H. M. P. Couchman

• Professor at McMaster University

Far-ultraviolet (FUV) radiation greatly exceeds UV, supernovae (SNe), and winds in the energy budget of young star clusters but is poorly modelled in galaxy simulations. We present results of the first isolated galaxy disc simulations to include photoelectric heating of gas via dust grains from FUV radiation self-consistently, using a ray-tracing a...

Far-Ultraviolet (FUV) radiation greatly exceeds ultraviolet, supernovae and winds in the energy budget of young star clusters but is poorly modelled in galaxy simulations. We present results of the first full isolated galaxy disk simulations to include FUV radiation self-consistently. This is the first science application of the TREVR radiative tra...

We present Tree-based REVerse Ray Tracing (trevr), a general algorithm for computing the radiation field, including absorption, in astrophysical simulations. trevr is designed to handle large numbers of sources and absorbers; it is based on a tree data structure and is thus suited to codes that use trees for their gravity or hydrodynamics solvers (...

We present TREVR (Tree-based REVerse Ray Tracing), a general algorithm for computing the radiation field, including absorption, in astrophysical simulations. TREVR is designed to handle large numbers of sources and absorbers; it is based on a tree data structure and is thus suited to codes that use trees for their gravity or hydrodynamics solvers (...

We present a new method to study the characteristic scales of collapse and fragmentation in galactic disks. Clump formation is seeded in simulations via controlled perturbations with a specified wavelength and velocity. These are applied to otherwise quiet gas disks ranging from analogues of present day spirals to gas-rich, high-redshift galaxies....

We have explored the outskirts of dark matter haloes out to 2.5 times the virial radius using a large sample of halos drawn from Illustris, along with a set of zoom simulations (MUGS). Using these, we make a systematic exploration of the shape profile beyond R$_{vir}$. In the mean sphericity profile of Illustris halos we identify a dip close to the...

We have explored the outskirts of dark matter haloes out to 2.5 times the virial radius using a large sample of halos drawn from Illustris, along with a set of zoom simulations (MUGS). Using these, we make a systematic exploration of the shape profile beyond R$_{vir}$. In the mean sphericity profile of Illustris halos we identify a dip close to the...

Maps of the Rees–Sciama (RS) effect are simulated using the parallel N-body code, HYDRA, and a run-time ray-tracing procedure. A method designed for the analysis of small, square cosmic microwave background (CMB) maps is applied to our RS maps. Each of these techniques has been tested and successfully applied in previous papers. Within a range of a...

We explore the regulation of star formation in star-forming galaxies through a suite of high-resolution isolated galaxy simulations. We use the SPH code GASOLINE, including photoelectric heating and metal cooling, which produces a multi-phase interstellar medium. We show that representative star formation and feedback sub-grid models naturally lead...

We explore the regulation of star formation in star-forming galaxies through a suite of high-resolution isolated galaxy simulations. We use the SPH code GASOLINE, including photoelectric heating and metal cooling, which produces a multi-phase interstellar medium. We show that representative star formation and feedback sub-grid models naturally lead...

We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations include key physics such as evaporation and conduction, neglected in prior work, and required to correctly model superbubbles resulting from stellar feedback. We show that for galaxies with...

We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations include key physics such as evaporation and conduction, neglected in prior work, and required to correctly model superbubbles resulting from stellar feedback. We show that for galaxies with...

Efficient estimators of Fourier-space statistics for large number of objects rely on Fast Fourier Transforms (FFTs), which are affected by aliasing from unresolved small scale modes due to the finite FFT grid. Aliasing takes the form of a sum over images, each of them corresponding to the Fourier content displaced by increasing multiples of the sam...

We explore the chemical distribution of stars in a simulated galaxy. Using simulations of the same initial conditions but with two different feedback schemes (MUGS and MaGICC), we examine the features of the age-metallicity relation (AMR), and the three-dimensional age-metallicity-[O/Fe] distribution, both for the galaxy as a whole and decomposed i...

We explore the effect of galactic environment on properties of molecular clouds. Using clouds formed in a large-scale galactic disc simulation, we measure the observable properties from synthetic column density maps. We confirm that a significant fraction of unbound clouds forms naturally in a galactic disc environment and that a mixed population o...

We present the first cosmological galaxy evolved using the modern smoothed particle hydrodynamics (SPH) code gasoline2 with superbubble feedback. We show that superbubble-driven galactic outflows powered by Type II supernovae alone can produce L* galaxies with flat rotation curves with circular velocities ∼ 200 km s− 1, low bulge-to-disc ratios, an...

We present a new analytic estimate for the energy required to create a constant density core within a dark matter halo. Our new estimate, based on more realistic assumptions, leads to a required energy that is orders of magnitude lower than is claimed in earlier work. We define a core size based on the logarithmic slope of the dark matter density p...

An Adaptative-Particle-Particle-Particle-Mesh code (HYDRA) plus a ray-tracing procedure was used in [1] to perform an exhaustive analysis of the weak lensing anisotropy. Other nonlinear Cosmic Microwave Background anisotropies, such as the Rees-Sciamaand the Sunyaev-Zel.dovicheffects are also being studied by using the same tools. Here we present s...

Several years ago, we designed a particular ray tracing method. Combined with a Hydra parallel code (without baryons), it may compute some CMB anisotropies: weak lensing (WL) and Rees-Sciama (RS) effects. Only dark matter is fully necessary to estimate these effects. For very small angular scales, we made an exhaustive study leading to a lensing co...

We examine gas accretion and subsequent star formation in representative galaxies from the McMaster Unbiased Galaxy Simulations. Accreted gas is bimodal with a natural temperature division at 105 K, near the peak of the cooling curve. Cold-mode accretion dominates inflows at early times, creating a peak in total accretion at redshift z = 2–4 and de...

We present a new stellar feedback model that reproduces superbubbles. Superbubbles from clustered young stars evolve quite differently to individual supernovae and are substantially more efficient at generating gas motions. The essential new components of the model are thermal conduction, subgrid evaporation and a subgrid multiphase treatment for c...

We present a new stellar feedback model that reproduces superbubbles. Superbubbles from clustered young stars evolve quite differently to individual supernovae and are substantially more efficient at generating gas motions. The essential new components of the model are thermal conduction, sub-grid evaporation and a sub-grid multi-phase treatment fo...

From FFP6 to FFP11,wepresented the advances in our Cosmic Microwave Background (CMB) anisotropy computations using N-body Hydra Codes. For such computations, codes without baryons were used: First sequential versions and afterwards parallel ones. With both of them we computed the weak lensing and the Rees-Sciama contributions to the CMB angular pow...

We present a framework that explains the commonly observed variation in light element abundances in globular clusters. If globular clusters form in the centres of dwarf galaxies, they will be pumped on to larger orbits as star formation progresses. The potential well will only retain the moderate velocity asymptotic giant branch (AGB) ejecta, the e...

The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be "painted" onto dark matter particles in progenitor satellites; (2) pure dark matter simulations that do not form a luminous galaxy can be used. We estimate the magnitude...

We study the effect of warm dark matter (WDM) on hydrodynamic simulations of galaxy formation as part of the Making Galaxies in a Cosmological Context (MaGICC) project. We simulate three different galaxies using three WDM candidates of 1, 2 and 5 keV and compare results with pure cold dark matter simulations. WDM slightly reduces star formation and...

We present a cosmological hydrodynamical simulation of a representative volume of the Universe, as part of the Making Galaxies in a Cosmological Context (MaGICC) project. MaGICC uses a thermal implementation for supernova and early stellar feedback. This work tests the feedback model at lower resolution across a range of galaxy masses, morphologies...

We analyse the structure and chemical enrichment of a Milky Way-like galaxy with a stellar mass of 2 10^{10} M_sun, formed in a cosmological hydrodynamical simulation. It is disk-dominated with a flat rotation curve, and has a disk scale length similar to the Milky Way's, but a velocity dispersion that is ~50% higher. Examining stars in narrow [Fe/...

We analyze the orbits of stars and dark matter particles in the halo of a disk galaxy formed in a cosmological hydrodynamical simulation. The halo is oblate within the inner ~20 kpc and triaxial beyond this radius. About 43% of orbits are short axis tubes - the rest belong to orbit families that characterize triaxial potentials (boxes, long-axis tu...

By means of high-resolution cosmological hydrodynamical simulations of Milky Way (MW) 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 subcomponents, we compare the predicted MDFs to those observed in...

The high-resolution, SPH galaxies of the McMaster Unbiased Galaxy Survey (MUGS) are used to examine the satellite systems of sixteen model host galaxies. Each galaxy has a different mass, angular momentum and merger history that yield a rich set of satellite luminosity functions. With new observations of distant satellite systems, we can compare th...

We examine the chemical properties of 5 cosmological hydrodynamical simulations of an M33-like disc galaxy which have been shown to be consistent with the morphological characteristics and bulk scaling relations expected of late-type spirals. These simulations are part of the Making Galaxies In a Cosmological Context (MaGICC) Project, in which stel...

We introduce the Making Galaxies In a Cosmological Context (MAGICC) programme of smoothed particle hydrodynamics simulations. We describe a parameter study of galaxy formation simulations of an L* galaxy that uses early stellar feedback combined with supernova feedback to match the stellar mass–halo mass relationship. While supernova feedback alone...

We present a new model for the formation of stellar halos in dwarf galaxies. We demonstrate that the stars and star clusters that form naturally in the inner regions of dwarfs are expected to migrate from the gas-rich, star-forming center to join the stellar spheroid. For dwarf galaxies, this process could be the dominant source of halo stars. The...

We present a study of satellites in orbit around simulated host galaxies. The cumulative number of luminous satellites at z = 0 is similar to the observed system of satellites orbiting the Milky Way, although an analysis of the satellite mass function reveals an order of magnitude more dark satellites than luminous. Our results demonstrate that...

Recent observations of the cosmic microwave background anisotropy indicate that, at very small angular scales, the power of the CMB angular spectrum is smaller than that suggested by previous observations. Moreover, new recent simulations of the lensing effect conducted by us -at the same scales- give powers larger than those obtained in previous n...

We compare the results of thirteen cosmological gasdynamical codes used to simulate the formation of a galaxy in the LCDM structure formation paradigm. The various runs differ in their hydrodynamical treatment (SPH, moving-mesh and AMR) but share the same initial conditions and adopt their latest published model of cooling, star formation and feedb...

We examine radial and vertical metallicity gradients using a suite of disk galaxy simulations, supplemented with two classic chemical evolution approaches. We determine the rate of change of gradient and reconcile differences between extant models and observations within the `inside-out' disk growth paradigm. A sample of 25 disks is used, consistin...

A clear prediction of the Cold Dark Matter model is the existence of cuspy dark matter halo density profiles on all mass scales. This is not in agreement with the observed rotation curves of spiral galaxies, challenging on small scales the otherwise successful CDM paradigm. In this work we employ high resolution cosmological hydro-dynamical simulat...

We explore the circumgalactic medium (CGM) of two simulated star-forming galaxies with luminosities L ≈ 0.1 and 1 L⋆ generated using the smooth particle hydrodynamic code gasoline. These simulations are part of the Making Galaxies In a Cosmological Context (magicc) program in which the stellar feedback is tuned to match the stellar mass–halo mass r...

Encoded within the morphological structure of galaxies are clues related to their formation and evolutionary history. Recent advances pertaining to the statistics of galaxy morphology include sophisticated measures of concentration (C), asymmetry (A) and clumpiness (S). In this study, these three parameters (CAS) have been applied to a suite of sim...

We present a study of satellites in orbit around a high-resolution, smoothed particle hydrodynamics (SPH) galaxy simulated in a cosmological context. The simulated galaxy is approximately of the same mass as the Milky Way. The cumulative number of luminous satellites at z= 0 is similar to the observed system of satellites orbiting the Milky Way alt...

We present a study of satellites in orbit around a high-resolution, smoothed particle hydrodynamics (SPH) galaxy simulated in a cosmological context. The simulated galaxy is approximately the same mass as the Milky Way. The cumulative number of luminous satellites at z = 0 is similar to the observed system of satellites orbiting the Milky Way altho...

We describe the first parallel implementation of an adaptive particle-particle, particle-mesh code with smoothed particle hydrodynamics. Parallelisation of the serial code, "Hydra," is achieved by using CRAFT, a Cray proprietary language which allows rapid implementation of a serial code on a parallel machine by allowing global addressing of distri...

AP3M is an adaptive particle-particle, particle-mesh code. It is older than Hydra but faster and more memory-efficient for dark-matter only calculations. The Adaptive P3M technique (AP3M) is built around the standard P3M algorithm. AP3M produces fully equivalent forces to P3M but represents a more efficient implementation of the force splitting ide...

We present the McMaster Unbiased Galaxy Simulations (MUGS), the first nine galaxies of an unbiased selection ranging in total mass from 5 × 1011 M⊙ to 2 × 1012 M⊙ simulated using N-body smoothed particle hydrodynamics at high resolution. The simulations include a treatment of low-temperature metal cooling, UV background radiation, star formation an...

It has been hypothesized that the cosmic microwave background (CMB) provides a temperature floor for collapsing protostars that can regulate the process of star formation and result in a top-heavy initial mass function (IMF) at high metallicity and high redshift. We examine whether this hypothesis has any testable observational consequences. First...

We estimate the impact of weak lensing by strongly nonlinear cosmological structures on the cosmic microwave background. Accurate calculation of large ℓ 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 Parti...

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 P...

We demonstrate a significant difference in the angular momentum transport properties of galactic disks between regions in which the interstellar medium is single phase or two phase. Our study is motivated by observations of H I in extended galactic disks which indicate velocity dispersions of non-thermal origin, suggesting that turbulence in the ga...

We show that current clustering observations of quasars and luminous AGN can be explained by a merger model augmented by feedback from outflows. Using numerical simulations large enough to study clustering out to 25 comoving h-1 Mpc, we calculate correlation functions, biases, and correlation lengths as a function of AGN redshift and optical and X-...

The evolution of the two-point correlation function, ξ(r, z), and the pairwise velocity dispersion, σ(r, z), for both the matter, ξρρ, and halo population, ξhh, in three different cosmological models, (Ω0, λ0) = (1, 0), (0.2, 0), and (0.2, 0.8), are described. If the evolution of ξ is parameterized by ξ(r, z) = (1 + z)-(3+)ξ(r, 0), where ξ(r, 0) =...

We have simulated the formation of an X-ray cluster in a cold dark matter universe using 12 different codes. The codes span the range of numerical techniques and implementations currently in use, including smoothed particle hydrodynamics (SPH) and grid methods with fixed, deformable, or multilevel meshes. The goal of this comparison is to assess th...

We present a smoothed particle hydrodynamic simulation that reproduces a galaxy that is a moderate facsimile of those observed. The primary failing point of previous simulations of disk formation, namely, excessive transport of angular momentum from gas to dark matter, is ameliorated by the inclusion of a supernova feedback algorithm that allows en...

We present a study of hydrodynamic drag forces in smoothed particle hydrodynamic (SPH) simulations. In particular, the deceleration of a resolution-limited cold clump of gas moving through a hot medium is examined. The drag at subsonic velocities exceeds that expected from simple dynamics-based arguments. The excess is shown to be a result of the h...

Using a large set of high-resolution numerical simulations incorporating nonequilibrium molecular hydrogen chemistry and a constant source of external radiation, we study gas collapse in previously photoionized minigalaxies with virial temperatures less than 104 K in the early universe (redshifts z = 10-20). We confirm that the mechanism of positiv...

We discuss early results from the first N-body/hydrodynamical simulation to resolve the formation of galaxies in a volume large enough for their clustering properties to be reliably determined. The simulation follows the formation of galaxies by gas cooling within dark halos of mass a few times 1011 M☉ and above, in a flat cold dark matter universe...

We show that current clustering observations of quasars and luminous AGN can be explained by a merger model augmented by feedback from outflows. Using numerical simulations large enough to study clustering out to 25 comoving h^{-1} Mpc, we calculate correlation functions, biases, and correlation lengths as a function of AGN redshift and optical and...

Summary form only given. Large-scale computation has achieved a pivotal role in many areas of astrophysics and cosmology. Not only does increasing computational power allow us to better model the huge range of spatial and temporal scales in the universe, but simulations provide in many cases the only laboratory in which we may actively experiment o...

For simulations of fluid dynamics in astrophysics, physical viscosity and diffusion are typically neglected. However, in this high Reynolds number regime, real fluids become highly turbulent and turbulent processes mediate substantial transport of momentum and heat that is diffusive in nature. In the absence of models for these processes, code-depe...

Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major fac...

Dwarf galaxies pose significant challenges for cosmological models. In particular, current models predict a dark matter density that is divergent at the center, in sharp contrast with observations which indicate an approximately constant central density core. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major...

One of the most important and poorly-understood issues in structure formation is the role of outflows driven by active galactic nuclei (AGN). Using large-scale cosmological simulations, we compute the impact of such outflows on the small-scale distribution of the cosmic microwave background (CMB). Like gravitationally-heated structures, AGN outflow...

The standard cosmological model, now strongly constrained by direct observations of the Universe at early epochs, is very successful in describing the evolution of structure on large and intermediate scales. Unfortunately, serious contradictions remain on smaller, galactic scales. Among the main small-scale problems is a significant and persistent...

(Abridged) We explore the idea that the anti-hierarchical turn-off observed in the quasar population arises from self-regulating feedback, via an outflow mechanism. Using a detailed hydrodynamic simulation we calculate the luminosity function of quasars down to a redshift of z=1 in a large, cosmologically representative volume. Outflows are include...

We examine the role of quasars, and the black holes that power them, in cosmological evolution. By using a model of black hole growth and the associated wind and jet heating processes, we simulate a population of active galactic nuclei interacting with the intergalactic medium in a cosmologically representative volume. The use of a representative v...

The standard cosmological model, now strongly constrained by direct observation at early epochs, is very successful in describing the structure of the evolved universe on large and intermediate scales. Unfortunately, serious contradictions remain on smaller, galactic scales. Among the major small-scale problems is a significant and persistent discr...

Higher order cumulants of point processes, such as skew and kurtosis, require significant computational effort to calculate. The traditional counts-in-cells method implicitly requires a large amount of computation since, for each sampling sphere, a count of particles is necessary. Although alternative methods based on tree algorithms can reduce exe...

Particle methods play a central role in numerical simulations of cosmic structure. These methods are particularly important for simulations of two-component universes that include both baryonic and ``dark matter.'' Particles are used to model both the collisionless dark matter---using a classical inverse square law gravitational attraction---and, w...

We discuss the design and implementation of HYDRA_OMP a parallel implementation of the Smoothed Particle Hydrodynamics-Adaptive P3M (SPH-AP3M) code HYDRA. The code is designed primarily for conducting cosmological hydrodynamic simulations and is written in Fortran77+OpenMP. A number of optimizations for RISC processors and SMP-NUMA architectures ha...

Higher order cumulants of point processes, such as skew and kurtosis, require significant computational effort to calculate. The traditional counts-in-cells method implicitly requires a large amount of computation since, for each sampling sphere, a count of particles is necessary. Although alternative methods based on tree algorithms can reduce exe...

By fitting a flexible stellar anisotropy model to the observed surface brightness and line-of-sight velocity dispersion profiles of Draco we derive a sequence of cosmologically plausible two-component (stars + dark matter) models for this galaxy. The models are consistent with all the available observations and can have either cuspy Navarro-Frenk-W...

We explore the recently proposed idea that the Galactic dwarf spheroidal galaxies are significantly (by 2 orders of magnitude) more massive than the conventional mass estimates of {˜}107 M&sun;. In the larger mass case, the observed distribution of stars in these galaxies should have been entirely shaped by internal processes (formation and dynamic...

The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this m...

We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N≥ 1012 cm−2 and 316 Mg ii and 82 Fe ii absorption components with N≥ 1011.5 cm−2 in 19 high signal-to-noise ratio (60–100 pixel−1), high-resolution (R = 45 000) quasar spectra. C iv and Si iv trace each other...

We propose a simple model for the formation of dwarf spheroidal galaxies, in which stars are assumed to have formed from isothermal gas in hydrostatic equilibrium inside extended dark matter halos. After expelling the leftover gas, the stellar system undergoes a dynamical relaxation inside the dark matter halo. These models can adequately describe...

Higher order cumulants of point processes, such as skew and kurtosis, require significant computational effort to calculate. The traditional counts-in-cells method implicitly requires a large amount of computation since, for each sampling sphere, a count of particles is necessary. Although alternative methods based on tree algorithms can reduce exe...

This paper presents a new interactive parallel visualization method for large particle datasets by directly rendering individual particles based on a parallel rendering cluster. A frame rate of 9 frames-per-second is achieved for 2563 particles using 7 render nodes and a display node. This provides real time interaction and interactive exploration...

We discuss the design and implementation of a parallel adaptive P 3 M code, for massively parallel architectures. The code, although primarily designed for conducting gravitational simulations in a cosmological context, also includes a Smoothed Particle Hydrodynamics solver. The code is written in a combination of C, FORTRAN 77 and FORTRAN 90. The...

We show, by adopting a plausible model for star formation and energetic feedback in cosmological simulations of galaxy formation, that we are able to alleviate the angular momentum problem which has bedeviled many previous attempts to generate realistic disc galaxies in Cold Dark Matter cosmogonies. This paper highlights the "cooling catastrophe" a...

The rennaissance of HPC capability in Canada over the last two to three years is providing outstanding opportunities for researchers to repatriate their codes, skills and training. I will describe the vision of SHARC-Net to build in S-W Ontario a vibrant culture of HPC: an environment of technology and people which is widely recognised as being a v...

We show, by adopting a plausible model for star formation and energetic feedback in cosmological simulations of galaxy formation, that we are able to alleviate the angular momentum problem which has bedeviled many previous attempts to generate realistic disc galaxies in Cold Dark Matter cosmogonies. This paper highlights the “cooling catastrophe” a...

We present the results of a large library of cosmological N-body simulations, using power-law initial spectra. The non-linear evolution of the matter power spectra is compared with the predictions of existing analytic scaling formulae based on the work of Hamilton et al. The scaling approach has assumed that highly non-linear structures obey 'stabl...

We use gigaparticle N-body simulations to study galaxy cluster populations in Hubble volumes of LambdaCDM (Omega(m) = 0.3, Omega(Lambda) = 0.7) and tauCDM (Omega(m) = 1) world models. Mapping past light cones of locations in the computational space, we create mock sky surveys of dark matter structure to z similar or equal to 1.4 over 10,000 deg(2)...

hydrampi is a portable parallel N-body solver, based on the adaptive P3M algorithm. This Fortran90 code is parallelised using a non-trivial task-farm and two domain decompositions: a 2D cycle of blocks and a slab distribution, using both MPI-1.1 and MPI-2 communications routines. Specifically, MPI_Put and MPI_Get are employed extensively in associa...

We create mock pencil-beam redshift surveys from very large cosmological N-body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model (τCDM) and a flat model with Ω0=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation part...

We have extracted over 400 clusters, covering more than two decades in mass, from three simulations of the τCDM cosmology. This represents the largest uniform catalogue of simulated clusters ever produced. The clusters exhibit a wide variety of density profiles. Only a minority are well-fitted in their outer regions by the widely used density profi...

We calculate the cooling times at constant density for halos with virial temperatures from 100 K to 10^5 K that originate from a 3-sigma fluctuation of a CDM power spectrum in three different cosmologies. Our intention is to determine the first objects that can cool to low temperatures, but not to follow their dynamical evolution. We identify two g...

We have performed cosmological simulations in a $\Lambda$CDM cosmology with and without radiative cooling, in order to study the effect of cooling on the cluster scaling relations. Our simulations consist of 4.1 million particles each of gas and dark matter within a box-size of 100 $h^{-1}$ Mpc and the run with cooling is the largest of its kind to...

We have performed cosmological simulations in a $\Lambda$CDM cosmology with and without radiative cooling, in order to study the effect of cooling on the cluster scaling relations. Our simulations consist of 4.1 million particles each of gas and dark matter within a box-size of 100 $h^{-1}$ Mpc and the run with cooling is the largest of its kind to...

We combine data from a number of N-body simulations to predict the abundance of dark haloes in cold dark matter (CDM) universes over more than four orders of magnitude in mass. A comparison of different simulations suggests that the dominant uncertainty in our results is systematic and is smaller than 10–30 per cent at all masses, depending on the...

We create mock pencil-beam redshift surveys from very large cosmological $N$-body simulations of two Cold Dark Matter cosmogonies, an Einstein-de Sitter model ($\tau$CDM) and a flat model with $\Omega_0 =0.3$ and a cosmological constant ($\Lambda$CDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et a...

We use very large cosmological N-body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model (τCDM) and a flat low density model with a cosmological constant (ΛCDM). Our simu...

We present results of large N-body-hydrodynamic simulations of galaxy formation. Our simulations follow the formation of galaxies in cubic volumes of side 100Mpc, in two versions of the cold dark matter (CDM) cosmogony: the standard, Omega=1 SCDM model and the flat, Omega=0.3 LCDM model. Over 2000 galaxies form in each of these simulations. We exam...