Cosmological N-body Simulation
Lake, George
1994-05-01
.90ex> }}} The ``N'' in N-body calculations has doubled every year for the last two decades. To continue this trend, the UW N-body group is working on algorithms for the fast evaluation of gravitational forces on parallel computers and establishing rigorous standards for the computations. In these algorithms, the computational cost per time step is ~ 10(3) pairwise forces per particle. A new adaptive time integrator enables us to perform high quality integrations that are fully temporally and spatially adaptive. SPH--smoothed particle hydrodynamics will be added to simulate the effects of dissipating gas and magnetic fields. The importance of these calculations is two-fold. First, they determine the nonlinear consequences of theories for the structure of the Universe. Second, they are essential for the interpretation of observations. Every galaxy has six coordinates of velocity and position. Observations determine two sky coordinates and a line of sight velocity that bundles universal expansion (distance) together with a random velocity created by the mass distribution. Simulations are needed to determine the underlying structure and masses. The importance of simulations has moved from ex post facto explanation to an integral part of planning large observational programs. I will show why high quality simulations with ``large N'' are essential to accomplish our scientific goals. This year, our simulations have N >~ 10(7) . This is sufficient to tackle some niche problems, but well short of our 5 year goal--simulating The Sloan Digital Sky Survey using a few Billion particles (a Teraflop-year simulation). Extrapolating past trends, we would have to ``wait'' 7 years for this hundred-fold improvement. Like past gains, significant changes in the computational methods are required for these advances. I will describe new algorithms, algorithmic hacks and a dedicated computer to perform Billion particle simulations. Finally, I will describe research that can be enabled by
Cosmological N -body simulations including radiation perturbations
DEFF Research Database (Denmark)
Brandbyge, Jacob; Rampf, Cornelius; Tram, Thomas
2017-01-01
Cosmological $N$-body simulations are the standard tool to study the emergence of the observed large-scale structure of the Universe. Such simulations usually solve for the gravitational dynamics of matter within the Newtonian approximation, thus discarding general relativistic effects such as th......Cosmological $N$-body simulations are the standard tool to study the emergence of the observed large-scale structure of the Universe. Such simulations usually solve for the gravitational dynamics of matter within the Newtonian approximation, thus discarding general relativistic effects...
Adaptive Techniques for Clustered N-Body Cosmological Simulations
Menon, Harshitha; Zheng, Gengbin; Jetley, Pritish; Kale, Laxmikant; Quinn, Thomas; Governato, Fabio
2014-01-01
ChaNGa is an N-body cosmology simulation application implemented using Charm++. In this paper, we present the parallel design of ChaNGa and address many challenges arising due to the high dynamic ranges of clustered datasets. We focus on optimizations based on adaptive techniques for scaling to more than 128K cores. We demonstrate strong scaling on up to 512K cores of Blue Waters evolving 12 and 24 billion particles. We also show strong scaling of highly clustered datasets on up to 128K cores.
The New Horizon Run Cosmological N-Body Simulations
Kim, Juhan; Rossi, Graziano; Lee, Sang Min; Gott, J Richard
2011-01-01
We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using 6000^3 = 216 billions and 7210^3 = 374 billion particles, spanning a volume of (7.200 Gpc/h)^3 and (10.815 Gpc/h)^3, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to 1.25x10^11 M_sun/h, allowing to resolve galaxy-size halos with mean particle separations of 1.2 Mpc/h and 1.5 Mpc/h, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the LCDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scal...
Cosmological $N$-body simulations including radiation perturbations
Brandbyge, Jacob; Tram, Thomas; Leclercq, Florent; Fidler, Christian; Hannestad, Steen
2016-01-01
Cosmological $N$-body simulations are the standard tool to study the emergence of the observed large-scale structure of the Universe. Such simulations usually solve for the gravitational dynamics of matter within the Newtonian approximation, thus discarding general relativistic effects such as the coupling between matter and radiation ($\\equiv$ photons and neutrinos). In this paper we investigate novel hybrid simulations which incorporate interactions between radiation and matter to the leading order in General Relativity, whilst evolving the matter dynamics in full non-linearity according to Newtonian theory. Our hybrid simulations come with a relativistic space-time and make it possible to investigate structure formation in a unified framework. In the present work we focus on simulations initialized at $z=99$, and show that the extracted matter power spectrum receives up to $3\\%$ corrections on very large scales through radiation. Our numerical findings compare favourably with linear analytical results from...
Improving initial conditions for cosmological N-body simulations
Garrison, Lehman H.; Eisenstein, Daniel J.; Ferrer, Douglas; Metchnik, Marc V.; Pinto, Philip A.
2016-10-01
In cosmological N-body simulations, the representation of dark matter as discrete `macroparticles' suppresses the growth of structure, such that simulations no longer reproduce linear theory on small scales near kNyquist. Marcos et al. demonstrate that this is due to sparse sampling of modes near kNyquist and that the often-assumed continuum growing modes are not proper growing modes of the particle system. We develop initial conditions (ICs) that respect the particle linear theory growing modes and then rescale the mode amplitudes to account for growth suppression. These ICs also allow us to take advantage of our very accurate N-body code ABACUS to implement second-order Lagrangian perturbation theory (2LPT) in configuration space. The combination of 2LPT and rescaling improves the accuracy of the late-time power spectra, halo mass functions, and halo clustering. In particular, we achieve 1 per cent accuracy in the power spectrum down to kNyquist, versus kNyquist/4 without rescaling or kNyquist/13 without 2LPT, relative to an oversampled reference simulation. We anticipate that our 2LPT will be useful for large simulations where fast Fourier transforms are expensive and that rescaling will be useful for suites of medium-resolution simulations used in cosmic emulators and galaxy survey mock catalogues. Code to generate ICs is available at https://github.com/lgarrison/zeldovich-PLT.
Improving Initial Conditions for Cosmological $N$-Body Simulations
Garrison, Lehman H; Ferrer, Douglas; Metchnik, Marc V; Pinto, Philip A
2016-01-01
In cosmological $N$-body simulations, the representation of dark matter as discrete "macroparticles" suppresses the growth of structure. This effect occurs even on scales many times larger than the particle spacing; for example, modes above $k_{\\rm Nyquist}/4$ inherit a 1 to 3% error in the matter power spectrum at $z=1$. Particle linear theory (PLT) (Marcos et al. 2006) analytically describes this effect for particle lattices and reveals that the continuum growing modes are not the proper lattice growing modes, which excites transient power. We develop initial conditions with the correct growing modes and additionally rescale these modes to account for growth suppression. We also introduce a scheme for computing second-order Lagrangian perturbation theory (2LPT) from direct force calculations without using Fourier transforms. We test rescaling and our 2LPT by comparing the $z=1$ haloes and power spectra with those of an oversampled reference simulation. The combination of rescaling and 2LPT achieves 1% accur...
N-body simulations of coupled dark energy cosmologies
Baldi, Marco; Robbers, Georg; Springel, Volker
2008-01-01
If the accelerated expansion of the Universe at the present epoch is driven by a dark energy scalar field, there may well be a non-trivial coupling between the dark energy and the cold dark matter (CDM) fluid. Such interactions give rise to new features in cosmological structure growth, like an additional long-range attractive force between CDM particles, or variations of the dark matter particle mass with time. We have implemented these effects in the N-body code GADGET-2 and present results of a series of high-resolution N-body simulations where the dark energy component is directly interacting with the cold dark matter. As a consequence of the new physics, CDM and baryon distributions evolve differently both in the linear and in the nonlinear regime of structure formation. Already on large scales a linear bias develops between these two components, which is further enhanced by the nonlinear evolution. We also find, in contrast with previous work, that the density profiles of CDM halos are less concentrated...
Black Hole Growth from Cosmological N-body Simulations
Micic, Miroslav; Sigurdsson, Steinn
2008-01-01
(Abridged) We use high resolution cosmological N-body simulations to study the growth of intermediate to supermassive black holes from redshift 49 to zero. We track the growth of black holes from the seeds of population III stars to black holes in the range of 10^3 < M < 10^7 Msun -- not quasars, but rather IMBH to low-mass SMBHs. These lower mass black holes are the primary observable for the Laser Interferometer Space Antenna (LISA). The large-scale dynamics of the black holes are followed accurately within the simulation down to scales of 1 kpc; thereafter, we follow the merger analytically from the last dynamical friction phase to black hole coalescence. We find that the merger rate of these black holes is R~25 per year between 8 < z < 11 and R = 10 per year at z=3. Before the merger occurs the incoming IMBH may be observed with a next generation of X-ray telescopes as a ULX source with a rate of about ~ 3 - 7 per year for 1 < z < 5. We develop an analytic prescription that captures the ...
Numerical techniques for large cosmological N-body simulations
Energy Technology Data Exchange (ETDEWEB)
Efstathiou, G.; Davis, M.; Frenk, C.S.; White, S.D.M.
1985-02-01
We describe and compare techniques for carrying out large N-body simulations of the gravitational evolution of clustering in the fundamental cube of an infinite periodic universe. In particular, we consider both particle mesh (PM) codes and P/sup 3/M codes in which a higher resolution force is obtained by direct summation of contributions from neighboring particles. We discuss the mesh-induced anisotropies in the forces calculated by these schemes, and the extent to which they can model the desired 1/r/sup 2/ particle-particle interaction. We also consider how transformation of the time variable can improve the efficiency with which the equations of motion are integrated. We present tests of the accuracy with which the resulting schemes conserve energy and are able to follow individual particle trajectories. We have implemented an algorithm which allows initial conditions to be set up to model any desired spectrum of linear growing mode density fluctuations. A number of tests demonstrate the power of this algorithm and delineate the conditions under which it is effective. We carry out several test simulations using a variety of techniques in order to show how the results are affected by dynamic range limitations in the force calculations, by boundary effects, by residual artificialities in the initial conditions, and by the number of particles employed. For most purposes cosmological simulations are limited by the resolution of their force calculation rather than by the number of particles they can employ. For this reason, while PM codes are quite adequate to study the evolution of structure on large scale, P/sup 3/M methods are to be preferred, in spite of their greater cost and complexity, whenever the evolution of small-scale structure is important.
2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for Cosmological Simulation
Warren, Michael S.
2014-01-01
We report on improvements made over the past two decades to our adaptive treecode N-body method (HOT). A mathematical and computational approach to the cosmological N-body problem is described, with performance and scalability measured up to 256k (218) processors. We present error analysis and scientific application results from a series of more than ten 69 billion (40963) particle cosmological simulations, accounting for 4×1020 floating point operations. These results include the first simul...
2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for Cosmological Simulation
Warren, Michael S.
2013-01-01
We report on improvements made over the past two decades to our adaptive treecode N-body method (HOT). A mathematical and computational approach to the cosmological N-body problem is described, with performance and scalability measured up to 256k ($2^{18}$) processors. We present error analysis and scientific application results from a series of more than ten 69 billion ($4096^3$) particle cosmological simulations, accounting for $4 \\times 10^{20}$ floating point operations. These results inc...
Cosmological N-body simulations with suppressed variance
Angulo, Raul E.; Pontzen, Andrew
2016-10-01
We present and test a method that dramatically reduces variance arising from the sparse sampling of wavemodes in cosmological simulations. The method uses two simulations which are fixed (the initial Fourier mode amplitudes are fixed to the ensemble average power spectrum) and paired (with initial modes exactly out of phase). We measure the power spectrum, monopole and quadrupole redshift-space correlation functions, halo mass function and reduced bispectrum at z = 1. By these measures, predictions from a fixed pair can be as precise on non-linear scales as an average over 50 traditional simulations. The fixing procedure introduces a non-Gaussian correction to the initial conditions; we give an analytic argument showing why the simulations are still able to predict the mean properties of the Gaussian ensemble. We anticipate that the method will drive down the computational time requirements for accurate large-scale explorations of galaxy bias and clustering statistics, and facilitating the use of numerical simulations in cosmological data interpretation.
Building Merger Trees from Cosmological N-body Simulations
Tweed, D; Blaizot, J; Colombi, S; Slyz, A
2009-01-01
Although a fair amount of work has been devoted to growing Monte-Carlo merger trees which resemble those built from an N-body simulation, comparatively little effort has been invested in quantifying the caveats one necessarily encounters when one extracts trees directly from such a simulation. To somewhat revert the tide, this paper seeks to provide its reader with a comprehensive study of the problems one faces when following this route. The first step to building merger histories of dark matter haloes and their subhaloes is to identify these structures in each of the time outputs (snapshots) produced by the simulation. Even though we discuss a particular implementation of such an algorithm (called AdaptaHOP) in this paper, we believe that our results do not depend on the exact details of the implementation but extend to most if not all (sub)structure finders. To illustrate this point, we compare AdaptaHOP s results to the standard Friend- Of-Friend algorithm (FOF), widely utilized in the astrophysical commu...
Numerical techniques for large cosmological N-body simulations
Efstathiou, G.; Davis, M.; White, S. D. M.; Frenk, C. S.
1985-01-01
Techniques for carrying out large N-body simulations of the gravitational evolution of clustering in the fundamental cube of an infinite periodic universe are described and compared. The accuracy of the forces derived from several commonly used particle mesh schemes is examined, showing how submesh resolution can be achieved by including short-range forces between particles by direct summation techniques. The time integration of the equations of motion is discussed, and the accuracy of the codes for various choices of 'time' variable and time step is tested by considering energy conservation as well as by direct analysis of particle trajectories. Methods for generating initial particle positions and velocities corresponding to a growing mode representation of a specified power spectrum of linear density fluctuations are described. The effects of force resolution are studied and different simulation schemes are compared. An algorithm is implemented for generating initial conditions by varying the number of particles, the initial amplitude of density fluctuations, and the initial peculiar velocity field.
2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for Cosmological Simulation
Directory of Open Access Journals (Sweden)
Michael S. Warren
2014-01-01
Full Text Available We report on improvements made over the past two decades to our adaptive treecode N-body method (HOT. A mathematical and computational approach to the cosmological N-body problem is described, with performance and scalability measured up to 256k (218 processors. We present error analysis and scientific application results from a series of more than ten 69 billion (40963 particle cosmological simulations, accounting for 4×1020 floating point operations. These results include the first simulations using the new constraints on the standard model of cosmology from the Planck satellite. Our simulations set a new standard for accuracy and scientific throughput, while meeting or exceeding the computational efficiency of the latest generation of hybrid TreePM N-body methods.
2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for Cosmological Simulation
Warren, Michael S
2013-01-01
We report on improvements made over the past two decades to our adaptive treecode N-body method (HOT). A mathematical and computational approach to the cosmological N-body problem is described, with performance and scalability measured up to 256k ($2^{18}$) processors. We present error analysis and scientific application results from a series of more than ten 69 billion ($4096^3$) particle cosmological simulations, accounting for $4 \\times 10^{20}$ floating point operations. These results include the first simulations using the new constraints on the standard model of cosmology from the Planck satellite. Our simulations set a new standard for accuracy and scientific throughput, while meeting or exceeding the computational efficiency of the latest generation of hybrid TreePM N-body methods.
Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations
Gaite, Jose
2013-01-01
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos, it is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.
Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations
Directory of Open Access Journals (Sweden)
José Gaite
2013-05-01
Full Text Available Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.
Fast Generation of Ensembles of Cosmological N-Body Simulations via Mode-Resampling
Energy Technology Data Exchange (ETDEWEB)
Schneider, M D; Cole, S; Frenk, C S; Szapudi, I
2011-02-14
We present an algorithm for quickly generating multiple realizations of N-body simulations to be used, for example, for cosmological parameter estimation from surveys of large-scale structure. Our algorithm uses a new method to resample the large-scale (Gaussian-distributed) Fourier modes in a periodic N-body simulation box in a manner that properly accounts for the nonlinear mode-coupling between large and small scales. We find that our method for adding new large-scale mode realizations recovers the nonlinear power spectrum to sub-percent accuracy on scales larger than about half the Nyquist frequency of the simulation box. Using 20 N-body simulations, we obtain a power spectrum covariance matrix estimate that matches the estimator from Takahashi et al. (from 5000 simulations) with < 20% errors in all matrix elements. Comparing the rates of convergence, we determine that our algorithm requires {approx}8 times fewer simulations to achieve a given error tolerance in estimates of the power spectrum covariance matrix. The degree of success of our algorithm indicates that we understand the main physical processes that give rise to the correlations in the matter power spectrum. Namely, the large-scale Fourier modes modulate both the degree of structure growth through the variation in the effective local matter density and also the spatial frequency of small-scale perturbations through large-scale displacements. We expect our algorithm to be useful for noise modeling when constraining cosmological parameters from weak lensing (cosmic shear) and galaxy surveys, rescaling summary statistics of N-body simulations for new cosmological parameter values, and any applications where the influence of Fourier modes larger than the simulation size must be accounted for.
Initial Conditions for Accurate N-Body Simulations of Massive Neutrino Cosmologies
Zennaro, Matteo; Villaescusa-Navarro, Francisco; Carbone, Carmelita; Sefusatti, Emiliano; Guzzo, Luigi
2016-01-01
The set-up of the initial conditions in cosmological N-body simulations is usually implemented by rescaling the desired low-redshift linear power spectrum to the required starting redshift consistently with the Newtonian evolution of the simulation. The implementation of this practical solution requires more care in the context of massive neutrino cosmologies, mainly because of the non-trivial scale-dependence of the linear growth that characterises these models. In this work we consider a simple two-fluid, Newtonian approximation for cold dark matter and massive neutrinos perturbations that can reproduce the cold matter linear evolution predicted by Boltzmann codes such as CAMB or CLASS with a 0.1% accuracy or below for all redshift relevant to nonlinear structure formation. We use this description, in the first place, to quantify the systematic errors induced by several approximations often assumed in numerical simulations, including the typical set-up of the initial conditions for massive neutrino cosmolog...
Effects of the initial conditions on cosmological $N$-body simulations
L'Huillier, Benjamin; Kim, Juhan
2014-01-01
Cosmology is entering an era of percent level precision due to current large observational surveys. This precision in observation is now demanding more accuracy from numerical methods and cosmological simulations. In this paper, we study the accuracy of $N$-body numerical simulations and their dependence on changes in the initial conditions and in the simulation algorithms. For this purpose, we use a series of cosmological $N$-body simulations with varying initial conditions. We test the influence of the initial conditions, namely the pre-initial configuration (preIC), the order of the Lagrangian perturbation theory (LPT), and the initial redshift, on the statistics associated with the large scale structures of the universe such as the halo mass function, the density power spectrum, and the maximal extent of the large scale structures. We find that glass or grid pre-initial conditions give similar results at $z\\lesssim 2$. However, the initial excess of power in the glass initial conditions yields a subtle di...
Initial conditions for accurate N-body simulations of massive neutrino cosmologies
Zennaro, M.; Bel, J.; Villaescusa-Navarro, F.; Carbone, C.; Sefusatti, E.; Guzzo, L.
2017-04-01
The set-up of the initial conditions in cosmological N-body simulations is usually implemented by rescaling the desired low-redshift linear power spectrum to the required starting redshift consistently with the Newtonian evolution of the simulation. The implementation of this practical solution requires more care in the context of massive neutrino cosmologies, mainly because of the non-trivial scale-dependence of the linear growth that characterizes these models. In this work, we consider a simple two-fluid, Newtonian approximation for cold dark matter and massive neutrinos perturbations that can reproduce the cold matter linear evolution predicted by Boltzmann codes such as CAMB or CLASS with a 0.1 per cent accuracy or below for all redshift relevant to non-linear structure formation. We use this description, in the first place, to quantify the systematic errors induced by several approximations often assumed in numerical simulations, including the typical set-up of the initial conditions for massive neutrino cosmologies adopted in previous works. We then take advantage of the flexibility of this approach to rescale the late-time linear power spectra to the simulation initial redshift, in order to be as consistent as possible with the dynamics of the N-body code and the approximations it assumes. We implement our method in a public code (REPS rescaled power spectra for initial conditions with massive neutrinos https://github.com/matteozennaro/reps) providing the initial displacements and velocities for cold dark matter and neutrino particles that will allow accurate, i.e. 1 per cent level, numerical simulations for this cosmological scenario.
Stable clustering and the resolution of dissipationless cosmological N-body simulations
Benhaiem, David; Labini, Francesco Sylos
2016-01-01
The determination of the resolution of cosmological N-body simulations, i.e., the range of scales in which quantities measured in them represent accurately the continuum limit, is an important open question. We address it here using scale-free models, for which self-similarity provides a powerful tool to control resolution. Such models also provide a robust testing ground for the so-called stable clustering approximation, which gives simple predictions for them. Studying large N-body simulations of such models with different force smoothing, we find that these two issues are in fact very closely related: our conclusion is that resolution in the non-linear regime extends, in practice, down to the scale at which stable clustering breaks down. Physically the association of the two scales is in fact simple to understand: stable clustering fails to be a good approximation when there are strong interactions of structures (in particular merging) and it is precisely such non-linear processes which are sensitive to fl...
Halo statistics analysis within medium volume cosmological N-body simulation
Directory of Open Access Journals (Sweden)
Martinović N.
2015-01-01
Full Text Available In this paper we present halo statistics analysis of a ΛCDM N body cosmological simulation (from first halo formation until z = 0. We study mean major merger rate as a function of time, where for time we consider both per redshift and per Gyr dependence. For latter we find that it scales as the well known power law (1 + zn for which we obtain n = 2.4. The halo mass function and halo growth function are derived and compared both with analytical and empirical fits. We analyse halo growth through out entire simulation, making it possible to continuously monitor evolution of halo number density within given mass ranges. The halo formation redshift is studied exploring possibility for a new simple preliminary analysis during the simulation run. Visualization of the simulation is portrayed as well. At redshifts z = 0−7 halos from simulation have good statistics for further analysis especially in mass range of 1011 − 1014 M./h. [176021 ’Visible and invisible matter in nearby galaxies: theory and observations
Characterization of the cosmological nonlinear path of single galaxies in N-body Simulations
Stalder Díaz, Diego Herbin; Rosa, Reinaldo; Clua, Esteban; Campanharo, Andriana
Turbulent-like behaviour is an important and recent ingredient in the investigation of large scale structure formation in the observable universe [1,2]. Recently, an established statistical method was used to demonstrate the importance of considering chaotic advection (or Lagrange turbulence) in combination with gravitational instabilities in the LambdaCDM simulations performed from the Virgo Consortium (VC). However, the Hubble volumes simulated from GADGET-VC algoritm have some limitations for direct lagrangian data analysis due to the large amount of data and no real time computation for particle kinetic velocity along the dark matter structure evolution. We use our COsmic LAgrangian TUrbulence Simulator (COLATUS) [3], based on GPU/CUDA technology, to perform gravitational Cosmological N-body simulations and tracking the particles paths. In this work we discuss the chaotic advection behavior of tracers galaxies based on the angular velocity fluctuation analysis of single particles during its trajectory to the gravitational collapse of super clusters at low redshifts. [1] Caretta et al., A&A doi:10.1051/0004-6361:20079105 [2] Rosa et al., CCP doi: 10.1016/j.cpc.2008.11.018 [3] Stalder et al., AIP doi: 10.1063/1.4756992
Stable clustering and the resolution of dissipationless cosmological N-body simulations
Benhaiem, David; Joyce, Michael; Sylos Labini, Francesco
2017-10-01
The determination of the resolution of cosmological N-body simulations, i.e. the range of scales in which quantities measured in them represent accurately the continuum limit, is an important open question. We address it here using scale-free models, for which self-similarity provides a powerful tool to control resolution. Such models also provide a robust testing ground for the so-called stable clustering approximation, which gives simple predictions for them. Studying large N-body simulations of such models with different force smoothing, we find that these two issues are in fact very closely related: our conclusion is that the accuracy of two-point statistics in the non-linear regime starts to degrade strongly around the scale at which their behaviour deviates from that predicted by the stable clustering hypothesis. Physically the association of the two scales is in fact simple to understand: stable clustering fails to be a good approximation when there are strong interactions of structures (in particular merging) and it is precisely such non-linear processes which are sensitive to fluctuations at the smaller scales affected by discretization. Resolution may be further degraded if the short distance gravitational smoothing scale is larger than the scale to which stable clustering can propagate. We examine in detail the very different conclusions of studies by Smith et al. and Widrow et al. and find that the strong deviations from stable clustering reported by these works are the results of over-optimistic assumptions about scales resolved accurately by the measured power spectra, and the reliance on Fourier space analysis. We emphasize the much poorer resolution obtained with the power spectrum compared to the two-point correlation function.
Joyce, Michael
2007-01-01
We apply a recently developed perturbative formalism which describes the evolution under their self-gravity of particles displaced from a perfect lattice to quantify precisely, up to shell crossing, the effects of discreteness in dissipationless cosmological N-body simulations. We give simple expressions, explicitly dependent on the particle density, for the evolution of power in each mode as a function of red-shift. For typical starting red-shifts the effect of finite particle number is to {\\it slow down} slightly the growth of power compared to that in the fluid limit (e.g. by about ten percent at half the Nyquist frequency), and to induce also dispersion in the growth as a function of direction at a comparable level. Further, above the Nyquist frequency, purely discrete power generated in the initial conditions is amplified. We note that, at fixed particle number, the effects of discreteness increase as the initial red-shift $z_{\\rm init}$ is increased, with divergence from the fluid limit as $z_{\\rm init}...
TreePM: A Code for Cosmological N-Body Simulations
Indian Academy of Sciences (India)
J. S. Bagla
2002-09-01
We describe the TreePM method for carrying out large N-Body simulations to study formation and evolution of the large scale structure in the Universe. This method is a combination of Barnes and Hut tree code and Particle-Mesh code. It combines the automatic inclusion of periodic boundary conditions of PM simulations with the high resolution of tree codes. This is done by splitting the gravitational force into a short range and a long range component. We describe the splitting of force between these two parts.We outline the key differences between TreePM and some other N-Body methods.
Gravitational N-body Simulations
Trenti, M
2008-01-01
Gravitational N-body simulations, that is numerical solutions of the equations of motions for N particles interacting gravitationally, are widely used tools in astrophysics, with applications from few body or solar system like systems all the way up to galactic and cosmological scales. In this article we present a summary review of the field highlighting the main methods for N-body simulations and the astrophysical context in which they are usually applied.
Cosmological Perturbation Theory as a Tool for Estimating Box-Scale Effects in N-body Simulations
Orban, Chris
2013-01-01
In performing cosmological N-body simulations, it is widely appreciated that the growth of structure on the largest scales within a simulation box will be inhibited by the finite size of the simulation volume. Following ideas set forth in Seto 1999, this paper shows that standard (a.k.a. 1-loop) cosmological perturbation theory (SPT) can be used to predict at an order-of-magnitude level the deleterious effect of the box scale on the power spectrum of density fluctuations in simulation volumes. Alternatively, this approach can be used to quickly estimate post facto the effect of the box scale on power spectrum results from existing simulations. In this way SPT can help determine whether larger box sizes or other more-sophisticated methods are needed to achieve a particular level of precision for a given application (e.g. simulations to measure the non-linear evolution of baryon acoustic oscillations). I focus on SPT in this note and show that its predictions are order-of-magnitude accurate compared to N-body s...
Indian Academy of Sciences (India)
Jayanti Prasad
2007-06-01
In this study we show how errors due to finite box size affect formation and the destruction rate for haloes in cosmological N-body simulations. In an earlier study we gave an analytic prescription of finding the corrections in the mass function. Following the same approach, in this paper we give analytical expressions for corrections in the formation rate, destruction rate and the rate of change in comoving number density, and compute their expected values for the power law ( = -2) and LCDM models.
Brooks, A M; Booth, C M; Willman, B; Gardner, J P; Wadsley, J; Stinson, G; Quinn, T
2006-01-01
We examine the origin and evolution of the mass-metallicity (M-Z) relationship for galaxies using high resolution cosmological SPH + N-Body simulations that include a physically motivated description of the effects of supernovae feedback and subsequent metal enrichment. Our simulations allow us to distinguish between two possible sources that contribute to both the origin of the mass-metallicity relationship and to the low chemical yield observed in low galaxy masses: 1) metal loss due to gas outflow, or 2) inefficient star formation at the lowest galaxy masses. Our simulated galaxies are in excellent agreement with the observed M-Z relationship, both at z=0 and z=2. We find that gas mass loss becomes increasingly important at decreasing galaxy masses for our simulations, This mass loss results in a low effective yield for our lowest mass galaxies in good agreement with observational results. By considering all the gas that has ever belonged to a galaxy (back to z=3), we find the metallicity is unchanged from...
Evolution and Statistics of Non-Sphericity of Dark Matter Halos from Cosmological N-Body Simulation
Suto, Daichi; Nishimichi, Takahiro; Sasaki, Shin; Suto, Yasushi
2016-01-01
We revisit the non-sphericity of cluster-mass scale halos from cosmological N-body simulation on the basis of triaxial modelling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turn-around epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting nonsphericity of halos exhibits weak but robust mass dependence in a statistical fashion; massive halos are more spherical up to the turn-around, but gradually become less spherical by z = 0. This is clearly inconsistent with the EC prediction; massive halos are usually more spherical. In addition, at z=0, inner regions of the halos are less spherical than outer regions, i.e., the density distribution inside the halos is highly inhomogeneous and therefore not se...
Orban, Chris
2012-01-01
In setting up initial conditions for cosmological N-body simulations there are, fundamentally, two choices: either maximizing the correspondence of the initial density field to the assumed fourier-space clustering or, instead, matching to the real-space clustering. As a stringent test of both approaches, I perform ensembles of simulations using power law models and exploit the self-similarity of these initial conditions to quantify the accuracy of the results. Originally proposed by Pen 1997 and implemented by Sirko 2005, I show that the real-space motivated approach, which allows the DC mode to vary, performs well in exhibiting the expected self-similar behavior in the mean xi(r) and P(k) and in both methods this behavior extends below the scale of the initial mean interparticle spacing. I also test the real-space method with simulations of a simplified, powerlaw model for baryon acoustic oscillations, again with success, and mindful of the need to generate mock catalogs using simulations I show extensive po...
Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation
Suto, Daichi; Kitayama, Tetsu; Nishimichi, Takahiro; Sasaki, Shin; Suto, Yasushi
2016-10-01
We revisit the non-sphericity of cluster-mass-scale halos from cosmological N-body simulation on the basis of triaxial modeling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turnaround epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting non-sphericity of halos exhibits weak but robust mass dependence in a statistical fashion; massive halos are more spherical up to the turnaround, but gradually become less spherical by z = 0. This is clearly inconsistent with the EC prediction: massive halos are usually more spherical. In addition, at z = 0, inner regions of the simulated halos are less spherical than outer regions; that is, the density distribution inside the halos is highly inhomogeneous and therefore not self-similar (concentric ellipsoids with the same axis ratio and orientation). This is also inconsistent with the homogeneous density distribution that is commonly assumed in EC. Since most of previous fitting formulae for the probability distribution function (PDF) of the axis ratio of triaxial ellipsoids have been constructed under the self-similarity assumption, they are not accurate. Indeed, we compute the PDF of the projected axis ratio a1/a2 directly from the simulation data without the self-similarity assumption, and find that it is very sensitive to the assumption. The latter needs to be carefully taken into account in direct comparison with observations, and therefore we provide an empirical fitting formula for the PDF of a1/a2. Our preliminary analysis suggests that the derived PDF of a1/a2 roughly agrees with the current weak-lensing observations. More importantly, the present results will be useful for future exploration of the non
Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation
Suto, Daichi; Kitayama, Tetsu; Nishimichi, Takahiro; Sasaki, Shin; Suto, Yasushi
2016-12-01
We revisit the non-sphericity of cluster-mass-scale halos from cosmological N-body simulation on the basis of triaxial modeling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turnaround epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting non-sphericity of halos exhibits weak but robust mass dependence in a statistical fashion; massive halos are more spherical up to the turnaround, but gradually become less spherical by z = 0. This is clearly inconsistent with the EC prediction: massive halos are usually more spherical. In addition, at z = 0, inner regions of the simulated halos are less spherical than outer regions; that is, the density distribution inside the halos is highly inhomogeneous and therefore not self-similar (concentric ellipsoids with the same axis ratio and orientation). This is also inconsistent with the homogeneous density distribution that is commonly assumed in EC. Since most of previous fitting formulae for the probability distribution function (PDF) of the axis ratio of triaxial ellipsoids have been constructed under the self-similarity assumption, they are not accurate. Indeed, we compute the PDF of the projected axis ratio a1/a2 directly from the simulation data without the self-similarity assumption, and find that it is very sensitive to the assumption. The latter needs to be carefully taken into account in direct comparison with observations, and therefore we provide an empirical fitting formula for the PDF of a1/a2. Our preliminary analysis suggests that the derived PDF of a1/a2 roughly agrees with the current weak-lensing observations. More importantly, the present results will be useful for future exploration of the non
Makiya, Ryu; Enoki, Motohiro; Ishiyama, Tomoaki; Kobayashi, Masakazu A. R.; Nagashima, Masahiro; Okamoto, Takashi; Okoshi, Katsuya; Oogi, Taira; Shirakata, Hikari
2016-04-01
We present a new cosmological galaxy formation model, ν2GC, as an updated version of our previous model νGC. We adopt the so-called "semi-analytic" approach, in which the formation history of dark matter halos is computed by N-body simulations, while the baryon physics such as gas cooling, star formation, and supernova feedback are simply modeled by phenomenological equations. Major updates of the model are as follows: (1) the merger trees of dark matter halos are constructed in state-of-the-art N-body simulations, (2) we introduce the formation and evolution process of supermassive black holes and the suppression of gas cooling due to active galactic nucleus (AGN) activity, (3) we include heating of the intergalactic gas by the cosmic UV background, and (4) we tune some free parameters related to the astrophysical processes using a Markov chain Monte Carlo method. Our N-body simulations of dark matter halos have unprecedented box size and mass resolution (the largest simulation contains 550 billion particles in a 1.12 Gpc h-1 box), enabling the study of much smaller and rarer objects. The model was tuned to fit the luminosity functions of local galaxies and mass function of neutral hydrogen. Local observations, such as the Tully-Fisher relation, the size-magnitude relation of spiral galaxies, and the scaling relation between the bulge mass and black hole mass were well reproduced by the model. Moreover, the model also reproduced well the cosmic star formation history and redshift evolution of rest-frame K-band luminosity functions. The numerical catalog of the simulated galaxies and AGNs is publicly available on the web.
Precision cosmology in muddy waters: Cosmological constraints and N-body codes
Smith, Robert E; Potter, Doug; Marian, Laura; Crocce, Martin; Moore, Ben
2012-01-01
Future large-scale structure surveys of the Universe will aim to constrain the cosmological model and the true nature of dark energy with unprecedented accuracy. In order for these surveys to achieve their designed goals, they will require predictions for the nonlinear matter power spectrum to sub-percent accuracy. Through the use of a large ensemble of cosmological N-body simulations, we demonstrate that if we do not understand the uncertainties associated with simulating structure formation, i.e. knowledge of the `true' simulation parameters, and simply seek to marginalize over them, then the constraining power of such future surveys can be significantly reduced. However, for the parameters {n_s, h, Om_b, Om_m}, this effect can be largely mitigated by adding the information from a CMB experiment, like Planck. In contrast, for the amplitude of fluctuations sigma8 and the time-evolving equation of state of dark energy {w_0, w_a}, the mitigation is mild. On marginalizing over the simulation parameters, we find...
Elsen, Erich; Houston, Mike; Pande, Vijay; Hanrahan, Pat; Darve, Eric
2007-01-01
Commercial graphics processors (GPUs) have high compute capacity at very low cost, which makes them attractive for general purpose scientific computing. In this paper we show how graphics processors can be used for N-body simulations to obtain improvements in performance over current generation CPUs. We have developed a highly optimized algorithm for performing the O(N^2) force calculations that constitute the major part of stellar and molecular dynamics simulations. In some of the calculations, we achieve sustained performance of nearly 100 GFlops on an ATI X1900XTX. The performance on GPUs is comparable to specialized processors such as GRAPE-6A and MDGRAPE-3, but at a fraction of the cost. Furthermore, the wide availability of GPUs has significant implications for cluster computing and distributed computing efforts like Folding@Home.
The effect of early radiation in N-body simulations of cosmic structure formation
DEFF Research Database (Denmark)
Adamek, Julian; Brandbyge, Jacob; Fidler, Christian
2017-01-01
Newtonian N-body simulations have been employed successfully over the past decades for the simulation of the cosmological large-scale structure. Such simulations usually ignore radiation perturbations (photons and massless neutrinos) and the impact of general relativity (GR) beyond the background...
Machine Learning and Cosmological Simulations
Kamdar, Harshil; Turk, Matthew; Brunner, Robert
2016-01-01
We explore the application of machine learning (ML) to the problem of galaxy formation and evolution in a hierarchical universe. Our motivations are two-fold: (1) presenting a new, promising technique to study galaxy formation, and (2) quantitatively evaluating the extent of the influence of dark matter halo properties on small-scale structure formation. For our analyses, we use both semi-analytical models (Millennium simulation) and N-body + hydrodynamical simulations (Illustris simulation). The ML algorithms are trained on important dark matter halo properties (inputs) and galaxy properties (outputs). The trained models are able to robustly predict the gas mass, stellar mass, black hole mass, star formation rate, $g-r$ color, and stellar metallicity. Moreover, the ML simulated galaxies obey fundamental observational constraints implying that the population of ML predicted galaxies is physically and statistically robust. Next, ML algorithms are trained on an N-body + hydrodynamical simulation and applied to an N-body only simulation (Dark Sky simulation, Illustris Dark), populating this new simulation with galaxies. We can examine how structure formation changes with different cosmological parameters and are able to mimic a full-blown hydrodynamical simulation in a computation time that is orders of magnitude smaller. We find that the set of ML simulated galaxies in Dark Sky obey the same observational constraints, further solidifying ML's place as an intriguing and promising technique in future galaxy formation studies and rapid mock galaxy catalog creation.
The effect of early radiation in N-body simulations of cosmic structure formation
Adamek, Julian; Brandbyge, Jacob; Fidler, Christian; Hannestad, Steen; Rampf, Cornelius; Tram, Thomas
2017-09-01
Newtonian N-body simulations have been employed successfully over the past decades for the simulation of the cosmological large-scale structure. Such simulations usually ignore radiation perturbations (photons and massless neutrinos) and the impact of general relativity (GR) beyond the background expansion. This approximation can be relaxed and we discuss three different approaches that are accurate to leading order in GR. For simulations that start at redshift less than about 100, we find that the presence of early radiation typically leads to per cent-level effects on the numerical power spectra at large scales. Our numerical results agree across the three methods, and we conclude that all of the three methods are suitable for simulations in a standard cosmology. Two of the methods modify the N-body evolution directly, while the third method can be applied as a post-processing prescription.
RAY-RAMSES: a code for ray tracing on the fly in N-body simulations
Barreira, Alexandre; Bose, Sownak; Li, Baojiu
2016-01-01
We present a ray tracing code to compute integrated cosmological observables on the fly in AMR N-body simulations. Unlike conventional ray tracing techniques, our code takes full advantage of the time and spatial resolution attained by the N-body simulation by computing the integrals along the line of sight on a cell-by-cell basis through the AMR simulation grid. Moroever, since it runs on the fly in the N-body run, our code can produce maps of the desired observables without storing large (or any) amounts of data for post-processing. We implemented our routines in the RAMSES N-body code and tested the implementation using an example of weak lensing simulation. We analyse basic statistics of lensing convergence maps and find good agreement with semi-analytical methods. The ray tracing methodology presented here can be used in several cosmological analysis such as Sunyaev-Zel'dovich and integrated Sachs-Wolfe effect studies as well as modified gravity. Our code can also be used in cross-checks of the more conv...
Sapporo: N-body simulation library for GPUs
Gaburov, Evghenii; Harfst, Stefan; Portegies Zwart, Simon
2012-10-01
Sapporo mimics the behavior of GRAPE hardware and uses the GPU to perform high-precision gravitational N-body simulations. It makes use of CUDA and therefore only works on NVIDIA GPUs. N-body codes currently running on GRAPE-6 can switch to Sapporo by a simple relinking of the library. Sapporo's precision is comparable to that of GRAPE-6, even though internally the GPU hardware is limited to single precision arithmetics. This limitation is effectively overcome by emulating double precision for calculating the distance between particles.
gevolution: a cosmological N-body code based on General Relativity
Adamek, Julian; Durrer, Ruth; Kunz, Martin
2016-01-01
We present a new N-body code, gevolution, for the evolution of large scale structure in the Universe. Our code is based on a weak field expansion of General Relativity and calculates all six metric degrees of freedom in Poisson gauge. N-body particles are evolved by solving the geodesic equation which we write in terms of a canonical momentum such that it remains valid also for relativistic particles. We validate the code by considering the Schwarzschild solution and, in the Newtonian limit, by comparing with the Newtonian N-body code Gadget-2. We then proceed with a simulation of large scale structure in a Universe with massive neutrinos where we study the gravitational slip induced by the neutrino shear stress. The code can be extended to include different kinds of dark energy or modified gravity models and going beyond the usually adopted quasi-static approximation. Our code is publicly available.
Constraints on sigma(8) from galaxy clustering in N-body simulations and semi-analytic models
Harker, Geraint; Cole, Shaun; Jenkins, Adrian
2007-01-01
We generate mock galaxy catalogues for a grid of different cosmologies, using rescaled N-body simulations in tandem with a semi-analytic model run using consistent parameters. Because we predict the galaxy bias, rather than fitting it as a nuisance parameter, we obtain an almost pure constraint on s
Constraints on sigma(8) from galaxy clustering in N-body simulations and semi-analytic models
Harker, Geraint; Cole, Shaun; Jenkins, Adrian
2007-01-01
We generate mock galaxy catalogues for a grid of different cosmologies, using rescaled N-body simulations in tandem with a semi-analytic model run using consistent parameters. Because we predict the galaxy bias, rather than fitting it as a nuisance parameter, we obtain an almost pure constraint on
N-body simulations in modified Newtonian dynamics
Nipoti, C.; Londrillo, P.; Ciotti, L.
2011-01-01
We describe some results obtained with N-MODY, a code for N-body simulations of collisionless stellar systems in modified Newtonian dynamics (MOND). We found that a few fundamental dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter. In particular, violent relaxation, phase mixing and galaxy merging take significantly longer in MOND than in Newtonian gravity, while dynamical friction is more effective in a MOND system than in an equivalent Newtonian system with dark matter.
Simulating cosmologies beyond $\\Lambda$CDM with PINOCCHIO
Rizzo, Luca Alberto; Monaco, Pierluigi; Munari, Emiliano; Borgani, Stefano; Castorina, Emanuele; Sefusatti, Emiliano
2016-01-01
We present a method that extends the capabilities of the PINpointing Orbit-Crossing Collapsed HIerarchical Objects (PINOCCHIO) code, allowing it to generate accurate dark matter halo mock catalogues in cosmological models where the linear growth factor and the growth rate depend on scale. Such cosmologies comprise, among others, models with massive neutrinos and some classes of modified gravity theories. We validate the code by comparing the halo properties from PINOCCHIO against N-body simulations, focusing on cosmologies with massive neutrinos: $\
Second-order variational equations for N-body simulations
Rein, Hanno
2016-01-01
First-order variational equations are widely used in N-body simulations to study how nearby trajectories diverge from one another. These allow for efficient and reliable determinations of chaos indicators such as the Maximal Lyapunov characteristic Exponent (MLE) and the Mean Exponential Growth factor of Nearby Orbits (MEGNO). In this paper we lay out the theoretical framework to extend the idea of variational equations to higher order. We explicitly derive the differential equations that govern the evolution of second-order variations in the N-body problem. Going to second order opens the door to new applications, including optimization algorithms that require the first and second derivatives of the solution, like the classical Newton's method. Typically, these methods have faster convergence rates than derivative-free methods. Derivatives are also required for Riemann manifold Langevin and Hamiltonian Monte Carlo methods which provide significantly shorter correlation times than standard methods. Such impro...
Cosmological simulations of multicomponent cold dark matter.
Medvedev, Mikhail V
2014-08-15
The nature of dark matter is unknown. A number of dark matter candidates are quantum flavor-mixed particles but this property has never been accounted for in cosmology. Here we explore this possibility from the first principles via extensive N-body cosmological simulations and demonstrate that the two-component dark matter model agrees with observational data at all scales. Substantial reduction of substructure and flattening of density profiles in the centers of dark matter halos found in simulations can simultaneously resolve several outstanding puzzles of modern cosmology. The model shares the "why now?" fine-tuning caveat pertinent to all self-interacting models. Predictions for direct and indirect detection dark matter experiments are made.
Superlarge-Scale Structure in N-body Simulations
Doroshkevich, A. G.; Müller, V; Retzlaff, J.; Turchaninov, V.
1999-01-01
The simulated matter distribution on large scales is studied using core-sampling, cluster analysis, inertia tensor analysis, and minimal spanning tree techniques. Seven simulations in large boxes for five cosmological models with COBE normalized CDM-like power spectra are studied. The wall-like Super Large Scale Structure with parameters similar to the observed one is found for the OCDM and LCDM models with Omega_m h = 0.3 & 0.245. In these simulations, the rich structure elements with a typi...
Stochasticity in N-body Simulations of Disc Galaxies
Sellwood, J A
2009-01-01
We demonstrate that the chaotic nature of N-body systems can lead to macroscopic variations in the outcomes of collisionless simulations containing rotationally supported discs. The unavoidable stochasticity that afflicts all simulations generally causes mild differences between the evolution of similar models but, in order to illustrate that this is not always true, we present a case that shows extreme bimodal divergence. We identify and give explicit illustrations of several sources of stochasticity, and also show that macroscopic variations in the outcomes can originate from differences at the round-off error level. We obtain somewhat more consistent results from simulations in which the halo is set up with great care compared with those started from more approximate equilibria, but we have been unable to eliminate diverging behaviour entirely because the main sources of stochasticity are intrinsic to the disc. We demonstrate that the divergent behaviour occurs in two different types of code and is indepen...
Cosmological simulations using GCMHD+
Barnes, David J.; Kawata, Daisuke; Wu, Kinwah
2012-03-01
Radio observations of galaxy clusters show that the intracluster medium is permeated by ? magnetic fields. The origin and evolution of these cosmological magnetic fields is currently not well understood, and so their impact on the dynamics of structure formation is not known. Numerical simulations are required to gain a greater understanding and produce predictions for the next generation of radio telescopes. We present the galactic chemodynamics smoothed particle magnetohydrodynamics (SPMHD) code (GCMHD+), which is an MHD implementation for the cosmological smoothed particle hydrodynamics code GCD+. The results of 1D, 2D and 3D tests are presented and the performance of the code is shown relative to the ATHENA grid code. GCMHD+ shows good agreement with the reference solutions produced by ATHENA. The code is then used to simulate the formation of a galaxy cluster with a simple primordial magnetic field embedded in the gas. A homogeneous seed field of 3.5 × 10-11 G is amplified by a factor of 103 during the formation of the cluster. The results show good agreement with the profiles found in other magnetic cluster simulations of similar resolution.
Cosmological neutrino simulations at extreme scale
Emberson, J. D.; Yu, Hao-Ran; Inman, Derek; Zhang, Tong-Jie; Pen, Ue-Li; Harnois-Déraps, Joachim; Yuan, Shuo; Teng, Huan-Yu; Zhu, Hong-Ming; Chen, Xuelei; Xing, Zhi-Zhong
2017-08-01
Constraining neutrino mass remains an elusive challenge in modern physics. Precision measurements are expected from several upcoming cosmological probes of large-scale structure. Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering. Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process. We incorporate neutrinos into the cosmological N-body code CUBEP3M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem. We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes. We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run, named TianNu, which uses 86% of the machine (13 824 compute nodes). With a total of 2.97 trillion particles, TianNu is currently the world’s largest cosmological N-body simulation and improves upon previous neutrino simulations by two orders of magnitude in scale. We finish with a discussion of the unanticipated computational challenges that were encountered during the TianNu runtime.
Second-order variational equations for N-body simulations
Rein, Hanno; Tamayo, Daniel
2016-07-01
First-order variational equations are widely used in N-body simulations to study how nearby trajectories diverge from one another. These allow for efficient and reliable determinations of chaos indicators such as the Maximal Lyapunov characteristic Exponent (MLE) and the Mean Exponential Growth factor of Nearby Orbits (MEGNO). In this paper we lay out the theoretical framework to extend the idea of variational equations to higher order. We explicitly derive the differential equations that govern the evolution of second-order variations in the N-body problem. Going to second order opens the door to new applications, including optimization algorithms that require the first and second derivatives of the solution, like the classical Newton's method. Typically, these methods have faster convergence rates than derivative-free methods. Derivatives are also required for Riemann manifold Langevin and Hamiltonian Monte Carlo methods which provide significantly shorter correlation times than standard methods. Such improved optimization methods can be applied to anything from radial-velocity/transit-timing-variation fitting to spacecraft trajectory optimization to asteroid deflection. We provide an implementation of first- and second-order variational equations for the publicly available REBOUND integrator package. Our implementation allows the simultaneous integration of any number of first- and second-order variational equations with the high-accuracy IAS15 integrator. We also provide routines to generate consistent and accurate initial conditions without the need for finite differencing.
Superlarge-Scale Structure in N-body Simulations
Doroshkevich, A G; Retzlaff, J; Turchaninov, V I
1999-01-01
The simulated matter distribution on large scales is studied using core-sampling, cluster analysis, inertia tensor analysis, and minimal spanning tree techniques. Seven simulations in large boxes for five cosmological models with COBE normalized CDM-like power spectra are studied. The wall-like Super Large Scale Structure with parameters similar to the observed one is found for the OCDM and LCDM models with Omega_m h = 0.3 & 0.245. In these simulations, the rich structure elements with a typical value for the largest extension of above the mean. These rich elements are formed due to the anisotropic nonlinear compression of sheets with original size of ~(15 - 25) h^{-1} Mpc. They surround low-density regions with a typical diameter ~(50 - 70) h^{-1} Mpc. The statistical characteristics of these structures are found to be approximately consistent with observations and theoretical expectations. The cosmological models with higher matter density Ømega_m=1 in CDM with Harrison-Zeldovich or tilted power spectr...
Superlarge-scale structure in N-body simulations
Doroshkevich, A. G.; Müller, V.; Retzlaff, J.; Turchaninov, V.
1999-07-01
The simulated matter distribution on large scales is studied using core-sampling, cluster analysis, inertia tensor analysis and minimal spanning tree techniques. Seven simulations in large boxes for five cosmological models with COBE-normalized CDM-like power spectra are studied. A wall-like superlarge-scale structure with parameters similar to the observed one is found for the OCDM and ΛCDM models with Οmh = 0.2-0.3. In these simulations, the rich structure elements with a typical value for the largest extension of ~(30 - 50) h-1 Mpc incorporate ~40 per cent of matter with overdensity of about 10 above the mean. These rich elements are formed by the anisotropic non-linear compression of sheets with an original size of ~(15-25) h-1 Mpc. They surround low-density regions with a typical diameter ~(50-70) h-1 Mpc. The statistical characteristics of these structures are found to be approximately consistent with observations and theoretical expectations. The cosmological models with higher matter density Ωm=1 in CDM with Harrison-Zeldovich or tilted power spectra cannot reproduce the characteristics of the observed galaxy distribution because of the very strong disruption of the rich structure elements. Another model with a broken scale-invariant initial power spectrum (BCDM) does not show enough matter concentration in the rich structure elements.
Cosmological Simulations using GCMHD+
Barnes, David J; Wu, Kinwah
2011-01-01
Radio observations of galaxy clusters show that the intra cluster medium is permeated by \\mu G magnetic fields. The origin and evolution of these cosmological magnetic fields is currently not well understood and so their impact on the dynamics of structure formation is not known. Numerical simulations are required to gain a greater understanding and produce predictions for the next generation of radio telescopes. We present the galactic chemodynamics smoothed particle magnetohydrodynamic (SPMHD) code (GCMHD+), which is an MHD implementation for the cosmological smoothed particle hydrodynamic code GCD+. The results of 1, 2 and 3 dimensional tests are presented and the performance of the code is shown relative to the ATHENA grid code. GCMHD+ shows good agreement with the reference solutions produced by ATHENA. The code is then used to simulate the formation of a galaxy cluster with a simple primordial magnetic field embedded in the gas. A homogeneous seed field of 10^-11 G is amplified by a factor of 10^3 durin...
N-Body Simulations of Galaxies in the Cluster Environment
Humphrey, Nicholas; Berrington, R. C.
2010-01-01
We present numerous N-body simulations of galaxy clusters consisting of up to 600,000 total particles and 50 galaxies each to characterize the evolution of galaxies in the cluster environment. These simulations were run on the Ball State University (BSU) College of Science and Humanities (CSH) 64-node Beowulf Cluster. Because the velocity dispersion (σ) is a tracer of a galaxies’ potential well and therefore its mass, we will use it to examine the mass evolution of the galaxies in the simulations by fitting a function to the σ of the galaxies. The strength of this function is its direct comparison to observational data. We further investigate the evolution of the galaxy structure parameters through the use of projected mass radii and line-of-sight (LOS) σ. Additionally, we discuss the use of alternate orbital parameters such as Vesc to investigate the potential wells of the galaxies. Our goal is to isolate the mass and luminosity evolution from the environmental effects on the evolution of elliptical galaxies. This project is a subset of a continuing study whose intent is to combine observational data with numerical techniques to study the effects of a galaxies’ environment on its mass evolution and internal dynamics.
A numerical relativity scheme for cosmological simulations
Daverio, David; Mitsou, Ermis
2016-01-01
Fully non-linear cosmological simulations may prove relevant in understanding relativistic/non-linear features and, therefore, in taking full advantage of the upcoming survey data. We propose a new 3+1 integration scheme which is based on the presence of a perfect fluid (hydro) field, evolves only physical states by construction and passes the robustness test on an FLRW space-time. Although we use General Relativity as an example, the idea behind that scheme is applicable to any generally-covariant modified gravity theory and/or matter content, including a N-body sector.
Splotch: Visualizing Cosmological Simulations
Dolag, K; Gheller, C; Imboden, S
2008-01-01
We present a light and fast, public available, ray-tracer {\\tt Splotch} software tool which supports the effective visualization of cosmological simulations data. We describe the algorithm it relies on, which is designed in order to deal with point-like data, optimizing the ray-tracing calculation by ordering the particles as a function of their ``depth'' defined as a function of one of the coordinates or other associated parameter. Realistic three-dimensional impressions are reached through a composition of the final color in each pixel properly calculating emission and absorption of individual volume elements. We describe several scientific as well as public applications realized with {\\tt Splotch}. We emphasize how different datasets and configurations lead to remarkable different results in terms of the images and animations. A few of these results are available online.
Spurious Small-Scale Structure & Discreteness-Driven Relaxation in Cosmological Simulations
Power, Chris; Obreschkow, Danail; Hobbs, Alexander; Lewis, Geraint F
2016-01-01
There is strong evidence that cosmological N-body simulations dominated by Warm Dark Matter (WDM) contain spurious or unphysical haloes, most readily apparent as regularly spaced low-mass haloes strung along filaments. We show that spurious haloes are a feature of traditional N-body simulations of cosmological structure formation models, including WDM and Cold Dark Matter (CDM) models, in which gravitational collapse proceeds in an initially anisotropic fashion, and arises naturally as a consequence of discreteness-driven relaxation. We demonstrate this using controlled N-body simulations of plane-symmetric collapse and show that spurious haloes are seeded at shell crossing by localised velocity perturbations induced by the discrete nature of the density field, and that their characteristic separation should be approximately the mean inter-particle separation of the N-body simulation, which is fixed by the mass resolution within the volume. Using cosmological N-body simulations in which particles are split in...
GRACOS: Scalable and Load Balanced P3M Cosmological N-body Code
Shirokov, A; Shirokov, Alexander; Bertschinger, Edmund
2005-01-01
We present a parallel implementation of the particle-particle/particle-mesh (P3M) algorithm for distributed memory clusters. The GRACOS (GRAvitational COSmology) code uses a hybrid method for both computation and domain decomposition. Long-range forces are computed using a Fourier transform gravity solver on a regular mesh; the mesh is distributed across parallel processes using a static one-dimensional slab domain decomposition. Short-range forces are computed by direct summation of close pairs; particles are distributed using a dynamic domain decomposition based on a space-filling Hilbert curve. A nearly-optimal method was devised to dynamically repartition the particle distribution so as to maintain load balance even for extremely inhomogeneous mass distributions. Tests using $800^3$ simulations on a 40-processor beowulf cluster showed good load balance and scalability up to 80 processes. We discuss the limits on scalability imposed by communication and extreme clustering and suggest how they may be remove...
N-body simulation of the Stephan's Quintet
Renaud, Florent; Xu, C Kevin
2010-01-01
The evolution of compact groups of galaxies may represent one of the few places in the nearby universe in which massive galaxies are being forged through a complex set of processes involving tidal interaction, ram-pressure stripping, and perhaps finally "dry-mergers" of galaxies stripped of their cool gas. Using collisionless N-body simulations, we propose a possible scenario for the formation of one of the best studied compact groups: Stephan's Quintet. We define a serial approach which allows us to consider the history of the group as sequence of galaxy-galaxy interactions seen as relatively separate events in time, but chained together in such a way as to provide a plausible scenario that ends in the current configuration of the galaxies. By covering a large set of parameters, we claim that it is very unlikely that both major tidal tails of the group have been created by the interaction between the main galaxy and a single intruder. We propose instead a scenario based on two satellites orbiting the main di...
N-body simulations with a cosmic vector for dark energy
Carlesi, Edoardo; Yepes, Gustavo; Gottloeber, Stefan; Jimenez, Jose Beltran; Maroto, Antonio L
2012-01-01
We present the results of a series of cosmological $N$-body simulations of a Vector Dark Energy (VDE) model, performed using a suitably modified version of the publicly available \\texttt{GADGET}-2 code. The setups of our simulations were calibrated pursuing a twofold aim: 1) to analyze the large scale distribution of massive objects and 2) to determine the properties of halo structure in this different ramework.We observe that structure formation is enhanced in VDE, since the mass function at high redshift is boosted up to a factor of ten with respect to \\LCDM, possibly alleviating tensions with the observations of massive clusters at high redshifts and early reionization epoch. Significant differences can also be found for the value of the growth factor, that in VDE shows a completely different behaviour, and in the distribution of voids, which in this cosmology are on average smaller and less abundant. We further studied the structure of dark matter haloes more massive than $5\\times10^{13}$\\hMsun, finding t...
N-body simulations of collective effects in spiral and barred galaxies
Zhang, X.
2016-10-01
We present gravitational N-body simulations of the secular morphological evolution of disk galaxies induced by density wave modes. In particular, we address the demands collective effects place on the choice of simulation parameters, and show that the common practice of the use of a large gravity softening parameter was responsible for the failure of past simulations to correctly model the secular evolution process in galaxies, even for those simulations where the choice of basic state allows an unstable mode to emerge, a prerequisite for obtaining the coordinated radial mass flow pattern needed for secular evolution of galaxies along the Hubble sequence. We also demonstrate that the secular evolution rates measured in our improved simulations agree to an impressive degree with the corresponding rates predicted by the recently-advanced theories of dynamically-driven secular evolution of galaxies. The results of the current work, besides having direct implications on the cosmological evolution of galaxies, also shed light on the general question of how irreversibility emerges from a nominally reversible physical system.
GRACOS: Scalable and Load Balanced P3M Cosmological N-body Code
Shirokov, Alexander; Bertschinger, Edmund
2010-10-01
The GRACOS (GRAvitational COSmology) code, a parallel implementation of the particle-particle/particle-mesh (P3M) algorithm for distributed memory clusters, uses a hybrid method for both computation and domain decomposition. Long-range forces are computed using a Fourier transform gravity solver on a regular mesh; the mesh is distributed across parallel processes using a static one-dimensional slab domain decomposition. Short-range forces are computed by direct summation of close pairs; particles are distributed using a dynamic domain decomposition based on a space-filling Hilbert curve. A nearly-optimal method was devised to dynamically repartition the particle distribution so as to maintain load balance even for extremely inhomogeneous mass distributions. Tests using 800(3) simulations on a 40-processor beowulf cluster showed good load balance and scalability up to 80 processes. There are limits on scalability imposed by communication and extreme clustering which may be removed by extending the algorithm to include adaptive mesh refinement.
Koda, Jun
2011-01-01
Self-Interacting Dark Matter (SIDM) is a collisional form of cold dark matter (CDM), originally proposed to solve problems that arose when the collisionless CDM theory of structure formation was compared with observations of galaxies on small scales. The quantitative impact of the proposed elastic collisions on structure formation has been estimated previously by Monte Carlo N-body simulations and by a conducting fluid model, with apparently diverging results. To improve this situation, we make direct comparisons between new Monte Carlo N-body simulations and solutions of the conducting fluid model, for isolated SIDM haloes of fixed mass. This allows us to separate cleanly the effects of gravothermal relaxation from those of continuous mass accretion in an expanding background universe. When these two methods are previously applied to halo formation with cosmological boundary conditions, they disagreed by an order of magnitude about the size of the scattering cross section required to solve the so-called 'cus...
Spurious haloes and discreteness-driven relaxation in cosmological simulations
Power, C.; Robotham, A. S. G.; Obreschkow, D.; Hobbs, A.; Lewis, G. F.
2016-10-01
There is strong evidence that cosmological N-body simulations dominated by warm dark matter (WDM) contain spurious or unphysical haloes, most readily apparent as regularly spaced low-mass haloes strung along filaments. We show that spurious haloes are a feature of traditional N-body simulations of cosmological structure formation models, including WDM and cold dark matter models, in which gravitational collapse proceeds in an initially anisotropic fashion, and arises naturally as a consequence of discreteness-driven relaxation. We demonstrate this using controlled N-body simulations of plane-symmetric collapse and show that spurious haloes are seeded at shell crossing by localized velocity perturbations induced by the discrete nature of the density field, and that their characteristic separation should be approximately the mean inter-particle separation of the N-body simulation, which is fixed by the mass resolution within the volume. Using cosmological N-body simulations in which particles are split into two collisionless components of fixed mass ratio, we find that the spatial distribution of the two components show signatures of discreteness-driven relaxation on both large and small scales. Adopting a spline kernel gravitational softening that is of order the comoving mean inter-particle separation helps to suppress the effect of discreteness-driven relaxation, but cannot eliminate it completely. These results provide further motivation for recent developments of new algorithms, which include, for example, revisions of the traditional N-body approach by means of spatially adaptive anistropric gravitational softenings or explicit solution of the evolution of dark matter in phase space.
Estimating small angular scale CMB anisotropy with high resolution N-body simulations: weak lensing
Fullana, M J; Thacker, R J; Couchman, H M P; Sáez, D
2010-01-01
We estimate the impact of weak lensing by strongly nonlinear cosmological structures on the cosmic microwave background. Accurate calculation of large $\\ell$ multipoles requires N-body simulations and ray-tracing schemes with both high spatial and temporal resolution. To this end we have developed a new code that combines a gravitational Adaptive Particle-Particle, Particle-Mesh (AP3M) solver with a weak lensing evaluation routine. The lensing deviations are evaluated while structure evolves during the simulation so that all evolution steps--rather than just a few outputs--are used in the lensing computations. The new code also includes a ray-tracing procedure that avoids periodicity effects in a universe that is modeled as a 3-D torus in the standard way. Results from our new simulations are compared with previous ones based on Particle-Mesh simulations. We also systematically investigate the impact of box volume, resolution, and ray-tracing directions on the variance of the computed power spectra. We find t...
Genus Statistics of the Virgo N-body simulations and the 1.2-Jy Redshift Survey
Springel, V; Colberg, J M; Couchman, H M P; Efstathiou, G P; Frenk, C S; Jenkins, A R; Pearce, F R; Nelson, A H; Peacock, J A; Thomas, P A
1997-01-01
We study the topology of the Virgo N-body simulations and compare it to the 1.2-Jy redshift survey of IRAS galaxies by means of the genus statistic. Four high-resolution simulations of variants of the CDM cosmology are considered: a flat standard model (SCDM), a variant of it with more large-scale power (tCDM), and two low density universes, one open (OCDM) and one flat (LCDM). The fully sampled N-body simulations are examined down to strongly nonlinear scales, both with spatially fixed smoothing, and with an adaptive smoothing technique. While the tCDM, LCDM, and OCDM simulations have very similar genus statistics in the regime accessible to fixed smoothing, they can be separated with adaptive smoothing at small mass scales. In order to compare the N-body models with the 1.2-Jy survey, we extract large ensembles of mock catalogues from the simulations. These mock surveys are used to test for systematic effects in the genus analysis and to establish the distribution of errors of the genus curve. We find that ...
Faster, Better, Cheaper N-Body with Abacus
Ferrer, Douglas; Eisenstein, D.; Metchnik, M. V.; Pinto, P. A.
2014-01-01
We introduce Abacus, a cosmological N-body code based on a novel gravity solver. Abacus can obtain machine precision force accuracy at significantly greater speeds than any other currently available N-body code. This speed lets us run large-scale cosmological simulations on a single $8000 workstation built with commodity hardware. We present the results of a 40963 particle cosmological simulation, and examine the shift of the BAO acoustic scale bias as a first science application.
Cosmological simulations using a static scalar-tensor theory
Energy Technology Data Exchange (ETDEWEB)
RodrIguez-Meza, M A [Depto. de Fisica, Instituto Nacional de Investigaciones Nucleares, Col. Escandon, Apdo. Postal 18-1027, 11801 Mexico D.F (Mexico); Gonzalez-Morales, A X [Departamento Ingenierias, Universidad Iberoamericana, Prol. Paseo de la Reforma 880 Lomas de Santa Fe, Mexico D.F. Mexico (Mexico); Gabbasov, R F [Depto. de Fisica, Instituto Nacional de Investigaciones Nucleares, Col. Escandon, Apdo. Postal 18-1027, 11801 Mexico D.F (Mexico); Cervantes-Cota, Jorge L [Depto. de Fisica, Instituto Nacional de Investigaciones Nucleares, Col. Escandon, Apdo. Postal 18-1027, 11801 Mexico D.F (Mexico)
2007-11-15
We present {lambda}CDM N-body cosmological simulations in the framework of of a static general scalar-tensor theory of gravity. Due to the influence of the non-minimally coupled scalar field, the gravitational potential is modified by a Yukawa type term, yielding a new structure formation dynamics. We present some preliminary results and, in particular, we compute the density and velocity profiles of the most massive group.
N-body Simulations with Live Stellar Evolution
Church, Ross P; Hurley, Jarrod R
2009-01-01
An N-body code containing live stellar evolution through combination of the software packages NBODY6 and STARS is presented. Operational details of the two codes are outlined and the changes that have been made to combine them discussed. We have computed the evolution of clusters of 10 000 stars using the combined code and we compare the results with those obtained using NBODY6 and the synthetic stellar evolution code SSE. We find that, providing the physics package within STARS is set up correctly to match the parameters of the models used to construct SSE, the results are very similar. This provides a good indication that the new code is working well. We also demonstrate how this physics can be changed simply in the new code with convective overshooting as an example. Similar changes in SSE would require considerable reworking of the model fits. We conclude by outlining proposed future development of the code to include more complete models of single stars and binary star systems.
Cosmological neutrino simulations at extreme scale
Emberson, J D; Inman, Derek; Zhang, Tong-Jie; Pen, Ue-Li; Harnois-Deraps, Joachim; Yuan, Shuo; Teng, Huan-Yu; Zhu, Hong-Ming; Chen, Xuelei; Xing, Zhi-Zhong
2016-01-01
Constraining neutrino mass remains an elusive challenge in modern physics. Precision measurements are expected from several upcoming cosmological probes of large-scale structure. Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering. Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process. We incorporate neutrinos into the cosmological N-body code CUBEP3M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem. We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes. We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run, named TianNu, which uses 86% of the machine (13,824 compute nodes). With a total of 2.97 tr...
Cosmological Simulations using Grid Middleware
Caniou, Y; Depardon, B; Courtois, H; Teyssier, R
2006-01-01
One way to access the aggregated power of a collection of heterogeneous machines is to use a grid middleware, such as DIET, GridSolve or NINF. It addresses the problem of monitoring the resources, of handling the submissions of jobs and as an example the inherent transfer of input and output data, in place of the user. In this paper we present how to run cosmological simulations using the RAMSES application along with the DIET middleware. We will describe how to write the corresponding DIET client and server. The remainder of the paper is organized as follows: Section 2 presents the DIET middleware. Section 3 describes the RAMSES cosmological software and simulations, and how to interface it with DIET. We show how to write a client and a server in Section 4. Finally, Section 5 presents the experiments realized on Grid'5000, the French Research Grid, and we conclude in Section 6.
N-body Simulation of Binary Star Mass Transfer
Hutyra, Taylor; Sumpter, William
2017-01-01
Over 70% of the stars in our galaxy are multiple star systems, many of which are two stars that orbit around a common center of mass. The masses of the individual stars can be found using Newton’s and Kepler’s Laws. This allows astronomers to use these systems as astrophysical laboratories to study properties and processes of stars and galaxies. Among the many types observed, the dynamics of contact systems are the most interesting because they exhibit mass transfer, which changes the composition and function of both stars. The process by which this mass exchange takes place is not well understood. The lack of extensive mass transfer analysis, inadequate theoretical models, and the large time scale of this process are reasons for our limited understanding. In this work, a model was made to give astronomers a method for gaining a deeper knowledge and visual intuition of how the mass transfer between binary stars takes place. We have built the foundations for a simulation of arbitrary systems, which we plan to elaborate on in the future to include thermodynamics and nuclear processes.
Simulating cosmologies beyond ΛCDM with PINOCCHIO
Rizzo, Luca A.; Villaescusa-Navarro, Francisco; Monaco, Pierluigi; Munari, Emiliano; Borgani, Stefano; Castorina, Emanuele; Sefusatti, Emiliano
2017-01-01
We present a method that extends the capabilities of the PINpointing Orbit-Crossing Collapsed HIerarchical Objects (PINOCCHIO) code, allowing it to generate accurate dark matter halo mock catalogues in cosmological models where the linear growth factor and the growth rate depend on scale. Such cosmologies comprise, among others, models with massive neutrinos and some classes of modified gravity theories. We validate the code by comparing the halo properties from PINOCCHIO against N-body simulations, focusing on cosmologies with massive neutrinos: νΛCDM. We analyse the halo mass function, halo two-point correlation function and halo power spectrum, showing that PINOCCHIO reproduces the results from simulations with the same level of precision as the original code (~ 5–10%). We demonstrate that the abundance of halos in cosmologies with massless and massive neutrinos from PINOCCHIO matches very well the outcome of simulations, and point out that PINOCCHIO can reproduce the Ων–σ8 degeneracy that affects the halo mass function. We finally show that the clustering properties of the halos from PINOCCHIO matches accurately those from simulations both in real and redshift-space, in the latter case up to k = 0.3 h Mpc‑1. We emphasize that the computational time required by PINOCCHIO to generate mock halo catalogues is orders of magnitude lower than the one needed for N-body simulations. This makes this tool ideal for applications like covariance matrix studies within the standard ΛCDM model but also in cosmologies with massive neutrinos or some modified gravity theories.
Radio Relics in Cosmological Simulations
Indian Academy of Sciences (India)
M. Hoeft; S. E. Nuza; S. Gottlöber; R. J. van Weeren; H. J. A. Röttgering; M. Brüggen
2011-12-01
Radio relics have been discovered in many galaxy clusters. They are believed to trace shock fronts induced by cluster mergers. Cosmological simulations allow us to study merger shocks in detail since the intra-cluster medium is heated by shock dissipation. Using high resolution cosmological simulations, identifying shock fronts and applying a parametric model for the radio emission allows us to simulate the formation of radio relics. We analyze a simulated shock front in detail. We find a rather broad Mach number distribution. The Mach number affects strongly the number density of relativistic electrons in the downstream area, hence, the radio luminosity varies significantly across the shock surface. The abundance of radio relics can be modeled with the help of the radio power probability distribution which aims at predicting radio relic number counts. Since the actual electron acceleration efficiency is not known, predictions for the number counts need to be normalized by the observed number of radio relics. For the characteristics of upcoming low frequency surveys we find that about thousand relics are awaiting discovery.
Visualizing Astrophysical N-body Systems
Dubinski, John
2008-01-01
I begin with a brief history of N-body simulation and visualization and then go on to describe various methods for creating images and animations of modern simulations in cosmology and galactic dynamics. These techniques are incorporated into a specialized particle visualization software library called MYRIAD that is designed to render images within large parallel N-body simulations as they run. I present several case studies that explore the application of these methods to animations of star clusters, interacting galaxies and cosmological structure formation.
Terapixel imaging of cosmological simulations
Feng, Yu; Di Matteo, Tiziana; Khandai, Nishikanta; Sargent, Randy; Nourbakhsh, Illah; Dille, Paul; Bartley, Chris; Springel, Volker; Jana, Anirban; Gardner, Jeffrey
2011-01-01
The increasing size of cosmological simulations has led to the need for new visualization techniques. We focus on Smoothed Particle Hydrodynamical (SPH) simulations run with the GADGET code and describe methods for visually accessing the entire simulation at full resolution. The simulation snapshots are rastered and processed on supercomputers into images that are ready to be accessed through a web interface (GigaPan). This allows any scientist with a web-browser to interactively explore simulation datasets in both in spatial and temporal dimensions, datasets which in their native format can be hundreds of terabytes in size or more. We present two examples, the first a static terapixel image of the MassiveBlack simulation, a P-GADGET SPH simulation with 65 billion particles, and the second an interactively zoomable animation of a different simulation with more than one thousand frames, each a gigapixel in size. Both are available for public access through the GigaPan web interface. We also make our imaging so...
A hybrid SPH/N-body method for star cluster simulations
Hubber, D A; Smith, R; Goodwin, S P
2013-01-01
We present a new hybrid Smoothed Particle Hydrodynamics (SPH)/N-body method for modelling the collisional stellar dynamics of young clusters in a live gas background. By deriving the equations of motion from Lagrangian mechanics we obtain a formally conservative combined SPH/N-body scheme. The SPH gas particles are integrated with a 2nd order Leapfrog, and the stars with a 4th order Hermite scheme. Our new approach is intended to bridge the divide between the detailed, but expensive, full hydrodynamical simulations of star formation, and pure N-body simulations of gas-free star clusters. We have implemented this hybrid approach in the SPH code SEREN (Hubber et al. 2011) and perform a series of simple tests to demonstrate the fidelity of the algorithm and its conservation properties. We investigate and present resolution criteria to adequately resolve the density field and to prevent strong numerical scattering effects. Future developments will include a more sophisticated treatment of binaries.
The cosmological simulation code GADGET-2
Springel, V
2005-01-01
We discuss the cosmological simulation code GADGET-2, a new massively parallel TreeSPH code, capable of following a collisionless fluid with the N-body method, and an ideal gas by means of smoothed particle hydrodynamics (SPH). Our implementation of SPH manifestly conserves energy and entropy in regions free of dissipation, while allowing for fully adaptive smoothing lengths. Gravitational forces are computed with a hierarchical multipole expansion, which can optionally be applied in the form of a TreePM algorithm, where only short-range forces are computed with the `tree'-method while long-range forces are determined with Fourier techniques. Time integration is based on a quasi-symplectic scheme where long-range and short-range forces can be integrated with different timesteps. Individual and adaptive short-range timesteps may also be employed. The domain decomposition used in the parallelisation algorithm is based on a space-filling curve, resulting in high flexibility and tree force errors that do not depe...
The impact of initial conditions in N-body simulations of debris discs
Thilliez, E
2015-01-01
Numerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative tran...
TreePM Method for Two-Dimensional Cosmological Simulations
Indian Academy of Sciences (India)
Suryadeep Ray
2004-09-01
We describe the two-dimensional TreePM method in this paper. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle–Mesh method. We describe the splitting of force between the PM and the Tree parts. We also estimate error in force for a realistic configuration. Finally, we discuss some tests of the code.
Block Time Step Storage Scheme for Astrophysical N-body Simulations
Cai, Maxwell Xu; Kouwenhoven, M B N; Assmann, Paulina; Spurzem, Rainer
2015-01-01
Astrophysical research in recent decades has made significant progress thanks to the availability of various $N$-body simulation techniques. With the rapid development of high-performance computing technologies, modern simulations have been able to take the computing power of massively parallel clusters with more than $10^5$ GPU cores. While unprecedented accuracy and dynamical scales have been achieved, the enormous amount of data being generated continuously poses great challenges for the subsequent procedures of data analysis and archiving. As an urgent response to these challenges, in this paper we propose an adaptive storage scheme for simulation data, inspired by the block time step integration scheme found in a number of direct $N$-body integrators available nowadays. The proposed scheme, namely the block time step storage scheme, works by minimizing the data redundancy with assignments of data with individual output frequencies as required by the researcher. As demonstrated by benchmarks, the proposed...
A new paradigm for reproducing and analyzing N-body simulations of planetary systems
Rein, Hanno; Tamayo, Daniel
2017-01-01
The reproducibility of experiments is one of the main principles of the scientific method. However, numerical N-body experiments, especially those of planetary systems, are currently not reproducible. In the most optimistic scenario, they can only be replicated in an approximate or statistical sense. Even if authors share their full source code and initial conditions, differences in compilers, libraries, operating systems or hardware often lead to qualitatively different results. We provide a new set of easy-to-use, open-source tools that address the above issues, allowing for exact (bit-by-bit) reproducibility of N-body experiments. In addition to generating completely reproducible integrations, we show that our framework also offers novel and innovative ways to analyze these simulations. As an example, we present a high-accuracy integration of the Solar System spanning 10 Gyrs, requiring several weeks to run on a modern CPU. In our framework we can not only easily access simulation data at predefined intervals for which we save snapshots, but at any time during the integration. We achieve this by integrating an on-demand reconstructed simulation forward in time from the nearest snapshot. This allows us to extract arbitrary quantities at any point in the saved simulation exactly (bit-by-bit), and within seconds rather than weeks. We believe that the tools we present in this paper offer a new paradigm for how N-body simulations are run, analyzed, and shared across the community.
Jiang, C Y; Lin, W P
2009-01-01
Following our previous work(Jiang et al.(2008)), in which we studied the merger time-scale of galaxies in a high-resolution cosmological hydro/N-body simulation, we investigate the potential influence of uncertainties in the numerical implementation of baryonic physics on the merger time-scale. The simulation used in the previous work suffers from the overcooling problem which causes the central galaxies of large halos too massive. This may result in a shortened merger time-scale compared to that in the real universe. We run a similar simulation, but the stellar mass is significantly reduced to model another extreme case of low stellar mass. Our result shows that the merger time-scale is little affected by the star formation recipes, except for the satellites in nearly radial orbits which show a 22 percent higher time-scale in the lower stellar mass case. Since the radial orbits only account for a small part of the satellites' orbits, the fitting formula in Jiang et al.(2008) is still applicable to a reasonab...
Long-lived double-barred galaxies in N-body simulations
Shen, Juntai
2010-01-01
Many barred galaxies harbor small-scale secondary bars in the center. The evolution of such double-barred galaxies is still not well understood, partly because of a lack of realistic N-body models with which to study them. Here we report the generation of such systems in the presence of rotating pseudobulges. We demonstrate with high mass and force resolution collisionless N-body simulations that long-lived secondary bars can form spontaneously without requiring gas, contrary to previous claims. We find that secondary bars rotate faster than primary ones. The rotation is not rigid: the secondary bars pulsate, with their amplitude and pattern speed oscillating as they rotate through the primary bars. This self-consistent study supports previous work based on orbital analysis in the potential of two rigidly rotating bars. We also characterize the density and kinematics of the N-body simulations of the double-barred galaxies, compare with observations to achieve a better understanding of such galaxies. The pulsa...
The GENGA Code: Gravitational Encounters in N-body simulations with GPU Acceleration
Grimm, Simon L
2014-01-01
We describe a GPU implementation of a hybrid symplectic N-body integrator, GENGA (Gravitational ENcounters with Gpu Acceleration), designed to integrate planet and planetesimal dynamics in the late stage of planet formation and stability analysis of planetary systems. GENGA is based on the integration scheme of the Mercury code (Chambers 1999), which handles close encounters with very good energy conservation. It uses mixed variable integration (Wisdom & Holman 1991) when the motion is a perturbed Kepler orbit and combines this with a direct N-body Bulirsch-Stoer method during close encounters. The GENGA code supports three simulation modes: Integration of up to 2048 massive bodies, integration with up to a million test particles, or parallel integration of a large number of individual planetary systems. GENGA is written in CUDA C and runs on all Nvidia GPUs with compute capability of at least 2.0. All operations are performed in parallel, including the close encounter detection and the grouping of indepe...
BARRED GALAXY PHOTOMETRY: COMPARING RESULTS FROM THE CANANEA SAMPLE WITH N-BODY SIMULATIONS
Directory of Open Access Journals (Sweden)
E. Athanassoula
2009-01-01
Full Text Available We compare the results of the photometrical analysis of barred galaxies with those of a similar analysis from N-body simulations. The photometry is for a sample of nine barred galaxies observed in the J and Ks bands with the CANICA near infrared (NIR camera at the 2.1 m telescope of the Observatorio Astrofisico Guillermo Haro (OAGH in Cananea, Sonora, Mexico. The comparison includes radial ellipticity pro les and surface brightness (density for the N-body galaxies pro les along the bar major and minor axes. We nd very good agreement, arguing that the exchange of angular momentum within the galaxy plays a determinant role in the evolution of barred galaxies.
N-MODY: A Code for Collisionless N-body Simulations in Modified Newtonian Dynamics
Londrillo, Pasquale; Nipoti, Carlo
2011-02-01
N-MODY is a parallel particle-mesh code for collisionless N-body simulations in modified Newtonian dynamics (MOND). N-MODY is based on a numerical potential solver in spherical coordinates that solves the non-linear MOND field equation, and is ideally suited to simulate isolated stellar systems. N-MODY can be used also to compute the MOND potential of arbitrary static density distributions. A few applications of N-MODY indicate that some astrophysically relevant dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter.
In situ and in-transit analysis of cosmological simulations
Friesen, Brian; Almgren, Ann; Lukić, Zarija; Weber, Gunther; Morozov, Dmitriy; Beckner, Vincent; Day, Marcus
2016-08-01
Modern cosmological simulations have reached the trillion-element scale, rendering data storage and subsequent analysis formidable tasks. To address this circumstance, we present a new MPI-parallel approach for analysis of simulation data while the simulation runs, as an alternative to the traditional workflow consisting of periodically saving large data sets to disk for subsequent `offline' analysis. We demonstrate this approach in the compressible gasdynamics/ N-body code Nyx, a hybrid MPI+OpenMP code based on the BoxLib framework, used for large-scale cosmological simulations. We have enabled on-the-fly workflows in two different ways: one is a straightforward approach consisting of all MPI processes periodically halting the main simulation and analyzing each component of data that they own (` in situ'). The other consists of partitioning processes into disjoint MPI groups, with one performing the simulation and periodically sending data to the other `sidecar' group, which post-processes it while the simulation continues (`in-transit'). The two groups execute their tasks asynchronously, stopping only to synchronize when a new set of simulation data needs to be analyzed. For both the in situ and in-transit approaches, we experiment with two different analysis suites with distinct performance behavior: one which finds dark matter halos in the simulation using merge trees to calculate the mass contained within iso-density contours, and another which calculates probability distribution functions and power spectra of various fields in the simulation. Both are common analysis tasks for cosmology, and both result in summary statistics significantly smaller than the original data set. We study the behavior of each type of analysis in each workflow in order to determine the optimal configuration for the different data analysis algorithms.
Belleman, R.G.; Bédorf, J.; Portegies Zwart, S.F.
2008-01-01
We present the results of gravitational direct N-body simulations using the graphics processing unit (GPU) on a commercial NVIDIA GeForce 8800GTX designed for gaming computers. The force evaluation of the N-body problem is implemented in "Compute Unified Device Architecture" (CUDA) using the GPU to
Belleman, R.G.; Bédorf, J.; Portegies Zwart, S.F.
2008-01-01
We present the results of gravitational direct N-body simulations using the graphics processing unit (GPU) on a commercial NVIDIA GeForce 8800GTX designed for gaming computers. The force evaluation of the N-body problem is implemented in "Compute Unified Device Architecture" (CUDA) using the GPU to
Scale-dependent bias induced by local non-Gaussianity: A comparison to N-body simulations
Desjacques, Vincent; Iliev, Ilian
2008-01-01
We investigate the effect of primordial non-Gaussianity of the local type on the auto- and cross-power spectrum of dark matter haloes using a series of large N-body simulations of the LCDM cosmology. Theoretical models predict a scale-dependent bias correction \\Delta b(k,f_NL) that depends on the linear halo bias b(M). We measure the power spectra for a range of halo mass and redshifts covering the relevant range of existing galaxy and quasar populations. We show that auto and cross-correlation analyses of bias are consistent with each other. We find that, on large scales (k 1.5. At smaller scales, the effect in simulations is suppressed relative to theoretical predictions, in qualitative agreement with the expectations based on peak-background split. The suppression relative to the theory reaches a factor of three at k=0.1 h/Mpc. We give a fitting formula for it, which should be used when analysing observational data. The current limits on f_NL from Slosar et al. (2008) come mostly from very large scales and...
Self-Consistent Cosmological Simulations of DGP Braneworld Gravity
Energy Technology Data Exchange (ETDEWEB)
Schmidt, Fabian [Univ. of Chicago, IL (United States). Kavli Inst. for Cosmological Physics (KICP)
2009-09-01
We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati braneworld model, by solving the full non-linear equations of motion for the scalar degree of freedom in this model, the brane bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes non-linear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to General Relativity. The code uses a multi-grid relaxation scheme to solve the non-linear field equation in the quasi-static approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. However, the type of non-linear interactions of the brane-bending mode, which are the focus of this study, are generic to a wide class of braneworld cosmologies. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane bending mode. This allows us to isolate the effects of the non-linear self-couplings of the field which are noticeable already on quasi-linear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane bending mode within cosmological structure formation. We find that, independently of CMB constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.
Simulations of structure formation in interacting dark energy cosmologies
Baldi, Marco
2009-01-01
The evidence in favor of a dark energy component dominating the Universe, and driving its presently accelerated expansion, has progressively grown during the last decade of cosmological observations. If this dark energy is given by a dynamic scalar field, it may also have a direct interaction with other matter fields in the Universe, in particular with cold dark matter. Such interaction would imprint new features on the cosmological background evolution as well as on the growth of cosmic structure, like an additional long-range fifth-force between massive particles, or a variation in time of the dark matter particle mass. We review here the implementation of these new physical effects in the N-body code GADGET-2, and we discuss the outcomes of a series of high-resolution N-body simulations for a selected family of interacting dark energy models, as already presented in Baldi et al. [20]. We interestingly find, in contrast with previous claims, that the inner overdensity of dark matter halos decreases in these...
N-Body Galaxy Dynamics Simulations on a Homogeneous Beowulf Cluster
Gipson, B.; McBride, W. R.; Kornreich, D. A.
2004-12-01
The galactic distribution of dark matter in disk galaxies remains an important problem in astrophysics. Modern methods in determining this distribution rely heavily on N--Body simulations. To this end we have developed a variable time step Piet Hut N--Body simulator, run using MPICH on a homogeneous 12 processor (x86) Beowulf cluster. The Hut Algorithm allows for the efficient, accurate calculation of forces between millions of points in a reasonable time. Additionally, subdividing the space into octants allows for the efficient creation O(N log (N)) of mutual nearest-neighbor data for all points. Such data are necessary for the inclusion of smoothed particle hydrodynamics (gas clouds, etc) as well as for merging the frequent, tightly bound, rapidly rotating, binary systems that decrease performance in this type of simulation. Initial tests have shown strong agreement with exhaustive O(N2) calculation results. Simulating 10,000 points yielded a total relative error of 0.32% with the exhaustive case, executing in 3.3 seconds on the cluster. General system-level tests have also been performed, including determining collapse times for cold and isothermal spherical distributions; all resulting in good agreement with analytical results. Tests on the Kuz'min galactic distribution have also resulted in expected rotational rates. We discuss the oscillatory behavior of such distributions within several constant potentials with the intention of further eliciting the distribution of dark matter within our own galaxy.
Large-scale N-body simulations of the viscous overstability in Saturn's rings
Rein, Hanno
2012-01-01
We present results from large-scale particle simulations of the viscous overstability in Saturn's rings. The overstability generates a variety of structure on scales covering a few hundred metres to several kilometres, including axisymmetric wavetrains and larger-scale modulations. Such patterns have been observed in Saturn's rings by the Cassini spacecraft. Our simulations model the collisional evolution of particles in a co-rotating patch of the disk. These are the largest N-body simulations of the viscous overstability yet performed. The radial box size is five orders of magnitude larger than a typical particle radius, and so describes a 20-50 km radial portion of the rings. Its evolution is tracked for more than 10,000 orbits. In agreement with hydrodynamics, our N-body simulations reveal that the viscous overstability exhibits a rich set of dynamics characterised by nonlinear travelling waves with wavelengths of a few hundred meters. In addition, wave defects, such as sources and shocks, punctuate this b...
An Accelerating Solution for N-Body MOND Simulation with FPGA-SoC
Directory of Open Access Journals (Sweden)
Bo Peng
2016-01-01
Full Text Available As a modified-gravity proposal to handle the dark matter problem on galactic scales, Modified Newtonian Dynamics (MOND has shown a great success. However, the N-body MOND simulation is quite challenged by its computation complexity, which appeals to acceleration of the simulation calculation. In this paper, we present a highly integrated accelerating solution for N-body MOND simulations. By using the FPGA-SoC, which integrates both FPGA and SoC (system on chip in one chip, our solution exhibits potentials for better performance, higher integration, and lower power consumption. To handle the calculation bottleneck of potential summation, on one hand, we develop a strategy to simplify the pipeline, in which the square calculation task is conducted by the DSP48E1 of Xilinx 7 series FPGAs, so as to reduce the logic resource utilization of each pipeline; on the other hand, advantages of particle-mesh scheme are taken to overcome the bottleneck on bandwidth. Our experiment results show that 2 more pipelines can be integrated in Zynq-7020 FPGA-SoC with the simplified pipeline, and the bandwidth requirement is reduced significantly. Furthermore, our accelerating solution has a full range of advantages over different processors. Compared with GPU, our work is about 10 times better in performance per watt and 50% better in performance per cost.
Creating mock catalogues of stellar haloes from cosmological simulations
Lowing, Ben; Kennedy, Rachel; Cooper, Andrew; Helly, John; Frenk, Carlos; Cole, Shaun
2014-01-01
We present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmological simulations and show how the catalogues can be used to test and interpret observational data. The catalogues are constructed from a combination of methods. A semi-analytic galaxy formation model is used to calculate the star formation history in haloes in an N-body simulation and dark matter particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the Aquarius simulations of Milky Way mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibi...
Simulating nonlinear cosmological structure formation with massive neutrinos
Banerjee, Arka
2016-01-01
We present a new method for simulating cosmologies that contain massive particles with thermal free streaming motion, such as massive neutrinos or warm/hot dark matter. This method combines particle and fluid descriptions of the thermal species to eliminate the shot noise known to plague conventional N-body simulations. We describe this method in detail, along with results for a number of test cases to validate our method, and check its range of applicability. Using this method, we demonstrate that massive neutrinos can produce a significant scale-dependence in the large-scale biasing of deep voids in the matter field. We show that this scale-dependence may be quantitatively understood using an extremely simple spherical expansion model which reproduces the behavior of the void bias for different neutrino parameters.
Wang, Yang Ocean; Kang, Xi; Dutton, Aaron; Yu, Yu; Macciò, Andrea V
2014-01-01
Observations have shown that the spatial distribution of satellite galaxies is not random, but aligned with the major axes of central galaxies. This alignment is dependent on galaxy properties, such that red satellites are more strongly aligned than blue satellites. Theoretical work done to interpret this phenomena has found that it is due to the non-spherical nature of dark matter halos. However, most studies over-predict the alignment signal under the assumption that the central galaxy shape follows the shape of the host halo. It is also not clear whether the color dependence of alignment is due to an assembly bias or an evolution effect. In this paper we study these problems using a cosmological N-body simulation. Subhalos are used to trace the positions of satellite galaxies. It is found that the shape of dark matter halos are mis-aligned at different radii. If the central galaxy shares the same shape as the inner host halo, then the alignment effect is weaker and agrees with observational data. However, ...
Oogi, Taira; Ishiyama, Tomoaki; Kobayashi, Masakazu A R; Makiya, Ryu; Nagashima, Masahiro
2015-01-01
We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z=4 (a few 1e+11 Msun) to z=1 (a few 1e+12 Msun), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar--galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increas...
Large-scale N-body simulations of the viscous overstability in Saturn's rings
Rein, Hanno; Latter, Henrik N.
2013-05-01
We present results from large-scale particle simulations of the viscous overstability in Saturn's rings. The overstability generates a variety of structures on scales covering a few hundred metres to several kilometres, including axisymmetric wavetrains and their larger scale modulations. Such patterns have been observed in Saturn's rings by the Cassini spacecraft. Our simulations model the collisional evolution of ring particles in a corotating patch of the disc. These are the largest N-body simulations of the viscous overstability yet performed. The radial box size is five orders of magnitude larger than a typical particle radius, and so describes a 20-50 km radial portion of the rings. Its evolution is tracked for more than 10 000 orbits. In agreement with hydrodynamics, our N-body simulations reveal that the viscous overstability exhibits a rich set of dynamics characterized by non-linear travelling waves with wavelengths of a few hundred metres. In addition, wave defects, such as sources and shocks, punctuate this bed of waves and break them up into large-scale divisions of radial width ˜5 km. We find that the wavelength of the travelling waves is positively correlated with the mean optical depth. In order to assess the role of the numerical boundary conditions and also background ring structure, we include simulations of broad spreading rings and simulations with a gradient in the background surface density. Overall, our numerical results and approach provide a tool with which to interpret Cassini occultation observations of microstructure in Saturn's rings. We present an example of such a synthetic occultation observation and discuss what features to expect. We make the entire source code freely available.
Evolution of star cluster systems in isolated galaxies: first results from direct N-body simulations
Rossi, L. J.; Bekki, K.; Hurley, J. R.
2016-11-01
The evolution of star clusters is largely affected by the tidal field generated by the host galaxy. It is thus in principle expected that under the assumption of a `universal' initial cluster mass function the properties of the evolved present-day mass function of star cluster systems should show a dependence on the properties of the galactic environment in which they evolve. To explore this expectation, a sophisticated model of the tidal field is required in order to study the evolution of star cluster systems in realistic galaxies. Along these lines, in this work we first describe a method developed for coupling N-body simulations of galaxies and star clusters. We then generate a data base of galaxy models along the Hubble sequence and calibrate evolutionary equations to the results of direct N-body simulations of star clusters in order to predict the clusters' mass evolution as function of the galactic environment. We finally apply our methods to explore the properties of evolved `universal' initial cluster mass functions and any dependence on the host galaxy morphology and mass distribution. The preliminary results show that an initial power-law distribution of the masses `universally' evolves into a lognormal distribution, with the properties correlated with the stellar mass and stellar mass density of the host galaxy.
Million-Body Star Cluster Simulations: Comparisons between Monte Carlo and Direct $N$-body
Rodriguez, Carl L; Wang, Long; Chatterjee, Sourav; Rasio, Frederic A; Spurzem, Rainer
2016-01-01
We present the first detailed comparison between million-body globular cluster simulations computed with a H\\'enon-type Monte Carlo code, CMC, and a direct $N$-body code, NBODY6++GPU. Both simulations start from an identical cluster model with $10^6$ particles, and include all of the relevant physics needed to treat the system in a highly realistic way. With the two codes "frozen" (no fine-tuning of any free parameters or internal algorithms of the codes) we find excellent agreement in the overall evolution of the two models. Furthermore, we find that in both models, large numbers of stellar-mass black holes (> 1000) are retained for 12 Gyr. Thus, the very accurate direct $N$-body approach confirms recent predictions that black holes can be retained in present-day, old globular clusters. We find only minor disagreements between the two models and attribute these to the small-$N$ dynamics driving the evolution of the cluster core for which the Monte Carlo assumptions are less ideal. Based on the overwhelming g...
Roth, Nina
2011-01-01
We test third-order standard perturbation theory (SPT) as an approximation to non-linear cosmological structure formation. A novel approach is used to numerically calculate the three-dimensional dark matter density field using SPT from the initial conditions of two high-resolution cosmological simulations. The calculated density field is compared to the non-linear dark matter field of the simulations both point-by-point and statistically. For smoothing scales above 8 Mpc/h it shows a good agreement up to redshift 0. We present a simple fitting formula to relate the linear and non-linear density contrast that accurately recovers the non-linear time evolution for 0 <= z <= 10 at the per cent level. To address the problem of biasing between the matter field and the haloes identified in the simulation, we employ the Eulerian local bias model (ELB), including non-linear bias up to the third order. The bias parameters are obtained by fitting a scatter plot of halo and matter density (both from the simulation ...
Hierarchical Tree Algorithm for Collisional N-body Simulations on GRAPE
Fukushige, Toshiyuki
2016-01-01
We present an implementation of the hierarchical tree algorithm on the individual timestep algorithm (the Hermite scheme) for collisional $N$-body simulations, running on GRAPE-9 system, a special-purpose hardware accelerator for gravitational many-body simulations. Such combination of the tree algorithm and the individual timestep algorithm was not easy on the previous GRAPE system mainly because its memory addressing scheme was limited only to sequential access to a full set of particle data. The present GRAPE-9 system has an indirect memory addressing unit and a particle memory large enough to store all particles data and also tree nodes data. The indirect memory addressing unit stores interaction lists for the tree algorithm, which is constructed on host computer, and, according to the interaction lists, force pipelines calculate only the interactions necessary. In our implementation, the interaction calculations are significantly reduced compared to direct $N^2$ summation in the original Hermite scheme. ...
An Analysis of the Large Scale N-body Simulation using the Minkowski Functionals
Nakagami, T; Schmalzing, J; Jing, Y; Nakagami, Takamichi; Matsubara, Takahiko; Schmalzing, Jens; Jing, Yipeng
2004-01-01
We analyze the Minkowski functionals with a large $N$-body simulation of a standard $\\Lambda$CDM model, focusing on transition scales between linear and non-linear gravitational evolution. We numerically calculate the Minkowski functionals with sufficient accuracies to investigate the transition scales, 10--$50\\himpc$. The results are compared with analytic formulae of linear and second-order perturbation theories. We first show that the skewness parameters of the density fluctuations, which are important in second-order analytic formulae of the Minkowski functionals, are in good agreement with the perturbation theory. Considering relative differences between the Minkowski functionals of the analytic formulae and that of the simulation data, we evaluate accuracy levels of the predictions of the perturbation theory. When the straightforward threshold $\
GLOBAL HIGH-RESOLUTION N-BODY SIMULATION OF PLANET FORMATION. I. PLANETESIMAL-DRIVEN MIGRATION
Energy Technology Data Exchange (ETDEWEB)
Kominami, J. D. [Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-Ku, Tokyo (Japan); Daisaka, H. [Hitotsubashi University, Kunitachi-shi, Tokyo (Japan); Makino, J. [RIKEN Advanced Institute for Computational Science, Chuo-ku, Kobe, Hyogo (Japan); Fujimoto, M., E-mail: kominami@mail.jmlab.jp, E-mail: daisaka@phys.science.hit-u.ac.jp, E-mail: makino@mail.jmlab.jp, E-mail: fujimoto.masaki@jaxa.jp [Japan Aerospace Exploration Agency, Sagamihara-shi, Kanagawa (Japan)
2016-03-01
We investigated whether outward planetesimal-driven migration (PDM) takes place or not in simulations when the self-gravity of planetesimals is included. We performed N-body simulations of planetesimal disks with a large width (0.7–4 au) that ranges over the ice line. The simulations consisted of two stages. The first-stage simulations were carried out to see the runaway growth phase using the planetesimals of initially the same mass. The runaway growth took place both at the inner edge of the disk and at the region just outside the ice line. This result was utilized for the initial setup of the second-stage simulations, in which the runaway bodies just outside the ice line were replaced by the protoplanets with about the isolation mass. In the second-stage simulations, the outward migration of the protoplanet was followed by the stopping of the migration due to the increase of the random velocity of the planetesimals. Owing to this increase of random velocities, one of the PDM criteria derived in Minton and Levison was broken. In the current simulations, the effect of the gas disk is not considered. It is likely that the gas disk plays an important role in PDM, and we plan to study its effect in future papers.
Global High-resolution $N$-body Simulation of Planet Formation I. Planetesimal Driven Migration
Kominami, Junko; Makino, Junichiro; Fujimoto, Masaki
2016-01-01
We investigated whether outward Planetesimal Driven Migration (PDM) takes place or not in simulations when the self gravity of planetesimals is included. We performed $N$-body simulations of planetesimal disks with large width (0.7 - 4AU) which ranges over the ice line. The simulations consisted of two stages. The first stage simulations were carried out to see the runaway growth phase using the planetesimals of initially the same mass. The runaway growth took place both at the inner edge of the disk and at the region just outside the ice line. This result was utilized for the initial setup of the second stage simulations in which the runaway bodies just outside the ice line were replaced by the protoplanets with about the isolation mass. In the second stage simulations, the outward migration of the protoplanet was followed by the stopping of the migration due to the increase of the random velocity of the planetesimals. Due to this increase of random velocities, one of the PDM criteria derived in Minton and L...
A parallel implementation of a new fast algorithm for N-body simulations
Londrillo, P; Ciotti, L
2002-01-01
A new, momentum preserving fast Poisson solver for N-body systems sharing effective O(N) computational complexity, has been recently developed by Dehnen (2000, 2002). We have implemented the proposed algorithms in a Fortran-90 code, and parallelized it by a domain decomposition using the MPI routines. The code has been applied to intensive numerical investigations of galaxy mergers, in particular focusing on the possible origin of some of the observed scaling relations of elliptical galaxies. We found that the Fundamental Plane is preserved by an equal mass merging hierarchy, while it is not in a scenario where galaxies grow by accretion of smaller stellar systems. In addition, both the Faber-Jackson and Kormendy relations are not reproduced by our simulations.
Visualizing a Large-Scale Structure of Production Network by N-Body Simulation
Fujiwara, Y.
Our recent study of a nation-wide production network uncovered acommunity structure, namely how firms are connected by supplier-customer links into tightly-knit groups with high density in intra-groups and with lower connectivity in inter-groups. Here we propose a method to visualize the community structure by a graph layout based on a physical analogy. The layout can be calculated in a practical computation-time and is possible to be accelerated by a special-purpose device of GRAPE (gravity pipeline) developed for astrophysical N-body simulation. We show that the method successfully identifies the communities in a hierarchical way by applying it to the manufacturing sector comprising tenth million nodes and a half million edges. In addition, we discuss several limitations of this method, and propose a possible way to avoid all those problems.
Speeding up N-body simulations of modified gravity: chameleon screening models
Bose, Sownak; Li, Baojiu; Barreira, Alexandre; He, Jian-hua; Hellwing, Wojciech A.; Koyama, Kazuya; Llinares, Claudio; Zhao, Gong-Bo
2017-02-01
We describe and demonstrate the potential of a new and very efficient method for simulating certain classes of modified gravity theories, such as the widely studied f(R) gravity models. High resolution simulations for such models are currently very slow due to the highly nonlinear partial differential equation that needs to be solved exactly to predict the modified gravitational force. This nonlinearity is partly inherent, but is also exacerbated by the specific numerical algorithm used, which employs a variable redefinition to prevent numerical instabilities. The standard Newton-Gauss-Seidel iterative method used to tackle this problem has a poor convergence rate. Our new method not only avoids this, but also allows the discretised equation to be written in a form that is analytically solvable. We show that this new method greatly improves the performance and efficiency of f(R) simulations. For example, a test simulation with 5123 particles in a box of size 512 Mpc/h is now 5 times faster than before, while a Millennium-resolution simulation for f(R) gravity is estimated to be more than 20 times faster than with the old method. Our new implementation will be particularly useful for running very high resolution, large-sized simulations which, to date, are only possible for the standard model, and also makes it feasible to run large numbers of lower resolution simulations for covariance analyses. We hope that the method will bring us to a new era for precision cosmological tests of gravity.
Singularity free N-body simulations called 'Dynamic Universe Model' don't require dark matter
Naga Parameswara Gupta, Satyavarapu
For finding trajectories of Pioneer satellite (Anomaly), New Horizons satellite going to Pluto, the Calculations of Dynamic Universe model can be successfully applied. No dark matter is assumed within solar system radius. The effect on the masses around SUN shows as though there is extra gravitation pull toward SUN. It solves the Dynamics of Extra-solar planets like Planet X, satellite like Pioneer and NH for 3-Position, 3-velocity 3-accelaration for their masses, considering the complex situation of Multiple planets, Stars, Galaxy parts and Galaxy centre and other Galaxies Using simple Newtonian Physics. It already solved problems Missing mass in Galaxies observed by galaxy circular velocity curves successfully. Singularity free Newtonian N-body simulations Historically, King Oscar II of Sweden an-nounced a prize to a solution of N-body problem with advice given by Güsta Mittag-Leffler in 1887. He announced `Given a system of arbitrarily many mass points that attract each according to Newton's law, under the assumption that no two points ever collide, try to find a representation of the coordinates of each point as a series in a variable that is some known function of time and for all of whose values the series converges uniformly.'[This is taken from Wikipedia]. The announced dead line that time was1st June 1888. And after that dead line, on 21st January 1889, Great mathematician Poincaré claimed that prize. Later he himself sent a telegram to journal Acta Mathematica to stop printing the special issue after finding the error in his solution. Yet for such a man of science reputation is important than money. [ Ref Book `Celestial mechanics: the waltz of the planets' By Alessandra Celletti, Ettore Perozzi, page 27]. He realized that he has been wrong in his general stability result! But till now nobody could solve that problem or claimed that prize. Later all solutions resulted in singularities and collisions of masses, given by many people
N-body simulations of terrestrial planet formation under the influence of a hot Jupiter
Energy Technology Data Exchange (ETDEWEB)
Ogihara, Masahiro [Observatoire de la Côte d' Azur, Boulevard de l' Observatoire, F-06304 Nice Cedex 4 (France); Kobayashi, Hiroshi; Inutsuka, Shu-ichiro, E-mail: omasahiro@oca.eu, E-mail: ogihara@nagoya-u.jp [Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan)
2014-06-01
We investigate the formation of multiple-planet systems in the presence of a hot Jupiter (HJ) using extended N-body simulations that are performed simultaneously with semianalytic calculations. Our primary aims are to describe the planet formation process starting from planetesimals using high-resolution simulations, and to examine the dependences of the architecture of planetary systems on input parameters (e.g., disk mass, disk viscosity). We observe that protoplanets that arise from oligarchic growth and undergo type I migration stop migrating when they join a chain of resonant planets outside the orbit of an HJ. The formation of a resonant chain is almost independent of our model parameters, and is thus a robust process. At the end of our simulations, several terrestrial planets remain at around 0.1 AU. The formed planets are not equal mass; the largest planet constitutes more than 50% of the total mass in the close-in region, which is also less dependent on parameters. In the previous work of this paper, we have found a new physical mechanism of induced migration of the HJ, which is called a crowding-out. If the HJ opens up a wide gap in the disk (e.g., owing to low disk viscosity), crowding-out becomes less efficient and the HJ remains. We also discuss angular momentum transfer between the planets and disk.
Observable Properties of Double-Barred Galaxies in N-Body Simulations
Shen, Juntai
2007-01-01
Although at least one quarter of early-type barred galaxies host secondary stellar bars embedded in their large-scale primary counterparts, the dynamics of such double barred galaxies are still not well understood. Recently we reported success at simulating such systems in a repeatable way in collisionless systems. In order to further our understanding of double-barred galaxies, here we characterize the density and kinematics of the N-body simulations of these galaxies. This will facilitate comparison with observations and lead to a better understanding of the observed double-barred galaxies. We find the shape and size of our simulated secondary bars are quite reasonable compared to the observed ones. We demonstrate that an authentic decoupled secondary bar may produce only a weak twist of the kinematic minor axis in the stellar velocity field, due to the relatively large random motion of stars in the central region. We also find that the edge-on nuclear bars are probably not related to boxy peanut-shaped bul...
`Grandeur in this view of life': N-body simulation models of the Galactic habitable zone
Vukotić, B.; Steinhauser, D.; Martinez-Aviles, G.; Ćirković, M. M.; Micic, M.; Schindler, S.
2016-07-01
We present an isolated Milky-Way-like simulation in the GADGET2 N-body smoothed particle hydrodynamics (SPH) code. The Galactic disc star formation rate (SFR) surface densities and a stellar mass indicative of the Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life-friendly environments. SFR and stellar component density are calculated by averaging the GADGET2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from 10 to 15 kpc cylindrical galactocentric distance in a 10-Gyr simulated time span. At 10 Gyr, the simulation results imply the following. Stellar particles that have spent almost all of their lifetime in habitable-friendly conditions typically reside at ˜16 kpc from the Galactic Centre and are ˜3 Gyr old. Stellar particles that have spent ≥90 per cent of their 4-5 Gyr long lifetime in habitable-friendly conditions are also predominantly found in the outskirts of the Galactic disc. Fewer than 1 per cent of these particles can be found at a typical Solar system galactocentric distance of 8-10 kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disc around stellar hosts younger than the Sun.
"Grandeur in this view of life": N-body simulation models of the Galactic habitable zone
Vukotić, B; Martinez-Aviles, G; Ćirković, M M; Micic, M; Schindler, S
2016-01-01
We present an isolated Milky Way-like simulation in GADGET2 N-body SPH code. The Galactic disk star formation rate (SFR) surface densities and stellar mass indicative of Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life friendly environments. SFR and stellar component density are calculated averaging the GADGET2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from $10$ to $15$ kpc cylindrical galactocentric distance in $10$ Gyr simulated time span. At $10$ Gyr the simulation results imply the following. Stellar particles which have spent almost all of their life time in habitable friendly conditions reside typically at $\\sim16$ kpc from Galactic centre and are $\\sim 3$ Gyr old. Stellar particles that have spent $\\ge 90 \\%$ of their $4-5$ Gyr long life time in habitable friendly conditions, are also predominantly found in the outskirts of the Galactic disk. Less then $1 \\%$ of thes...
Seeding Black Holes in Cosmological Simulations
Taylor, Philip
2014-01-01
We present a new model for the formation of black holes in cosmological simulations, motivated by the first star formation. Black holes form from high density peaks of primordial gas, and grow via both gas accretion and mergers. Massive black holes heat the surrounding material, suppressing star formation at the centres of galaxies, and driving galactic winds. We perform an investigation into the physical effects of the model parameters, and obtain a `best' set of these parameters by comparing the outcome of simulations to observations. With this best set, we successfully reproduce the cosmic star formation rate history, black hole mass -- velocity dispersion relation, and the size -- velocity dispersion relation of galaxies. The black hole seed mass is 10^3Msun, which is orders of magnitude smaller than has been used in previous cosmological simulations with active galactic nuclei, but suggests that the origin of the seed black holes is the death of Population III stars.
Testing Subhalo Abundance Matching in Cosmological Smoothed Particle Hydrodynamics Simulations
Simha, Vimal; Dave, Romeel; Fardal, Mark; Katz, Neal; Oppenheimer, Benjamin D
2010-01-01
Subhalo abundance matching (SHAM) is a technique for populating simulated dark matter distributions with galaxies, assuming a monotonic relation between a galaxy's stellar mass or luminosity and the mass of its parent dark matter halo or subhalo. We examine the accuracy of SHAM in two cosmological SPH simulations, one of which includes momentum-driven winds. The SPH simulations indeed show a nearly monotonic relation between stellar mass and halo mass provided that, for satellite galaxies, we use the mass of the subhalo at the epoch when it became a satellite. In each simulation, the median relation for central and satellite galaxies is nearly identical, though a somewhat larger fraction of satellites are outliers. SHAM-assigned masses (at z=0-2), luminosities (R-band at z=0), or star formation rates (at z=2) have a 68% scatter of 0.09-0.15 dex relative to the true simulation values. When we apply SHAM to the subhalo population of collisionless N-body simulation with the same initial conditions as the SPH run...
Zhu, Hongyu; Alam, Shadab; Croft, Rupert A. C.; Ho, Shirley; Giusarma, Elena
2017-10-01
Large redshift surveys of galaxies and clusters are providing the first opportunities to search for distortions in the observed pattern of large-scale structure due to such effects as gravitational redshift. We focus on non-linear scales and apply a quasi-Newtonian approach using N-body simulations to predict the small asymmetries in the cross-correlation function of two galaxy different populations. Following recent work by Bonvin et al., Zhao and Peacock and Kaiser on galaxy clusters, we include effects which enter at the same order as gravitational redshift: the transverse Doppler effect, light-cone effects, relativistic beaming, luminosity distance perturbation and wide-angle effects. We find that all these effects cause asymmetries in the cross-correlation functions. Quantifying these asymmetries, we find that the total effect is dominated by the gravitational redshift and luminosity distance perturbation at small and large scales, respectively. By adding additional subresolution modelling of galaxy structure to the large-scale structure information, we find that the signal is significantly increased, indicating that structure on the smallest scales is important and should be included. We report on comparison of our simulation results with measurements from the SDSS/BOSS galaxy redshift survey in a companion paper.
Beyond the Halo: Redefining environment with unbound matter in N-body simulations
Shattow, Genevieve M
2015-01-01
Approximately half of the matter in the Universe is "unbound" at z = 0, according to N-body simulations such as the Millennium Run. Here, we use the milli-Millennium simulation to examine the distribution of unbound matter in relation to the dark matter halos which host galaxies. We measure the unbound matter within two types of windows, using a halo dependent radius and a fixed radius at several different scales. We also consider the timescales over which a halo can accrete the local unbound matter at z = 2 and z = 0. Finally, we compare the unbound matter to observable properties of galaxies, such as local galaxy count environment and stellar mass. We find that halos at z = 2 can accrete far more of the nearby unbound matter over a Hubble time than halos at z = 0 and that 78% of particles within 5 $R_{vir}$ of a halo at z = 2 will be accreted by z = 0, compared to 36% of particles within 5 $h^{-1}$ Mpc of the halo. We also find that galaxy count environment is closely related to the amount of nearby unbound...
Cosmological simulations with TreeSPH
Katz, N; Hernquist, L E; Katz, Neal; Weinberg, David H; Hernquist, Lars
1995-01-01
We describe numerical methods for incorporating gas dynamics into cosmological simulations and present illustrative applications to the cold dark matter (CDM) scenario. Our evolution code, a version of TreeSPH (Hernquist \\& Katz 1989) generalized to handle comoving coordinates and periodic boundary conditions, combines smoothed--particle hydrodynamics (SPH) with the hierarchical tree method for computing gravitational forces. The Lagrangian hydrodynamics approach and individual time steps for gas particles give the algorithm a large dynamic range, which is essential for studies of galaxy formation in a cosmological context. The code incorporates radiative cooling for an optically thin, primordial composition gas in ionization equilibrium with a user-specified ultraviolet background. We adopt a phenomenological prescription for star formation that gradually turns cold, dense, Jeans-unstable gas into collisionless stars, returning supernova feedback energy to the surrounding medium. In CDM simulations, some...
The GENGA code: gravitational encounters in N-body simulations with GPU acceleration
Energy Technology Data Exchange (ETDEWEB)
Grimm, Simon L.; Stadel, Joachim G., E-mail: sigrimm@physik.uzh.ch [Institute for Computational Science, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland)
2014-11-20
We describe an open source GPU implementation of a hybrid symplectic N-body integrator, GENGA (Gravitational ENcounters with Gpu Acceleration), designed to integrate planet and planetesimal dynamics in the late stage of planet formation and stability analyses of planetary systems. GENGA uses a hybrid symplectic integrator to handle close encounters with very good energy conservation, which is essential in long-term planetary system integration. We extended the second-order hybrid integration scheme to higher orders. The GENGA code supports three simulation modes: integration of up to 2048 massive bodies, integration with up to a million test particles, or parallel integration of a large number of individual planetary systems. We compare the results of GENGA to Mercury and pkdgrav2 in terms of energy conservation and performance and find that the energy conservation of GENGA is comparable to Mercury and around two orders of magnitude better than pkdgrav2. GENGA runs up to 30 times faster than Mercury and up to 8 times faster than pkdgrav2. GENGA is written in CUDA C and runs on all NVIDIA GPUs with a computing capability of at least 2.0.
GPU accelerated Hybrid Tree Algorithm for Collision-less N-body Simulations
Watanabe, Tsuyoshi
2014-01-01
We propose a hybrid tree algorithm for reducing calculation and communication cost of collision-less N-body simulations. The concept of our algorithm is that we split interaction force into two parts: hard-force from neighbor particles and soft-force from distant particles, and applying different time integration for the forces. For hard-force calculation, we can efficiently reduce the calculation and communication cost of the parallel tree code because we only need data of neighbor particles for this part. We implement the algorithm on GPU clusters to accelerate force calculation for both hard and soft force. As the result of implementing the algorithm on GPU clusters, we were able to reduce the communication cost and the total execution time to 40% and 80% of that of a normal tree algorithm, respectively. In addition, the reduction factor relative the normal tree algorithm is smaller for large number of processes, and we expect that the execution time can be ultimately reduced down to about 70% of the norma...
Bar Diagnostics in Edge-On Spiral Galaxies. III. N-Body Simulations of Disks
Bureau, M
2004-01-01
Present in over 45% of local spirals, boxy and peanut-shaped bulges are generally interpreted as edge-on bars and may represent a key phase in the evolution of bulges. Aiming to test such claims, the kinematic properties of self-consistent 3D N-body simulations of bar-unstable disks are studied. Using Gauss-Hermite polynomials to describe the stellar kinematics, a number of characteristic bar signatures are identified in edge-on disks: 1) a major-axis light profile with a quasi-exponential central peak and a plateau at moderate radii (Freeman Type II profile); 2) a ``double-hump'' rotation curve; 3) a sometime flat central velocity dispersion peak with a plateau at moderate radii and occasional local central minimum and secondary peak; 4) an h3-V correlation over the projected bar length. All those kinematic features are spatially correlated and can easily be understood from the orbital structure of barred disks. They thus provide a reliable and easy-to-use tool to identify edge-on bars. Interestingly, they a...
A Performance Comparison of Different Graphics Processing Units Running Direct N-Body Simulations
Capuzzo-Dolcetta, Roberto
2013-01-01
Hybrid computational architectures based on the joint power of Central Processing Units and Graphic Processing Units (GPUs) are becoming popular and powerful hardware tools for a wide range of simulations in biology, chemistry, engineering, physics, etc.. In this paper we present a comparison of performance of various GPUs available on market when applied to the numerical integration of the classic, gravitational, N-body problem. To do this, we developed an OpenCL version of the parallel code (HiGPUs) to use for these tests, because this version is the only apt to work on GPUs of different makes. The main general result is that we confirm the reliability, speed and cheapness of GPUs when applied to the examined kind of problems (i.e. when the forces to evaluate are dependent on the mutual distances, as it happens in gravitational physics and molecular dynamics). More specifically, we find that also the cheap GPUs built to be employed just for gaming applications are very performant in terms of computing speed...
Peculiar velocities in redshift space: formalism, N-body simulations and perturbation theory
Okumura, Teppei; Vlah, Zvonimir; Desjacques, Vincent
2013-01-01
Direct measurements of peculiar velocities of galaxies and clusters of galaxies can in principle provide explicit information on the three dimensional mass distribution, but this information is modulated by the fact that velocity field is sampled at galaxy positions, and is thus probing galaxy momentum. We derive expressions for the cross power spectrum between the density and momentum field and the auto spectrum of the momentum field in redshift space, by extending the distribution function method to these statistics. The resulting momentum cross and auto power spectra in redshift space are expressed as infinite sums over velocity moment correlators in real space, as is the case for the density power spectrum in redshift space. We compare the predictions of the velocity statistics to those measured from N-body simulations for both dark matter and halos. We find that in redshift space linear theory predictions for the density-momentum cross power spectrum as well as for the momentum auto spectrum fail to pred...
N-body simulations of planetary accretion around M dwarf stars
Ogihara, Masahiro
2009-01-01
We have investigated planetary accretion from planetesimals in terrestrial planet regions inside the ice line around M dwarf stars through N-body simulations including tidal interactions with disk gas. Because of low luminosity of M dwarfs, habitable zones (HZs) are located in inner regions. In the close-in HZ, type-I migration and the orbital decay induced by eccentricity damping are efficient according to the high disk gas density in the small orbital radii. In the case of full efficiency of type-I migration predicted by the linear theory, we found that protoplanets that migrate to the vicinity of the host star undergo close scatterings and collisions, and 4 to 6 planets eventually remain in mutual mean motion resonances and their orbits have small eccentricities and they are stable both before and after disk gas decays. In the case of slow migration, the resonant capture is so efficient that densely-packed ~ 40 small protoplanets remain in mutual mean motion resonances. In this case, they start orbit cross...
Voids in cosmological simulations over cosmic time
Wojtak, Radosław; Abel, Tom
2016-01-01
We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard LambdaCDM cosmological model and study evolution of basic properties of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift z=0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in in...
Two-Body Relaxation in Cosmological Simulations
Binney, J; Binney, James; Knebe, Alexander
2002-01-01
The importance of two-body relaxation in cosmological simulations is explored with simulations in which there are two species of particles. The cases of mass ratio sqrt(2):1 and 4:1 are investigated. Simulations are run with both a fixed softening length and adaptive softening using the publicly available codes GADGET and MLAPM, respectively. The effects of two-body relaxation are detected in both the density profiles of halos and the mass function of halos. The effects are more pronounced with a fixed softening length, but even in this case they are not so large as to suggest that results obtained with one mass species are significantly affected by two-body relaxation. The simulations that use adaptive softening are slightly less affected by two-body relaxation and produce slightly higher central densities in the largest halos. They run about three times faster than the simulations that use a fixed softening length.
On effects of resolution in dissipationless cosmological simulations
Knebe, A; Gottlöber, S; Klypin, A A; Knebe, Alexander; Kravtsov, Andrey V.; Gottloeber, Stefan; Klypin, Anatoly
2000-01-01
We present a study of numerical effects in dissipationless cosmological simulations. The numerical effects are evaluated and studied by comparing results of a series of 64^3-particle simulations of varying force resolution and number of time steps, performed using three different N-body techniques: the Particle Mesh (PM), the adaptive P3M (AP3M) code, and the Adaptive Refinement Tree (ART) code. This study can therefore be interesting both as an analysis of numerical effects and as a systematic comparison of different codes. We find that the AP3M and the ART codes produce similar results, given that convergence is reached within the code type. We also find that numerical effects may affect the high-resolution simulations in ways that have not been discussed before. In particular, our study revealed the presence of two-body scattering, effects of which can be greatly amplified by inaccuracies of time integration. This process appears to affect the correlation function of matter, mass function and inner density...
Direct N-body simulations of globular clusters - III. Palomar 4 on an eccentric orbit
Zonoozi, Akram Hasani; Haghi, Hosein; Kroupa, Pavel; Küpper, Andreas H. W.; Baumgardt, Holger
2017-01-01
Palomar 4 is a low-density globular cluster with a current mass ≈30000 M⊙in the outer halo of the Milky Way with a two-body relaxation time of the order of a Hubble time. Yet, it is strongly mass segregated and contains a stellar mass function depleted of low-mass stars. Pal 4 was either born this way or it is a result of extraordinary dynamical evolution. Since two-body relaxation cannot explain these signatures alone, enhanced mass loss through tidal shocking may have had a strong influence on Pal 4. Here, we compute a grid of direct N-body simulations to model Pal 4 on various eccentric orbits within the Milky Way potential to find likely initial conditions that reproduce its observed mass, half-light radius, stellar MF-slope and line-of-sight velocity dispersion. We find that Pal 4 is most likely orbiting on an eccentric orbit with an eccentricity of e ≈ 0.9 and pericentric distance of Rp ≈ 5 kpc. In this scenario, the required 3D half-mass radius at birth is similar to the average sizes of typical GCs (Rh ≈ 4 - 5 pc), while its birth mass is about M0 ≈ 105 M⊙. We also find a high degree of primordial mass segregation among the cluster stars, which seems to be necessary in every scenario we considered. Thus, using the tidal effect to constrain the perigalactic distance of the orbit of Pal 4, we predict that the proper motion of Pal 4 should be in the range -0.52 ≤ μδ ≤ -0.38 mas yr-1 and -0.30 ≤ μαcos δ ≤ -0.15 mas yr-1.
Ogihara, Masahiro
2012-01-01
As the number of discovered extrasolar planets has been increasing, diversity of planetary systems requires studies of new formation scenarios. It is important to study satellite formation in circumplanetary disks, which is often viewed as analogous to formation of rocky planets in protoplanetary disks. We investigated satellite formation from satellitesimals around giant planets through N-body simulations that include gravitational interactions with a circumplanetary gas disk. Our main aim is to reproduce the observable properties of the Galilean satellites around Jupiter through numerical simulations, as previous N-body simulations have not explained the origin of the resonant configuration. We performed accretion simulations based on the work of Sasaki et al. (2010), in which an inner cavity is added to the model of Canup & Ward (2002, 2006). We found that several satellites are formed and captured in mutual mean motion resonances outside the disk inner edge and are stable after rapid disk gas dissipat...
A Keplerian-based Hamiltonian Splitting for Gravitational $N$-body Simulations
Ferrari, G Gonçalves; Zwart, S F Portegies
2014-01-01
We developed a Keplerian-based Hamiltonian splitting for solving the gravitational $N$-body problem. This splitting allows us to approximate the solution of a general $N$-body problem by a composition of multiple, independently evolved $2$-body problems. While the Hamiltonian splitting is exact, we show that the composition of independent $2$-body problems results in a non-symplectic non-time-symmetric first-order map. A time-symmetric second-order map is then constructed by composing this basic first-order map with its self-adjoint. The resulting method is precise for each individual $2$-body solution and produces quick and accurate results for near-Keplerian $N$-body systems, like planetary systems or a cluster of stars that orbit a supermassive black hole. The method is also suitable for integration of $N$-body systems with intrinsic hierarchies, like a star cluster with primordial binaries. The superposition of Kepler solutions for each pair of particles makes the method excellently suited for parallel co...
Cool Core Clusters from Cosmological Simulations
Rasia, E; Murante, G; Planelles, S; Beck, A M; Biffi, V; Ragone-Figueroa, C; Granato, G L; Steinborn, L K; Dolag, K
2015-01-01
We present results obtained from a set of cosmological hydrodynamic simulations of galaxy clusters, aimed at comparing predictions with observational data on the diversity between cool-core and non-cool-core clusters. Our simulations include the effects of stellar and AGN feedback and are based on an improved version of the Smoothed-Particle-Hydrodynamics code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical instabilities by including a suitable artificial thermal diffusion. In this Letter, we focus our analysis on the entropy profiles, our primary diagnostic to classify the degree of cool-coreness of clusters, and on the iron profiles. In keeping with observations, our simulated clusters display a variety of behaviors in entropy profiles: they range from steadily decreasing profiles at small radii, characteristic of cool-core systems, to nearly flat core isentropic profiles, characteristic of non cool-core systems. Using observational criteria to distinguish between the two classes of...
The ν2GC simulations: Quantifying the dark side of the universe in the Planck cosmology
Ishiyama, Tomoaki; Enoki, Motohiro; Kobayashi, Masakazu A. R.; Makiya, Ryu; Nagashima, Masahiro; Oogi, Taira
2015-08-01
We present the evolution of dark matter halos in six large cosmological N-body simulations, called the ν2GC (New Numerical Galaxy Catalog) simulations on the basis of the ΛCDM cosmology consistent with observational results obtained with the Planck satellite. The largest simulation consists of 81923 (550 billion) dark matter particles in a box of 1.12 h-1 Gpc (a mass resolution of 2.20 × 108 h-1 M⊙). Among simulations utilizing boxes larger than 1 h-1 Gpc, our simulation yields the highest resolution simulation that has ever been achieved. A ν2GC simulation with the smallest box consists of eight billion particles in a box of 70 h-1 Mpc (a mass resolution of 3.44 × 106 h-1 M⊙). These simulations can follow the evolution of halos over masses of eight orders of magnitude, from small dwarf galaxies to massive clusters. Using the unprecedentedly high resolution and powerful statistics of the ν2GC simulations, we provide statistical results of the halo mass function, mass accretion rate, formation redshift, and merger statistics, and present accurate-fitting functions for the Planck cosmology. By combining the ν2GC simulations with our new semianalytic galaxy formation model, we are able to prepare mock catalogs of galaxies and active galactic nuclei, which will be publicly available in the near future.
Voids in cosmological simulations over cosmic time
Wojtak, Radosław; Powell, Devon; Abel, Tom
2016-06-01
We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well-developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids' evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard Λ-cold-dark-matter cosmological model and study evolution of basic properties of typical voids (with effective radii 6 h-1 Mpc < Rv < 20 h-1 Mpc at redshift z = 0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in initial conditions. Shapes of voids evolve in a collective way which barely modifies the overall distribution of the axial ratios. The evolution appears to have a weak impact on mutual alignments of voids implying that the present state is in large part set up by the primordial density field. We present evolution of dark matter density profiles computed on isodensity surfaces which comply with the actual shapes of voids. Unlike spherical density profiles, this approach enables us to demonstrate development of theoretically predicted bucket-like shape of the final density profiles indicating a wide flat core and a sharp transition to high-density void walls.
Merlin, Emiliano; Buonomo, Umberto; Grassi, Tommaso; Piovan, Lorenzo; Chiosi, Cesare
2009-01-01
We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on...
Initial Conditions for Large Cosmological Simulations
Prunet, S; Aubert, D; Pogosyan, D; Teyssier, R; Gottlöber, S
2008-01-01
This technical paper describes a software package that was designed to produce initial conditions for large cosmological simulations in the context of the Horizon collaboration. These tools generalize E. Bertschinger's Grafic1 software to distributed parallel architectures and offer a flexible alternative to the Grafic2 software for ``zoom'' initial conditions, at the price of large cumulated cpu and memory usage. The codes have been validated up to resolutions of 4096^3 and were used to generate the initial conditions of large hydrodynamical and dark matter simulations. They also provide means to generate constrained realisations for the purpose of generating initial conditions compatible with, e.g. the local group, or the SDSS catalog.
Peuten, M.; Zocchi, A.; Gieles, M.; Hénault-Brunet, V.
2017-09-01
Lowered isothermal models, such as the multimass Michie-King models, have been successful in describing observational data of globular clusters. In this study, we assess whether such models are able to describe the phase space properties of evolutionary N-body models. We compare the multimass models as implemented in limepy (Gieles & Zocchi) to N-body models of star clusters with different retention fractions for the black holes and neutron stars evolving in a tidal field. We find that multimass models successfully reproduce the density and velocity dispersion profiles of the different mass components in all evolutionary phases and for different remnants retention. We further use these results to study the evolution of global model parameters. We find that over the lifetime of clusters, radial anisotropy gradually evolves from the low- to the high-mass components and we identify features in the properties of observable stars that are indicative of the presence of stellar-mass black holes. We find that the model velocity scale depends on mass as m-δ, with δ ≃ 0.5 for almost all models, but the dependence of central velocity dispersion on m can be shallower, depending on the dark remnant content, and agrees well with that of the N-body models. The reported model parameters, and correlations amongst them, can be used as theoretical priors when fitting these types of mass models to observational data.
The Milky Way system in LCDM cosmological simulations
Guo, Qi; Frenk, Carlos; Helly, John; Hellwing, Wojciech
2015-01-01
We apply a semi-analytic galaxy formation model to two high resolution cosmological N-body simulations to investigate analogues of the Milky Way system. We select these according to observed properties of the Milky Way rather than by halo mass as in most previous work. For disk-dominated central galaxies with stellar mass (5--7) x 10d10Msun, the median host halo mass is 1.4 x 10d12Msun, with 1 sigma dispersion in the range [0.86, 3.1] x 10d12Msun, consistent with dynamical measurements of the Milky Way halo mass. For any given halo mass, the probability of hosting a Milky Way system is low, with a maximum of ~20% in haloes of mass ~10d12Msun. The model reproduces the V-band luminosity function and radial profile of the bright (MV 30 km/s. Our model predicts that around half of the dark matter subhaloes with Vmax > 20 km/s host satellites fainter than MV = -9 and so may be missing from existing surveys.
PKDGRAV3: Beyond Trillion Particle Cosmological Simulations for the Next Era of Galaxy Surveys
Potter, Douglas; Teyssier, Romain
2016-01-01
We report on the successful completion of a 2 trillion particle cosmological simulation to z=0 run on the Piz Daint supercomputer (CSCS, Switzerland), using 4000+ GPU nodes for a little less than 80h of wall-clock time or 350,000 node hours. Using multiple benchmarks and performance measurements on the US Oak Ridge National Laboratory Titan supercomputer, we demonstrate that our code PKDGRAV3, delivers, to our knowledge, the fastest time-to-solution for large-scale cosmological N-body simulations. This was made possible by using the Fast Multipole Method in conjunction with individual and adaptive particle time steps, both deployed efficiently (and for the first time) on supercomputers with GPU-accelerated nodes. The very low memory footprint of PKDGRAV3 allowed us to run the first ever benchmark with 8 trillion particles on Titan, and to achieve perfect scaling up to 18000 nodes and a peak performance of 10 Pflops.
Cosmological particle-in-cell simulations with ultra-light axion dark matter
Veltmaat, Jan
2016-01-01
We study cosmological structure formation with ultra-light axion dark matter (or "fuzzy dark matter", FDM) using a particle-mesh scheme to account for the quantum pressure arising in the Madelung formulation of the Schr\\"odinger-Poisson equations. Sub-percent level energy conservation and correct linear behavior are demonstrated. Whereas the code gives rise to the same core-halo profiles as direct simulations of the Schr\\"odinger equation, it does not reproduce the detailed interference patterns at the resolution used here. In cosmological simulations with FDM inital conditions, we find a maximum relative difference of O($10\\%$) in the power spectrum near the quantum Jeans length compared to using a standard N-body code with identical initial conditions. This shows that the effect of quantum pressure during nonlinear structure formation cannot be neglected for precision constraints on a dark matter component consisting of ultra-light axions.
Cosmological particle-in-cell simulations with ultralight axion dark matter
Veltmaat, Jan; Niemeyer, Jens C.
2016-12-01
We study cosmological structure formation with ultralight axion dark matter, or "fuzzy dark matter" (FDM), using a particle-mesh scheme to account for the quantum pressure arising in the Madelung formulation of the Schrödinger-Poisson equations. Subpercent-level energy conservation and correct linear behavior are demonstrated. Whereas the code gives rise to the same core-halo profiles as direct simulations of the Schrödinger equation, it does not reproduce the detailed interference patterns. In cosmological simulations with FDM initial conditions, we find a maximum relative difference of O(10%) in the power spectrum near the quantum Jeans length compared to using a standard N -body code with identical initial conditions. This shows that the effect of quantum pressure during nonlinear structure formation cannot be neglected for precision constraints on a dark matter component consisting of ultralight axions.
An improved SPH scheme for cosmological simulations
Beck, A. M.; Murante, G.; Arth, A.; Remus, R.-S.; Teklu, A. F.; Donnert, J. M. F.; Planelles, S.; Beck, M. C.; Förster, P.; Imgrund, M.; Dolag, K.; Borgani, S.
2016-01-01
We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we implement and test a vast majority of SPH improvement in the developer version of GADGET-3. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity including high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard GADGET-SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic discs to be colder and more extended and galaxy clusters showing entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard GADGET-SPH, thus becoming the core of an efficient code for large cosmological simulations.
The MultiDark Database: Release of the Bolshoi and MultiDark Cosmological Simulations
Riebe, Kristin; Enke, Harry; Forero-Romero, Jaime; Gottloeber, Stefan; Klypin, Anatoly; Lemson, Gerard; Prada, Francisco; Primack, Joel R; Steinmetz, Matthias; Turchaninov, Victor
2011-01-01
We present the online MultiDark Database -- a Virtual Observatory-oriented, relational database for hosting various cosmological simulations. The data is accessible via an SQL (Structured Query Language) query interface, which also allows users to directly pose scientific questions, as shown in a number of examples in this paper. Further examples for the usage of the database are given in its extensive online documentation. The database is based on the same technology as the Millennium Database, a fact that will greatly facilitate the usage of both suites of cosmological simulations. The first release of the MultiDark Database hosts two 8.6 billion particle cosmological N-body simulations: the Bolshoi (250/h Mpc simulation box, 1/h kpc resolution) and MultiDark Run1 simulation (MDR1, or BigBolshoi, 1000/h Mpc simulation box, 7/h kpc resolution). The extraction methods for halos/subhalos from the raw simulation data, and how this data is structured in the database are explained in this paper. With the first da...
An Archive and Tools for Cosmological Simulations inside the Virtual Observatory
Manzato, P.; Molinaro, M.; Gasparo, F.; Smareglia, R.; Taffoni, G.; Pasian, F.; Gheller, C.; Becciani, U.; Costa, A.; Costa, V.; Grillo, A.; Comparato, M.
2008-08-01
The Italian Theoretical Virtual Observatory (ITVO) is a test-bed project for the inclusion of theoretical data and related tools inside the International Virtual Observatory Alliance (IVOA, Hanisch & Quinn, 2003). We started cooperating with the IVOA community to develop standards and tools applicable to the theoretical data obtained from cosmological simulations. The database structure has been created with the main purpose of defining a structure for the cosmological simulations, generic enough to be able to ingest metadata from many types of simulations (N-body, N-body + SPH, Mesh, N-Body + AMR, etc.). The goals are the following: to provide searching criteria through which a single query can get data from different kinds of simulations archives; to develop appropriate IVOA tools to visualize and analyze the data; finally to make possible an easy comparison between theoretical and observational data. VisIVO has been used to find and visualize N-D boxes data, whereas Aladin has been modified to study the 2-D maps and permit the search for simulated galaxy clusters; we have now also generated a code that creates on-the-fly the profiles of ten quantities of the simulated galaxy clusters produced by the Gadget-2 code which can be easily visualized by TOPCAT. All of these tools can be connected to each other using the PLASTIC hub, a software specifically designed to provide interoperability among astronomical VO applications. This project is being developed as part of the VO-Tech/DS4, ITVO and VObs.it projects.
COOL CORE CLUSTERS FROM COSMOLOGICAL SIMULATIONS
Energy Technology Data Exchange (ETDEWEB)
Rasia, E.; Borgani, S.; Murante, G.; Planelles, S.; Biffi, V.; Granato, G. L. [INAF, Osservatorio Astronomico di Trieste, via Tiepolo 11, I-34131, Trieste (Italy); Beck, A. M.; Steinborn, L. K.; Dolag, K. [Universitäts-Sternwarte München, Scheinerstr.1, D-81679 München (Germany); Ragone-Figueroa, C., E-mail: rasia@oats.inaf.it [Instituto de Astronomá Teórica y Experimental (IATE), Consejo Nacional de Investigaciones Cientiíficas y Técnicas de la República Argentina (CONICET), Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, X5000BGR, Córdoba (Argentina)
2015-11-01
We present results obtained from a set of cosmological hydrodynamic simulations of galaxy clusters, aimed at comparing predictions with observational data on the diversity between cool-core (CC) and non-cool-core (NCC) clusters. Our simulations include the effects of stellar and active galactic nucleus (AGN) feedback and are based on an improved version of the smoothed particle hydrodynamics code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical instabilities by including a suitable artificial thermal diffusion. In this Letter, we focus our analysis on the entropy profiles, the primary diagnostic we used to classify the degree of cool-coreness of clusters, and the iron profiles. In keeping with observations, our simulated clusters display a variety of behaviors in entropy profiles: they range from steadily decreasing profiles at small radii, characteristic of CC systems, to nearly flat core isentropic profiles, characteristic of NCC systems. Using observational criteria to distinguish between the two classes of objects, we find that they occur in similar proportions in both simulations and observations. Furthermore, we also find that simulated CC clusters have profiles of iron abundance that are steeper than those of NCC clusters, which is also in agreement with observational results. We show that the capability of our simulations to generate a realistic CC structure in the cluster population is due to AGN feedback and artificial thermal diffusion: their combined action allows us to naturally distribute the energy extracted from super-massive black holes and to compensate for the radiative losses of low-entropy gas with short cooling time residing in the cluster core.
Machine Learning and Cosmological Simulations II: Hydrodynamical Simulations
Kamdar, Harshil M; Brunner, Robert J
2015-01-01
We extend a machine learning (ML) framework presented previously to model galaxy formation and evolution in a hierarchical universe using N-body + hydrodynamical simulations. In this work, we show that ML is a promising technique to study galaxy formation in the backdrop of a hydrodynamical simulation. We use the Illustris Simulation to train and test various sophisticated machine learning algorithms. By using only essential dark matter halo physical properties and no merger history, our model predicts the gas mass, stellar mass, black hole mass, star formation rate, $g-r$ color, and stellar metallicity fairly robustly. Our results provide a unique and powerful phenomenological framework to explore the galaxy-halo connection that is built upon a solid hydrodynamical simulation. The promising reproduction of the listed galaxy properties demonstrably place ML as a promising and a significantly more computationally efficient tool to study small-scale structure formation. We find that ML mimics a full-blown hydro...
A Monte Carlo Simulation Framework for Testing Cosmological Models
Directory of Open Access Journals (Sweden)
Heymann Y.
2014-10-01
Full Text Available We tested alternative cosmologies using Monte Carlo simulations based on the sam- pling method of the zCosmos galactic survey. The survey encompasses a collection of observable galaxies with respective redshifts that have been obtained for a given spec- troscopic area of the sky. Using a cosmological model, we can convert the redshifts into light-travel times and, by slicing the survey into small redshift buckets, compute a curve of galactic density over time. Because foreground galaxies obstruct the images of more distant galaxies, we simulated the theoretical galactic density curve using an average galactic radius. By comparing the galactic density curves of the simulations with that of the survey, we could assess the cosmologies. We applied the test to the expanding-universe cosmology of de Sitter and to a dichotomous cosmology.
A Parallel Monte Carlo Code for Simulating Collisional N-body Systems
Pattabiraman, Bharath; Liao, Wei-Keng; Choudhary, Alok; Kalogera, Vassiliki; Memik, Gokhan; Rasio, Frederic A
2012-01-01
We present a new parallel code for computing the dynamical evolution of collisional N-body systems with up to N~10^7 particles. Our code is based on the the H\\'enon Monte Carlo method for solving the Fokker-Planck equation, and makes assumptions of spherical symmetry and dynamical equilibrium. The principal algorithmic developments involve optimizing data structures, and the introduction of a parallel random number generation scheme, as well as a parallel sorting algorithm, required to find nearest neighbors for interactions and to compute the gravitational potential. The new algorithms we introduce along with our choice of decomposition scheme minimize communication costs and ensure optimal distribution of data and workload among the processing units. The implementation uses the Message Passing Interface (MPI) library for communication, which makes it portable to many different supercomputing architectures. We validate the code by calculating the evolution of clusters with initial Plummer distribution functi...
Li, Shuo; Liu, F. K.; Berczik, Peter; Spurzem, Rainer
2017-01-01
Supermassive black hole binaries (SMBHBs) are productions of the hierarchical galaxy formation model. There are many close connections between a central SMBH and its host galaxy because the former plays very important roles on galaxy formation and evolution. For this reason, the evolution of SMBHBs in merging galaxies is a fundamental challenge. Since there are many discussions about SMBHB evolution in a gas-rich environment, we focus on the quiescent galaxy, using tidal disruption (TD) as a diagnostic tool. Our study is based on a series of numerical, large particle number, direct N-body simulations for dry major mergers. According to the simulation results, the evolution can be divided into three phases. In phase I, the TD rate for two well separated SMBHs in a merging system is similar to that for a single SMBH in an isolated galaxy. After two SMBHs approach close enough to form a bound binary in phase II, the disruption rate can be enhanced by ∼2 orders of magnitude within a short time. This “boosted” disruption stage finishes after the SMBHB evolves to a compact binary system in phase III, corresponding to a reduction in disruption rate back to a level of a few times higher than in phase I. We also discuss how to correctly extrapolate our N-body simulation results to reality, and the implications of our results to observations.
Baushev, A N; Campusano, L E; Escala, A; Muñoz, R R; Palma, G A
2016-01-01
Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density profiles for galaxy central regions. While simulations suggest a cuspy and universal profile (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by (Baushev, 2015). We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy profile is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. T...
Testing lowered isothermal models with direct N-body simulations of globular clusters
Zocchi, Alice; Hénault-Brunet, Vincent; Varri, Anna Lisa
2016-01-01
Several self-consistent models have been proposed, aiming at describing the phase space distribution of stars in globular clusters. This study explores the ability of the recently proposed LIMEPY models (Gieles & Zocchi) to reproduce the dynamical properties of direct N-body models of a cluster in a tidal field, during its entire evolution. These dynamical models include prescriptions for the truncation and the degree of radially-biased anisotropy contained in the system, allowing us to explore the interplay between the role of anisotropy and tides in various stages of the life of star clusters. We show that the amount of anisotropy in an initially tidally underfilling cluster increases in the pre-collapse phase, and then decreases with time, due to the effect of the external tidal field on its spatial truncation. This is reflected in the correspondent model parameters, and the best-fit models reproduce the main properties of the cluster at all stages of its evolution, except for the phases immediately pr...
Testing lowered isothermal models with direct N-body simulations of globular clusters
Zocchi, Alice; Gieles, Mark; Hénault-Brunet, Vincent; Varri, Anna Lisa
2016-10-01
Several self-consistent models have been proposed, aiming at describing the phase-space distribution of stars in globular clusters. This study explores the ability of the recently proposed LIMEPY models to reproduce the dynamical properties of direct N-body models of a cluster in a tidal field, during its entire evolution. These dynamical models include prescriptions for the truncation and the degree of radially biased anisotropy contained in the system, allowing us to explore the interplay between the role of anisotropy and tides in various stages of the life of star clusters. We show that the amount of anisotropy in an initially tidally underfilling cluster increases in the pre-collapse phase, and then decreases with time, due to the effect of the external tidal field on its spatial truncation. This is reflected in the correspondent model parameters, and the best-fitting models reproduce the main properties of the cluster at all stages of its evolution, except for the phases immediately preceding and following core collapse. We also notice that the best-fitting LIMEPY models are significantly different from isotropic King models, especially in the first part of the evolution of the cluster. Our results put limits on the amount of radial anisotropy that can be expected for clusters evolving in a tidal field, which is important to understand other factors that could give rise to similar observational signatures, such as the presence of an intermediate-mass black hole.
A modified parallel tree code for N-body simulation of the Large Scale Structure of the Universe
Becciani, U
2000-01-01
N-body codes to perform simulations of the origin and evolution of the Large Scale Structure of the Universe have improved significantly over the past decade both in terms of the resolution achieved and of reduction of the CPU time. However, state-of-the-art N-body codes hardly allow one to deal with particle numbers larger than a few 10^7, even on the largest parallel systems. In order to allow simulations with larger resolution, we have first re-considered the grouping strategy as described in Barnes (1990) (hereafter B90) and applied it with some modifications to our WDSH-PT (Work and Data SHaring - Parallel Tree) code. In the first part of this paper we will give a short description of the code adopting the Barnes and Hut algorithm \\cite{barh86} (hereafter BH), and in particular of the memory and work distribution strategy applied to describe the {\\it data distribution} on a CC-NUMA machine like the CRAY-T3E system. In the second part of the paper we describe the modification to the Barnes grouping strate...
Antoniadou, Kyriaki I
2016-01-01
Mounting discoveries of debris discs orbiting newly-formed stars and white dwarfs (WDs) showcase the importance of modeling the long-term evolution of small bodies in exosystems. WD debris discs are in particular thought to form from very long-term (0.1-5.0 Gyr) instability between planets and asteroids. However, the time-consuming nature of $N$-body integrators which accurately simulate motion over Gyrs necessitates a judicious choice of initial conditions. The analytical tools known as \\textit{periodic orbits} can circumvent the guesswork. Here, we begin a comprehensive analysis directly linking periodic orbits with $N$-body integration outcomes with an extensive exploration of the planar circular restricted three-body problem (CRTBP) with an outer planet and inner asteroid near or inside of the $2$:$1$ mean motion resonance. We run nearly 1000 focused simulations for the entire age of the Universe (14 Gyr) with initial conditions mapped to the phase space locations surrounding the unstable and stable perio...
Dindar, Saleh; Juric, Mario; Yeo, Young In; Gao, Jianwei; Boley, Aaron C; Nelson, Benjamin; Peters, Jorg
2012-01-01
We present Swarm-NG, a C++ library for the efficient direct integration of many n-body systems using highly-parallel Graphics Processing Unit (GPU), such as NVIDIA's Tesla T10 and M2070 GPUs. While previous studies have demonstrated the benefit of GPUs for n-body simulations with thousands to millions of bodies, Swarm-NG focuses on many few-body systems, e.g., thousands of systems with 3...15 bodies each, as is typical for the study of planetary systems. Swarm-NG parallelizes the simulation, including both the numerical integration of the equations of motion and the evaluation of forces using NVIDIA's "Compute Unified Device Architecture" (CUDA) on the GPU. Swarm-NG includes optimized implementations of 4th order time-symmetrized Hermite integration and mixed variable symplectic integration, as well as several sample codes for other algorithms to illustrate how non-CUDA-savvy users may themselves introduce customized integrators into the Swarm-NG framework. To optimize performance, we analyze the effect of GP...
The MultiDark Database: Release of the Bolshoi and MultiDark cosmological simulations
Riebe, K.; Partl, A. M.; Enke, H.; Forero-Romero, J.; Gottlöber, S.; Klypin, A.; Lemson, G.; Prada, F.; Primack, J. R.; Steinmetz, M.; Turchaninov, V.
2013-08-01
We present the online {MultiDark Database} - a Virtual Observatory-oriented, relational database for hosting various cosmological simulations. The data is accessible via an SQL (Structured Query Language) query interface, which also allows users to directly pose scientific questions, as shown in a number of examples in this paper. Further examples for the usage of the database are given in its extensive online documentation. The database is based on the same technology as the Millennium Database, a fact that will greatly facilitate the usage of both suites of cosmological simulations. The first release of the {MultiDark Database} hosts two 8.6 billion particle cosmological N-body simulations: the Bolshoi (250 h-1 Mpc simulation box, 1 h-1 kpc resolution) and MultiDark Run1 simulation (MDR1, or BigBolshoi, 1000 h-1 Mpc simulation box, 7 h-1 kpc resolution). The extraction methods for halos/subhalos from the raw simulation data, and how this data is structured in the database are explained in this paper. With the first data release, users get full access to halo/subhalo catalogs, various profiles of the halos at redshifts z=0-15, and raw dark matter data for one time-step of the Bolshoi and four time-steps of the MultiDark simulation. Later releases will also include galaxy mock catalogs and additional merger trees for both simulations as well as new large volume simulations with high resolution. This project is further proof of the viability to store and present complex data using relational database technology. We encourage other simulators to publish their results in a similar manner.
Machine learning and cosmological simulations - II. Hydrodynamical simulations
Kamdar, Harshil M.; Turk, Matthew J.; Brunner, Robert J.
2016-04-01
We extend a machine learning (ML) framework presented previously to model galaxy formation and evolution in a hierarchical universe using N-body + hydrodynamical simulations. In this work, we show that ML is a promising technique to study galaxy formation in the backdrop of a hydrodynamical simulation. We use the Illustris simulation to train and test various sophisticated ML algorithms. By using only essential dark matter halo physical properties and no merger history, our model predicts the gas mass, stellar mass, black hole mass, star formation rate, g - r colour, and stellar metallicity fairly robustly. Our results provide a unique and powerful phenomenological framework to explore the galaxy-halo connection that is built upon a solid hydrodynamical simulation. The promising reproduction of the listed galaxy properties demonstrably place ML as a promising and a significantly more computationally efficient tool to study small-scale structure formation. We find that ML mimics a full-blown hydrodynamical simulation surprisingly well in a computation time of mere minutes. The population of galaxies simulated by ML, while not numerically identical to Illustris, is statistically robust and physically consistent with Illustris galaxies and follows the same fundamental observational constraints. ML offers an intriguing and promising technique to create quick mock galaxy catalogues in the future.
Michikoshi, Shugo; Inutsuka, Shu-ichiro
2010-01-01
We investigate the formation process of planetesimals from the dust layer by the gravitational instability in the gas disk using local $N$-body simulations. The gas is modeled as a background laminar flow. We study the formation process of planetesimals and its dependence on the strength of the gas drag. Our simulation results show that the formation process is divided into three stages qualitatively: the formation of wake-like density structures, the creation of planetesimal seeds, and their collisional growth. The linear analysis of the dissipative gravitational instability shows that the dust layer is secularly unstable although Toomre's $Q$ value is larger than unity. However, in the initial stage, the growth time of the gravitational instability is longer than that of the dust sedimentation and the decrease in the velocity dispersion. Thus, the velocity dispersion decreases and the disk shrinks vertically. As the velocity dispersion becomes sufficiently small, the gravitational instability finally become...
Antoniadou, Kyriaki I.; Veras, Dimitri
2016-09-01
Mounting discoveries of debris discs orbiting newly-formed stars and white dwarfs (WDs) showcase the importance of modeling the long-term evolution of small bodies in exosystems. WD debris discs are in particular thought to form from very long-term (0.1-5.0 Gyr) instability between planets and asteroids. However, the time-consuming nature of N-body integrators which accurately simulate motion over Gyrs necessitates a judicious choice of initial conditions. The analytical tools known as periodic orbits can circumvent the guesswork. Here, we begin a comprehensive analysis directly linking periodic orbits with N-body integration outcomes with an extensive exploration of the planar circular restricted three-body problem (CRTBP) with an outer planet and inner asteroid near or inside of the 2:1 mean motion resonance. We run nearly 1000 focused simulations for the entire age of the Universe (14 Gyr) with initial conditions mapped to the phase space locations surrounding the unstable and stable periodic orbits for that commensurability. In none of our simulations did the planar CRTBP architecture yield a long-timescale (≳ 0.25% of the age of the Universe) asteroid-star collision. The pericentre distance of asteroids which survived beyond this timescale (≈35 Myr) varied by at most about 60%. These results help affirm that collisions occur too quickly to explain WD pollution in the planar CRTBP 2:1 regime, and highlight the need for further periodic orbit studies with the eccentric and inclined TBP architectures and other significant orbital period commensurabilities.
Antoniadou, Kyriaki I.; Veras, Dimitri
2016-12-01
Mounting discoveries of debris discs orbiting newly formed stars and white dwarfs (WDs) showcase the importance of modelling the long-term evolution of small bodies in exosystems. WD debris discs are, in particular, thought to form from very long-term (0.1-5.0 Gyr) instability between planets and asteroids. However, the time-consuming nature of N-body integrators which accurately simulate motion over Gyrs necessitates a judicious choice of initial conditions. The analytical tools known as periodic orbits can circumvent the guesswork. Here, we begin a comprehensive analysis directly linking periodic orbits with N-body integration outcomes with an extensive exploration of the planar circular restricted three-body problem (CRTBP) with an outer planet and inner asteroid near or inside of the 2:1 mean motion resonance. We run nearly 1000 focused simulations for the entire age of the Universe (14 Gyr) with initial conditions mapped to the phase space locations surrounding the unstable and stable periodic orbits for that commensurability. In none of our simulations did the planar CRTBP architecture yield a long-time-scale (≳0.25 per cent of the age of the Universe) asteroid-star collision. The pericentre distance of asteroids which survived beyond this time-scale (≈35 Myr) varied by at most about 60 per cent. These results help affirm that collisions occur too quickly to explain WD pollution in the planar CRTBP 2:1 regime, and highlight the need for further periodic orbit studies with the eccentric and inclined TBP architectures and other significant orbital period commensurabilities.
Baldi, Marco
2016-01-01
Persisting tensions between the cosmological constraints derived from low-redshift probes and the ones obtained from temperature and polarisation anisotropies of the Cosmic Microwave Background -- although not yet providing compelling evidence against the $\\Lambda $CDM model -- seem to consistently indicate a slower growth of density perturbations as compared to the predictions of the standard cosmological scenario. Such behavior is not easily accommodated by the simplest extensions of General Relativity, such as f(R) models, which generically predict an enhanced growth rate. In the present work we present the outcomes of a suite of large N-body simulations carried out in the context of a cosmological model featuring a non-vanishing scattering cross section between the dark matter and the dark energy fields, for two different parameterisations of the dark energy equation of state. Our results indicate that these Dark Scattering models have very mild effects on many observables related to large-scale structure...
Speeding up $N$-body simulations of modified gravity: Chameleon screening models
Bose, Sownak; Barreira, Alexandre; He, Jian-hua; Hellwing, Wojciech A; Koyama, Kazuya; Llinares, Claudio; Zhao, Gong-Bo
2016-01-01
We describe and demonstrate the potential of a new and very efficient method for simulating certain classes of modified gravity theories, such as the widely studied $f(R)$ gravity models. High resolution simulations for such models are currently very slow due to the highly nonlinear partial differential equation that needs to be solved exactly to predict the modified gravitational force. This nonlinearity is partly inherent, but is also exacerbated by the specific numerical algorithm used, which employs a variable redefinition to prevent numerical instabilities. The standard Newton-Gauss-Seidel iterative method used to tackle this problem has a poor convergence rate. Our new method not only avoids this, but also allows the discretised equation to be written in a form that is analytically solvable. We show that this new method greatly improves the performance and efficiency of $f(R)$ simulations. For example, a test simulation with $512^3$ particles in a box of size $512 \\, \\mathrm{Mpc}/h$ is now 5 times faste...
GRAPE-5: A Special-Purpose Computer for N-body Simulation
Kawai, Atsushi; Fukushige, Toshiyuki; Makino, Junichiro; Taiji, Makoto
1999-01-01
We have developed a special-purpose computer for gravitational many-body simulations, GRAPE-5. GRAPE-5 is the successor of GRAPE-3. Both consist of eight custom pipeline chips (G5 chip and GRAPE chip). The difference between GRAPE-5 and GRAPE-3 are: (1) The G5 chip contains two pipelines operating at 80 MHz, while the GRAPE chip had one at 20 MHz. Thus, the calculation speed of the G5 chip and that of GRAPE-5 board are 8 times faster than that of GRAPE chip and GRAPE-3 board. (2) The GRAPE-5 ...
Kay, S T; Aghanim, N; Blanchard, A; Liddle, A R; Puget, J L; Sadat, R; Thomas, P A; Kay, Scott T.; Silva, Antonio C. da; Aghanim, Nabila; Blanchard, Alain; Liddle, Andrew R.; Puget, Jean-Loup; Sadat, Rachida; Thomas, Peter A.
2006-01-01
We present results from a study of the X-ray cluster population that forms within the CLEF cosmological hydrodynamics simulation, a large N-body/SPH simulation of the Lambda CDM cosmology with radiative cooling, star formation and feedback. The scaled projected temperature and entropy profiles at z=0 are in good agreement with recent high-quality observations of cool core clusters, suggesting that the simulation grossly follows the processes that structure the intracluster medium (ICM) in these objects. Cool cores are a ubiquitous phenomenon in the simulation at low and high redshift, regardless of a cluster's dynamical state. This is at odds with the observations and so suggests there is still a heating mechanism missing from the simulation. Using a simple, observable measure of the concentration of the ICM, which correlates with the apparent mass deposition rate in the cluster core, we find a large dispersion within regular clusters at low redshift, but this diminishes at higher redshift, where strong "cool...
Star Formation History of Dwarf Galaxies in Cosmological Hydrodynamic Simulations
Directory of Open Access Journals (Sweden)
Kentaro Nagamine
2010-01-01
Full Text Available We examine the past and current work on the star formation (SF histories of dwarf galaxies in cosmological hydrodynamic simulations. The results obtained from different numerical methods are still somewhat mixed, but the differences are understandable if we consider the numerical and resolution effects. It remains a challenge to simulate the episodic nature of SF history in dwarf galaxies at late times within the cosmological context of a cold dark matter model. More work is needed to solve the mysteries of SF history of dwarf galaxies employing large-scale hydrodynamic simulations on the next generation of supercomputers.
Modelling the dynamics of a hypothetical Planet X by way of gravitational N-body simulator
Cowley, Michael; Hughes, Stephen
2017-03-01
This paper describes a novel activity to model the dynamics of a Jupiter-mass, trans-Neptunian planet of a highly eccentric orbit. Despite a history rooted in modern astronomy, ‘Planet X’, a hypothesised hidden planet lurking in our outer Solar System, has often been touted by conspiracy theorists as the cause of past mass extinction events on Earth, as well as other modern-day doomsday scenarios. Frequently dismissed as pseudoscience by astronomers, these stories continue to draw the attention of the public by provoking mass media coverage. Targeted at junior undergraduate levels, this activity allows students to debunk some of the myths surrounding Planet X by using simulation software to demonstrate that such a large-mass planet with extreme eccentricity would be unable to enter our Solar System unnoticed, let alone maintain a stable orbit.
The Halo Bispectrum in N-body Simulations with non-Gaussian Initial Conditions
Sefusatti, Emiliano; Desjacques, Vincent
2011-01-01
We present measurements of the bispectrum of dark matter halos in numerical simulations with non-Gaussian initial conditions of the local type. We show, in the first place, that the overall effect of primordial non-Gaussianity on the halo bispectrum is larger than on the halo power spectrum when all measurable configurations are taken into account. We then compare our measurements with a tree-level perturbative prediction finding good agreement at large scale when the constant Gaussian bias parameter, both linear and quadratic, and their constant non-Gaussian corrections are fitted for. The best-fit values of the Gaussian bias factors and their non-Gaussian, scale-independent corrections are in qualitative agreement with the peak-background split expectations. In particular, we show that the effect of non-Gaussian initial conditions on squeezed configurations is fairly large (up to 30% for f_NL=100 at redshift z=0.5) and results from contributions of similar amplitude induced by the initial matter bispectrum,...
A Multirate Variable-timestep Algorithm for N-body Solar System Simulations with Collisions
Sharp, P. W.; Newman, W. I.
2016-03-01
We present and analyze the performance of a new algorithm for performing accurate simulations of the solar system when collisions between massive bodies and test particles are permitted. The orbital motion of all bodies at all times is integrated using a high-order variable-timestep explicit Runge-Kutta Nyström (ERKN) method. The variation in the timestep ensures that the orbital motion of test particles on eccentric orbits or close to the Sun is calculated accurately. The test particles are divided into groups and each group is integrated using a different sequence of timesteps, giving a multirate algorithm. The ERKN method uses a high-order continuous approximation to the position and velocity when checking for collisions across a step. We give a summary of the extensive testing of our algorithm. In our largest simulation—that of the Sun, the planets Earth to Neptune and 100,000 test particles over 100 million years—the relative error in the energy after 100 million years was of the order of 10-11.
Distribution function approach to redshift space distortions: N-body simulations
Okumura, Teppei; McDonald, Patrick; Desjacques, Vincent
2011-01-01
Measurement of redshift-space distortions (RSD) offers an attractive method to directly probe the cosmic growth history of density perturbations. A distribution function approach where RSD can be written as a sum over density weighted velocity moment correlators has recently been developed. We use Nbody simulations to investigate the individual contributions and convergence of this expansion for dark matter. If the series is expanded as a function of powers of mu, cosine of the angle between the Fourier mode and line of sight, there are a finite number of terms contributing at each order. We present these terms and investigate their contribution to the total as a function of wavevector k. For mu^2 the correlation between density and momentum dominates on large scales. Higher order corrections, which act as a Finger-of-God (FoG) term, contribute 1% at k~0.015h/Mpc, 10% at k~0.05h/Mpc at z=0, while for k>0.15h/Mpc they dominate and make the total negative. These higher order terms are dominated by density-energ...
Modern Cosmology: Interactive Computer Simulations that use Recent Observational Surveys
Moldenhauer, Jacob; Stone, Keenan; Shuler, Ezekiel
2013-01-01
We present a collection of new, open-source computational tools for numerically modeling recent large-scale observational data sets using modern cosmology theory. Specifically, these tools will allow both students and researchers to constrain the parameter values in competitive cosmological models, thereby discovering both the accelerated expansion of the universe and its composition (e.g., dark matter and dark energy). These programs have several features to help the non-cosmologist build an understanding of cosmological models and their relation to observational data: a built-in collection of several real observational data sets; sliders to vary the values of the parameters that define different cosmological models; real-time plotting of simulated data; and $\\chi^2$ calculations of the goodness of fit for each choice of parameters (theory) and observational data (experiment). The current list of built-in observations includes several recent supernovae Type Ia surveys, baryon acoustic oscillations, the cosmi...
Exponents of non-linear clustering in scale-free one dimensional cosmological simulations
Benhaiem, David; Sicard, François
2012-01-01
One dimensional versions of cosmological N-body simulations have been shown to share many qualitative behaviours of the three dimensional problem. They can resolve a large range of time and length scales, and admit exact numerical integration. We use such models to study how non-linear clustering depends on initial conditions and cosmology. More specifically, we consider a family of models which, like the 3D EdS model, lead for power-law initial conditions to self-similar clustering characterized in the strongly non-linear regime by power-law behaviour of the two point correlation function. We study how the corresponding exponent \\gamma depends on the initial conditions, characterized by the exponent n of the power spectrum of initial fluctuations, and on a single parameter \\kappa controlling the rate of expansion. The space of initial conditions/cosmology divides very clearly into two parts: (1) a region in which \\gamma depends strongly on both n and \\kappa and where it agrees very well with a simple general...
Modified Baryonic Dynamics: two-component cosmological simulations with light sterile neutrinos
Energy Technology Data Exchange (ETDEWEB)
Angus, G.W.; Gentile, G. [Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, 1050 Belgium (Belgium); Diaferio, A. [Dipartimento di Fisica, Università di Torino, Via P. Giuria 1, Torino, I-10125 Italy (Italy); Famaey, B. [Observatoire astronomique de Strasbourg, CNRS UMR 7550, Université de Strasbourg, 11 rue de l' Université, Strasbourg, F-67000 France (France); Heyden, K.J. van der, E-mail: garry.angus@vub.ac.be, E-mail: diaferio@ph.unito.it, E-mail: benoit.famaey@astro.unistra.fr, E-mail: gianfranco.gentile@ugent.be, E-mail: heyden@ast.uct.ac.za [Astrophysics, Cosmology and Gravity Centre, Dept. of Astronomy, University of Cape Town, Private Bag X3, Rondebosch, 7701 South Africa (South Africa)
2014-10-01
In this article we continue to test cosmological models centred on Modified Newtonian Dynamics (MOND) with light sterile neutrinos, which could in principle be a way to solve the fine-tuning problems of the standard model on galaxy scales while preserving successful predictions on larger scales. Due to previous failures of the simple MOND cosmological model, here we test a speculative model where the modified gravitational field is produced only by the baryons and the sterile neutrinos produce a purely Newtonian field (hence Modified Baryonic Dynamics). We use two-component cosmological simulations to separate the baryonic N-body particles from the sterile neutrino ones. The premise is to attenuate the over-production of massive galaxy cluster halos which were prevalent in the original MOND plus light sterile neutrinos scenario. Theoretical issues with such a formulation notwithstanding, the Modified Baryonic Dynamics model fails to produce the correct amplitude for the galaxy cluster mass function for any reasonable value of the primordial power spectrum normalisation.
Simulating the Effect of Non-Linear Mode-Coupling in Cosmological Parameter Estimation
Kiessling, A; Heavens, A F
2011-01-01
Fisher Information Matrix methods are commonly used in cosmology to estimate the accuracy that cosmological parameters can be measured with a given experiment, and to optimise the design of experiments. However, the standard approach usually assumes both data and parameter estimates are Gaussian-distributed. Further, for survey forecasts and optimisation it is usually assumed the power-spectra covariance matrix is diagonal in Fourier-space. But in the low-redshift Universe, non-linear mode-coupling will tend to correlate small-scale power, moving information from lower to higher-order moments of the field. This movement of information will change the predictions of cosmological parameter accuracy. In this paper we quantify this loss of information by comparing naive Gaussian Fisher matrix forecasts with a Maximum Likelihood parameter estimation analysis of a suite of mock weak lensing catalogues derived from N-body simulations, based on the SUNGLASS pipeline, for a 2-D and tomographic shear analysis of a Eucl...
Ultra-Light Axion Dark Matter and its impacts on dark halo structure in $N$-body simulation
Zhang, Jiajun; Cheung, Kingman; Chu, Ming-Chung
2016-01-01
The Ultra-Light Axion (ULA) is a dark matter candidate with mass $\\mathcal{O}(10^{-22})$eV and its de Broglie wavelength is of order kpc. Such an axion, also called the Fuzzy Dark Matter (FDM), thermalizes via the gravitational force and forms a Bose-Einstein condensate. Recent studies suggested that the quantum pressure from the FDM can significantly affect the structure formation in the small scale, thus alleviating the so-called "small-scale crisis". In this paper, we develop a new technique to discretize the quantum pressure and illustrate the interactions among the FDM particles in the $N$-body simulation, which accurately simulates the formation of the dark-matter halo and its inner structure. In a self-gravitationally-bound virialized halo, we find a constant density core, called solitonic core, with size of around 1 kpc, which is consistent with the theoretical prediction. The density distribution outside the core follows a normal CDM prediction described by the Einasto profile. However, the core dens...
Pearson, David William
Many parameters of modern cosmology have been determined to incredible precision at present, including tight constraints on two rather mysterious components of the Universe, dark matter and dark energy. Large Scale structure may be uniquely able to place constraints on both of these components, particularly structures that are loosely gravitationally bound. In such structures, the effects of dark energy's outward push is only slightly less than gravity's inward pull, giving the best chance for detection of dark energy in their dynamics. This work aims to answer whether these structures could potentially serve as a laboratory for studying dark energy, by simulating the dynamics of superclusters both including and excluding its effects. Also, by comparing simulation results with an observational dynamical analysis, dark matter content and possibly the effects of dark energy can be constrained. For this purpose four potentially bound superclusters were identified: the Aquarius, Corona Borealis, Microscopium, and Shapley superclusters. Their dynamics were simulated with N-body software written by the author. It is shown that there is a difference in the line-of-sight velocity dispersions of superclusters depending on whether the effects of dark energy are included or not, but this difference is small enough that it would not be detectable due to observational uncertainties. A new method of supercluster mass estimation, named SCM+FP, is presented, combining knowledge of the dynamics and the spherical collapse model to determine the mass. Also, a new analytical model for the extent of gravitationally bound structure is presented, arising from a simple modification of the spherical collapse model which is supported by simulation results. Further results include the most conclusive evidence to date of extended bound structure in the Corona Borealis supercluster along with evidence that there is extended bound structure in the Shapley supercluster, each with a core of five
Merlin, Emiliano; Grassi, Tommaso; Piovan, Lorenzo; Chiosi, Cesare
2009-01-01
We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on the Smoothed Particle Hydrodynamics algorithm. It includes special features such as adaptive softening lengths with correcting extra-terms, and modern formulations of SPH and artificial viscosity. It is designed to be run in parallel on multiple CPUs to optimize the performance and save computational time. We describe the code in detail, and present the results of a number of standard hydrodynamical tests.
Cosmological structure formation shocks and cosmic rays in hydrodynamical simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences fo...
Bode, P; Bode, Paul; Ostriker, Jeremiah P.
2003-01-01
An improved implementation of an N-body code for simulating collisionless cosmological dynamics is presented. TPM (Tree-Particle-Mesh) combines the PM method on large scales with a tree code to handle particle-particle interactions at small separations. After the global PM forces are calculated, spatially distinct regions above a given density contrast are located; the tree code calculates the gravitational interactions inside these denser objects at higher spatial and temporal resolution. The new implementation includes individual particle time steps within trees, an improved treatment of tidal forces on trees, new criteria for higher force resolution and choice of time step, and parallel treatment of large trees. TPM is compared to P^3M and a tree code (GADGET) and is found to give equivalent results in significantly less time. The implementation is highly portable (requiring a Fortran compiler and MPI) and efficient on parallel machines. The source code can be found at http://astro.princeton.edu/~bode/TPM/
Andrew, Keith; Taylor, Lisa
2013-01-01
Using survey data and numerical LCDM modeling we establish an optimized fit to the generalized Reduced Void Probability Function, RVPF, of Mikjian used to establish a statistical foundation to any physical process associated with hierarchical clustering. We use a numerical N-body cosmological simulation code, GADGET-2, to investigate the sensitivity of the distribution of voids characterized by the RVPF to a general hierarchical reduced void parameter, a. The void parameter is related to the Levy stability index of the distribution and Fischer critical exponent used in clustering models. We numerically simulate the evolution of the universe from a redshift of z=50 to the current epoch at z=0 in order to generate RVPFs. GADGET-2 is an N-body/smoothed particle hydrodynamics, SPH, code that we ran in MPI parallelizable mode on an HPC Beowulf cluster. The numerical data sets are compared to observational data from the Sloan digital sky Survey, SDSS, CfA, the Deep2 Galaxy Redshift Survey, and the 2dF Survey. We fi...
Clues to the 'Magellanic Galaxy' from cosmological simulations
Sales, Laura V.; Navarro, Julio F.; Cooper, Andrew P.; White, Simon D. M.; Frenk, Carlos S.; Helmi, Amina
2011-01-01
We use cosmological simulations from the Aquarius Project to study the orbital history of the Large Magellanic Cloud (LMC) and its potential association with other satellites of the Milky Way (MW). We search for dynamical analogues to the LMC and find a subhalo that matches the LMC position and velo
Mergers and star formation in SPH cosmological simulations
Tissera, P B
1999-01-01
The star formation rate history of galactic objects in hydrodynamical cosmological simulations are analyzed in relation to their merger histories. The findings suggest that massive mergers produce more efficient starbursts and that, depending on the internal structure of the objects, double starbursts could also occur.
Cosmological Simulations of Isotropic Conduction in Galaxy Clusters
Smith, Britton D; Voit, G Mark; Ventimiglia, David; Skillman, Samuel W
2013-01-01
Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of ten galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, but not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the in...
Rubakov, V A
2014-01-01
In these lectures we first concentrate on the cosmological problems which, hopefully, have to do with the new physics to be probed at the LHC: the nature and origin of dark matter and generation of matter-antimatter asymmetry. We give several examples showing the LHC cosmological potential. These are WIMPs as cold dark matter, gravitinos as warm dark matter, and electroweak baryogenesis as a mechanism for generating matter-antimatter asymmetry. In the remaining part of the lectures we discuss the cosmological perturbations as a tool for studying the epoch preceeding the conventional hot stage of the cosmological evolution.
Cervantes-Sodi, B; Park, Changbom; Kim, Juhan
2008-01-01
We use a sample of galaxies from the Sloan Digital Sky Survey (SDSS) to search for correlations between the $\\lambda$ spin parameter and the environment and mass of galaxies. In order to calculate the total value of $\\lambda$ for each observed galaxy, we employed a simple model of the dynamical structure of the galaxies which allows a rough estimate of the value of $\\lambda$ using only readily obtainable observables from the luminous galaxies. Use of a large volume limited sample (upwards of 11,000) allows reliable inferences of mean values and dispersions of $\\lambda$ distributions. We find, in agreement with some N-body cosmological simulations, no significant dependence of $\\lambda$ on the environmental density of the galaxies. For the case of mass, our results show a marked correlation with $\\lambda$, in the sense that low mass galaxies present both higher mean values of $\\lambda$ and associated dispersions, than high mass galaxies. This last direct empirical result, at odds with expectations from N-body ...
The Effect of Corner Modes in the Initial Conditions of Cosmological Simulations
Falck, B; Neyrinck, M C; Wang, J; Szalay, A S
2016-01-01
In view of future high precision large scale structure surveys, it is important to quantify percent and sub-percent level effects in cosmological $N$-body simulations from which theoretical predictions are drawn. One such effect involves the choice of whether to set all modes above the one-dimensional Nyquist frequency, the so-called "corner" modes, to zero in the initial conditions. By comparing simulations with and without these modes, we find that at $z>6$, the difference in the matter power spectrum is large at wavenumbers just below $k_{\\rm{Ny}}$, reducing to below 2% at all scales by $z\\sim 3$. Including corner modes results in a better match between a low-resolution simulation and a high-resolution simulation at wavenumbers around the Nyquist frequency of the low-resolution simulation. The differences in mass functions are 3% for the smallest halos at $z=6$ for the simulation resolution studied here ($m_p \\sim 10^{11}h^{-1}\\,M_{\\odot}$), but we find no significant difference in the stacked profiles of ...
Courbin, F; Revaz, Y; Sluse, D; Faure, C; Tewes, M; Eulaers, E; Koleva, M; Asfandiyarov, I; Dye, S; Magain, P; van Winckel, H; Coles, J; Saha, P; Ibrahimov, M; Meylan, G
2010-01-01
We present accurate time delays for the quadruply imaged quasar HE 0435-1223, from the COSMOGRAIL collaboration. A new way of turning the delays into H0 is proposed, using Nbody realisations of the lensing galaxy. The delays are measured from 575 independent photometric points obtained between January 2004 and March 2010. With 6 years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measure delta_t(BA) = 8.4+/-2.1 days, delta_t(BC) = 7.8+/-0.8 days and delta_t(BD) = -6.5+/-0.7 days. HST NICMOS2 images are deconvolved in order to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. In combination with VLT spectroscopy of the lens, the HST images are used to estimate the baryonic fraction, fb, in the Einstein radius. We measure fb = 0.65+0.13-0.10 if the lensing galaxy has a Kroupa IMF and fb = 0.45+0.04-0.07 if it has a Salpeter IMF. N-body realis...
Limousin, Marceau; Sommer-Larsen, Jesper; Natarajan, Priyamvada; Milvang-Jensen, Bo
2009-05-01
We analyze high-resolution, N-body hydrodynamical simulations of fiducial galaxy clusters to probe tidal stripping of the dark matter subhalos. These simulations include a prescription for star formation allowing us to track the fate of the stellar component as well. We investigate the effect of tidal stripping on cluster galaxies hosted in these dark matter subhalos as a function of projected cluster-centric radius. To quantify the extent of the dark matter halos of cluster galaxies, we introduce the half-mass radius r 1/2 as a diagnostic, and study its evolution with projected cluster-centric distance R as a function of redshift. We find a well-defined trend for (r 1/2, R): the closer the galaxies are to the center of the cluster, the smaller the half-mass radius. Interestingly, this trend is inferred in all redshift frames examined in this work ranging from z = 0 to z = 0.7. At z = 0, galaxy halos in the central regions of clusters are found to be highly truncated, with the most compact half-mass radius of 10 kpc. We also find that r 1/2 depends on luminosity and we present scaling relations of r 1/2 with galaxy luminosity. The corresponding total mass of the cluster galaxies is also found to increase with projected cluster-centric distance and luminosity, but with more scatter than the (r 1/2, R) trend. Comparing the distribution of stellar mass to total mass for cluster galaxies, we find that the dark matter component is preferentially stripped, whereas the stellar component is much less affected by tidal forces. We compare these results with galaxy-galaxy lensing probes of r 1/2 and find qualitative agreement. Future surveys with space-based telescopes such as DUNE and SNAP, that combine wide-field and high-resolution imaging, will be able to probe the predicted (r 1/2, R) relation observationally.
Cosmological MHD simulations of cluster formation with anisotropic thermal conduction
Ruszkowski, M; Bruggen, M; Parrish, I; Oh, S Peng
2010-01-01
(abridged) The ICM has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially. Using cosmological simulations of the Santa Barbara cluster we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and SKA and future X-ray spectroscopic stu...
Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization of gas in virialising structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. Our formalism is applicable both to ordinary non-relativistic thermal gas, and to plasmas composed of CRs and thermal gas. To this end, we derive an analytical solution to the one-dimensional Riemann shock tube problem for a composite plasma of CRs and thermal gas. We apply our methods to study the properties of structure formation shocks in high-resolution hydrodynamic simulations of the LCDM model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers M~2 which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external ...
RAMSES-CH: a new chemodynamical code for cosmological simulations
Few, C. G.; Courty, S.; Gibson, B. K.; Kawata, D.; Calura, F.; Teyssier, R.
2012-07-01
We present a new chemodynamical code -RAMSES-CH- for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code RAMSES, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling and supernova feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si and Fe. We include the contribution of Type Ia and Type II supernovae, in addition to low- and intermediate-mass asymptotic giant branch stars, relaxing the instantaneous recycling approximation. The new chemical evolution modules are highly flexible and portable, lending themselves to ready exploration of variations in the underpinning stellar and nuclear physics. We apply RAMSES-CH to the cosmological simulation of a typical L★ galaxy, demonstrating the successful recovery of the basic empirical constraints regarding [α/Fe]-[Fe/H] and Type Ia/II supernova rates.
RAMSES-CH: A New Chemodynamical Code for Cosmological Simulations
Few, C Gareth; Gibson, Brad K; Kawata, Daisuke; Calura, Francesco; Teyssier, Romain
2012-01-01
We present a new chemodynamical code - Ramses-CH - for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code Ramses, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling, and supernovae feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si, and Fe. We include the contribution of Type Ia and II supernovae, in addition to low- and intermediate-mass asymptotic giant branch stars, relaxing the instantaneous recycling approximation. The new chemical evolution modules are highly flexible and portable, lending themselves to ready exploration of variations in the underpining stellar and nuclear physics. We apply Ramses-CH to the cosmological simulation of a typical L\\star galaxy, demonstrating the successful recovery of the basic empirical constraints regarding, [{\\alpha}/Fe]-[Fe/H] and Type Ia/II supernovae rates.
Implementing the DC Mode in Cosmological Simulations with Supercomoving Variables
Energy Technology Data Exchange (ETDEWEB)
Gnedin, Nickolay Y; Kravtsov, Andrey V; Rudd, Douglas H
2011-06-02
As emphasized by previous studies, proper treatment of the density fluctuation on the fundamental scale of a cosmological simulation volume - the 'DC mode' - is critical for accurate modeling of spatial correlations on scales ~> 10% of simulation box size. We provide further illustration of the effects of the DC mode on the abundance of halos in small boxes and show that it is straightforward to incorporate this mode in cosmological codes that use the 'supercomoving' variables. The equations governing evolution of dark matter and baryons recast with these variables are particularly simple and include the expansion factor, and hence the effect of the DC mode, explicitly only in the Poisson equation.
Cosmological Simulations on a Grid of Computers
Depardon, Benjamin; Desprez, Frédéric; Blaizot, Jérémy; Courtois, Hélène M
2010-01-01
The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in GALICS and MOMAF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling efficiencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values. The computation time needed is so large, that we need to run on a grid of computers. Hence, we model GALICS and MOMAF execution time and output files size, and run the simulation using a grid middleware: DIET. All the complexity of accessing resources, scheduling simulations and managing data is harnessed by DIET and hidden behind a web portal accessible to the users.
Interactive Exploration of Cosmological Dark-Matter Simulation Data.
Scherzinger, Aaron; Brix, Tobias; Drees, Dominik; Volker, Andreas; Radkov, Kiril; Santalidis, Niko; Fieguth, Alexander; Hinrichs, Klaus H
2017-01-01
The winning entry of the 2015 IEEE Scientific Visualization Contest, this article describes a visualization tool for cosmological data resulting from dark-matter simulations. The proposed system helps users explore all aspects of the data at once and receive more detailed information about structures of interest at any time. Moreover, novel methods for visualizing and interactively exploring dark-matter halo substructures are proposed.
RAMSES-CH: A New Chemodynamical Code for Cosmological Simulations
Few, C. Gareth; Courty, Stephanie; Gibson, Brad K.; Kawata, Daisuke; Calura, Francesco; Teyssier, Romain
2012-01-01
We present a new chemodynamical code - Ramses-CH - for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code Ramses, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling, and supernovae feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si, and Fe. We include the contribution of Type Ia and II supernovae, in ad...
RAMSES-CH: a new chemodynamical code for cosmological simulations
Few, C. G.; Courty, S.; Gibson, B. K.; Kawata, D; Calura, F.; Teyssier, R.
2012-01-01
We present a new chemodynamical code -RAMSES-CH- for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code RAMSES, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling and supernova feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si and Fe. We include the contribution of Type Ia and Type II supernovae, in ad...
Cosmological simulations of the high-redshift radio universe
Kawata, Daisuke; Gibson, Brad K.; Windhorst, Rogier A.
2004-01-01
Using self-consistent cosmological simulations of disc galaxy formation, we analyse the 1.4 GHz radio flux from high-redshift progenitors of present-day normal spirals within the context of present-day and planned next-generation observational facilities. We demonstrate that while current radio facilities such as the Very Large Array (VLA) are unlikely to trace these progenitors beyond redshifts z
Simulating Our Cosmological Neighborhood: Mock Catalogs for Velocity Analysis
Kolatt, Tsafrir; Dekel, Avishai; Ganon, Galit; Willick, Jeffrey
1995-01-01
We describe the construction of an N-body simulation that mimics the true velocity and mass-density fields in a box of side 256\\hmpc about the Local Group , and the production of mock catalogs that mimic in detail current catalogs of redshifts and peculiar velocities. Our main purpose is to provide a tool for developing and testing reconstruction methods, but the different components of the method can be used on their own in other applications. The initial conditions are based on the IRAS 1.2...
Cattaneo, A.; Blaizot, J.; Devriendt, J.; Guiderdoni, B.
2005-12-01
This is the first paper of a series on the methods and results of the Active Galactic Nuclei In Cosmological Simulations (AGNICS) project, which incorporates the physics of active galactic nuclei (AGNs) into Galaxies In Cosmological Simulations (GalICS), a galaxy formation model that combines large cosmological N-body simulations of dark matter hierarchical clustering and a semi-analytic approach to the physics of the baryons. The project explores the quasar-galaxy link in a cosmological perspective, in response to growing observational evidence for a close relation between supermassive black holes (SMBHs) and spheroids. The key problems are the quasar fuelling mechanism, the origin of the black hole (BH)-to-bulge mass relation, the causal and chronological link between BH growth and galaxy formation, the properties of quasar hosts and the role of AGN feedback in galaxy formation. This first paper has two goals. The first is to describe the general structure and assumptions that provide the framework for the AGNICS series. The second is to apply AGNICS to studying the joint formation of SMBHs and spheroids in galaxy mergers. We investigate under what conditions this scenario can reproduce the local distribution of SMBHs in nearby galaxies and the evolution of the quasar population. AGNICS contains two star formation modes: a quiescent mode in discs and a starburst mode in proto-spheroids, the latter triggered by mergers and disc instabilities. Here we assume that BH growth is linked to the starburst mode. The simplest version of this scenario, in which the BH accretion rate and the star formation rate in the starburst component are simply related by a constant of proportionality, does not to reproduce the cosmic evolution of the quasar population. A model in which , where ρburst is the density of the gas in the starburst and ζ~= 0.5, can explain the evolution of the quasar luminosity function in B band and X-rays (taking into account the presence of obscured AGNs
Simulating the Nature of Science: Cosmology Distilled
Erickson, Tim
2006-12-01
We will show the latest version of our nature-of-science simulation system, in which students work in groups as researchers to uncover the structure of the (simulated and abstract) universe. They make observations, develop hypotheses, and publish their results. This community of scholars gradually builds up an understanding of their new field of research, as revealed in their journal articles. Along the way, the student-researchers see their hypotheses shattered by new data, and even have to deal with funding issues, since observations are not free. Some teachers are enthusiastic about this as a way to do writing across the curriculum. More important, though, is how experiences like this can help students see how science really works: that it takes teamwork, diverse ideas, and tenacity in addition to plain old smarts. It also helps students distinguish between conjectures that are truly scientific and those that aren't. This work is supported by NSF; we'll show how the system works.
Effects of simulated cosmological magnetic fields on the galaxy population
Marinacci, Federico
2015-01-01
We investigate the effects of varying the intensity of the primordial magnetic seed field on the global properties of the galaxy population in ideal MHD cosmological simulations performed with the moving-mesh code AREPO. We vary the seed field in our calculations in a range of values still compatible with the current cosmological upper limits. We show that above a critical intensity of $\\simeq 10^{-9}\\,{\\rm G}$ the additional pressure arising from the field strongly affects the evolution of gaseous structures, leading to a suppression of the cosmic star formation history. The suppression is stronger for larger seed fields, and directly reflects into a lower galaxy number density at fixed stellar mass and a less massive stellar component at fixed virial mass at all mass scales. These signatures may be used, in addition to the existing methods, to derive tighter constraints on primordial magnetic seed field intensities.
An improved SPH scheme for cosmological simulations
Beck, A M; Arth, A; Remus, R -S; Teklu, A F; Donnert, J M F; Planelles, S; Beck, M C; Foerster, P; Imgrund, M; Dolag, K; Borgani, S
2015-01-01
We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we combine, implement, modify and test a vast majority of SPH improvement techniques in the latest instalment of the GADGET code. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity, which includes a high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and largely improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modi...
Cosmological simulations of Milky Way-sized galaxies
Colin, Pedro; Roca-Fabrega, Santi; Valenzuela, Octavio
2016-01-01
We introduce a new set of eight Milky Way-sized cosmological simulations performed using the AMR code ART + Hydrodynamics in a LCDM cosmology. The set of zoom-in simulations covers present-day virial masses in the 0.83-1.56 x 10^12 msun range and is carried out with our simple but effective deterministic star formation (SF) and ``explosive' stellar feedback prescriptions. The work is focused on showing the goodness of the simulated set of ``field' Milky Way-sized galaxies. Our results are as follows. (a) The circular velocity curves of our simulated galaxies are nearly flat. (b) Runs ending with a significant disk component, for their stellar masses, have V_max, radius, SF rate, gas fraction, and specific angular momentum values consistent with observations of late-type galaxies. (C) The two most spheroid-dominated galaxies formed in halos with late active merger histories, but other run that ends also as spheroid-dominated, never had major mergers. (d) Our simulations are consistent with the empirical stella...
Vittorio, Nicola
2017-01-01
Modern cosmology has changed significantly over the years, from the discovery to the precision measurement era. The data now available provide a wealth of information, mostly consistent with a model where dark matter and dark energy are in a rough proportion of 3:7. The time is right for a fresh new textbook which captures the state-of-the art in cosmology. Written by one of the world's leading cosmologists, this brand new, thoroughly class-tested textbook provides graduate and undergraduate students with coverage of the very latest developments and experimental results in the field. Prof. Nicola Vittorio shows what is meant by precision cosmology, from both theoretical and observational perspectives.
Baldi, Marco; Simpson, Fergus
2017-02-01
Persisting tensions between the cosmological constraints derived from low-redshift probes and the ones obtained from temperature and polarization anisotropies of the cosmic microwave background (CMB) - although not yet providing compelling evidence against the Λcold dark matter model - seem to consistently indicate a slower growth of density perturbations as compared to the predictions of the standard cosmological scenario. Such behaviour is not easily accommodated by the simplest extensions of General Relativity, such as f(R) models, which generically predict an enhanced growth rate. In this work, we present the outcomes of a suite of large N-body simulations carried out in the context of a cosmological model featuring a non-vanishing scattering cross-section between the dark matter and the dark energy fields, for two different parametrizations of the dark energy equation of state. Our results indicate that these dark scattering models have very mild effects on many observables related to large-scale structures formation and evolution, while providing a significant suppression of the amplitude of linear density perturbations and the abundance of massive clusters. Our simulations therefore confirm that these models offer a promising route to alleviate existing tensions between low-redshift measurements and those of the CMB.
How well do cosmological simulations reproduce individual-halo properties?
Trenti, M; Hallman, E J; Skillman, S W; Shull, J M
2010-01-01
Cosmological simulations of galaxy formation often rely on prescriptions for star formation and feedback that depend on halo properties such as halo mass, central over-density, and virial temperature. In this paper we address the convergence of individual halo properties, based on their number of particles N, focusing in particular on the mass of halos near the resolution limit of a simulation. While it has been established that the halo mass function is sampled on average down to N~30 particles, we show that individual halo properties exhibit significant scatter, and some systematic biases, as one approaches the resolution limit. We carry out a series of cosmological simulations using the Gadget2 and Enzo codes with N_p=64^3 to N_p=1024^3 total particles, keeping the same large-scale structure in the simulation box. We consider boxes from l_{box} = 8 Mpc/h to l_{box} = 512 Mpc/h to probe different halo masses and formation redshifts. We cross-identify dark matter halos in boxes at different resolutions and m...
Cosmological simulations of dwarf galaxies with cosmic ray feedback
Chen, Jingjing; Bryan, Greg L.; Salem, Munier
2016-08-01
We perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic rays (CRs) generated by supernovae, including the effect of diffusion. We first look at the effect of varying the uncertain CR parameters by repeatedly simulating a single galaxy. Then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8 to 30 × 1010 M⊙. We find that including CR feedback (with diffusion) consistently leads to disc-dominated systems with relatively flat rotation curves and constant star formation rates. In contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. The CR simulations very well match the observed baryonic Tully-Fisher relation, but have a lower gas fraction than in real systems. We also find that the dark matter cores of the CR feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core.
Cosmological Simulations of Dwarf Galaxies with Cosmic Ray Feedback
Chen, Jingjing; Salem, Munier
2016-01-01
We perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic-rays generated by supernovae, including the effect of diffusion. We first look at the effect of varying the uncertain cosmic ray parameters by repeatedly simulating a single galaxy. Then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8-30 $\\times 10^{10}$ Msun. We find that including cosmic ray feedback (with diffusion) consistently leads to disk dominated systems with relatively flat rotation curves and constant star formation rates. In contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. The CR simulations very well match the observed baryonic Tully-Fisher relation, but have a lower gas fraction than in real systems. We also find that the dark matter cores of the CR feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core.
Cosmological Structure Formation Shocks and Cosmic Rays in Hydrodynamical Simulations
Pfrommer, C.; Springel, V.; Enβlin, T. A.; Jubelgas, M.
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences for our understanding of the spatial distribution of CRs in the large-scale structure. In high resolution simulations of galaxy clusters, we find a low contribution of the averaged CR pressure, due to the small acceleration efficiency of lower Mach numbers of flow shocks inside halos and the softer adiabatic index of CRs. These effects disfavour CRs when a composite of thermal gas and CRs is adiabatically compressed. However, within cool core regions, the CR pressure reaches equipartition with the thermal pressure leading, to a lower effective adiabatic index and thus to an enhanced compressibility of the central intracluster medium. This effect increases the central density and pressure of the cluster, and thus the resulting X-ray emission and the central Sunyaev-Zel'dovich flux decrement. The integrated Sunyaev-Zel'dovich effect, however, is only slightly changed.
Cosmological Markov Chain Monte Carlo simulation with Cmbeasy
Müller, C M
2004-01-01
We introduce a Markov Chain Monte Carlo simulation and data analysis package for the cosmological computation package Cmbeasy. We have taken special care in implementing an adaptive step algorithm for the Markov Chain Monte Carlo in order to improve convergence. Data analysis routines are provided which allow to test models of the Universe against up-to-date measurements of the Cosmic Microwave Background, Supernovae Ia and Large Scale Structure. The observational data is provided with the software for convenient usage. The package is publicly available as part of the Cmbeasy software at www.cmbeasy.org.
Examining subgrid models of supermassive black holes in cosmological simulation
Sutter, P M
2010-01-01
While supermassive black holes (SMBHs) play an important role in galaxy and cluster evolution, at present they can only be included in large-scale cosmological simulation via subgrid techniques. However, these subgrid models have not been studied in a systematic fashion. Using a newly-developed fast, parallel spherical overdensity halo finder built into the simulation code FLASH, we perform a suite of dark matter-only cosmological simulations to study the effects of subgrid model choice on relations between SMBH mass and dark matter halo mass and velocity dispersion. We examine three aspects of SMBH subgrid models: the choice of initial black hole seed mass, the test for merging two black holes, and the frequency of applying the subgrid model. We also examine the role that merging can play in determining the relations, ignoring the complicating effects of SMBH-driven accretion and feedback. We find that the choice of subgrid model can dramatically affect the black hole merger rate, the cosmic SMBH mass densit...
Chon, Sunmyon; Hosokawa, Takashi; Yoshida, Naoki
2016-01-01
Gravitational collapse of a massive primordial gas cloud is thought to be a promising path for the formation of supermassive blackholes in the early universe. We study conditions for the so-called direct collapse (DC) blackhole formation in a fully cosmological context. We combine a semi-analytic model of early galaxy formation with halo merger trees constructed from dark matter $N$-body simulations. We locate a total of 68 possible DC sites in a volume of $20\\;h^{-1}\\;\\mathrm{Mpc}$ on a side. We then perform hydrodynamics simulations for 42 selected halos to study in detail the evolution of the massive clouds within them. We find only two successful cases where the gas clouds rapidly collapse to form stars. In the other cases, gravitational collapse is prevented by the tidal force exerted by a nearby massive halo, which otherwise should serve as a radiation source necessary for DC. Ram pressure stripping disturbs the cloud approaching the source. In many cases, a DC halo and its nearby light source halo merg...
Jeltema, Tesla E; Burns, Jack O; Motl, Patrick M
2007-01-01
We use Enzo, a hybrid Eulerian AMR/N-body code including non-gravitational heating and cooling, to explore the morphology of the X-ray gas in clusters of galaxies and its evolution in current generation cosmological simulations. We employ and compare two observationally motivated structure measures: power ratios and centroid shift. Overall, the structure of our simulated clusters compares remarkably well to low-redshift observations, although some differences remain that may point to incomplete gas physics. We find no dependence on cluster structure in the mass-observable scaling relations, T_X-M and Y_X-M, when using the true cluster masses. However, estimates of the total mass based on the assumption of hydrostatic equilibrium, as assumed in observational studies, are systematically low. We show that the hydrostatic mass bias strongly correlates with cluster structure and, more weakly, with cluster mass. When the hydrostatic masses are used, the mass-observable scaling relations and gas mass fractions depen...
Ševecek, Pavel; Broz, Miroslav; Nesvorny, David; Durda, Daniel D.; Asphaug, Erik; Walsh, Kevin J.; Richardson, Derek C.
2016-10-01
Detailed models of asteroid collisions can yield important constrains for the evolution of the Main Asteroid Belt, but the respective parameter space is large and often unexplored. We thus performed a new set of simulations of asteroidal breakups, i.e. fragmentations of intact targets, subsequent gravitational reaccumulation and formation of small asteroid families, focusing on parent bodies with diameters D = 10 km.Simulations were performed with a smoothed-particle hydrodynamics (SPH) code (Benz & Asphaug 1994), combined with an efficient N-body integrator (Richardson et al. 2000). We assumed a number of projectile sizes, impact velocities and impact angles. The rheology used in the physical model does not include friction nor crushing; this allows for a direct comparison to results of Durda et al. (2007). Resulting size-frequency distributions are significantly different from scaled-down simulations with D = 100 km monolithic targets, although they may be even more different for pre-shattered targets.We derive new parametric relations describing fragment distributions, suitable for Monte-Carlo collisional models. We also characterize velocity fields and angular distributions of fragments, which can be used as initial conditions in N-body simulations of small asteroid families. Finally, we discuss various uncertainties related to SPH simulations.
Self-Consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
Oñorbe, Jose; Lukić, Zarija
2016-01-01
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize, and perhaps more importantly, spuriously heat the IGM, much earlier z ~ 15 than they should. This problem arises because at z > 6, where observational constraints are non-existent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and generate self-consistent photoionization and photoheating rates to model any chosen reionization history. Following this approach, we run a suite of hydrodynamical simulations of different reionization scenarios, and explore the impact of the timing of ...
Evolution of the gas kinematics of galaxies in cosmological simulations
De Rossi, Maria E
2013-01-01
We studied the evolution of the gas kinematics of galaxies by performing hydrodynamical simulations in a cosmological scenario. We paid special attention to the origin of the scatter of the Tully-Fisher relation and the features which could be associated with mergers and interactions. We extended the study by De Rossi et al. (2010) and analysed their whole simulated sample which includes both, gas disc-dominated and spheroid-dominated systems. We found that mergers and interactions can affect the rotation curves directly or indirectly inducing a scatter in the Tully-Fisher Relation larger than the simulated evolution since z=3. In agreement with previous works, kinematical indicators which combine the rotation velocity and dispersion velocity in their definitions lead to a tighter relation. In addition, when we estimated the rotation velocity at the maximum of the rotation curve, we obtained the best proxy for the potential well regardless of morphology.
Modelling neutral hydrogen in galaxies using cosmological hydrodynamical simulations
Duffy, Alan R; Battye, Richard A; Booth, C M; Vecchia, Claudio Dalla; Schaye, Joop
2011-01-01
The characterisation of the atomic and molecular hydrogen content of high-redshift galaxies is a major observational challenge that will be addressed over the coming years with a new generation of radio telescopes. We investigate this important issue by considering the states of hydrogen across a range of structures within high-resolution cosmological hydrodynamical simulations. Additionally, our simulations allow us to investigate the sensitivity of our results to numerical resolution and to sub-grid baryonic physics (especially feedback from supernovae and active galactic nuclei). We find that the most significant uncertainty in modelling the neutral hydrogen distribution arises from our need to model a self-shielding correction in moderate density regions. Future simulations incorporating radiative transfer schemes will be vital to improve on our empirical self-shielding threshold. Irrespective of the exact nature of the threshold we find that while the atomic hydrogen mass function evolves only mildly fro...
A divergence-cleaning scheme for cosmological SPMHD simulations
Stasyszyn, F A; Beck, A M
2012-01-01
In magnetohydrodynamics (MHD), the magnetic field is evolved by the induction equation and coupled to the gas dynamics by the Lorentz force. We perform numerical smoothed particle magnetohydrodynamics (Spmhd) simulations and study the influence of a numerical magnetic divergence. For instabilities arising from divergence B related errors, we find the hyperbolic/parabolic cleaning scheme suggested by Dedner et al. 2002 to give good results and prevent numerical artifacts from growing. Additionally, we demonstrate that certain current Spmhd implementations of magnetic field regularizations give rise to unphysical instabilities in long-time simulations. We also find this effect when employing Euler potentials (divergenceless by definition), which are not able to follow the winding-up process of magnetic field lines properly. Furthermore, we present cosmological simulations of galaxy cluster formation at extremely high resolution including the evolution of magnetic fields. We show synthetic Faraday rotation maps ...
Cosmological simulations of isotropic conduction in galaxy clusters
Energy Technology Data Exchange (ETDEWEB)
Smith, Britton; O' Shea, Brian W.; Voit, G. Mark; Ventimiglia, David [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Skillman, Samuel W., E-mail: smit1685@msu.edu [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Science, University of Colorado, Boulder, CO 80309 (United States)
2013-12-01
Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of 10 galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, though not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density, but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM), instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ∼5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that, despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable, unless its effects are more pronounced in clusters hotter than those we have simulated.
Molecular hydrogen regulated star formation in cosmological SPH simulations
Thompson, Robert; Jaacks, Jason; Choi, Jun-Hwan
2013-01-01
It has been shown observationally that star formation (SF) correlates tightly with the presence of molecular hydrogen (H2). Therefore it would be important to investigate its implication on galaxy formation in a cosmological context. In the present work, we track the H2 mass fraction within our cosmological smoothed particle hydrodynamics (SPH) code GADGET-3 using an equilibrium analytic model by Krumholz et al. This model allows us to regulate the star formation in our simulation by the local abundance of H2 rather than the total cold gas density, and naturally introduce the dependence of star formation on metallicity. We investigate implications of the equilibrium H2-based SF model on galaxy population properties, such as the stellar-to-halo mass ratio (SHMR), baryon fraction, cosmic star formation rate density (SFRD), galaxy specific SFR, galaxy stellar mass functions (GSMF), and Kennicutt-Schmidt (KS) relationship. The advantage of our work over the previous ones is having a large sample of simulated gala...
Disk galaxies with broken luminosity profiles from cosmological simulations
Martínez-Serrano, Francisco J; Doménech-Moral, Mariola; Domínguez-Tenreiro, Rosa
2009-01-01
We simulate the cosmological formation of three disk galaxies using the zoom-in technique and including a detailed treatment of chemical evolution and cooling. The resulting galaxies have a rather high disk-to-total ratio for a cosmological simulation and thin stellar disks. They present a break in the luminosity profile at 3.0 +- 0.5 disk scale lengths, while showing an exponential mass profile without any apparent breaks, in line with recent observational results. Since the stellar mass profile is exponential, only differences in the stellar populations can be the cause of the luminosity break. Although we find a cutoff for the star formation rate imposed by a density threshold in our star formation model, it does not coincide with the luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star formation going on between both radii. The color profiles and the age profiles are "U-shaped", with the minimum for both profiles located approximately at the break radius. The SFR to stellar mass rat...
Energy Technology Data Exchange (ETDEWEB)
Morisseau, Francois [Laboratoire de Physique Corpusculaire de CAEN, ENSICAEN, Universite de Caen Basse-Normandie, UFR des Sciences, 6 bd Marechal Juin, 14050 Caen Cedex (France)
2006-05-15
The Classical N-body Dynamics (CNBD) is dedicated to the simulation of collisions between classical systems. The 2-body interaction used here has the properties of the Van der Waals potential and depends on just a few parameters. This work has two main goals. First, some theoretical approaches assume that the dynamical stage of the collisions plays an important role. Moreover, colliding nuclei are supposed to present a 1. order liquid-gas phase transition. Several signals have been introduced to show this transition. We have searched for two of them: the bimodality of the mass asymmetry and negative heat capacity. We have found them and we give an explanation of their presence in our calculations. Second, we have improved the interaction by adding a Coulomb like potential and by taking into account the stronger proton-neutron interaction in nuclei. Then we have figured out the relations that exist between the parameters of the 2-body interaction and the properties of the systems. These studies allow us to fit the properties of the classical systems to those of the nuclei. In this manuscript the first results of this fit are shown. (author)
Formation of Compact Clusters from High Resolution Hybrid Cosmological Simulations
Richardson, Mark L A; Gray, William J
2013-01-01
The early Universe hosted a large population of small dark matter `minihalos' that were too small to cool and form stars on their own. These existed as static objects around larger galaxies until acted upon by some outside influence. Outflows, which have been observed around a variety of galaxies, can provide this influence in such a way as to collapse, rather than disperse the minihalo gas. Gray & Scannapieco performed an investigation in which idealized spherically-symmetric minihalos were struck by enriched outflows. Here we perform high-resolution cosmological simulations that form realistic minihalos, which we then extract to perform a large suite of simulations of outflow-minihalo interactions including non-equilibrium chemical reactions. In all models, the shocked minihalo forms molecules through non-equilibrium reactions, and then cools to form dense chemically homogenous clumps of star-forming gas. The formation of these high-redshift clusters will be observable with the next generation of telesc...
Cosmological simulations of galaxy formation with cosmic rays
Salem, Munier; Hummels, Cameron
2014-01-01
We investigate the dynamical impact of cosmic rays in cosmological simulations of galaxy formation using adaptive-mesh refinement simulations of a $10^{12}$ solar mass halo. In agreement with previous work, a run with only our standard thermal energy feedback model results in a massive spheroid and unrealistically peaked rotation curves. However, the addition of a simple two-fluid model for cosmic rays drastically changes the morphology of the forming disk. We include an isotropic diffusive term and a source term tied to star formation due to (unresolved) supernova-driven shocks. Over a wide range of diffusion coefficients, the CRs generate thin, extended disks with a significantly more realistic (although still not flat) rotation curve. We find that the diffusion of CRs is key to this process, as they escape dense star forming clumps and drive outflows within the more diffuse ISM.
Viscosity in cosmological simulations of clusters of galaxies
Br"uggen, M
2005-01-01
The physics of the intracluster medium, in particular the values for the thermal conductivity and the viscosity are largely unknown and subject to an ongoing debate. Here, we study the effect of viscosity on the thermal state of the intracluster medium using three-dimensional cosmological simulations of structure formation. It is shown that viscosity, provided it is not too far off from the unmagnetised Spitzer value, has a significant effect on cluster profiles. In particular, it aids in heating the cool cores of clusters. The central cooling time of the most massive clusters in our simulation is increased by more than an order of magnitude. In large clusters, viscous heating may help to establish an entropy floor and to prevent a cooling catastrophe.
The velocity field in MOND cosmology
Candlish, G N
2016-01-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to $\\Lambda$CDM, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard $\\Lambda$CDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAyMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field ...
Churchill, Christopher
2011-10-01
The mammoth challenge for contemporary studies of galaxy formation and evolution are to establish detailed models in the cosmological context in which both the few parsec scale physics within galaxies are self-consistently unified and made consistent with the observed universe of galaxies. They key diagnostics reside with the gas physics, which dictate virtually every aspect of galaxy formation and evolution. The small scale physics includes stellar feedback, gas cooling, heating, and advection and the multiphase interstellar medium; the large scale physics includes intergalactic accretion, local merging, effects of supernovae driven winds, and the development of extended metal-enriched gas halos.Absorption line data have historically proven to be {and shall in the future} virtually the most powerful tool for understanding gas physics on all spatial scales over the majority of the age of the universe- the key to success. Simply stated, absorption lines are one of astronomy's most powerful observational windows on the universe {galaxy formation, galaxy winds, IGM metal enrichment, etc.}. The high quality and vast numbers of absorption line data {obtained with HST and FUSE} probe a broad range of gas structures {ISM, HVCs, halos, IGM} over the full cosmic span when galaxies are actively evolving.We propose to use LCDM hydrodynamic cosmological simulations employing a Eulerian Gasdynamics plus N-body Adaptive Refinement Tree {ART} code to develop and refine our understanding of stellar feedback physics and its role in governing the gas physics that regulates the evolution of galaxies and the IGM. We aim to substantially progress our understanding of all possible gas phases embedded within and extending far from galaxies. Our methodology is to apply a series of quantitative observational constraints from absorption line systems to better understand extended galaxy halos and the influence of the cosmological environment of the simulated galaxies: {1} galaxy halos
Ignat'ev, Yurii
2016-01-01
On the basis of qualitative analysis of the system of differential equations of the standard cosmological model it is shown that in the case of zero cosmological constant this system has a stable center corresponding to zero values of potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has an oscillating character and changes from $-2$ (braking), to $+1$ (acceleration). Average value of the cosmological acceleration is negative and is equal to $-1/2$. Oscillations of the cosmological acceleration happen on the background of rapidly falling Hubble constant. In the case of nonzero value of the cosmological constant depending on its value there are possible three various qualitative behavior typ...
Magnetic fields in cosmological simulations of disk galaxies
Pakmor, R; Springel, V
2013-01-01
Observationally, magnetic fields reach equipartition with thermal energy and cosmic rays in the interstellar medium of disk galaxies such as the Milky Way. However, thus far cosmological simulations of the formation and evolution of galaxies have usually neglected magnetic fields. We employ the moving-mesh code \\textsc{Arepo} to follow for the first time the formation and evolution of a Milky Way-like disk galaxy in its full cosmological context while taking into account magnetic fields. We find that a prescribed tiny magnetic seed field grows exponentially by a small-scale dynamo until it saturates around $z=4$ with a magnetic energy of about $10\\%$ of the kinetic energy in the center of the galaxy's main progenitor halo. By $z=2$, a well-defined gaseous disk forms in which the magnetic field is further amplified by differential rotation, until it saturates at an average field strength of $\\sim 6 \\mu \\mathrm{G}$ in the disk plane. In this phase, the magnetic field is transformed from a chaotic small-scale fi...
Diverse Structural Evolution at z > 1 in Cosmologically Simulated Galaxies
Snyder, Gregory F; Moody, Christopher; Peth, Michael; Freeman, Peter; Ceverino, Daniel; Primack, Joel; Dekel, Avishai
2014-01-01
From mock Hubble Space Telescope images, we quantify non-parametric statistics of galaxy morphology, thereby predicting the emergence of relationships among stellar mass, star formation, and observed rest-frame optical structure at 1 10^10 M_sun contain relatively more disc-dominated light profiles than those with lower mass, reflecting significant disc brightening in some haloes at 1 10^10 M_sun. We analyze a cosmological major merger at z~1.5 and find that the newly proposed MID morphology diagnostics trace later stages while G-M20 trace earlier ones. MID is sensitive also to clumpy star-forming discs. The observability time of typical MID-enhanced events in our simulation sample is less than 100 Myr. A larger sample of cosmological assembly histories may be required to calibrate such diagnostics in the face of their sensitivity to viewing angle, segmentation algorithm, and various phenomena such as clumpy star formation and minor mergers.
Baushev, A. N.
2015-03-01
While N-body simulations suggest a cuspy profile in the centra of the dark matter halos of galaxies, the majority of astronomical observations favor a relatively soft cored density distribution of these regions. The routine method of testing the convergence of N-body simulations (in particular, the negligibility of two-body scattering effect) is to find the conditions under which formed structures is insensitive to numerical parameters. The results obtained with this approach suggest a surprisingly minor role of the particle collisions: the central density profile remains untouched and close to the Navarro-Frenk-White shape, even if the simulation time significantly exceeds the collisional relaxation time τr . In order to check the influence of the unphysical test body collisions we use the Fokker-Planck equation. It turns out that a profile ρ ∝r-β where β ≃ 1 is an attractor: the Fokker-Planck diffusion transforms any reasonable initial distribution into it in a time shorter than τr , and then the cuspy profile should survive much longer than τr , since the Fokker-Planck diffusion is self-compensated if β ≃ 1 . Thus the purely numerical effect of test body scattering may create a stable NFW-like pseudosolution. Moreover, its stability may be mistaken for the simulation convergence. We present analytical estimations for this potential bias effect and call for numerical tests. For that purpose, we suggest a simple test that can be performed as the simulation progresses and would indicate the magnitude of the collisional influence and the veracity of the simulation results.
Evolution of Supermassive Black Holes from Cosmological Simulations
Filloux, Ch; Pacheco, J A de Freitas; Silk, J
2009-01-01
The correlations between the mass of supermassive black holes and properties of their host galaxies are investigated through cosmological simulations. Black holes grow from seeds of 100 solar masses inserted into density peaks present in the redshift range 12-15. Seeds grow essentially by accreting matter from a nuclear disk and also by coalescences resulting from merger episodes. At z=0, our simulations reproduce the black hole mass function and the correlations of the black hole mass both with stellar velocity dispersion and host dark halo mass. Moreover, the evolution of the black hole mass density derived from the present simulations agrees with that derived from the bolometric luminosity function of quasars, indicating that the average accretion history of seeds is adequately reproduced . However, our simulations are unable to form black holes with masses above $10^9 M_{\\odot}$ at $z\\sim 6$, whose existence is inferred from the bright quasars detected by the Sloan survey in this redshift range.
Properties of HI discs in the Auriga cosmological simulations
Marinacci, Federico; Grand, Robert J. J.; Pakmor, Rüdiger; Springel, Volker; Gómez, Facundo A.; Frenk, Carlos S.; White, Simon D. M.
2017-01-01
We analyse the properties of the HI gas distribution in the Auriga project, a set of magnetohydrodynamic cosmological simulations performed with the moving-mesh code AREPO and a physics model for galaxy formation that succeeds in forming realistic late-type galaxies in the 30 Milky Way-sized haloes simulated in this project. We use a simple approach to estimate the neutral hydrogen fraction in our simulation set, which treats low-density and star-forming gas separately, and we explore two different prescriptions to subtract the contribution of molecular hydrogen from the total HI content. The HI gas in the vast majority of the systems forms extended discs although more disturbed morphologies are present. Notwithstanding the general good agreement with observed HI properties - such as radial profiles and the mass-diameter relation - the Auriga galaxies are systematically larger and more gas-rich than typical nearby galaxies. Interestingly, the amount of HI gas outside the disc plane correlates with the star formation rate, consistent with a picture where most of this extra-planar HI gas originates from a fountain-like flow. Our findings are robust with respect to the different assumptions adopted for computing the molecular hydrogen fraction and do not vary significantly over a wide range of numerical resolution. The HI modelling introduced in this paper can be used in future work to build artificial interferometric HI data cubes, allowing an even closer comparison of the gas dynamics in simulated galaxies with observations.
Through Thick and Thin - HI Absorption in Cosmological Simulations
Altay, Gabriel; Schaye, Joop; Crighton, Neil H M; Vecchia, Claudio Dalla
2010-01-01
We investigate the column density distribution function of neutral hydrogen at redshift z = 3 using a cosmological simulation of galaxy formation from the OverWhelmingly Large Simulations (OWLS) project. The base simulation includes gravity, hydrodynamics, star formation, supernovae feedback, stellar winds, chemodynamics, and element-by-element cooling in the presence of a uniform UV background. Self-shielding and formation of molecular hydrogen are treated in post-processing, without introducing any free parameters, using an accurate reverse ray-tracing algorithm and an empirical relation between gas pressure and molecular mass fraction. The simulation reproduces the observed z = 3 abundance of Ly-A forest, Lyman Limit and Damped Ly-A HI absorption systems probed by quasar sight lines over ten orders of magnitude in column density. Self-shielding flattens the column density distribution for NHI > 10^18 cm-2, while the conversion to fully neutral gas and conversion of HI to H2 steepen it around column densiti...
Dust properties of Lyman break galaxies in cosmological simulations
Yajima, Hidenobu; Thompson, Robert; Choi, Jun-Hwan
2013-01-01
Recent observations have indicated the existence of dust in high-redshift galaxies, however, the dust properties in them are still unknown. Here we present theoretical constraints on dust properties in Lyman break galaxies (LBGs) at z=3 by post-processing a cosmological smoothed particle hydrodynamics simulation with radiative transfer calculations. We calculate the dust extinction in 2800 dark matter halos using the metallicity information of individual gas particles in our simulation. We use only bright galaxies with rest-frame UV magnitude M_1700 < -20 mag, and study the dust size, dust-to-metal mass ratio, and dust composition. From the comparison of calculated color excess between B and V-band (i.e., E(B-V)) and the observations, we constrain the typical dust size, and show that the best-fitting dust grain size is ~ 0.05 micron, which is consistent with the results of theoretical dust models for Type-II supernova. Our simulation with the dust extinction effect can naturally reproduce the observed rest...
Properties of HI discs in the Auriga cosmological simulations
Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Gómez, Facundo; Frenk, Carlos; White, Simon
2016-01-01
We analyse the properties of the HI gas distribution in the Auriga project, a set of magnetohydrodynamic cosmological simulations performed with the moving-mesh code AREPO and a physics model for galaxy formation that succeeds in forming realistic late-type galaxies in the 30 Milky Way-sized haloes simulated in this project. We use a simple approach to estimate the neutral hydrogen fraction in our simulation set, which treats low-density and star-forming gas separately, and we explore two different prescriptions to subtract the contribution of molecular hydrogen from the total HI content. The HI gas in the vast majority of the systems forms extended discs although more disturbed morphologies are present. Notwithstanding the general good agreement with observed HI properties -- such as radial profiles and the mass-diameter relation -- the Auriga galaxies are systematically larger and more gas-rich than typical nearby galaxies. Interestingly, the amount of HI gas outside the disc plane correlates with the star ...
Properties of Cosmological Filaments extracted from Eulerian Simulations
Gheller, Claudio; Favre, Jean; Brüggen, Marcus
2015-01-01
Using a new parallel algorithm implemented within the VisIt framework, we analysed large cosmological grid simulations to study the properties of baryons in filaments. The procedure allows us to build large catalogues with up to $\\sim 3 \\cdot 10^4$ filaments per simulated volume and to investigate the properties of cosmic filaments for very large volumes at high resolution (up to $300^3 ~\\rm Mpc^3$ simulated with $2048^3$ cells). We determined scaling relations for the mass, volume, length and temperature of filaments and compared them to those of galaxy clusters. The longest filaments have a total length of about $200 ~\\rm Mpc$ with a mass of several $10^{15} M_{\\odot}$. We also investigated the effects of different gas physics. Radiative cooling significantly modifies the thermal properties of the warm-hot-intergalactic medium of filaments, mainly by lowering their mean temperature via line cooling. On the other hand, powerful feedback from active galactic nuclei in surrounding halos can heat up the gas in ...
N-Body Simulation of the Formation of the Earth-Moon System from a Single Giant Impact
Eiland, Justin C; Hokr, Brett H; Highland, Justin L; Wyatt, Bryant M
2013-01-01
The giant impact hypothesis is the dominant theory of how the Earth-Moon system was formed. Models have been created that can produce a disk of debris with the proper mass and composition to create our Moon. Models have also been created which start with a disk of debris that eventually coalesces into a Moon. To date, no model has been created that produces a stable Earth-Moon system in a single simulation. Here we combine two recently published ideas in this field, along with a new gravity-centered model, and generate such a simulation. In addition, we show how the method can produce a heterogeneous, iron-deficient Moon made of mantle material from both colliding bodies, and a resultant Earth whose equatorial plane is significantly tilted off the ecliptic plane. The accuracy of the simulation adds credence to the theory that our Moon was born from the violent union of two heavenly bodies.
Achieving Convergence in Galaxy Formation Models by Augmenting N-body Merger Trees
Benson, Andrew J; Cole, Shaun
2016-01-01
Accurate modeling of galaxy formation in a hierarchical, cold dark matter universe requires the use of sufficiently high-resolution merger trees to obtain convergence in the predicted properties of galaxies. When semi-analytic galaxy formation models are applied to cosmological N-body simulation merger trees, it is often the case that those trees have insufficient resolution to give converged galaxy properties. We demonstrate a method to augment the resolution of N-body merger trees by grafting in branches of Monte Carlo merger trees with higher resolution, but which are consistent with the pre-existing branches in the N-body tree. We show that this approach leads to converged galaxy properties.
Gerritsen, JPE; Icke, [No Value
1997-01-01
We present numerical simulations of isolated disk galaxies including gas dynamics and star formation. The gas is allowed to cool to 10 K, while heating of the gas is provided by the far-ultraviolet flux of all stars. Stars are allowed to form from the gas according to a Jeans instability criterion:
Gerritsen, JPE; Icke, [No Value
1997-01-01
We present numerical simulations of isolated disk galaxies including gas dynamics and star formation. The gas is allowed to cool to 10 K, while heating of the gas is provided by the far-ultraviolet flux of all stars. Stars are allowed to form from the gas according to a Jeans instability criterion:
Simulating our cosmological neighborhood mock catalogs for velocity analysis
Kolatt, T S; Ganon, G; Willick, J; Kolatt, Tsafrir; Dekel, Avishai; Ganon, Galit; Willick, Jeffrey
1995-01-01
We describe the construction of an N-body simulation that mimics the true velocity and mass-density fields in a box of side 256\\hmpc about the Local Group , and the production of mock catalogs that mimic in detail current catalogs of redshifts and peculiar velocities. Our main purpose is to provide a tool for developing and testing reconstruction methods, but the different components of the method can be used on their own in other applications. The initial conditions are based on the IRAS 1.2Jy redshift survey, assuming that galaxies trace mass and \\Omega=1. A density field smoothed is recovered from the redshift survey, using quasi-linear theory and a power-preserving filter. The corresponding potential field is traced back to the linear regime using the Zel'dovich-Bernoulli equation. Small-scale power is added by means of constrained realization to mimic fluctuations on galactic scales. The gravitating system is evolved forward in time with a PM code of 2\\hmpc resolution. The result reproduces the real dyna...
A High Throughput Workflow Environment for Cosmological Simulations
Erickson, Brandon M S; Evrard, August E; Becker, Matthew R; Busha, Michael T; Kravtsov, Andrey V; Marru, Suresh; Pierce, Marlon; Wechsler, Risa H
2012-01-01
The next generation of wide-area sky surveys offer the power to place extremely precise constraints on cosmological parameters and to test the source of cosmic acceleration. These observational programs will employ multiple techniques based on a variety of statistical signatures of galaxies and large-scale structure. These techniques have sources of systematic error that need to be understood at the percent-level in order to fully leverage the power of next-generation catalogs. Simulations of large-scale structure provide the means to characterize these uncertainties. We are using XSEDE resources to produce multiple synthetic sky surveys of galaxies and large-scale structure in support of science analysis for the Dark Energy Survey. In order to scale up our production to the level of fifty 10^10-particle simulations, we are working to embed production control within the Apache Airavata workflow environment. We explain our methods and report how the workflow has reduced production time by 40% compared to manua...
The Neutral Hydrogen Content of Galaxies in Cosmological Hydrodynamic Simulations
Davé, Romeel; Oppenheimer, Benjamin D; Kollmeier, Juna A; Weinberg, David H
2013-01-01
We examine the global HI properties of galaxies in quarter-billion particle cosmological hydrodynamic simulations, focusing on how our main adjustable physical process, galactic outflows, impacts HI content. In addition to the three outflow models considered in our earlier papers, we present a new one (ezw) motivated by high resolution interstellar medium simulations, in which the scalings of wind speeds and mass loading factors follow those expected for momentum-driven outflows for larger galaxies, and energy-driven outflows for dwarfs (sigma<75 km/s). To obtain predicted HI masses, we employ a simple but effective local correction for particle self-shielding, as well as an observationally-constrained transition from neutral to molecular hydrogen. We find that our ezw model produces an HI mass function whose shape agrees well with observations from the ALFALFA survey, having a low mass end slope of -1.3, while other models agree less well. Outflows critically govern the HI content in low-mass galaxies, wi...
Stellar feedback from HMXBs in cosmological hydrodynamical simulations
Artale, M C; Pellizza, L J
2015-01-01
We explored the role of X-ray binaries composed by a black hole and a massive stellar companion (BHXs) as sources of kinetic feedback by using hydrodynamical cosmological simulations. Following previous results, our BHX model selects low metal-poor stars ($Z = [0,10^{-4}]$) as possible progenitors. The model that better reproduces observations assumes that a $\\sim 20\\%$ fraction of low-metallicity black holes are in binary systems which produce BHXs. These sources are estimated to deposit $\\sim 10^{52}$ erg of kinetic energy per event. With these parameters and in the simulated volume, we find that the energy injected by BHXs represents $\\sim 30\\%$ of the total energy released by SNII and BHX events at redshift $z\\sim7$ and then decreases rapidly as baryons get chemically enriched. Haloes with virial masses smaller than $\\sim 10^{10} \\,M_{\\odot}$ (or $T_{\\rm vir} \\lesssim 10^5 $ K) are the most directly affected ones by BHX feedback. These haloes host galaxies with stellar masses in the range $10^7 - 10^8$ M$...
Clues to the "Magellanic Galaxy" from Cosmological Simulations
Sales, Laura V; Cooper, Andrew P; White, Simon D M; Frenk, Carlos S; Helmi, Amina
2011-01-01
We use cosmological simulations from the Aquarius Project to study the orbital history of the Large Magellanic Cloud (LMC) and its potential association with other satellites of the Milky Way (MW). We search for dynamical analogs to the LMC and find a subhalo that matches the LMC position and velocity at either of its two most recent pericentric passages. This suggests that the LMC is not necessarily on its first approach to the MW, provided that the virial mass of the Milky Way is M_200 ~1.8e12 M_sun. The simulation results yield specific predictions for the position and velocity of systems associated with the LMC prior to infall. If on first approach, most should lie close to the LMC because the Galactic tidal field has not yet had enough time to disperse them. If on second approach, the list of potential associates increases substantially. Interestingly, our analysis rules out an LMC association for Draco and Ursa Minor, two of the dwarf spheroidals suggested by Lynden-Bell & Lynden-Bell to form part o...
Metallicity gradients of disc stars for a cosmologically simulated galaxy
Rahimi, Awat; Kawata, Daisuke; Allende Prieto, Carlos; Brook, Chris B.; Gibson, Brad K.; Kiessling, Alina
2011-08-01
We analyse for the first time the radial abundance gradients of the disc stars of a disc galaxy simulated with our three-dimensional, fully cosmological chemodynamical galaxy evolution code GCD+. We study how [Fe/H], [N/O], [O/Fe], [Mg/Fe] and [Si/Fe] vary with galactocentric radius. For the young stars of the disc, we found a negative slope for [Fe/H] and [N/O] but a positive [O/Fe], [Mg/Fe] and [Si/Fe] slope with radius. By analysing the star formation rate at different radii, we found that the simulated disc contains a greater fraction of young stars in the outer regions, while the old stars tend to be concentrated in the inner parts of the disc. This can explain the positive [α/Fe] gradient as well as the negative [N/O] gradient with radius. This radial trend is a natural outcome of an inside-out formation of the disc, regardless of its size and can thus explain the recently observed positive [α/Fe] gradients in the Milky Way disc open clusters.
Metallicity gradients of disc stars for a cosmologically simulated galaxy
Rahimi, Awat; Prieto, Carlos Allende; Brook, Chris B; Gibson, Brad K; Kiessling, Alina
2011-01-01
We analyse for the first time the radial abundance gradients of the disc stars of a disc galaxy simulated with our three dimensional, fully cosmological chemodynamical galaxy evolution code GCD+. We study how [Fe/H], [N/O], [O/Fe], [Mg/Fe] and [Si/Fe] vary with galactocentric radius. For the young stars of the disc, we found a negative slope for [Fe/H] and [N/O] but a positive [O/Fe], [Mg/Fe] and [Si/Fe] slope with radius. By analysing the star formation rate (SFR) at different radii, we found that the simulated disc contains a greater fraction of young stars in the outer regions, while the old stars tend to be concentrated in the inner parts of the disc. This can explain the positive [alpha/Fe] gradient as well as the negative [N/O] gradient with radius. This radial trend is a natural outcome of an inside-out formation of the disc, regardless of its size and can thus explain the recently observed positive [alpha/Fe] gradients in the Milky Way disc open clusters.
Multi-Scale Initial Conditions For Cosmological Simulations
Energy Technology Data Exchange (ETDEWEB)
Hahn, Oliver; /KIPAC, Menlo Park; Abel, Tom; /KIPAC, Menlo Park /ZAH, Heidelberg /HITS, Heidelberg
2011-11-04
We discuss a new algorithm to generate multi-scale initial conditions with multiple levels of refinements for cosmological 'zoom-in' simulations. The method uses an adaptive convolution of Gaussian white noise with a real-space transfer function kernel together with an adaptive multi-grid Poisson solver to generate displacements and velocities following first- (1LPT) or second-order Lagrangian perturbation theory (2LPT). The new algorithm achieves rms relative errors of the order of 10{sup -4} for displacements and velocities in the refinement region and thus improves in terms of errors by about two orders of magnitude over previous approaches. In addition, errors are localized at coarse-fine boundaries and do not suffer from Fourier-space-induced interference ringing. An optional hybrid multi-grid and Fast Fourier Transform (FFT) based scheme is introduced which has identical Fourier-space behaviour as traditional approaches. Using a suite of re-simulations of a galaxy cluster halo our real-space-based approach is found to reproduce correlation functions, density profiles, key halo properties and subhalo abundances with per cent level accuracy. Finally, we generalize our approach for two-component baryon and dark-matter simulations and demonstrate that the power spectrum evolution is in excellent agreement with linear perturbation theory. For initial baryon density fields, it is suggested to use the local Lagrangian approximation in order to generate a density field for mesh-based codes that is consistent with the Lagrangian perturbation theory instead of the current practice of using the Eulerian linearly scaled densities.
Parallel Time-Space Processing Model Based Fast N-body Simulation%并行时空处理模型下的快速N-body算法
Institute of Scientific and Technical Information of China (English)
王伟; 曾栩鸿; 王福焕; 傅丽丽; 曾国荪
2011-01-01
图形处理器(graphic processing unit,GPU)的最新发展已经能够以低廉的成本提供高性能的通用计算.基于GPU的CUDA (compute unified device architecture)和OpenCL (open computing language)编程模型为程序员提供了充足的类似于C语言的应用程序接口(application programming interface,API),便于程序员发挥GPU的并行计算能力.采用图形硬件进行加速计算,通过一种新的GPU处理模型—并行时间空间模型,对现有GPU上的N-body实现进行了分析,从而提出了一种新的GPU上快速仿真N-body问题的算法,并在AMD的HD Radeon 5850上进行了实现.实验结果表明,相对于CPU上的实现,获得了400倍左右的加速；相对于已有GPU上的实现,也获得了2至5倍的加速.%With the development of graphic processing unit (GPU), the general processing with high performance can be achieved with low cost. The GPU based compute unified device architecture (CUDA) and open computing language (OpenCL) programming model provide adequate application programming interfaces (APIs) similar to C language, which can be utilized by programmer with the power of GPU parallel processing. This paper presents a novel parallel implementation algorithm of N-body gravitational simulation on GPU. The algorithm uses graphics hardware to accelerate computation, and is optimized to N-body computation based on parallel time-space processing model (PTPM) on GPUs. The paper also analyzes the current implementations of GPU, and gives a new method on implementing N-body algorithm on HD Radeon 5850 GPU of AMD. Experimental results show that this method achieves an acceleration of 400 times compared with CPU, and an acceleration up to 2-5 times compared with GPU.
Time Evolution of Galaxy Scaling Relations in Cosmological Simulations
Taylor, Philip
2016-01-01
We predict the evolution of galaxy scaling relationships from cosmological, hydrodynamical simulations, that reproduce the scaling relations of present-day galaxies. Although we do not assume co-evolution between galaxies and black holes a priori, we are able to reproduce the black hole mass--velocity dispersion relation. This relation does not evolve, and black holes actually grow along the relation from significantly less massive seeds than have previously been used. AGN feedback does not very much affect the chemical evolution of our galaxies. In our predictions, the stellar mass--metallicity relation does not change its shape, but the metallicity significantly increases from $z\\sim2$ to $z\\sim1$, while the gas-phase mass-metallicity relation does change shape, having a steeper slope at higher redshifts ($z\\lesssim3$). Furthermore, AGN feedback is required to reproduce observations of the most massive galaxies at $z\\lesssim1$, specifically their positions on the star formation main sequence and galaxy mass...
Galactic Winds in Cosmological Simulations of the Circumgalactic Medium
Barai, Paramita; Borgani, Stefano; Tescari, Edoardo; Tornatore, Luca; Dolag, Klaus; Killedar, Madhura; Monaco, Pierluigi; D'Odorico, Valentina; Cristiani, Stefano
2012-01-01
(Abridged) We explore new observationally-constrained sub-resolution models of galactic outflows and investigate their impact on the circumgalactic medium (CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic simulations, including star formation, chemical enrichment, and four cases of SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind (CW), a radially varying wind (RVWa) where the outflow velocity has a positive correlation with galactocentric distance (r), and a RVW with additional dependence on halo mass (RVWb). Overall, we find that the outflows expel metal-enriched gas away from galaxies, significantly quench star formation, and enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy centers are most sensitive to the choice of the wind model for halo masses (10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case, except that it substantially enriches the CGM: the carbon metallicity (Z_C) is 10 times higher in RVWb than in N...
Barred galaxies in the EAGLE cosmological hydrodynamical simulation
Algorry, David G; Abadi, Mario G; Sales, Laura V; Bower, Richard G; Crain, Robert A; Vecchia, Claudio Dalla; Frenk, Carlos S; Schaller, Matthieu; Schaye, Joop; Theuns, Tom
2016-01-01
We examine the properties of barred disc galaxies in a LCDM cosmological hydrodynamical simulation from the EAGLE project. Our study follows the formation of 269 discs identified at z = 0 in the stellar mass range 10.6 < log Mstr /M < 11. These discs show a wide range of bar strengths, from unbarred discs to weak bars to strongly barred systems (= 20%). Bars in these systems develop after redshift = 1.3, on timescales that depend sen- sitively on the strength of the pattern. Strong bars develop relatively quickly (in a few Gyr, = 10 disc rotation periods) in systems that are disc dominated, gas poor, and have declining rotation curves. Weak bars develop more slowly in systems where the disc is less gravitation- ally important, and are still growing at z = 0. Unbarred galaxies are comparatively gas-rich discs whose rotation speeds do not exceed the maximum circular velocity of the halos they inhabit. Bar lengths compare favourably with observations, ranging from 0.2 to 0.8 times the radius containing 90%...
How Galaxies Become Red: Insights from Cosmological Simulations
Cen, Renyue
2013-01-01
An analysis of more than 3000 galaxies resolved at better than 114pc/h at z=0.62 in a LAOZI cosmological adaptive mesh refinement hydrodynamic simulation is performed and insights gained on quenching and color migration. The vast majority of red galaxies are found to be within three virial radii of a larger galaxy, at the onset of quenching. We shall thus call this mechanism ``environment quenching", which encompasses satellite quenching. Two physical processes are largely responsible: ram-pressure stripping first disconnects the galaxy from the cold gas supply on large scales, followed by a longer period of cold gas starvation taking place in high velocity dispersion environment, during the early part of which the existing dense cold gas in the central region (=<10kpc) is consumed by in situ star formation. Quenching is found to be more efficient but not faster, on average, in denser environment. Throughout quenching galaxies follow nearly vertical tracks in the color-stellar-mass diagram. In contrast, in...
EMMA: an AMR cosmological simulation code with radiative transfer
Aubert, Dominique; Ocvirk, Pierre
2015-01-01
EMMA is a cosmological simulation code aimed at investigating the reionization epoch. It handles simultaneously collisionless and gas dynamics, as well as radiative transfer physics using a moment-based description with the M1 approximation. Field quantities are stored and computed on an adaptive 3D mesh and the spatial resolution can be dynamically modified based on physically-motivated criteria. Physical processes can be coupled at all spatial and temporal scales. We also introduce a new and optional approximation to handle radiation : the light is transported at the resolution of the non-refined grid and only once the dynamics have been fully updated, whereas thermo-chemical processes are still tracked on the refined elements. Such an approximation reduces the overheads induced by the treatment of radiation physics. A suite of standard tests are presented and passed by EMMA, providing a validation for its future use in studies of the reionization epoch. The code is parallel and is able to use graphics proc...
Tanikawa, Ataru; Yoshikawa, Kohji; Okamoto, Takashi; Nitadori, Keigo
2012-02-01
We present a high-performance N-body code for self-gravitating collisional systems accelerated with the aid of a new SIMD instruction set extension of the x86 architecture: Advanced Vector eXtensions (AVX), an enhanced version of the Streaming SIMD Extensions (SSE). With one processor core of Intel Core i7-2600 processor (8 MB cache and 3.40 GHz) based on Sandy Bridge micro-architecture, we implemented a fourth-order Hermite scheme with individual timestep scheme ( Makino and Aarseth, 1992), and achieved the performance of ˜20 giga floating point number operations per second (GFLOPS) for double-precision accuracy, which is two times and five times higher than that of the previously developed code implemented with the SSE instructions ( Nitadori et al., 2006b), and that of a code implemented without any explicit use of SIMD instructions with the same processor core, respectively. We have parallelized the code by using so-called NINJA scheme ( Nitadori et al., 2006a), and achieved ˜90 GFLOPS for a system containing more than N = 8192 particles with 8 MPI processes on four cores. We expect to achieve about 10 tera FLOPS (TFLOPS) for a self-gravitating collisional system with N ˜ 10 5 on massively parallel systems with at most 800 cores with Sandy Bridge micro-architecture. This performance will be comparable to that of Graphic Processing Unit (GPU) cluster systems, such as the one with about 200 Tesla C1070 GPUs ( Spurzem et al., 2010). This paper offers an alternative to collisional N-body simulations with GRAPEs and GPUs.
Cosmological Shocks in Eulerian Simulations: Main Properties and Cosmic Rays Acceleration
Vazza, F; Gheller, C
2008-01-01
Aims: morpholgies, number and energy distributions of Cosmological Shock Waves from a set of ENZO cosmological simulations are produced, along with a study of the connection with Cosmic Rays processes in different environments. Method: we perform cosmological simulations with the public release of the PPM code ENZO, adopt a simple and physically motivated numerical setup to follow the evolution of cosmic structures at the resolution of 125kpc per cell, and characterise shocks with a new post processing scheme. Results: we estimate the efficency of the acceleration of Cosmic Ray particles and present the first comparison of our results with existing limits from observations of galaxy clusters.
Concordance cosmology without dark energy
Rácz, Gábor; Beck, Róbert; Szapudi, István; Csabai, István
2016-01-01
According to the general relativistic Birkhoff's theorem, spherically symmetric regions in an isotropic universe behave like mini-universes with their own cosmological parameters. We estimate local expansion rates for a large number of such regions, and use the volume-averaged increment of the scale parameter at each time step in an otherwise standard cosmological $N$-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical backreaction calculation. We show that a volume-averaged simulation with the $\\Omega_m=1$ Einstein--de~Sitter setting in each region closely tracks the expansion and structure growth history of a $\\Lambda$CDM cosmology, and confirm the numerical results with analytic calculations as well. The very similar expansion history guarantees consistency with the concordance model and, due to the small but characte...
The Impact of Simulations in Cosmology and Galaxy Formation A summary of the Workshop NOVICOSMO 2008
Salucci, Paolo; Frenk, Carlos; Moscardini, Lauro; Viel, Matteo
2008-01-01
In the study of the process of cosmic structure formation numerical simulations are crucial tools to interface observational data to theoretical models and to investigate issues otherwise unexplored. Enormous advances have been achieved in the last years thanks to the availability of sophisticated codes, now allowing to tackle the problem of cosmic structure formation and subsequent evolution by covering larger and larger dynamical ranges. Moreover, computational cosmology is the ideal interpretative framework for the overwhelming amount of new data from extragalactic surveys and from large sample of individual objects. The Workshop Novicosmo 2008 "The Impact of Simulations in Cosmology and Galaxy Formation' held in SISSA was aimed at providing the state-of-the-art on the latest numerical simulations in Cosmology and in Galaxy Formation. Particular emphasis was given to the implementation of new physical processes in simulation codes, to the comparison between different codes and numerical schemes and how to ...
Semi-Analytic Galaxy Formation in Massive Neutrinos Cosmologies
Fontanot, Fabio; Bianchi, Davide; Viel, Matteo
2014-01-01
The present constraints on neutrino masses led to the revision of their cosmological role, as the presence of a cosmological neutrino background is a clear prediction of the current standard cosmological models. In this paper, we extend the study of the impact of such background on the spatial distribution of both Dark Matter (DM) and galaxies in the Universe, by coupling N-body numerical simulations with semi-analytic models (SAMs) of galaxy formation. Starting from the same initial conditions, massive neutrino cosmologies predict a slower evolution of DM perturbations with respect to the corresponding LCDM cosmology and a suppression on the matter power spectrum on small and intermediate scales. The resulting statistical properties of model galaxies reflect the different growth of the Large Scale Structure, but we explicitly show that most of the deviations from a LCDM realisation are due to the different $\\sigma_8$ associated with the massive neutrino cosmologies. We thus conclude that an independent estim...
Stasyszyn, F; Dolag, K; Beck, R; Donnert, J
2010-01-01
Using cosmological MHD simulations of the magnetic field in galaxy clusters and filaments we evaluate the possibility to infer the magnetic field strength in filaments by measuring cross-correlation functions between Faraday Rotation Measures (RM) and the galaxy density field. We also test the reliability of recent estimates considering the problem of data quality and Galactic foreground (GF) removal in current datasets. Besides the two self-consistent simulations of cosmological magnetic fields based on primordial seed fields and galactic outflows analyzed here, we also explore a larger range of models scaling up the resulting magnetic fields of one of the simulations. We find that, if an unnormalized estimator for the cross-correlation functions and a GF removal procedure is used, the detectability of the cosmological signal is only possible for future instruments (e.g. SKA and ASKAP). However, mapping of the observed RM signal to the underlying magnetization of the Universe (both in space and time) is an e...
High Performance P3M N-body code: CUBEP3M
Harnois-Deraps, Joachim; Iliev, Ilian T; Merz, Hugh; Emberson, J D; Desjacques, Vincent
2012-01-01
This paper presents CUBEP3M, a high performance, publicly-available, cosmological N-body code and describes many utilities and extensions that have been added to the standard package, including a runtime halo finder, a non-Gaussian initial conditions generator, a tuneable accuracy, and a system of unique particle identification. CUBEP3M is fast, has a memory imprint up to three times lower than other widely used N-body codes, and has been run on up to 20,000 cores, achieving close to ideal weak scaling even at this problem size. It is well suited and has already been used for a broad number of science applications that require either large samples of non-linear realizations or very large dark matter N-body simulations, including cosmological reionization, baryonic acoustic oscillations, weak lensing or non-Gaussian statistics. We discuss the structure, the accuracy, any known systematic effects, and the scaling performance of the code and its utilities, when applicable.
Holley-Bockelmann, Kelly; Dunn, Glenna; Bellovary, Jillian M.; Christensen, Charlotte
2016-01-01
Luminous quasars detected at redshifts z > 6 require that the first black holes form early and grow to ~109 solar masses within one Gyr. Our work uses cosmological simulations to study the formation and early growth of direct collapse black holes. In the pre-reionization epoch, molecular hydrogen (H2) causes gas to fragment and form Population III stars, but Lyman-Werner radiation can suppress H2 formation and allow gas to collapse directly into a massive black hole. The critical flux required to inhibit H2 formation, Jcrit, is hotly debated, largely due to the uncertainties in the source radiation spectrum, H2 self-shielding, and collisional dissociation rates. Here, we test the power of the direct collapse model in a non-uniform Lyman-Werner radiation field, using an updated version of the SPH+N-body tree code Gasoline with H2 non-equilibrium abundance tracking, H2 cooling, and a modern SPH implementation. We vary Jcrit from 30 to 104 J21 to study the effect on seed black holes, focusing on black hole formation as a function of environment, halo mass, metallicity, and proximity of the Lyman-Werner source. We discuss the constraints on massive black hole occupation fraction in the quasar epoch, and implications for reionization, high-redshift X-ray background radiation, and gravitational waves.
The formation of disc galaxies in high resolution moving-mesh cosmological simulations
Marinacci, Federico; Springel, Volker
2013-01-01
We present cosmological hydrodynamical simulations of eight Milky Way-sized haloes that have been previously studied with dark matter only in the Aquarius project. For the first time, we employ the moving-mesh code AREPO in zoom simulations combined with a new comprehensive model for galaxy formation physics designed for large cosmological simulations. Our simulations form in most of the eight haloes strongly disc-dominated systems with realistic rotation curves, close to exponential surface density profiles, a stellar-mass to halo-mass ratio that matches expectations from abundance matching techniques, and galaxy sizes and ages consistent with expectations from large galaxy surveys in the local Universe. There is no evidence for any dark matter core formation in our simulations, even so they include repeated baryonic outflows by supernova-driven winds and black hole quasar feedback. The simulations significantly improve upon the results obtained for the same objects in some of the earlier work based on the S...
The BAHAMAS project: Calibrated hydrodynamical simulations for large-scale structure cosmology
McCarthy, Ian G; Bird, Simeon; Brun, Amandine M C Le
2016-01-01
The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterise the dark matter, dark energy, and other aspects of our cosmological framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here we construct a new suite of large-volume cosmological hydrodynamical simulations (called BAHAMAS, for BAryons and HAloes of MAssive Systems) where subgrid models of stellar and Active Galactic Nucleus (AGN) feedback have been calibrated to reproduce the present...
Qualitative Analysis and Numerical Simulation of Equations of the Standard Cosmological Model
Ignat'ev, Yurii
2016-01-01
On the basis of qualitative theory of differential equations it is shown that dynamic system based on the system of Einstein - Klein - Gordon equations with regard to Friedman Universe has a stable center corresponding to zero values of scalar potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has a microscopic oscillating character ($T\\sim 2\\pi mt$), while macroscopic value of the cosmological acceleration varies from $+1$ at inflation stage after which if decreases fast to $-1/2$ (non-relativistic stage), and then slowly tends to $-1$ (ultrarelativistic stage).
N-body Merger Trees and Halo Properties
Jiang, Lilian; Cole, Shaun; Frenk, Carlos S
2013-01-01
We present the Dhalo algorithm which analyses a series of cosmological N-body simulation snapshots to define a self-consistent set of dark matter haloes and merger trees describing their evolution. The advantage over the more common FoF haloes is that the Dhalo algorithm maintains as distinct haloes objects that can be prematurely linked into a single FoF group by tenuous bridges of particles or by the onset of the overlap of their outer diffuse haloes. It is important to understand the properties of the haloes defined by this new algorithm to ensure the assumptions made in galform are consistent with the simulation. We generate FoF and Dhalo catalogues for the Millennium Simulation II and compare their properties. About 90% of the Dhaloes have a bijective match with a FoF halo. The remaining 10% are typically secondary components of large FoF haloes. While a significant fraction FoF haloes are split into more than one Dhalo we find that there is little difference in their overall halo mass functions. Compare...
Zooming in on major mergers: dense, starbursting gas in cosmological simulations
Sparre, Martin; Springel, Volker
2016-11-01
We introduce the `Illustris zoom simulation project', which allows the study of selected galaxies forming in the Λcold dark matter (ΛCDM) cosmology with a 40 times better mass resolution than in the parent large-scale hydrodynamical Illustris simulation. We here focus on the starburst properties of the gas in four cosmological simulations of major mergers. The galaxies in our high-resolution zoom runs exhibit a bursty mode of star formation with gas consumption time-scales 10 times shorter than for the normal star formation mode. The strong bursts are only present in the simulations with the highest resolution, hinting that a too low resolution is the reason why the original Illustris simulation showed a dearth of starburst galaxies. Very pronounced bursts of star formation occur in two out of four major mergers we study. The high star formation rates, the short gas consumption time-scales and the morphology of these systems strongly resemble observed nuclear starbursts. This is the first time that a sample of major mergers is studied through self-consistent cosmological hydrodynamical simulations instead of using isolated galaxy models setup on a collision course. We also study the orbits of the colliding galaxies and find that the starbursting gas preferentially appears in head-on mergers with very high collision velocities. Encounters with large impact parameters do typically not lead to the formation of starbursting gas.
Comparisons of Cosmological MHD Galaxy Cluster Simulations to Radio Observations
Xu, Hao; Murgia, Matteo; Li, Hui; Collins, David C; Norman, Michael L; Cen, Renyue; Feretti, Luigina; Giovannini, Gabriele
2012-01-01
Radio observations of galaxy clusters show that there are $\\mu$G magnetic fields permeating the intra-cluster medium (ICM), but it is hard to accurately constrain the strength and structure of the magnetic fields without the help of advanced computer simulations. We present qualitative comparisons of synthetic VLA observations of simulated galaxy clusters to radio observations of Faraday Rotation Measure (RM) and radio halos. The cluster formation is modeled using adaptive mesh refinement (AMR) magneto-hydrodynamic (MHD) simulations with the assumption that the initial magnetic fields are injected into the ICM by active galactic nuclei (AGNs) at high redshift. In addition to simulated clusters in Xu et al. (2010, 2011), we present a new simulation with magnetic field injections from multiple AGNs. We find that the cluster with multiple injection sources is magnetized to a similar level as in previous simulations with a single AGN. The RM profiles from simulated clusters, both $|RM|$ and the dispersion of RM (...
Cosmological perturbations beyond linear order
CERN. Geneva
2013-01-01
Cosmological perturbation theory is the standard tool to understand the formation of the large scale structure in the Universe. However, its degree of applicability is limited by the growth of the amplitude of the matter perturbations with time. This problem can be tackled with by using N-body simulations or analytical techniques that go beyond the linear calculation. In my talk, I'll summarise some recent efforts in the latter that ameliorate the bad convergence of the standard perturbative expansion. The new techniques allow better analytical control on observables (as the matter power spectrum) over scales very relevant to understand the expansion history and formation of structure in the Universe.
Concordance cosmology without dark energy
Rácz, Gábor; Dobos, László; Beck, Róbert; Szapudi, István; Csabai, István
2017-07-01
According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution of structure on the expansion rate. Using our algorithm, a simulation with an initial Ωm = 1 Einstein-de Sitter setting closely tracks the expansion and structure growth history of the Λ cold dark matter (ΛCDM) cosmology. Due to small but characteristic differences, our model can be distinguished from the ΛCDM model by future precision observations. Moreover, our model can resolve the emerging tension between local Hubble constant measurements and the Planck best-fitting cosmology. Further improvements to the simulation are necessary to investigate light propagation and confirm full consistency with cosmic microwave background observations.
SPOKES: an End-to-End Simulation Facility for Spectroscopic Cosmological Surveys
Nord, B; Refregier, A; Gamper, La; Gamper, Lu; Hambrecht, B; Chang, C; Forero-Romero, J E; Serrano, S; Cunha, C; Coles, O; Nicola, A; Busha, M; Bauer, A; Saunders, W; Jouvel, S; Kirk, D; Wechsler, R
2016-01-01
The nature of dark matter, dark energy and large-scale gravity pose some of the most pressing questions in cosmology today. These fundamental questions require highly precise measurements, and a number of wide-field spectroscopic survey instruments are being designed to meet this requirement. A key component in these experiments is the development of a simulation tool to forecast science performance, define requirement flow-downs, optimize implementation, demonstrate feasibility, and prepare for exploitation. We present SPOKES (SPectrOscopic KEn Simulation), an end-to-end simulation facility for spectroscopic cosmological surveys designed to address this challenge. SPOKES is based on an integrated infrastructure, modular function organization, coherent data handling and fast data access. These key features allow reproducibility of pipeline runs, enable ease of use and provide flexibility to update functions within the pipeline. The cyclic nature of the pipeline offers the possibility to make the science outpu...
Evolution of cosmic filaments and of their galaxy population from MHD cosmological simulations
Gheller, Claudio; Brueggen, Marcus; Alpaslan, Mehmet; Holwerda, Benne Willem; Hopkins, Andrew; Liske, Jochen
2016-01-01
Despite containing about a half of the total matter in the Universe, at most wavelengths the filamentary structure of the cosmic web is difficult to observe. In this work, we use large unigrid cosmological simulations to investigate how the geometrical, thermodynamical and magnetic properties of cosmological filaments vary with mass and redshift (z $\\leq 1$). We find that the average temperature, length, volume and magnetic field of filaments are tightly log-log correlated with the underlying total gravitational mass. This reflects the role of self-gravity in shaping their properties and enables statistical predictions of their observational properties based on their mass. We also focus on the properties of the simulated population of galaxy-sized halos within filaments, and compare their properties to the results obtained from the spectroscopic GAMA survey. Simulated and observed filaments with the same length are found to contain an equal number of galaxies, with very similar distribution of halo masses. Th...
Tremmel, Michael; Governato, Fabio; Volonteri, Marta; Quinn, Tom; Pontzen, Andrew; Anderson, Lauren
2016-01-01
We present a novel implementation of supermassive black hole (SMBH) formation, dynamics, and accretion in the massively parallel tree+SPH code, ChaNGa. This approach improves the modeling of SMBHs in fully cosmological simulations, allowing for a more detailed analysis of SMBH-galaxy co-evolution throughout cosmic time. Our scheme includes novel, physically motivated models for SMBH formation, dynamics and sinking timescales within galaxies, and SMBH accretion of rotationally supported gas. The sub-grid parameters that regulate star formation (SF) and feedback from SMBHs and SNe are optimized against a comprehensive set of z = 0 galaxy scaling relations using a novel, multi-dimensional parameter search. We have incorporated our new SMBH implementation and parameter optimization onto a new set of high resolution, large-scale cosmological simulations called Romulus. We present initial results from our flagship simulation, Romulus25, showing that our SMBH model results in SF efficiency, SMBH masses, and global c...
Light-Cone Effect of Radiation Fields in Cosmological Radiative Transfer Simulations
Ahn, Kyungjin
2015-01-01
We present a novel method to implement time-delayed propagation of radiation fields in cosmological radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative transfer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.
The cosmological principle is not in the sky
Park, Chan-Gyung; Hyun, Hwasu; Noh, Hyerim; Hwang, Jai-chan
2017-08-01
The homogeneity of matter distribution at large scales, known as the cosmological principle, is a central assumption in the standard cosmological model. The case is testable though, thus no longer needs to be a principle. Here we perform a test for spatial homogeneity using the Sloan Digital Sky Survey Luminous Red Galaxies (LRG) sample by counting galaxies within a specified volume with the radius scale varying up to 300 h-1 Mpc. We directly confront the large-scale structure data with the definition of spatial homogeneity by comparing the averages and dispersions of galaxy number counts with allowed ranges of the random distribution with homogeneity. The LRG sample shows significantly larger dispersions of number counts than the random catalogues up to 300 h-1 Mpc scale, and even the average is located far outside the range allowed in the random distribution; the deviations are statistically impossible to be realized in the random distribution. This implies that the cosmological principle does not hold even at such large scales. The same analysis of mock galaxies derived from the N-body simulation, however, suggests that the LRG sample is consistent with the current paradigm of cosmology, thus the simulation is also not homogeneous in that scale. We conclude that the cosmological principle is neither in the observed sky nor demanded to be there by the standard cosmological world model. This reveals the nature of the cosmological principle adopted in the modern cosmology paradigm, and opens a new field of research in theoretical cosmology.
Narayanan, Desika
2014-10-01
As the most luminous, heavily star-forming galaxies in the Universe, Submillimeter Galaxies at z 2-4 are key players in galaxy evolution. Since their discovery, SMGs have received significant attention from HST in characterizing their physical morphology, stellar masses, and star formation histories. Unfortunately, these physical constraints have been difficult for theorists to reconcile with galaxy formation simulations. Previous generations of simulations have all either {a} neglected baryons; {b} neglected radiative transfer {and connecting to observations}; or {c} neglected cosmological conditions. Here, we propose to conduct the first ever cosmological hydrodynamic simulations of Submillimeter Galaxy formation that couple with bona fide 3D dust radiative transfer calculations. These ultra-high resolution simulations {parsec-scale} will be the first to resolve the sites of dust obscuration, the cosmic growth history of SMGs, and their evolutionary destiny. Our proposal has two principle goals: {1} Develop the first ever model for SMG formation from cosmological simulations that include both baryons and dust radiative transfer; {2} Capitalize on our parsec-scale resolution to understand the connection between the physical properties of star-forming regions in high-z starbursts, and recent IMF constraints from present-epoch massive galaxies.
COMPARISONS OF COSMOLOGICAL MAGNETOHYDRODYNAMIC GALAXY CLUSTER SIMULATIONS TO RADIO OBSERVATIONS
Energy Technology Data Exchange (ETDEWEB)
Xu Hao; Li Hui; Collins, David C. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Govoni, Federica; Murgia, Matteo [INAF-Osservatorio Astronomico di Cagliari, Poggio dei Pini, Strada 54, I-09012 Capoterra (Italy); Norman, Michael L. [Center for Astrophysics and Space Science, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States); Cen Renyue [Department of Astrophysical Science, Princeton University, Princeton, NJ 08544 (United States); Feretti, Luigina; Giovannini, Gabriele, E-mail: hao_xu@lanl.gov, E-mail: hli@lanl.gov, E-mail: dccollins@lanl.gov, E-mail: mlnorman@ucsd.edu, E-mail: fgovoni@oa-cagliari.inaf.it, E-mail: matteo@oa-cagliari.inaf.it, E-mail: cen@astro.princeton.edu, E-mail: lferetti@ira.inaf.it, E-mail: ggiovann@ira.inaf.it [INAF-Istituto di Radioastronomia, Via P.Gobetti 101, I-40129 Bologna (Italy)
2012-11-01
Radio observations of galaxy clusters show that there are {mu}G magnetic fields permeating the intracluster medium (ICM), but it is hard to accurately constrain the strength and structure of the magnetic fields without the help of advanced computer simulations. We present qualitative comparisons of synthetic Very Large Array observations of simulated galaxy clusters to radio observations of Faraday rotation measure (RM) and radio halos. The cluster formation is modeled using adaptive mesh refinement magnetohydrodynamic simulations with the assumption that the initial magnetic fields are injected into the ICM by active galactic nuclei (AGNs) at high redshift. In addition to simulated clusters in Xu et al., we present a new simulation with magnetic field injections from multiple AGNs. We find that the cluster with multiple injection sources is magnetized to a similar level as in previous simulations with a single AGN. The RM profiles from simulated clusters, both |RM| and the dispersion of RM ({sigma}{sub RM}), are consistent at a first order with the radial distribution from observations. The correlations between the {sigma}{sub RM} and X-ray surface brightness from simulations are in a broad agreement with the observations, although there is an indication that the simulated clusters could be slightly overdense and less magnetized with respect to those in the observed sample. In addition, the simulated radio halos agree with the observed correlations between the radio power versus the cluster X-ray luminosity and between the radio power versus the radio halo size. These studies show that the cluster-wide magnetic fields that originate from AGNs and are then amplified by the ICM turbulence match observations of magnetic fields in galaxy clusters.
Tanikawa, Ataru; Okamoto, Takashi; Nitadori, Keigo
2011-01-01
We present a high-performance N-body code for astronomical collisional systems accelerated with the aid of a new SIMD instruction set extension of the x86 architecture: Advanced Vector eXtensions (AVX), an enhanced version of the Streaming SIMD Extensions (SSE). With one processor core of Intel Core i7-2600 processor (8MB cache and 3.40 GHz) based on Sandy Bridge micro-architecture, we achieved the performance of ~ 20 giga floating point number operations per second (GFlops) for double-precision accuracy, which is two times and five times higher than that of the previously developed code implemented with the SSE instructions (Nitadori et al., 2006b), and that of a code implemented without any explicit use of SIMD instructions with the same processor core. We have parallelized the collisional N-body code by using so-called NINJA scheme (Nitadori et al., 2006a), and achieved ~ 90 GFlops for a system containing more than N = 8192 particles with 8 MPI processes on four cores. We can expect to achieve about 10 ter...
Off The Beaten Path: Modeling the Dynamics of Supermassive Black Holes in Cosmological Simulations
Tremmel, Michael J.; Governato, Fabio; Volonteri, Marta; Quinn, Thomas R.
2015-01-01
Cosmological simulations are an essential tool to understand the co-evolution of supermassive black holes (SMBHs) and their host galaxies. However, the limited resolution of these simulations presents unique challenges to successfully modeling black hole dynamics. We present a novel, physically motivated method for improving the dynamics of black holes in cosmological simulations, by accounting for the unresolved dynamical friction that SMBHs feel from stars and dark matter. We show how this approach, which naturally scales with resolution, is a major step forward compared to more commonly used 'advection' models that often assume SMBHs sink very rapidly toward the center of their host galaxies. Here, we demonstrate that our method is able to prevent numerical heating of SMBHs while allowing for realistic dynamics.Our implementation will allow us to more realistically model SMBH dynamics, accretion, and mergers in cosmological simulations, giving us the ability to better understand how SMBHs grow with their host galaxies. This also provides an opportunity for more detailed studies of SMBHs in dwarf galaxies, which can give crucial insight into constraining black hole seed formation models.
Stickley, Nathaniel R; Masters, Daniel; de Putter, Roland; Doré, Olivier; Bock, Jamie
2016-01-01
Highly accurate models of the galaxy population over cosmological volumes are necessary in order to predict the performance of upcoming cosmological missions. We present a data-driven model of the galaxy population constrained by deep 0.1-8 $\\rm \\mu m$ imaging and spectroscopic data in the COSMOS survey, with the immediate goal of simulating the spectroscopic redshift performance of the proposed SPHEREx mission. SPHEREx will obtain over the full-sky $R\\sim41$ spectrophotometry at moderate spatial resolution ($\\sim6"$) over the wavelength range 0.75-4.18 $\\rm \\mu m$ and $R\\sim135$ over the wavelength range 4.18-5 $\\rm \\mu m$. We show that our simulation accurately reproduces a range of known galaxy properties, encapsulating the full complexity of the galaxy population and enables realistic, full end-to-end simulations to predict mission performance. Finally, we discuss potential applications of the simulation framework to future cosmology missions and give a description of released data products.
Direct cosmological simulations of the growth of black holes and galaxies
Di Matteo, Tiziana; Springel, Volker; Hernquist, Lars; Sijacki, Debora
2007-01-01
We investigate the coupled formation and evolution of galaxies and their embedded supermassive black holes using state-of-the-art hydrodynamic simulations of cosmological structure formation. For the first time, we self-consistently follow the dark matter dynamics, radiative gas cooling, star formation, as well as black hole growth and associated feedback processes, starting directly from initial conditions appropriate for the LambdaCDM cosmology. Our modeling of the black hole physics is based on an approach we have developed in simulations of isolated galaxy mergers. Here we examine: (i) the predicted global history of black hole mass assembly (ii) the evolution of the local black hole-host mass correlations and (iii) the conditions that allow rapid growth of the first quasars, and the properties of their hosts and descendants today. We find a total black hole mass density in good agreement with observational estimates. The black hole accretion rate density peaks at lower redshift and evolves more strongly ...
Zoomed cosmological simulations of Milky Way sized halos in f(R)-gravity
Arnold, Christian; Puchwein, Ewald
2016-01-01
We investigate the impact of f(R) modified gravity on the internal properties of Milky Way sized dark matter halos in a set of cosmological zoom simulations of seven halos from the Aquarius suite, carried out with our code MG-GADGET in the Hu & Sawicki f(R) model. Also, we calculate the fifth forces in ideal NFW-halos as well as in our cosmological simulations and compare them against analytic model predictions for the fifth force inside spherical objects. We find that these theoretical predictions match the forces in the ideal halos very well, whereas their applicability is somewhat limited for realistic cosmological halos. Our simulations show that f(R) gravity significantly affects the dark matter density profile of Milky Way sized objects as well as their circular velocities. In unscreened regions, the velocity dispersions are increased by up to 40% with respect to LCDM for viable f(R) models. This difference is larger than reported in previous works. The Solar circle is fully screened in $f_{R0} = -1...
Zoomed cosmological simulations of Milky Way-sized haloes in f(R) gravity
Arnold, Christian; Springel, Volker; Puchwein, Ewald
2016-10-01
We investigate the impact of f(R) modified gravity on the internal properties of Milky Way-sized dark matter haloes in a set of cosmological zoom simulations of seven haloes from the Aquarius suite, carried out with our code MG-GADGET in the Hu & Sawicki f(R) model. Also, we calculate the fifth forces in ideal NFW-haloes as well as in our cosmological simulations and compare them against analytic model predictions for the fifth force inside spherical objects. We find that these theoretical predictions match the forces in the ideal haloes very well, whereas their applicability is somewhat limited for realistic cosmological haloes. Our simulations show that f(R) gravity significantly affects the dark matter density profile of Milky Way-sized objects as well as their circular velocities. In unscreened regions, the velocity dispersions are increased by up to 40 per cent with respect to ΛCDM for viable f(R) models. This difference is larger than reported in previous works. The Solar circle is fully screened in bar{f}_{R0} = -10^{-6} models for Milky Way-sized haloes, while this location is unscreened for slightly less massive objects. Within the scope of our limited halo sample size, we do not find a clear dependence of the concentration parameter of dark matter haloes on bar{f}_{R0}.
Modeling the galaxy/light-mass connection with cosmological simulations
Tasitsiomi, A
2006-01-01
I review some results on the galaxy/light-mass connection obtained by dissipationless simulations in combination with a simple, non-parametric model to connect halo circular velocity to the luminosity of the galaxy they would host. I focus on the galaxy-mass correlation and mass-to-light ratios obtained from galaxy up to cluster scales. The predictions of this simple scheme are shown to be in very good agreement with SDSS observations.
Machine Learning and Cosmological Simulations I: Semi-Analytical Models
Kamdar, Harshil M.; Turk, Matthew J.; Brunner, Robert J.
2015-01-01
We present a new exploratory framework to model galaxy formation and evolution in a hierarchical universe by using machine learning (ML). Our motivations are two-fold: (1) presenting a new, promising technique to study galaxy formation, and (2) quantitatively analyzing the extent of the influence of dark matter halo properties on galaxies in the backdrop of semi-analytical models (SAMs). We use the influential Millennium Simulation and the corresponding Munich SAM to train and test various so...
Evolution of dwarf galaxies simulated in the cosmological LCDM scenario
Gonzalez-Samaniego, Alejandro; Colin, Pedro; Avila-Reese, Vladimir; Rodriguez-Puebla, Aldo; Valenzuela, Octavio
2014-03-01
We present results from numerical simulations of low-mass galaxies with the aim to explore the way their stellar masses are assembled. We analyze how the mass assembly histories of the parent halo determine the growth of their host galaxy and its implications on the current paradigm of formation and evolution of low-mass structures in the LCDM scenario. We have found that low-mass galaxies simulated in this scenario assemble their stellar masses following roughly the dark matter halo assembly, which seems to be in tension with the downsizing trend suggested by current observational inferences. We show that there is no more room to increase the strength of feedback from astrophysical processes in order to deviate strongly the stellar mass assembly from the dark halo one, as has been recently invoked to solve some of the potential issues faced by CDM-based simulations of dwarf galaxies. Alejandro González acknowledges finacial support from UNAM, Fundacion UNAM, and the APS to attend this meeting.
The BAHAMAS project: calibrated hydrodynamical simulations for large-scale structure cosmology
McCarthy, Ian G.; Schaye, Joop; Bird, Simeon; Le Brun, Amandine M. C.
2017-03-01
The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterize the dark matter, dark energy, and other aspects of our cosmological framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure, one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here, we construct a new suite of large-volume cosmological hydrodynamical simulations (called BAHAMAS, for BAryons and HAloes of MAssive Systems), where subgrid models of stellar and active galactic nucleus feedback have been calibrated to reproduce the present-day galaxy stellar mass function and the hot gas mass fractions of groups and clusters in order to ensure the effects of feedback on the overall matter distribution are broadly correct. We show that the calibrated simulations reproduce an unprecedentedly wide range of properties of massive systems, including the various observed mappings between galaxies, hot gas, total mass, and black holes, and represent a significant advance in our ability to mitigate the primary systematic uncertainty in most present large-scale structure tests.
Norman, Michael L; So, Geoffrey C; Harkness, Robsert P
2013-01-01
We describe an extension of the {\\em Enzo} code to enable the direct numerical simulation of inhomogeneous reionization in large cosmological volumes. By direct we mean all dynamical, radiative, and chemical properties are solved self-consistently on the same mesh, as opposed to a postprocessing approach which coarse-grains the radiative transfer. We do, however, employ a simple subgrid model for star formation, which we calibrate to observations. The numerical method presented is a modification of an earlier method presented in Reynolds et al. Radiation transport is done in the grey flux-limited diffusion (FLD) approximation, which is solved by implicit time integration split off from the gas energy and ionization equations, which are solved separately. This results in a faster and more robust scheme for cosmological applications compared to the earlier method. The FLD equation is solved using the {\\em hypre} optimally scalable geometric multigrid solver from LLNL. By treating the ionizing radiation as a gri...
Cosmology with AGN dust time lags-simulating the new VEILS survey
Hönig, S. F.; Watson, D.; Kishimoto, M.; Gandhi, P.; Goad, M.; Horne, K.; Shankar, F.; Banerji, M.; Boulderstone, B.; Jarvis, M.; Smith, M.; Sullivan, M.
2017-01-01
The time lag between optical and near-infrared continuum emission in active galactic nuclei (AGN) shows a tight correlation with luminosity and has been proposed as a standardizable candle for cosmology. In this paper, we explore the use of these AGN hot-dust time lags for cosmological model fitting under the constraints of the new VISTA Extragalactic Infrared Legacy Survey (VEILS). This new survey will target a 9 deg2 field observed in J and Ks band with a 14-d cadence and will run for 3 yr. The same area will be covered simultaneously in the optical griz bands by the Dark Energy Survey, providing complementary time-domain optical data. We perform realistic simulations of the survey setup, showing that we expect to recover dust time lags for about 450 objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of 0.1 4.
Cosmology with AGN dust time lags -- Simulating the new VEILS survey
Hönig, S F; Kishimoto, M; Gandhi, P; Goad, M; Horne, K; Shankar, F; Banerji, M; Boulderstone, B; Jarvis, M; Smith, M; Sullivan, M
2016-01-01
The time lag between optical and near-infrared continuum emission in active galactic nuclei (AGN) shows a tight correlation with luminosity and has been proposed as a standardisable candle for cosmology. In this paper, we explore the use of these AGN hot-dust time lags for cosmological model fitting under the constraints of the new VISTA Extragalactic Infrared Legacy Survey VEILS. This new survey will target a 9 deg^2 field observed in J- and Ks-band with a 14-day cadence and will run for three years. The same area will be covered simultaneously in the optical griz bands by the Dark Energy Survey, providing complementary time-domain optical data. We perform realistic simulations of the survey setup, showing that we expect to recover dust time lags for about 450 objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of 0.1 4.
A physical model for cosmological simulations of galaxy formation
Vogelsberger, Mark; Sijacki, Debora; Torrey, Paul; Springel, Volker; Hernquist, Lars; ),
2013-01-01
We present a new comprehensive model of the physics of galaxy formation designed for large-scale hydrodynamical simulations of structure formation using the moving mesh code AREPO. Our model includes primordial and metal line cooling with self-shielding corrections, stellar evolution and feedback processes, gas recycling, chemical enrichment, a novel subgrid model for the metal loading of outflows, black hole (BH) seeding, BH growth and merging procedures, quasar- and radio-mode feedback, and a prescription for radiative electro-magnetic (EM) feedback from active galactic nuclei (AGN). Stellar feedback is realised through kinetic outflows. The scaling of the mass loading of galactic winds can be set to be either energy or momentum driven, or a mixture of both. The metal mass loading of outflows can be adjusted independently of the wind mass loading. This is required to simultaneously reproduce the stellar mass content of low mass haloes and their gas oxygen abundances. Radiative EM AGN feedback is implemented...
SWIFT: task-based hydrodynamics and gravity for cosmological simulations
Theuns, Tom; Schaller, Matthieu; Gonnet, Pedro
2015-01-01
Simulations of galaxy formation follow the gravitational and hydrodynamical interactions between gas, stars and dark matter through cosmic time. The huge dynamic range of such calculations severely limits strong scaling behaviour of the community codes in use, with load-imbalance, cache inefficiencies and poor vectorisation limiting performance. The new swift code exploits task-based parallelism designed for many-core compute nodes interacting via MPI using asynchronous communication to improve speed and scaling. A graph-based domain decomposition schedules interdependent tasks over available resources. Strong scaling tests on realistic particle distributions yield excellent parallel efficiency, and efficient cache usage provides a large speed-up compared to current codes even on a single core. SWIFT is designed to be easy to use by shielding the astronomer from computational details such as the construction of the tasks or MPI communication. The techniques and algorithms used in SWIFT may benefit other compu...
The Distribution of Satellites Around Central Galaxies in a Cosmological Hydrodynamical Simulation
Dong, Xuce; Kang, Xi; Wang, Yang O; Dutton, Aaron A; Macciò, Andrea V
2014-01-01
Observations have shown that the spatial distribution of satellite galaxies is not random, but rather, it is aligned with the major axes of central galaxies. The strength of the alignment is dependent on the properties of both satellites and centrals. Theoretical studies using dissipationless N-body simulations are limited by their inability to directly predict the shape of central galaxies. Using hydrodynamical simulations including gas cooling, star formation and feedback, we carry out a study of galaxy alignment and its dependence on galaxy properties predicted directly from the simulations. We found that the observed alignment signal is well produced, as is the color dependence: red satellites and red centrals both show stronger alignments than their blue counterparts. The reason for the stronger alignment of red satellites is that most of them stay in the inner region of the dark matter halo, where the shape of central galaxy traces better the dark matter distribution. The dependence of alignment on the ...
Constraints on Physical Properties of z~6 Galaxies Using Cosmological Hydrodynamic Simulations
Finlator, K; Oppenheimer, B
2006-01-01
We introduce SPOC, a new code for constraining the physical properties of observed galaxies through a Bayesian likelihood comparison with galaxies drawn from simulations. SPOC inputs an object's photometry and outputs probability distributions of stellar mass, star formation rate (SFR), age, metallicity, dust extinction, and redshift (if none is given) for that galaxy. We apply SPOC, employing model galaxies drawn from cosmological hydrodynamic simulations, to Abell 2218 KESR (z~6.7) and five other z>5.5 galaxies for which published rest-frame ultraviolet and optical measurements are available. We compare the outcome of using our simulated galaxies' star formation histories (SFHs) versus using simple one-parameter SFHs such as constant, exponentially-decaying, and rising (a new form we introduce motivated by typical SFHs seen in our simulated galaxies). We show that simulated galaxies match these observations at least as well as simple SFHs, with similar favored values obtained for the intrinsic physical para...
Pawlik, Andreas H; Vecchia, Claudio Dalla
2015-01-01
We present a suite of cosmological radiation-hydrodynamical simulations of the assembly of galaxies driving the reionization of the intergalactic medium (IGM) at z >~ 6. The simulations account for the hydrodynamical feedback from photoionization heating and the explosion of massive stars as supernovae (SNe). Our reference simulation, which was carried out in a box of size 25 comoving Mpc/h using 2 x 512^3 particles, produces a reasonable reionization history and matches the observed UV luminosity function of galaxies. Simulations with different box sizes and resolutions are used to investigate numerical convergence, and simulations in which either SNe or photoionization heating or both are turned off, are used to investigate the role of feedback from star formation. Ionizing radiation is treated using accurate radiative transfer at the high spatially adaptive resolution at which the hydrodynamics is carried out. SN feedback strongly reduces the star formation rates (SFRs) over nearly the full mass range of s...
The nature of compact groups of galaxies from cosmological simulations
Mamon, G A
2009-01-01
The nature of compact groups (CGs) of galaxies, apparently so dense that the galaxies often overlap, is still a subject of debate: Are CGs roughly as dense in 3D as they appear in projection? Or are they caused by chance alignments of galaxies along the line-of-sight within larger virialized groups, or within even longer filamentary structures? The nature of CGs is re-appraised using the redshift zero outputs of three galaxy formation models, applied to the dissipationless Millennium Simulation. The same selection criteria are applied to mock galaxy catalogs from these models as have been applied by Hickson and co-workers in redshift space. We find 50 times as many mock CGs as the 'HCGs' found by Hickson within a distance corresponding to 9000 km/s. This very low (2%) completeness is caused by Hickson missing groups that were either faint, near the surface brightness threshold, of small angular size and with a dominant brightest galaxy. We find that most CGs are physically dense, regardless of the precise thr...
Machine learning and cosmological simulations - I. Semi-analytical models
Kamdar, Harshil M.; Turk, Matthew J.; Brunner, Robert J.
2016-01-01
We present a new exploratory framework to model galaxy formation and evolution in a hierarchical Universe by using machine learning (ML). Our motivations are two-fold: (1) presenting a new, promising technique to study galaxy formation, and (2) quantitatively analysing the extent of the influence of dark matter halo properties on galaxies in the backdrop of semi-analytical models (SAMs). We use the influential Millennium Simulation and the corresponding Munich SAM to train and test various sophisticated ML algorithms (k-Nearest Neighbors, decision trees, random forests, and extremely randomized trees). By using only essential dark matter halo physical properties for haloes of M > 1012 M⊙ and a partial merger tree, our model predicts the hot gas mass, cold gas mass, bulge mass, total stellar mass, black hole mass and cooling radius at z = 0 for each central galaxy in a dark matter halo for the Millennium run. Our results provide a unique and powerful phenomenological framework to explore the galaxy-halo connection that is built upon SAMs and demonstrably place ML as a promising and a computationally efficient tool to study small-scale structure formation.
Machine Learning and Cosmological Simulations I: Semi-Analytical Models
Kamdar, Harshil M; Brunner, Robert J
2016-01-01
We present a new exploratory framework to model galaxy formation and evolution in a hierarchical universe by using machine learning (ML). Our motivations are two-fold: (1) presenting a new, promising technique to study galaxy formation, and (2) quantitatively analyzing the extent of the influence of dark matter halo properties on galaxies in the backdrop of semi-analytical models (SAMs). We use the influential Millennium Simulation and the corresponding Munich SAM to train and test various sophisticated machine learning algorithms (k-Nearest Neighbors, decision trees, random forests and extremely randomized trees). By using only essential dark matter halo physical properties for haloes of $M>10^{12} M_{\\odot}$ and a partial merger tree, our model predicts the hot gas mass, cold gas mass, bulge mass, total stellar mass, black hole mass and cooling radius at z = 0 for each central galaxy in a dark matter halo for the Millennium run. Our results provide a unique and powerful phenomenological framework to explore...
Cosmology with AGN dust time lags - Simulating the new VEILS survey
Hönig, S. F.; Watson, D.; Kishimoto, M.; Gandhi, P.; Goad, M.; Horne, K.; Shankar, F.; Banerji, M.; Boulderstone, B.; Jarvis, M.; Smith, M.; Sullivan, M.
2016-10-01
The time lag between optical and near-infrared continuum emission in active galactic nuclei (AGN) shows a tight correlation with luminosity and has been proposed as a standardisable candle for cosmology. In this paper, we explore the use of these AGN hot-dust time lags for cosmological model fitting under the constraints of the new VISTA Extragalactic Infrared Legacy Survey VEILS. This new survey will target a 9 deg2 field observed in J- and Ks-band with a 14-day cadence and will run for three years. The same area will be covered simultaneously in the optical griz bands by the Dark Energy Survey, providing complementary time-domain optical data. We perform realistic simulations of the survey setup, showing that we expect to recover dust time lags for about 450 objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of 0.1 AGN as well as in the normalisation of the lag-luminosity relation, we are able to constrain Ω _Λ in ΛCDM with similar accuracy as current supernova samples. We discuss the benefits of combining AGN and supernovae for cosmology and connect the present work to future attempts to reach out to redshifts of z > 4.
Tortora, C; Napolitano, N R; Antonuccio-Delogu, V; Meza, A; Sommer-Larsen, J; Capaccioli, M
2010-01-01
The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar mass. Dwarf galaxies show null age gradient with a tail of high and positive values for systems in groups and cluster outskirts. Massive systems have generally zero age gradients which turn to positive for the most massive ones. Metallicity gradients are distributed around zero in dwarf galaxies and become more negative with mass; massive galaxies have steeper negative metallicity gradients, but the trend flatten with mass. In particular, fossil groups are characterized by a tighter distribution of both age and metallicity gradients. We find a good agreement with both local observations and independent simulations. The results are also discussed in terms of the central age and metallicity, as well as the total colour, specific star formation and velocity dispersion.
Gurzadyan's Problem 5 and improvement of softenings for cosmological simulations using the PP method
Eingorn, Maxim
2014-01-01
This Letter is devoted to different modifications of two standard softenings of the gravitational attraction, which are commonly used in cosmological simulations based on the particle-particle (PP) method, and their comparison. It is demonstrated that some of the proposed alternatives lead to almost the same accuracy as in the case of the pure Newtonian interaction, even despite the fact that the force resolution is allowed to equal half the minimum interparticle distance. The revealed way of precision improvement gives an opportunity to succeed in solving Gurzadyan's Problem 5 and bring modern computer codes up to a higher standard.
Made-to-measure N-body systems
Syer, D
1996-01-01
We describe an algorithm for constructing N-body realisations of equilibrium stellar systems. The algorithm complements existing orbit-based modelling techniques using linear programming or other optimization algorithms. The equilibria are constructed by integrating an N-body system while slowly adjusting the masses of the particles until the time-averaged density field and other observables converge to a prescribed value. The procedure can be arranged to maximise a linear combination of the entropy of the system and the \\chi^2 statistic for the observables. The equilibria so produced may be useful as initial conditions for N-body simulations or for modelling observations of individual galaxies.
Crosby, Brian D; Smith, Britton D; Turk, Matthew J; Hahn, Oliver
2013-01-01
We present a semi-analytic, computationally inexpensive model to identify halos capable of forming a Population III star in cosmological simulations across a wide range of times and environments. This allows for a much more complete and representative set of Population III star forming halos to be constructed, which will lead to Population III star formation simulations that more accurately reflect the diversity of Population III stars, both in time and halo mass. This model shows that Population III and chemically enriched stars coexist beyond the formation of the first generation of stars in a cosmological simulation until at least z~10, and likely beyond, though Population III stars form at rates that are 4-6 orders of magnitude lower than chemically enriched stars by z=10. A catalog of more than 40,000 candidate Population III forming halos were identified, with formation times temporally ranging from z=30 to z=10, and ranging in mass from 2.3x10^5 M_sun to 1.2x10^10 M_sun. At early times, the environment...
Hackstein, S.; Vazza, F.; Brüggen, M.; Sigl, G.; Dundovic, A.
2016-11-01
We use the CRPROPA code to simulate the propagation of ultrahigh energy cosmic rays (with energy ≥1018eV and pure proton composition) through extragalactic magnetic fields that have been simulated with the cosmological ENZO code. We test both primordial and astrophysical magnetogenesis scenarios in order to investigate the impact of different magnetic field strengths in clusters, filaments and voids on the deflection of cosmic rays propagating across cosmological distances. We also study the effect of different source distributions of cosmic rays around simulated Milky Way-like observers. Our analysis shows that the arrival spectra and anisotropy of events are rather insensitive to the distribution of extragalactic magnetic fields, while they are more affected by the clustering of sources within an ˜50 Mpc distance to observers. Finally, we find that in order to reproduce the observed degree of isotropy of cosmic rays at ˜EeV energies, the average magnetic fields in cosmic voids must be ˜ 0.1 nG, providing limits on the strength of primordial seed fields.
Hackstein, Stefan; Brueggen, Marcus; Sigl, Guenter; Dundovic, Andrej
2016-01-01
We use the CRPropa code to simulate the propagation of ultra high energy cosmic rays (with energy $\\geq 10^{18} \\rm eV$ and pure proton composition) through extragalactic magnetic fields that have been simulated with the cosmological ENZO code.We test both primordial and astrophysical magnetogenesis scenarios in order to investigate the impact of different magnetic field strengths in clusters, filaments and voids on the deflection of cosmic rays propagating across cosmological distances. We also study the effect of different source distributions of cosmic rays around simulated Milky-Way like observers. Our analysis shows that the arrival spectra and anisotropy of events are rather insensitive to the distribution of extragalactic magnetic fields, while they are more affected by the clustering of sources within a $\\sim 50$ Mpc distance to observers. Finally, we find that in order to reproduce the observed degree of isotropy of cosmic rays at $\\sim $ EeV energies, the average magnetic fields in cosmic voids must...
Evolution of cosmic filaments and of their galaxy population from MHD cosmological simulations
Gheller, C.; Vazza, F.; Brüggen, M.; Alpaslan, M.; Holwerda, B. W.; Hopkins, A. M.; Liske, J.
2016-10-01
Despite containing about a half of the total matter in the Universe, at most wavelengths the filamentary structure of the cosmic web is difficult to observe. In this work, we use large unigrid cosmological simulations to investigate how the geometrical, thermodynamical and magnetic properties of cosmological filaments vary with mass and redshift (z ≤ 1). We find that the average temperature, length, volume and magnetic field of filaments scales well with their total mass. This reflects the role of self-gravity in shaping their properties and enables statistical predictions of their observational properties based on their mass. We also focus on the properties of the simulated population of galaxy-sized haloes within filaments, and compare their properties to the results obtained from the spectroscopic GAMA survey. Simulated and observed filaments with the same length are found to contain an equal number of galaxies, with very similar distribution of masses. The total number of galaxies within each filament and the total/average stellar mass in galaxies can now be used to predict also the large-scale properties of the gas in the host filaments across tens or hundreds of Mpc in scale. These results are the first steps towards the future use of galaxy catalogues in order to select the best targets for observations of the warm-hot intergalactic medium.
Chemical evolution using SPH cosmological simulations. I implementation, tests and first results
Mosconi, M B; Lambas, D G; Cora, S A
2000-01-01
We develop a model to implement metal enrichment in a cosmological context based on the hydrodynamical AP3MSPH code described by Tissera, Lambas and Abadi (1997). The star formation model is based on the Schmidt law and has been modified in order to describe the transformation of gas into stars in more detail. The enrichment of the interstellar medium due to supernovae I and II explosions is taken into account by assuming a Salpeter Initial Mass Function and different nucleosynthesis models.The different chemical elements are mixed within the gaseous medium according to the Smooth Particle Hydrodynamics technique.We have performed cosmological simulations in a standard Cold Dark Matter scenario and we present results of the analysis of the star formation and chemical properties of the interstellar medium and stellar population of the simulated galactic objects. We have compared the results of the simulations with an implementation of the one-zone Simple Model, finding significant differences in the global met...
Muratov, Alexander L; Faucher-Giguere, Claude-Andre; Hopkins, Philip F; Quataert, Eliot; Murray, Norman
2015-01-01
We present an analysis of the galaxy-scale gaseous outflows from the FIRE (Feedback in Realistic Environments) simulations. This suite of hydrodynamic cosmological zoom simulations provides a sample of halos where star-forming giant molecular clouds are resolved to z=0, and features an explicit stellar feedback model on small scales. In this work, we focus on quantifying the gas mass ejected out of galaxies in winds and how this material travels through the halo. We correlate these quantities to star formation in galaxies throughout cosmic history. Our simulations reveal that a significant portion of every galaxy's evolution, particularly at high redshift, is dominated by bursts of star formation, which are followed by powerful gusts of galactic outflow that sweep up a large fraction of gas in the interstellar medium and send it through the circumgalactic medium. The dynamical effect of these outflows can significantly limit the amount of star formation within the affected galaxy. At low redshift, however, su...
A physical model for cosmological simulations of galaxy formation: multi-epoch validation
Torrey, Paul; Genel, Shy; Sijacki, Debora; Springel, Volker; Hernquist, Lars
2013-01-01
We present a multi-epoch analysis of the galaxy populations formed within the cosmological hydrodynamical simulations presented in Vogelsberger et al. (2013). These simulations explore the performance of a recently implemented feedback model which includes primordial and metal line radiative cooling with self-shielding corrections; stellar evolution with associated mass loss and chemical enrichment; feedback by stellar winds; black hole seeding, growth and merging; and AGN quasar- and radio-mode heating with a phenomenological prescription for AGN electro-magnetic feedback. We illustrate the impact of the model parameter choices on the resulting simulated galaxy population properties at high and intermediate redshifts. We demonstrate that our scheme is capable of producing galaxy populations that broadly reproduce the observed galaxy stellar mass function extending from redshift z=0 to z=3. We also characterise the evolving galactic B-band luminosity function, stellar mass to halo mass ratio, star formation m...
The metal enrichment of passive galaxies in cosmological simulations of galaxy formation
Okamoto, Takashi; Lacey, Cedric G; Frenk, Carlos S
2016-01-01
Massive early-type galaxies have higher metallicities and higher ratios of $\\alpha$ elements to iron than their less massive counterparts. Reproducing these correlations has long been a problem for hierarchical galaxy formation theory, both in semi-analytic models and cosmological hydrodynamic simulations. We show that a simulation in which gas cooling in massive dark haloes is quenched by radio-mode active galactic nuclei (AGNs) feedback naturally reproduces the observed trend between $\\alpha$/Fe and the velocity dispersion of galaxies, $\\sigma$. The quenching occurs earlier for more massive galaxies. Consequently, these galaxies complete their star formation before $\\alpha$/Fe is diluted by the contribution from type Ia supernovae. For galaxies more massive than $\\sim 10^{11}~M_\\odot$ whose $\\alpha$/Fe correlates positively with stellar mass, we find an inversely correlated mass-metallicity relation. This is a common problem in simulations in which star formation in massive galaxies is quenched either by qu...
Ab Initio Cosmological Simulations of CR7 as an Active Black Hole
Smidt, Joseph; Johnson, Jarrett L
2016-01-01
We present the first ab initio cosmological simulations of a CR7-like object which approximately reproduce the observed line widths and strengths. In our model, CR7 is powered by a massive (2.23 x 10^7 M_Sun), accreting (0.25 Eddington) supermassive black hole (BH). Our model takes into account multi-dimensional effects, X-ray feedback, secondary ionizations and primordial chemistry. We estimate Ly-alpha line widths by post-processing simulation output with Monte Carlo radiative transfer and calculate emissivity contributions from radiative recombination and collisional excitation. We find the luminosities in the Lyman-alpha and He II 1640 angstrom lines to be 5.0 x 10^44 and 2.4 x 10^43 erg/s, respectively, in agreement with the observed values of > 8.3 x 10^43 and 2.0 x 10^43 erg/s. We also find that the black hole heats the halo and renders it unable to produce stars as required to keep the halo metal free. These results demonstrate the viability of the BH hypothesis for CR7 in a cosmological context. Assu...
Parallel HOP: A Scalable Halo Finder for Massive Cosmological Data Sets
Skory, Stephen; Norman, Michael L; Coil, Alison L
2010-01-01
Modern N-body cosmological simulations contain billions ($10^9$) of dark matter particles. These simulations require hundreds to thousands of gigabytes of memory, and employ hundreds to tens of thousands of processing cores on many compute nodes. In order to study the distribution of dark matter in a cosmological simulation, the dark matter halos must be identified using a halo finder, which establishes the halo membership of every particle in the simulation. The resources required for halo finding are similar to the requirements for the simulation itself. In particular, simulations have become too extensive to use commonly-employed halo finders, such that the computational requirements to identify halos must now be spread across multiple nodes and cores. Here we present a scalable-parallel halo finding method called Parallel HOP for large-scale cosmological simulation data. Based on the halo finder HOP, it utilizes MPI and domain decomposition to distribute the halo finding workload across multiple compute n...
Karl, Simon J.; Aarseth, Sverre J.; Naab, Thorsten; Haehnelt, Martin G.; Spurzem, Rainer
2015-09-01
We present a hybrid code combining the OpenMP-parallel tree code VINE with an algorithmic chain regularization scheme. The new code, called `rVINE', aims to significantly improve the accuracy of close encounters of massive bodies with supermassive black holes (SMBHs) in galaxy-scale numerical simulations. We demonstrate the capabilities of the code by studying two test problems, the sinking of a single massive black hole to the centre of a gas-free galaxy due to dynamical friction and the hardening of an SMBH binary due to close stellar encounters. We show that results obtained with rVINE compare well with NBODY7 for problems with particle numbers that can be simulated with NBODY7. In particular, in both NBODY7 and rVINE we find a clear N-dependence of the binary hardening rate, a low binary eccentricity and moderate eccentricity evolution, as well as the conversion of the galaxy's inner density profile from a cusp to a core via the ejection of stars at high velocity. The much larger number of particles that can be handled by rVINE will open up exciting opportunities to model stellar dynamics close to SMBHs much more accurately in a realistic galactic context. This will help to remedy the inherent limitations of commonly used tree solvers to follow the correct dynamical evolution of black holes in galaxy-scale simulations.
How to Zoom: Bias, Contamination, and Lagrange Volumes in Multimass Cosmological Simulations
Onorbe, Jose; Maller, Ariyeh H; Bullock, James S; Rocha, Miguel; Hahn, Oliver
2013-01-01
We perform a suite of multimass cosmological zoom simulations of individual dark matter halos and explore how to best select Lagrangian regions for resimulation without contaminating the halo of interest with low-resolution particles. Such contamination can lead to significant errors in the gas distribution of hydrodynamical simulations, as we show. For a fixed Lagrange volume, we find that the chance of contamination increases systematically with the level of zoom. In order to avoid contamination, the Lagrangian volume selected for resimulation must increase monotonically with the resolution difference between parent box and the zoom region. We provide a simple formula for selecting Lagrangian regions (in units of the halo virial volume) as a function of the level of zoom required. We also explore the degree to which a halo's Lagrangian volume correlates with other halo properties (concentration, spin, formation time, shape, etc.) and find no significant correlation. There is a mild correlation between Lagra...
Wainwright, Carroll L; Peiris, Hiranya V; Aguirre, Anthony; Lehner, Luis; Liebling, Steven L
2014-01-01
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. We develop and implement an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. We first simulate the entire collision spacetime, from nucleation to reheating, inside each bubble. Taking advantage of the collision's hyperbolic symmetry, simulations are performed with a 1+1-dimensional fully relativistic code that uses adaptive mesh refinement. We then calculate the comoving curvature perturbation in an open Friedmann-Robertson-Walker universe, which is used to determine, in the Sachs-Wolfe approximation, the temperature anisotropies of the cosmic microwave background radiation. For a fiducial Lagrangian, t...
The radiation energy component of the Hubble function and a LCDM cosmological simulation
Aceves, Hector
2013-01-01
We study some effects the inclusion of the radiation energy component in the universe, Omega_r, can have on several quantities of interest for the large-scale structure of the universe in a LCDM cosmological simulation; started at a very high redshift (z=500). In particular we compute the power spectrum density, the halo mass function, and the concentration-mass relation for haloes. We find that Omega_r has an important contribution in the long-term nonlinear evolution of structures in the universe. For instance, a lower matter density power, by approx 50%, in all scales is obtained when compared with a simulation without the radiation term. Also, haloes formed with the Omega_r taken into account are approx 20% less concentrated than when not included in the Hubble function.
Cai, Rong-Gen; Yang, Tao
2017-02-01
We investigate the constraint ability of the gravitational wave (GW) as the standard siren on the cosmological parameters by using the third-generation gravitational wave detector: the Einstein Telescope. The binary merger of a neutron with either a neutron or black hole is hypothesized to be the progenitor of a short and intense burst of γ rays; some fraction of those binary mergers could be detected both through electromagnetic radiation and gravitational waves. Thus we can determine both the luminosity distance and redshift of the source separately. We simulate the luminosity distances and redshift measurements from 100 to 1000 GW events. We use two different algorithms to constrain the cosmological parameters. For the Hubble constant H0 and dark matter density parameter Ωm, we adopt the Markov chain Monte Carlo approach. We find that with about 500-600 GW events we can constrain the Hubble constant with an accuracy comparable to Planck temperature data and Planck lensing combined results, while for the dark matter density, GWs alone seem not able to provide the constraints as good as for the Hubble constant; the sensitivity of 1000 GW events is a little lower than that of Planck data. It should require more than 1000 events to match the Planck sensitivity. Yet, for analyzing the more complex dynamical property of dark energy, i.e., the equation of state w , we adopt a new powerful nonparametric method: the Gaussian process. We can reconstruct w directly from the observational luminosity distance at every redshift. In the low redshift region, we find that about 700 GW events can give the constraints of w (z ) comparable to the constraints of a constant w by Planck data with type-Ia supernovae. Those results show that GWs as the standard sirens to probe the cosmological parameters can provide an independent and complementary alternative to current experiments.
Tremmel, M.; Karcher, M.; Governato, F.; Volonteri, M.; Quinn, T. R.; Pontzen, A.; Anderson, L.; Bellovary, J.
2017-09-01
We present a novel implementation of supermassive black hole (SMBH) formation, dynamics and accretion in the massively parallel tree+SPH code, ChaNGa. This approach improves the modelling of SMBHs in fully cosmological simulations, allowing for a more detailed analysis of SMBH-galaxy co-evolution throughout cosmic time. Our scheme includes novel, physically motivated models for SMBH formation, dynamics and sinking timescales within galaxies and SMBH accretion of rotationally supported gas. The sub-grid parameters that regulate star formation (SF) and feedback from SMBHs and SNe are optimized against a comprehensive set of z = 0 galaxy scaling relations using a novel, multidimensional parameter search. We have incorporated our new SMBH implementation and parameter optimization into a new set of high-resolution, large-scale cosmological simulations called Romulus. We present initial results from our flagship simulation, Romulus25, showing that our SMBH model results in SF efficiency, SMBH masses and global SF and SMBH accretion histories at high redshift that are consistent with observations. We discuss the importance of SMBH physics in shaping the evolution of massive galaxies and show how SMBH feedback is much more effective at regulating SF compared to SNe feedback in this regime. Further, we show how each aspect of our SMBH model impacts this evolution compared to more common approaches. Finally, we present a science application of this scheme studying the properties and time evolution of an example dual active galactic nucleus system, highlighting how our approach allows simulations to better study galaxy interactions and SMBH mergers in the context of galaxy-BH co-evolution.
Karl, S J; Naab, T; Haehnelt, M G; Spurzem, R
2015-01-01
We present a hybrid code combining the OpenMP-parallel tree code VINE with an algorithmic chain regularization scheme. The new code, called "rVINE", aims to significantly improve the accuracy of close encounters of massive bodies with supermassive black holes in galaxy-scale numerical simulations. We demonstrate the capabilities of the code by studying two test problems, the sinking of a single massive black hole to the centre of a gas-free galaxy due to dynamical friction and the hardening of a supermassive black hole binary due to close stellar encounters. We show that results obtained with rVINE compare well with NBODY7 for problems with particle numbers that can be simulated with NBODY7. In particular, in both NBODY7 and rVINE we find a clear N-dependence of the binary hardening rate, a low binary eccentricity and moderate eccentricity evolution, as well as the conversion of the galaxy's inner density profile from a cusp to a a core via the ejection of stars at high velocity. The much larger number of par...
Younger, Joshua D
2007-01-01
We perform a set of non--radiative cosmological simulations of a preheated intracluster medium in which the entropy of the gas was uniformly boosted at high redshift. The results of these simulations are used first to test the current analytic techniques of preheating via entropy input in the smooth accretion limit. When the unmodified profile is taken directly from simulations, we find that this model is in excellent agreement with the results of our simulations. This suggests that preheated efficiently smoothes the accreted gas, and therefore a shift in the unmodified profile is a good approximation even with a realistic accretion history. When we examine the simulation results in detail, we do not find strong evidence for entropy amplification, at least for the high-redshift preheating model adopted here. In the second section of the paper, we compare the results of the preheating simulations to recent observations. We show -- in agreement with previous work -- that for a reasonable amount of preheating, a...
Testing X-ray Measurements of Galaxy Cluster Outskirts with Cosmological Simulations
Avestruz, Camille; Nagai, Daisuke; Vikhlinin, Alexey
2014-01-01
The study of galaxy cluster outskirts has emerged as one of the new frontiers in extragalactic astrophysics and cosmology with the advent of new observations in X-ray and microwave. However, the thermodynamic properties and chemical enrichment of this diffuse and azimuthally asymmetric component of the intra-cluster medium are still not well understood. This work, for the first time, systematically explores potential observational biases in these regions. To assess X-ray measurements of galaxy cluster properties at large radii ($>{R}_{500c}$), we use mock Chandra analyses of cosmological galaxy cluster simulations. The pipeline is identical to that used for Chandra observations, but the biases discussed in this paper are relevant for all X-ray observations outside of ${R}_{500c}$. We find the following from our analysis: (1) filament regions can contribute as much as a factor of 3 to the emission measure, (2) X-ray temperatures and metal abundances from model fitted mock X-ray spectra respectively vary to the...
Zavala, J; Frenk, Carlos S
2007-01-01
We investigate the evolution of angular momentum in simulations of galaxy formation in a cold dark matter universe. We analyse two model galaxies produced in the N-body/hydrodynamic simulations of Okamoto et al. Starting from identical initial conditions, but using different assumptions for the baryonic physics, one of the simulations produced a bulge-dominated galaxy and the other one a disk-dominated galaxy. The main difference is the treatment of star formation and feedback, both of which were designed to be more efficient in the disk-dominated object. We find that the specific angular momentum of the disk-dominated galaxy tracks the evolution of the angular momentum of the dark matter halo very closely: the angular momentum grows as predicted by linear theory until the epoch of maximum expansion and remains constant thereafter. By contrast, the evolution of the angular momentum of the bulge-dominated galaxy resembles that of the central, most bound halo material: it also grows at first according to linear...
Lovell, Mark R; Boyarsky, Alexey; Crain, Robert A; Frenk, Carlos S; Hellwing, Wojciech A; Ludlow, Aaron D; Navarro, Julio F; Ruchayskiy, Oleg; Sawala, Till; Schaller, Matthieu; Schaye, Joop; Theuns, Tom
2016-01-01
We study galaxy formation in sterile neutrino dark matter models that differ significantly from both cold and from `warm thermal relic' models. We use the EAGLE code to carry out hydrodynamic simulations of the evolution of pairs of galaxies chosen to resemble the Local Group, as part of the APOSTLE simulations project. We compare cold dark matter (CDM) with two sterile neutrino models with 7 keV mass: one, the warmest among all models of this mass (LA120) and the other, a relatively cold case (LA10). We show that the lower concentration of sterile neutrino subhalos compared to their CDM counterparts makes the inferred inner dark matter content of galaxies like Fornax (or Magellanic Clouds) less of an outlier in the sterile neutrino cosmologies. In terms of the galaxy number counts the LA10 simulations are \\emph{indistinguishable} from CDM when one takes into account halo-to-halo (or `simulation-to-simulation') scatter. In order for the LA120 model to match the number of Local Group dwarf galaxies, a higher f...
Cosmological MHD Simulations of Galaxy Cluster Radio Relics: Insights and Warnings for Observations
Skillman, Samuel W; Hallman, Eric J; O'Shea, Brian W; Burns, Jack O; Li, Hui; Collins, David C; Norman, Michael L
2012-01-01
Non-thermal radio emission from cosmic ray electrons in the vicinity of merging galaxy clusters is an important tracer of cluster merger activity, and is the result of complex physical processes that involve magnetic fields, particle acceleration, gas dynamics, and radiation. In particular, objects known as radio relics are thought to be the result of shock-accelerated electrons that, when embedded in a magnetic field, emit synchrotron radiation in the radio wavelengths. In order to properly model this emission, we utilize the adaptive mesh refinement simulation of the magnetohydrodynamic evolution of a galaxy cluster from cosmological initial conditions. We locate shock fronts and apply models of cosmic ray electron acceleration that are then input into radio emission models. We have determined the thermodynamic properties of this radio-emitting plasma and constructed synthetic radio observations to compare to observed galaxy clusters. We find a significant dependence of the observed morphology and radio rel...
E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
Springel, Volker
2009-01-01
Hydrodynamic cosmological simulations at present usually employ either the Lagrangian SPH technique, or Eulerian hydrodynamics on a Cartesian mesh with adaptive mesh refinement. Both of these methods have disadvantages that negatively impact their accuracy in certain situations. We here propose a novel scheme which largely eliminates these weaknesses. It is based on a moving unstructured mesh defined by the Voronoi tessellation of a set of discrete points. The mesh is used to solve the hyperbolic conservation laws of ideal hydrodynamics with a finite volume approach, based on a second-order unsplit Godunov scheme with an exact Riemann solver. The mesh-generating points can in principle be moved arbitrarily. If they are chosen to be stationary, the scheme is equivalent to an ordinary Eulerian method with second order accuracy. If they instead move with the velocity of the local flow, one obtains a Lagrangian formulation of hydrodynamics that does not suffer from the mesh distortion limitations inherent in othe...
Analisys of the Luminosity-Stellar Mass-Metallicity Relation in cosmological simulations
De Rossi, M E; Scannapieco, C; Rossi, Maria Emilia De; Tissera, Patricia Beatriz; Scannapieco, Cecilia
2006-01-01
We study the Luminosity-Metallicity Relation and the Stellar Mass-Metallicity Relation by performing chemo-dynamical simulations in a cosmological scenario. Our results predict a tight linear correlation between oxygen chemical abundance and luminosity for galactic systems up to z=3. The Luminosity-Metallicity Relation evolves with redshift in such a way that systems at a given oxygen abundance were ~3 dex brighter at z=3 compared to local ones, in good agreement with observations. We determin also a characteristic stellar mass M_c~10^(10.2) M_sun/h above which the Stellar Mass-Metallicity Relation starts to flatten. We encounter that this mass arises as a consequence of the hierarchical aggregation of structure in a LCDM universe and segregates two galactic populations with different astophysical properties.
Energy Technology Data Exchange (ETDEWEB)
Wainwright, Carroll L.; Aguirre, Anthony [SCIPP and Department of Physics, University of California, Santa Cruz, CA, 95064 (United States); Johnson, Matthew C. [Department of Physics and Astronomy, York University, Toronto, On, M3J 1P3 (Canada); Peiris, Hiranya V. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Lehner, Luis [Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5 (Canada); Liebling, Steven L., E-mail: cwainwri@ucsc.edu, E-mail: mjohnson@perimeterinstitute.ca, E-mail: h.peiris@ucl.ac.uk, E-mail: aguirre@scipp.ucsc.edu, E-mail: llehner@perimeterinstitute.ca, E-mail: steve.liebling@liu.edu [Department of Physics, Long Island University, Brookville, NY, 11548 (United States)
2014-03-01
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. We develop and implement an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. We first simulate the collision spacetime by solving Einstein's equations, starting from nucleation and ending at reheating. Taking advantage of the collision's hyperbolic symmetry, the simulations are performed with a 1+1-dimensional fully relativistic code that uses adaptive mesh refinement. We then calculate the comoving curvature perturbation in an open Friedmann-Robertson-Walker universe, which is used to determine the temperature anisotropies of the cosmic microwave background radiation. For a fiducial Lagrangian, the anisotropies are well described by a power law in the cosine of the angular distance from the center of the collision signature. For a given form of the Lagrangian, the resulting observational predictions are inherently statistical due to stochastic elements of the bubble nucleation process. Further uncertainties arise due to our imperfect knowledge about inflationary and pre-recombination physics. We characterize observational predictions by computing the probability distributions over four phenomenological parameters which capture these intrinsic and model uncertainties. This represents the first fully-relativistic set of predictions from an ensemble of scalar field models giving rise to eternal inflation, yielding significant differences from previous non-relativistic approximations. Thus, our results provide a basis for a rigorous confrontation of these theories with cosmological data.
Bard, D; Chang, C; May, M; Kahn, S M; AlSayyad, Y; Ahmad, Z; Bankert, J; Connolly, A; Gibson, R R; Gilmore, K; Grace, E; Haiman, Z; Hannel, M; Huffenberger, K M; Jernigan, J G; Jones, L; Krughoff, S; Lorenz, S; Marshall, S; Meert, A; Nagarajan, S; Peng, E; Peterson, J; Rasmussen, A P; Shmakova, M; Sylvestre, N; Todd, N; Young, M
2013-01-01
The statistics of peak counts in reconstructed shear maps contain information beyond the power spectrum, and can improve cosmological constraints from measurements of the power spectrum alone if systematic errors can be controlled. We study the effect of galaxy shape measurement errors on predicted cosmological constraints from the statistics of shear peak counts with the Large Synoptic Survey Telescope (LSST). We use the LSST image simulator in combination with cosmological N-body simulations to model realistic shear maps for different cosmological models. We include both galaxy shape noise and, for the first time, measurement errors on galaxy shapes. We find that the measurement errors considered have relatively little impact on the constraining power of shear peak counts for LSST.
Cosmic Explosions, Life in the Universe, and the Cosmological Constant.
Piran, Tsvi; Jimenez, Raul; Cuesta, Antonio J; Simpson, Fergus; Verde, Licia
2016-02-26
Gamma-ray bursts (GRBs) are copious sources of gamma rays whose interaction with a planetary atmosphere can pose a threat to complex life. Using recent determinations of their rate and probability of causing massive extinction, we explore what types of universes are most likely to harbor advanced forms of life. We use cosmological N-body simulations to determine at what time and for what value of the cosmological constant (Λ) the chances of life being unaffected by cosmic explosions are maximized. Life survival to GRBs favors Lambda-dominated universes. Within a cold dark matter model with a cosmological constant, the likelihood of life survival to GRBs is governed by the value of Λ and the age of the Universe. We find that we seem to live in a favorable point in this parameter space that minimizes the exposure to cosmic explosions, yet maximizes the number of main sequence (hydrogen-burning) stars around which advanced life forms can exist.
Ibata, Rodrigo A; Lewis, Geraint F; Martin, Nicolas F; Conn, Anthony; Elahi, Pascal; Arias, Veronica; Fernando, Nuwanthika
2014-01-01
In a recent contribution, Bahl \\& Baumgardt investigated the incidence of planar alignments of satellite galaxies in the Millennium-II simulation, and concluded that vast thin planes of dwarf galaxies, similar to that observed in the Andromeda galaxy (M31), occur frequently by chance in $\\Lambda$-Cold Dark Matter cosmology. However, their analysis did not capture the essential fact that the observed alignment is simultaneously radially extended, yet thin, and kinematically unusual. With the caveat that the Millennium-II simulation may not have sufficient mass resolution to identify confidently simulacra of low-luminosity dwarf galaxies, we re-examine that simulation for planar structures, using the same method as employed by Ibata et al. (2013) on the real M31 satellites. We find that 0.04\\% of host galaxies display satellite alignments that are at least as extreme as the observations, when we consider their extent, thickness and number of members rotating in the same sense. We further investigate the ang...
The evolution of galaxy metallicity scaling relations in cosmological hydrodynamical simulations
De Rossi, Maria E; Font, Andreea S; McCarthy, Ian G
2015-01-01
The evolution of the metal content of galaxies and its relations to other global properties [such as total stellar mass (M*), circular velocity, star formation rate (SFR), halo mass, etc.] provides important constraints on models of galaxy formation. Here we examine the evolution of metallicity scaling relations of simulated galaxies in the Galaxies-Intergalactic Medium Interaction Calculation suite of cosmological simulations. We make comparisons to observations of the correlation of gas-phase abundances with M* (the mass-metallicity relation, MZR), as well as with both M* and SFR or gas mass fraction (the so-called 3D fundamental metallicity relations, FMRs). The simulated galaxies follow the observed local MZR and FMRs over an order of magnitude in M*, but overpredict the metallicity of massive galaxies (log M* > 10.5), plausibly due to inefficient feedback in this regime. We discuss the origin of the MZR and FMRs in the context of galactic outflows and gas accretion. We examine the evolution of mass-metal...
Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation
Chisari, Nora Elisa; Laigle, Clotilde; Dubois, Yohan; Pichon, Christophe; Devriendt, Julien; Slyz, Adrianne; Miller, Lance; Gavazzi, Raphael; Benabed, Karim
2015-01-01
The intrinsic alignments of galaxies are recognised as a contaminant to weak gravitational lensing measurements. In this work, we study the alignment of galaxy shapes and spins at low redshift (z~0.5) in Horizon-AGN, an adaptive-mesh-refinement hydrodynamical cosmological simulation box of 100 Mpc/h a side with AGN feedback implementation. We find that spheroidal galaxies in the simulation show a tendency to be aligned radially towards over-densities in the dark matter density field and other spheroidals. This trend is in agreement with observations, but the amplitude of the signal depends strongly on how shapes are measured and how galaxies are selected in the simulation. Disc galaxies show a tendency to be oriented tangentially around spheroidals in three-dimensions. While this signal seems suppressed in projection, this does not guarantee that disc alignments can be safely ignored in future weak lensing surveys. The shape alignments of luminous galaxies in Horizon-AGN are in agreement with observations and...
The stellar metallicity distribution of disc galaxies and bulges in cosmological simulations
Calura, F; Michel-Dansac, L; Stinson, G S; Pilkington, K; House, E L; Brook, C B; Few, C G; Bailin, J; Couchman, H M P; Wadsley, J; .,
2012-01-01
By means of high-resolution cosmological hydrodynamical simulations of Milky Way-like disc galaxies, we conduct an analysis of the associated stellar metallicity distribution functions (MDFs). After undertaking a kinematic decomposition of each simulation into spheroid and disc sub-components, we compare the predicted MDFs to those observed in the solar neighbourhood and the Galactic bulge. The effects of the star formation density threshold are visible in the star formation histories, which show a modulation in their behaviour driven by the threshold. The derived MDFs show median metallicities lower by 0.2-0.3 dex than the MDF observed locally in the disc and in the Galactic bulge. Possible reasons for this apparent discrepancy include the use of low stellar yields and/or centrally-concentrated star formation. The dispersions are larger than the one of the observed MDF; this could be due to simulated discs being kinematically hotter relative to the Milky Way. The fraction of low metallicity stars is largely ...
The metal enrichment of passive galaxies in cosmological simulations of galaxy formation
Okamoto, Takashi; Nagashima, Masahiro; Lacey, Cedric G.; Frenk, Carlos S.
2017-02-01
Massive early-type galaxies have higher metallicities and higher ratios of α elements to iron than their less massive counterparts. Reproducing these correlations has long been a problem for hierarchical galaxy formation theory, both in semi-analytic models and cosmological hydrodynamic simulations. We show that a simulation in which gas cooling in massive dark haloes is quenched by radio-mode active galactic nuclei (AGNs) feedback naturally reproduces the observed trend between α/Fe and the velocity dispersion of galaxies, σ. The quenching occurs earlier for more massive galaxies. Consequently, these galaxies complete their star formation before α/Fe is diluted by the contribution from Type Ia supernovae. For galaxies more massive than ˜1011 M⊙, whose α/Fe correlates positively with stellar mass, we find an inversely correlated mass-metallicity relation. This is a common problem in simulations in which star formation in massive galaxies is quenched either by quasar- or radio-mode AGN feedback. The early suppression of gas cooling in progenitors of massive galaxies prevents them from recapturing enriched gas ejected as winds. Simultaneously reproducing the [α/Fe]-σ relation and the mass-metallicity relation is, thus, difficult in the current framework of galaxy formation.
Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations
Nelson, Katherine L.; Nagai, Daisuke
2015-01-01
Cosmological constraints from X-ray and microwave observations of galaxy clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in galaxy clusters is one of the major sources of astrophysical uncertainties, which result in large bias and scatter in the hydrostatic mass estimate. In this work, we analyze a sample of massive galaxy clusters from the Omega500 high-resolution hydrodynamic cosmological simulation to examine the effects of dynamical state on non-thermal pressure. We use the Adaptive Refinement Tree (ART) code, an Eulerian grid-based adaptive refinement mesh code, which is well suited for modeling shock heating of gas and generation of bulk and turbulent motions from cosmic accretion. We examine the effects of cluster mergers on the hydrostatic mass bias and the evolution of non-thermal pressure. We find that during a major merger about a third of the total pressure support in the system is in non-thermal pressure from random gas motions, which leads to a ~30% bias in the hydrostatic mass estimate. Even after the clusters relax, we find a residual 10% bias due to the residual non-thermal pressure sustained by continuous gas accretion and minor mergers in cluster outskirts. However, when the non-thermal pressure support is accounted for in the mass estimates of relaxed clusters, we are able to recover the true mass to within a few percent. Moreover, by accounting for the additional pressure contribution from gas accelerations, we find that the bias in the HSE can be reduced by about half for our whole cluster sample. We also characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find a universal, redshift-independent fitting formula for describing the fractional pressure support due to bulk motions. Within the relation, we find that the mass accretion rate has a systematic effect on the amount of non-thermal pressure in clusters
Numerical Convergence in the Dark Matter Halos Properties Using Cosmological Simulations
Mosquera-Escobar, X. E.; Muñoz-Cuartas, J. C.
2017-07-01
Nowadays, the accepted cosmological model is the so called -Cold Dark Matter (CDM). In such model, the universe is considered to be homogeneous and isotropic, composed of diverse components as the dark matter and dark energy, where the latter is the most abundant one. Dark matter plays an important role because it is responsible for the generation of gravitational potential wells, commonly called dark matter halos. At the end, dark matter halos are characterized by a set of parameters (mass, radius, concentration, spin parameter), these parameters provide valuable information for different studies, such as galaxy formation, gravitational lensing, etc. In this work we use the publicly available code Gadget2 to perform cosmological simulations to find to what extent the numerical parameters of the simu- lations, such as gravitational softening, integration time step and force calculation accuracy affect the physical properties of the dark matter halos. We ran a suite of simulations where these parameters were varied in a systematic way in order to explore accurately their impact on the structural parameters of dark matter halos. We show that the variations on the numerical parameters affect the structural pa- rameters of dark matter halos, such as concentration, virial radius, and concentration. We show that these modifications emerged when structures become non- linear (at redshift 2) for the scale of our simulations, such that these variations affected the formation and evolution structure of halos mainly at later cosmic times. As a quantitative result, we propose which would be the most appropriate values for the numerical parameters of the simulations, such that they do not affect the halo properties that are formed. For force calculation accuracy we suggest values smaller or equal to 0.0001, integration time step smaller o equal to 0.005 and for gravitational softening we propose equal to 1/60th of the mean interparticle distance, these values, correspond to the
Substructure in the Stellar Halos of the Aquarius Simulations
Helmi, Amina; Cooper, A. P.; White, S. D. M.; Cole, S.; Frenk, C. S.; Navarro, J. F.
2011-01-01
We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities
Davé, Romeel; Finlator, Kristian
2011-01-01
We examine the growth of the stellar content of galaxies from z=3-0 in cosmological hydrodynamic simulations incorporating parameterised galactic outflows. Without outflows, galaxies overproduce stellar masses (M*) and star formation rates (SFRs) compared to observations. Winds introduce a three-tier form for the galaxy stellar mass and star formation rate functions, where the middle tier depends on differential (i.e. mass-dependent) recycling of ejected wind material back into galaxies. A tight M*-SFR relation is a generic outcome of all these simulations, and its evolution is well-described as being powered by cold accretion, although current observations at z>2 suggest that star formation in small early galaxies must be highly suppressed. Roughly one-third of z=0 galaxies at masses below M^* are satellites, and star formation in satellites is not much burstier than in centrals. All models fail to suppress star formation and stellar mass growth in massive galaxies at z<2, indicating the need for an exter...
Martizzi, Davide; Moore, Ben
2011-01-01
We use 500 pc resolution cosmological simulations of a Virgo-like galaxy cluster to study the properties of the brightest cluster galaxy (BCG) that forms at the center of the halo. We compared two simulations; one incorporating only supernovae feedback and a second that also includes prescriptions for black hole growth and the resulting AGN feedback from gas accretion. As previous work has shown, with supernovae feedback alone we are unable to reproduce any of the observed properties of massive cluster ellipticals. The resulting BCG is rotating quickly, has a high Sersic index, a strong mass excess in the center and a total central density profile falling more steeply than isothermal. Furthermore, it is far too efficient at converting most of the available baryons into stars which is strongly constrained by abundance matching. With a treatment of black hole dynamics and AGN feedback the BCG properties are in good agreement with data: they rotate slowly, have a cored surface density profile, a flat or rising v...
Cen, Renyue
2016-01-01
Utilizing high-resolution cosmological hydrodynamic simulations we investigate various ultra-violet absorption lines in the circumgalactic medium of star forming galaxies at low redshift, in hopes of checking and alleviating the claimed observational conundrum of the ratio of NV to OVI absorbers, among others. We find a satisfactory agreement between simulations and extant observational data with respect to the ratios of the following four line pairs examined, NV/OVI, SiIV/OVI, NIII/OVI and NII/OVI. For the pairs involving nitrogen lines, we examine two cases of nitrogen abundance, one with constant N/O ratio and the other with varying N/O ratio, with the latter motivated by theoretical considerations of two different synthetic sources of nitrogen that is empirically verified independently. Along a separate vector, for all line pairs, we examine two cases of radiation field, one with the Haardt-Madau background radiation field and the other with an additional local radiation field sourced by hot gas in the ho...
Galaxy Evolution in Cosmological Simulations with Outflows II: Metallicities and Gas Fractions
Davé, Romeel; Oppenheimer, Benjamin D
2011-01-01
We use cosmological hydrodynamic simulations to investigate how inflows, star formation, and outflows govern the the gaseous and metal content of galaxies. In our simulations, galaxy metallicities are established by a balance between inflows and outflows as governed by the mass outflow rate, implying that the mass-metallicity relation reflects how the outflow rate varies with stellar mass. Gas content is set by a competition between inflow into and gas consumption within the ISM, the latter being governed by the star formation law, while the former is impacted by both wind recycling and preventive feedback. Stochasticity in the inflow rate moves galaxies off the equilibrium mass-metallicity and mass-gas fraction relations in a manner correlated with the SFR, and the scatter is set by the timescale to re-equilibrate. The evolution of both relations from z=3-0 is slow, as individual galaxies tend to evolve mostly along the relations. Gas fractions at a given stellar mass slowly decrease with time because the co...
Baryonic and dark matter distribution in cosmological simulations of spiral galaxies
Mollitor, Pol; Teyssier, Romain
2014-01-01
We study three high resolution cosmological hydrodynamical simulations of Milky Way-sized halos including a comparison with the corresponding DM-only counterparts performed with the adaptive mesh refinement code RAMSES. We analyse the stellar and the gas distribution and find one of our simulated galaxies with interesting Milky Way-like features with regard to several observational tests. Thanks to consistently tuned star formation rate and supernovae feedback, we manage to obtain an extended disk and a flat rotation curve with a circular velocity and a dark matter density in the solar neighbourhood in agreement with observations. With a careful look at the derivation of the stellar-to-halo mass ratio, we also obtain competitive values for this criterion. Concerning the dark matter distribution, we explicitly show the interaction with the baryons and show how the dark matter is first contracted by star formation and then cored by feedback processes. Analysing the clump spectrum, we find a shift in mass with r...
Gravitational torque-driven black hole growth and feedback in cosmological simulations
Anglés-Alcázar, Daniel; Davé, Romeel; Faucher-Giguère, Claude-André; Özel, Feryal; Hopkins, Philip F.
2017-01-01
We investigate black hole-host galaxy scaling relations in cosmological simulations with a self-consistent black hole growth and feedback model. Our sub-grid accretion model captures the key scalings governing angular momentum transport by gravitational torques from galactic scales down to parsec scales, while our kinetic feedback implementation enables the injection of outflows with properties chosen to match observed nuclear outflows (star formation-driven winds are not included to isolate the effects of black hole feedback). We show that `quasar mode' feedback can have a large impact on the thermal properties of the intergalactic medium and the growth of galaxies and massive black holes for kinetic feedback efficiencies as low as 0.1 per cent relative to the bolometric luminosity. None the less, our simulations indicate that the black hole-host scaling relations are only weakly dependent on the effects of black hole feedback on galactic scales, since black hole feedback suppresses the growth of galaxies and massive black holes by a similar amount. In contrast, the rate at which gravitational torques feed the central black hole relative to the host galaxy star formation rate governs the slope and normalization of the black hole-host correlations. Our results suggest that a common gas supply regulated by gravitational torques is the primary driver of the observed co-evolution of black holes and galaxies.
Evaluating galactic habitability using high-resolution cosmological simulations of galaxy formation
Forgan, Duncan; Dayal, Pratika; Cockell, Charles; Libeskind, Noam
2017-01-01
We present the first model that couples high-resolution simulations of the formation of local group galaxies with calculations of the galactic habitable zone (GHZ), a region of space which has sufficient metallicity to form terrestrial planets without being subject to hazardous radiation. These simulations allow us to make substantial progress in mapping out the asymmetric three-dimensional GHZ and its time evolution for the Milky Way (MW) and Triangulum (M33) galaxies, as opposed to works that generally assume an azimuthally symmetric GHZ. Applying typical habitability metrics to MW and M33, we find that while a large number of habitable planets exist as close as a few kiloparsecs from the galactic centre, the probability of individual planetary systems being habitable rises as one approaches the edge of the stellar disc. Tidal streams and satellite galaxies also appear to be fertile grounds for habitable planet formation. In short, we find that both galaxies arrive at similar GHZs by different evolutionary paths, as measured by the first and third quartiles of surviving biospheres. For the MW, this interquartile range begins as a narrow band at large radii, expanding to encompass much of the Galaxy at intermediate times before settling at a range of 2-13 kpc. In the case of M33, the opposite behaviour occurs - the initial and final interquartile ranges are quite similar, showing gradual evolution. This suggests that Galaxy assembly history strongly influences the time evolution of the GHZ, which will affect the relative time lag between biospheres in different galactic locations. We end by noting the caveats involved in such studies and demonstrate that high-resolution cosmological simulations will play a vital role in understanding habitability on galactic scales, provided that these simulations accurately resolve chemical evolution.
Galaxy evolution in cosmological simulations with outflows - II. Metallicities and gas fractions
Davé, Romeel; Finlator, Kristian; Oppenheimer, Benjamin D.
2011-09-01
We use cosmological hydrodynamic simulations to investigate how inflows, star formation and outflows govern the gaseous and metal content of galaxies within a hierarchical structure formation context. In our simulations, galaxy metallicities are established by a balance between inflows and outflows as governed by the mass outflow rate, implying that the mass-metallicity relation reflects how the outflow rate varies with stellar mass. Gas content, meanwhile, is set by a competition between inflow into and gas consumption within the interstellar medium, the latter being governed by the star formation law, while the former is impacted by both wind recycling and preventive feedback. Stochastic variations in the inflow rate move galaxies off the equilibrium mass-metallicity and mass-gas fraction relations in a manner correlated with the star formation rate, and the scatter is set by the time-scale to re-equilibrate. The evolution of both relations from z= 3 → 0 is slow, as individual galaxies tend to evolve mostly along the relations. Gas fractions at a given stellar mass slowly decrease with time because the cosmic inflow rate diminishes faster than the consumption rate, while metallicities slowly increase as infalling gas becomes more enriched. Observations from z˜ 3 → 0 are better matched by simulations employing momentum-driven wind scalings rather than constant wind speeds, but all models predict too low gas fractions at low masses and too high metallicities at high masses. All our models reproduce observed second-parameter trends of the mass-metallicity relation with the star formation rate and environment, indicating that these are a consequence of equilibrium and not feedback. Overall, the analytical framework of our equilibrium scenario broadly captures the relevant physics establishing the galaxy gas and metal content in simulations, which suggests that the cycle of baryonic inflows and outflows centrally governs the cosmic evolution of these properties
Comparing photometric results of real and N-body bars
Athanassoula, E; Carrasco, L; Bosma, A; De Souza, R E; Recillas, E
2009-01-01
We compare the results of the photometrical analysis of barred galaxies with those of a similar analysis from N-body simulations. The photometry is for a sample of nine barred galaxies observed in the J and Ks bands with the CANICA near infrared (NIR) camera at the 2.1-m telescope of the Observatorio Astrofisico Guillermo Haro (OAGH) in Cananea, Sonora, Mexico. The comparison includes radial ellipticity profiles and surface brightness (density for the N-body galaxies) profiles along the bar major and minor axes. We find very good agreement, arguing that the exchange of angular momentum within the galaxy plays a determinant role in the evolution of barred galaxies.
Evolution of star clusters in a cosmological tidal field
2013-01-01
We present a method to couple N-body star cluster simulations to a cosmological tidal field, using the Astrophysical Multipurpose Software Environment. We apply this method to star clusters embedded in the CosmoGrid dark matter-only LambdaCDM simulation. Our star clusters are born at z = 10 (corresponding to an age of the Universe of about 500 Myr) by selecting a dark matter particle and initializing a star cluster with 32,000 stars on its location. We then follow the dynamical evolution of t...
Li, Xiao-Dong; Forero-Romero, Jaime E; Kim, Juhan
2014-01-01
We propose a method based on the redshift dependence of the Alcock-Paczynski (AP) test to measure the expansion history of the Universe. It uses the isotropy of the galaxy density gradient field to constrain cosmological parameters. If the density parameter $\\Omega_m$ or the dark energy equation of state $w$ are incorrectly chosen, the gradient field appears to be anisotropic with the degree of anisotropy varying with redshift. We use this effect to constrain the cosmological parameters governing the expansion history of the Universe. Although redshift-space distortions (RSD) induced by galaxy peculiar velocities also produce anisotropies in the gradient field, these effects are close to uniform in magnitude over a large range of redshift. This makes the redshift variation of the gradient field anisotropy relatively insensitive to the RSD. By testing the method on mock surveys drawn from the Horizon Run 3 cosmological N-body simulations, we demonstrate that the cosmological parameters can be estimated without...
Large Scale Impact of the Cosmological Population of Expanding Radio Galaxies
Barai, Paramita
2008-01-01
We seek to compute the fraction of the volume of the Universe filled by expanding cocoons of the cosmological population of radio galaxies over the Hubble time as well as the magnetic field infused by them, in order to assess their importance in the cosmic evolution of the Universe. Using N-body $\\Lambda$CDM simulations, radio galaxies distributed according to the observed radio luminosity function are allowed to evolve in a cosmological volume as using well defined prescriptions for their expansion. We find that the radio galaxies permeate $10 - 30%$ of the total volume with $\\sim 10^{-8}$ G magnetic field by the present epoch.
Validity of Hydrostatic Equilibrium in Galaxy Clusters from Cosmological Hydrodynamical Simulations
Suto, Daichi; Kitayama, Tetsu; Sasaki, Shin; Suto, Yasushi; Cen, Renyue
2013-01-01
We examine the validity of the hydrostatic equilibrium (HSE) assumption for galaxy clusters using one of the highest-resolution cosmological hydrodynamical simulations. We define and evaluate several effective mass terms corresponding to the Euler equations of the gas dynamics, and quantify the degree of the validity of HSE in terms of the mass estimate. We find that the mass estimated under the HSE assumption (the HSE mass) deviates from the true mass by up to ~ 30 %. This level of departure from HSE is consistent with the previous claims, but our physical interpretation is rather different. We demonstrate that the inertial term in the Euler equations makes a negligible contribution to the total mass, and the overall gravity of the cluster is balanced by the thermal gas pressure gradient and the gas acceleration term. Indeed the deviation from the HSE mass is well explained by the acceleration term at almost all radii. We also clarify the confusion of previous work due to the inappropriate application of the...
Cai, Rong-Gen
2016-01-01
We investigate the gravitational wave (GW) as the standard siren to estimate the constraint ability of cosmological parameters using the third-generation gravitational wave detector: Einstein Telescope. The binary merger of a neutron with either a neutron or black hole is hypothesized to be the progenitor of a short and intense burst of $\\gamma$-rays, some fraction of those binary mergers could be detected both through electromagnetic radiation and gravitational wave. Thus we can determine both the luminosity distance and redshift of the source separately. We simulate the luminosity distance and redshift measurements from 100 to 1000 GW events. We adopt Markov chain Monte Carlo method to constrain the Hubble constant and dark matter density parameter, we find that with about 500-600 GW events we can constrain the Hubble constant with an accuracy comparable to \\textit{Planck} temperature data and \\textit{Planck} lensing combined results, while for the dark matter density, it needs about 1000 GW events. Then we...
On the dynamical state of galaxy clusters: insights from cosmological simulations II.
Cui, Weiguang; Power, Chris; Borgani, Stefano; Knebe, Alexander; Lewis, Geraint F.; Murante, Giuseppe; Poole, Gregory B.
2016-10-01
Using a suite of cosmology simulations of a sample of >120 galaxy clusters with log (MDM, vir) ≤ 14.5. We compare clusters that form in purely dark matter run and their counterparts in hydro runs and investigate 4 independent parameters, that are normally used to classify dynamical state. We find that the virial ratio η in hydro-dynamical runs is ˜10 per cent lower than in the DM run, and there is no clear separation between the relaxed and unrelaxed clusters for any parameter. Further, using the velocity dispersion deviation parameter ζ, which is defined as the ratio between cluster velocity dispersion σ and the theoretical prediction σ _t = √{G M_{total}/R}, we find that there is a linear correlation between the virial ratio η and this ζ parameter. We propose to use this ζ parameter, which can be easily derived from observed galaxy clusters, as a substitute of the η parameter to quantify the cluster dynamical state.
Heavy Dust Obscuration of z = 7 Galaxies in a Cosmological Hydrodynamic Simulation
Kimm, Taysun; Cen, Renyue
2013-10-01
Hubble Space Telescope observations with the Wide Field Camera 3/Infrared reveal that galaxies at z ~ 7 have very blue ultraviolet (UV) colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. We investigate UV and optical properties of the high-z galaxies in the standard cold dark matter model using a high-resolution adaptive mesh refinement cosmological hydrodynamic simulation. For this purpose, we perform panchromatic three-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5 × 108-3 × 1010 M ⊙ with three parameters: the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (f esc). Our stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. We find that our heavily dust-attenuated galaxies (AV ~ 1.8) can also reasonably match modest UV-optical colors, blue UV slopes, as well as UV luminosity functions, provided that a significant fraction (~10%) of light directly escapes from them. The observed UV slope and scatter are better explained with a Small-Magellanic-Cloud-type extinction curve, whereas a Milky-Way-type curve also predicts blue UV colors due to the 2175 Å bump. We expect that upcoming observations by the Atacama Large Millimeter/submillimeter Array will be able to test this heavily obscured model.
Heavy dust obscuration of z=7 galaxies in a cosmological hydrodynamic simulation
Kimm, Taysun
2013-01-01
Hubble Space Telescope observations with Wide Field Camera 3/IR reveal that galaxies at z~7 have very blue ultraviolet (UV) colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. We investigate UV and optical properties of the high-z galaxies in the standard cold dark matter model using a high-resolution adaptive mesh refinement cosmological hydrodynamic simulation. For this purpose, we perform panchromatic three-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5x10^8-3x10^{10} Msun with three parameters, the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (\\fesc). Our stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. We find that our heavily dust-attenuated galaxies (A_V~1.8) can also reasonably match modest UV-optical colors, blue UV slopes, as well as UV luminosity functions, provided that a sig...
Warps and waves in the stellar discs of the Auriga cosmological simulations
Gómez, Facundo A.; White, Simon D. M.; Grand, Robert J. J.; Marinacci, Federico; Springel, Volker; Pakmor, Rüdiger
2017-03-01
Recent studies have revealed an oscillating asymmetry in the vertical structure of the Milky Way's disc. Here, we analyse 16 high-resolution, fully cosmological simulations of the evolution of individual Milky Way-sized galaxies, carried out with the magnetohydrodynamic code AREPO. At redshift zero, about 70 per cent of our galactic discs show strong vertical patterns, with amplitudes that can exceed 2 kpc. Half of these are typical 'integral sign' warps. The rest are oscillations similar to those observed in the Milky Way. Such structures are thus expected to be common. The associated mean vertical motions can be as large as 30 km s-1. Cold disc gas typically follows the vertical patterns seen in the stars. These perturbations have a variety of causes: close encounters with satellites, distant fly-bys of massive objects, accretion of misaligned cold gas from halo infall or from mergers. Tidally induced vertical patterns can be identified in both young and old stellar populations, whereas those originating from cold gas accretion are seen mainly in the younger populations. Galaxies with regular or at most weakly perturbed discs are usually, but not always, free from recent interactions with massive companions, although we have one case where an equilibrium compact disc reforms after a merger.
Sanchez, N Nicole; Holley-Bockelmann, Kelly; Tremmel, Michael; Brooks, Alyson; Governato, Fabio; Quinn, Tom; Volonteri, Marta; Wadsley, James
2016-01-01
Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the present epoch whose evolution is characterized by several major mergers to isolate the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which analyzed the accretion of high mass, high redshift galaxies and their central black holes, and found that the gas content of the central black hole reflects what is accreted by the host galaxy halo. In this study, we find that a merger-rich galaxy will have a central SMBH preferentially fed by merger gas. Moreover, we find that nearly 30$\\%$ of the accreted mass budget of the SMBH enters the galaxy through the two major mergers in its history, which may account for the increase of merger-gas fueling the SMBH. Through an investigation of the angular momentum of th...
Star cluster formation in cosmological simulations. I. properties of young clusters
Li, Hui; Gnedin, Nickolay Y; Meng, Xi; Semenov, Vadim A; Kravtsov, Andrey V
2016-01-01
We present a new implementation of star formation in cosmological simulations, by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift, by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is $\\alpha\\approx 1.8-2$, while the cutoff at high mass scales with the star formation rate. A related trend is a positive correlation between the surface density of star formation rate and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clust...
Compaction and Quenching of High-z Galaxies: Blue and Red Nuggets in Cosmological Simulations
Zolotov, Adi; Mandelker, Nir; Tweed, Dylan; Inoue, Shigeki; DeGraf, Colin; Ceverino, Daniel; Primack, Joel
2014-01-01
We use cosmological simulations to study a characteristic evolution pattern of high redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs undergo phases of dissipative contraction into compact, star-forming systems (blue nuggets) at z~4-2. The peak of gas compaction marks the onset of central gas depletion and inside-out quenching into compact ellipticals (red nuggets) by z~2. These are sometimes surrounded by gas rings or grow extended dry stellar envelopes. The compaction occurs at a roughly constant specific star-formation rate (SFR), and the quenching occurs at a constant stellar surface density within the inner kpc (Sigma_1). Massive galaxies quench earlier, faster, and at a higher Sigma_1 than lower-mass galaxies, which compactify and attempt to quench more than once. This evolution pattern is consistent with the way galaxies populate the SFR-radius-mass space, and with gradients and scatter across the main sequence. The compaction is triggered by an intense inflow episode, involving me...
A unified model for AGN feedback in cosmological simulations of structure formation
Sijacki, Debora; Di Matteo, Tiziana; Hernquist, Lars
2007-01-01
We discuss a numerical model for black hole growth and its associated feedback processes that for the first time allows cosmological simulations of structure formation to simultaneously follow the build up of the cosmic population of galaxies and active galactic nuclei. Our model assumes that seed black holes are present at early cosmic epochs at the centres of forming halos. We then track their growth from gas accretion and mergers with other black holes in the course of cosmic time. For black holes that are active, we distinguish between two distinct modes of feedback, depending on the black hole accretion rate itself. Black holes that accrete at high rates are assumed to be in a `quasar regime', where we model their feedback by thermally coupling a small fraction of their bolometric luminosity to the surrounding gas. For black holes with low accretion rates, we conjecture that most of their feedback occurs in mechanical form, where AGN-driven bubbles are injected into a gaseous environment. Using our new m...
Far-Infrared Properties of Lyman Break Galaxies from Cosmological Simulations
Cen, Renyue
2011-01-01
Utilizing state-of-the-art, adaptive mesh-refinement cosmological hydrodynamic simulations with ultra-high resolution (114h-1pc) and large sample size (>3300 galaxies of stellar mass >10^9Msun), we show how the stellar light of Lyman Break Galaxies at z=2 is distributed between optical/ultra-violet (UV) and far-infrared (FIR) bands. With a single scalar parameter for dust obscuration we can simultaneously reproduce the observed UV luminosity function for the entire range (3-100 Msun/yr) and extant FIR luminosity function at the bright end (>20Msun/yr). We quantify that galaxies more massive or having higher SFR tend to have larger amounts of dust obscuration mostly due to a trend in column density and in a minor part due to a mass (or SFR)-metallicity relation. It is predicted that the FIR luminosity function in the range SFR=1-100Msun/yr is a powerlaw with a slope about -1.7. We further predict that there is a "galaxy desert" at SFR(FIR) < 0.02 (SFR(UV)/10Msun/yr)^2.1 Msun/yr in the SFR(UV)-SFR(FIR) plane...
Pike, Simon R; Newton, Richard D A; Thomas, Peter A; Jenkins, Adrian
2014-01-01
We present results from a new set of 30 cosmological simulations of galaxy clusters, including the effects of radiative cooling, star formation, supernova feedback, black hole growth and AGN feedback. We first demonstrate that our AGN model is capable of reproducing the observed cluster pressure profile at redshift, z~0, once the AGN heating temperature of the targeted particles is made to scale with the final virial temperature of the halo. This allows the ejected gas to reach larger radii in higher-mass clusters than would be possible had a fixed heating temperature been used. Such a model also successfully reduces the star formation rate in brightest cluster galaxies and broadly reproduces a number of other observational properties at low redshift, including baryon, gas and star fractions; entropy profiles outside the core; and the X-ray luminosity-mass relation. Our results are consistent with the notion that the excess entropy is generated via selective removal of the densest material through radiative c...
Using gaps in N-body tidal streams to probe missing satellites
Energy Technology Data Exchange (ETDEWEB)
Ngan, W. H. W.; Carlberg, R. G., E-mail: ngan@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S3H4 (Canada)
2014-06-20
We use N-body simulations to model the tidal disruption of a star cluster in a Milky-Way-sized dark matter halo, which results in a narrow stream comparable to (but slightly wider than) Pal-5 or GD-1. The mean Galactic dark matter halo is modeled by a spherical Navarro-Frenk-White potential with subhalos predicted by the ΛCDM cosmological model. The distribution and mass function of the subhalos follow the results from the Aquarius simulation. We use a matched filter approach to look for 'gaps' in tidal streams at 12 length scales from 0.1 kpc to 5 kpc, which appear as characteristic dips in the linear densities along the streams. We find that, in addition to the subhalos' perturbations, the epicyclic overdensities (EOs) due to the coherent epicyclic motions of particles in a stream also produce gap-like signals near the progenitor. We measure the gap spectra—the gap formation rates as functions of gap length—due to both subhalo perturbations and EOs, which have not been accounted for together by previous studies. Finally, we project the simulated streams onto the sky to investigate issues when interpreting gap spectra in observations. In particular, we find that gap spectra from low signal-to-noise observations can be biased by the orbital phase of the stream. This indicates that the study of stream gaps will benefit greatly from high-quality data from future missions.
Energy Technology Data Exchange (ETDEWEB)
Skillman, Samuel W.; Hallman, Eric J.; Burns, Jack O. [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Science, University of Colorado, Boulder, CO 80309 (United States); Xu, Hao; Li, Hui; Collins, David C. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); O' Shea, Brian W. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Norman, Michael L., E-mail: samuel.skillman@colorado.edu [Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093 (United States)
2013-03-01
Non-thermal radio emission from cosmic-ray electrons in the vicinity of merging galaxy clusters is an important tracer of cluster merger activity, and is the result of complex physical processes that involve magnetic fields, particle acceleration, gas dynamics, and radiation. In particular, objects known as radio relics are thought to be the result of shock-accelerated electrons that, when embedded in a magnetic field, emit synchrotron radiation in the radio wavelengths. In order to properly model this emission, we utilize the adaptive mesh refinement simulation of the magnetohydrodynamic evolution of a galaxy cluster from cosmological initial conditions. We locate shock fronts and apply models of cosmic-ray electron acceleration that are then input into radio emission models. We have determined the thermodynamic properties of this radio-emitting plasma and constructed synthetic radio observations to compare observed galaxy clusters. We find a significant dependence of the observed morphology and radio relic properties on the viewing angle of the cluster, raising concerns regarding the interpretation of observed radio features in clusters. We also find that a given shock should not be characterized by a single Mach number. We find that the bulk of the radio emission comes from gas with T > 5 Multiplication-Sign 10{sup 7} K, {rho} {approx} 10{sup -28}-10{sup -27} g cm{sup -3}, with magnetic field strengths of 0.1-1.0 {mu}G, and shock Mach numbers of M {approx} 3-6. We present an analysis of the radio spectral index which suggests that the spatial variation of the spectral index can mimic synchrotron aging. Finally, we examine the polarization fraction and position angle of the simulated radio features, and compare to observations.
Bar-driven evolution and quenching of spiral galaxies in cosmological simulations
Spinoso, Daniele; Bonoli, Silvia; Dotti, Massimo; Mayer, Lucio; Madau, Piero; Bellovary, Jillian
2017-03-01
We analyse the outputs of the cosmological 'zoom-in' hydrodynamical simulation ErisBH to study a strong stellar bar which naturally emerges in the late evolution of the simulated Milky Way-type galaxy. We focus on the analysis of the formation and evolution of the bar and on its effects on the galactic structure, the gas distribution and the star formation. A large central region in the ErisBH disc becomes bar unstable after z ∼ 1.4, but a clear bar starts to grow significantly only after z ≃ 0.4, possibly triggered by the interaction with a massive satellite. At z ≃ 0.1, the bar stabilizes and reaches its maximum radial extent of l ≈ 2.2 kpc. As the bar grows, it becomes prone to buckling instability. The actual buckling event, observable at z ≃ 0.1, results in the formation of a boxy-peanut bulge clearly discernible at z = 0. During its early growth, the bar exerts a strong torque on the gas and drives gas inflows that enhance the nuclear star formation on sub-kpc scales. Later on, as the bar reaches its maximum length and strength, the gas within its extent is nearly all consumed into stars, leaving behind a gas-depleted region in the central ∼2 kpc. Observations would more likely identify a prominent, large-scale bar at the stage when the galactic central region has already been gas depleted, giving a hint at the fact that bar-driven quenching may play an important role in the evolution of disc-dominated galaxies.
Simulations of the WFIRST Supernova Survey and Forecasts of Cosmological Constraints
Energy Technology Data Exchange (ETDEWEB)
Hounsell, R. [Illinois U., Urbana, Astron. Dept.; Scolnic, D. [Chicago U., KICP; Foley, R. J. [UC, Santa Cruz; Kessler, R. [Chicago U., KICP; Miranda, V. [Pennsylvania U.; Avelino, A. [Harvard-Smithsonian Ctr. Astrophys.; Bohlin, R. C. [Baltimore, Space Telescope Sci.; Filippenko, A. V. [UC, Berkeley; Frieman, J. [Fermilab; Jha, S. W. [Rutgers U., Piscataway; Kelly, P. L. [UC, Berkeley; Kirshner, R. P. [Xerox, Palo Alto; Mandel, K. [Harvard-Smithsonian Ctr. Astrophys.; Rest, A. [Baltimore, Space Telescope Sci.; Riess, A. G. [Johns Hopkins U.; Rodney, S. A. [South Carolina U.; Strolger, L. [Baltimore, Space Telescope Sci.
2017-02-06
The Wide Field InfraRed Survey Telescope (WFIRST) was the highest rankedlarge space-based mission of the 2010 New Worlds, New Horizons decadal survey.It is now a NASA mission in formulation with a planned launch in themid-2020's. A primary mission objective is to precisely constrain the nature ofdark energy through multiple probes, including Type Ia supernovae (SNe Ia).Here, we present the first realistic simulations of the WFIRST SN survey basedon current hardware specifications and using open-source tools. We simulate SNlight curves and spectra as viewed by the WFIRST wide-field channel (WFC)imager and integral field channel (IFC) spectrometer, respectively. We examine11 survey strategies with different time allocations between the WFC and IFC,two of which are based upon the strategy described by the WFIRST ScienceDefinition Team, which measures SN distances exclusively from IFC data. Wepropagate statistical and, crucially, systematic uncertainties to predict thedark energy task force figure of merit (DETF FoM) for each strategy. Theincrease in FoM values with SN search area is limited by the overhead times foreach exposure. For IFC-focused strategies the largest individual systematicuncertainty is the wavelength-dependent calibration uncertainty, whereas forWFC-focused strategies, it is the intrinsic scatter uncertainty. We find thatthe best IFC-focused and WFC-exclusive strategies have comparable FoM values.Even without improvements to other cosmological probes, the WFIRST SN surveyhas the potential to increase the FoM by more than an order of magnitude fromthe current values. Although the survey strategies presented here have not beenfully optimized, these initial investigations are an important step in thedevelopment of the final hardware design and implementation of the WFIRSTmission.
Energy Technology Data Exchange (ETDEWEB)
Heitmann, Katrin [Los Alamos National Laboratory; Habib, Salman [Los Alamos National Laboratory; Higdon, David [Los Alamos National Laboratory; Williams, Brian J [Los Alamos National Laboratory; White, Martin [Los Alamos National Laboratory; Wagner, Christian [Los Alamos National Laboratory
2008-01-01
The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the 'Coyote Universe' suite -- can be used to predict the nonlinear matter power spectrum at the required accuracy over a prior parameter range set by cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.
Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters
Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; Meng, Xi; Semenov, Vadim A.; Kravtsov, Andrey V.
2017-01-01
We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is α ≈ 1.8{--}2, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. Comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.
Energy Technology Data Exchange (ETDEWEB)
Levine, Robyn Deborah [Univ. of Colorado, Boulder, CO (United States)
2008-01-01
Supermassive black holes (SMBHs) are ubiquitous in the centers of galaxies. Their formation and subsequent evolution is inextricably linked to that of their host galaxies, and the study of galaxy formation is incomplete without the inclusion of SMBHs. The present work seeks to understand the growth and evolution of SMBHs through their interaction with the host galaxy and its environment. In the first part of the thesis (Chap. 2 and 3), we combine a simple semi-analytic model of outflows from active galactic nuclei (AGN) with a simulated dark matter density distribution to study the impact of SMBH feedback on cosmological scales. We find that constraints can be placed on the kinetic efficiency of such feedback using observations of the filling fraction of the Lyα forest. We also find that AGN feedback is energetic enough to redistribute baryons over cosmological distances, having potentially significant effects on the interpretation of cosmological data which are sensitive to the total matter density distribution (e.g. weak lensing). However, truly assessing the impact of AGN feedback in the universe necessitates large-dynamic range simulations with extensive treatment of baryonic physics to first model the fueling of SMBHs. In the second part of the thesis (Chap. 4-6) we use a hydrodynamic adaptive mesh refinement simulation to follow the growth and evolution of a typical disk galaxy hosting a SMBH, in a cosmological context. The simulation covers a dynamical range of 10 million allowing us to study the transport of matter and angular momentum from super-galactic scales all the way down to the outer edge of the accretion disk around the SMBH. Focusing our attention on the central few hundred parsecs of the galaxy, we find the presence of a cold, self-gravitating, molecular gas disk which is globally unstable. The global instabilities drive super-sonic turbulence, which maintains local stability and allows gas to fuel a SMBH without first fragmenting completely
Can we distinguish early dark energy from a cosmological constant?
Shi, Difu; Baugh, Carlton M.
2016-07-01
Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology using recent measurements of the cosmic microwave background and baryon acoustic oscillations. The best-fitting models favour no EDE; here we consider extreme examples which are in mild tension with current observations in order to explore the observational consequences of a maximally allowed amount of EDE. We study the non-linear evolution of cosmic structure in EDE cosmologies using large-volume N-body simulations. Many large-scale structure statistics are found to be very similar between the Λ cold dark matter (ΛCDM) and EDE models. We find that EDE cosmologies predict fewer massive haloes in comparison to ΛCDM, particularly at high redshifts. The most promising way to distinguish EDE from ΛCDM is to measure the power spectrum on large scales, where differences of up to 15 per cent are expected.
Rodriguez-Puebla, Aldo; Primack, Joel; Klypin, Anatoly; Lee, Christoph; Hellinger, Doug
2016-01-01
We report and provide fitting functions for the abundance of dark matter halos and subhalos as a function of mass, circular velocity, and redshift from the new Bolshoi-Planck and MultiDark-Planck $\\Lambda$CDM cosmological simulations, based on the Planck cosmological parameters. We also report the halo mass accretion rates, which may be connected with galaxy star formation rates. We show that the higher cosmological matter density of the Planck parameters compared with the WMAP parameters leads to higher abundance of massive halos at high redshifts. We find that the median halo spin parameter $\\lambda_{\\rm B} = J(2M_{\\rm vir}R_{\\rm vir}V_{\\rm vir})^{-1}$ is nearly independent of redshift, leading to predicted evolution of galaxy sizes that is consistent with observations, while the significant decrease with redshift in median $\\lambda_{\\rm P} = J|E|^{-1/2}G^{-1}M^{-5/2}$ predicts more decrease in galaxy sizes than is observed. Using the Tully-Fisher and Faber-Jackson relations between galaxy velocity and mass...
Vlasov versus N-body: the H\\'enon sphere
Colombi, S; Peirani, S; Plum, G; Suto, Y
2015-01-01
We perform a detailed comparison of the phase-space density traced by the particle distribution in Gadget simulations to the result obtained with a spherical Vlasov solver using the splitting algorithm. The systems considered are apodized H\\'enon spheres with two values of the virial ratio, R ~ 0.1 and 0.5. After checking that spherical symmetry is well preserved by the N-body simulations, visual and quantitative comparisons are performed. In particular we introduce new statistics, correlators and entropic estimators, based on the likelihood of whether N-body simulations actually trace randomly the Vlasov phase-space density. When taking into account the limits of both the N-body and the Vlasov codes, namely collective effects due to the particle shot noise in the first case and diffusion and possible nonlinear instabilities due to finite resolution of the phase-space grid in the second case, we find a spectacular agreement between both methods, even in regions of phase-space where nontrivial physical instabi...
Zentner, A R
2003-01-01
Improvements in observational techniques have transformed cosmology into a field inundated with ever-expanding, high-quality data sets and driven cosmology toward a standard model where the classic cosmological parameters are accurately measured. I briefly discuss some of the methods used to determine cosmological parameters, particularly primordial nucleosynthesis, the magnitude- redshift relation of supernovae, and cosmic microwave background anisotropy. I demonstrate how cosmological data can be used to complement particle physics and constrain extensions to the Standard Model. Specifically, I present bounds on light particle species and the properties of unstable, weakly-interacting, massive particles. Despite the myriad successes of the emerging standard cosmological model, unanswered questions linger. Numerical simulations of structure formation predict galactic central densities that are considerably higher than observed. They also reveal hundreds of satellites orbiting Milky Way-like galaxies while th...
Non-linear structure formation in the `Running FLRW' cosmological model
Bibiano, Antonio; Croton, Darren J.
2016-07-01
We present a suite of cosmological N-body simulations describing the `Running Friedmann-Lemaïtre-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Lambda cold dark matter (ΛCDM) with a time-evolving vacuum density, Λ(z), and time-evolving gravitational Newton's coupling, G(z). In this paper, we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realization of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalization choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the deviations of R-FLRW from ΛCDM, which could be readily exploited by future cosmological observations to test and further constrain the model.
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations
Pietroni, Massimo
2008-01-01
Nonlinear effects are crucial in order to compute the cosmological matter power spectrum to the accuracy required by future generation surveys. Here, a new approach is presented, in which the power spectrum and the bispectrum are obtained -at any redshift and for any momentum scale- by integrating a coupled system of differential equations. The solution of the equations corresponds, in perturbation theory, to the summation of an infinite class of corrections. Compared to other resummation frameworks, the scheme discussed here is particularly suited to cosmologies other than LambdaCDM, such as those based on modifications of gravity and those containing massive neutrinos. As a first application, we compute the Baryonic Acoustic Oscillation feature of the power spectrum, and compare the results with perturbation theory, the halo model, and N-body simulations. The density-velocity and velocity-velocity power spectra are also computed, showing that they are much less contaminated by nonlinearities than the densit...
Pairwise velocities in the "Running FLRW" cosmological model
Bibiano, Antonio; Croton, Darren J.
2017-01-01
We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the "Running Friedmann-Lemaître-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends ΛCDM with a time-evolving vacuum energy density, ρ _Λ. To enforce local conservation of matter a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and σ8 at z = 0 for almost all scenarios considered, which remains even when we look back to epochs as early as z = 2. We also investigate various Coupled Dark Energy models, some of which show minimal degeneracy, and reveal interesting deviations from ΛCDM which could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.
Sapporo2: a versatile direct N-body library
Bédorf, Jeroen; Gaburov, Evghenii; Portegies Zwart, Simon
2015-10-01
Astrophysical direct N-body methods have been one of the first production algorithms to be implemented using NVIDIA's CUDA architecture. Now, almost seven years later, the GPU is the most used accelerator device in astronomy for simulating stellar systems. In this paper we present the implementation of the Sapporo2 N-body library, which allows researchers to use the GPU for N-body simulations with little to no effort. The first version, released five years ago, is actively used, but lacks advanced features and versatility in numerical precision and support for higher order integrators. In this updated version we have rebuilt the code from scratch and added support for OpenCL, multi-precision and higher order integrators. We show how to tune these codes for different GPU architectures and present how to continue utilizing the GPU optimal even when only a small number of particles (N OpenCL support the library is also able to run on CPUs and other accelerators that support OpenCL.
Sapporo2: A versatile direct $N$-body library
Bédorf, Jeroen; Zwart, Simon Portegies
2015-01-01
Astrophysical direct $N$-body methods have been one of the first production algorithms to be implemented using NVIDIA's CUDA architecture. Now, almost seven years later, the GPU is the most used accelerator device in astronomy for simulating stellar systems. In this paper we present the implementation of the Sapporo2 $N$-body library, which allows researchers to use the GPU for $N$-body simulations with little to no effort. The first version, released five years ago, is actively used, but lacks advanced features and versatility in numerical precision and support for higher order integrators. In this updated version we have rebuilt the code from scratch and added support for OpenCL, multi-precision and higher order integrators. We show how to tune these codes for different GPU architectures and present how to continue utilizing the GPU optimal even when only a small number of particles ($N < 100$) is integrated. This careful tuning allows Sapporo2 to be faster than Sapporo1 even with the added options and d...
Chaotic dynamics in N-body systems
Boekholt, Tjarda Coenraad Nico
2015-01-01
Ever since Isaac Newton in 1687 posed the N-body problem, astronomers have been looking for its solutions in order to understand the evolution of dynamical systems, such as our own solar system, star clusters and galaxies. The main difficulty is that small errors grow exponentially, so that numerica
Chaotic dynamics in N-body systems
Boekholt, Tjarda Coenraad Nico
2015-01-01
Ever since Isaac Newton in 1687 posed the N-body problem, astronomers have been looking for its solutions in order to understand the evolution of dynamical systems, such as our own solar system, star clusters and galaxies. The main difficulty is that small errors grow exponentially, so that
Booth, C M
2009-01-01
(Abridged) We present a method that tracks the growth of supermassive black holes (BHs) and the feedback from AGN in cosmological simulations. Our model is a substantially modified version of the one by Springel et al. (2005). Because cosmological simulations lack both the resolution and the physics to model the multiphase interstellar medium, they tend to strongly underestimate the Bondi-Hoyle accretion rate. To allow low-mass BHs to grow, it is therefore necessary to increase the predicted Bondi-Hoyle rates in dense gas by large, ad-hoc factors. We explore the physical regimes where the use of such factors is reasonable, and through this introduce a new prescription for gas accretion. Feedback from AGN is modeled by coupling a fraction of the rest-mass energy of the accreted gas thermally into the surrounding medium. We describe the implementation as well as the limitations of the model and motivate all the changes relative to previous work. We investigate the robustness of the predictions for the cosmic st...
Wetzel, Andrew R; Kim, Ji-hoon; Faucher-Giguere, Claude-Andre; Keres, Dusan; Quataert, Eliot
2016-01-01
Low-mass "dwarf" galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present the first results from the Latte Project: the Milky Way on FIRE (Feedback in Realistic Environments). This simulation models the formation of a MW-mass galaxy to z = 0 within LCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon mass of 7070 M_sun at spatial resolution down to 1 pc. Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the internal structure of dwarf galaxies that form around a MW-mass host down to M_star > 10^5 M_sun. Latte's population of ...
Cora, S A; Lambas, D G; Mosconi, M B
2000-01-01
We present preliminary results on the effects of mergers on the chemical properties of galactic objects in hierarchical clustering scenarios. We adopt a hydrodynamical chemical code that allows to describe the coupled evolution of dark matter and baryons within a cosmological context. We found that disk-like and spheroid-like objects have distinctive metallicity patterns that may be the result of different evolution.
Thermodynamic evolution of cosmological baryonic gas: I. Influence of non-equipartition processes
Courty, S
2003-01-01
Using N-body/hydrodynamic simulations, the influence of non-equipartition processes on the thermal and dynamical properties of cosmological baryonic gas is investigated. We focus on a possible departure from equilibrium between electrons, ions and neutral atoms in low temperature (10^4-10^6 K) and weakly ionized regions of the intergalactic medium. The simulations compute the energy exchanges between ions, neutrals and electrons, without assuming thermal equilibrium. They include gravitation, shock heating and cooling processes, and follow self-consistently the chemical evolution of a primordial composition hydrogen-helium plasma without assuming collisional ionization equilibrium. At high redshift, a significant fraction of the intergalactic medium is found to be warmer and weakly ionized in simulations with non-equipartition processes than in simulations in which the cosmological plasma is considered to be in thermodynamic equilibrium. With a semi-analytical study of the out of equilibrium regions we show t...
A refined sub-grid model for black hole accretion and AGN feedback in large cosmological simulations
Bachmann, Lisa K; Hirschmann, Michaela; Prieto, M Almudena; Remus, Rhea-Silvia
2014-01-01
In large scale cosmological hydrodynamic simulations simplified sub-grid models for gas accretion onto black holes and AGN feedback are commonly used. Such models typically depend on various free parameters, which are not well constrained. We present a new advanced model containing a more detailed description of AGN feedback, where those parameters reflect the results of recent observations. The model takes the dependency of these parameters on the black hole properties into account and describes a continuous transition between the feedback processes acting in the so-called radio-mode and quasar-mode. In addition, we implement a more detailed description of the accretion of gas onto black holes by distinguishing between hot and cold gas accretion. Our new implementations prevent black holes from gaining too much mass, particularly at low redshifts so that our simulations are now very successful in reproducing the observed present-day black hole mass function. Our new model also suppresses star formation in ma...
Wang, Liang; Stinson, Gregory S; Macciò, Andrea V; Penzo, Camilla; Kang, Xi; Keller, Ben W; Wadsley, James
2015-01-01
We introduce project NIHAO (Numerical Investigation of a Hundred Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical simulations performed using the GASOLINE code, with an improved implementation of the SPH algorithm. The haloes in our study range from dwarf to Milky Way masses, and represent an unbiased sampling of merger histories, concentrations and spin parameters. The particle masses and force softenings are chosen to resolve the mass profile to below 1% of the virial radius at all masses, ensuring that galaxy half-light radii are well resolved. Using the same treatment of star formation and stellar feedback for every object, the simulated galaxies reproduce the observed inefficiency of galaxy formation across cosmic time as expressed through the stellar mass vs halo mass relation, and the star formation rate vs stellar mass relation. We thus conclude that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than t...
The shape of dark matter haloes in the Aquarius simulations : evolution and memory
Vera-Ciro, Carlos A.; Sales, Laura V.; Helmi, Amina; Frenk, Carlos S.; Navarro, Julio F.; Springel, Volker; Vogelsberger, Mark; White, Simon D. M.
2011-01-01
We use the high-resolution cosmological N-body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time
The shape of dark matter haloes in the Aquarius simulations: evolution and memory
Vera-Ciro, Carlos A.; Sales, Laura V.; Helmi, Amina; Frenk, Carlos S.; Navarro, Julio F.; Springel, Volker; Vogelsberger, Mark; White, Simon D. M.
2011-01-01
We use the high-resolution cosmological N-body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time
The shape of dark matter haloes in the Aquarius simulations : Evolution and memory
Vera-Ciro, C.A.; Sales, L. V.; Helmi, A.; Reyle, C; Robin, A; Schultheis, M
2012-01-01
We use the high resolution cosmological N-body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way-type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time
The shape of dark matter haloes in the Aquarius simulations: Evolution and memory
Vera-Ciro, C. A.; Sales, L. V.; Helmi, A.
2012-01-01
We use the high resolution cosmological N-body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way-type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time
Rodríguez-Puebla, Aldo; Behroozi, Peter; Primack, Joel; Klypin, Anatoly; Lee, Christoph; Hellinger, Doug
2016-10-01
We report and provide fitting functions for the abundance of dark matter haloes and subhaloes as a function of mass, circular velocity, and redshift from the new Bolshoi-Planck and MultiDark-Planck ΛCDM cosmological simulations, based on the Planck parameters. We also report halo mass accretion rates and concentrations. We show that the higher cosmological matter density of the Planck parameters compared with the WMAP parameters leads to higher abundance of massive haloes at high redshifts. We find that the median halo spin parameter {λ _B}= J(√{2}M_virR_virV_vir)^{-1} is nearly independent of redshift, leading to predicted evolution of galaxy sizes that is consistent with observations, while the significant decrease with redshift in median {λ _P}= J|E|^{-1/2}G^{-1}M^{-5/2} predicts more decrease in galaxy sizes than is observed. Using the Tully-Fisher and Faber-Jackson relations between galaxy velocity and mass, we show that a simple model of how galaxy velocity is related to halo maximum circular velocity leads to increasing overprediction of cosmic stellar mass density as redshift increases beyond z ˜ 1, implying that such velocity-mass relations must change at z ≳ 1. By making a realistic model of how observed galaxy velocities are related to halo circular velocity, we show that recent optical and radio observations of the abundance of galaxies are in good agreement with our ΛCDM simulations. Our halo demographics are based on updated versions of the ROCKSTAR and CONSISTENT TREES codes, and this paper includes appendices explaining all of their outputs. This paper is an introduction to a series of related papers presenting other analyses of the Bolshoi-Planck and MultiDark-Planck simulations.
Grieb, Jan Niklas; Salazar-Albornoz, Salvador; Scoccimarro, Román; Crocce, Martín; Vecchia, Claudio Dalla; Montesano, Francesco; Gil-Marín, Héctor; Ross, Ashley J; Beutler, Florian; Rodríguez-Torres, Sergio; Chuang, Chia-Hsun; Prada, Francisco; Kitaura, Francisco-Shu; Cuesta, Antonio J; Eisenstein, Daniel J; Percival, Will J; Vargas-Magana, Mariana; Tinker, Jeremy L; Tojeiro, Rita; Brownstein, Joel R; Maraston, Claudia; Nichol, Robert C; Olmstead, Matthew D; Samushia, Lado; Seo, Hee-Jong; Streblyanska, Alina; Zhao, Gong-bo
2016-01-01
We extract cosmological information from the anisotropic power spectrum measurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new FFT-based estimators, we measure the power spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles l > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias, and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular diameter distance, the Hubble parameter, and the cosmic growth rate, and explore the cosmological implications of our full shape clustering measurements in combination with CMB and SN Ia data. Assuming a {\\Lambda}CDM cosmology, we constra...
Shimizu, Ikkoh; Yoshida, Naoki; Okamoto, Takashi
2015-01-01
We have performed very large and high resolution cosmological hydrodynamics simulations in order to investigate detectability of nebular lines in the rest-frame UV to optical wavelength range from galaxies at z>7. We use a light-cone output to select galaxies at z~7-10 by the same color and magnitude criteria as real observations (Hubble Ultra Deep Survey). The UV dust attenuation is ~ 0.5 mag for galaxies with H160 10 galaxies will be found with the next generation telescopes such as the JWST, the Wide-Field Infrared Survey Telescope (WFIRST) and Wide-field Imaging Surveyor for High-Redshift (WISH) (11 9 galaxy candidates (MACS1149JD and MACS0647JD1) can be detectable using even the current facilities such as the VLT/X-Shooter and the Keck/MOSFIRE with high probability.
DEFF Research Database (Denmark)
Velonà, A. D Romeo; Sommer-Larsen, J.; Napolitano, N. R.;
2013-01-01
We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star......-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided...... groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M * plane...
Non-linear structure formation in the "Running FLRW" cosmological model
Bibiano, Antonio
2016-01-01
We present a suite of cosmological N-body simulations describing the "Running Friedmann-Lema{\\"i}tre-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends {\\Lambda}CDM with a time-evolving vacuum density, {\\Lambda}(z), and time-evolving gravitational Newton's coupling, G(z). In this paper we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realisation of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalisation choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the...
Sokołowska, Aleksandra; Capelo, Pedro R.; Fall, S. Michael; Mayer, Lucio; Shen, Sijing; Bonoli, Silvia
2017-02-01
We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way–sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *–M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation {j}* \\propto {M}* α past major mergers, with α ∼ 0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α ∼ 1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.
Feldmann, Robert
2014-01-01
Observations show a prevalence of high redshift galaxies with large stellar masses and predominantly passive stellar populations. A variety of processes have been suggested that could reduce the star formation in such galaxies to observed levels, including quasar mode feedback, virial shock heating, or galactic winds driven by stellar feedback. However, the main quenching mechanisms have yet to be identified. Here we study the origin of star formation quenching using Argo, a cosmological zoom-in simulation that follows the evolution of a massive galaxy at $z\\geq{}2$. This simulation adopts the same sub-grid recipes of the Eris simulations, which have been shown to form realistic disk galaxies, and, in one version, adopts also a mass and spatial resolution identical to Eris. The resulting galaxy has properties consistent with those of observed, massive (M_* ~ 1e11 M_sun) galaxies at z~2 and with abundance matching predictions. Our models do not include AGN feedback indicating that supermassive black holes like...
Cosmological shock waves: clues to the formation history of haloes
Planelles, Susana
2012-01-01
Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal weak shocks related with evolutionary events within haloes, and external strong shocks associated with large-scale events. The shock distribution function contains information on the abundances and strength of the different shocks, and it can be fitted by a double power law with a break in the slope around a Mach number of 2...
Cosmological Structure Formation in Decaying Dark Matter Models
Cheng, Dalong; Tang, Jiayu
2015-01-01
The standard cold dark matter (CDM) model predicts too many and too dense small structures. We consider an alternative model that the dark matter undergoes two-body decays with cosmological lifetime $\\tau$ into only one type of massive daughters with non-relativistic recoil velocity $V_k$. This decaying dark matter model (DDM) can suppress the structure formation below its free-streaming scale at time scale comparable to $\\tau$. Comparing with warm dark matter (WDM), DDM can better reduce the small structures while being consistent with high redshfit observations. We study the cosmological structure formation in DDM by performing self-consistent N-body simulations and point out that cosmological simulations are necessary to understand the DDM structures especially on non-linear scales. We propose empirical fitting functions for the DDM suppression of the mass function and the mass-concentration relation, which depend on the decay parameters lifetime $\\tau$ and recoil velocity $V_k$, and redshift. The fitting ...
Cosmology and cluster halo scaling relations
Araya-Melo, Pablo A.; van de Weygaert, Rien; Jones, Bernard J. T.
2009-01-01
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 s
Iliev, Ilian Tzankov
observations. TIS reproduces many of the average properties of halos in simulations of the Cold Dark Matter (CDM) model to good accuracy, suggesting it is a useful analytical approximation for halos which form from realistic initial conditions. It matches the density profiles of halos found in CDM N-body simulations outside the innermost region, while avoiding the steep central cusp of the latter which is in apparent conflict with observations. Based on the TIS we also predict the virial temperature and integrated mass distribution of the X-ray clusters formed in the CDM model as found by detailed, 3D, numerical gas and N-body dynamical simulations remarkably well. Our model may also be relevant to nonstandard CDM models, like self-interacting dark matter, recently proposed to resolve this conflict. A possible solution to the problems of the standard CDM model which does not require modification of the microscopic nature of the dark matter is to take proper account of the gasdynamical effects, including feedback caused by energy release during the process of structure formation. Such effects are of particular importance during the reionization of the universe by the first objects that form out of the expanding background. We study the effects of external ionizing radiation on the collapse of cosmological pancakes. We also investigate the effects and observational signatures of ionization fronts during reionization which sweep through the intergalactic medium and photoevaporate cosmological minihalos they encounter.
Ostriker, J P; Ostriker, Jeremiah P; Cen, Renyue
1996-01-01
We compute, including a current state-of-the-art treatment of hydrodynamical processes, heating and cooling, a variety of cosmological models into the extreme nonlinear phase to enable comparisons with observations. First, we note the common, model independent results. All have a mean (z=0) temperature of 10^{4.5}-10^{5.5}\\Kel, set essentially by photoheating processes. Most gas is in one of two components: either at the photoheating floor 10^{4.5}\\Kel and primarily in low density regions or else shock heated to 10^5-10^6\\Kel and in regions of moderate overdensity (in caustics and near groups and clusters). It presents a major observational challenge to observationally detect this second, abundant component as it is neither an efficient radiator nor absorber. About 2\\% to 10\\% of the baryons cool and collapse into galaxies forming on caustics and migrating to clusters. About 1\\%-2\\% of baryons are in the very hot X-ray emitting gas near cluster cores, in good agreement with observations. These correspondances...
Wang, Liang; Dutton, Aaron A.; Stinson, Gregory S.; Macciò, Andrea V.; Penzo, Camilla; Kang, Xi; Keller, Ben W.; Wadsley, James
2015-11-01
We introduce project NIHAO (Numerical Investigation of a Hundred Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical simulations performed using the GASOLINE code, with an improved implementation of the SPH algorithm. The haloes in our study range from dwarf (M200 ˜ 5 × 109 M⊙) to Milky Way (M200 ˜ 2 × 1012 M⊙) masses, and represent an unbiased sampling of merger histories, concentrations and spin parameters. The particle masses and force softenings are chosen to resolve the mass profile to below 1 per cent of the virial radius at all masses, ensuring that galaxy half-light radii are well resolved. Using the same treatment of star formation and stellar feedback for every object, the simulated galaxies reproduce the observed inefficiency of galaxy formation across cosmic time as expressed through the stellar mass versus halo mass relation, and the star formation rate versus stellar mass relation. We thus conclude that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than the Milky Way.
Counts-in-Cylinders in the Sloan Digital Sky Survey with Comparisons to N-Body
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Berrier, Heather D.; Barton, Elizabeth J.; /UC, Irvine; Berrier, Joel C.; /Arkansas U.; Bullock, James S.; /UC, Irvine; Zentner, Andrew R.; /Pittsburgh U.; Wechsler, Risa H. /KIPAC, Menlo Park /SLAC
2010-12-16
Environmental statistics provide a necessary means of comparing the properties of galaxies in different environments and a vital test of models of galaxy formation within the prevailing, hierarchical cosmological model. We explore counts-in-cylinders, a common statistic defined as the number of companions of a particular galaxy found within a given projected radius and redshift interval. Galaxy distributions with the same two-point correlation functions do not necessarily have the same companion count distributions. We use this statistic to examine the environments of galaxies in the Sloan Digital Sky Survey, Data Release 4. We also make preliminary comparisons to four models for the spatial distributions of galaxies, based on N-body simulations, and data from SDSS DR4 to study the utility of the counts-in-cylinders statistic. There is a very large scatter between the number of companions a galaxy has and the mass of its parent dark matter halo and the halo occupation, limiting the utility of this statistic for certain kinds of environmental studies. We also show that prevalent, empirical models of galaxy clustering that match observed two- and three-point clustering statistics well fail to reproduce some aspects of the observed distribution of counts-in-cylinders on 1, 3 and 6-h{sup -1}Mpc scales. All models that we explore underpredict the fraction of galaxies with few or no companions in 3 and 6-h{sup -1} Mpc cylinders. Roughly 7% of galaxies in the real universe are significantly more isolated within a 6 h{sup -1} Mpc cylinder than the galaxies in any of the models we use. Simple, phenomenological models that map galaxies to dark matter halos fail to reproduce high-order clustering statistics in low-density environments.
Scannapieco, C.
2013-06-01
I use cosmological hydrodynamical simulations to study the formation and evolution of galaxies similar in mass to the Milky Way. First, I use a set of eight simulations where the haloes have a great variety of merger and formation histories, to investigate how similar or diverse these galaxies are at the present epoch, and how their final properties are related to the particular formation history of the galaxy. I find that rotationally-supported disks are present in 7 of the 8 galaxies at {z˜ 2}-3; however, only half of the galaxies have significant disks at z=0. Both major mergers and the accretion of gas that is misaligned with the preexisting stellar disk contribute to the transfer of material from the disks to the spheroidal components, lowering the disk-to-total ratios during evolution. I also present and discuss recent results of the Aquila Project, which compares the predictions of 13 different numerical codes for the properties of a galaxy in a \\Lambda cold dark matter universe. All simulations use a unique initial condition and are analysed in the exact same way, allowing a fair comparison of results. We find large code-to-code variations in stellar masses, star formation rates, galaxy sizes and morphologies. We also find that the way feedback is implemented is the main cause of the differences, although some differences might also result from the use of different numerical technique. Our results show that state-of-the-art simulations cannot yet uniquely predict the properties of the baryonic component of a galaxy, even when the assembly history of its host halo is fully specified.
The Challenge of the Largest Structures in the Universe to Cosmology
Park, Changbom; Kim, Juhan; Gott, J Richard; Kim, Sungsoo S; Kim, Kap-Sung
2012-01-01
Large galaxy redshift surveys have long been used to constrain cosmological models and structure formation scenarios. In particular, the largest structures discovered observationally are thought to carry critical information on the amplitude of large-scale density fluctuations or homogeneity of the universe, and have often challenged the standard cosmological framework. The Sloan Great Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts doubt on the concordance cosmological model with a cosmological constant (i.e. the flat LCDM model). Here we show that the existence of the SGW is perfectly consistent with the LCDM model, a result that only our very large cosmological N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report on the discovery of a void complex in the SDSS much larger than the SGW, and show that such size of the largest void is also predicted in the LCDM paradigm. Our results demonstrate that an initially homogeneous isotropic universe with primor...
Jones, Bernard J. T.
2017-04-01
Preface; Notation and conventions; Part I. 100 Years of Cosmology: 1. Emerging cosmology; 2. The cosmic expansion; 3. The cosmic microwave background; 4. Recent cosmology; Part II. Newtonian Cosmology: 5. Newtonian cosmology; 6. Dark energy cosmological models; 7. The early universe; 8. The inhomogeneous universe; 9. The inflationary universe; Part III. Relativistic Cosmology: 10. Minkowski space; 11. The energy momentum tensor; 12. General relativity; 13. Space-time geometry and calculus; 14. The Einstein field equations; 15. Solutions of the Einstein equations; 16. The Robertson–Walker solution; 17. Congruences, curvature and Raychaudhuri; 18. Observing and measuring the universe; Part IV. The Physics of Matter and Radiation: 19. Physics of the CMB radiation; 20. Recombination of the primeval plasma; 21. CMB polarisation; 22. CMB anisotropy; Part V. Precision Tools for Precision Cosmology: 23. Likelihood; 24. Frequentist hypothesis testing; 25. Statistical inference: Bayesian; 26. CMB data processing; 27. Parametrising the universe; 28. Precision cosmology; 29. Epilogue; Appendix A. SI, CGS and Planck units; Appendix B. Magnitudes and distances; Appendix C. Representing vectors and tensors; Appendix D. The electromagnetic field; Appendix E. Statistical distributions; Appendix F. Functions on a sphere; Appendix G. Acknowledgements; References; Index.
GANDALF: Graphical Astrophysics code for N-body Dynamics And Lagrangian Fluids
Hubber, David; Rosotti, Giovanni
2016-02-01
GANDALF, a successor to SEREN (ascl:1102.010), is a hybrid self-gravitating fluid dynamics and collisional N-body code primarily designed for investigating star formation and planet formation problems. GANDALF uses various implementations of Smoothed Particle Hydrodynamics (SPH) to perform hydrodynamical simulations of gas clouds undergoing gravitational collapse to form new stars (or other objects), and can perform simulations of pure N-body dynamics using high accuracy N-body integrators, model the intermediate phase of cluster evolution, and provide visualizations via its python interface as well as interactive simulations. Although based on many of the SEREN routines, GANDALF has been largely re-written from scratch in C++ using more optimal algorithms and data structures.
Galaxy Pairs in cosmological simulations: Effects of interactions on star formation
Perez, M J; Lambas, D G; Scannapieco, C; Tissera, Patricia B.; Lambas, Diego G.; Scannapieco, Cecilia
2005-01-01
We carried out a statistical analysis of galaxy pairs in hydrodynamical Lambda-CDM simulations. We focused on the triggering of star formation by interactions and analysed the enhancement of star formation activity in terms of orbital parameters. By comparing to a suitable sample of simulated galaxies without a nearby companion, we find that close encounters (r<30 kpc/h) may effectively induce star formation. However, our results suggest that the stability properties of systems and the spatial proximity are both relevant factors in the process of triggering star formation by tidal interactions. In order to assess the effects of projection and spurious pairs in observational samples, we also constructed and analysed samples of pairs of galaxies in the simulations obtained in projection. We found a good agreement with observational results with a threshold at rp ~ 25 kpc/h for interactions to effectively enhance star formation activity. For pairs within rp < 100 kpc/h, we estimated a ~27% contamination by...
Nishimichi, Takahiro
2013-01-01
We examine how well we can explain the large-scale anisotropic clustering of Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey with mock galaxies assigned to subhalos identified in a large suite of high-resolution cosmological simulations. Instead of relying on an analytical model, we vary the parameters that characterize the condition of subhalos to host LRGs and search for the best-fit parameters to the observed multipole moments of the power spectrum using the Markov-chain Monte Carlo method. After demonstrating that we cannot find a reasonable fit to the observation when we assign mock LRGs only to the central population of subhalos sitting at the center of their host halos, we show that simple models using both centrals and satellites can simultaneously fit the multipole moments up to hexadecapole at large scale ($k\\lesssim0.3\\,h\\mathrm{Mpc}^{-1}$). The multiplicity function measured from the best-fit mock catalogs shows good agreement with the observation, when the mean spacial number density...
Zhuravleva, I; Schekochihin, A A; Lau, E T; Nagai, D; Gaspari, M; Allen, S W; Nelson, K; Parrish, I J
2014-01-01
We address the problem of evaluating the power spectrum of the velocity field of the ICM using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: $(\\delta\\rho_k/\\rho)^2 = \\eta_1^2 (V_{1,k}/c_s)^2$, where $\\delta\\rho_k/\\rho$ is the spectral amplitude of the density perturbations at wave number $k$, $V_{1,k}^2=V_k^2/3$ is the mean square component of the velocity field, $c_s$ is the sound speed, and $\\eta_1$ is a dimensionless constant of order unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find $\\eta_1\\approx 1 \\pm 0.3$. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proporti...
Formation and Settling of a Disc Galaxy During the Last 8 Billion Years in a Cosmological Simulation
Ceverino, Daniel; Dekel, Avishai; Kassin, Susan A
2016-01-01
We present results of a high-resolution zoom cosmological simulation of the evolution of a low-mass galaxy with a maximum velocity of V=100 km/s at z=0, using the initial conditions from the AGORA project (Kim et al 2014). The final disc-dominated galaxy matches local disc scaling relations. The galaxy evolves from a compact, dispersion-dominated galaxy into a rotation-dominated but dynamically hot disc in about 0.5 Gyr (from z=1.4 to z=1.2). The disc dynamically cools down for the following 7 Gyr, as the gas velocity dispersion decreases over time, in agreement with observations. The primary cause of this slow evolution of velocity dispersion in this low-mass galaxy is stellar feedback. It is related to the decline in gas fraction, and to the associated gravitational disk instability, as the disc slowly settles from a global Toomre Q>1 turbulent disc to a marginally unstable disc (Q=1).
van de Voort, Freeke; Hopkins, Philip F; Keres, Dusan; Faucher-Giguere, Claude-Andre
2014-01-01
We quantify the stellar abundances of neutron-rich r-process nuclei in cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback In Realistic Environments project. The galaxy is enriched with r-process elements by binary neutron star (NS) mergers and with iron and other metals by supernovae. These calculations include key hydrodynamic mixing processes not present in standard semi-analytic chemical evolution models, such as galactic winds and hydrodynamic flows associated with structure formation. We explore a range of models for the rate and delay time of NS mergers, intended to roughly bracket the wide range of models consistent with current observational constraints. We show that NS mergers can produce [r-process/Fe] abundance ratios and scatter that appear reasonably consistent with observational constraints. At low metallicity, [Fe/H]<-2, we predict there is a wide range of stellar r-process abundance ratios, with both supersolar and subsolar abundances. Low-metallicity stars or sta...
Viel, M; Viel, Matteo; Haehnelt, Martin G.
2006-01-01
(abridged) The flux power spectrum of the Lyman-alpha forest in quasar (QSO) absorption spectra is sensitive to a wide range of cosmological and astrophysical parameters and instrumental effects. Modelling the flux power spectrum in this large parameter space to an accuracy comparable to the statistical uncertainty of large samples of QSO spectra is very challenging. We use here a coarse grid of hydrodynamical simulations run with GADGET-2 to obtain a ``best guess'' model around which we calculate a finer grid of flux power spectra using a Taylor expansion of the flux power spectrum to first order. We find that the SDSS flux power spectrum alone is able to constrain a wide range of parameters including the amplitude of the matter power spectrum sigma_8, the matter density Omega_m, the spectral index of primordial density fluctuations n, the effective optical depth tau_eff and its evolution. The thermal history of the Intergalactic Medium (IGM) is, however, poorly constrained and the SDSS data favour either an...
Keung Chan, Tsang; Keres, Dusan; Oñorbe, Jose; Hopkins, Philip F.; Muratov, Alexander; Faucher-Giguere, Claude-Andre; Quataert, Eliot
2016-06-01
We study the distribution of cold dark matter (CDM) in cosmological simulations from the FIRE (Feedback In Realistic Environments) project, which incorporates explicit stellar feedback in the multi-phase ISM, with energetics from stellar population models. We find that stellar feedback, without ``fine-tuned'' parameters, greatly alleviates small-scale problems in CDM. Feedback causes bursts of star formation and outflows, altering the DM distribution. As a result, the inner slope of the DM halo profile (α) shows a strong mass dependence: profiles are shallow at Mh ˜ 1010-1011 M⊙ and steepen at higher/lower masses. The resulting core sizes and slopes are consistent with observations. Because the star formation efficiency, Ms/Mh is strongly halo mass dependent, a rapid change in α occurs around Mh ˜1010M⊙, (Ms˜106-107M⊙) as sufficient feedback energy becomes available to perturb the DM. Large cores are not established during the period of rapid growth of halos because of ongoing DM mass accumulation. Instead, cores require several bursts of star formation after the rapid buildup has completed. Stellar feedback dramatically reduces circular velocities in the inner kpc of massive dwarfs; this could be sufficient to explain the ``Too Big To Fail'' problem without invoking non-standard DM. Finally, feedback and baryonic contraction in Milky Way-mass halos produce DM profiles slightly shallower than the Navarro-Frenk-White profile, consistent with the normalization of the observed Tully-Fisher relation.
Sanders, RH; Papantonopoulos, E
2005-01-01
I discuss the classical cosmological tests, i.e., angular size-redshift, flux-redshift, and galaxy number counts, in the light of the cosmology prescribed by the interpretation of the CMB anisotropies. The discussion is somewhat of a primer for physicists, with emphasis upon the possible systematic
Brandenberger, R H; Brandenberger, Robert H.; Magueijo, Joao
1999-01-01
We review a few off-the-beaten-track ideas in cosmology. They solve a variety of fundamental problems; also they are fun. We start with a description of non-singular dilaton cosmology. In these scenarios gravity is modified so that the Universe does not have a singular birth. We then present a variety of ideas mixing string theory and cosmology. These solve the cosmological problems usually solved by inflation, and furthermore shed light upon the issue of the number of dimensions of our Universe. We finally review several aspects of the varying speed of light theory. We show how the horizon, flatness, and cosmological constant problems may be solved in this scenario. We finally present a possible experimental test for a realization of this theory: a test in which the Supernovae results are to be combined with recent evidence for redshift dependence in the fine structure constant.
Bonometto, S A; Musco, I; Mainini, R; Maccio', A V
2014-01-01
Models including an energy transfer from CDM to DE are widely considered in the literature, namely to allow DE a significant high-z density. Strongly Coupled cosmologies assume a much larger coupling between DE and CDM, together with the presence of an uncoupled warm DM component, as the role of CDM is mostly restricted to radiative eras. This allows us to preserve small scale fluctuations even if the warm particle, possibly a sterile neutrino, is quite light, O(100 eV). Linear theory and numerical simulations show that these cosmologies agree with LCDM on supergalactic scales; e.g., CMB spectra are substantially identical. Simultaneously, simulations show that they significantly ease problems related to the properties of MW satellites and cores in dwarfs. SC cosmologies also open new perspectives on early black hole formation, and possibly lead towards unificating DE and inflationary scalar fields.
Initial conditions, Discreteness and non-linear structure formation in cosmology
Sylos-Labini, F; Gabrielli, A; Joyce, M; Labini, Francesco Sylos; Baertschiger, Thierry; Gabrielli, Andrea; Joyce, Michael
2002-01-01
In this lecture we address three different but related aspects of the initial continuous fluctuation field in standard cosmological models. Firstly we discuss the properties of the so-called Harrison-Zeldovich like spectra. This power spectrum is a fundamental feature of all current standard cosmological models. In a simple classification of all stationary stochastic processes into three categories, we highlight with the name ``super-homogeneous'' the properties of the class to which models like this, with $P(0)=0$, belong. In statistical physics language they are well described as glass-like. Secondly, the initial continuous density field with such small amplitude correlated Gaussian fluctuations must be discretised in order to set up the initial particle distribution used in gravitational N-body simulations. We discuss the main issues related to the effects of discretisation, particularly concerning the effect of particle induced fluctuations on the statistical properties of the initial conditions and on th...
Churchill, Christopher W; Trujillo-Gomez, Sebastian; Kacprzak, Glenn G; Klypin, Anatoly
2014-01-01
We study the circumgalactic medium (CGM) of a z=0.54 simulated dwarf galaxy using hydroART simulations. We present our analysis methods, which emulate observations, including objective absorption line detection, apparent optical depth (AOD) measurements, Voigt profile (VP) decomposition, and ionization modelling. By comparing the inferred CGM gas properties from the absorption lines directly to the gas selected by low ionization HI and MgII, and by higher ionization CIV and OVI absorption, we examine how well observational analysis methods recover the "true" properties of CGM gas. In this dwarf galaxy, low ionization gas arises in kiloparsec "cloud" structures, but high ionization gas arises in multiple extended structures spread over 100 kpc; due to complex velocity fields, highly separated structures give rise to absorption at similar velocities. We show that AOD and VP analysis fails to accurately characterize the spatial, kinematic, and thermal conditions of high ionization gas. We find that HI absorption...
Cosmological Simulations with Scale-Free Initial Conditions; 1, Adiabatic Hydrodynamics
Owen, J M; Evrard, A E; Hernquist, L E; Katz, N; Weinberg, David H.; Evrard, August E.; Hernquist, Lars; Katz, Neal
1997-01-01
We analyze hierarchical structure formation based on scale-free initial conditions in an Einstein-de Sitter universe, including a baryonic component. We present three independent, smoothed particle hydrodynamics (SPH) simulations, performed with two different SPH codes (TreeSPH and P3MSPH) at two resolutions. Each simulation is based upon identical initial conditions, which consist of Gaussian distributed initial density fluctuations that have an n=-1 power spectrum. The baryonic material is modeled as an ideal gas subject only to shock heating and adiabatic heating and cooling. The evolution is expected to be self-similar in time, and under certain restrictions we identify the expected scalings for many properties of the distribution of collapsed objects in all three realizations. The distributions of dark matter masses, baryon masses, and mass and emission weighted temperatures scale quite reliably. However, the density estimates in the central regions of these structures are determined by the degree of num...
Evaluating Galactic Habitability Using High Resolution Cosmological Simulations of Galaxy Formation
Forgan, Duncan; Cockell, Charles; Libeskind, Noam
2015-01-01
We present the first model that couples high-resolution simulations of the formation of Local Group galaxies with calculations of the galactic habitable zone (GHZ), a region of space which has sufficient metallicity to form terrestrial planets without being subject to hazardous radiation. These simulations allow us to make substantial progress in mapping out the asymmetric three-dimensional GHZ and its time evolution for the Milky Way (MW) and Triangulum (M33) galaxies, as opposed to works that generally assume an azimuthally symmetric GHZ. Applying typical habitability metrics to MW and M33, we find that while a large number of habitable planets exist as close as a few kiloparsecs from the galactic centre, the probability of individual planetary systems being habitable rises as one approaches the edge of the stellar disc. Tidal streams and satellite galaxies also appear to be fertile grounds for habitable planet formation. In short, we find that both galaxies arrive at similar GHZs by different evolutionary ...
Cosmological Three-Point Function: Testing The Halo Model Against Simulations
Fosalba, P; Szapudi, I; Fosalba, Pablo; Pan, Jun; Szapudi, Istvan
2005-01-01
We perform detailed comparison of the semi-analytic halo model predictions with measurements in numerical simulations of the two and three point correlation functions (3PCF), as well as power spectrum and bispectrum. We discuss the accuracy and self-consistency of the halo model description of gravitational clustering in the non-linear regime and constrain halo model parameters. We exploit the recently proposed multipole expansion of three point statistics that expresses rotation invariance in the most natural way. This not only offers technical advantages by reducing the integrals required for the halo model predictions, but amounts to a convenient way of compressing the information contained in the 3PCF. We find that, with an appropriate choice of the halo boundary and mass function cut-off, halo model predictions are in good agreement with the bispectrum measured in numerical simulations. However, the halo model predicts less than the observed configuration dependence of the 3PCF on ~ Mpc scales. This effe...
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Cunha, Carlos E. [KIPAC, Menlo Park; Huterer, Dragan [Michigan U.; Lin, Huan [Fermilab; Busha, Michael T. [Zurich U.; Wechsler, Risa H. [SLAC
2014-10-11
We use N-body-spectro-photometric simulations to investigate the impact of incompleteness and incorrect redshifts in spectroscopic surveys to photometric redshift training and calibration and the resulting effects on cosmological parameter estimation from weak lensing shear-shear correlations. The photometry of the simulations is modeled after the upcoming Dark Energy Survey and the spectroscopy is based on a low/intermediate resolution spectrograph with wavelength coverage of 5500{\\AA} < {\\lambda} < 9500{\\AA}. The principal systematic errors that such a spectroscopic follow-up encounters are incompleteness (inability to obtain spectroscopic redshifts for certain galaxies) and wrong redshifts. Encouragingly, we find that a neural network-based approach can effectively describe the spectroscopic incompleteness in terms of the galaxies' colors, so that the spectroscopic selection can be applied to the photometric sample. Hence, we find that spectroscopic incompleteness yields no appreciable biases to cosmology, although the statistical constraints degrade somewhat because the photometric survey has to be culled to match the spectroscopic selection. Unfortunately, wrong redshifts have a more severe impact: the cosmological biases are intolerable if more than a percent of the spectroscopic redshifts are incorrect. Moreover, we find that incorrect redshifts can also substantially degrade the accuracy of training set based photo-z estimators. The main problem is the difficulty of obtaining redshifts, either spectroscopically or photometrically, for objects at z > 1.3. We discuss several approaches for reducing the cosmological biases, in particular finding that photo-z error estimators can reduce biases appreciably.
Li, Xiao-Dong; Park, Changbom; Sabiu, Cristiano G.; Park, Hyunbae; Cheng, Cheng; Kim, Juhan; Hong, Sungwook E.
2017-08-01
We develop a methodology to use the redshift dependence of the galaxy 2-point correlation function (2pCF) across the line of sight, ξ ({r}\\perp ), as a probe of cosmological parameters. The positions of galaxies in comoving Cartesian space varies under different cosmological parameter choices, inducing a redshift-dependent scaling in the galaxy distribution. This geometrical distortion can be observed as a redshift-dependent rescaling in the measured ξ ({r}\\perp ). We test this methodology using a sample of 1.75 billion mock galaxies at redshifts 0, 0.5, 1, 1.5, and 2, drawn from the Horizon Run 4 N-body simulation. The shape of ξ ({r}\\perp ) can exhibit a significant redshift evolution when the galaxy sample is analyzed under a cosmology differing from the true, simulated one. Other contributions, including the gravitational growth of structure, galaxy bias, and the redshift space distortions, do not produce large redshift evolution in the shape. We show that one can make use of this geometrical distortion to constrain the values of cosmological parameters governing the expansion history of the universe. This method could be applicable to future large-scale structure surveys, especially photometric surveys such as DES and LSST, to derive tight cosmological constraints. This work is a continuation of our previous works as a strategy to constrain cosmological parameters using redshift-invariant physical quantities.
N-body lensed CMB maps: lensing extraction and characterization
Antolini, Claudia; Martinelli, Matteo; Carbone, Carmelita; Baccigalupi, Carlo
2013-01-01
We reconstruct shear maps and angular power spectra from simulated weakly lensed total intensity (TT) and polarised (EB) maps of the Cosmic Microwave Background (CMB) anisotropies, obtained using Born approximated ray-tracing through the N-body simulated Cold Dark Matter (CDM) structures in the Millennium Simulations (MS). We compare the recovered signal with the ${\\Lambda}$CDM prediction, on the whole interval of angular scales which is allowed by the finite box size, extending from the degree scale to the arcminute, by applying a quadratic estimator in the flat sky limit; we consider PRISM-like instrumental specification for future generation CMB satellites, corresponding to arcminute angular resolution of 3.2' and sensitivity of 2.43 ${\\mu}$K-arcmin. The noise bias in the simulations closely follows the estimator prediction, becoming dominated by limits in the angular resolution for the EB signal, at l ${\\simeq}$ 1500. The de-biased signal shows no visible departure from predictions of the weak lensing pow...
Probing cosmology with weak lensing selected clusters I: Halo approach and all-sky simulations
Shirasaki, Masato; Yoshida, Naoki
2015-01-01
Weak gravitational lensing enables us to search clusters without the conventional assumption on the relation between visible and dark matter. We explore a variety of statistics of clusters selected with cosmic shear measurement by utilizing both analytic models and large numerical simulations. We first develop a halo model to predict the abundance and the clustering of weak lensing selected clusters. Observational effects such as galaxy shape noise are included in our model. We then generate realistic mock weak lensing catalogs to test the accuracy of our analytic model. To this end, we perform full-sky ray-tracing simulations that allow us to have multiple realizations of a large continuous area. We model the masked regions on the sky using the actual positions of bright stars, and generate 200 mock weak lensing catalogs with sky coverage of $\\sim$1000 squared degrees. We utilize the large set of mock catalogs to evaluate the covariance matrices between the local and non-local statistics. We show that our th...
Lin, David; Rocha, Miguel E.; Primack, Joel R.
2015-01-01
Dark matter halos existing around visible galaxies are important for studies of galaxy formation and evolution. Since dark matter does not interact with light and cannot be observed directly, studies of dark matter halos are advanced by computer simulations. Normally, halos are defined by their virialized regions; however, regions that are non-virialized can still be gravitationally bound, like the collision-bound Milky Way and Andromeda galaxies. Our project is the first comprehensive characterization of gravitationally bound halo structures, their properties, and their evolution. This study found the bound regions surrounding every dark matter halo from a 100 Mpc cube of the Bolshoi Simulation at redshifts 0, 1, and 2. We optimized computation by removing subhalos, implementing a search radius, and parallelizing code across 160 supercomputer cores. Then, we created a mass function, circular velocity function, and correlation function to describe these regions. The evolution of these properties was consistent with predictions from a ΛCDM universe model. We characterized the sizes and shapes of these bound regions across different mass intervals and redshifts. Most bound regions are elongated, although they become more spheroidal with time. The results enable astronomers to predict how dark matter halos behave in non-virialized regions of space and deepen our understanding of galaxy formation.
GARROTXA cosmological simulations of Milky Way like galaxies - I. Hot gas and the missing baryons
Roca-Fàbrega, Santi; Colín, Pedro; Figueras, Francesca; Krongold, Yair; Velázquez, Héctor
2015-01-01
We introduce a new set of simulations of a Milky Way like galaxy using the AMR code ART + hydrodynamics in a $\\Lambda$CDM cosmogony. The simulation series is named GARROTXA and follow the formation of a late type galaxy from z=60 with a final virial mass of \\sim$7.4$\\times$10$^{11}$M$_{\\odot}$. This system has no major mergers since z=3 and at z=0 becomes a disk late-type spiral galaxy. Several of its large scale properties fall inside recent observational limits of our Galaxy, like the rotation curve shape, the presence of a stellar bar and flare, and a gaseous disk warp, as well as the stellar and baryonic mass. Here, as a first scientific exploitation of the model we study the total amount and spatial distribution of hot X-ray luminous gas. We do not observe in our models a significant presence of a hot gas thick disk as has been recently discussed in observational studies. The analysis of hot gas mock observations (column density and emission measure) revealed that commonly used hypothesis assumed to deri...
Galaxy pairs in cosmological simulations: effects of interactions on colours and chemical abundances
Perez, M J; Lambas, D G; Scannapieco, C; Tissera, P B; Lambas, Diego G.; Rossi, Maria E. De; Scannapieco, Cecilia; Tissera, Patricia B.
2006-01-01
We perform an statistical analysis of galaxies in pairs in a Lambda-CDM scenario by using the chemical GADGET-2 of Scannapieco et al. (2005) in order to study the effects of galaxy interactions on colours and metallicities. We find that galaxy-galaxy interactions can produce a bimodal colour distribution with galaxies with significant recent star formation activity contributing mainly to blue colours. In the simulations, the colours and the fractions of recently formed stars of galaxies in pairs depend on environment more strongly than those of galaxies without a close companion, suggesting that interactions play an important role in galaxy evolution. If the metallicity of the stellar populations is used as the chemical indicator, we find that the simulated galaxies determine luminosity-metallicity and stellar mass-metallicity relations which do not depend on the presence of a close companion. However, in the case of the luminosity-metallicity relation, at a given level of enrichment, we detect a systematic d...
Ryan, M.
1972-01-01
The study of cosmological models by means of equations of motion in Hamiltonian form is considered. Hamiltonian methods applied to gravity seem to go back to Rosenfeld (1930), who constructed a quantum-mechanical Hamiltonian for linearized general relativity theory. The first to notice that cosmologies provided a simple model in which to demonstrate features of Hamiltonian formulation was DeWitt (1967). Applications of the ADM formalism to homogeneous cosmologies are discussed together with applications of the Hamiltonian formulation, giving attention also to Bianchi-type universes. Problems involving the concept of superspace and techniques of quantization are investigated.
Simulations of solitonic core mergers in ultra-light axion dark matter cosmologies
Schwabe, Bodo; Engels, Jan F
2016-01-01
Using three-dimensional simulations, we study the dynamics and final structure of merging solitonic cores predicted to form in ultra-light axion dark matter halos. The classical, Newtonian equations of motion of a self-gravitating scalar field are described by the Schr\\"odinger-Poisson equations. We investigate mergers of ground state (boson star) configurations with varying mass ratios, relative phases, orbital angular momenta and initial separation with the primary goal to understand the mass loss of the emerging core by gravitational cooling. Previous results showing that the final density profiles have solitonic cores and NFW-like tails are confirmed. In binary mergers, the final core mass does not depend on initial phase difference or angular momentum and only depends on mass ratio, total initial mass, and total energy of the system. For non-zero angular momenta, the otherwise spherical cores become rotating ellipsoids. The results for mergers of multiple cores are qualitatively identical.
Simulations of solitonic core mergers in ultralight axion dark matter cosmologies
Schwabe, Bodo; Niemeyer, Jens C.; Engels, Jan F.
2016-08-01
Using three-dimensional simulations, we study the dynamics and final structure of merging solitonic cores predicted to form in ultralight axion dark matter halos. The classical, Newtonian equations of motion of a self-gravitating scalar field are described by the Schrödinger-Poisson equations. We investigate mergers of ground state (boson star) configurations with varying mass ratios, relative phases, orbital angular momenta and initial separation with the primary goal to understand the mass loss of the emerging core by gravitational cooling. Previous results showing that the final density profiles have solitonic cores and Navarro-Frenk-White-like tails are confirmed. In binary mergers, the final core mass does not depend on initial phase difference or angular momentum and only depends on mass ratio, total initial mass, and total energy of the system. For nonzero angular momenta, the otherwise spherical cores become rotating ellipsoids. The results for mergers of multiple cores are qualitatively identical.
Towards a more realistic population of bright spiral galaxies in cosmological simulations
Aumer, Michael; White, Simon D. M.; Naab, Thorsten; Scannapieco, Cecilia
2013-10-01
We present an update to the multiphase smoothed particle hydrodynamics galaxy formation code by Scannapieco et al. We include a more elaborate treatment of the production of metals, cooling rates based on individual element abundances and a scheme for the turbulent diffusion of metals. Our supernova feedback model now transfers energy to the interstellar medium (ISM) in kinetic and thermal form, and we include a prescription for the effects of radiation pressure from massive young stars on the ISM. We calibrate our new code on the well-studied Aquarius haloes and then use it to simulate a sample of 16 galaxies with halo masses between 1 × 1011 and 3 × 1012 M⊙. In general, the stellar masses of the sample agree well with the stellar mass to halo mass relation inferred from abundance matching techniques for redshifts z = 0-4. There is however a tendency to overproduce stars at z > 4 and to underproduce them at z metallicities at z = 0-3. Remaining discrepancies can be connected to deviations from predictions for star formation histories from abundance matching. At z = 0, the model galaxies show realistic morphologies, stellar surface density profiles, circular velocity curves and stellar metallicities, but overly flat metallicity gradients. 15 out of 16 of our galaxies contain disc components with kinematic disc fraction ranging between 15 and 65 per cent. The disc fraction depends on the time of the last destructive merger or misaligned infall event. Considering the remaining shortcomings of our simulations we conclude that even higher kinematic disc fractions may be possible for Λ cold dark matter haloes with quiet merger histories, such as the Aquarius haloes.
Shimizu, Ikkoh; Inoue, Akio K.; Okamoto, Takashi; Yoshida, Naoki
2016-10-01
We have performed very large and high-resolution cosmological hydrodynamic simulations in order to investigate detectability of nebular lines in the rest-frame ultraviolet (UV) to optical wavelength range from galaxies at z > 7. We find that the expected line fluxes are very well correlated with the apparent UV magnitudes. The C IV 1549 Å and C III] 1909 Å lines of galaxies brighter than 26 AB magnitudes are detectable with current facilities such as the Very Large Telescope (VLT) XShooter and the Keck Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE). Metal lines such as C IV 1549 Å, C III] 1909 Å, [O II] 3727 Å and [O III] 4959/5007 Å are good targets for spectroscopic observation with the Thirty-Metre Telescope (TMT), European Extremely Large Telescope (E-ELT), Giant Magellan Telescope (GMT) and James Webb Space Telescope (JWST). We also expect Hα and Hβ lines to be detectable with these telescopes. Additionally, we predict the detectability of nebular lines for z > 10 galaxies, which will be found with JWST, the Wide-Field Infrared Survey Telescope (WFIRST) and First Light And Reionization Explorer (FLARE) (11 ≤ z ≤ 15). We conclude that the C IV 1549 Å, C III] 1909 Å, [O III] 4959/5007 Å and Hβ lines from even z ˜15 galaxies could be strong targets for TMT, E-ELT and JWST. We also find that magnification by gravitational lensing is of great help in detecting such high-z galaxies. According to our model, the C III] 1909 Å line in z > 9 galaxy candidates is detectable even using current facilities.
Belinski, V
2009-01-01
The talk at international conference in honor of Ya. B. Zeldovich 95th Anniversary, Minsk, Belarus, April 2009. The talk represents a review of the old results and contemporary development on the problem of cosmological singularity.
Lesgourgues, Julien; Miele, Gennaro; Pastor, Sergio
2013-01-01
The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis, their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and the statistical mechanics in the expanding Universe, before discussing the history of neutrinos in chronological order from the very early stages until today. This timely book will interest graduate students and researchers in astrophysics, cosmology and particle physics, who work with either a theoretical or experimental focus.
The Nature of Massive Transition Galaxies in CANDELS, GAMA, and Cosmological Simulations
Pandya, Viraj; Somerville, Rachel S; Choi, Ena; Barro, Guillermo; Wuyts, Stijn; Taylor, Edward N; Behroozi, Peter; Kirkpatrick, Allison; Faber, Sandra M; Primack, Joel; Koo, David C; McIntosh, Daniel H; Kocevski, Dale; Bell, Eric F; Dekel, Avishai; Fang, Jerome J; Ferguson, Henry C; Grogin, Norman; Koekemoer, Anton M; Lu, Yu; Mantha, Kameswara; Mobasher, Bahram; Newman, Jeffrey; Pacifici, Camilla; Papovich, Casey; van der Wel, Arjen; Yesuf, Hassen M
2016-01-01
It is common practice to speak of a "green valley" that hosts galaxies whose colors are intermediate relative to those in the "blue cloud" and the "red sequence." In this study, we raise several questions about how galaxies might transition between the star-forming main sequence (SFMS) and varying "degrees of quiescence" from $z=3$ to $z\\sim0$. We develop a physically and statistically motivated definition of "transition galaxies" based on their uniquely intermediate specific star formation rates, which relieves ambiguities associated with color-based selections and allows us to more cleanly compare observations to theoretical models. Our analysis is focused on galaxies with stellar mass $M_*>10^{10}M_{\\odot}$, and is enabled by GAMA and CANDELS observations, a semi-analytic model (SAM) of galaxy formation, and a hydrodynamical simulation with state-of-the-art mechanical AGN feedback. In both the observations and the SAM, transition galaxies tend to have intermediate S\\'ersic indices, half-light radii, and su...
Towards a more realistic population of bright spiral galaxies in cosmological simulations
Aumer, Michael; Naab, Thorsten; Scannapieco, Cecilia
2013-01-01
We present an update to the multiphase SPH galaxy formation code by Scannapieco et al. We include a more elaborate treatment of the production of metals, cooling rates based on individual element abundances, and a scheme for the turbulent diffusion of metals. Our SN feedback model now transfers energy to the ISM in kinetic and thermal form, and we include a prescription for the effects of radiation pressure from massive young stars on the ISM. We calibrate our new code on the well studied Aquarius haloes and then use it to simulate a sample of 16 galaxies with halo masses between 1x10^11 and 3x10^12 M_sun. In general, the stellar masses of the sample agree well with the stellar mass to halo mass relation inferred from abundance matching techniques for redshifts z=0-4. There is however a tendency to overproduce stars at z>4 and to underproduce them at z<0.5 in the least massive haloes. Overly high SFRs at z<1 for the most massive haloes are likely connected to the lack of AGN feedback in our model. The s...
Algebraic Approach to the N-Body Long Range Scattering
Dereziński, Jan
It is proven that if J, h are bounded continuous functions and H is an N-body Schrödinger operator then there exists s-lim limits {t-> ±∞ } eitH J ((x)/(t))h (H)e-itH. Limits of this form are used to study the N-body long range scattering.
Evolution of star clusters in a cosmological tidal field
Rieder, Steven; Langelaan, Paul; Makino, Junichiro; McMillan, Stephen L W; Zwart, Simon Portegies
2013-01-01
We present a method to couple N-body star cluster simulations to a cosmological tidal field, using the Astrophysical Multipurpose Software Environment. We apply this method to star clusters embedded in the CosmoGrid dark matter-only LambdaCDM simulation. Our star clusters are born at z = 10 (corresponding to an age of the Universe of about 500 Myr) by selecting a dark matter particle and initializing a star cluster with 32,000 stars on its location. We then follow the dynamical evolution of the star cluster within the cosmological environment. We compare the evolution of star clusters in two Milky-Way size haloes with a different accretion history. The mass loss of the star clusters is continuous irrespective of the tidal history of the host halo, but major merger events tend to increase the rate of mass loss. From the selected two dark matter haloes, the halo that experienced the larger number of mergers tends to drive a smaller mass loss rate from the embedded star clusters, even though the final masses of ...
Modeling the Lyα Forest in Collisionless Simulations
Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.
2016-08-01
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%-80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.
Energy Technology Data Exchange (ETDEWEB)
Wesson, P.S.
1979-10-01
The Cosmological Principle states: the universe looks the same to all observers regardless of where they are located. To most astronomers today the Cosmological Principle means the universe looks the same to all observers because density of the galaxies is the same in all places. A new Cosmological Principle is proposed. It is called the Dimensional Cosmological Principle. It uses the properties of matter in the universe: density (rho), pressure (p), and mass (m) within some region of space of length (l). The laws of physics require incorporation of constants for gravity (G) and the speed of light (C). After combining the six parameters into dimensionless numbers, the best choices are: 8..pi..Gl/sup 2/ rho/c/sup 2/, 8..pi..Gl/sup 2/ rho/c/sup 4/, and 2 Gm/c/sup 2/l (the Schwarzchild factor). The Dimensional Cosmological Principal came about because old ideas conflicted with the rapidly-growing body of observational evidence indicating that galaxies in the universe have a clumpy rather than uniform distribution. (SC)
FRIGA, A New Approach To Identify Isotopes and Hypernuclei In N-Body Transport Models
Fèvre, A Le; Aichelin, J; Hartnack, Ch; Kireyev, V; Bratkovskaya, E
2015-01-01
We present a new algorithm to identify fragments in computer simulations of relativistic heavy ion collisions. It is based on the simulated annealing technique and can be applied to n-body transport models like the Quantum Molecular Dynamics. This new approach is able to predict isotope yields as well as hyper-nucleus production. In order to illustrate its predicting power, we confront this new method to experimental data, and show the sensitivity on the parameters which govern the cluster formation.
Energy Technology Data Exchange (ETDEWEB)
Romeo Velona, A. D.; Gavignaud, I.; Meza, A. [Departamento de Ciencias Fisicas, Universidad Andres Bello, Av. Republica 220, Santiago (Chile); Sommer-Larsen, J. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, DK-2100 Copenhagen (Denmark); Napolitano, N. R. [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy); Antonuccio-Delogu, V. [INAF-Osservatorio Astrofisico di Catania, v. S. Sofia 78, I-95123 Catania (Italy); Cielo, S., E-mail: aro@oact.inaf.it [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
2013-06-20
We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided that the highest mass bin of the brightest central galaxies is excluded. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the subsample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. The scatter of the passive sample is dominated by low-mass galaxies at all redshifts and keeps constant over cosmic times. The mean metallicity is highest in cluster cores and lowest in normal groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M{sub *} plane at high redshift, whose scatter increases with time alongside the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the SF galaxies, while on the contrary more active
Sanders, Robert H
2016-01-01
The advent of sensitive high-resolution observations of the cosmic microwave background radiation and their successful interpretation in terms of the standard cosmological model has led to great confidence in this model's reality. The prevailing attitude is that we now understand the Universe and need only work out the details. In this book, Sanders traces the development and successes of Lambda-CDM, and argues that this triumphalism may be premature. The model's two major components, dark energy and dark matter, have the character of the pre-twentieth-century luminiferous aether. While there is astronomical evidence for these hypothetical fluids, their enigmatic properties call into question our assumptions of the universality of locally determined physical law. Sanders explains how modified Newtonian dynamics (MOND) is a significant challenge for cold dark matter. Overall, the message is hopeful: the field of cosmology has not become frozen, and there is much fundamental work ahead for tomorrow's cosmologis...
Narimani, Ali; Scott, Douglas
2011-01-01
Although it is possible that some fundamental physical constants could vary in time, it is important to only consider dimensionless combinations, such as the fine structure constant or the equivalent coupling constant for gravity. Once all such dimensionless numbers have been given, then we can be sure that our cosmological picture is governed by the same physical laws as that of another civilization with an entirely different set of units. An additional feature of the standard model of cosmology raises an extra complication, namely that the epoch at which we live is a crucial part of the model. This can be defined by giving the value of any one of the evolving cosmological parameters. It takes some care to avoid inconsistent results for constraints on variable constants, which could be caused by effectively fixing more than one parameter today. We show examples of this effect by considering in some detail the physics of Big Bang nucleosynthesis, recombination and microwave background anisotropies, being care...
High performance N-body simulation on computational grids
D.J. Groen
2010-01-01
Een N-bodysimulatie is een simulatie van een dynamisch systeem van deeltjes, meestal onder invloed van natuurkundige krachten zoals zwaartekracht. Gravitationele N-bodysimulaties zijn essentiële instrumenten om inzicht te krijgen in de vorming van sterrenhopen, sterrenstelsels en het universum als g
N-Body Simulations of Small Galaxy Groups (Parte A
Directory of Open Access Journals (Sweden)
H. Aceves
2002-01-01
Full Text Available Se presenta una serie de simulaciones de N-cuerpos destinadas a estudiar la dinámica de grupos pequeños de galaxias. En particular, se comparan los resultados obtenidos con las propiedades dinámicas de los grupos de Hickson. Se consideran condiciones iniciales partiendo de una expansión máxima` y de equilibrio virial, y no se considera un halo oscuro común primigenio. Se encuentra muy buena concordancia con las propiedades de grupos péquennos de galaxias, y las propiedades de los grupos compactos de Hickson son reproducidas adecuadamente por aquellos sistemas que se encuentran en un estado avanzado de un colapso gravitacional. No se encuentra un problema de `sobre-fusión` de las galaxias. Para grupos que comienzan en virial, se encuentra que una fracción importante ( 40% puede durar por 10 Gyr sin colapsarse completamente. Los resultados encontrados proporcionan una solución alternativa al problema de sobre-fusión para los grupos de Hickson. Asimismo, se encuentra que la razón masa-luminosidad de los grupos de Hickson podrá ser similar a la de cúmulos de galaxias, sugiriendo que ambos tienen aproximadamente la misma fracción de materia bariònica a masa total.
Kiselev, V V
2012-01-01
A huge value of cosmological constant characteristic for the particle physics and the inflation of early Universe are inherently related to each other: one can construct a fine-tuned superpotential, which produces a flat potential of inflaton with a constant density of energy V=\\Lambda^4 after taking into account for leading effects due to the supergravity, so that an introduction of small quantum loop-corrections to parameters of this superpotential naturally results in the dynamical instability relaxing the primary cosmological constant by means of inflationary regime. The model phenomenologically agrees with observational data on the large scale structure of Universe at \\Lambda~10^{16} GeV.
Statistics, Computation, and Modeling in Cosmology
Jewell, Jeff; Guiness, Joe; SAMSI 2016 Working Group in Cosmology
2017-01-01
Current and future ground and space based missions are designed to not only detect, but map out with increasing precision, details of the universe in its infancy to the present-day. As a result we are faced with the challenge of analyzing and interpreting observations from a wide variety of instruments to form a coherent view of the universe. Finding solutions to a broad range of challenging inference problems in cosmology is one of the goals of the “Statistics, Computation, and Modeling in Cosmology” workings groups, formed as part of the year long program on ‘Statistical, Mathematical, and Computational Methods for Astronomy’, hosted by the Statistical and Applied Mathematical Sciences Institute (SAMSI), a National Science Foundation funded institute. Two application areas have emerged for focused development in the cosmology working group involving advanced algorithmic implementations of exact Bayesian inference for the Cosmic Microwave Background, and statistical modeling of galaxy formation. The former includes study and development of advanced Markov Chain Monte Carlo algorithms designed to confront challenging inference problems including inference for spatial Gaussian random fields in the presence of sources of galactic emission (an example of a source separation problem). Extending these methods to future redshift survey data probing the nonlinear regime of large scale structure formation is also included in the working group activities. In addition, the working group is also focused on the study of ‘Galacticus’, a galaxy formation model applied to dark matter-only cosmological N-body simulations operating on time-dependent halo merger trees. The working group is interested in calibrating the Galacticus model to match statistics of galaxy survey observations; specifically stellar mass functions, luminosity functions, and color-color diagrams. The group will use subsampling approaches and fractional factorial designs to statistically and
Modeling the Lyman-alpha Forest in Collisionless Simulations
Sorini, Daniele; Lukić, Zarija; Hennawi, Joseph F
2016-01-01
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present Iteratively Matched Statistics (IMS), a novel method to accurately model the Lyman-alpha forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyman-alpha forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can perfectly reproduce line-of-sight observables, such as the PDF and power spe...
A Novel Approach to Visualizing Dark Matter Simulations
Kaehler, Ralf; Abel, Tom
2012-01-01
In the last decades cosmological N-body dark matter simulations have enabled ab initio studies of the formation of structure in the Universe. Gravity amplified small density fluctuations generated shortly after the Big Bang, leading to the formation of galaxies in the cosmic web. These calculations have led to a growing demand for methods to analyze time-dependent particle based simulations. Rendering methods for such N-body simulation data usually employ some kind of splatting approach via point based rendering primitives and approximate the spatial distributions of physical quantities using kernel interpolation techniques, common in SPH (Smoothed Particle Hydrodynamics)-codes. This paper proposes three GPU-assisted rendering approaches, based on a new, more accurate method to compute the physical densities of dark matter simulation data. It uses full phase-space information to generate a tetrahedral tessellation of the computational domain, with mesh vertices defined by the simulation's dark matter particle...
Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
2016-08-01
Low-mass “dwarf” galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z=0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 {M}⊙ with gas kernel/softening that adapts down to 1 {pc} (with a median of 25{--}60 {pc} at z=0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around an MW-mass host down to {M}{star}≳ {10}5 {M}⊙ . Latte’s population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) diverse range of star formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at {M}{star}≳ {10}5 {M}⊙ that does not suffer from the “missing satellites” or “too big to fail” problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard ΛCDM cosmology.
Cosmological Evolution and Hierarchical Galaxy Formation
Percival, W J
1999-01-01
We calculate the rate at which dark matter halos merge to form higher mass systems. Two complementary derivations using Press-Schechter theory are given, both of which result in the same equation for the formation rate. First, a derivation using the properties of the Brownian random walks within the framework of Press-Schechter theory is presented. We then use Bayes' theorem to obtain the same result from the standard Press-Schechter mass function. The rate obtained is shown to be in good agreement with results from Monte-Carlo and N-body simulations. We illustrate the usefulness of this formula by calculating the expected cosmological evolution in the rate of star formation that is due to short-lived, merger-induced starbursts. The calculated evolution is well-matched to the observed evolution in ultraviolet luminosity density, in contrast to the lower rates of evolution that are derived from semi-analytic models that do not include a dominant contribution from starbursts. Hence we suggest that the bulk of t...
Plionis, M.
2004-07-01
The recent scientific efforts in Astrophysics & Cosmology have brought a revolution to our understanding of the Cosmos. Amazing results is the outcome of amazing experiments! The huge scientific, technological & financial effort that has gone into building the 10-m class telescopes as well as many space and balloon observatories, essential to observe the multitude of cosmic phenomena in their manifestations at different wavelengths, from gamma-rays to the millimetre and the radio, has given and is still giving its fruits of knowledge. These recent scientific achievements in Observational and Theoretical Cosmology were presented in the "Multiwavelength Cosmology" conference that took place on beautiful Mykonos island in the Aegean between 17 and 20 June 2003. More than 180 Cosmologists from all over the world gathered for a four-day intense meeting in which recent results from large ground based surveys (AAT/2-df, SLOAN) and space missions (WMAP, Chandra, XMM, ISO, HST) were presented and debated, providing a huge impetus to our knowledge of the Cosmos. The future of the subject (experiments, and directions of research) was also discussed. The conference was devoted mostly on the constraints on Cosmological models and galaxy formation theories that arise from the study of the high redshift Universe, from clusters of galaxies, and their evolution, from the cosmic microwave background, the large-scale structure and star-formation history. Link: http://www.wkap.nl/prod/b/1-4020-1971-8
Marsh, David J E
2015-01-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also extraordinarily well-motivated within high energy physics, and so axion cosmology offers us a unique view onto these theories. I present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via the CMB and structure formation up to the present-day Universe. I briefly review the motivation and models for axions in particle physics and string theory. The primary focus is on the population of ultralight axions created via vacuum realignment, and its role as a dark matter (DM) candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute l...
Minimal coupling schemes in N-body reaction theory
Energy Technology Data Exchange (ETDEWEB)
Picklesimer, A.; Tandy, P.C.; Thaler, R.M.
1982-08-01
A new derivation of the N-body equations of Bencze, Redish, and Sloan is obtained through the use of Watson-type multiple scattering techniques. The derivation establishes an intimate connection between these partition-labeled N-body equations and the particle-labeled Rosenberg equations. This result yields new insight into the implicit role of channel coupling in, and the minimal dimensionality of, the partition-labeled equations.
Naab, T; Emsellem, E; Cappellari, M; Krajnovic, D; McDermid, R M; Alatalo, K; Bayet, E; Blitz, L; Bois, M; Bournaud, F; Bureau, M; Crocker, A; Davies, R L; Davis, T A; de Zeeuw, P T; Duc, P -A; Hirschmann, M; Johansson, P H; Khochfar, S; Kuntschner, H; Morganti, R; Oosterloo, T; Sarzi, M; Scott, N; Serra, P; van de Ven, G; Weijmans, A; Young, L M
2013-01-01
We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies and their satellites. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion, and higher-order Gauss-Hermite moments $h_3$ and $h_4$ are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the $\\lambda_{\\mathrm{R}}$-parameter. The velocity, velocity dispersion, $h_3$, and $h_4$ fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS$^{\\rm{3D}}$ survey. This includes fast (regular), slow, and misaligned rotation, hot spheroids with embedded cold disk components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a signi...
Theoretical accuracy in cosmological growth estimation
Bose, Benjamin; Koyama, Kazuya; Hellwing, Wojciech A.; Zhao, Gong-Bo; Winther, Hans A.
2017-07-01
We elucidate the importance of the consistent treatment of gravity-model specific nonlinearities when estimating the growth of cosmological structures from redshift space distortions (RSD). Within the context of standard perturbation theory (SPT), we compare the predictions of two theoretical templates with redshift space data from COLA (comoving Lagrangian acceleration) simulations in the normal branch of DGP gravity (nDGP) and general relativity (GR). Using COLA for these comparisons is validated using a suite of full N-body simulations for the same theories. The two theoretical templates correspond to the standard general relativistic perturbation equations and those same equations modeled within nDGP. Gravitational clustering nonlinear effects are accounted for by modeling the power spectrum up to one-loop order and redshift space clustering anisotropy is modeled using the Taruya, Nishimichi and Saito (TNS) RSD model. Using this approach, we attempt to recover the simulation's fiducial logarithmic growth parameter f . By assigning the simulation data with errors representing an idealized survey with a volume of 10 Gpc3/h3 , we find the GR template is unable to recover fiducial f to within 1 σ at z =1 when we match the data up to kmax=0.195 h /Mpc . On the other hand, the DGP template recovers the fiducial value within 1 σ . Further, we conduct the same analysis for sets of mock data generated for generalized models of modified gravity using SPT, where again we analyze the GR template's ability to recover the fiducial value. We find that for models with enhanced gravitational nonlinearity, the theoretical bias of the GR template becomes significant for stage IV surveys. Thus, we show that for the future large data volume galaxy surveys, the self-consistent modeling of non-GR gravity scenarios will be crucial in constraining theory parameters.
The effective field theory of cosmological large scale structures
Energy Technology Data Exchange (ETDEWEB)
Carrasco, John Joseph M. [Stanford Univ., Stanford, CA (United States); Hertzberg, Mark P. [Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Senatore, Leonardo [Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
2012-09-20
Large scale structure surveys will likely become the next leading cosmological probe. In our universe, matter perturbations are large on short distances and small at long scales, i.e. strongly coupled in the UV and weakly coupled in the IR. To make precise analytical predictions on large scales, we develop an effective field theory formulated in terms of an IR effective fluid characterized by several parameters, such as speed of sound and viscosity. These parameters, determined by the UV physics described by the Boltzmann equation, are measured from N-body simulations. We find that the speed of sound of the effective fluid is c^{2}_{s} ≈ 10^{–6}c^{2} and that the viscosity contributions are of the same order. The fluid describes all the relevant physics at long scales k and permits a manifestly convergent perturbative expansion in the size of the matter perturbations δ(k) for all the observables. As an example, we calculate the correction to the power spectrum at order δ(k)^{4}. As a result, the predictions of the effective field theory are found to be in much better agreement with observation than standard cosmological perturbation theory, already reaching percent precision at this order up to a relatively short scale k ≃ 0.24h Mpc^{–1}.
Dynamical instability and statistical behaviour of N-body systems
Cipriani, Piero; Di Bari, Maria
1998-12-01
In this paper, we argue about a synthetic characterization of the qualitative properties of generic many-degrees-of-freedom (mdf) dynamical systems (DS's) by means of a geometric description of the dynamics [Geometro-Dynamical Approach (GDA)]. We exhaustively describe the mathematical framework needed to link geometry and dynamical (in)stability, discussing in particular which geometrical quantity is actually related to instability and why some others cannot give, in general, any indication of the occurrence of chaos. The relevance of the Schur theorem to select such Geometrodynamic Indicators (GDI) of instability is then emphasized, as its implications seem to have been underestimated in some of the previous works. We then compare the analytical and numerical results obtained by us and by Pettini and coworkers concerning the FPU chain, verifying a complete agreement between the outcomes of averaging the relevant GDI's over phase space (Casetti and Pettini, 1995) and our findings (Cipriani, 1993), obtained in a more conservative way, time-averaging along geodesics. Along with the check of the ergodic properties of GDI's, these results confirm that the mechanism responsible for chaos in realistic DS's largely depends on the fluctuations of curvatures rather than on their negative values, whose occurrence is very unlikely. On these grounds we emphasize the importance of the virialization process, which separates two different regimes of instability. This evolutionary path, predicted on the basis of analytical estimates, receives clear support from numerical simulations, which, at the same time, confirm also the features of the evolution of the GDI's along with their dependence on the number of degrees of freedom, N, and on the other relevant parameters of the system, pointing out the scarce relevance of negative curvature (for N ≫ 1) as a source of instability. The general arguments outlined above, are then concretely applied to two specific N-body problems
Bothun, Greg
2011-10-01
Ever since Aristotle placed us, with certainty, in the Center of the Cosmos, Cosmological models have more or less operated from a position of known truths for some time. As early as 1963, for instance, it was ``known'' that the Universe had to be 15-17 billion years old due to the suspected ages of globular clusters. For many years, attempts to determine the expansion age of the Universe (the inverse of the Hubble constant) were done against this preconceived and biased notion. Not surprisingly when more precise observations indicated a Hubble expansion age of 11-13 billion years, stellar models suddenly changed to produce a new age for globular cluster stars, consistent with 11-13 billion years. Then in 1980, to solve a variety of standard big bang problems, inflation was introduced in a fairly ad hoc manner. Inflation makes the simple prediction that the net curvature of spacetime is zero (i.e. spacetime is flat). The consequence of introducing inflation is now the necessary existence of a dark matter dominated Universe since the known baryonic material could comprise no more than 1% of the necessary energy density to make spacetime flat. As a result of this new cosmological ``truth'' a significant world wide effort was launched to detect the dark matter (which obviously also has particle physics implications). To date, no such cosmological component has been detected. Moreover, all available dynamical inferences of the mass density of the Universe showed in to be about 20% of that required for closure. This again was inconsistent with the truth that the real density of the Universe was the closure density (e.g. Omega = 1), that the observations were biased, and that 99% of the mass density had to be in the form of dark matter. That is, we know the universe is two component -- baryons and dark matter. Another prevailing cosmological truth during this time was that all the baryonic matter was known to be in galaxies that populated our galaxy catalogs. Subsequent
Antonov problem and quasi-equilibrium states in N-body system
Taruya, A; Taruya, Atsushi; Sakagami, Masa-aki
2005-01-01
In this paper, a quantitative characterization for the evolutionary sequence of stellar self-gravitating system is investigated, focusing on the pre-collapse stage of the long-term dynamical evolution. In particular, we consider the quasi-equilibrium behaviors of the N-body systems in the setup of the so-called Antonov problem, i.e., self-gravitating N-body system confined in an adiabatic wall and try to seek a possible connection with thermostatistics of self-gravitating systems. For this purpose, a series of long-term N-body simulations with various initial conditions are performed. We found that a quasi-equilibrium sequence away from the thermal equilibrium can be characterized by the one-parameter family of the stellar models. Especially, the stellar polytropic distribution satisfying the effective equation of state $P\\propto\\rho^{1+1/n}$ provides an excellent approximation to the evolutionary sequence of the N-body system. Based on the numerical results, we discuss a link between the quasi-equilibrium st...
Marsh, David J. E.
2016-07-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also well-motivated within high energy physics, appearing in theories related to CP-violation in the standard model, supersymmetric theories, and theories with extra-dimensions, including string theory, and so axion cosmology offers us a unique view onto these theories. I review the motivation and models for axions in particle physics and string theory. I then present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via BBN, the CMB, reionization and structure formation, up to the present-day Universe. Topics covered include: axion dark matter (DM); direct and indirect detection of axions, reviewing existing and future experiments; axions as dark radiation; axions and the cosmological constant problem; decays of heavy axions; axions and stellar astrophysics; black hole superradiance; axions and astrophysical magnetic fields; axion inflation, and axion DM as an indirect probe of inflation. A major focus is on the population of ultralight axions created via vacuum realignment, and its role as a DM candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute lower bound on DM particle mass is established. It is ma > 10-24eV from linear observables, extending to ma ≳ 10-22eV from non-linear observables, and has the potential to reach ma ≳ 10-18eV in the future. These bounds are weaker if the axion is not all of the DM, giving rise to limits on the relic density at low mass. This leads to the exciting possibility that the effects of axion DM on structure formation could one day be detected
Simulating Cosmic Structure Formation
Weinberg, D H; Hernquist, L E; Weinberg, David H.; Katz, Neal; Hernquist, Lars
1997-01-01
We describe cosmological simulation techniques and their application to studies of cosmic structure formation, with particular attention to recent hydrodynamic simulations of structure in the high redshift universe. Collisionless N-body simulations with Gaussian initial conditions produce a pattern of sheets, filaments, tunnels, and voids that resembles the observed large scale galaxy distribution. Simulations that incorporate gas dynamics and dissipation form dense clumps of cold gas with sizes and masses similar to the luminous parts of galaxies. Models based on inflation and cold dark matter predict a healthy population of high redshift galaxies, including systems with star formation rates of 20 M_{\\sun}/year at z=6. At z~3, most of the baryons in these models reside in the low density intergalactic medium, which produces fluctuating Lyman-alpha absorption in the spectra of background quasars. The physical description of this ``Lyman-alpha forest'' is particularly simple if the absorption spectrum is viewe...
Phantom of RAMSES (POR): A new Milgromian dynamics N-body code
Lüghausen, Fabian; Kroupa, Pavel
2014-01-01
Since its first formulation in 1983, Milgromian dynamics (MOND) has been very successful in predicting the gravitational potential of galaxies from the distribution of baryons alone, including general scaling relations and detailed rotation curves of large statistical samples of individual galaxies covering a large range of masses and sizes. Most predictions however rely on static models, and only a handful of N-body codes have been developed over the years to investigate the consequences of the Milgromian framework for the dynamics of complex evolving dynamical systems. In this work, we present a new Milgromian N-body code, which is a customized version of the RAMSES code (Teyssier 2002) and thus comes with all its features: it includes particles and gas dynamics, and importantly allows for high spatial resolution of complex systems due to the adaptive mesh refinement (AMR) technique. It further allows the direct comparison between Milgromian simulations and standard Newtonian simulations with dark matter pa...
Speeding up N-body Calculations on Machines without Hardware Square Root
Directory of Open Access Journals (Sweden)
Alan H. Karp
1992-01-01
Full Text Available The most time consuming part of an N-body simulation is computing the components of the accelerations of the particles. On most machines the slowest part of computing the acceleration is in evaluating r-3/2, which is especially true on machines that do the square root in software. This note shows how to cut the time for this part of the calculation by a factor of 3 or more using standard Fortran.
Neves, J C S
2015-01-01
In the Nietzschean philosophy, the concept of force from physics is important to build one of its main concepts: the will to power. The concept of force, which Nietzsche found out in the Classical Mechanics, almost disappears in the physics of the XX century with the Quantum Field Theory and General Relativity. Is the Nietzschean world as contending forces, a Dionysian cosmology, possible in the current science?
Alvarez, Enrique
1985-01-01
Some cosmological consequences of the assumption that superstrings are more fundamental objects than ordinary local quantum fields are examined. We study, in particular, the dependence of both the string tension and the temperature of the primordial string soup on cosmic time. A particular scenario is proposed in which the universe undergoes a contracting ``string phase'' before the ordinary ``big bang,'' which according to this picture is nothing but the outcome of the transition from nonlocal to local fundamental physics.
Grant, E.; Murdin, P.
2000-11-01
During the early Middle Ages (ca 500 to ca 1130) scholars with an interest in cosmology had little useful and dependable literature. They relied heavily on a partial Latin translation of PLATO's Timaeus by Chalcidius (4th century AD), and on a series of encyclopedic treatises associated with the names of Pliny the Elder (ca AD 23-79), Seneca (4 BC-AD 65), Macrobius (fl 5th century AD), Martianus ...
Brax, Philippe
2016-01-01
We investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. These models can be seen as the low-energy description of invariant field theories under a global Abelian symmetry. The scalar field is then identified with the Goldstone mode of the broken symmetry. It turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. This leads to a complete screening of the fifth force in the Solar System and between compact objects, through the ultralocal screening mechanism. On the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. Interestingly, it can either amplify or damp Newtonian gravity, depending on the model parameters. We also study the background cosmology and the linear cosmological perturbations. The background cosmology is hardly different f...
Modeling Merging Galaxies using MINGA - Improving Restricted N-body by Dynamical Friction
Petsch, Hanns P
2008-01-01
Modeling interacting galaxies to reproduce observed systems is still a challenge due to the extended parameter space (among other problems). Orbit and basic galaxy parameters can be tackled by fast simulation techniques like the restricted N-body method, applied in the fundamental work by Toomre & Toomre (1972). This approach allows today for the study of millions of models in a short time. One difficulty for the classical restricted N-body method is the missing orbital decay, not allowing for galaxy mergers. Here we present an extension of the restricted N-body method including dynamical friction. This treatment has been developed by a quantitative comparison with a set of self-consistent merger simulations. By varying the dynamical friction (formalism, strength and direction), we selected the best-fitting parameters for a set of more than 250000 simulations. We show that our treatment reliably reproduces the orbital decay and tidal features of merging disk galaxies for mass ratios up to q=1/3 between ho...
Modeling merging galaxies using MINGA: Improving restricted N-body by dynamical friction
Petsch, H. P.; Theis, Ch.
2008-12-01
Modeling interacting galaxies to reproduce observed systems is still a challenge due to the extended parameter space (among other problems). Orbit and basic galaxy parameters can be tackled by fast simulation techniques like the restricted {N}-body method, applied in the fundamental work by Toomre & Toomre (1972). This approach allows today for the study of millions of models in a short time. One difficulty for the classical restricted {N}-body method is the missing orbital decay, not allowing for galaxy mergers. Here we present an extension of the restricted {N}-body method including dynamical friction. This treatment has been developed by a quantitative comparison with a set of self-consistent merger simulations. By varying the dynamical friction (formalism, strength and direction), we selected the best-fitting parameters for a set of more than 250 000 simulations. We show that our treatment reliably reproduces the orbital decay and tidal features of merging disk galaxies for mass ratios up to q=1/3 between host and satellite. We implemented this technique into our genetic algorithm based modeling code {MINGA} and present first results.
Gill, S P D; Gibson, B K; Flynn, C; Ibata, R A; Lewis, G F; Gill, Stuart P.D.; Knebe, Alexander; Gibson, Brad K.; Flynn, Chris; Ibata, Rodrigo A.; Lewis, Geraint F.
2002-01-01
An adaptive multi grid approach to simulating the formation of structure from collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle Mesh) is one of the most efficient serial codes available on the cosmological 'market' today. As part of Swinburne University's role in the development of the Square Kilometer Array, we are implementing hydrodynamics, feedback, and radiative transfer within the MLAPM adaptive mesh, in order to simulate baryonic processes relevant to the interstellar and intergalactic media at high redshift. We will outline our progress to date in applying the existing MLAPM to a study of the decay of satellite galaxies within massive host potentials.
Multiple scattering and N-body approaches to nuclear reactions
Energy Technology Data Exchange (ETDEWEB)
Picklesimer, A.; Tandy, P.C.; Thaler, R.M.
1983-02-01
The relationship between conventional multiple scattering approaches and the recently developed N-body approaches to nuclear reactions is considered with a view towards elastic scattering applications. Connectivity expansions in the N-body approach and multiple scattering expansions in the Watson approach are developed by a common technique so that a comparison of the physical content of each can be made. In the N-body case this leads to a new derivation of the equations of Bencze, Redish, and Sloan in both particle-labelled and partition-labelled form and this yields new insight into minimal dimensionality of these equations and into the role of channel coupling schemes within this formulation. The relative simplicity and generality with which these results are obtained is designed to be easily understood by those unfamiliar with N-body formalisms. The two approaches are contrasted first for the three-particle problem and subsequently for the many-body problem. We argue that a strict adherence to the connected-kernel property which is advantageous for the three-particle problem may not be so advantageous for the many-body elastic scattering problem. Undesirable physical characteristics of the connectivity expansion for elastic scattering are identified and their rectification is discussed. The off-shell transformation associated with the N-body approach is examined critically. The origin of the multiplicity of N-body coupling schemes is elucidated. It is shown that a modified concept of connectivity, called inclusive connectivity, can be introduced to guide expansions which can be truncated in a physically meaningful way. The inclusive connectivity expansion is seen to be identical to the spectator expansion for an elementary projectile but differs in the case of a composite projectile.
Minimal coupling schemes in N-body reaction theory
Picklesimer, A.; Tandy, P. C.; Thaler, R. M.
1982-08-01
A new derivation of the N-body equations of Bencze, Redish, and Sloan is obtained through the use of Watson-type multiple scattering techniques. The derivation establishes an intimate connection between these partition-labeled N-body equations and the particle-labeled Rosenberg equations. This result yields new insight into the implicit role of channel coupling in, and the minimal dimensionality of, the partition-labeled equations. NUCLEAR REACTIONS Scattering theory, multiple scattering, connected kernel reaction theory, minimal coupling, coupling schemes.
New Orbits for the n-Body Problem
Vanderbei, R J
2003-01-01
In this paper, we consider minimizing the action functional as a method for numerically discovering periodic solutions to the $n$-body problem. With this method, we can find a large number of choreographies and other more general solutions. We show that most of the solutions found, including all but one of the choreographies, are unstable. It appears to be much easier to find unstable solutions to the $n$-body problem than stable ones. Simpler solutions are more likely to be stable than exotic ones.
Simple Choreographies of the Planar Newtonian N-Body Problem
Yu, Guowei
2017-08-01
In the N-body problem, a simple choreography is a periodic solution, where all masses chase each other on a single loop. In this paper we prove that for the planar Newtonian N-body problem with equal masses, N ≧ 3, there are at least 2 N-3 + 2[( N-3)/2] different main simple choreographies. This confirms a conjecture given by Chenciner et al. (Geometry, mechanics, and dynamics. Springer, New York, pp 287-308, 2002). All the simple choreoagraphies we prove belong to the linear chain family.
Religion, theology and cosmology
Directory of Open Access Journals (Sweden)
John T. Fitzgerald
2013-10-01
Full Text Available Cosmology is one of the predominant research areas of the contemporary world. Advances in modern cosmology have prompted renewed interest in the intersections between religion, theology and cosmology. This article, which is intended as a brief introduction to the series of studies on theological cosmology in this journal, identifies three general areas of theological interest stemming from the modern scientific study of cosmology: contemporary theology and ethics; cosmology and world religions; and ancient cosmologies. These intersections raise important questions about the relationship of religion and cosmology, which has recently been addressed by William Scott Green and is the focus of the final portion of the article.
Cosmology Constraints from the Weak Lensing Peak Counts and the Power Spectrum in CFHTLenS
Liu, Jia; Haiman, Zoltan; Hui, Lam; Kratochvil, Jan M; May, Morgan
2014-01-01
Lensing peaks have been proposed as a useful statistic, containing cosmological information from non-Gaussianities that is inaccessible from traditional two-point statistics such as the power spectrum or two-point correlation functions. Here we examine constraints on cosmological parameters from weak lensing peak counts, using the publicly available data from the 154 deg^2 CFHTLenS survey. We utilize a new suite of ray-tracing N-body simulations on a grid of 91 cosmological models, covering broad ranges of the three parameters Omega_m, sigma_8, and w, and replicating the galaxy sky positions, redshifts, and shape noise in the CFHTLenS observations. We then build an emulator that interpolates the power spectrum and the peak counts to an accuracy of <= 5%, and compute the likelihood in the three-dimensional parameter space (Omega_m, sigma_8, w) from both observables. We find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales...
Boeyens, Jan CA
2010-01-01
The composition of the most remote objects brought into view by the Hubble telescope can no longer be reconciled with the nucleogenesis of standard cosmology and the alternative explanation, in terms of the LAMBDA-Cold-Dark-Matter model, has no recognizable chemical basis. A more rational scheme, based on the chemistry and periodicity of atomic matter, opens up an exciting new interpretation of the cosmos in terms of projective geometry and general relativity. The response of atomic structure to environmental pressure predicts non-Doppler cosmical redshifts and equilibrium nucleogenesis by alp
Bojowald, Martin
1999-01-01
A complete model of the universe needs at least three parts: (1) a complete set of physical variables and dynamical laws for them, (2) the correct solution of the dynamical laws, and (3) the connection with conscious experience. In quantum cosmology, item (2) is the quantum state of the cosmos. Hartle and Hawking have made the `no-boundary' proposal, that the wavefunction of the universe is given by a path integral over all compact Euclidean 4-dimensional geometries and matter fields that hav...
Fabris, J C; Rodrigues, D C; Batista, C E M; Daouda, M H
2012-01-01
We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity, which is based on a modification of the usual matter conservation law. We show that, besides its application to the generalized Chaplygin gas model, other cosmological models based on Rastall's theory have many interesting and unexpected new features.
Cosmology with Clusters of Galaxies
Borgani, Stefano
I reviewed in my talk recent results on the cosmological constraints that can be obtained by following the evolution of the population of galaxy clusters. Using extended samples of X-ray selected clusters, I have shown how they can be used to trace this evolution out to redshift z ~ 1. This evolution can be compared to model predictions and, therefore, to constrain cosmological parameters, such as the density parameter Omega_m and the shape and amplitude of the power spectrum of density perturbations. I have emphasized that the robustness of such constraints is quite sensitive to the relation between cluster collapsed mass and X-ray luminosity and temperature. This demonstrates that our ability to place significant constraints on cosmology using clusters of galaxies relies on our capability to understand the physical processes, which determine the properties of the intra-cluster medium (ICM). In this context, I have discussed how numerical simulations of cluster formation in cosmological context can play an important role in uderstanding the ICM physics. I have presented results from a very large cosmological simulation, which also includes the hydrodynamical description of the cosmic baryons, the processes of star formation and feedback from the stellar populations. The results from this simulation represent a unique baseline to describe the processes of formation and evolution of clusters of galaxies.
The inner structure of dwarf sized halos in Warm and Cold Dark Matter cosmologies
Gonzalez-Samaniego, Alejandro; Colin, Pedro
2015-01-01
By means of N-body+Hydrodynamics zoom-in simulations we study the evolution of the inner dark matter and stellar mass distributions of central dwarf galaxies formed in halos of virial masses mh=2-3x10^10 Msun at z=0, both in a WDM and CDM cosmology. The half-mode mass in the WDM power spectrum of our simulations is Mv= 2x 10^10 Msun. In the dark matter only simulations halo density profiles are well described by the NFW parametric fit in both cosmologies, though the WDM halos have concentrations lower by factors 1.5--2.0 than their CDM counterparts. In the hydrodynamical simulations, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase-space density profiles of the WDM halos but not of the CDM ones. The density slope measured at ~ 0.02xRv, alpha, becomes shallow in periods of 2 to 5 Gyr in the WDM runs. We explore whether this flattening process correlates with the global SF, Ms/Mv ratio, gas outflow, and internal specific angular momentum histories. We do not ...
Phantom of RAMSES (POR): A new Milgromian dynamicsN-body code
Lüghausen, Fabian; Famaey, Benoit; Kroupa, Pavel
2015-02-01
Since its first formulation in 1983, Milgromian dynamics (MOND) has been very successful in predicting the gravitational potential of galaxies from the distribution of baryons alone, including general scaling relations and detailed rotation curves of large statistical samples of individual galaxies covering a large range of masses and sizes. Most predictions however rely on static models, and only a handful of N-body codes have been developed over the years to investigate the consequences of the Milgromian framework for the dynamics of complex evolving dynamical systems. In this work, we present a new Milgromian N-body code, which is a customized version of the RAMSES code (Teyssier 2002) and thus comes with all its features: it includes particles and gas dynamics, and importantly allows for high spatial resolution of complex systems due to the adaptive mesh refinement (AMR) technique. It further allows the direct comparison between Milgromian simulations and standard Newtonian simulations with dark matter particles. We provide basic tests of this customized code and demonstrate its performance by presenting N-body computations of dark-matter-free spherical equilibrium models as well as dark-matter-free disk galaxies in Milgromian dynamics.
Ma, Xiangcheng; Hopkins, Philip F; Faucher-Giguere, Claude-Andre; Quataert, Eliot; Keres, Dusan; Murray, Norman
2015-01-01
We present a series of high-resolution (20-2000 Msun, 0.1-4 pc) cosmological zoom-in simulations at z~6 from the Feedback In Realistic Environment (FIRE) project. These simulations cover halo masses 10^9-10^11 Msun and rest-frame ultraviolet magnitude Muv = -9 to -19. These simulations include explicit models of the multi-phase ISM, star formation, and stellar feedback, which produce reasonable galaxy properties at z = 0-6. We post-process the snapshots with a radiative transfer code to evaluate the escape fraction (fesc) of hydrogen ionizing photons. We find that the instantaneous fesc has large time variability (0.01%-20%), while the time-averaged fesc over long time-scales generally remains ~5%, considerably lower than the estimate in many reionization models. We find no strong dependence of fesc on galaxy mass or redshift. In our simulations, the intrinsic ionizing photon budgets are dominated by stellar populations younger than 3 Myr, which tend to be buried in dense birth clouds. The escaping photons mo...
Collisionless Stellar Hydrodynamics as an Efficient Alternative to N-body Methods
Mitchell, Nigel L; Hensler, Gerhard
2012-01-01
For simulations that deal only with dark matter or stellar systems, the conventional N-body technique is fast, memory efficient, and relatively simple to implement. However when including the effects of gas physics, mesh codes are at a distinct disadvantage compared to SPH. Whilst implementing the N-body approach into SPH codes is fairly trivial, the particle-mesh technique used in mesh codes to couple collisionless stars and dark matter to the gas on the mesh, has a series of significant scientific and technical limitations. These include spurious entropy generation resulting from discreteness effects, poor load balancing and increased communication overhead which spoil the excellent scaling in massively parallel grid codes. We propose the use of the collisionless Boltzmann moment equations as a means to model collisionless material as a fluid on the mesh, implementing it into the massively parallel FLASH AMR code. This approach, which we term "collisionless stellar hydrodynamics" enables us to do away with ...
Directory of Open Access Journals (Sweden)
Pierluigi Monaco
2016-10-01
Full Text Available Precision cosmology has recently triggered new attention on the topic of approximate methods for the clustering of matter on large scales, whose foundations date back to the period from the late 1960s to early 1990s. Indeed, although the prospect of reaching sub-percent accuracy in the measurement of clustering poses a challenge even to full N-body simulations, an accurate estimation of the covariance matrix of clustering statistics, not to mention the sampling of parameter space, requires usage of a large number (hundreds in the most favourable cases of simulated (mock galaxy catalogs. Combination of few N-body simulations with a large number of realizations performed with approximate methods gives the most promising approach to solve these problems with a reasonable amount of resources. In this paper I review this topic, starting from the foundations of the methods, then going through the pioneering efforts of the 1990s, and finally presenting the latest extensions and a few codes that are now being used in present-generation surveys and thoroughly tested to assess their performance in the context of future surveys.
Bradley, D Ian; Fisher, Shaun N; Guénault, Anthony M; Haley, Richard P; Kopu, Juha; Martin, Hazel; Pickett, George R; Roberts, John E; Tsepelin, Viktor
2008-08-28
This study presents measurements of the transport of quasiparticle excitations in the B phase of superfluid 3He at temperatures below 0.2Tc. We find that creating and then removing a layer of A-phase superfluid leads to a measurable increase in the thermal impedance of the background B phase. This increase must be due to the survival of defects created as the AB and BA interfaces on either side of the A-phase layer annihilate. We speculate that a new type of defect may have been formed. The highly ordered A-B interface may be a good analogy for branes discussed in current cosmology. If so, these experiments may provide insight into how the annihilation of branes can lead to the formation of topological defects such as cosmic strings.