we predict that a black hole binary will merge within $10^{7}$yrs; therefore these results imply that in a merger of gas-rich galaxies, any massive central black holes will coalescence soon after the galaxies merge. Our work thus supports scenarios of massive black hole evolution and growth where hierarchical merging plays an important role. The final coalescence of the black holes leads to gravitational radiation emission that would be detectable up to high redshift by LISA. We show that similar physical effects are important for the formation of close binary stars.Comment: 38 pages, 14 figures, submitted to Ap

Shapes and Alignments of Galaxy Cluster Halos

We present distribution functions and spatial correlations of the shapes of dark matter halos derived from Hubble Volume simulations of a LambdaCDM universe. We measure both position and velocity shapes within spheres encompassing mean density 200 times the critical value, and calibrate small-N systematic errors using Poisson realizations of isothermal spheres and higher resolution simulations. For halos more massive than 3x10^{14} Msun/h, the shape distribution function peaks at (minor/major, intermediate/major) axial ratios of (0.64,0.76) in position, and is rounder in velocity, peaking at (0.72,0.82). Halo shapes are rounder at lower mass and/or redshift; the mean minor axis ratio in position follows (M,z) = c_{15,0} [1-\alpha\ln(M/10^{15}Msun/h)] (1+z)^{-\epsilon}, with c_{15,0}=0.631 \pm 0.001, \alpha=0.023 \pm 0.002 and \epsilon=0.086 \pm 0.004. Position and velocity principal axes are well aligned in direction, with median alignment angle $22^\circ$, and the axial ratios in these spaces are correlated in magnitude. We investigate mark correlations of halo pair orientations using two measures: a simple scalar product shows $\ge 1$ alignment extending to 30 \hinv \mpc while a filamentary statistic exhibits non-random alignment extending to scales \sims 200 \hinv \mpc, ten times the sample two-point correlation length and well into the regime of negative two-point correlation. Cluster shapes are unaffected by the large-scale environment; the shape distribution of supercluster members is consistent with that of the general population.Comment: 12 pages, 8 figures, submitted to Ap

The Beginning and Evolution of the Universe

We review the current standard model for the evolution of the Universe from an early inflationary epoch to the complex hierarchy of structure seen today. We summarize and provide key references for the following topics: observations of the expanding Universe; the hot early Universe and nucleosynthesis; theory and observations of the cosmic microwave background; Big Bang cosmology; inflation; dark matter and dark energy; theory of structure formation; the cold dark matter model; galaxy formation; cosmological simulations; observations of galaxies, clusters, and quasars; statistical measures of large-scale structure; and measurement of cosmological parameters. We conclude with discussion of some open questions in cosmology. This review is designed to provide a graduate student or other new worker in the field an introduction to the cosmological literature.Comment: 69 pages. Invited review article for Publications of the Astronomical Society of the Pacific. Supplementary references, tables, and more concise PDF file at http://www.physics.drexel.edu/univers

Statistical characteristics of formation and evolution of structure in the universe

An approximate statistical description of the formation and evolution of structure of the universe based on the Zel'dovich theory of gravitational instability is proposed. It is found that the evolution of DM structure shows features of self-similarity and the main structure characteristics can be expressed through the parameters of initial power spectrum and cosmological model. For the CDM-like power spectrum and suitable parameters of the cosmological model the effective matter compression reaches the observed scales $R_{wall}\sim$20 -- 25$h^{-1}$Mpc with the typical mean separation of wall-like elements $D_{SLSS}\sim$50 -- 70$h^{-1}$Mpc. This description can be directly applied to the deep pencil beam galactic surveys and absorption spectra of quasars. For larger 3D catalogs and simulations it can be applied to results obtained with the core-sampling analysis. It is shown that the interaction of large and small scale perturbations modulates the creation rate of early Zel'dovich pancakes and generates bias on the SLSS scale. For suitable parameters of the cosmological model and reheating process this bias can essentially improve the characteristics of simulated structure of the universe. The models with $0.3\leq \Omega_m \leq 0.5$ give the best description of the observed structure parameters. The influence of low mass "warm" dark matter particles, such as a massive neutrino, will extend the acceptable range of $\Omega_m$ and $h$.Comment: 20pages, 7 figures, MNRAS in pres

Constraints on the Detectability of Cosmic Topology from Observational Uncertainties

Recent observational results suggest that our universe is nearly flat and well modelled within a $\Lambda$CDM framework. The observed values of $\Omega_{m}$ and $\Omega_{\Lambda}$ inevitably involve uncertainties. Motivated by this, we make a systematic study of the necessary and sufficient conditions for undetectability as well as detectability (in principle) of cosmic topology (using pattern repetition) in presence of such uncertainties. We do this by developing two complementary methods to determine detectability for nearly flat universes. Using the first method we derive analytical conditions for undetectability for infinite redshift, the accuracy of which is then confirmed by the second method. Estimates based on WMAP data together with other measurements of the density parameters are used to illustrate both methods, which are shown to provide very similar results for high redshifts.Comment: 16 pages, 1 figure, LaTeX2

Dark matter and structure formation a review

This paper provides a review of the variants of dark matter which are thought to be fundamental components of the universe and their role in origin and evolution of structures and some new original results concerning improvements to the spherical collapse model. In particular, I show how the spherical collapse model is modified when we take into account dynamical friction and tidal torques

Comprehensive characterization of 536 patient-derived xenograft models prioritizes candidatesfor targeted treatment

Development of candidate cancer treatments is a resource-intensive process, with the research community continuing to investigate options beyond static genomic characterization. Toward this goal, we have established the genomic landscapes of 536 patient-derived xenograft (PDX) models across 25 cancer types, together with mutation, copy number, fusion, transcriptomic profiles, and NCI-MATCH arms. Compared with human tumors, PDXs typically have higher purity and fit to investigate dynamic driver events and molecular properties via multiple time points from same case PDXs. Here, we report on dynamic genomic landscapes and pharmacogenomic associations, including associations between activating oncogenic events and drugs, correlations between whole-genome duplications and subclone events, and the potential PDX models for NCI-MATCH trials. Lastly, we provide a web portal having comprehensive pan-cancer PDX genomic profiles and source code to facilitate identification of more druggable events and further insights into PDXs' recapitulation of human tumors