Dust effects on LGRB host galaxies in cosmological simulations
NASA Astrophysics Data System (ADS)
Bignone, L. A.; Pellizza, L. J.; Tissera, P. B.
2016-08-01
The very energetic long gamma-ray bursts (LGRBs) constitute an extremely important tool to study the cosmological evolution of the Universe up to very high redshift. In this work we study the properties of LGRB host galaxies using numerical simulations of galaxy formation. We combine the galaxy catalogue of a hydrodynamical cosmological simulation with a model for LGRBs, which includes constrains for the mass and metallicity of their progenitors. This allows us to analyse the chemical and physical properties of both LGRBs and their hosts. A current problem is to disentangle the bias introduced on the observed host properties by a possible metallicity dependence of the progenitors, from the selection effects produced by dust obscuration in the hosts. We explore this issue by modelling the effect of dust in host galaxies, using radiative transfer codes. In this work we present preliminary results of this research line.
Splotch: visualizing cosmological simulations
NASA Astrophysics Data System (ADS)
Dolag, K.; Reinecke, M.; Gheller, C.; Imboden, S.
2008-12-01
We present a light and fast, publicly available, ray-tracer 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 parameters. Realistic three-dimensional impressions are reached through a composition of the final colour in each pixel properly calculating emission and absorption of individual volume elements. We describe several scientific as well as public applications realized with Splotch. We emphasize how different datasets and configurations lead to remarkably different results in terms of the images and animations. A few of these results are available online.
Effects of baryons on the dark matter distribution in cosmological hydrodynamical simulations
NASA Astrophysics Data System (ADS)
Schaller, Matthieu
2015-09-01
Simulations including solely dark matter performed over the last three decades have delivered an accurate and robust description of the cosmic web and dark matter structures. With the advent of more precise cosmological probes, planned and ongoing, and dark matter detection experiments, this numerical modelling has to be improved to incorporate the complex non-linear and energetic processes taking place during galaxy formation. We use the ``Evolution and Assembly of GaLaxies and their Environment'' (EAGLE) suite of cosmological simulations to investigate the effects of baryons and astrophysical processes on the underlying dark matter distribution. Many effects are expected and we investigate (i): the modification of the profile of halos from the Navarro-Frenk-White profile shape found in collisionless simulations, including the changes in the dark matter profiles themselves, (ii) the changes of the inner density profiles of rich clusters, where observations have suggested a deviation from the standard cold dark matter paradigm, (iii) the offset created by astrophysical process between the centre of galaxies and the centre of the dark matter halo in which they reside and, (iv) the changes in the shape of the dark matter profile due to baryons in the centre of Milky Way halos and the impact these changes have on the morphology of the annihilation signal that could be observed as an indirect proof of the existence of dark matter. In all cases we find that the baryons play a significant role and change the results found in collisionless simulations dramatically. This highlights the need for more simulations like EAGLE to better understand and analyse future cosmology surveys. We also conduct a thorough study of the hydrodynamics solver parameters used in these simulations, assess their impact on the simulated galaxy population and show how robust some of the EAGLE results are against such variations.
BAO in Cosmological Simulations
NASA Astrophysics Data System (ADS)
Mateus, N.; Muñoz-Cuartas, J. C.
2017-07-01
According to ΛCDM paradigm, in the early universe the radiation and baryonic matter were coupled due to Thomson scattering. While, dark matter density fluctuations caused gravitational instabilities. These two competing forces caused baryonic acoustic oscillations (BAO) to appear. As the universe continued expanding and cooling, the formation of atoms led to the recombination epoch and decoupling. Afterwards, the oscillations were no longer subject to radiation pressure causing them to stop. Hence, an imprint in the distribution of matter must be present. The scale of this imprint is around 150Mpc and it is used as a standard ruler. A way to study the clustering of matter distribution is through the power spectrum. It measures it through oscillation modes, i. e., a single mode includes all possible information about at a specific scale. Then, BAO can be found as an oscillation present at certain scales. For a cosmological simulation, it is necessary to construct the density field for a point masses distribution. In the present work, the CIC window is used for such task. From this, it is possible to construct the power spectrum through a fast fourier transform. Several corrections as shot noise and aliasing have to be performed for the power spectrum calculation. In this work, the power spectrum was calculated for the MDPL Multidark simulation, as well as, for different halo populations obtained from MDPL simulations, i.e., M>=1e11 M⊙, 1e12 M⊙ and 1e13 M⊙. As a main result, we have shown the BAO signal estimated for the MDPL Multidark simulation. The power spectrum for different halo populations indicates that the tracer halo population affects the BAO signal. It is expected that the amplitude of the BAO increases with the scale of the population studied, although this has to be further quantified.
The Effect of Corner Modes in the Initial Conditions of Cosmological Simulations
NASA Astrophysics Data System (ADS)
Falck, B.; McCullagh, N.; Neyrinck, M. C.; Wang, J.; Szalay, A. S.
2017-03-01
In view of future high-precision large-scale structure surveys, it is important to quantify the percent and subpercent level effects in cosmological N-body simulations from which theoretical predictions are drawn. One such effect involves deciding whether to zero all modes above the one-dimensional Nyquist frequency, the so-called “corner” modes, in the initial conditions. We investigate this effect by comparing power spectra, density distribution functions, halo mass functions, and halo profiles in simulations with and without these modes. For a simulation with a mass resolution of {m}p∼ {10}11 {h}-1 {M}ȯ , we find that at z> 6, the difference in the matter power spectrum is large at wavenumbers above ∼80% of {k}{Ny}, reducing to below 2% at all scales by z∼ 3. Including corner modes results in a better match between low- and high-resolution simulations at wavenumbers around the Nyquist frequency of the low-resolution simulation, but the effect of the corner modes is smaller than the effect of particle discreteness. The differences in mass functions are 3% for the smallest halos at z = 6 for the {m}p∼ {10}11 {h}-1 {M}ȯ simulation, but we find no significant difference in the stacked profiles of well-resolved halos at z≤slant 6. Thus removing power at | {\\boldsymbol{k}}| > {k}{Ny} in the initial conditions of cosmological simulations has a small effect on small scales and high redshifts, typically below a few percent.
Simulating reionization in numerical cosmology
NASA Astrophysics Data System (ADS)
Sokasian, Aaron
2003-11-01
The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized. I present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by various sets of sources. The method requires relatively few time steps and can be employed with simulations of high resolution. First, I explore the reionization history of Helium II by z < 6 quasars. Comparisons between HeII opacities measured observationally and inferred from our analysis reveal that the uncertainties in the empirical luminosity function provide enough leeway to provide a satisfactory match. A property common to all the calculations is that the epoch of Helium II reionization must have occurred between 3≲
Simulating the effect of non-linear mode coupling in cosmological parameter estimation
NASA Astrophysics Data System (ADS)
Kiessling, A.; Taylor, A. N.; Heavens, A. F.
2011-09-01
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 optimize the design of experiments. However, the standard approach usually assumes both data and parameter estimates are Gaussian-distributed. Further, for survey forecasts and optimization it is usually assumed that the power-spectrum covariance matrix is diagonal in Fourier space. However, 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 naïve 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 2D and tomographic shear analysis of a Euclid-like survey. In both cases, we find that the 68 per cent confidence area of the Ωm-σ8 plane increases by a factor of 5. However, the marginal errors increase by just 20-40 per cent. We propose a new method to model the effects of non-linear shear-power mode coupling in the Fisher matrix by approximating the shear-power distribution as a multivariate Gaussian with a covariance matrix derived from the mock weak lensing survey. We find that this approximation can reproduce the 68 per cent confidence regions of the full maximum likelihood analysis in the Ωm-σ8 plane to high accuracy for both 2D and tomographic weak lensing surveys. Finally, we perform a multiparameter analysis of Ωm, σ8, h, ns, w0 and wa to compare the Gaussian and non-linear mode-coupled Fisher matrix contours. The 6D volume of the 1σ error contours for the non-linear Fisher analysis is a factor of 3 larger than for the Gaussian case, and the shape of the 68 per cent confidence
The entropy core in galaxy clusters: numerical and physical effects in cosmological grid simulations
NASA Astrophysics Data System (ADS)
Vazza, F.
2011-01-01
A flat distribution of low gas entropy in the core region of galaxy clusters is a feature commonly found in Eulerian cosmological simulations, at variance with most standard simulations of smoothed particle hydrodynamics fashion. From the literature, it is still unclear whether this difference is entirely due to numerical artefacts (e.g. spurious transfer from gravitational energy to thermal energy), physical mechanisms (e.g. enhanced mixing in Eulerian codes) or a mixture of both. This issue is related to many still open lines of research in the characterization of the dynamical evolution of the baryons in galaxy clusters: the origin of the cool-core/non-cool-core bi-modality, the diffusion of metals within galaxy clusters, the interplay between active galactic nuclei (AGN) and the intra-cluster medium, etc. In this work, we aim at constraining to what extent the entropy core is affected by numerical effects, and which are the physical reasons for its production in cosmological runs. To this end, we run a set of 30 high-resolution re-simulations of a ˜3 × 1014 M⊙ h-1 cluster of galaxies with a quiet dynamical history, using modified versions of the cosmological adaptive mesh refinement code ENZO and investigating many possible (physical and numerical) details involved in the production of entropy in simulated galaxy clusters. We report that the occurrence of a flat entropy core in the innermost region of a massive cluster is mainly due to hydrodynamical processes resolved by the numerical code (e.g. shocks and mixing motions) and that additional spurious effects of numerical origin (e.g. artificial heating due to softening effects) affect the size and level of the entropy core only in a minor way. Using Lagrangian tracers we show that the entropy profile of non-radiative simulations is produced by a mechanism of `sorting in entropy' which takes place with regularity during the cluster evolution. The evolution of tracers illustrates that the flat entropy core
Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations
NASA Astrophysics Data System (ADS)
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
Machine Learning and Cosmological Simulations
NASA Astrophysics Data System (ADS)
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.
High Resolution TPM Cosmological Simulations
NASA Astrophysics Data System (ADS)
Xu, Guohong
1995-01-01
Cosmological simulation of galaxy formation is a grand challenge problem for both astrophysicists and numerical methodologists. The large dynamic range required to simulate structure formation properly stimulates a search for fast and accurate algorithm which can be fitted into the the front end massively parallel computers. In this thesis, we present our efforts to approach this problem. We proposed and implemented a novel algorithm TPM to perform large cosmological N-body simulations on parallel machines. The TPM method combines the advantages of the fast Particle-Mesh (PM) method and the accurate TREE method. We classify the particles in the simulation box to be PM particles and TREE particles according to their local density. Since structure forms at high density regions, we apply the accurate TREE method to the particles in these regions. The fact that the gravity equation is linear allows us to linearly combine the forces calculated using different methods. Individual objects interact with each other through tidal force, which changes slower than the internal evolution of an object. Thus we can allow individual time steps for each object, which is represented by a group of particles in the same TREE. We parallelize the method by throw each processor a different TREE to process, and several processors can collaborate with each other to evolve the same TREE when necessary. This mechanism gives the code high efficiency on massively parallel computers. With the TPM code, we can easily perform N = 128^ {3} particle simulations with high force resolution (~1/7680 of box size). We have also performed simulations with N = 256^3 particles with the best dynamic range achieved in this field. We put special attention when selecting the parameters of the cosmological models in our simulations. The COBE normalization is taken as a standard to normalize the initial condition, while the results from large scale sky surveys are also taken into consideration. In this thesis we
TERAPIXEL IMAGING OF COSMOLOGICAL SIMULATIONS
Feng Yu; Croft, Rupert A. C.; Di Matteo, Tiziana; Khandai, Nishikanta; Sargent, Randy; Nourbakhsh, Illah; Dille, Paul; Bartley, Chris; Springel, Volker; Jana, Anirban; Gardner, Jeffrey
2011-12-01
The increasing size of cosmological simulations has led to the need for new visualization techniques. We focus on smoothed particle hydrodynamic (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 data sets in both spatial and temporal dimensions and data sets 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 1000 frames, each a gigapixel in size. Both are available for public access through the GigaPan Web interface. We also make our imaging software publicly available.
Cosmological simulations of DGP braneworld gravity
NASA Astrophysics Data System (ADS)
Schmidt, Fabian
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.
Seeing the difference between cosmological simulations.
Haroz, Steve; Heitmann, Katrin
2008-01-01
As cosmology simulations help us understand the universe, we must understand how the results of different simulations vary. Visualization and modern graphics hardware can now provide the ability to visually explore these differences interactively.
On the effect of galactic outflows in cosmological simulations of disc galaxies
NASA Astrophysics Data System (ADS)
Valentini, Milena; Murante, Giuseppe; Borgani, Stefano; Monaco, Pierluigi; Bressan, Alessandro; Beck, Alexander M.
2017-09-01
We investigate the impact of galactic outflow modelling on the formation and evolution of a disc galaxy, by performing a suite of cosmological simulations with zoomed-in initial conditions (ICs) of a Milky Way-sized halo. We verify how sensitive the general properties of the simulated galaxy are to the way in which stellar feedback triggered outflows are implemented, keeping ICs, simulation code and star formation (SF) model all fixed. We present simulations that are based on a version of the gadget3 code where our sub-resolution model is coupled with an advanced implementation of smoothed particle hydrodynamics that ensures a more accurate fluid sampling and an improved description of gas mixing and hydrodynamical instabilities. We quantify the strong interplay between the adopted hydrodynamic scheme and the sub-resolution model describing SF and feedback. We consider four different galactic outflow models, including the one introduced by Dalla Vecchia & Schaye (2012) and a scheme that is inspired by the Springel & Hernquist (2003) model. We find that the sub-resolution prescriptions adopted to generate galactic outflows are the main shaping factor of the stellar disc component at low redshift. The key requirement that a feedback model must have to be successful in producing a disc-dominated galaxy is the ability to regulate the high-redshift SF (responsible for the formation of the bulge component), the cosmological infall of gas from the large-scale environment, and gas fall-back within the galactic radius at low redshift, in order to avoid a too high SF rate at z = 0.
NASA Astrophysics Data System (ADS)
Tolish, Alexander; Wald, Robert M.
2016-08-01
The "memory effect" is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to memory depends only on the cosmological scale factor at the source and observation events, not on the detailed expansion history of the universe. In particular, for sources at the same luminosity distance, the memory effect in a spatially flat FLRW spacetime is enhanced over the Minkowski case by a factor of (1 +z ).
Cosmological perturbation theory as a tool for estimating box-scale effects in N-body simulations
NASA Astrophysics Data System (ADS)
Orban, Chris
2014-07-01
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 by Seto Astrophys. J. 523, 24 (1999), this paper shows that standard (also known as one-loop) cosmological perturbation theory (SPT) [E. T. Vishniac, Mon. Not. R. Astron. Soc. 203, 345 (1983)] can be used to predict, in an approximate way, 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 nonlinear evolution of baryon acoustic oscillations). I focus on SPT in this paper and show that its predictions differ only by about a factor of 2 or less from the measured suppression inferred from both power law and ΛCDM N-body simulations. It should be possible to improve the accuracy of these predictions through using more-sophisticated perturbation theory models. An Appendix compares power spectrum measurements from the power law simulations at outputs where box-scale effects are minimal to perturbation theory models and previously published fitting functions. These power spectrum measurements are included with this paper to aid efforts to develop new perturbation theory models.
HYBRID COSMOLOGICAL SIMULATIONS WITH STREAM VELOCITIES
Richardson, Mark L. A.; Scannapieco, Evan; Thacker, Robert J.
2013-07-10
In the early universe, substantial relative ''stream'' velocities between the gas and dark matter arise due to radiation pressure and persist after recombination. To assess the impact of these velocities on high-redshift structure formation, we carry out a suite of high-resolution adaptive mesh refinement (AMR) cosmological simulations, which use smoothed particle hydrodynamic data sets as initial conditions, converted using a new tool developed for this work. These simulations resolve structures with masses as small as a few 100 M{sub Sun }, and we focus on the 10{sup 6} M{sub Sun} ''mini-halos'' in which the first stars formed. At z Almost-Equal-To 17, the presence of stream velocities has only a minor effect on the number density of halos below 10{sup 6} M{sub Sun }, but it greatly suppresses gas accretion onto all halos and the dark matter structures around them. Stream velocities lead to significantly lower halo gas fractions, especially for Almost-Equal-To 10{sup 5} M{sub Sun} objects, an effect that is likely to depend on the orientation of a halo's accretion lanes. This reduction in gas density leads to colder, more compact radial profiles, and it substantially delays the redshift of collapse of the largest halos, leading to delayed star formation and possibly delayed reionization. These many differences suggest that future simulations of early cosmological structure formation should include stream velocities to properly predict gas evolution, star formation, and the epoch of reionization.
Voids in cosmological simulations over cosmic time
NASA Astrophysics Data System (ADS)
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.
Cosmological N-body Simulation
NASA Astrophysics Data System (ADS)
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
Simulated Studies of Supernova Cosmology for LSST
NASA Astrophysics Data System (ADS)
Biswas, Rahul
2017-01-01
We discuss methods for simulating Type Ia SN observations from LSST based on the Operation Simulation (OpSim) ouptuts supplied by the LSST project and emperical, data driven models of supernovae. Such simulations can be used to assess the Survey strategies implemented in OpSim in terms of the success of different programs in supernova cosmology based on the results of analysis of the simulations.
Cosmological N -body simulations including radiation perturbations
NASA Astrophysics Data System (ADS)
Brandbyge, Jacob; Rampf, Cornelius; Tram, Thomas; Leclercq, Florent; Fidler, Christian; Hannestad, Steen
2017-03-01
Cosmological N-body simulations are the standard tools 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 (≡ photons and neutrinos). In this Letter, we investigate novel hybrid simulations that 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 this work, we focus on simulations initialized at z = 99 and show that the extracted matter power spectrum receives up to 3 per cent corrections on very large scales through radiation. Our numerical findings compare favourably with linear analytical results from Fidler et al., from which we deduce that there cannot be any significant non-linear mode-coupling induced through linear radiation corrections.
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.
Implementing the DC Mode in Cosmological Simulations with Supercomoving Variables
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.
COOL CORE CLUSTERS FROM COSMOLOGICAL SIMULATIONS
Rasia, E.; Borgani, S.; Murante, G.; Planelles, S.; Biffi, V.; Granato, G. L.; Beck, A. M.; Steinborn, L. K.; Dolag, K.; Ragone-Figueroa, C.
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.
Cosmological simulations with disformally coupled symmetron fields
NASA Astrophysics Data System (ADS)
Hagala, R.; Llinares, C.; Mota, D. F.
2016-01-01
Context. We investigate statistical properties of the distribution of matter at redshift zero in disformal gravity by using N-body simulations. The disformal model studied here consists of a conformally coupled symmetron field with an additional exponential disformal term. Aims: We conduct cosmological simulations to discover the impact of the new disformal terms in the matter power spectrum, halo mass function, and radial profile of the scalar field. Methods: We calculated the disformal geodesic equation and the equation of motion for the scalar field. We then implemented these equations into the N-body code Isis, which is a modified gravity version of the code Ramses. Results: The presence of a conformal symmetron field increases both the power spectrum and mass function compared to standard gravity on small scales. Our main finding is that the newly added disformal terms tend to counteract these effects and can make the evolution slightly closer to standard gravity. We finally show that the disformal terms give rise to oscillations of the scalar field in the centre of the dark matter haloes.
Data Simulation for 21 cm Cosmology Experiments
NASA Astrophysics Data System (ADS)
Pober, Jonathan
2017-01-01
21 cm cosmologists seek a measurement of the hyperfine line of neutral hydrogen from very high redshifts. While this signal has the potential to provide an unprecedented view into the early universe, it is also buried under exceedingly bright foreground emission. Over the last several years, 21 cm cosmology research has led to an improved understanding of how low frequency radio interferometers will affect the separation of cosmological signal from foregrounds. This talk will describe new efforts to incorporate this understanding into simulations of the most realistic data sets for the Precision Array for Probing the Epoch of Reionization (PAPER), the Murchison Widefield Array (MWA), and the Hydrogen Epoch of Reionization Array (HERA). These high fidelity simulations are essential for robust algorithm design and validation of early results from these experiments.
Cosmological neutrino simulations at extreme scale
Emberson, J. D.; Yu, Hao-Ran; Inman, Derek; ...
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 ofmore » 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.« less
Cosmological neutrino simulations at extreme scale
NASA Astrophysics Data System (ADS)
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.
Cosmological neutrino simulations at extreme scale
Emberson, Jeffrey D; Yu, Hao-Ran; Inman, Derek; Zhang, Tong-Jie; Pen, Ue-Li; Harnois-Deraps, Joachim; Yuan, Shuo; Teng, Huan-Yu; Zhu, Hong-Ming; Chen, Xuelei; Xing, Zhi-Zhong
2017-01-01
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 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.
General relativistic screening in cosmological simulations
NASA Astrophysics Data System (ADS)
Hahn, Oliver; Paranjape, Aseem
2016-10-01
We revisit the issue of interpreting the results of large volume cosmological simulations in the context of large-scale general relativistic effects. We look for simple modifications to the nonlinear evolution of the gravitational potential ψ that lead on large scales to the correct, fully relativistic description of density perturbations in the Newtonian gauge. We note that the relativistic constraint equation for ψ can be cast as a diffusion equation, with a diffusion length scale determined by the expansion of the Universe. Exploiting the weak time evolution of ψ in all regimes of interest, this equation can be further accurately approximated as a Helmholtz equation, with an effective relativistic "screening" scale ℓ related to the Hubble radius. We demonstrate that it is thus possible to carry out N-body simulations in the Newtonian gauge by replacing Poisson's equation with this Helmholtz equation, involving a trivial change in the Green's function kernel. Our results also motivate a simple, approximate (but very accurate) gauge transformation—δN(k )≈δsim(k )×(k2+ℓ-2)/k2 —to convert the density field δsim of standard collisionless N -body simulations (initialized in the comoving synchronous gauge) into the Newtonian gauge density δN at arbitrary times. A similar conversion can also be written in terms of particle positions. Our results can be interpreted in terms of a Jeans stability criterion induced by the expansion of the Universe. The appearance of the screening scale ℓ in the evolution of ψ , in particular, leads to a natural resolution of the "Jeans swindle" in the presence of superhorizon modes.
A Large number of fast cosmological simulations
NASA Astrophysics Data System (ADS)
Koda, Jun; Kazin, E.; Blake, C.
2014-01-01
Mock galaxy catalogs are essential tools to analyze large-scale structure data. Many independent realizations of mock catalogs are necessary to evaluate the uncertainties in the measurements. We perform 3600 cosmological simulations for the WiggleZ Dark Energy Survey to obtain the new improved Baron Acoustic Oscillation (BAO) cosmic distance measurements using the density field "reconstruction" technique. We use 1296^3 particles in a periodic box of 600/h Mpc on a side, which is the minimum requirement from the survey volume and observed galaxies. In order to perform such large number of simulations, we developed a parallel code using the COmoving Lagrangian Acceleration (COLA) method, which can simulate cosmological large-scale structure reasonably well with only 10 time steps. Our simulation is more than 100 times faster than conventional N-body simulations; one COLA simulation takes only 15 minutes with 216 computing cores. We have completed the 3600 simulations with a reasonable computation time of 200k core hours. We also present the results of the revised WiggleZ BAO distance measurement, which are significantly improved by the reconstruction technique.
Cosmological N-body simulations and their analysis
NASA Astrophysics Data System (ADS)
Stadel, Joachim Gerhard
The goal of this work is to show how large cosmological N-body simulations are computed, how structures within such simulations can be identified with observed galaxies, and how the weak gravitational lensing effect of large scale structure introduces changes in the observed brightness of high redshift sources. We describe PKDGRAV, a fully parallel N-body code that can both spatially adapt to large ranges in particle densities, and temporally adapt to large ranges in dynamical timescales. Care has been taken to insure that the code runs efficiently on a variety of parallel architectures. This has led us to using a non-standard data structure for efficiently calculating the gravitational forces, a variant on the k-D tree, and a new method for treating periodic boundary conditions. A major problem with the interpretation of cosmological N-body simulations has always been identifying the positions and velocities of the ``galaxies'' in simulations. Observational constraints almost always concern the position and velocities of galaxies, not of the dark matter background. We present our grouping algorithm, SKID, which can identify galaxy halos independent of the environment in which the halo is found, a property that is very important given the large dynamic range in background densities present in cosmological simulations. PKDGRAV has been used to perform many very high resolution cosmological N-body simulations. We give an overview of some of the scientific program that has been enabled by this code. We present the magnification distributions due to weak lensing through all the intervening large scale structure from an observer to a source at z = 1. We show that the distribution is a highly skewed one with a shifted mode implying a slight demagnification bias and an extended tail toward high magnification. We investigate the implications of these results on the observations of high redshift type-Ia supernovae and show how these can be used to provide a new cosmological
Effect of radiative transfer on damped Lyα and Lyman limit systems in cosmological SPH simulations
NASA Astrophysics Data System (ADS)
Yajima, Hidenobu; Choi, Jun-Hwan; Nagamine, Kentaro
2012-12-01
We study the effect of local stellar radiation and ultraviolet background (UVB) radiation on the physical properties of damped Lyα systems (DLAs) and Lyman limit systems (LLSs) at z = 3 using cosmological smoothed particle hydrodynamics simulations. We post-process our simulations with the authentic radiation transfer (ART) code for radiative transfer of local stellar radiation and UVB radiation. We find that the DLA and LLS cross-sections are significantly reduced by the UVB radiation, whereas the local stellar radiation does not affect them very much except in the low-mass haloes. This is because the clumpy high-density clouds near young star clusters effectively absorb most of the ionizing photons from young stars. We also find that the UVB model with a simple density threshold for the self-shielding effect can reproduce the observed column density distribution function of DLAs and LLSs very well, and we validate this model by direct radiative transfer calculations of stellar radiation and UVB radiation with high angular resolution. We show that, with a self-shielding treatment, the DLAs have an extended distribution around star-forming regions typically on ˜10-30 kpc scales, and LLSs are surrounding DLAs on ˜30-60 kpc scales. The DLA gas is less extended than the virial radius of the halo, and LLSs are distributed over the similar scale to the virial radius of the host halo. Our simulations suggest that the median properties of DLA host haloes are Mh = 2.4 × 1010 M⊙, SFR = 0.3 M⊙ yr-1, M★ = 2.4 × 108 M⊙ and Z/Z⊙ = 0.1. About 30 per cent of DLAs are hosted by haloes having SFR = 1-20 M⊙ yr-1, which is the typical star formation rate (SFR) range for Lyman break galaxies (LBGs). More than half of DLAs are hosted by the LBGs that are fainter than the current observational limit. Our results suggest that fractional contribution to LLSs from lower mass haloes is greater than for DLAs. Therefore, the median values of LLS host haloes are somewhat lower
Cosmological Effects in Planetary Science
NASA Technical Reports Server (NTRS)
Blume, H. J.; Wilson, T. L.
2010-01-01
In an earlier discussion of the planetary flyby anomaly, a preliminary assessment of cosmological effects upon planetary orbits exhibiting the flyby anomaly was made. A more comprehensive investigation has since been published, although it was directed at the Pioneer anomaly and possible effects of universal rotation. The general subject of Solar System anomalies will be examined here from the point of view of planetary science.
Anisotropic thermal conduction in cosmological cluster formation simulations
NASA Astrophysics Data System (ADS)
Ruszkowski, Mateusz; Parrish, Ian; Brueggen, Marcus
2009-05-01
We investigate the role of the magnetothermal instability (MTI) in the cosmological cluster formation simulations. Our simulations self-consistently incorporate the effects of the field amplification by the structure formation (i.e., gravitational collapse and shearing) and by anisotropic thermal conduction, as well as the effects of violent sloshing motions (e.g., due to mergers) that tend to slow down the field growth. We quantify the effects of these processes on the temperature and density profiles, the strength and topology of the magnetic fields as well as the effective thermal conduction in the intarcluster medium.
IMPLEMENTING THE DC MODE IN COSMOLOGICAL SIMULATIONS WITH SUPERCOMOVING VARIABLES
Gnedin, Nickolay Y.; Kravtsov, Andrey V.; Rudd, Douglas H. E-mail: andrey@oddjob.uchicago.edu
2011-06-01
As emphasized by previous studies, proper treatment of the density fluctuation on the fundamental scale of a cosmological simulation volume-the {sup D}C mode{sup -}is critical for accurate modeling of spatial correlations on scales {approx}> 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.
A web portal for hydrodynamical, cosmological simulations
NASA Astrophysics Data System (ADS)
Ragagnin, A.; Dolag, K.; Biffi, V.; Cadolle Bel, M.; Hammer, N. J.; Krukau, A.; Petkova, M.; Steinborn, D.
2017-07-01
This article describes a data centre hosting a web portal for accessing and sharing the output of large, cosmological, hydro-dynamical simulations with a broad scientific community. It also allows users to receive related scientific data products by directly processing the raw simulation data on a remote computing cluster. The data centre has a multi-layer structure: a web portal, a job control layer, a computing cluster and a HPC storage system. The outer layer enables users to choose an object from the simulations. Objects can be selected by visually inspecting 2D maps of the simulation data, by performing highly compounded and elaborated queries or graphically by plotting arbitrary combinations of properties. The user can run analysis tools on a chosen object. These services allow users to run analysis tools on the raw simulation data. The job control layer is responsible for handling and performing the analysis jobs, which are executed on a computing cluster. The innermost layer is formed by a HPC storage system which hosts the large, raw simulation data. The following services are available for the users: (I) CLUSTERINSPECT visualizes properties of member galaxies of a selected galaxy cluster; (II) SIMCUT returns the raw data of a sub-volume around a selected object from a simulation, containing all the original, hydro-dynamical quantities; (III) SMAC creates idealized 2D maps of various, physical quantities and observables of a selected object; (IV) PHOX generates virtual X-ray observations with specifications of various current and upcoming instruments.
Cosmology with peculiar velocities: observational effects
NASA Astrophysics Data System (ADS)
Andersen, P.; Davis, T. M.; Howlett, C.
2016-12-01
In this paper we investigate how observational effects could possibly bias cosmological inferences from peculiar velocity measurements. Specifically, we look at how bulk flow measurements are compared with theoretical predictions. Usually bulk flow calculations try to approximate the flow that would occur in a sphere around the observer. Using the Horizon Run 2 simulation we show that the traditional methods for bulk flow estimation can overestimate the magnitude of the bulk flow for two reasons: when the survey geometry is not spherical (the data do not cover the whole sky), and when the observations undersample the velocity distributions. Our results may explain why several bulk flow measurements found bulk flow velocities that seem larger than those expected in standard Λ cold dark matter cosmologies. We recommend a different approach when comparing bulk flows to cosmological models, in which the theoretical prediction for each bulk flow measurement is calculated specifically for the geometry and sampling rate of that survey. This means that bulk flow values will not be comparable between surveys, but instead they are comparable with cosmological models, which is the more important measure.
Effective perfect fluids in cosmology
Ballesteros, Guillermo; Bellazzini, Brando E-mail: brando.bellazzini@pd.infn.it
2013-04-01
We describe the cosmological dynamics of perfect fluids within the framework of effective field theories. The effective action is a derivative expansion whose terms are selected by the symmetry requirements on the relevant long-distance degrees of freedom, which are identified with comoving coordinates. The perfect fluid is defined by requiring invariance of the action under internal volume-preserving diffeomorphisms and general covariance. At lowest order in derivatives, the dynamics is encoded in a single function of the entropy density that characterizes the properties of the fluid, such as the equation of state and the speed of sound. This framework allows a neat simultaneous description of fluid and metric perturbations. Longitudinal fluid perturbations are closely related to the adiabatic modes, while the transverse modes mix with vector metric perturbations as a consequence of vorticity conservation. This formalism features a large flexibility which can be of practical use for higher order perturbation theory and cosmological parameter estimation.
Self-Consistent Cosmological Simulations of DGP Braneworld Gravity
Schmidt, Fabian
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.
An improved SPH scheme for cosmological simulations
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Saharian, A. A.
2016-09-01
We investigate the vacuum expectation value of the current density for a charged scalar field on a slice of anti-de Sitter (AdS) space with toroidally compact dimensions. Along the compact dimensions periodicity conditions are imposed on the field operator with general phases and the presence of a constant gauge field is assumed. The latter gives rise to Aharonov-Bohm-like effects on the vacuum currents. The current density along compact dimensions is a periodic function of the gauge field flux with the period equal to the flux quantum. It vanishes on the AdS boundary and, near the horizon, to the leading order, it is conformally related to the corresponding quantity in Minkowski bulk for a massless field. For large values of the length of the compact dimension compared with the AdS curvature radius, the vacuum current decays as power-law for both massless and massive fields. This behavior is essentially different from the corresponding one in Minkowski background, where the currents for a massive field are suppressed exponentially.
Modeling galactic chemical evolution in cosmological simulations
NASA Astrophysics Data System (ADS)
Peruta, Carolyn Cynthia
The most fundamental challenges to models of galactic chemical evolution (GCE) are uncertainties in the basic inputs, including the properties of the stellar initial mass function (IMF), stellar nucleosynthetic yields, and the rate of return of mass and energy to the interstellar and intergalactic medium by Type Ia and II supernovae and stellar winds. In this dissertation, we provide a critical examination of widely available stellar nucleosynthetic yield data, with an eye toward modeling GCE in the broad scope of cosmological hydrodynamical simulations. We examine the implications of uncertain inputs for the Galactic stellar IMF, and nucleosynthetic yields from stellar-evolution calculations, on our ability to ask detailed questions regarding the observed Galactic chemical-abundance patterns. We find a marked need for stellar feedback data from stars of initial mass 8 to 12 Msun and above 40 M sun, and for initial stellar metallicities above and below solar, Z sun=0.02. We find the largest discrepancies amongst nucleosynthetic yield calculations are due to various groups' treatment of hot bottom burning, formation of the 13C pocket in asymptotic giant-branch (AGB) stars, and details of mass loss, rotation, and convection in all stars. Our model of GCE is used to post-process simulations to explore in greater detail the nucleosynthetic evolution of the stellar populations and interstellar/intergalactic medium, and to compare directly to the chemical abundances of the Milky Way stellar halo and dwarf spheroidal galaxy stellar populations.
Cosmological simulations of dwarf galaxies with cosmic ray feedback
NASA Astrophysics Data System (ADS)
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.
Spurious haloes and discreteness-driven relaxation in cosmological simulations
NASA Astrophysics Data System (ADS)
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.
The Effective Field Theory of nonsingular cosmology
NASA Astrophysics Data System (ADS)
Cai, Yong; Wan, Youping; Li, Hai-Guang; Qiu, Taotao; Piao, Yun-Song
2017-01-01
In this paper, we explore the nonsingular cosmology within the framework of the Effective Field Theory (EFT) of cosmological perturbations. Due to the recently proved no-go theorem, any nonsingular cosmological models based on the cubic Galileon suffer from pathologies. We show how the EFT could help us clarify the origin of the no-go theorem, and offer us solutions to break the no-go. Particularly, we point out that the gradient instability can be removed by using some spatial derivative operators in EFT. Based on the EFT description, we obtain a realistic healthy nonsingular cosmological model, and show the perturbation spectrum can be consistent with the observations.
Halo Spin Parameter in Cosmological Simulations
NASA Astrophysics Data System (ADS)
Ahn, Jieun; Kim, Juhan; Shin, Jihye; Kim, Sungsoo S.; Choi, Yun-Young
2014-04-01
Using a cosmological ΛCDM simulation, we analyze the differences between the widely-used spin parameters suggested by Peebles and Bullock. The dimensionless spin parameter λ proposed by Peebles is theoretically well-justified but includes an annoying term, the potential energy, which cannot be directly obtained from observations and is computationally expensive to calculate in numerical simulations. The Bullock's spin parameter λ^' avoids this problem assuming the isothermal density profile of a virialized halo in the Newtonian potential model. However, we find that there exists a substantial discrepancy between λ and λ^' depending on the adopted potential model (Newtonian or Plummer) to calculate the halo total energy and that their redshift evolutions differ to each other significantly. Therefore, we introduce a new spin parameter, λ^{''}, which is simply designed to roughly recover the value of λ but to use the same halo quantities as used in λ^'. If the Plummer potential is adopted, the λ^{''} is related to the Bullock's definition as λ^{''} = 0.80× (1 + z)^{-1/12} λ^'. Hence, the new spin parameter λ^{''} distribution becomes consistent with a log-normal distribution frequently seen for the λ^' while its mean value is much closer to that of λ. On the other hand, in case of the Newtonian potential model, we obtain the relation of λ^{''}=(1+z)^{-1/8}λ^{'}; there is no significant difference at z = 0 as found by others but λ^{'} becomes more overestimated than λ or λ^{''} at higher redshifts. We also investigate the dependence of halo spin parameters on halo mass and redshift. We clearly show that although the λ^' for small-mass halos with M_h < 2× 10^{12} M_odot seems redshift independent after z=1, all the spin parameters explored, on the whole, show a stronger correlation with the increasing halo mass at higher redshifts.
EXAMINING SUBGRID MODELS OF SUPERMASSIVE BLACK HOLES IN COSMOLOGICAL SIMULATION
Sutter, P. M.; Ricker, P. M. E-mail: pmricker@illinois.ed
2010-11-10
Although 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 density, and the low-redshift relations to halo properties. We also find that it is possible to reproduce observations of the low-redshift relations without accretion and feedback, depending on the choice of subgrid model.
Cosmological simulations of isotropic conduction in galaxy clusters
Smith, Britton; O'Shea, Brian W.; Voit, G. Mark; Ventimiglia, David; Skillman, Samuel W.
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.
Cosmological simulations of the first galaxies
NASA Astrophysics Data System (ADS)
Latife, Muhammad Abdul
2011-09-01
The study of the cosmos has mesmerized humans since many centuries. Our present knowledge of the Universe is based on the standard Big Bang theory. The detection of the cosmic microwave background (CMB) is one of the strongest evidences of the Big Bang model. The isotropy of the CMB shows that the Universe is very isotropic on the large scales. The CMB also shows a spectrum of very small density fluctuations that form the seeds for structures in the Universe. The formation of the first objects (i.e., first stars and quasars) at the end of dark ages is an outstanding issue in the modern cosmology. They were formed when the Universe was about 400 million years old as shown in the figure 1. During the past decade, the study of primordial objects has gained a lot of interest but still many questions remain unanswered about their formation. In this thesis, we have addressed some of the key questions pertaining to the formation of the first objects. It is generally believed that structures in the early Universe are formed out of small density perturbations as a result of a gravitational instability. These perturbations are produced due to quantum fluctuations in the gravitational potential during the early Universe. They collapse under self-gravity to form small structures. They merge with each other to form bigger structures and this scenario is called hierarchical scenario of structure formation. The growth of structures depends upon the contents of the Universe. The Universe comprises 70% dark energy which is responsible for its expansion. It was realized in early 80s that most of the matter in the Universe is not comprised of atoms. Rather, non-luminous source of gravity was found to be essential to explain the rotation curves of galaxies which we call dark matter. The Universe comprises 23% dark matter and only 4% atoms that is the model known as Lambda cold dark matter (LCDM). In the very begining, density perturbations are small. They grow linearly and equations
N-body simulations for coupled scalar-field cosmology
Li Baojiu; Barrow, John D.
2011-01-15
We describe in detail the general methodology and numerical implementation of consistent N-body simulations for coupled-scalar-field models, including background cosmology and the generation of initial conditions (with the different couplings to different matter species taken into account). We perform fully consistent simulations for a class of coupled-scalar-field models with an inverse power-law potential and negative coupling constant, for which the chameleon mechanism does not work. We find that in such cosmological models the scalar-field potential plays a negligible role except in the background expansion, and the fifth force that is produced is proportional to gravity in magnitude, justifying the use of a rescaled gravitational constant G in some earlier N-body simulation works for similar models. We then study the effects of the scalar coupling on the nonlinear matter power spectra and compare with linear perturbation calculations to see the agreement and places where the nonlinear treatment deviates from the linear approximation. We also propose an algorithm to identify gravitationally virialized matter halos, trying to take account of the fact that the virialization itself is also modified by the scalar-field coupling. We use the algorithm to measure the mass function and study the properties of dark-matter halos. We find that the net effect of the scalar coupling helps produce more heavy halos in our simulation boxes and suppresses the inner (but not the outer) density profile of halos compared with the {Lambda}CDM prediction, while the suppression weakens as the coupling between the scalar field and dark-matter particles increases in strength.
Analyzing and Visualizing Cosmological Simulations with ParaView
Woodring, Jonathan; Heitmann, Katrin; Ahrens, James P; Fasel, Patricia; Hsu, Chung-Hsing; Habib, Salman; Pope, Adrian
2011-01-01
The advent of large cosmological sky surveys - ushering in the era of precision cosmology - has been accompanied by ever larger cosmological simulations. The analysis of these simulations, which currently encompass tens of billions of particles and up to a trillion particles in the near future, is often as daunting as carrying out the simulations in the first place. Therefore, the development of very efficient analysis tools combining qualitative and quantitative capabilities is a matter of some urgency. In this paper, we introduce new analysis features implemented within ParaView, a fully parallel, open-source visualization toolkit, to analyze large N-body simulations. A major aspect of ParaView is that it can live and operate on the same machines and utilize the same parallel power as the simulation codes themselves. In addition, data movement is in a serious bottleneck now and will become even more of an issue in the future; an interactive visualization and analysis tool that can handle data in situ is fast becoming essential. The new features in ParaView include particle readers and a very efficient halo finder that identifies friends-of-friends halos and determines common halo properties, including spherical overdensity properties. In combination with many other functionalities already existing within ParaView, such as histogram routines or interfaces to programming languages like Python, this enhanced version enables fast, interactive, and convenient analyses of large cosmological simulations. In addition, development paths are available for future extensions.
Halo Core Tracking for Galaxy Placement in Cosmological Simulations
NASA Astrophysics Data System (ADS)
Korytov, Danila
2017-01-01
Synthetic galaxy catalogs are an important product of cosmological simulations. Upcoming surveys, such as LSST, require high volume and high resolution simulations for generating large object catalogs. These catalogs have many uses including testing and improving analysis pipelines, predictions for different cosmologies and investigations of systematic errors. Dark matter (DM) only simulations are able to reach the required volume and resolution but need an accurate prescription for galaxy placement within DM halos. We present a method for galaxy placement. For halos above a characteristic mass, central DM simulation particles are taken as tracer particles for a galaxy. These halo ``cores'' are tracked through the simulation and may merge with other ``cores'' or be ripped apart by halo tidal forces. We examine how accurately we can reproduce galaxy cluster profiles, two point correlation functions and other galaxy statistics.
The effective field theory of nonsingular cosmology: II
NASA Astrophysics Data System (ADS)
Cai, Yong; Li, Hai-Guang; Qiu, Taotao; Piao, Yun-Song
2017-06-01
Based on the effective field theory (EFT) of cosmological perturbations, we explicitly clarify the pathology in nonsingular cubic Galileon models and show how to cure it in EFT with new insights into this issue. With the least set of EFT operators that are capable to avoid instabilities in nonsingular cosmologies, we construct a nonsingular model dubbed the Genesis-inflation model, in which a slowly expanding phase (namely, Genesis) with increasing energy density is followed by slow-roll inflation. The spectrum of the primordial perturbation may be simulated numerically, which shows itself a large-scale cutoff, as the large-scale anomalies in CMB might be a hint for.
Cosmological fluid mechanics with adaptively refined large eddy simulations
NASA Astrophysics Data System (ADS)
Schmidt, W.; Almgren, A. S.; Braun, H.; Engels, J. F.; Niemeyer, J. C.; Schulz, J.; Mekuria, R. R.; Aspden, A. J.; Bell, J. B.
2014-06-01
We investigate turbulence generated by cosmological structure formation by means of large eddy simulations using adaptive mesh refinement. In contrast to the widely used implicit large eddy simulations, which resolve a limited range of length-scales and treat the effect of turbulent velocity fluctuations below the grid scale solely by numerical dissipation, we apply a subgrid-scale model for the numerically unresolved fraction of the turbulence energy. For simulations with adaptive mesh refinement, we utilize a new methodology that allows us to adjust the scale-dependent energy variables in such a way that the sum of resolved and unresolved energies is globally conserved. We test our approach in simulations of randomly forced turbulence, a gravitationally bound cloud in a wind, and the Santa Barbara cluster. To treat inhomogeneous turbulence, we introduce an adaptive Kalman filtering technique that separates turbulent velocity fluctuations on resolved length-scales from the non-turbulent bulk flow. From the magnitude of the fluctuating component and the subgrid-scale turbulence energy, a total turbulent velocity dispersion of several 100 km s-1 is obtained for the Santa Barbara cluster, while the low-density gas outside the accretion shocks is nearly devoid of turbulence. The energy flux through the turbulent cascade and the dissipation rate predicted by the subgrid-scale model correspond to dynamical time-scales around 5 Gyr, independent of numerical resolution.
Cosmological simulations of Milky Way-sized galaxies
NASA Astrophysics Data System (ADS)
Colín, Pedro; Avila-Reese, Vladimir; Roca-Fàbrega, Santi; Valenzuela, Octavio
2016-10-01
We introduce a new set of eight Milky Way-sized cosmological simulations performed using the AMR code Adaptive Refinement Tree + Hydrodynamics in a ΛCDM cosmology. The set of zoom-in simulations covers present-day virial masses that range from 8.3× {10}11 {M}⊙ to 1.56× {10}12 {M}⊙ and is carried out with our simple but effective prescriptions for deterministic star formation (SF) and “explosive” stellar feedback. The work focuses on showing the goodness of the simulated set of “field” Milky Way-sized galaxies. To this end, we compare some of the predicted physical quantities with the corresponding observed ones. Our results are as follows. (a) In agreement with some previous works, we found curves of circular velocity that are flat or slightly peaked. (b) All simulated galaxies with a significant disk component are consistent with the observed Tully-Fisher, radius-mass, and cold gas-stellar mass correlations of late-type galaxies. (c) The disk-dominated galaxies have stellar specific angular momenta in agreement with those of late-type galaxies, with values around 103 km s-1 kpc-1. (d) The SF rates at z = 0 of all runs but one are comparable to those estimated for the star-forming galaxies. (e) The two most spheroid-dominated galaxies formed in halos with late active merger histories and late bursts of SF, but the other run that ends also dominated by a spheroid never had major mergers. (f) The simulated galaxies lie in the semi-empirical correlation of stellar to halo mass of local central galaxies, and those that end up as disk-dominated evolve mostly along the low-mass branch of this correlation. Moreover, the growth histories of baryonic and stellar mass of these galaxies are proportional to their growth histories of halo mass over the last 6.5-10 Gyr. (g) Within the virial radii of the simulations, ≈ 25 % -50% of the baryons are missed; the amount of gas in the halo is similar to the amount in stars in the galaxy, and most of this gas is in
Simulating cosmologies beyond ΛCDM with PINOCCHIO
NASA Astrophysics Data System (ADS)
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.
Effective Friedmann model from multidimensional cosmologies
NASA Astrophysics Data System (ADS)
Zhuk, A.
2006-10-01
We investigate the possibility of the construction of the conventional Friedmann cosmology for our observable Universe if the underlying theory is the multidimensional Kaluza-Klein model. We show that the effective Friedmann model obtained by dynamic compactification of the multidimensional model is faced with too strong variations in the fundamental constants. On the other hand, models with stable compactification of the internal space are free from this problem and also result in conventional four-dimensonal cosmological behaviour for our Universe. We prove a no-go theorem, which shows that stable compactification of the internal spaces is possible only if the equations of state in the external and internal spaces are properly adjusted to each other. With a proper choice of parameters (fine tuning), the effective cosmological constant in this model provides the late-time acceleration of the Universe.
Euclid Cosmological Simulations Requirements and Implementation Plan
NASA Technical Reports Server (NTRS)
Kiessling, Alina
2012-01-01
Simulations are essential for the successful undertaking of the Euclid mission. The simulations requirements for the Euclid mission are vast ! It is an enormous undertaking that includes development of software and acquisition of hardware facilities. The simulations requirements are currently being finalised - please contact myself or Elisabetta Semboloni if you would like to add/modify any r equi r ements (or if you would like to be involved in the development of the simulations).
Dust properties of Lyman-break galaxies in cosmological simulations
NASA Astrophysics Data System (ADS)
Yajima, Hidenobu; Nagamine, Kentaro; Thompson, Robert; Choi, Jun-Hwan
2014-04-01
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 haloes using the metallicity information of individual gas particles in our simulation. We use only bright galaxies with rest-frame ultraviolet (UV) magnitude M1700 < -20 mag, and study the dust size, dust-to-metal mass ratio, and dust composition. From the comparison of calculated colour 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 μm, 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-frame UV luminosity function of LBGs at z = 3 without assuming an ad hoc constant extinction value. In addition, in order to reproduce the observed mean E(B - V), we find that the dust-to-metal mass ratio needs to be similar to that of the local galaxies, and that the graphite dust is dominant or at least occupy half of dust mass.
NASA Astrophysics Data System (ADS)
Harrison, Edward
2000-03-01
Cosmology: The Science of the Universe is a broad introduction to the science of modern cosmology, with emphasis on its historical origins. The first edition of this best-selling book received worldwide acclaim for its lucid style and wide-ranging exploration of the universe. This eagerly awaited second edition updates and greatly extends the first with seven new chapters that explore early scientific cosmology, Cartesian and Newtonian world systems, cosmology after Newton and before Einstein, special relativity, observational cosmology, inflation and creation of the universe. All chapters conclude with a section entitled Reflections containing provocative topics that will foster lively debate. The new Projects section, also at the end of each chapter, raises questions and issues to challenge the reader.
Cosmological smoothed particle hydrodynamics simulations: the entropy equation
NASA Astrophysics Data System (ADS)
Springel, Volker; Hernquist, Lars
2002-07-01
We discuss differences in simulation results that arise between the use of either the thermal energy or the entropy as an independent variable in smoothed particle hydrodynamics (SPH). In this context, we derive a new version of SPH that, when appropriate, manifestly conserves both energy and entropy if smoothing lengths are allowed to adapt freely to the local mass resolution. To test various formulations of SPH, we consider point-like energy injection, as in certain models of supernova feedback, and find that powerful explosions are well represented by SPH even when the energy is deposited into a single particle, provided that the entropy equation is integrated. If the thermal energy is instead used as an independent variable, unphysical solutions can be obtained for this problem. We also examine the radiative cooling of gas spheres that collapse and virialize in isolation, and of haloes that form in cosmological simulations of structure formation. When applied to these problems, the thermal energy version of SPH leads to substantial overcooling in haloes that are resolved with up to a few thousand particles, while the entropy formulation is biased only moderately low for these haloes under the same circumstances. For objects resolved with much larger particle numbers, the two approaches yield consistent results. We trace the origin of the differences to systematic resolution effects in the outer parts of cooling flows. When the thermal energy equation is integrated and the resolution is low, the compressional heating of the gas in the inflow region is underestimated, violating entropy conservation and improperly accelerating cooling. The cumulative effect of this overcooling can be significant. In cosmological simulations of moderate size, we find that the fraction of baryons which cool and condense can be reduced by up to a factor ~2 if the entropy equation is employed rather than the thermal energy equation, partly explaining discrepancies with semi
In situ and in-transit analysis of cosmological simulations
Friesen, Brian; Almgren, Ann; Lukic, Zarija; ...
2016-08-24
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 haltingmore » 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.« less
In situ and in-transit analysis of cosmological simulations
NASA Astrophysics Data System (ADS)
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.
Statistical Properties of Supercluster-like Filaments from Cosmological Simulations
NASA Astrophysics Data System (ADS)
Yan, Heling; Fan, Zuhui
2011-03-01
In this paper, we study large-scale structures from numerical simulations, paying particular attention to supercluster-like structures. A grid-density-contour-based algorithm is adopted to locate connected groups. With the increase of the linking density threshold from the cosmic average density, the foam-like cosmic web is subsequently broken into individual supercluster-like groups and further halos. To be in accordance with normal friends-of-friends halos with the linking length of 0.2 in units of the average separation of particles, halos in this paper are defined as groups with the linking density threshold ρ/\\bar{ρ}=1+δ =80, where ρ is the grid density, and \\bar{\\rho } is the average mass density of the universe. Groups with lower linking densities are then generally referred to as supercluster-like groups. By analyzing sets of cosmological simulations with varying cosmological parameters, we find that a universal mass function exists not only for halos but also for low-density supercluster-like groups until the linking density threshold decreases to 1 + δ ~ 8 where the global percolation of large-scale structures occurs. We further show that the mass functions of different groups can be well described by the Jenkins form with the parameters being dependent on the linking density threshold. On the other hand, these low-density supercluster-like groups cannot be directly associated with the predictions from the excursion set theory with effective barriers obtained from dynamical collapse models, and the peak-exclusion effect must be taken into account. Including such an effect, the mass function of groups with the linking density threshold 1 + δ = 16 is in good agreement with that from the excursion set theory with a nearly flat effective barrier. A simplified analysis of the ellipsoidal collapse model indicates that the barrier for collapses along two axes to form filaments is approximately flat in scales. Thus, in our analyses, we define groups
Three-dimensional Visualization of Cosmological and Galaxy Formation Simulations
NASA Astrophysics Data System (ADS)
Thooris, Bruno; Pomarède, Daniel
2011-12-01
Our understanding of the structuring of the Universe from large-scale cosmological structures down to the formation of galaxies now largely benefits from numerical simulations. The RAMSES code, relying on the Adaptive Mesh Refinement technique, is used to perform massively parallel simulations at multiple scales. The interactive, immersive, three-dimensional visualization of such complex simulations is a challenge that is addressed using the SDvision software package. Several rendering techniques are available, including ray-casting and isosurface reconstruction, to explore the simulated volumes at various resolution levels and construct temporal sequences. These techniques are illustrated in the context of different classes of simulations. We first report on the visualization of the HORIZON Galaxy Formation Simulation at MareNostrum, a cosmological simulation with detailed physics at work in the galaxy formation process. We then carry on in the context of an intermediate zoom simulation leading to the formation of a Milky-Way like galaxy. Finally, we present a variety of simulations of interacting galaxies, including a case-study of the Antennae Galaxies interaction.
Ruszkowski, M.; Lee, D.; Parrish, I.; Oh, S. Peng E-mail: dongwook@flash.uchicago.edu E-mail: iparrish@astro.berkeley.edu
2011-10-20
The intracluster medium (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 whenever the temperature gradient points in the direction opposite to gravitational acceleration. Using cosmological simulations of cluster formation 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 rearrangements 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 the Square Kilometer Array and future X-ray spectroscopic studies with the International X-ray Observatory. We demonstrate that radiative cooling boosts the amplification of the magnetic field by about two orders of magnitude beyond what is expected in the non-radiative cases. This effect is caused by the compression of the gas and frozen-in magnetic field as it accumulates in the cluster center. At z = 0 the field is amplified by a factor of about 10{sup 6} compared to the uniform magnetic field that evolved due to the universal expansion alone. Interestingly, the runs that include both radiative cooling and thermal conduction exhibit stronger magnetic field amplification than purely radiative runs. In these cases, buoyant restoring forces depend on the temperature gradients rather than the steeper entropy gradients. Thus, the ICM is more easily mixed and the winding up of the frozen-in magnetic
Cosmological Simulations on a Grid of Computers
NASA Astrophysics Data System (ADS)
Depardon, Benjamin; Caron, Eddy; Desprez, Frédéric; Blaizot, Jérémy; Courtois, Hélène
2010-06-01
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.
How to model AGN feedback in cosmological simulations?
NASA Astrophysics Data System (ADS)
Sijacki, Debora
2015-08-01
Hydrodynamical cosmological simulations are one of the most powerful tools to study the formation and evolution of galaxies in the fully non-linear regime. Despite several recent successes in simulating Milky Way look-alikes, self-consistent, ab-initio models are still a long way off. In this talk I will review numerical and physical uncertainties plaguing current state-of-the-art cosmological simulations of galaxy formation. I will then discuss which feedback mechanisms are needed to reproduce realistic stellar masses and galaxy morphologies in the present day Universe and argue that the black hole feedback is necessary for the quenching of massive galaxies. I will then demonstrate how black hole - host galaxy scaling relations depend on galaxy morphology and colour, highlighting the implications for the co-evolutionary picture between galaxies and their central black holes. In the second part of the talk I will present a novel method that permits to resolve gas flows around black holes all the way from large cosmological scales to the Bondi radii of black holes themselves. I will demonstrate that with this new numerical technique it is possible to estimate much more accurately gas properties in the vicinity of black holes than has been feasible before in galaxy and cosmological simulations, allowing to track reliably gas angular momentum transport from Mpc to pc scales. Finally, I will also discuss if AGN-driven outflows are more likely to be energy- or momentum-driven and what implications this has for the redshift evolution of black hole - host galaxy scaling relations.
Fundamental metallicity scaling relations in cosmological simulations
NASA Astrophysics Data System (ADS)
De Rossi, M. E.; Theuns, T.; Font, A. S.; McCarthy, I. G.
2016-08-01
In this work, we analyse metallicity scaling relations of galaxies by using Galaxies-Intergalactic Medium Interaction Calculation simulations. Our results show that stellar metallicity correlates with stellar mass, in agreement with observations. At a given mass, systems with lower gas fractions or lower star formation rates are, on average, more metal-enriched. In addition, satellite galaxies tend to have higher metallicities that central galaxies of similar masses. The relation between mass and stellar metallicity does not evolve significantly with redshift. These trends obtained for the stellar phase are weaker than those found for the gas component in previous studies.
Simulating the Nature of Science: Cosmology Distilled
NASA Astrophysics Data System (ADS)
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.
Effective scenario of loop quantum cosmology.
Ding, You; Ma, Yongge; Yang, Jinsong
2009-02-06
Semiclassical states in isotropic loop quantum cosmology are employed to show that the improved dynamics has the correct classical limit. The effective Hamiltonian for the quantum cosmological model with a massless scalar field is thus obtained, which incorporates also the next to leading order quantum corrections. The possibility that the higher order correction terms may lead to significant departure from the leading order effective scenario is revealed. If the semiclassicality of the model is maintained in the large scale limit, there are great possibilities for a k=0 Friedmann expanding universe to undergo a collapse in the future due to the quantum gravity effect. Thus the quantum bounce and collapse may contribute a cyclic universe in the new scenario.
Some Dynamical Effects of the Cosmological Constant
NASA Astrophysics Data System (ADS)
Axenides, M.; Floratos, E. G.; Perivolaropoulos, L.
Newton's law gets modified in the presence of a cosmological constant by a small repulsive term (antigravity) that is proportional to the distance. Assuming a value of the cosmological constant consistent with the recent SnIa data (Λ~=10-52 m-2), we investigate the significance of this term on various astrophysical scales. We find that on galactic scales or smaller (less than a few tens of kpc), the dynamical effects of the vacuum energy are negligible by several orders of magnitude. On scales of 1 Mpc or larger however we find that the vacuum energy can significantly affect the dynamics. For example we show that the velocity data in the local group of galaxies correspond to galactic masses increased by 35% in the presence of vacuum energy. The effect is even more important on larger low density systems like clusters of galaxies or superclusters.
Effect of inflation on anisotropic cosmologies
Jensen, L.G.; Stein-Schabes, J.A.
1986-03-01
The effects of anisotropic cosmologies on inflation are studied. By properly formulating the field equations it is possible to show that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today. Furthermore, we shall show that it takes a very long time for anisotropies to become visible in the observable part of the Universe. It is interesting to note that the time scale will be independent of the Bianchi Model and of the initial anisotropy. 6 refs.
Diverse structural evolution at z > 1 in cosmologically simulated galaxies
NASA Astrophysics Data System (ADS)
Snyder, Gregory F.; Lotz, Jennifer; Moody, Christopher; Peth, Michael; Freeman, Peter; Ceverino, Daniel; Primack, Joel; Dekel, Avishai
2015-08-01
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 < z < 3. We measure automated diagnostics of galaxy morphology in cosmological simulations of the formation of 22 central galaxies with 9.3 < log10M*/M⊙ < 10.7. These high-spatial-resolution zoom-in calculations enable accurate modelling of the rest-frame UV and optical morphology. Even with small numbers of galaxies, we find that structural evolution is neither universal nor monotonic: galaxy interactions can trigger either bulge or disc formation, and optically bulge-dominated galaxies at this mass may not remain so forever. Simulated galaxies with M* > 1010M⊙ contain relatively more disc-dominated light profiles than those with lower mass, reflecting significant disc brightening in some haloes at 1 < z < 2. By this epoch, simulated galaxies with specific star formation rates below 10- 9.7 yr- 1 are more likely than normal star-formers to have a broader mix of structural types, especially at M* > 1010 M⊙. We analyse a cosmological major merger at z ˜ 1.5 and find that the newly proposed Multimode-Intensity-Deviation (MID) morphology diagnostics trace later merger stages while Gini-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 <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.
Infrared properties of z = 7 galaxies from cosmological simulations
Cen, Renyue; Kimm, Taysun
2014-02-10
Three-dimensional panchromatic dust radiative transfer calculations are performed on a set of 198 galaxies of stellar masses in the range of 5 × 10{sup 8} to 3 × 10{sup 10} M {sub ☉} from a cosmological hydrodynamic simulation (resolved at 29 h {sup –1} pc) at z ∼ 7. In a companion paper, the stellar mass and UV luminosity functions and the UV-optical and FUV-NUV colors are shown to be in good agreement with observations if a Small Magellanic Cloud type dust extinction curve is adopted. Here, we make useful predictions, self-consistently, of the infrared properties of these z ∼ 7 simulated galaxies that can be confronted with upcoming ALMA data. Our findings are as follows. (1) The effective radius in the rest-frame MIPS70 μm band is in the range of 80-400 pc proper for z = 7 galaxies with L {sub FIR} = 10{sup 11.3}-10{sup 12} L {sub ☉}. (2) The median of the peak wavelength of the far-infrared (FIR) spectral energy distribution is in the range of 45-60 μm, depending on the dust-to-metal ratio. (3) For star formation rate in the range of 3-100 M {sub ☉} yr{sup –1}, the median FIR to bolometric luminosity ratio is 60%-90%. (4) The FIR luminosity function displays a power law in the high end with a slope of –3.1 ± 0.4 instead of the usual exponential decline.
Galactic winds in cosmological simulations of the circumgalactic medium
NASA Astrophysics Data System (ADS)
Barai, Paramita; Viel, Matteo; Borgani, Stefano; Tescari, Edoardo; Tornatore, Luca; Dolag, Klaus; Killedar, Madhura; Monaco, Pierluigi; D'Odorico, Valentina; Cristiani, Stefano
2013-04-01
We explore new observationally constrained subresolution models of galactic outflows and investigate their impact on the circumgalactic medium (CGM) in the redshift range z = 2-4. We perform cosmological hydrodynamic simulations, including star formation, chemical enrichment and four cases of supernovae-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 the star formation, reduce the central galactic metallicity and enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy centres are most sensitive to the choice of the wind model for halo masses in the range (109-1011) M⊙. We infer that outflows in the RVWb model are least effective, with results similar to the NW case, except that the CGM is enriched more. Moreover, we find that the models CW and RVWa are similar, both showing the impact of effective winds, with the following notable differences. RVWa causes a greater suppression of star formation rate at z ≤ 5, and has a higher fraction of low-density (δ < 10), warm-hot (104-106 K) gas than in CW. Outflows in CW produce a higher and earlier enrichment of some intergalactic medium phases than in RVWa. By visual inspection, we note that the RVWa model shows galactic discs more pronounced than all the other wind models. We predict that some observational diagnostics are more promising to distinguish between different outflow driving mechanisms in galaxies: ZC of the CGM gas at r ˜ (30-300) h-1 kpc comoving, and C IV fraction of the inner gas at r < (4-5) h-1 kpc comoving.
Two-body relaxation in simulated cosmological haloes
NASA Astrophysics Data System (ADS)
El-Zant, Amr A.
2006-08-01
This paper aims to quantify, in a general manner that does not directly resort to large-scale calculations, discreteness effects acting on the dynamics of dark matter haloes forming in the context of cosmological simulations. By generalizing the standard formulation of two-body relaxation to the case when the size and mass distributions are variable, and parametrizing the time evolution using established empirical relations, we find that the dynamics of a million-particle halo is noise-dominated within the inner per cent of the final virial radius. Far larger particle numbers (~108) are required for the rms perturbations to the velocity to drop to the 10per cent level there. The radial scaling of the relaxation time is simple and strong: trelax ~r2, implying that numbers >>108 are required to faithfully model the very inner regions; artificial relaxation may thus constitute an important factor, contributing to the contradictory claims concerning the persistence of a power-law density cusp to the very centre. The cores of substructure haloes can be many relaxation times old. Since relaxation first causes their expansion before recontraction occurs, it may render them either more difficult or easier to disrupt, depending on their orbital parameters. This may modify the characteristics of the subhalo distribution; and if, as suggested by several authors, it is parent-satellite interactions that determine halo profiles, the overall structure of the system may be affected. We derive simple closed form formulae for the characteristic relaxation time of both parents and satellites, and an elementary argument deducing the weak N-scaling reported by Diemand et al. when the main contribution comes from relaxing subhaloes.
Maps of CMB lensing deflection from N-body simulations in Coupled Dark Energy Cosmologies
Carbone, Carmelita; Baldi, Marco; Baccigalupi, Carlo E-mail: marco.baldi5@unibo.it E-mail: bacci@sissa.it
2013-09-01
We produce lensing potential and deflection-angle maps in order to simulate the weak gravitational lensing of the Cosmic Microwave Background (CMB) via ray-tracing through the COupled Dark Energy Cosmological Simulations (CoDECS), the largest suite of N-body simulations to date for interacting Dark Energy cosmologies. The constructed maps faithfully reflect the N-body cosmic structures on a range of scales going from the arcminute to the degree scale, limited only by the resolution and extension of the simulations. We investigate the variation of the lensing pattern due to the underlying Dark Energy (DE) dynamics, characterised by different background and perturbation behaviours as a consequence of the interaction between the DE field and Cold Dark Matter (CDM). In particular, we study in detail the results from three cosmological models differing in the background and perturbations evolution at the epoch in which the lensing cross section is most effective, corresponding to a redshift of ∼ 1, with the purpose to isolate their imprints in the lensing observables, regardless of the compatibility of these models with present constraints. The scenarios investigated here include a reference ΛCDM cosmology, a standard coupled DE (cDE) scenario, and a ''bouncing'' cDE scenario. For the standard cDE scenario, we find that typical differences in the lensing potential result from two effects: the enhanced growth of linear CDM density fluctuations with respect to the ΛCDM case, and the modified nonlinear dynamics of collapsed structures induced by the DE-CDM interaction. As a consequence, CMB lensing highlights the DE impact in the cosmological expansion, even in the degenerate case where the amplitude of the linear matter density perturbations, parametrised through σ{sub 8}, is the same in both the standard cDE and ΛCDM cosmologies. For the ''bouncing'' scenario, we find that the two opposite behaviours of the lens density contrast and of the matter abundance lead to
Comparing AMR and SPH Cosmological Simulations. I. Dark Matter and Adiabatic Simulations
NASA Astrophysics Data System (ADS)
O'Shea, Brian W.; Nagamine, Kentaro; Springel, Volker; Hernquist, Lars; Norman, Michael L.
2005-09-01
We compare two cosmological hydrodynamic simulation codes in the context of hierarchical galaxy formation: the Lagrangian smoothed particle hydrodynamics (SPH) code GADGET, and the Eulerian adaptive mesh refinement (AMR) code Enzo. Both codes represent dark matter with the N-body method but use different gravity solvers and fundamentally different approaches for baryonic hydrodynamics. The SPH method in GADGET uses a recently developed ``entropy conserving'' formulation of SPH, while for the mesh-based Enzo two different formulations of Eulerian hydrodynamics are employed: the piecewise parabolic method (PPM) extended with a dual energy formulation for cosmology, and the artificial viscosity-based scheme used in the magnetohydrodynamics code ZEUS. In this paper we focus on a comparison of cosmological simulations that follow either only dark matter, or also a nonradiative (``adiabatic'') hydrodynamic gaseous component. We perform multiple simulations using both codes with varying spatial and mass resolution with identical initial conditions. The dark matter-only runs agree generally quite well provided Enzo is run with a comparatively fine root grid and a low overdensity threshold for mesh refinement, otherwise the abundance of low-mass halos is suppressed. This can be readily understood as a consequence of the hierarchical particle-mesh algorithm used by Enzo to compute gravitational forces, which tends to deliver lower force resolution than the tree-algorithm of GADGET at early times before any adaptive mesh refinement takes place. At comparable force resolution we find that the latter offers substantially better performance and lower memory consumption than the present gravity solver in Enzo. In simulations that include adiabatic gasdynamics we find general agreement in the distribution functions of temperature, entropy, and density for gas of moderate to high overdensity, as found inside dark matter halos. However, there are also some significant differences in
HOW WELL DO COSMOLOGICAL SIMULATIONS REPRODUCE INDIVIDUAL HALO PROPERTIES?
Trenti, Michele; Smith, Britton D.; Hallman, Eric J.; Skillman, Samuel W.; Shull, J. Michael
2010-03-10
Cosmological simulations of galaxy formation often rely on prescriptions for star formation and feedback that depend on halo properties such as halo mass, central overdensity, 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 {approx} 20-30 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{sub p} = 64{sup 3} to N{sub p} = 1024{sup 3} total particles, keeping the same large-scale structure in the simulation box. We consider boxes of small (l{sub box} = 8 Mpc h {sup -1}), medium (l{sub box} = 64 Mpc h {sup -1}), and large (l{sub box} = 512 Mpc h {sup -1}) size to probe different halo masses and formation redshifts. We cross-identify dark matter halos in boxes at different resolutions and measure the scatter in their properties. The uncertainty in the mass of single halos depends on the number of particles (scaling approximately as N {sup -1/3}), but the rarer the density peak, the more robust its identification. The virial radius of halos is very stable and can be measured without bias for halos with N {approx}> 30. In contrast, the average density within a sphere containing 25% of the total halo mass is severely underestimated (by more than a factor 2) and the halo spin is moderately overestimated for N {approx}< 100. If sub-grid physics is implemented upon a cosmological simulation, we recommend that rare halos ({approx}3sigma peaks) be resolved with N {approx}> 100 particles and common halos ({approx}1sigma peaks) with N {approx}> 400 particles to avoid excessive numerical noise and possible systematic biases in the
COSMOLOGICAL SIMULATIONS OF GALAXY FORMATION WITH COSMIC RAYS
Salem, Munier; Bryan, Greg L.; Hummels, Cameron
2014-12-20
We investigate the dynamical impact of cosmic rays (CR) in cosmological simulations of galaxy formation using adaptive-mesh refinement simulations of a 10{sup 12} M {sub ☉} 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 CRs 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 interstellar medium.
Simulating nonlinear cosmological structure formation with massive neutrinos
NASA Astrophysics Data System (ADS)
Banerjee, Arka; Dalal, Neal
2016-11-01
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.
High-redshift clumpy discs and bulges in cosmological simulations
NASA Astrophysics Data System (ADS)
Ceverino, Daniel; Dekel, Avishai; Bournaud, Frederic
2010-06-01
We analyse the first cosmological simulations that recover the fragmentation of high-redshift galactic discs driven by cold streams. The fragmentation is recovered owing to an AMR resolution better than 70pc with cooling below 104K. We study three typical star-forming galaxies in haloes of ~5 × 1011Msolar at z ~= 2.3 when they were not undergoing a major merger. The steady gas supply by cold streams leads to gravitationally unstable, turbulent discs, which fragment into giant clumps and transient features on a dynamical time-scale. The disc clumps are not associated with dark-matter haloes. The clumpy discs are self-regulated by gravity in a marginally unstable state. Clump migration and angular-momentum transfer on an orbital time-scale help the growth of a central bulge with a mass comparable to the disc. The continuous gas input keeps the system of clumpy disc and bulge in a near steady state for several Gyr. The average star formation rate, much of which occurs in the clumps, follows the gas accretion rate of ~45Msolaryr-1. The simulated galaxies resemble in many ways the observed star-forming galaxies at high redshift. Their properties are consistent with the simple theoretical framework presented in Dekel, Sari & Ceverino. In particular, a two-component analysis reveals that the simulated discs are indeed marginally unstable, and the time evolution confirms the robustness of the clumpy configuration in a cosmological steady state. By z ~ 1, the simulated systems are stabilized by a dominant stellar spheroid, demonstrating the process of `morphological quenching' of star formation. We demonstrate that the disc fragmentation is not a numerical artefact once the Jeans length is kept larger than nearly seven resolution elements, i.e. beyond the standard Truelove criterion.
Population statistics of galaxy cluster halos in cosmological simulations
NASA Astrophysics Data System (ADS)
Stanek, Rebecca M.
The number of massive structures in the universe is determined by a small set of cosmological parameters characterizing its content, geometry, and expansion rate. Survey counts of massive clusters of galaxies can constrain these parameters, but require a statistical model relating total cluster mass to relevant, observable signals, such X-ray luminosity, X-ray temperature, and galaxy count. I present empirical and computational efforts to improve estimates of this statistical relationship, with an emphasis on measures of the hot intracluster gas. First, I present my work calibrating the relationship between galaxy cluster mass and X-ray luminosity. This work compared observed cluster counts from the REFLEX survey to expectations for LCDM cosmologies derived from a halo mass function. In this comparison, I obtained the first measurement of the scatter and discuss possible systematic biases in parameter estimates due to the scatter. I extended my work on mass selection functions to a full suite of X-ray and Sunyaev-Zeldovich (SZ) signals in the Millennium Gas Simulations (MGS). The MGS are hydrodynamic simulations in a 500 h -1 Mpc box, with two treatments of the gas physics: a model with only shock-heating and gravity ( GO ) and a simple preheating model ( PH ). From the MGS, I present scaling relations among multiple signals, including a covariance matrix, for about ~4000 massive halos. Finally, I investigate the total halo mass function with two pairs of simulations: the MGS and a pair of high-resolution simulations which include a GO model and a refined treatment including cooling, star formation, and supernova feedback (CSF ). The CSF and PH models have baryon fractions which differ from the GO models, and therefore systematic shifts in halo mass at fixed number density. These mass shifts result in a ~30% deviation in number density at fixed mass from a halo mass function calibrated with only dark matter, significantly higher than the 5% statistical uncertainty
Effect of the cosmological constant on the bending of light and the cosmological lens equation
NASA Astrophysics Data System (ADS)
Arakida, Hideyoshi; Kasai, Masumi
2012-01-01
We revisit the effect of cosmological constant Λ on the light deflection and its role in the cosmological lens equation. First, we reexamine the motion of photon in the Schwarzschild spacetime, and explicitly describe the trajectory of photon and deflection angle α up to the second order in G. Then the discussion is extended to the contribution of the cosmological constant Λ in the Schwarzschild-de Sitter or Kottler spacetime. Contrary to the previous arguments, we emphasize the following points: (a) the cosmological constant Λ does appear in the orbital equation of light, (b) nevertheless the bending angle of light α does not change its form even if Λ≠0 since the contribution of Λ is thoroughly absorbed into the definition of the impact parameter, and (c) the effect of Λ is completely involved in the angular diameter distance DA.
Cosmological particle-in-cell simulations with ultralight axion dark matter
NASA Astrophysics Data System (ADS)
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.
Improving initial conditions for cosmological N-body simulations
NASA Astrophysics Data System (ADS)
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.
Generalized effective description of loop quantum cosmology
NASA Astrophysics Data System (ADS)
Ashtekar, Abhay; Gupt, Brajesh
2015-10-01
The effective description of loop quantum cosmology (LQC) has proved to be a convenient platform to study phenomenological implications of the quantum bounce that resolves the classical big bang singularity. Originally, this description was derived using Gaussian quantum states with small dispersions. In this paper we present a generalization to incorporate states with large dispersions. Specifically, we derive the generalized effective Friedmann and Raychaudhuri equations and propose a generalized effective Hamiltonian which are being used in an ongoing study of the phenomenological consequences of a broad class of quantum geometries. We also discuss an interesting interplay between the physics of states with larger dispersions in standard LQC, and of sharply peaked states in (hypothetical) LQC theories with larger area gap.
Fast Generation of Ensembles of Cosmological N-Body Simulations via Mode-Resampling
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.
Machine learning and cosmological simulations - II. Hydrodynamical simulations
NASA Astrophysics Data System (ADS)
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.
Creating mock catalogues of stellar haloes from cosmological simulations
NASA Astrophysics Data System (ADS)
Lowing, Ben; Wang, Wenting; Cooper, Andrew; Kennedy, Rachel; Helly, John; Cole, Shaun; Frenk, Carlos
2015-01-01
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 Λ cold dark matter 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 flexibility of the mock catalogues. We show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. We also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stellar populations, allow streams to be easily identified.
NASA Technical Reports Server (NTRS)
Sehgal, Neelima; Trac, Hy; Acquaviva, Viviana; Ade, Peter A. R.; Aguirre, Paula; Amiri, Mandana; Appel, John W.; Barrientos, L. Felipe; Battistelli, Elia S.; Bond, J. Richard; Brown, Ben; Burger, Bryce; Chervenak, Jay; Das, Sudeep; Devlin, Mark J.; Dicker, Simon R.; Doriese, W. Bertrand; Dunkley, Joanna; Duenner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P.; Fowler, Joseph W.; Hajian, Amir; Halpern, Mark; Wollack, Ed
2010-01-01
We present constraints on cosmological parameters based on a sample of Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 optically-confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 square degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive systems to reduce the degeneracy between unknown cluster astrophysics and cosmology derived from SZ surveys. We describe the scaling relation between cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives (sigma)8 = 0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological model with WMAP 7-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7-year constraints alone. Fixing the scaling relation between cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by X-ray observations, we find (sigma)8 + 0.821 +/- 0.044 and w = -1.05 +/- 0.20. These results are consistent with constraints from WMAP 7 plus baryon acoustic oscillations plus type Ia supernova which give (sigma)8 = 0.802 +/- 0.038 and w = -0.98 +/- 0.053. A stacking analysis of the clusters in this sample compared to clusters simulated assuming the fiducial model also shows good agreement. These results suggest that, given the sample of clusters used here, both the astrophysics of massive clusters and the cosmological parameters derived from them are broadly consistent with current models.
Sehgal, Neelima; Trac, Hy; Acquaviva, Viviana; Ade, Peter A.R.; Aguirre, Paula; Amiri, Mandana; Appel, John W.; Barrientos, L.Felipe; Battistelli, Elia S.; Bond, J.Richard; Brown, Ben; Burger, Bryce; Chervenak, Jay; Das, Sudeep; Devlin, Mark J.; Dicker, Simon R.; Doriese, W.Bertrand; Dunkley, Joanna; Dunner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P.
2011-08-18
We present constraints on cosmological parameters based on a sample of Sunyaev-Zeldovich-selected galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 optically-confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 square degrees of sky surveyed during 2008 at 148GHz. We focus on the most massive systems to reduce the degeneracy between unknown cluster astrophysics and cosmology derived from SZ surveys. We describe the scaling relation between cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives {sigma}{sub 8} = 0.851 {+-} 0.115 and w = -1.14 {+-} 0.35 for a spatially-flat wCDM cosmological model with WMAP 7-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7-year constraints alone. Fixing the scaling relation between cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by X-ray observations, we find {sigma}{sub 8} = 0.821 {+-} 0.044 and w = -1.05 {+-} 0.20. These results are consistent with constraints from WMAP 7 plus baryon acoustic oscillations plus type Ia supernoava which give {sigma}{sub 8} = 0.802 {+-} 0.038 and w = -0.98 {+-} 0.053. A stacking analysis of the clusters in this sample compared to clusters simulated assuming the fiducial model also shows good agreement. These results suggest that, given the sample of clusters used here, both the astrophysics of massive clusters and the cosmological parameters derived from them are broadly consistent with current models.
Fueling galaxy growth through gas accretion in cosmological simulations
NASA Astrophysics Data System (ADS)
Nelson, Dylan Rubaloff
Despite significant advances in the numerical modeling of galaxy formation and evolution, it is clear that a satisfactory theoretical picture of how galaxies acquire their baryons across cosmic time remains elusive. In this thesis we present a computational study which seeks to address the question of how galaxies get their gas. We make use of new, more robust simulation techniques and describe the first investigations of cosmological gas accretion using a moving-mesh approach for solving the equations of continuum hydrodynamics. We focus first on a re-examination of past theoretical conclusions as to the relative importance of different accretion modes for galaxy growth. We study the rates and nature of gas accretion at z=2, comparing our new simulations run with the Arepo code to otherwise identical realizations run with the smoothed particle hydrodynamics code Gadget. We find significant physical differences in the thermodynamic history of accreted gas, explained in terms of numerical inaccuracies in SPH. In contrast to previous results, we conclude that hot mode accretion generally dominates galaxy growth, while cold gas filaments experience increased heating and disruption. Next, we consider the impact of feedback on our results, including models for galactic-scale outflows driven by stars as well as the energy released from supermassive black holes. We find that feedback strongly suppresses the inflow of "smooth" mode gas at all redshifts, regardless of its temperature history. Although the geometry of accretion at the virial radius is largely unmodified, strong galactic-fountain recycling motions dominate the inner halo. We measure a shift in the characteristic timescale of accretion, and discuss implications for semi-analytical models of hot halo gas cooling. To overcome the resolution limitations of cosmological volumes, we simulate a suite of eight individual 1012 solar mass halos down to z=2. We quantify the thermal and dynamical structure of the gas in
The large-scale properties of simulated cosmological magnetic fields
NASA Astrophysics Data System (ADS)
Marinacci, Federico; Vogelsberger, Mark; Mocz, Philip; Pakmor, Rüdiger
2015-11-01
We perform uniformly sampled large-scale cosmological simulations including magnetic fields with the moving mesh code AREPO. We run two sets of MHD simulations: one including adiabatic gas physics only; the other featuring the fiducial feedback model of the Illustris simulation. In the adiabatic case, the magnetic field amplification follows the B ∝ ρ2/3 scaling derived from `flux-freezing' arguments, with the seed field strength providing an overall normalization factor. At high baryon overdensities the amplification is enhanced by shear flows and turbulence. Feedback physics and the inclusion of radiative cooling change this picture dramatically. In haloes, gas collapses to much larger densities and the magnetic field is amplified strongly and to the same maximum intensity irrespective of the initial seed field of which any memory is lost. At lower densities a dependence on the seed field strength and orientation, which in principle can be used to constrain models of cosmic magnetogenesis, is still present. Inside the most massive haloes magnetic fields reach values of ˜ 10-100 μG, in agreement with galaxy cluster observations. The topology of the field is tangled and gives rise to rotation measure signals in reasonable agreement with the observations. However, the rotation measure signal declines too rapidly towards larger radii as compared to observational data.
FLY: MPI-2 High Resolution code for LSS Cosmological Simulations
NASA Astrophysics Data System (ADS)
Becciani, U.; Antonuccio, V.; Comparato, M.
2010-11-01
Cosmological simulations of structures and galaxies formations have played a fundamental role in the study of the origin, formation and evolution of the Universe. These studies improved enormously with the use of supercomputers and parallel systems and, recently, grid based systems and Linux clusters. Now we present the new version of the tree N-body parallel code FLY that runs on a PC Linux Cluster using the one side communication paradigm MPI-2 and we show the performances obtained. FLY is included in the Computer Physics Communication Program Library. This new version was developed using the Linux Cluster of CINECA, an IBM Cluster with 1024 Intel Xeon Pentium IV 3.0 Ghz. The results show that it is possible to run a 64 Million particle simulation in less than 15 minutes for each timestep, and the code scalability with the number of processors is achieved. This lead us to propose FLY as a code to run very large N-Body simulations with more than 10(9) particles with the higher resolution of a pure tree code.
FLY: MPI-2 high resolution code for LSS cosmological simulations
NASA Astrophysics Data System (ADS)
Becciani, U.; Antonuccio-Delogu, V.; Comparato, M.
2007-02-01
Cosmological simulations of structures and galaxies formations have played a fundamental role in the study of the origin, formation and evolution of the Universe. These studies improved enormously with the use of supercomputers and parallel systems and, recently, grid based systems and Linux clusters. Now we present the new version of the tree N-body parallel code FLY that runs on a PC Linux Cluster using the one side communication paradigm MPI-2 and we show the performances obtained. FLY is included in the Computer Physics Communication Program Library. This new version was developed using the Linux Cluster of CINECA, an IBM Cluster with 1024 Intel Xeon Pentium IV 3.0 GHz. The results show that it is possible to run a 64 million particle simulation in less than 15 minutes for each time-step, and the code scalability with the number of processors is achieved. This leads us to propose FLY as a code to run very large N-body simulations with more than 109 particles with the higher resolution of a pure tree code. The FLY new version is available at the CPC Program Library, http://cpc.cs.qub.ac.uk/summaries/ADSC_v2_0.html [U. Becciani, M. Comparato, V. Antonuccio-Delogu, Comput Phys. Comm. 174 (2006) 605].
Quantum effects in homogeneous multidimensional cosmologies
Szydlowski, M.; Szczesny, J.
1988-12-15
In the present paper we determine quantum distribution functions for a wide class of multidimensional cosmological models. The exact formulas for quantum distribution functions are given and their universal character at high and low temperatures shown. The obtained formulas provide us with the possibility to investigate the metric back reaction and to discuss the dimensional reduction problem. The assumption of the low-temperature approximation gives us the possibility to discuss the dynamics by using the methods of dynamical systems. Stable solutions, within the class FRW x S/sup 3/ x S/sup 3/ models, where FRW denotes Friedmann, Robertson and Walker, are discussed, and it is shown that only a zero-measure set of trajectories in the phase space leads to a solution with a static microspace. This analysis shows that, insofar as quantum effects lead to solutions with a static microspace, these solutions are unstable.
The BAHAMAS project: calibrated hydrodynamical simulations for large-scale structure cosmology
NASA Astrophysics Data System (ADS)
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.
The effective field theory of cosmological large scale structures
Carrasco, John Joseph M.; Hertzberg, Mark P.; Senatore, Leonardo
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}.
Formation of compact clusters from high resolution hybrid cosmological simulations
Richardson, Mark L. A.; Scannapieco, Evan; Gray, William J.
2013-11-20
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 and 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 reaction, and then cools to form dense, chemically homogenous clumps of star-forming gas. The formation of these high-redshift clusters may be observable with the next generation of telescopes and the largest of them should survive to the present-day, having properties similar to halo globular clusters.
Self-consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
NASA Astrophysics Data System (ADS)
Oñorbe, Jose; Hennawi, Joseph F.; Lukić, Zarija
2017-03-01
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 nonexistent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and we 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 reionization and its concomitant heat injection on the thermal state of the IGM. We present a comprehensive study of the pressure smoothing scale of IGM gas, illustrating its dependence on the details of both hydrogen and helium reionization, and argue that it plays a fundamental role in interpreting Lyα forest statistics and the thermal evolution of the IGM. The premature IGM heating we have uncovered implies that previous work has likely dramatically overestimated the impact of photoionization feedback on galaxy formation, which sets the minimum halo mass able to form stars at high redshifts. We make our new UVB photoionization and photoheating rates publicly available for use in future simulations.
Self-consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
Oñorbe, Jose; Hennawi, Joseph F.; Lukić, Zarija
2017-03-08
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. In this paper, we show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier (more » $$z\\sim 15$$) than they should. This problem arises because at $$z\\gt 6$$, where observational constraints are nonexistent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and we 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 reionization and its concomitant heat injection on the thermal state of the IGM. We present a comprehensive study of the pressure smoothing scale of IGM gas, illustrating its dependence on the details of both hydrogen and helium reionization, and argue that it plays a fundamental role in interpreting Lyα forest statistics and the thermal evolution of the IGM. The premature IGM heating we have uncovered implies that previous work has likely dramatically overestimated the impact of photoionization feedback on galaxy formation, which sets the minimum halo mass able to form stars at high redshifts. Finally, we make our new UVB photoionization and photoheating rates publicly available for use in future simulations.« less
Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
NASA Astrophysics Data System (ADS)
Pfrommer, C.; Springel, V.; Enßlin, T. A.; Jubelgas, M.
2006-03-01
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks play a decisive role not only for the thermalization of gas in virializing 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 analytic 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 Lambda cold dark matter (ΛCDM) model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external shocks with much higher Mach numbers up to , but they play only a minor role in the energy balance of thermalization. This is because of the higher pre-shock gas densities within non-linear structures, and the significant increase of the mean shock speed as the characteristic halo mass grows with cosmic time. We show that after the epoch of cosmic reionization the Mach number distribution is significantly modified by an efficient suppression of strong external shock waves due to the associated increase of the sound speed of the diffuse gas. Invoking a model for CR acceleration in shock waves, we find that the average strength of shock waves responsible for CR energy injection is higher than that for shocks that dominate the thermalization of the gas. This implies that the dynamical importance of shock-injected CRs is comparatively large in the low-density, peripheral halo infalling regions, but is less important for the weaker flow shocks
Multi-Scale Initial Conditions For Cosmological Simulations
Hahn, Oliver; 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.
Multi-scale initial conditions for cosmological simulations
NASA Astrophysics Data System (ADS)
Hahn, Oliver; Abel, Tom
2011-08-01
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 10-4 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.
A method of generating initial conditions for cosmological N-body simulations
Joyce, M.; Levesque, D.; Marcos, B.
2005-11-15
We investigate the possibility of generating initial conditions for cosmological N-body simulations by simulating a system whose correlations at thermal equilibrium approximate well those of cosmological density perturbations. The system is an appropriately modified version of the standard 'one component plasma' (OCP). We show first how a well-known semianalytic method can be used to determine the potential required to produce the desired correlations, and then verify our results for some cosmological type spectra with simulations of the full molecular dynamics. The advantage of the method, compared to the standard one, is that it gives by construction an accurate representation of both the real and reciprocal space correlation properties of the theoretical model. Furthermore the distributions are also statistically homogeneous and isotropic. We discuss briefly the modifications needed to implement the method to produce configurations appropriate for large N-body simulations in cosmology, and also the generation of initial velocities in this context.
Time evolution of galaxy scaling relations in cosmological simulations
NASA Astrophysics Data System (ADS)
Taylor, Philip; Kobayashi, Chiaki
2016-12-01
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 ˜ 2 to z ˜ 1, while the gas-phase mass-metallicity relation does change shape, having a steeper slope at higher redshifts (z ≲ 3). Furthermore, AGN feedback is required to reproduce observations of the most massive galaxies at z ≲ 1, specifically their positions on the star formation main sequence and galaxy mass-size relation.
Constraints on Dark Matter and Milky Way Satellite Galaxies from Cosmological Simulations
NASA Astrophysics Data System (ADS)
Rocha Gaso, Miguel Eduardo
Cosmological simulations describing the non-linear evolution of dark matter structures in the Universe have become an indispensable tool to study the predictions made by our standard model of cosmology, and to confront them with observations. In this thesis I present a new idea for using cosmological simulations to infer the accretion times of Milky Way satellite galaxies from their observed positions and kinematics. We find that Carina, Ursa Minor, and Sculptor were all accreted early, more than 8 Gyr ago. Five other dwarfs, including Sextans and Segue 1, are also probable early accreters, though with larger uncertainties. On the other extreme, Leo T is just falling into the Milky Way for the first time while Leo I fell ~2 Gyr ago and is now climbing out of the Milky Way's potential after its first perigalacticon. The energies of several other dwarfs, including Fornax and Hercules, point to intermediate infall times, 2--8 Gyr ago. Our analysis suggests that the Large Magellanic Cloud crossed inside the Milky Way virial radius recently, within the last ~4 billion years. Also I present new constrains on how strongly dark matter particles can interact with themselves. For this we use a set cosmological simulations that implement a new self-consistent algorithm to treat dark matter self-interactions. We find that self-interacting dark matter models with cross sections in the order sigma/m ≃ 0.5 cm2 /g ≃ 1 barn/GeV would be capable of reproducing the observed core sizes and central densities of dark matter halos in a wide range of scales, from tiny dwarf galaxies to large galaxy clusters, without violating any other observational constraints. Higher resolution simulations over a wider range of masses and properly accounting for the effects of baryonic processes that are not yet included in our simulation will be required to confirm our expectations and place better constraints. I discuss our plans for achieving this goal and show some preliminary results from a new
Barred galaxies in the EAGLE cosmological hydrodynamical simulation
NASA Astrophysics Data System (ADS)
Algorry, David G.; Navarro, Julio F.; Abadi, Mario G.; Sales, Laura V.; Bower, Richard G.; Crain, Robert A.; Dalla Vecchia, Claudio; Frenk, Carlos S.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom
2017-07-01
We examine the properties of barred disc galaxies in a ΛCDM 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 M*/M⊙ < 11. These discs show a wide range of bar strengths, from unbarred discs (≈60 per cent) to weak bars (≈20 per cent) and to strongly barred systems (≈20 per cent). Bars in these systems develop after redshift ≈1.3, on time-scales that depend sensitively on the strength of the pattern. Strong bars develop relatively quickly (in a few Gyr, or roughly ∼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 gravitationally 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 haloes they inhabit. Bar lengths compare favourably with observations, ranging from 0.2 to 0.8 times the radius containing 90 per cent of the stars. Bars slow down remarkably quickly as they grow, causing the inner regions of the surrounding dark halo to expand. At z = 0 strong bars in simulated galaxies have corotation radii roughly 10 times the bar length. Such slow bars are inconsistent with the few cases where pattern speeds have been measured or inferred observationally, a discrepancy that, if confirmed, might prove a challenge for disc galaxy formation in ΛCDM.
Bard, D.; Chang, C.; Kahn, S. M.; Gilmore, K.; Marshall, S.; Kratochvil, J. M.; Huffenberger, K. M.; May, M.; AlSayyad, Y.; Connolly, A.; Gibson, R. R.; Jones, L.; Krughoff, S.; Ahmad, Z.; Bankert, J.; Grace, E.; Hannel, M.; Lorenz, S.; Haiman, Z.; Jernigan, J. G.; and others
2013-09-01
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.
NASA Astrophysics Data System (ADS)
Gnedin, Oleg Y.; Kravtsov, Andrey V.; Klypin, Anatoly A.; Nagai, Daisuke
2004-11-01
The cooling of gas in the centers of dark matter halos is expected to lead to a more concentrated dark matter distribution. The response of dark matter to the condensation of baryons is usually calculated using the model of adiabatic contraction, which assumes spherical symmetry and circular orbits. In contrast, halos in the hierarchical structure formation scenarios grow via multiple violent mergers and accretion along filaments, and particle orbits in the halos are highly eccentric. We study the effects of the cooling of gas in the inner regions of halos using high-resolution cosmological simulations that include gas dynamics, radiative cooling, and star formation. We find that the dissipation of gas indeed increases the density of dark matter and steepens its radial profile in the inner regions of halos compared to the case without cooling. For the first time, we test the adiabatic contraction model in cosmological simulations and find that the standard model systematically overpredicts the increase of dark matter density in the inner 5% of the virial radius. We show that the model can be improved by a simple modification of the assumed invariant from M(r)r to M(r)r, where r and r are the current and orbit-averaged particle positions. This modification approximately accounts for orbital eccentricities of particles and reproduces simulation profiles to within 10%-20%. We present analytical fitting functions that accurately describe the transformation of the dark matter profile in the modified model and can be used for interpretation of observations.
Hsu, Chung-hsing; Ahrens, James P; Heitmann, Katrin
2009-01-01
We describe a visualization assisted process for the verification of cosmological simulation codes. The need for code verification stems from the requirement for very accurate predictions in order to interpret observational data confidently. We compare different simulation algorithms in order to reliably predict differences in simulation results and understand their dependence on input parameter settings.
Bispectrum Aliasing in Cosmological N-Body Simulations
NASA Astrophysics Data System (ADS)
Gómez-Giraldo, O. N.; Muñoz-Cuartas, J. C.
2017-07-01
We use numerical simulations to study the aliasing effect particularly on the bispectrum estimation. By contrasting the D20 scaling function against the classical mass assignment schemes, we got a smallest aliasing contribution obtained by the D20 function.
Validity of Hydrostatic Equilibrium in Galaxy Clusters from Cosmological Hydrodynamical Simulations
NASA Astrophysics Data System (ADS)
Suto, Daichi; Kawahara, Hajime; Kitayama, Tetsu; Sasaki, Shin; Suto, Yasushi; Cen, Renyue
2013-04-01
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 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 Jeans equations in considering the validity of HSE from the gas dynamics extracted from cosmological hydrodynamical simulations.
Mapping substructure in the HST Frontier Fields cluster lenses and in cosmological simulations
NASA Astrophysics Data System (ADS)
Natarajan, Priyamvada; Chadayammuri, Urmila; Jauzac, Mathilde; Richard, Johan; Kneib, Jean-Paul; Ebeling, Harald; Jiang, Fangzhou; van den Bosch, Frank; Limousin, Marceau; Jullo, Eric; Atek, Hakim; Pillepich, Annalisa; Popa, Cristina; Marinacci, Federico; Hernquist, Lars; Meneghetti, Massimo; Vogelsberger, Mark
2017-06-01
We map the lensing-inferred substructure in the first three clusters observed by the Hubble Space Telescope Frontier Fields (HSTFF) Initiative: Abell 2744 (z = 0.308), MACSJ 0416, (z = 0.396) and MACSJ 1149 (z = 0.543). Statistically resolving dark matter subhaloes down to ˜10^{9.5} M_{⊙}, we compare the derived subhalo mass functions (SHMFs) to theoretical predictions from analytical models and with numerical simulations in a Lambda cold dark matter (LCDM) cosmology. Mimicking our observational cluster member selection criteria in the HSTFF, we report excellent agreement in both amplitude and shape of the SHMF over four decades in subhalo mass (10^{9-13} M_{⊙}). Projection effects do not appear to introduce significant errors in the determination of SHMFs from simulations. We do not find evidence for a substructure crisis, analogous to the missing satellite problem in the Local Group, on cluster scales, but rather excellent agreement of the count-matched HSTFF SHMF down to Msubhalo/Mhalo ˜ 10-5. However, we do find discrepancies in the radial distribution of subhaloes inferred from HSTFF cluster lenses compared to determinations from simulated clusters. This suggests that although the selected simulated clusters match the HSTFF sample in mass, they do not adequately capture the dynamical properties and complex merging morphologies of these observed cluster lenses. Therefore, HSTFF clusters are likely observed in a transient evolutionary stage that is presently insufficiently sampled in cosmological simulations. The abundance and mass function of dark matter substructure in cluster lenses continues to offer an important test of the LCDM paradigm, and at present we find no tension between model predictions and observations.
Covariant effective action for loop quantum cosmology a la Palatini
Olmo, Gonzalo J.; Singh, Parampreet E-mail: psingh@perimeterinstitute.ca
2009-01-15
In loop quantum cosmology, non-perturbative quantum gravity effects lead to the resolution of the big bang singularity by a quantum bounce without introducing any new degrees of freedom. Though fundamentally discrete, the theory admits a continuum description in terms of an effective Hamiltonian. Here we provide an algorithm to obtain the corresponding effective action, establishing in this way the covariance of the theory for the first time. This result provides new insights on the continuum properties of the discrete structure of quantum geometry and opens new avenues to extract physical predictions such as those related to gauge invariant cosmological perturbations.
The effects of varying cosmological parameters on halo substructure
Dooley, Gregory A.; Griffen, Brendan F.; Ji, Alexander P.; Vogelsberger, Mark; Frebel, Anna; Zukin, Phillip; Hernquist, Lars E.
2014-05-01
We investigate how different cosmological parameters, such as those delivered by the WMAP and Planck missions, affect the nature and evolution of the dark matter halo substructure. We use a series of flat Λ cold dark matter cosmological N-body simulations of structure formation, each with a different power spectrum but with the same initial white noise field. Our fiducial simulation is based on parameters from the WMAP seventh year cosmology. We then systematically vary the spectral index, n{sub s} ; matter density, Ω {sub M}; and normalization of the power spectrum, σ{sub 8}, for seven unique simulations. Across these, we study variations in the subhalo mass function, mass fraction, maximum circular velocity function, spatial distribution, concentration, formation times, accretion times, and peak mass. We eliminate dependence of subhalo properties on host halo mass and average the values over many hosts to reduce variance. While the 'same' subhalos from identical initial overdensity peaks in higher σ{sub 8}, n{sub s} , and Ω {sub m} simulations accrete earlier and end up less massive and closer to the halo center at z = 0, the process of continuous subhalo accretion and destruction leads to a steady state distribution of these properties across all subhalos in a given host. This steady state mechanism eliminates cosmological dependence on all of the properties listed above except for subhalo concentration and V {sub max}, which remain greater for higher σ{sub 8}, n{sub s} , and Ω {sub m} simulations, and subhalo formation time, which remains earlier. We also find that the numerical technique for computing the scale radius and the halo finder that were used can significantly affect the concentration-mass relationship as computed for a simulation.
The Effects of Varying Cosmological Parameters on Halo Substructure
NASA Astrophysics Data System (ADS)
Dooley, Gregory A.; Griffen, Brendan F.; Zukin, Phillip; Ji, Alexander P.; Vogelsberger, Mark; Hernquist, Lars E.; Frebel, Anna
2014-05-01
We investigate how different cosmological parameters, such as those delivered by the WMAP and Planck missions, affect the nature and evolution of the dark matter halo substructure. We use a series of flat Λ cold dark matter cosmological N-body simulations of structure formation, each with a different power spectrum but with the same initial white noise field. Our fiducial simulation is based on parameters from the WMAP seventh year cosmology. We then systematically vary the spectral index, ns ; matter density, Ω M ; and normalization of the power spectrum, σ8, for seven unique simulations. Across these, we study variations in the subhalo mass function, mass fraction, maximum circular velocity function, spatial distribution, concentration, formation times, accretion times, and peak mass. We eliminate dependence of subhalo properties on host halo mass and average the values over many hosts to reduce variance. While the "same" subhalos from identical initial overdensity peaks in higher σ8, ns , and Ω m simulations accrete earlier and end up less massive and closer to the halo center at z = 0, the process of continuous subhalo accretion and destruction leads to a steady state distribution of these properties across all subhalos in a given host. This steady state mechanism eliminates cosmological dependence on all of the properties listed above except for subhalo concentration and V max, which remain greater for higher σ8, ns , and Ω m simulations, and subhalo formation time, which remains earlier. We also find that the numerical technique for computing the scale radius and the halo finder that were used can significantly affect the concentration-mass relationship as computed for a simulation.
NASA Astrophysics Data System (ADS)
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.
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 (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 4×10 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 accuracymore » and scientific throughput, while meeting or exceeding the computational efficiency of the latest generation of hybrid TreePM N-body methods.« less
Effective cosmological constant within the expanding axion universe
NASA Astrophysics Data System (ADS)
Pierpoint, M. P.; Kusmartsev, F. V.
2014-09-01
We show that the value of an effective cosmological constant, Λeff, is influenced by the dimensionality of the space. Results were obtained in the framework of the axion model describing expansion of the inhomogeneous universe. Λeff determines the tension of the space (i.e. elasticity), and is relaxed when extra dimensions are accessible. We demonstrate that the effective value of the cosmological constant may be tuned to be consistent with experimental observation. Inhomogeneities considered are representative of temperature fluctuations observed within the cosmic microwave background radiation.
Effects of cosmological constant on clustering of Galaxies
NASA Astrophysics Data System (ADS)
Hameeda, Mir; Upadhyay, Sudhaker; Faizal, Mir; Ali, Ahmed Farag
2016-12-01
In this paper, we analyse the effect of the expansion of the universe on the clustering of galaxies. We evaluate the configurational integral for interacting system of galaxies in an expanding universe by including effects produced by the cosmological constant. The gravitational partition function is obtained using this configuration integral. Thermodynamic quantities, specifically, Helmholtz free energy, entropy, internal energy, pressure and chemical potential are also derived for this system. It is observed that they depend on the modified clustering parameter for this system of galaxies. It is also demonstrated that these thermodynamical quantities get corrected because of the cosmological constant.
Is ΛCDM an effective CCDM cosmology?
Lima, J.A.S.; Santos, R.C.; Cunha, J.V. E-mail: cliviars@gmail.com
2016-03-01
We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating ΛCDM cosmology with just one dynamical free parameter. This kind of scenario includes the creation cold dark matter (CCDM) model [1] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to ΛCDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because ΛCDM may be only an effective cosmology.
On the Convergence in Effective Loop Quantum Cosmology
Corichi, Alejandro; Vukasinac, Tatjana; Zapata, Jose Antonio
2010-07-12
In Loop Quantum Cosmology (LQC) there is a discreteness parameter {lambda}, that has been heuristically associated to a fundamental granularity of quantum geometry. It is also possible to consider {lambda} as a regulator in the same spirit as that used in lattice field theory, where it specifies a regular lattice in the real line. A particular quantization of the k = 0 FLRW loop cosmological model yields a completely solvable model, known as solvable loop quantum cosmology(sLQC). In this contribution, we consider effective classical theories motivated by sLQC and study their {lambda}-dependence, with a special interest on the limit {lambda}{yields}0 and the role of the evolution parameter in the convergence of such limit.
Palatini approach to bouncing cosmologies and DSR-like effects
NASA Astrophysics Data System (ADS)
Olmo, Gonzalo J.
2012-05-01
It is shown that a quadratic gravitational Lagrangian in the Palatini formulation is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, in this theory field excitations propagating with different energy-densities perceive different background metrics, a fundamental characteristic of the DSR and Rainbow Gravity approaches. This theory, however, avoids the so-called soccer ball problem. Also, the resulting isotropic and anisotropic cosmologies are free from the big bang singularity. This singularity avoidance occurs non-perturbatively and shares some similitudes with the effective dynamics of loop quantum cosmology.
NASA Astrophysics Data System (ADS)
Corlies, Lauren N.
The halos of galaxies - consisting of gas, stars, and satellite galaxies - are formed and shaped by the most fundamental processes: hierarchical merging and the flow of gas into and out of galaxies. While these processes are hard to disentangle, metals are tied to the gas that fuels star formation and entrained in the wind that the deaths of these stars generate. As such, they can act as important indicators of the star formation, the chemical enrichment, and the outflow histories of galaxies. Thus, this thesis aims to take advantage of such metal signatures in the stars and gas to place observational constraints on current theories of galaxy evolution as implemented in cosmological simulations. The first two chapters consider the metallicities of stars in the stellar halo of the Milky Way and its surviving satellite dwarf galaxies. Chapter 2 pairs an N-body simulation with a semi-analytic model for supernova-driven winds to examine the early environment of a Milky Way-like galaxy. At z = 10, progenitors of surviving z = 0 satellite galaxies are found to sit preferentially on the outskirts of progenitor halos of the eventual main halo. The consequence of these positions is that main halo progenitors are found to more effectively cross-pollute each other than satellite progenitors. Thus, inhomogeneous cross-pollution as a result of different high-z spatial locations of different progenitors can help to explain observed differences in abundance patterns measured today. Chapter 3 expands this work into the analysis of a cosmological, hydrodynamical simulation of dwarf galaxies in the early universe. We find that simple assumptions for modeling the extent of supernova-driven winds used in Chapter 2 agree well with the simulation whereas the presence of inhomogeneous mixing in the simulation has a large effect on the stellar metallicities. Furthermore, the star-forming halos show both bursty and continuous SFHs, two scenarios proposed by stellar metallicity data
Forecasts for the detection of the magnetised cosmic web from cosmological simulations
NASA Astrophysics Data System (ADS)
Vazza, F.; Ferrari, C.; Brüggen, M.; Bonafede, A.; Gheller, C.; Wang, P.
2015-08-01
The cosmic web contains a large part of the total gas mass in the Universe, but it is difficult to detect at most wavelengths. Synchrotron emission from shock-accelerated electrons may offer the chance of imaging the cosmic web at radio wavelengths. In this work we use 3D cosmological ENZO-magnetohydrodynamic simulations (combined with a post-processing renormalisation of the magnetic field to bracket for missing physical ingredients and resolution effects) to produce models of the radio emission from the cosmic web. In post-processing we study the capabilities of 13 large radio surveys to detect this emission. We find that surveys by LOFAR, SKA1-LOW, and MWA have a chance of detecting the cosmic web, provided that the magnetisation level of the tenuous medium in filaments is of the order of ~1% of the thermal gas energy. Appendix A is available in electronic form at http://www.aanda.org
Côté, Benoit; Martel, Hugo; Drissen, Laurent
2013-11-10
We present a one-zone galactic chemical enrichment model that takes into account the contribution of stellar winds from massive stars under the effect of rotation, Type II supernovae, hypernovae, stellar winds from low- and intermediate-mass stars, and Type Ia supernovae. This enrichment model will be implemented in a galactic model designed to be used as a subgrid treatment for galaxy evolution and outflow generation in large-scale cosmological simulations, in order to study the evolution of the intergalactic medium. We test our enrichment prescription by comparing its predictions with the metallicity distribution function and the abundance patterns of 14 chemical elements observed in the Milky Way stars. To do so, we combine the effect of many stellar populations created from the star formation history of the Galaxy in the solar neighborhood. For each stellar population, we keep track of its specific mass, initial metallicity, and age. We follow the time evolution of every population in order to respect the time delay between the various stellar phases. Our model is able to reproduce the observed abundances of C, O, Na, Mg, Al, S, and Ca. For Si, Cr, Mn, Ni, Cu, and Zn, the fits are still reasonable, but improvements are needed. We marginally reproduce the nitrogen abundance in very low metallicity stars. Overall, our results are consistent with the predicted abundance ratios seen in previous studies of the enrichment history of the Milky Way. We have demonstrated that our semi-analytic one-zone model, which cannot deal with spatial information such as the metallicity gradient, can nevertheless successfully reproduce the global Galactic enrichment evolution obtained by more complex models, at a fraction of the computational cost. This model is therefore suitable for a subgrid treatment of chemical enrichment in large-scale cosmological simulations.
NASA Astrophysics Data System (ADS)
Côté, Benoit; Martel, Hugo; Drissen, Laurent
2013-11-01
We present a one-zone galactic chemical enrichment model that takes into account the contribution of stellar winds from massive stars under the effect of rotation, Type II supernovae, hypernovae, stellar winds from low- and intermediate-mass stars, and Type Ia supernovae. This enrichment model will be implemented in a galactic model designed to be used as a subgrid treatment for galaxy evolution and outflow generation in large-scale cosmological simulations, in order to study the evolution of the intergalactic medium. We test our enrichment prescription by comparing its predictions with the metallicity distribution function and the abundance patterns of 14 chemical elements observed in the Milky Way stars. To do so, we combine the effect of many stellar populations created from the star formation history of the Galaxy in the solar neighborhood. For each stellar population, we keep track of its specific mass, initial metallicity, and age. We follow the time evolution of every population in order to respect the time delay between the various stellar phases. Our model is able to reproduce the observed abundances of C, O, Na, Mg, Al, S, and Ca. For Si, Cr, Mn, Ni, Cu, and Zn, the fits are still reasonable, but improvements are needed. We marginally reproduce the nitrogen abundance in very low metallicity stars. Overall, our results are consistent with the predicted abundance ratios seen in previous studies of the enrichment history of the Milky Way. We have demonstrated that our semi-analytic one-zone model, which cannot deal with spatial information such as the metallicity gradient, can nevertheless successfully reproduce the global Galactic enrichment evolution obtained by more complex models, at a fraction of the computational cost. This model is therefore suitable for a subgrid treatment of chemical enrichment in large-scale cosmological simulations.
Cosmology with wide-field SZ cluster surveys: selection and systematic effects
NASA Astrophysics Data System (ADS)
Juin, J. B.; Yvon, D.; Réfrégier, A.; Yèche, C.
2007-04-01
The cosmological potential of large-scale structure observations for cosmology have been extensively discussed in the litterature. In particular, it has recently been shown how Sunyaev-Zel'dovich (SZ) cluster surveys can be used to constrain dark energy parameters. In this paper, we study whether selection and systematics effects will limit future wide-field SZ surveys from achieving their cosmological potential. For this purpose, we use a sky simulation and an SZ-cluster detection software presented in Pires et al. (2006, A&A, 455, 741), using the future Olimpo survey as a concrete example. We show that the SZ-cluster selection function and contamination of SZ-cluster catalogues are more complex than is usually assumed. In particular, the simulated field-to-field detected cluster counts variance can be a factor 3 larger than the expected Poisson fluctuations. We also study the impact of missing redshift information and of the uncertainty of the scaling relations for low mass clusters. We quantify, through hypothesis tests, how near-future SZ experiments can be used to discriminate between different structure formation models. Using a maximum likelihood approach, we then study the impact of these systematics on the joint measurement of cosmological models and of cluster scaling relations.
Nonsingular bouncing cosmology: Consistency of the effective description
NASA Astrophysics Data System (ADS)
Koehn, Michael; Lehners, Jean-Luc; Ovrut, Burt
2016-05-01
We explicitly confirm that spatially flat nonsingular bouncing cosmologies make sense as effective theories. The presence of a nonsingular bounce in a spatially flat universe implies a temporary violation of the null energy condition, which can be achieved through a phase of ghost condensation. We calculate the scale of strong coupling and demonstrate that the ghost-condensate bounce remains trustworthy throughout, and that all perturbation modes within the regime of validity of the effective description remain under control. For this purpose we require the perturbed action up to third order in perturbations, which we calculate in both flat and co-moving gauge—since these two gauges allow us to highlight different physical aspects. Our conclusion is that there exist healthy descriptions of nonsingular bouncing cosmologies providing a viable resolution of the big-bang singularities in cosmological models. Our results also suggest a variant of ekpyrotic cosmology, in which entropy perturbations are generated during the contracting phase, but are only converted into curvature perturbations after the bounce.
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Pawlik, Andreas H.; Schaye, Joop; Dalla Vecchia, Claudio
2015-08-01
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 h-1 comovingMpc using 2 × 5123 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 simulated galaxies and is required to yield SFRs in agreement with observations. Photoheating helps to suppress star formation in low-mass galaxies, but its impact on the cosmic SFR is small. Because the effect of photoheating is masked by the strong SN feedback, it does not imprint a signature on the UV galaxy luminosity function, although we note that our resolution is insufficient to model star-forming minihaloes cooling through molecular hydrogen transitions. Photoheating does provide a strong positive feedback on reionization because it smooths density fluctuations in the IGM, which lowers the IGM recombination rate substantially. Our simulations demonstrate a tight non-linear coupling of galaxy formation and reionization, motivating the need for the accurate and simultaneous inclusion of photoheating and SN feedback in models of the early Universe.
Cosmological Simulations of Galaxy Formation Including Hydrodynamics (hyper-abridged)
NASA Astrophysics Data System (ADS)
Summers, F. J.
1994-06-01
The formation of galaxies in hierarchical cosmogonies is studied using high resolution N-body plus SPH hydrodynamics simulations. The collapse of structure is followed self-consistently from Mpc scale filamentary structures to kpc scale galactic objects. The characteristics and formation processes of the galaxy like objects are studied in detail, along with the aggregation into a poor cluster. Related studies consider the effects of modelling star formation, the reliability of tracing galaxies in simulations, and tests of SPH methods. This submission serves first to notify that the full text and figures of my thesis are available in compressed PostScript form via anonymous ftp from astro.princeton.edu in the directory /summers/thesis (122 files, 19 MB compressed, 65 MB uncompressed). See the README file first. Second, this submission contains the title page, abstract, table of contents, introductory chapter, summary chapter, and references for my thesis. Those who are curious about the work may scan these pages to identify which chapters may be interesting to get via ftp.
Zooming in on major mergers: dense, starbursting gas in cosmological simulations
NASA Astrophysics Data System (ADS)
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.
The Biermann Battery In Cosmological Mhd Simulations Of Population III Star Formation
Xu, Hao; O' Shea, Brian W; Li, Hui; Li, Shengtai; Norman, Michael L; Collins, David C
2008-01-01
We report the results of the first self-consistent three-dimensional adaptive mesh refinement magnetohydrodynamical simulations of Population III star formation including the Biermann battery effect. We find that the Population III stellar cores formed including this effect are both qualitatively and quantitatively similar to those from hydrodynamics-only (non-MHD) cosmological simulations. We observe peak magnetic fields of {approx_equal} 10{sup -9} G in the center of our star-forming halo at z {approx_equal} 17.55 at a baryon density of n{sub B} {approx} 10{sup 10} cm{sup -3}. The magnetic fields created by the Biermann battery effect are predominantly formed early in the evolution of the primordial halo at low density and large spatial scales, and then grow through compression and by shear flows. The fields seen in this calculation are never large enough to be dynamically important (with {beta} {ge} 10{sup 15} at all times before the termination of our calculation), and should be considered the minimum possible fields in existence during Population III star formation. The lack of magnetic support lends credibility to assumptions made in previous calculations regarding the lack of importance of magnetic fields in Population III star formation. In addition, these magnetic fields may be seed fields for the stellar dynamo or the magnetorotational instability at higher densities and smaller spatial scales.
Probing cosmology with weak lensing selected clusters - I. Halo approach and all-sky simulations
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Hamana, Takashi; Yoshida, Naoki
2015-11-01
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 catalogues 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 catalogues with sky coverage of ˜1000 deg2. We show that our theoretical model agrees well with the ensemble average of statistics and their covariances calculated directly from the mock catalogues. With a typical selection threshold, ignoring shape noise correction causes overestimation of the clustering of weak lensing selected clusters with a level of about 10 per cent, and shape noise correction boosts the cluster abundance by a factor of a few. We calculate the cross-covariances using the halo model with accounting for the effective reduction of the survey area due to masks. The covariance of the cosmic shear auto power spectrum is affected by the mode-coupling effect that originates from sky masking. Our model and the results can be readily used for cosmological analysis with ongoing and future weak lensing surveys.
Anomaly-free cosmological perturbations in effective canonical quantum gravity
Barrau, Aurelien; Calcagni, Gianluca; Grain, Julien E-mail: bojowald@gravity.psu.edu E-mail: julien.grain@ias.u-psud.fr
2015-05-01
This article lays out a complete framework for an effective theory of cosmological perturbations with corrections from canonical quantum gravity. Since several examples exist for quantum-gravity effects that change the structure of space-time, the classical perturbative treatment must be rethought carefully. The present discussion provides a unified picture of several previous works, together with new treatments of higher-order perturbations and the specification of initial states.
NASA Astrophysics Data System (ADS)
Nagamine, K.; Springel, V.; Hernquist, L.
2004-02-01
We study the distribution of the star formation rate (SFR) and metallicity of damped Lyman α absorbers (DLAs) in the redshift range z= 0-4.5 using cosmological smoothed particle hydrodynamics (SPH) simulations of the Λ cold dark matter model. Our simulations include standard radiative cooling and heating with a uniform ultraviolet background, star formation, supernova (SN) feedback, as well as a phenomenological model for feedback by galactic winds. The latter allows us to examine, in particular, the effect of galactic outflows on the distribution of the SFR and metallicity of DLAs. We employ a `conservative entropy' formulation of SPH which alleviates numerical overcooling effects that affected earlier simulations. In addition, we utilize a series of simulations of varying box-size and particle number to investigate the impact of numerical resolution on our results. We find that there is a positive correlation between the projected stellar mass density and the neutral hydrogen column density (NHI) of DLAs for high NHI systems, and that there is a good correspondence in the spatial distribution of stars and DLAs in the simulations. The evolution of typical star-to-gas mass ratios in DLAs can be characterized by an increase from approximately 2 at z= 4.5 to 3 at z= 3, to 10 at z= 1 and finally to 20 at z= 0. We also find that the projected SFR density in DLAs follows the Kennicutt law well at all redshifts, and the simulated values are consistent with the recent observational estimates of this quantity by Wolfe, Prochaska & Gawiser. The rate of evolution in the mean metallicity of simulated DLAs as a function of redshift is mild, and is consistent with the rate estimated from observations. The predicted metallicity of DLAs is generally subsolar in our simulations, and there is a significant scatter in the distribution of DLA metallicity for a given NHI. However, we find that the median metallicity of simulated DLAs is close to that of Lyman-break galaxies, and is
Effective cosmological equations of induced f(R) gravity
Apostolopoulos, Pantelis S.; Tetradis, Nikolaos; Brouzakis, Nikolaos E-mail: nbruzak@ifae.es
2010-08-01
We expand the study of generalized brane cosmologies by allowing for an f( R-tilde ) gravity term on the brane, with R-tilde the curvature scalar derived from the induced metric. We also include arbitrary matter components on the brane and in the five-dimensional bulk. At low energies, the effect of the bulk on the brane evolution can be described through a mirage component, termed generalized dark radiation, in the effective four-dimensional field equations. Using the covariant formalism, we derive the exact form of these equations. We also derive an effective conservation equation involving the brane matter and the generalized dark radiation. At low energies the coupled brane-bulk system has a purely four-dimensional description. The applications of the formalism include generalizations of the Starobinsky model and the Dvali-Gabadadze-Porrati cosmology.
NASA Astrophysics Data System (ADS)
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.
Cosmological galaxy formation simulations using smoothed particle hydrodynamics
NASA Astrophysics Data System (ADS)
Stinson, G. S.; Bailin, J.; Couchman, H.; Wadsley, J.; Shen, S.; Nickerson, S.; Brook, C.; Quinn, T.
2010-10-01
We present the McMaster Unbiased Galaxy Simulations (MUGS), the first nine galaxies of an unbiased selection ranging in total mass from 5 × 1011Msolar to 2 × 1012Msolar 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 and physically motivated stellar feedback. Mock images of the simulations show that the simulations lie within the observed range of relations such as that between colour and magnitude and that between brightness and circular velocity (Tully-Fisher). The greatest discrepancy between the simulated galaxies and observed galaxies is the high concentration of material at the centre of the galaxies as represented by the centrally peaked rotation curves and the high bulge-to-total ratios of the simulations determined both kinematically and photometrically. This central concentration represents the excess of low angular momentum material that long has plagued morphological studies of simulated galaxies and suggests that higher resolutions and a more accurate description of feedback will be required to simulate more realistic galaxies. Even with the excess central mass concentrations, the simulations suggest the important role merger history and halo spin play in the formation of discs.
NASA Astrophysics Data System (ADS)
Dolag, Klaus; Remus, Rhea-Silvia; Teklu, Adelheid F.
2015-08-01
Recent, cosmological hydrodynamical simulations can cover very large dynamical ranges in the resolved structures, while following a large variety of physical processes which are important for the formation of galaxies and galaxy clusters. I will present the results from the "Magneticum" set of cosmological simulations with special emphasis on the outer stellar halos of galaxies and galaxy clusters. Our investigations show that -- despite the fact that the galaxies formed in our simulations can clearly be classified into different morphological types -- the outer stellar envelope shows a universal stellar profile, resulting in outer slopes which are very well in agreement with the still rare observational data currently available. For galaxy clusters, we find that despite the fact that the ICL component always shows a clear dynamical seperation from the BCG, the stellar profile in many galaxy clusters is characterized by a single sersic profile, covering the BCG and the ICL, very much in agreement with current, observational results.
Cosmology with AGN dust time lags-simulating the new VEILS survey
NASA Astrophysics Data System (ADS)
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 < z < 1.2. We use the lags recovered from our simulations to calculate precise distance moduli, establish a Hubble diagram, and fit cosmological models. Assuming realistic scatter in the distribution of the dust around the AGN as well as in the normalization 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.
Gravitational torque-driven black hole growth and feedback in cosmological simulations
NASA Astrophysics Data System (ADS)
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.
The MultiDark Database: Release of the Bolshoi and MultiDark cosmological simulations
NASA Astrophysics Data System (ADS)
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.
COMPARISONS OF COSMOLOGICAL MAGNETOHYDRODYNAMIC GALAXY CLUSTER SIMULATIONS TO RADIO OBSERVATIONS
Xu Hao; Li Hui; Collins, David C.; Govoni, Federica; Murgia, Matteo; Norman, Michael L.; Cen Renyue; Feretti, Luigina; Giovannini, Gabriele E-mail: hli@lanl.gov E-mail: mlnorman@ucsd.edu E-mail: matteo@oa-cagliari.inaf.it E-mail: lferetti@ira.inaf.it
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.
Initial conditions for accurate N-body simulations of massive neutrino cosmologies
NASA Astrophysics Data System (ADS)
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.
SPOKES: An end-to-end simulation facility for spectroscopic cosmological surveys
NASA Astrophysics Data System (ADS)
Nord, B.; Amara, A.; Réfrégier, 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.
2016-04-01
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 output an efficient measure for design optimization and feasibility testing. We present the architecture, first science, and computational performance results of the simulation pipeline. The framework is general, but for the benchmark tests, we use the Dark Energy Spectrometer (DESpec), one of the early concepts for the upcoming project, the Dark Energy Spectroscopic Instrument (DESI). We discuss how the SPOKES framework enables a rigorous process to optimize and exploit spectroscopic survey experiments in order to derive high-precision cosmological measurements optimally.
SPOKES: An end-to-end simulation facility for spectroscopic cosmological surveys
Nord, B.; Amara, A.; Refregier, A.; ...
2016-03-03
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, coherentmore » 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 output an efficient measure for design optimization and feasibility testing. We present the architecture, first science, and computational performance results of the simulation pipeline. The framework is general, but for the benchmark tests, we use the Dark Energy Spectrometer (DESpec), one of the early concepts for the upcoming project, the Dark Energy Spectroscopic Instrument (DESI). As a result, we discuss how the SPOKES framework enables a rigorous process to optimize and exploit spectroscopic survey experiments in order to derive high-precision cosmological measurements optimally.« less
Off The Beaten Path: Modeling the Dynamics of Supermassive Black Holes in Cosmological Simulations
NASA Astrophysics Data System (ADS)
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.
SPOKES: An end-to-end simulation facility for spectroscopic cosmological surveys
Nord, B.; Amara, A.; 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.
2016-03-03
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 output an efficient measure for design optimization and feasibility testing. We present the architecture, first science, and computational performance results of the simulation pipeline. The framework is general, but for the benchmark tests, we use the Dark Energy Spectrometer (DESpec), one of the early concepts for the upcoming project, the Dark Energy Spectroscopic Instrument (DESI). As a result, we discuss how the SPOKES framework enables a rigorous process to optimize and exploit spectroscopic survey experiments in order to derive high-precision cosmological measurements optimally.
NASA Astrophysics Data System (ADS)
Girdhar, Parth; Kobakhidze, Archil
2013-10-01
We describe a new phenomenon of zitterbewegung of a free Dirac particle in cosmological spacetimes. Unlike the similar effect theorized by Schrödinger in 1930, the cosmological zitterbewegung is a real, physically attainable effect, which originates from the mixing of positive and negative frequency modes of a field operator in cosmological spacetimes. We briefly discuss the potential for observing this effect in laboratory experiments with trapped ions.
PKDGRAV3: beyond trillion particle cosmological simulations for the next era of galaxy surveys
NASA Astrophysics Data System (ADS)
Potter, Douglas; Stadel, Joachim; Teyssier, Romain
2017-05-01
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 80 h 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 18,000 nodes and a peak performance of 10 Pflops.
NASA Astrophysics Data System (ADS)
Kafle, Prajwal R.; Robotham, Aaron; Lagos, Claudia; Driver, Simon P.
2017-01-01
We aim to discuss the dynamics of galaxies in group environment. We present our current findings on the contentious issue of the stellar mass segregation in galaxy groups using the Galaxy And Mass Assembly (GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological hydrodynamical simulation catalogues of galaxy groups. We will discuss our main results that show negligible mass segregation in galaxy groups, which also show a lack of redshift evolution.
Zoomed cosmological simulations of Milky Way-sized haloes in f(R) gravity
NASA Astrophysics Data System (ADS)
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}.
NASA Astrophysics Data System (ADS)
Puchwein, Ewald; Baldi, Marco; Springel, Volker
2013-11-01
We present a new massively parallel code for N-body and cosmological hydrodynamical simulations of modified gravity models. The code employs a multigrid-accelerated Newton-Gauss-Seidel relaxation solver on an adaptive mesh to efficiently solve for perturbations in the scalar degree of freedom of the modified gravity model. As this new algorithm is implemented as a module for the P-GADGET3 code, it can at the same time follow the baryonic physics included in P-GADGET3, such as hydrodynamics, radiative cooling and star formation. We demonstrate that the code works reliably by applying it to simple test problems that can be solved analytically, as well as by comparing cosmological simulations to results from the literature. Using the new code, we perform the first non-radiative and radiative cosmological hydrodynamical simulations of an f (R)-gravity model. We also discuss the impact of active galactic nucleus feedback on the matter power spectrum, as well as degeneracies between the influence of baryonic processes and modifications of gravity.
Levine, Robyn Deborah
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
Regular bouncing cosmological solutions in effective actions in four dimensions
NASA Astrophysics Data System (ADS)
Constantinidis, C. P.; Fabris, J. C.; Furtado, R. G.; Picco, M.
2000-02-01
We study cosmological scenarios resulting from effective actions in four dimensions which are, under some assumptions, connected with multidimensional, supergravity and string theories. These effective actions are labeled by the parameters ω, the dilaton coupling constant, and n which establishes the coupling between the dilaton and a scalar field originating from the gauge field existing in the original theories. There is a large class of bouncing as well as Friedmann-like solutions. We investigate under which conditions bouncing regular solutions can be obtained. In the case of the string effective action, regularity is obtained through the inclusion of contributions from the Ramond-Ramond sector of superstring.
On the Evolution of Galaxy Spin in a Cosmological Hydrodynamic Simulation of Galaxy Clusters
NASA Astrophysics Data System (ADS)
Choi, Hoseung; Yi, Sukyoung K.
2017-03-01
The traditional view of the morphology–spin connection is being challenged by recent integral field unit observations, as the majority of early-type galaxies are found to have a rotational component that is often as large as a dispersion component. Mergers are often suspected to be critical in galaxy spin evolution, yet the details of their roles are still unclear. We present the first results on the spin evolution of galaxies in cluster environments through a cosmological hydrodynamic simulation. Galaxies spin down globally with cosmic evolution. Major (mass ratios > 1/4) and minor (1/4 ≥slant mass ratios > 1/50) mergers are important contributors to the spin-down in particular in massive galaxies. Minor mergers appear to have stronger cumulative effects than major mergers. Surprisingly, the dominant driver of galaxy spin-down seems to be environmental effects rather than mergers. However, since multiple processes act in combination, it is difficult to separate their individual roles. We briefly discuss the caveats and future studies that are called for.
Evolution of dwarf galaxies simulated in the cosmological LCDM scenario
NASA Astrophysics Data System (ADS)
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.
Effective cosmological constant induced by stochastic fluctuations of Newton's constant
NASA Astrophysics Data System (ADS)
de Cesare, Marco; Lizzi, Fedele; Sakellariadou, Mairi
2016-09-01
We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector.
Effect of inhomogeneities on high precision measurements of cosmological distances
NASA Astrophysics Data System (ADS)
Peel, Austin; Troxel, M. A.; Ishak, Mustapha
2014-12-01
We study effects of inhomogeneities on distance measures in an exact relativistic Swiss-cheese model of the Universe, focusing on the distance modulus. The model has Λ CDM background dynamics, and the "holes" are nonsymmetric structures described by the Szekeres metric. The Szekeres exact solution of Einstein's equations, which is inhomogeneous and anisotropic, allows us to capture potentially relevant effects on light propagation due to nontrivial evolution of structures in an exact framework. Light beams traversing a single Szekeres structure in different ways can experience either magnification or demagnification, depending on the particular path. Consistent with expectations, we find a shift in the distance modulus μ to distant sources due to demagnification when the light beam travels primarily through the void regions of our model. Conversely, beams are magnified when they propagate mainly through the overdense regions of the structures, and we explore a small additional effect due to time evolution of the structures. We then study the probability distributions of Δ μ =μΛ CDM-μSC for sources at different redshifts in various Swiss-cheese constructions, where the light beams travel through a large number of randomly oriented Szekeres holes with random impact parameters. We find for Δ μ the dispersions 0.004 ≤σΔ μ≤0.008 mag for sources with redshifts 1.0 ≤z ≤1.5 , which are smaller than the intrinsic dispersion of, for example, magnitudes of type Ia supernovae. The shapes of the distributions we obtain for our Swiss-cheese constructions are peculiar in the sense that they are not consistently skewed toward the demagnification side, as they are in analyses of lensing in cosmological simulations. Depending on the source redshift, the distributions for our models can be skewed to either the demagnification or the magnification side, reflecting a limitation of these constructions. This could be the result of requiring the continuity of Einstein
Loop quantum cosmology of Bianchi IX: effective dynamics
NASA Astrophysics Data System (ADS)
Corichi, Alejandro; Montoya, Edison
2017-03-01
We study solutions to the effective equations for the Bianchi IX class of spacetimes within loop quantum cosmology (LQC). We consider Bianchi IX models whose matter content is a massless scalar field, by numerically solving the loop quantum cosmology effective equations, with and without inverse triad corrections. The solutions are classified using certain geometrically motivated classical observables. We show that both effective theories—with lapse N = V and N = 1—resolve the big bang singularity and reproduce the classical dynamics far from the bounce. Moreover, due to the positive spatial curvature, there is an infinite number of bounces and recollapses. We study the limit of large field momentum and show that both effective theories reproduce the same dynamics, thus recovering general relativity. We implement a procedure to identify amongst the Bianchi IX solutions, those that behave like k = 0,1 FLRW as well as Bianchi I, II, and VII0 models. The effective solutions exhibit Bianchi I phases with Bianchi II transitions and also Bianchi VII0 phases, which had not been studied before. We comment on the possible implications of these results for a quantum modification to the classical BKL behaviour.
Machine learning and cosmological simulations - I. Semi-analytical models
NASA Astrophysics Data System (ADS)
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.
Cosmology with kinematic Sunyaev-Zel'dovich effect measurements from ACTPol and future surveys
NASA Astrophysics Data System (ADS)
de Bernardis, Francesco
2016-03-01
ACTPol is the first polarization receiver for the Atacama Cosmology Telescope (ACT) that is observing the CMB sky with arcmin resolution over about 2000 sq. deg. Its upgrade, Advanced ACTPol, will observe the CMB in five frequency bands and over a larger area of the sky. These measurements will enable a number of astrophysical and cosmological studies. We focus on the kinematic SZ effect as measured through the mean pairwise momentum of galaxy clusters. The spectroscopic information is particularly valuable for these measurements and ACTPol is in a unique position for this kind of study due to its wide overlap with the Baryon Oscillation Spectroscopic Survey (BOSS). The pairwise kSZ signal is able to probe the growth and expansion history of the universe. Moreover, measurements of the kSZ effect can be used to test advanced hydrodynamical simulations of the Intra-Cluster Medium (ICM) and to constrain the baryon content of galaxy clusters. We report the latest kSZ results from ACTPol and BOSS and describe the potential strong constraints on cosmological parameters and practical challenges in the extraction and maximization of the signal-to-noise ratio. We discuss the main sources of systematic uncertainty and the progress towards realistic forecasts for future CMB instruments.
Gravitational lensing effects in a time-variable cosmological 'constant' cosmology
NASA Technical Reports Server (NTRS)
Ratra, Bharat; Quillen, Alice
1992-01-01
A scalar field phi with a potential V(phi) varies as phi exp -alpha(alpha is greater than 0) has an energy density, behaving like that of a time-variable cosmological 'constant', that redshifts less rapidly than the energy densities of radiation and matter, and so might contribute significantly to the present energy density. We compute, in this spatially flat cosmology, the gravitational lensing optical depth, and the expected lens redshift distribution for fixed source redshift. We find, for the values of alpha of about 4 and baryonic density parameter Omega of about 0.2 consistent with the classical cosmological tests, that the optical depth is significantly smaller than that in a constant-Lambda model with the same Omega. We also find that the redshift of the maximum of the lens distribution falls between that in the constant-Lambda model and that in the Einstein-de Sitter model.
Gravitational lensing effects in a time-variable cosmological 'constant' cosmology
NASA Technical Reports Server (NTRS)
Ratra, Bharat; Quillen, Alice
1992-01-01
A scalar field phi with a potential V(phi) varies as phi exp -alpha(alpha is greater than 0) has an energy density, behaving like that of a time-variable cosmological 'constant', that redshifts less rapidly than the energy densities of radiation and matter, and so might contribute significantly to the present energy density. We compute, in this spatially flat cosmology, the gravitational lensing optical depth, and the expected lens redshift distribution for fixed source redshift. We find, for the values of alpha of about 4 and baryonic density parameter Omega of about 0.2 consistent with the classical cosmological tests, that the optical depth is significantly smaller than that in a constant-Lambda model with the same Omega. We also find that the redshift of the maximum of the lens distribution falls between that in the constant-Lambda model and that in the Einstein-de Sitter model.
THE EFFECT OF PECULIAR VELOCITIES ON SUPERNOVA COSMOLOGY
Davis, Tamara M.; Sinclair, Benjamin; Hui, Lam; Frieman, Joshua A.; Kessler, Richard; Haugbolle, Troels; Sollerman, Jesper; Bassett, Bruce; Marriner, John; Moertsell, Edvard; Nichol, Robert C.; Richmond, Michael W.; Sako, Masao; Schneider, Donald P.; Smith, Mathew
2011-11-01
We analyze the effect that peculiar velocities have on the cosmological inferences we make using luminosity distance indicators, such as Type Ia supernovae. In particular we study the corrections required to account for (1) our own motion, (2) correlations in galaxy motions, and (3) a possible local under- or overdensity. For all of these effects we present a case study showing the impact on the cosmology derived by the Sloan Digital Sky Survey-II Supernova Survey (SDSS-II SN Survey). Correcting supernova (SN) redshifts for the cosmic microwave background (CMB) dipole slightly overcorrects nearby SNe that share some of our local motion. We show that while neglecting the CMB dipole would cause a shift in the derived equation of state of {Delta}w {approx} 0.04 (at fixed {Omega}{sub m}), the additional local-motion correction is currently negligible ({Delta}w {approx}< 0.01). We then demonstrate a covariance-matrix approach to statistically account for correlated peculiar velocities. This down-weights nearby SNe and effectively acts as a graduated version of the usual sharp low-redshift cut. Neglecting coherent velocities in the current sample causes a systematic shift of {Delta}w {approx} 0.02. This will therefore have to be considered carefully when future surveys aim for percent-level accuracy and we recommend our statistical approach to down-weighting peculiar velocities as a more robust option than a sharp low-redshift cut.
Early universe cosmology, effective supergravity, and invariants of algebraic forms
NASA Astrophysics Data System (ADS)
Sinha, Kuver
2015-09-01
The presence of light scalars can have profound effects on early universe cosmology, influencing its thermal history as well as paradigms like inflation and baryogenesis. Effective supergravity provides a framework to make quantifiable, model-independent studies of these effects. The Riemannian curvature of the Kähler manifold spanned by scalars belonging to chiral superfields, evaluated along supersymmetry breaking directions, provides an order parameter (in the sense that it must necessarily take certain values) for phenomena as diverse as slow roll modular inflation, nonthermal cosmological histories, and the viability of Affleck-Dine baryogenesis. Within certain classes of UV completions, the order parameter for theories with n scalar moduli is conjectured to be related to invariants of n -ary cubic forms (for example, for models with three moduli, the order parameter is given by a function on the ring of invariants spanned by the Aronhold invariants). Within these completions, and under the caveats spelled out, this may provide an avenue to obtain necessary conditions for the above phenomena that are in principle calculable given nothing but the intersection numbers of a Calabi-Yau compactification geometry. As an additional result, abstract relations between holomorphic sectional and bisectional curvatures are utilized to constrain Affleck-Dine baryogenesis on a wide class of Kähler geometries.
Bar-driven evolution and quenching of spiral galaxies in cosmological simulations
NASA Astrophysics Data System (ADS)
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.
Stellar feedback from high-mass X-ray binaries in cosmological hydrodynamical simulations
NASA Astrophysics Data System (ADS)
Artale, M. C.; Tissera, P. B.; Pellizza, L. J.
2015-04-01
We explored the role of X-ray binaries composed by a black hole and a massive stellar companion [black hole X-ray binaries (BHXs)] as sources of kinetic feedback by using hydrodynamical cosmological simulations. Following previous results, our BHX model selects metal-poor stars (Z = [0, 10-4]) as possible progenitors. The model that better reproduces observations assumes that an ˜20 per cent fraction of low-metallicity black holes are in binary systems which produces BHXs. These sources are estimated to deposit ˜1052 erg of kinetic energy per event. With these parameters and in the simulated volume, we find that the energy injected by BHXs represents ˜30 per cent of the total energy released by Type II supernova and BHX events at redshift z ˜ 7 and then decreases rapidly as baryons get chemically enriched. Haloes with virial masses smaller than ˜1010 M⊙ (or Tvir ≲ 105 K) are the most directly affected ones by BHX feedback. These haloes host galaxies with stellar masses in the range 107-108 M⊙. Our results show that BHX feedback is able to keep the interstellar medium warm, without removing a significant gas fraction, in agreement with previous analytical calculations. Consequently, the stellar-to-dark matter mass ratio is better reproduced at high redshift. Our model also predicts a stronger evolution of the number of galaxies as a function of the stellar mass with redshift when BHX feedback is considered. These findings support previous claims that the BHXs could be an effective source of feedback in early stages of galaxy evolution.
NASA Astrophysics Data System (ADS)
Angus, G. W.; Diaferio, Antonaldo
2011-10-01
We present a new particle mesh cosmological N-body code for accurately solving the modified Poisson equation of the quasi-linear formulation of modified Newtonian dynamics (MOND). We generate initial conditions for the Angus cosmological model, which is identical to Λ cold dark matter (ΛCDM) except that the CDM is switched for a single species of thermal sterile neutrinos. We set the initial conditions at z= 250 for a (512 Mpc h-1)3 box with 2563 particles, and we evolve them down to z= 0. We clearly demonstrate the ability of MOND to develop the large-scale structure in a hot dark matter cosmology and contradict the naive expectation that MOND cannot form galaxy clusters. We find that the correct order of magnitude of X-ray clusters (with TX > 4.5 keV) can be formed, but that we overpredict the number of very rich clusters and seriously underpredict the number of lower mass clusters. We present evidence that suggests the density profiles of our simulated clusters are compatible with those of the observed X-ray clusters in MOND. As a last test, we computed the relative velocity between pairs of haloes within 10 Mpc and find that pairs with velocities larger than 3000 km s-1, like the bullet cluster, can form without difficulty.
Skillman, Samuel W.; Hallman, Eric J.; Burns, Jack O.; Smith, Britton D.; O'Shea, Brian W.; Turk, Matthew J.
2011-07-10
Cosmological shocks are a critical part of large-scale structure formation, and are responsible for heating the intracluster medium in galaxy clusters. In addition, they are capable of accelerating non-thermal electrons and protons. In this work, we focus on the acceleration of electrons at shock fronts, which is thought to be responsible for radio relics-extended radio features in the vicinity of merging galaxy clusters. By combining high-resolution adaptive mesh refinement/N-body cosmological simulations with an accurate shock-finding algorithm and a model for electron acceleration, we calculate the expected synchrotron emission resulting from cosmological structure formation. We produce synthetic radio maps of a large sample of galaxy clusters and present luminosity functions and scaling relationships. With upcoming long-wavelength radio telescopes, we expect to see an abundance of radio emission associated with merger shocks in the intracluster medium. By producing observationally motivated statistics, we provide predictions that can be compared with observations to further improve our understanding of magnetic fields and electron shock acceleration.
NASA Astrophysics Data System (ADS)
Grand, Robert
2016-09-01
Simulations are playing an increasingly important role in probing the formation history of the Milky Way, including the formation of the thick/thin disc and origin of the metal distribution and chemo-dynamical relations. We introduce the Auriga project, a suite of high resolution cosmological-zoom simulations of Milky Way-sized galaxies simulated with the state-of-the-art cosmological magneto-hydrodynamical code AREPO, and present an analysis of the formation and evolution of the stellar disc(s) from early times to present day. In particular, we show that 'thickened discs' are mainly driven by a bar (if present) and interactions with satellites of masses log10 (M/ Mo ) >= 10, whereas other potential heating mechanisms such as spiral arms, radial migration, and adiabatic heating from mid-plane density growth are all sub-dominant. Interestingly, we find that even in cases of violent satellite interactions the disc reforms quickly (within a few giga years), producing a well-defined disc-bulge system. In nearly all simulations the overall structure of the disc becomes gradually more radially extended and vertically thinner with time, in support of the inside-out, upside-down formation scenario, and without the presence of a thin/thick disc dichotomy. In addition, we comment on the mass distribution of mono-abundance populations and their relation to the bulge and disc components, which are readily comparable to observations from surveys such as APOGEE and Gaia.
Escape fraction of ionizing photons from high-redshift galaxies in cosmological SPH simulations
NASA Astrophysics Data System (ADS)
Yajima, Hidenobu; Choi, Jun-Hwan; Nagamine, Kentaro
2011-03-01
Combing the three-dimensional radiative transfer (RT) calculation and cosmological smoothed particle hydrodynamics (SPH) simulations, we study the escape fraction of ionizing photons (fesc) of high-redshift galaxies at z= 3-6. Our simulations cover the halo mass range of Mh= 109-1012 M⊙. We post-process several hundred simulated galaxies with the Authentic Radiative Transfer (ART) code to study the halo mass dependence of fesc. In this paper, we restrict ourselves to the transfer of stellar radiation from local stellar population in each dark matter halo. We find that the average fesc steeply decreases as the halo mass increases, with a large scatter for the lower-mass haloes. The low-mass haloes with Mh˜ 109 M⊙ have large values of fesc (with an average of ˜0.4), whereas the massive haloes with Mh˜ 1011 M⊙ show small values of fesc (with an average of ˜0.07). This is because in our simulations, the massive haloes show more clumpy structure in gas distribution, and the star-forming regions are embedded inside these clumps, making it more difficult for the ionizing photons to escape. On the other hand, in low-mass haloes, there are often conical regions of highly ionized gas due to the shifted location of young star clusters from the centre of dark matter halo, which allows the ionizing photons to escape more easily than in the high-mass haloes. By counting the number of escaped ionizing photons, we show that the star-forming galaxies can ionize the intergalactic medium at z= 3-6. The main contributor to the ionizing photons is the haloes with Mh≲ 1010 M⊙ owing to their high fesc. The large dispersion in fesc suggests that there may be various sizes of H II bubbles around the haloes even with the same mass in the early stages of reionization. We also examine the effect of UV background radiation field on fesc using simple, four different treatments of UV background.
Gravitational lens effects of a cosmological density of compact objects
NASA Technical Reports Server (NTRS)
Canizares, C. R.
1983-01-01
Amplification of quasar light by a cosmological density of compact objects causes significant effects on many quasars in magnitude-limited samples. For lens masses solar mass less than 100,000 solar mass the continuum would be amplified by a magnitude or more but the line emission would not. Examination of the UV selected sample of Marshall et al. (1983) gives limits to more than 90 percent statistical confidence of Omega(c) less than 0.1 for a mass between 200 and 100,000 solar mass, where Omega(c) is the mean density of objects of mass M relative to the closure density. Preliminary results from an X-ray selected sample may probe to more than 0.1 solar mass and give a value for Omega(c) of less than one. These limits indicate that the remnants of an early population of massive stars cannot make a cosmologically significant contribution to the mass density of the universe. On a separate topic, recent work on the enhanced surface density of quasars near galaxies due to lensing by stars in the galaxy halos is reviewed.
Evolution of cosmic filaments and of their galaxy population from MHD cosmological simulations
NASA Astrophysics Data System (ADS)
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.
Vacuum effects in a spatially homogeneous and isotropic cosmological background.
NASA Astrophysics Data System (ADS)
Villalba, V. M.; Percoco, U.
The authors obtain, by separation of variables, an exact solution to the Klein Gordon equation in a cosmological, spatially closed, Robertson-Walker space-time with a positive cosmological constant. The model is associated with a universe filled with radiation. The authors analyze the phenomenon of particle creation for different values of the dimensionless coupling constant. They discuss the relevance of the cosmological constant in this process.
A short introduction to numerical methods used in cosmological N-body simulations
NASA Astrophysics Data System (ADS)
Hellwing, Wojciech
2015-12-01
We give a short introduction to modern numerical methods commonly used in cosmological N-body simulations. First, we present some simple considerations based on linear perturbation theory which indicate the necessity for N-body simulations. Then, based on a working example of the publicly available gadget-2 code, we describe particle mesh and Barnes-Hut oct-tree methods used in numerical gravity N-body solvers. We also briefly discuss methods used in an elementary hydrodynamic implementation used for baryonic gas. Next, we give a very basic description of time integration of equations of motion commonly used in N-body codes. Finally we describe the Zeldovitch approximation as an example method for generating initial conditions for computer simulations.
An Archive and Tools for Cosmological Simulations inside the Virtual Observatory
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
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
Casimir effect: running Newton constant or cosmological term
NASA Astrophysics Data System (ADS)
Polonyi, Janos; Regos, Eniko
2006-01-01
We argue that the instability of Euclidean Einstein gravity is an indication that the vacuum is non-perturbative and contains a condensate of the metric tensor in a manner reminiscent of Yang Mills theories. As a simple step toward the characterization of such a vacuum the value of the 1-loop effective action is computed for Euclidean de Sitter spaces as a function of the curvature when the unstable conformal modes are held fixed. Two phases are found, one where the curvature is large and gravitons should be confined and another one which appears to be weakly coupled and tends to be flat. The induced cosmological constant is positive or negative in the strongly or weakly curved phase, respectively. The relevance of the Casimir effect in understanding the UV sensitivity of gravity is pointed out.
Exploring cosmic strings: Observable effects and cosmological constraints
NASA Astrophysics Data System (ADS)
Sabancilar, Eray
Observation of cosmic (super)strings can serve as a useful hint to understand the fundamental theories of physics, such as grand unified theories (GUTs) and/or superstring theory. In this regard, I present new mechanisms to produce particles from cosmic (super)strings, and discuss their cosmological and observational effects in this dissertation. The first chapter is devoted to a review of the standard cosmology, cosmic (super)strings and cosmic rays. The second chapter discusses the cosmological effects of moduli. Moduli are relatively light, weakly coupled scalar fields, predicted in supersymmetric particle theories including string theory. They can be emitted from cosmic (super)string loops in the early universe. Abundance of such moduli is constrained by diffuse gamma ray background, dark matter, and primordial element abundances. These constraints put an upper bound on the string tension as strong as Gmu ≲ 10-28 for a wide range of modulus mass m. If the modulus coupling constant is stronger than gravitational strength, modulus radiation can be the dominant energy loss mechanism for the loops. Furthermore, modulus lifetimes become shorter for stronger coupling. Hence, the constraints on string tension Gmu and modulus mass m are significantly relaxed for strongly coupled moduli predicted in superstring theory. Thermal production of these particles and their possible effects are also considered. In the third chapter, moduli emitted from cosmic string cusps are studied. Highly boosted modulus bursts emanating from cusps subsequently decay into gluons and generate hadronic cascades which in turn produce large number of neutrinos. For reasonable values of the modulus mass and coupling constant, observable ultra high energy neutrino fluxes can be produced for a wide range of string tension Gmu. The fourth chapter discusses cosmic rays produced by the charged particles ejected from cusps of superconducting cosmic strings. In many particle physics theories, cosmic
Confrontation of top-hat spherical collapse against dark halos from cosmological N-body simulations
NASA Astrophysics Data System (ADS)
Suto, Daichi; Kitayama, Tetsu; Osato, Ken; Sasaki, Shin; Suto, Yasushi
2016-02-01
The top-hat spherical collapse model (TSC) is one of the most fundamental analytical frameworks to describe the non-linear growth of cosmic structure. TSC has motivated, and been widely applied in, various investigations even in the current era of precision cosmology. While numerous studies exist to examine its validity against numerical simulations in a statistical fashion, there are few analyses which compare the TSC dynamics in an individual object-wise basis, which is what we attempt in the present paper. We extract 100 halos at z = 0 from a cosmological N-body simulation according to the conventional TSC criterion for the spherical over-density. Then we trace back their spherical counterparts at earlier epochs. Just prior to the turn-around epoch of the halos, their dynamics are well approximated by TSC, but their turn-around epochs are systematically delayed and the virial radii are larger by ˜20% on average relative to the TSC predictions. We find that this systematic deviation can mainly be ascribed to the non-uniformity/inhomogeneity of dark matter density profiles and the non-zero velocity dispersions, both of which are neglected in TSC. In particular, the inside-out collapse and shell-crossing of dark matter halos play an important role in generating the significant velocity dispersion. The implications of the present result are briefly discussed.
A Gauss-Bonnet Cosmology with an Effective Time-Dependent Scalar Potential
NASA Astrophysics Data System (ADS)
El-Nabulsi, Rami Ahmad
2017-05-01
A special class of a Gauss-Bonnet minimal power-law cosmology characterised by an effective time-dependent scalar field potential is explored in this communication. Some new features related to the late-time cosmological dynamics are observed and discussed accordingly.
Cosmological zoom simulations of z = 2 galaxies: The impact of galactic outflows
Anglés-Alcázar, Daniel; Davé, Romeel; Özel, Feryal; Oppenheimer, Benjamin D.
2014-02-20
We use high-resolution cosmological zoom simulations with ∼200 pc resolution at z = 2 and various prescriptions for galactic outflows in order to explore the impact of winds on the morphological, dynamical, and structural properties of eight individual galaxies with halo masses ∼10{sup 11}-2 × 10{sup 12} M {sub ☉} at z = 2. We present a detailed comparison to spatially and spectrally resolved Hα and other observations of z ≈ 2 galaxies. We find that simulations without winds produce massive, compact galaxies with low gas fractions, super-solar metallicities, high bulge fractions, and much of the star formation concentrated within the inner kiloparsec. Strong winds are required to maintain high gas fractions, redistribute star-forming gas over larger scales, and increase the velocity dispersion of simulated galaxies, more in agreement with the large, extended, turbulent disks typical of high-redshift star-forming galaxies. Winds also suppress early star formation to produce high-redshift cosmic star formation efficiencies in better agreement with observations. Sizes, rotation velocities, and velocity dispersions all scale with stellar mass in accord with observations. Our simulations produce a diversity of morphological characteristics—among our three most massive galaxies, we find a quiescent grand-design spiral, a very compact star-forming galaxy, and a clumpy disk undergoing a minor merger; the clumps are evident in Hα but not in the stars. Rotation curves are generally slowly rising, particularly when calculated using azimuthal velocities rather than enclosed mass. Our results are broadly resolution-converged. These results show that cosmological simulations including outflows can produce disk galaxies similar to those observed during the peak epoch of cosmic galaxy growth.
Vacuum effects in a spatially homogeneous and isotropic cosmological background
NASA Astrophysics Data System (ADS)
Villalba, Victor M.; Percoco, Umberto
1992-03-01
We obtain, by separation of variables, an exact solution to the Klein-Gordon and Dirac equations in a cosmological, spatially-closed, Robertson-Walker space-time with a positive cosmological constant Lambda. The model is associated with a universe filled with radiation. We analyze the phenomenon of particle creation for different values of the dimensionless coupling constant xi.
NASA Astrophysics Data System (ADS)
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.
The diversity of evolutionary pathways of compact elliptical galaxies in cosmological simulations
NASA Astrophysics Data System (ADS)
Wellons, Sarah
2017-01-01
Observations of the high-redshift universe have revealed a population of galaxies which are already very massive (~1e11 solar masses at z=2) and have typical sizes of < 2 kpc, much smaller than their counterparts in the local universe. How such dense, massive galaxies form, and why they appear to be less common at low redshift, have been questions of interest for both theorists and observers. I will discuss these questions in the context of the Illustris simulation, a hydrodynamical cosmological simulation in which tens of thousands of galaxies form, evolve, and interact with each other, situated within a cosmological context. I select a group of massive compact galaxies at z=2 in the simulation and trace them back and forth in time to discover both how they formed at high redshift, and what they evolve into at the present day. I find a variety of both progenitors (compact galaxies form in the simulation either via central starbursts generally brought on by mergers, or by racing out to the tip of the SF main sequence and forming very early) and descendants (many formerly-compact galaxies lurk at the core of a more massive galaxy today, others were consumed in mergers, and some evolve passively and undisturbed). I will also discuss the implications of these results for observational methods of connecting galaxy populations across redshifts - in particular, the assumption of a constant cumulative comoving number density - and suggest an improvement to this method which takes the complexity and variety of galaxies' evolutionary paths into account.
X-ray properties of galaxy clusters and groups from a cosmological hydrodynamical simulation
NASA Astrophysics Data System (ADS)
Borgani, S.; Murante, G.; Springel, V.; Diaferio, A.; Dolag, K.; Moscardini, L.; Tormen, G.; Tornatore, L.; Tozzi, P.
2004-03-01
We present results on the X-ray properties of clusters and groups of galaxies, extracted from a large cosmological hydrodynamical simulation. We used the TREE+SPH code GADGET to simulate a concordance Λ cold dark matter cosmological model within a box of 192 h-1 Mpc on a side, 4803 dark matter particles and as many gas particles. The simulation includes radiative cooling assuming zero metallicity, star formation and supernova feedback. The very high dynamic range of the simulation allows us to cover a fairly large interval of cluster temperatures. We compute X-ray observables of the intracluster medium (ICM) for simulated groups and clusters and analyse their statistical properties. The simulated mass-temperature relation is consistent with observations once we mimic the procedure for mass estimates applied to real clusters. Also, with the adopted choices of Ωm= 0.3 and σ8= 0.8 for matter density and power spectrum normalization, respectively, the resulting X-ray temperature function agrees with the most recent observational determinations. The luminosity-temperature relation also agrees with observations for clusters with T>~ 2 keV. At the scale of groups, T<~ 1 keV, we find no change of slope in this relation. The entropy in central cluster regions is higher than predicted by gravitational heating alone, the excess being almost the same for clusters and groups. We also find that the simulated clusters appear to have suffered some overcooling. We find f*~= 0.2 for the fraction of baryons in stars within clusters, thus approximately twice as large as the value observed. Interestingly, temperature profiles of simulated clusters are found to increase steadily toward cluster centres. They decrease in the outer regions, much like observational data do at r>~ 0.2rvir, while not showing an isothermal regime followed by a smooth temperature decline in the innermost regions. Our results thus demonstrate the need for yet more efficient sources of energy feedback and
Towards a new cosmological Milky Way like galaxy simulation in the Gaia Era
NASA Astrophysics Data System (ADS)
Roca-Fàbrega, S.; Valenzuela, O.; Figueras, F.
2015-05-01
We present a new cosmological Milky Way (MW) like galaxy formation simulation including N-body + hydrodynamics using the adaptive mesh refinement (AMR) code ART (Kravtsov et al 1997, ApJS, 111, 73; Kravtsov 2003, ApJ, 590, L1}. The system has been evolved inside a 28 Mpc cosmological box with a spatial resolution of 109 pc. At z=0 the system has an M_{vir} = 7.33×10^{11} M_{⊙}. A well defined disk is formed inside the dark matter halo and the overall amount of gas and stars is comparable with MW observations. Several non-axisymmetric structures arise out of the disk (spirals, bars and warp) and also a thick disk component. Furthermore, a huge reservoir of hot gas is present at large distances from the disk, embedded in the dark matter halo. Our preliminar results reveal that the hot gas has a clearly anisotropic distribution and can be a part of the missing baryons in galaxies.
A toy model to test the accuracy of cosmological N-body simulations
NASA Astrophysics Data System (ADS)
Sylos Labini, F.
2013-04-01
The evolution of an isolated over-density represents a useful toy model to test the accuracy of a cosmological N-body code in the non-linear regime as it is approximately equivalent to that of a truly isolated cloud of particles, with same density profile and velocity distribution, in a non-expanding background. This is the case as long as the system size is smaller than the simulation box side, so that its interaction with the infinite copies can be neglected. In such a situation, the over-density rapidly undergoes to a global collapse forming a quasi stationary state in virial equilibrium. However, by evolving the system with a cosmological code (GADGET) for a sufficiently long time, a clear deviation from such quasi-equilibrium configuration is observed. This occurs in a time tLI that depends on the values of the simulation numerical parameters such as the softening length and the time-stepping accuracy, i.e. it is a numerical artifact related to the limited spatial and temporal resolutions. The analysis of the Layzer-Irvine cosmic energy equation confirms that this deviation corresponds to an unphysical dynamical regime. By varying the numerical parameters of the simulation and the physical parameters of the system we show that the unphysical behaviour originates from badly integrated close scatterings of high-velocity particles. We find that, while the structure may remain virialized in the unphysical regime, its density and velocity profiles are modified with respect to the quasi-equilibrium configurations, converging, however, to well defined shapes, the former characterised by a Navarro Frenk White-type behaviour.
Constraints on physical properties of z ~ 6 galaxies using cosmological hydrodynamic simulations
NASA Astrophysics Data System (ADS)
Finlator, Kristian; Davé, Romeel; Oppenheimer, Benjamin D.
2007-04-01
We conduct a detailed comparison of broad-band spectral energy distributions of six z >~ 5.5 galaxies against galaxies drawn from cosmological hydrodynamic simulations. We employ a new tool called SPOC (Simulated photometry-derived observational constraints), which constrains the physical properties of observed galaxies through a Bayesian likelihood comparison with model galaxies. We first show that SPOC self-consistently recovers the physical properties of a test sample of high-redshift galaxies drawn from our simulations, although dust extinction can yield systematic uncertainties at the ~50 per cent level. We then use SPOC to test whether our simulations can reproduce the observed photometry of six z > 5.5 galaxies drawn from the literature. We compare physical properties derived from simulated star formation histories (SFHs) versus assuming simple models such as constant, exponentially decaying and constantly rising. For five objects, our simulated galaxies match the observations at least as well as simple SFH models, with similar favoured values obtained for the intrinsic physical parameters such as stellar mass and star formation rate, but with substantially smaller uncertainties. Our results are broadly insensitive to simulation choices for galactic outflows and dust reddening. Hence the existence of early galaxies as observed is broadly consistent with current hierarchical structure formation models. However, one of the six objects has photometry that is best fitted by a bursty SFH unlike anything produced in our simulations, driven primarily by a high K-band flux. These findings illustrate how SPOC provides a robust tool for optimally utilizing hydrodynamic simulations (or any model that predicts galaxy SFHs) to constrain the physical properties of individual galaxies having only photometric data, as well as identify objects that challenge current models.
Nonlinear cosmological consistency relations and effective matter stresses
Ballesteros, Guillermo; Hollenstein, Lukas; Jain, Rajeev Kumar; Kunz, Martin E-mail: lukas.hollenstein@unige.ch E-mail: martin.kunz@unige.ch
2012-05-01
We propose a fully nonlinear framework to construct consistency relations for testing generic cosmological scenarios using the evolution of large scale structure. It is based on the covariant approach in combination with a frame that is purely given by the metric, the normal frame. As an example, we apply this framework to the ΛCDM model, by extending the usual first order conditions on the metric potentials to second order, where the two potentials start to differ from each other. We argue that working in the normal frame is not only a practical choice but also helps with the physical interpretation of nonlinear dynamics. In this frame, effective pressures and anisotropic stresses appear at second order in perturbation theory, even for ''pressureless'' dust. We quantify their effect and compare them, for illustration, to the pressure of a generic clustering dark energy fluid and the anisotropic stress in the DGP model. Besides, we also discuss the effect of a mismatch of the potentials on the determination of galaxy bias.
FLY. A parallel tree N-body code for cosmological simulations
NASA Astrophysics Data System (ADS)
Antonuccio-Delogu, V.; Becciani, U.; Ferro, D.
2003-10-01
FLY is a parallel treecode which makes heavy use of the one-sided communication paradigm to handle the management of the tree structure. In its public version the code implements the equations for cosmological evolution, and can be run for different cosmological models. This reference guide describes the actual implementation of the algorithms of the public version of FLY, and suggests how to modify them to implement other types of equations (for instance, the Newtonian ones). Program summary Title of program: FLY Catalogue identifier: ADSC Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADSC Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer for which the program is designed and others on which it has been tested: Cray T3E, Sgi Origin 3000, IBM SP Operating systems or monitors under which the program has been tested: Unicos 2.0.5.40, Irix 6.5.14, Aix 4.3.3 Programming language used: Fortran 90, C Memory required to execute with typical data: about 100 Mwords with 2 million-particles Number of bits in a word: 32 Number of processors used: parallel program. The user can select the number of processors >=1 Has the code been vectorized or parallelized?: parallelized Number of bytes in distributed program, including test data, etc.: 4615604 Distribution format: tar gzip file Keywords: Parallel tree N-body code for cosmological simulations Nature of physical problem: FLY is a parallel collisionless N-body code for the calculation of the gravitational force. Method of solution: It is based on the hierarchical oct-tree domain decomposition introduced by Barnes and Hut (1986). Restrictions on the complexity of the program: The program uses the leapfrog integrator schema, but could be changed by the user. Typical running time: 50 seconds for each time-step, running a 2-million-particles simulation on an Sgi Origin 3800 system with 8 processors having 512 Mbytes RAM for each processor. Unusual features of the program: FLY
NASA Astrophysics Data System (ADS)
Wainwright, Carroll L.; Johnson, Matthew C.; Peiris, Hiranya V.; Aguirre, Anthony; Lehner, Luis; Liebling, Steven L.
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.
NASA Astrophysics Data System (ADS)
Price, Sedona H.; Kriek, Mariska; Feldmann, Robert; Quataert, Eliot; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Barro, Guillermo
2017-07-01
Accurate measurements of galaxy masses and sizes are key to tracing galaxy evolution over time. Cosmological zoom-in simulations provide an ideal test bed for assessing the recovery of galaxy properties from observations. Here, we utilize galaxies with {M}* ˜ {10}10{--}{10}11.5 {M}⊙ at z ˜ 1.7-2 from the MassiveFIRE cosmological simulation suite, part of the Feedback in Realistic Environments (FIRE) project. Using mock multi-band images, we compare intrinsic galaxy masses and sizes to observational estimates. We find that observations accurately recover stellar masses, with a slight average underestimate of ˜ 0.06 {dex} and {{a}}˜ 0.15 {dex} scatter. Recovered half-light radii agree well with intrinsic half-mass radii when averaged over all viewing angles, with a systematic offset of ˜ 0.1 {dex} (with the half-light radii being larger) and a scatter of ˜ 0.2 {dex}. When using color gradients to account for mass-to-light variations, recovered half-mass radii also exceed the intrinsic half-mass radii by ˜ 0.1 {dex}. However, if not properly accounted for, aperture effects can bias size estimates by ˜ 0.1 {dex}. No differences are found between the mass and size offsets for star-forming and quiescent galaxies. Variations in viewing angle are responsible for ˜25% of the scatter in the recovered masses and sizes. Our results thus suggest that the intrinsic scatter in the mass-size relation may have previously been overestimated by ˜25%. Moreover, orientation-driven scatter causes the number density of very massive galaxies to be overestimated by ˜ 0.5 {dex} at {M}* ˜ {10}11.5 {M}⊙ .
The metal enrichment of passive galaxies in cosmological simulations of galaxy formation
NASA Astrophysics Data System (ADS)
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.
THE PRESSURE OF THE STAR-FORMING INTERSTELLAR MEDIUM IN COSMOLOGICAL SIMULATIONS
Munshi, Ferah; Quinn, Thomas R.; Governato, Fabio; Christensen, Charlotte; Wadsley, James; Loebman, Sarah; Shen, Sijing
2014-01-20
We examine the pressure of the star-forming interstellar medium (ISM) of Milky-Way-sized disk galaxies using fully cosmological SPH+N-body, high-resolution simulations. These simulations include explicit treatment of metal-line cooling in addition to dust and self-shielding, H{sub 2}-based star formation. The four simulated halos have masses ranging from a few times 10{sup 10} to nearly 10{sup 12} solar masses. Using a kinematic decomposition of these galaxies into present-day bulge and disk components, we find that the typical pressure of the star-forming ISM in the present-day bulge is higher than that in the present-day disk by an order of magnitude. We also find that the pressure of the star-forming ISM at high redshift is, on average, higher than ISM pressures at low redshift. This explains why the bulge forms at higher pressures: the disk assembles at lower redshift when the ISM exhibits lower pressure and the bulge forms at high redshift when the ISM has higher pressure. If ISM pressure and IMF variation are tied together, these results could indicate a time-dependent IMF in Milky-Way-like systems as well as a different IMF in the bulge and the disk.
Galaxy formation in semi-analytic models and cosmological hydrodynamic zoom simulations
NASA Astrophysics Data System (ADS)
Hirschmann, Michaela; Naab, Thorsten; Somerville, Rachel S.; Burkert, Andreas; Oser, Ludwig
2012-02-01
We present a detailed comparison between numerical cosmological hydrodynamic zoom simulations and the semi-analytic model (SAM) of Somerville et al., run within merger trees extracted from the simulations. The high-resolution simulations represent 48 individual haloes with virial masses in the range ?. They include radiative H and He cooling, photoionization, star formation and thermal supernova (SN) feedback. We compare with different SAM versions including only this complement of physical processes, and also ones including SN-driven winds, metal cooling and feedback from active galactic nuclei (AGN). Our analysis is focused on the cosmic evolution of the baryon content in galaxies and its division into various components (stars, cold gas and hot gas), as well as how those galaxies acquired their gas and stellar mass. Both the SAMs and simulations are compared with observational relations between halo mass and stellar mass, and between stellar mass and star formation rate, at low and high redshifts. We find some points of agreement and some important disagreements. SAMs that include the same physical processes as the simulations reproduce the total baryon fraction in haloes and the fraction of cold gas plus stars in the central galaxy to better than 20 per cent. However, the simulations turn out to have much higher star formation efficiencies (by about a factor of 10) than the SAMs, despite nominally being both normalized to the same empirical Kennicutt relation at z= 0. Therefore the cold gas is consumed much more rapidly in the simulations, and stars form much earlier. Also, simulations show a transition from stellar mass growth that is dominated by in situ formation of stars to growth that is predominantly through accretion of stars formed in external galaxies. In SAMs, stellar growth is always dominated by in situ star formation, because they significantly underpredict the fraction of mass growth from accreted stars relative to the simulations. In addition
Numerical Convergence in the Dark Matter Halos Properties Using Cosmological Simulations
NASA Astrophysics Data System (ADS)
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
Valkenburg, Wessel; Hu, Bin E-mail: hu@lorentz.leidenuniv.nl
2015-09-01
We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravity outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.
NASA Astrophysics Data System (ADS)
Ostriker, Jeremiah P.; Cen, Renyue
1996-06-01
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 104.5 - 105.5 K, set essentially by photoheating processes. Most gas is in one of two components: either at the photoheating floor 104.5 K and primarily in low-density regions, or else shock heated to 105-106 K and in regions of moderate overdensity (in caustics and near groups and clusters). It presents a major challenge to observationally detect this second, abundant component, since it is neither an efficient radiator nor an efficient absorber. About 2%-1O% 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 correspondences between the simulations and the real world imply that there is some significant truth to the underlying standard scenarios for the growth of structure. The differences among model predictions may help us find the path to the correct model. For COBE-normalized models, the most relevant differences concern epoch of structure formation. In the open variants having Ω = 0.3, with or without a cosmological constant, structure formation on galactic scales is well advanced at redshift z = 5, and reionization occurs early. But if observations require models for which most galaxy formation occurs more recently than z = 2, then the flat Ω = 1 models are to be preferred. The velocity dispersion on the 1 h-1 Mpc scale also provides a strong discriminant with, as expected, the ω = 1 models giving a much higher (perhaps too high) value for that statistic.
Supermassive Black Hole Growth and Merger Rates from Cosmological N-body Simulations
Micic, Miroslav; Holley-Bockelmann, Kelly; Sigurdsson, Steinn; Abel, Tom; /SLAC
2007-10-29
Understanding how seed black holes grow into intermediate and supermassive black holes (IMBHs and SMBHs, respectively) has important implications for the duty-cycle of active galactic nuclei (AGN), galaxy evolution, and gravitational wave astronomy. Most studies of the cosmological growth and merger history of black holes have used semianalytic models and have concentrated on SMBH growth in luminous galaxies. Using high resolution cosmological N-body simulations, we track the assembly of black holes over a large range of final masses - from seed black holes to SMBHs - over widely varying dynamical histories. We used the dynamics of dark matter halos to track the evolution of seed black holes in three different gas accretion scenarios. We have found that growth of a Sagittarius A* - size SMBH reaches its maximum mass M{sub SMBH}={approx}10{sup 6}M{sub {circle_dot}} at z{approx}6 through early gaseous accretion episodes, after which it stays at near constant mass. At the same redshift, the duty-cycle of the host AGN ends, hence redshift z=6 marks the transition from an AGN to a starburst galaxy which eventually becomes the Milky Way. By tracking black hole growth as a function of time and mass, we estimate that the IMBH merger rate reaches a maximum of R{sub max}=55 yr{sup -1} at z=11. From IMBH merger rates we calculate N{sub ULX}=7 per Milky Way type galaxy per redshift in redshift range 2 {approx}< z {approx}< 6.
Cosmological N-body Simulation of Galaxy and Large-Scale Structure Formation: The Gravity Frontier
NASA Astrophysics Data System (ADS)
Klypin, Anatoly
2015-04-01
One of the first N-body simulations done almost 50 years ago had only 200 self-gravitating particles. Even this first baby step made substantial impact on understanding how astronomical objects should form. Now powerful supercomputers and new algorithms allow astronomers produce N-body simulations that employ up to a trillion dark matter particles and produce vital theoretical predictions regarding formation, evolution, structure and statistics of objects ranging from dwarf galaxies to clusters and superclusters of galaxies. With only gravity involved in these theoretical models, one would naively expect that by now we should know everything we need about N-body dynamics of cosmological fluctuations. Not the case. It appears that the Universe was not cooperative and gave us divergencies in the initial conditions generated during the Inflation epoch and subsequent expansion of the Universe - the infinite phase-space density and divergent density fluctuations. Ever increasing observational demands on statistics and accuracy of theoretical predictions is another driving force for more realistic and larger N-body simulations. Large current and new planned observational projects such as BOSS, eBOSS, Euclid, LSST will bring information on spatial distribution, motion, and properties of millions of galaxies at different redshifts. Direct simulations of evolution of gas and formation of stars for millions of forming galaxies will not be available for years leaving astronomers with the only option - to develop methods to combine large N-body simulations with models of galaxy formation to produce accurate theoretical predictions. I will discuss the current status of the field and directions of its development.
Far sidelobe effects from panel gaps of the Atacama Cosmology Telescope
NASA Astrophysics Data System (ADS)
Fluxa Rojas, Pedro Antonio; Dünner, Rolando; Maurin, Loïc.; Choi, Steve K.; Devlin, Mark J.; Gallardo, Patricio A.; Ho, Shuay-Pwu P.; Koopman, Brian J.; Louis, Thibaut; McMahon, Jeffrey J.; Nati, Federico; Niemack, Michael D.; Newburgh, Laura; Page, Lyman A.; Salatino, Maria; Schillaci, Alessandro; Schmitt, Benjamin L.; Simon, Sara M.; Staggs, Suzanne T.; Wollack, Edward J.
2016-07-01
The Atacama Cosmology Telescope is a 6 meter diameter CMB telescope located at 5200 meters in the Chilean desert. ACT has made arc-minute scale maps of the sky at 90 and 150 GHz which have led to precise measurements of the fine angular power spectrum of the CMB fluctuations in temperature and polarization. One of the goals of ACT is to search for the B-mode polarization signal from primordial gravity waves, and thus extending ACT's data analysis to larger angular scales. This goal introduces new challenges in the control of systematic effects, including better understanding of far sidelobe effects that might enter the power spectrum at degree angular scales. Here we study the effects of the gaps between panels of the ACT primary and secondary reflectors in the worst case scenario in which the gaps remain open. We produced numerical simulations of the optics using GRASP up to 8 degrees away from the main beam and simulated timestreams for observations with this beam using real pointing information from ACT data. Maps from these simulated timestreams showed leakage from the sidelobes, indicating that this effect must be taken into consideration at large angular scales.
Far Sidelobe Effects from Panel Gaps of the Atacama Cosmology Telescope
NASA Technical Reports Server (NTRS)
Fluxa, Pedro R.; Duenner, Rolando; Maurin, Loiec; Choi, Steve K.; Devlin, Mark J.; Gallardo, Patricio A.; Shuay-Pwu, P. Ho; Koopman, Brian J.; Louis, Thibaut; Wollack, Edward J.
2016-01-01
The Atacama Cosmology Telescope is a 6 meter diameter CMB telescope located at 5200 meters in the Chilean desert. ACT has made arc-minute scale maps of the sky at 90 and 150 GHz which have led to precise measurements of the fine angular power spectrum of the CMB fluctuations in temperature and polarization. One of the goals of ACT is to search for the B-mode polarization signal from primordial gravity waves, and thus extending ACT's data analysis to larger angular scales. This goal introduces new challenges in the control of systematic effects, including better understanding of far sidelobe effects that might enter the power spectrum at degree angular scales. Here we study the effects of the gaps between panels of the ACT primary and secondary reflectors in the worst case scenario in which the gaps remain open. We produced numerical simulations of the optics using GRASP up to 8 degrees away from the main beam and simulated timestreams for observations with this beam using real pointing information from ACT data. Maps from these simulated timestreams showed leakage from the sidelobes, indicating that this effect must be taken into consideration at large angular scales.
Far Sidelobe Effects from Panel Gaps of the Atacama Cosmology Telescope
NASA Technical Reports Server (NTRS)
Fluxa, Pedro R.; Duenner, Rolando; Maurin, Loiec; Choi, Steve K.; Devlin, Mark J.; Gallardo, Patricio A.; Shuay-Pwu, P. Ho; Koopman, Brian J.; Louis, Thibaut; Wollack, Edward J.
2016-01-01
The Atacama Cosmology Telescope is a 6 meter diameter CMB telescope located at 5200 meters in the Chilean desert. ACT has made arc-minute scale maps of the sky at 90 and 150 GHz which have led to precise measurements of the fine angular power spectrum of the CMB fluctuations in temperature and polarization. One of the goals of ACT is to search for the B-mode polarization signal from primordial gravity waves, and thus extending ACT's data analysis to larger angular scales. This goal introduces new challenges in the control of systematic effects, including better understanding of far sidelobe effects that might enter the power spectrum at degree angular scales. Here we study the effects of the gaps between panels of the ACT primary and secondary reflectors in the worst case scenario in which the gaps remain open. We produced numerical simulations of the optics using GRASP up to 8 degrees away from the main beam and simulated timestreams for observations with this beam using real pointing information from ACT data. Maps from these simulated timestreams showed leakage from the sidelobes, indicating that this effect must be taken into consideration at large angular scales.
DARK MATTER HALOS IN THE STANDARD COSMOLOGICAL MODEL: RESULTS FROM THE BOLSHOI SIMULATION
Klypin, Anatoly A.; Trujillo-Gomez, Sebastian; Primack, Joel
2011-10-20
Lambda Cold Dark Matter ({Lambda}CDM) is now the standard theory of structure formation in the universe. We present the first results from the new Bolshoi dissipationless cosmological {Lambda}CDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was run in a volume 250 h{sup -1} Mpc on a side using {approx}8 billion particles with mass and force resolution adequate to follow subhalos down to the completeness limit of V{sub circ} = 50 km s{sup -1} maximum circular velocity. Using merger trees derived from analysis of 180 stored time steps we find the circular velocities of satellites before they fall into their host halos. Using excellent statistics of halos and subhalos ({approx}10 million at every moment and {approx}50 million over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, the abundance of halos as a function of their circular velocity, and the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum value of about 4.0 and then rises for higher values of halo mass-a new result. We present approximations for the velocity and mass functions of distinct halos as a function of redshift. We find that while the Sheth-Tormen (ST) approximation for the mass function of halos found by spherical overdensity is quite accurate at low redshifts, the ST formula overpredicts the abundance of halos by nearly an order of magnitude by z = 10. We find that the number of subhalos scales with the circular velocity of the host halo as V{sup 1/2}{sub host}, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function N(> V{sub sub}) scales as V{sup -3}{sub circ}. Combining the results of Bolshoi and Via Lactea-II simulations, we find that inside the virial radius
A FIRST ESTIMATE OF RADIO HALO STATISTICS FROM LARGE-SCALE COSMOLOGICAL SIMULATION
Sutter, P. M.; Ricker, P. M. E-mail: pmricker@illinois.edu
2012-11-10
We present a first estimate based on a cosmological gas dynamics simulation of galaxy cluster radio halo counts to be expected in forthcoming low-frequency radio surveys. Our estimate is based on a FLASH simulation of the {Lambda}CDM model for which we have assigned radio power to clusters via a model that relates radio emissivity to cluster magnetic field strength, intracluster turbulence, and density. We vary several free parameters of this model and find that radio halo number counts vary by up to a factor of two for average magnetic fields ranging from 0.2 to 3.1 {mu}G. However, we predict significantly fewer low-frequency radio halos than expected from previous semi-analytic estimates, although this discrepancy could be explained by frequency-dependent radio halo probabilities as predicted in reacceleration models. We find that upcoming surveys will have difficulty in distinguishing models because of large uncertainties and low number counts. Additionally, according to our modeling we find that expected number counts can be degenerate with both reacceleration and hadronic secondary models of cosmic-ray generation. We find that relations between radio power and mass and X-ray luminosity may be used to distinguish models, and by building mock radio sky maps we demonstrate that surveys such as LOFAR may have sufficient resolution and sensitivity to break this model degeneracy by imaging many individual clusters.
Effects of kination and scalar-tensor cosmologies on sterile neutrinos
Rehagen, Thomas; Gelmini, Graciela B. E-mail: gelmini@physics.ucla.edu
2014-06-01
We study the effects of kination and scalar-tensor pre-Big Bang Nucleosynthesis cosmologies on the non-resonant production of sterile neutrinos. We show that if the peak of the production rate of sterile neutrinos occurs during a non-standard cosmological phase, the relic number density of sterile neutrinos could be reduced with respect to the number expected in the standard cosmology. Consequently, current bounds on active-sterile neutrino mixing derived from the relic energy density of sterile neutrinos could be greatly relaxed. In particular, we show that the sterile neutrinos which could explain the anomalies found in short-baseline neutrino experiments are compatible with recent joint Planck upper limits on their contribution to the energy density of the Universe in a scalar-tensor or a low-reheating temperature pre-Big Bang Nucleosynthesis cosmology.
Ibata, Rodrigo A.; Martin, Nicolas F.; Ibata, Neil G.; Lewis, Geraint F.; Conn, Anthony; Elahi, Pascal; Arias, Veronica; Fernando, Nuwanthika
2014-03-20
In a recent contribution, Bahl and 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 Λ-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. 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 angular momentum properties of the co-planar satellites, and find that the median of the specific angular momentum derived from the line-of-sight velocities in the real M31 structure (1.3 × 10{sup 4} km s{sup –1} kpc) is very high compared to systems drawn from the simulations. This analysis confirms that it is highly unlikely that the observed structure around the Andromeda galaxy is due to a chance occurrence. Interestingly, the few extreme systems that are similar to M31 arise from the accretion of a massive sub-halo with its own spatially concentrated entourage of orphan satellites.
Evaluating galactic habitability using high-resolution cosmological simulations of galaxy formation
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
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
Nonlinear backreaction in cosmology
NASA Astrophysics Data System (ADS)
Green, Stephen Roland
This thesis, based on two papers by Green and Wald, investigates the problem of nonlinear backreaction in cosmology. We first analyze the problem in a general context by developing a new, mathematically precise framework for treating the effects of nonlinear phenomena occurring on small scales in general relativity. Our framework requires the metric to be close to a background metric (not necessarily a cosmological metric), but allows arbitrarily large stress-energy fluctuations on small scales. We prove that, within our framework, if the matter stress-energy tensor satisfies the weak energy condition (i.e., positivity of energy density in all frames), then the only effect that small-scale inhomogeneities can have on the background metric is to provide an effective stress-energy tensor that is traceless and satisfies the weak energy condition itself—corresponding to the presence of gravitational radiation. In particular, nonlinear effects produced by small-scale inhomogeneities cannot mimic the effects of dark energy. We also develop perturbation theory off of the background metric. We derive an equation for the long-wavelength part of the leading order deviation of the metric from the background metric, which contains the usual terms occurring in linearized perturbation theory plus additional contributions from the small-scale inhomogeneities. Next, we apply our framework to the cosmological context, specializing our background metric to be of the Friedmann-Lemaitre-Robertson-Walker form. We demonstrate that, in the case of dust matter, a cosmological constant, and vanishing spatial curvature (i.e., our universe today), Newtonian gravity alone provides a good
Effective gravitational couplings for cosmological perturbations in generalized Proca theories
NASA Astrophysics Data System (ADS)
De Felice, Antonio; Heisenberg, Lavinia; Kase, Ryotaro; Mukohyama, Shinji; Tsujikawa, Shinji; Zhang, Ying-li
2016-08-01
We consider the finite interactions of the generalized Proca theory including the sixth-order Lagrangian and derive the full linear perturbation equations of motion on the flat Friedmann-Lemaître-Robertson-Walker background in the presence of a matter perfect fluid. By construction, the propagating degrees of freedom (besides the matter perfect fluid) are two transverse vector perturbations, one longitudinal scalar, and two tensor polarizations. The Lagrangians associated with intrinsic vector modes neither affect the background equations of motion nor the second-order action of tensor perturbations, but they do give rise to nontrivial modifications to the no-ghost condition of vector perturbations and to the propagation speeds of vector and scalar perturbations. We derive the effective gravitational coupling Geff with matter density perturbations under a quasistatic approximation on scales deep inside the sound horizon. We find that the existence of intrinsic vector modes allows a possibility for reducing Geff. In fact, within the parameter space, Geff can be even smaller than the Newton gravitational constant G at the late cosmological epoch, with a peculiar phantom dark energy equation of state (without ghosts). The modifications to the slip parameter η and the evolution of the growth rate f σ8 are discussed as well. Thus, dark energy models in the framework of generalized Proca theories can be observationally distinguished from the Λ CDM model according to both cosmic growth and expansion history. Furthermore, we study the evolution of vector perturbations and show that outside the vector sound horizon the perturbations are nearly frozen and start to decay with oscillations after the horizon entry.
NASA Astrophysics Data System (ADS)
Park, Hyunbae; Shapiro, P.; Komatsu, E.
2012-01-01
We present a calculation of the kinetic Sunyaev-Zel'dovich (kSZ) effect on of the Comic Microwave Background fluctuation. We focus on the scale at the multipole moment of l = 3000 10000 that is currently being probed by the South Pole Telescope (SPT) and the Atacama Cosmology Telescope. For the post-reionization contribution of the total signal, we use the 3rd order perturbation theory (3PT) to model non-linearity of post-reionization epoch. We evaluate a non-linear expression for momentum powerspectrum in Ma and Fry (2002) with the 3PT density and velocity powerspectrum. And, we use the 3PT momentum powerspectrum to calculate the kSZ signal. We show that the 3PT is a reasonable approximation by comparing our result with previous work by Zhang, Pen and Trac (2004). For reionization contribution, we use our N-body radiative transfer simulations to take patchiness of ionization of intergalactic medium in reionization epoch into account. Using ionized fraction field in the simulation, we calculate the momentum field of the ionized gas. And, we correct for the missing power in finite size boxes of simulations. Finally, we show the kSZ calculation for different simulations with reionization scenarios. With contributions from each epoch, we predict total kSZ signal for different reionization history and put constraint on reionization scenario using an upper bound of the signal from recent SPT measurement.
The Effect of Color Choice on Learner Interpretation of a Cosmology Visualization
ERIC Educational Resources Information Center
Buck, Zoe
2013-01-01
As we turn more and more to high-end computing to understand the Universe at cosmological scales, dynamic visualizations of simulations will take on a vital role as perceptual and cognitive tools. In collaboration with the Adler Planetarium and University of California High-Performance AstroComputing Center (UC-HiPACC), I am interested in better…
The Effect of Color Choice on Learner Interpretation of a Cosmology Visualization
ERIC Educational Resources Information Center
Buck, Zoe
2013-01-01
As we turn more and more to high-end computing to understand the Universe at cosmological scales, dynamic visualizations of simulations will take on a vital role as perceptual and cognitive tools. In collaboration with the Adler Planetarium and University of California High-Performance AstroComputing Center (UC-HiPACC), I am interested in better…
NASA Astrophysics Data System (ADS)
Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Quataert, Eliot; Murray, Norman
2015-12-01
We present an analysis of the galaxy-scale gaseous outflows from the Feedback in Realistic Environments (FIRE) simulations. This suite of hydrodynamic cosmological zoom simulations resolves formation of star-forming giant molecular clouds to z = 0, and features an explicit stellar feedback model on small scales. Our simulations reveal that high-redshift galaxies undergo bursts of star formation followed by powerful gusts of galactic outflows that eject much of the interstellar medium and temporarily suppress star formation. At low redshift, however, sufficiently massive galaxies corresponding to L* progenitors develop stable discs and switch into a continuous and quiescent mode of star formation that does not drive outflows far into the halo. Mass-loading factors for winds in L* progenitors are η ≈ 10 at high redshift, but decrease to η ≪ 1 at low redshift. Although lower values of η are expected as haloes grow in mass over time, we show that the strong suppression of outflows with decreasing redshift cannot be explained by mass evolution alone. Circumgalactic outflow velocities are variable and broadly distributed, but typically range between one and three times the circular velocity of the halo. Much of the ejected material builds a reservoir of enriched gas within the circumgalactic medium, some of which could be later recycled to fuel further star formation. However, a fraction of the gas that leaves the virial radius through galactic winds is never regained, causing most haloes with mass Mh ≤ 1012 M⊙ to be deficient in baryons compared to the cosmic mean by z = 0.
BOOK REVIEW Planck Scale Effects in Astrophysics and Cosmology
NASA Astrophysics Data System (ADS)
Padmanabhan, Thanu
2007-08-01
It has been generally agreed that putting together the principles of quantum theory and general relativity will usher the next revolution in physics. The trouble, of course, is that we have been now waiting for several decades for this revolution to take place. While people get excited about different directions of development every once in a while (with some excitements propped up by a larger number of researchers than others), it is probably fair to say that nothing which can be called definitive progress has taken place in the last several decades. Given the state of affairs it is definitely worthwhile to keep an open mind regarding new ideas and have at least a small fraction of researchers working somewhat away from the mainstream. This could possibly lead to new insights which have been missed by the more conventional mainstream approaches and could even finally provide a much awaited breakthrough. The collection of articles in this book should probably be viewed against such a backdrop. A few of the articles contained in the book deal with topics which are probably not mainstream. But all the speakers have presented their ideas clearly and in a proper setting, making many of the articles quite useful for a person who wants to obtain a bird's eye view. The connecting thread is essentially whether some aspects of quantum gravitational physics can lead to potentially observable effects or provide explanations for known effects. The book also contains a few overview articles of exceptional clarity. In particular I would like to mention the one by E Alvarez on quantum gravity, the one by L Smolin on loop quantum gravity and J Martin's article on the origin of cosmological perturbations. The rest of the articles are more focussed on possible quantum gravity phenomenology and discuss diverse topics such as astrophysical bounds of Lorentz violations, doubly special relativity and the role of quantum form in quantum gravity phenomenon. I thoroughly enjoyed reading
Warps and waves in the stellar discs of the Auriga cosmological simulations
NASA Astrophysics Data System (ADS)
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.
HEAVY DUST OBSCURATION OF z = 7 GALAXIES IN A COSMOLOGICAL HYDRODYNAMIC SIMULATION
Kimm, Taysun; Cen, Renyue
2013-10-10
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 × 10{sup 8}-3 × 10{sup 10} M{sub ☉} with three parameters: the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (f{sub 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 (A{sub V} ∼ 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.
On the dynamical state of galaxy clusters: insights from cosmological simulations - II.
NASA Astrophysics Data System (ADS)
Cui, Weiguang; Power, Chris; Borgani, Stefano; Knebe, Alexander; Lewis, Geraint F.; Murante, Giuseppe; Poole, Gregory B.
2017-01-01
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 (DM) run and their counterparts in hydro-runs and investigate four 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.
EMMA: an adaptive mesh refinement cosmological simulation code with radiative transfer
NASA Astrophysics Data System (ADS)
Aubert, Dominique; Deparis, Nicolas; Ocvirk, Pierre
2015-11-01
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 three-dimensional 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 has 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 processing units (GPUs) to accelerate hydrodynamics and radiative transfer calculations. Depending on the optimizations and the compilers used to generate the CPU reference, global GPU acceleration factors between ×3.9 and ×16.9 can be obtained. Vectorization and transfer operations currently prevent better GPU performance and we expect that future optimizations and hardware evolution will lead to greater accelerations.
NASA Astrophysics Data System (ADS)
Buck, Z.
2013-04-01
As we turn more and more to high-end computing to understand the Universe at cosmological scales, visualizations of simulations will take on a vital role as perceptual and cognitive tools. In collaboration with the Adler Planetarium and University of California High-Performance AstroComputing Center (UC-HiPACC), I am interested in better understanding the use of visualizations to mediate astronomy learning across formal and informal settings. The aspect of my research that I present here uses quantitative methods to investigate how learners are relying on color to interpret dark matter in a cosmology visualization. The concept of dark matter is vital to our current understanding of the Universe, and yet we do not know how to effectively present dark matter visually to support learning. I employ an alternative treatment post-test only experimental design, in which members of an equivalent sample are randomly assigned to one of three treatment groups, followed by treatment and a post-test. Results indicate significant correlation (p < .05) between the color of dark matter in the visualization and survey responses, implying that aesthetic variations like color can have a profound effect on audience interpretation of a cosmology visualization.
NASA Astrophysics Data System (ADS)
Gasperini, Maurizio
2011-03-01
Preface; Acknowledgements; Notation, units and conventions; 1. A short review of standard and inflationary cosmology; 2. The basic string cosmology equations; 3. Conformal invariance and string effective action; 4. Duality symmetries and cosmological solutions; 5. Inflationary kinematics; 6. The string phase; 7. The cosmic background of relic gravitational waves; 8. Scalar perturbations and the anisotropy of the CMB radiation; 9. Dilaton phenomenology; 10. Elements of brane cosmology; Index.
Testing SMBH scaling relations using cosmological simulations and optical/near-IR imaging data
NASA Astrophysics Data System (ADS)
Mutlu Pakdil, Burcin; Seigar, Marc S.; Davis, Benjamin L.; Treuthardt, Patrick M.; Berrier, Joel
2017-01-01
The strong correlation between supermassive black hole (SMBH) mass and a number of measurable features of the host galaxies has generated great interest in the notion that galaxy formation and SMBH growth are closely linked. My dissertation has focused primarily on the SMBH-host galaxy scaling relations and their implications for galaxy evolution. First, we use the statistically tightest correlations with SMBH mass, which are the Sersic index for early-type galaxies and pitch angle for spiral galaxies, to predict the SMBH masses in our volume-limited sample, and derive the SMBH mass function (BHMF), and quantify the SMBH space density in our local universe. I will present the observational simplicity of our approach to estimate the local BHMF through imaging data only as well as our BHMF estimate and its implications. Our result is as of a particular interest because it is derived from a nearly complete sample within set limits and provides reliable data, especially for the low-mass end of the local BHMF.Next, we study the data from Illustris simulation project, which is a large cosmological simulation of galaxy formation. This simulation provides a statistically large and representative sample of objects, and makes it possible to disentangle the physical link between black holes and their host galaxies. We derive the spiral arm morphology in the multi-wavelength, and test the theories of spiral structure in the simulated disk galaxies. We further study the Illustris prediction for the SMBH mass-spiral arm pitch angle relation and check if the result produces the slope and normalization of the observed SMBH mass-spiral arm pitch angle relation. A careful assessment of the agreement/disagreement with observations is the primary test of the physics implemented in the simulation. I will present our results from the Illustris spiral galaxies, and discuss the implications on which galaxy types are strongly physically linked with their central SMBHs and which are much
Stable clustering and the resolution of dissipationless cosmological N-body simulations
NASA Astrophysics Data System (ADS)
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.
Cosmological and wormhole solutions in low-energy effective string theory
Cadoni, M. INFN, Sezione di Cagliari, Via Ada Negri 18, I---09127 Cagliari ); Cavaglia, M. INFN, Sezione di Cagliari, Via Ada Negri 18, I-09127 Cagliari )
1994-11-15
We derive and study a class of cosmological and wormhole solutions of low-energy effective string field theory. We consider a general four-dimensional string effective action where moduli of the compactified manifold and the electromagnetic field are present. The cosmological solutions of the two-dimensional effective theory obtained by dimensional reduction of the former are discussed. In particular we demonstrate that the two-dimensional theory possesses a scale-factor duality invariance. Eucidean four-dimensional instantons describing the nucleation of the baby universes are found and the probability amplitude for the nucleation process given.
NASA Astrophysics Data System (ADS)
Narimani, Ali; Moss, Adam; Scott, Douglas
2012-10-01
Although it is well known that any consideration of the variations of fundamental constants should be restricted to their dimensionless combinations, the literature on variations of the gravitational constant G is entirely dimensionfull. To illustrate applications of this to cosmology, we explicitly give a dimensionless version of the parameters of the standard cosmological model, and describe the physics of both Big Bang Nucleosynthesis and recombination in a dimensionless manner. Rigorously determining how to talk about the model in a way which avoids physical dimensions is a requirement for proceeding with a calculation to constrain time-varying fundamental constants. The issue that appears to have been missed in many studies is that in cosmology the strength of gravity is bound up in the cosmological equations, and the epoch at which we live is a crucial part of the model. We argue that it is useful to consider the hypothetical situation of communicating with another civilization (with entirely different units), comparing only dimensionless constants, in order to decide if we live in a Universe governed by precisely the same physical laws. In this thought experiment, we would also have to compare epochs, which can be defined by giving the value of any one of the evolving cosmological parameters. By setting things up carefully in this way one can avoid inconsistent results when considering variable constants, caused by effectively fixing more than one parameter today. We show examples of this effect by considering microwave background anisotropies, being careful to maintain dimensionlessness throughout. We present Fisher matrix calculations to estimate how well the fine structure constants for electromagnetism and gravity can be determined with future microwave background experiments. We highlight how one can be misled by simply adding G to the usual cosmological parameter set.
Differentiating G-inflation from string gas cosmology using the effective field theory approach
NASA Astrophysics Data System (ADS)
He, Minxi; Liu, Junyu; Lu, Shiyun; Zhou, Siyi; Cai, Yi-Fu; Wang, Yi; Brandenberger, Robert
2016-12-01
A characteristic signature of String Gas Cosmology is primordial power spectra for scalar and tensor modes which are almost scale-invariant but with a red tilt for scalar modes but a blue tilt for tensor modes. This feature, however, can also be realized in the so-called G-inflation model, in which Horndeski operators are introduced which leads to a blue tensor tilt by softly breaking the Null Energy Condition. In this article we search for potential observational differences between these two cosmologies by performing detailed perturbation analyses based on the Effective Field Theory approach. Our results show that, although both two models produce blue tilted tensor perturbations, they behave differently in three aspects. Firstly, String Gas Cosmology predicts a specific consistency relation between the index of the scalar modes ns and that of tensor ones nt, which is hard to be reproduced by G-inflation. Secondly, String Gas Cosmology typically predicts non-Gaussianities which are highly suppressed on observable scales, while G-inflation gives rise to observationally large non-Gaussianities because the kinetic terms in the action become important during inflation. However, after finely tuning the model parameters of G-inflation it is possible to obtain a blue tensor spectrum and negligible non-Gaussianities with a degeneracy between the two models. This degeneracy can be broken by a third observable, namely the scale dependence of the nonlinearity parameter, which vanishes for G-inflation but has a blue tilt in the case of String Gas Cosmology. Therefore, we conclude that String Gas Cosmology is in principle observationally distinguishable from the single field inflationary cosmology, even allowing for modifications such as G-inflation.
Cross Correlation between Ly-break Galaxies and Damped Lyα Systems in Cosmological SPH Simulations
NASA Astrophysics Data System (ADS)
Lee, Tae Song; Nagamine, K.
2007-12-01
We calculate the cross-correlation function (CCF) between damped Ly-α systems (DLAs) and Lyman break galaxies (LBGs) using cosmological hydrodynamic simulations at z=3. We compute the CCF in two different methods. First, we assume that there is one DLA in each dark matter halo. Second approach is the cross-section-weighted CCF using the direct simulation result of DLA cross section for each halo. We find that the cross-section-weighted CCF gives a steeper γ than the unweighted one, and agrees well with the result of Cooke et al. (2006). Finally, we compute angular CCF for direct comparison with observations.
NASA Astrophysics Data System (ADS)
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.
Modeling effective FRW cosmologies with perfect fluids from states of the hybrid quantum Gowdy model
NASA Astrophysics Data System (ADS)
Elizaga Navascués, Beatriz; Martín-Benito, Mercedes; Mena Marugán, Guillermo A.
2015-01-01
We employ recently developed approximation methods in the hybrid quantization of the Gowdy T3 model with linear polarization and a massless scalar field to obtain physically interesting solutions of this inhomogeneous cosmology. More specifically, we propose some particular approximate solutions of the quantum Gowdy model constructed in such a way that, for the Hamiltonian constraint, they effectively behave as those corresponding to a flat homogeneous and isotropic universe filled with a perfect fluid, even though these quantum states are far from being homogeneous and isotropic. We analyze how one can get different perfect fluid effective behaviors, including the cases of dust, radiation, and a cosmological constant.
Effect of Self-Calibration of Intrinsic Alignment on the Cosmological Parameter Constraints for LSST
NASA Astrophysics Data System (ADS)
Yao, Ji; Ishak, Mustapha; Troxel, Michael A.; Lin, Weikang
2017-01-01
Weak gravitational lensing (WL) is a powerful cosmological probe, however it is contaminated by the Intrinsic Alignment (IA) signal. The IA signal is now one of the major systematics in the present and future WL surveys. It can affect the lensing power spectrum at ~10% level and cause a misestimation of the cosmological parameters, especially in the dark energy equation of state where the misestimation can be up to 50% and the amplitude of matter power spectrum by up to 30% . The Self-Calibration (SC) technique has been introduced to subtract the shear intrinsic (GI) IA contamination in a photometric redshift (photo-z) survey, at a level of ~90%. In this work, we present a forecast analysis on the effect of using Self-Calibration to subtract the IA signal for an LSST like survey. We show the effect of constraining contours of cosmological parameters using the IA Self-Calibration.
Martel, Hugo; Barai, Paramita; Brito, William
2012-09-20
We combine an N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function {Phi}(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc){sup 3}, in a concordance {Lambda}CDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light (ICL). We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce ICL fractions f{sub ICL} that are sufficiently high to match observations. Our simulation produces 18 massive clusters (M{sub cl} > 10{sup 14} M{sub Sun }) with values of f{sub ICL} ranging from 1% to 58% at z = 0. There is a weak trend of f{sub ICL} to increase with cluster mass. The bulk of the ICL ({approx}60%) is provided by intermediate galaxies of total masses 10{sup 11}-10{sup 12} M{sub Sun} and stellar masses 6 Multiplication-Sign 10{sup 8} M{sub Sun} to 3 Multiplication-Sign 10{sup 10} M{sub Sun} that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the ICL is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f{sub ICL} tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the ICL is more centrally concentrated than the galactic light. Our results
A novel approach for accurate radiative transfer in cosmological hydrodynamic simulations
NASA Astrophysics Data System (ADS)
Petkova, Margarita; Springel, Volker
2011-08-01
accurately deal with non-equilibrium effects. We discuss several tests of the new method, including shadowing configurations in two and three dimensions, ionized sphere expansion in static and dynamic density fields and the ionization of a cosmological density field. The tests agree favourably with analytical expectations and results based on other numerical radiative transfer approximations.
Star cluster formation in cosmological simulations. I. Properties of young clusters
Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; ...
2017-01-03
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 ismore » $$\\alpha \\approx 1.8\\mbox{–}2$$, 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. As a result, 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.« less
FAR-INFRARED PROPERTIES OF LYMAN BREAK GALAXIES FROM COSMOLOGICAL SIMULATIONS
Cen Renyue
2011-12-15
Utilizing state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations with ultra-high resolution (114 h{sup -1} pc) and a large sample size ({>=}3300 galaxies of stellar mass {>=}10{sup 9} M{sub Sun }), we show how the stellar light of Lyman break galaxies at z = 2 is distributed between optical/ultraviolet (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 M{sub Sun} yr{sup -1}) and extant FIR luminosity function at the bright end ({>=}20 M{sub Sun} yr{sup -1}). We quantify that galaxies more massive or having higher star formation rate (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 = 1-100 M{sub Sun} yr{sup -1} is a power law with a slope of about -1.7. We further predict that there is a 'galaxy desert' at SFR{sub FIR} < 0.02(SFR{sub UV}/10 M{sub Sun} yr{sup -1}){sup 2.1} M{sub Sun} yr{sup -1} in the SFR{sub UV} - SFR{sub FIR} plane. Detailed distributions of SFR{sub FIR} at a fixed SFR{sub UV} are presented. Upcoming observations by the Atacama Large Millimeter Array should test this model. If confirmed, it validates the predictions of the standard cold dark matter model and has important implications on the intrinsic SFR function of galaxies at high redshift.
Early black holes in cosmological simulations: luminosity functions and clustering behaviour
NASA Astrophysics Data System (ADS)
DeGraf, Colin; Di Matteo, Tiziana; Khandai, Nishikanta; Croft, Rupert; Lopez, Julio; Springel, Volker
2012-08-01
We examine predictions for the quasar luminosity functions (QLFs) and quasar clustering at high redshift (z ≥ 4.75) using MassiveBlack, our new hydrodynamic cosmological simulation which includes a self-consistent model for black hole (BH) growth and feedback. We show that the model reproduces the Sloan QLF within observational constraints at z ≥ 5. We find that the high-z QLF is consistent with a redshift-independent occupation distribution of BHs among dark matter haloes (which we provide) such that the evolution of the QLF follows that of the halo mass function. The sole exception is the bright end at z = 6 and 7, where BHs in high-mass haloes tend to be unusually bright due to extended periods of Eddington growth caused by high-density cold flows into the halo centre. We further use these luminosity functions to make predictions for the number density of quasars in upcoming surveys, predicting that there should be ˜119 ± 28 (˜87 ± 28) quasars detectable in the F125W band of the WIDE (DEEP) fields of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) from z = 5 to 6, ˜19 ± 7 (˜18 ± 9) from z = 6 to 7 and ˜1.7 ± 1.5 (˜1.5 ± 1.5) from z = 7 to 8. We also investigate quasar clustering, finding that the correlation length is fully consistent with current constraints for Sloan quasars (r0 ˜ 17 h-1 Mpc at z = 4 for quasars above mi = 20.2) and grows slowly with redshift up to z = 6 (r0 ˜ 22 h-1 Mpc). Finally, we note that the quasar clustering strength depends weakly on luminosity for low LBH, but gets stronger at higher LBH as the BHs are found in higher mass haloes.
Compaction and quenching of high-z galaxies in cosmological simulations: blue and red nuggets
NASA Astrophysics Data System (ADS)
Zolotov, Adi; Dekel, Avishai; Mandelker, Nir; Tweed, Dylan; Inoue, Shigeki; DeGraf, Colin; Ceverino, Daniel; Primack, Joel R.; Barro, Guillermo; Faber, Sandra M.
2015-07-01
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 (Σ1). Massive galaxies quench earlier, faster, and at a higher Σ1 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-size-mass space, and with gradients and scatter across the main sequence. The compaction is triggered by an intense inflow episode, involving (mostly minor) mergers, counter-rotating streams or recycled gas, and is commonly associated with violent disc instability. The contraction is dissipative, with the inflow rate >SFR, and the maximum Σ1 anticorrelated with the initial spin parameter. The central quenching is triggered by the high SFR and stellar/supernova feedback (maybe also active galactic nucleus feedback) due to the high central gas density, while the central inflow weakens as the disc vanishes. Suppression of fresh gas supply by a hot halo allows the long-term maintenance of quenching once above a threshold halo mass, inducing the quenching downsizing.
Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; Mojahedi, Mojtaba Amir
2017-05-01
The aim of the paper is to study weak gravitational lensing of quantum (perturbed) and classical lukewarm black holes (QLBHs and CLBHs respectively) in the presence of cosmological parameter Λ. We apply a numerical method to evaluate the deflection angle of bending light rays, image locations θ of sample source β =-\\tfrac{π }{4}, and corresponding magnifications μ. There are no obtained real values for Einstein ring locations {θ }E(β =0) for CLBHs but we calculate them for QLBHs. As an experimental test of our calculations, we choose mass M of 60 types of the most massive observed galactic black holes acting as a gravitational lens and study quantum matter field effects on the angle of bending light rays in the presence of cosmological constant effects. We calculate locations of non-relativistic images and corresponding magnifications. Numerical diagrams show that the quantum matter effects cause absolute values of the quantum deflection angle to be reduced with respect to the classical ones. The sign of the quantum deflection angle is changed with respect to the classical values in the presence of the cosmological constant. This means dominance of the anti-gravity counterpart of the cosmological horizon on the angle of bending light rays with respect to absorbing effects of 60 local types of the most massive observed black holes. Variations of the image positions and magnifications are negligible when increasing dimensionless cosmological constant ɛ =\\tfrac{16{{Λ }}{M}2}{3}. The deflection angle takes positive (negative) values for CLBHs (QLBHs) and they decrease very fast (slowly) by increasing the closest distance x 0 of bending light ray and/or dimensionless cosmological parameter for sample giant black holes with 0.001< ɛ < 0.01.
Gauss-Bonnet braneworld cosmological effect on relic density of dark matter
Okada, Nobuchika; Okada, Satomi
2009-05-15
In Gauss-Bonnet braneworld cosmology, the Friedmann equation of our four-dimensional Universe on 3-brane is modified in a high energy regime (Gauss-Bonnet regime), while the standard expansion law is reproduced in low energies (standard regime). We investigate the Gauss-Bonnet braneworld cosmological effect on the thermal relic density of cold dark matter when the freeze-out of the dark matter occurs in the Gauss-Bonnet regime. We find that the resultant relic density is considerably reduced when the transition temperature, which connects the Gauss-Bonnet regime with the standard regime, is low enough. This result is in sharp contrast with the result previously obtained in the Randall-Sundrum braneworld cosmology, where the relic density is enhanced.
Cen, Renyue
2014-01-20
An analysis of more than 3000 galaxies resolved at better than 114 h{sup –1} pc at z = 0.62 in a 'LAOZI' cosmological adaptive mesh refinement hydrodynamic simulation is performed and insights are gained on star formation 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, when the specific star formation rate experiences the sharpest decline to fall below ∼10{sup –2}-10{sup –1} Gyr{sup –1} (depending on the redshift). Thus, we shall 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 a high velocity-dispersion environment, in which during the early part of the process, the existing dense cold gas in the central region (≤10 kpc) is consumed by in situ star formation. On average, quenching is found to be more efficient (i.e., a larger fraction of galaxies being quenched) but not faster (i.e., the duration being weakly dependent on the environment) in a denser environment. Throughout this quenching period and the ensuing one in the red sequence, galaxies follow nearly vertical tracks in the color-stellar mass diagram. In contrast, individual galaxies of all masses grow most of their stellar masses in the blue cloud, prior to the onset of quenching, and progressively more massive blue galaxies with already relatively older mean stellar ages continue to enter the red sequence. Consequently, correlations among observables of red galaxies—such as the age-mass relation— are largely inherited from their blue progenitors at the onset of quenching. While the color makeup of the entire galaxy population strongly depends on the environment, which is a direct result of environment quenching, physical properties of blue
Adaptive Mesh Refinement Cosmological Simulations of Cosmic Rays in Galaxy Clusters
NASA Astrophysics Data System (ADS)
Skillman, Samuel William
2013-12-01
Galaxy clusters are unique astrophysical laboratories that contain many thermal and non-thermal phenomena. In particular, they are hosts to cosmic shocks, which propagate through the intracluster medium as a by-product of structure formation. It is believed that at these shock fronts, magnetic field inhomogeneities in a compressing flow may lead to the acceleration of cosmic ray electrons and ions. These relativistic particles decay and radiate through a variety of mechanisms, and have observational signatures in radio, hard X-ray, and Gamma-ray wavelengths. We begin this dissertation by developing a method to find shocks in cosmological adaptive mesh refinement simulations of structure formation. After describing the evolution of shock properties through cosmic time, we make estimates for the amount of kinetic energy processed and the total number of cosmic ray protons that could be accelerated at these shocks. We then use this method of shock finding and a model for the acceleration of and radio synchrotron emission from cosmic ray electrons to estimate the radio emission properties in large scale structures. By examining the time-evolution of the radio emission with respect to the X-ray emission during a galaxy cluster merger, we find that the relative timing of the enhancements in each are important consequences of the shock dynamics. By calculating the radio emission expected from a given mass galaxy cluster, we make estimates for future large-area radio surveys. Next, we use a state-of-the-art magnetohydrodynamic simulation to follow the electron acceleration in a massive merging galaxy cluster. We use the magnetic field information to calculate not only the total radio emission, but also create radio polarization maps that are compared to recent observations. We find that we can naturally reproduce Mpc-scale radio emission that resemble many of the known double radio relic systems. Finally, motivated by our previous studies, we develop and introduce a
NASA Astrophysics Data System (ADS)
Chamcham, Khalil; Silk, Joseph; Barrow, John D.; Saunders, Simon
2017-04-01
Part I. Issues in the Philosophy of Cosmology: 1. Cosmology, cosmologia and the testing of cosmological theories George F. R. Ellis; 2. Black holes, cosmology and the passage of time: three problems at the limits of science Bernard Carr; 3. Moving boundaries? – comments on the relationship between philosophy and cosmology Claus Beisbart; 4. On the question why there exists something rather than nothing Roderich Tumulka; Part II. Structures in the Universe and the Structure of Modern Cosmology: 5. Some generalities about generality John D. Barrow; 6. Emergent structures of effective field theories Jean-Philippe Uzan; 7. Cosmological structure formation Joel R. Primack; 8. Formation of galaxies Joseph Silk; Part III. Foundations of Cosmology: Gravity and the Quantum: 9. The observer strikes back James Hartle and Thomas Hertog; 10. Testing inflation Chris Smeenk; 11. Why Boltzmann brains do not fluctuate into existence from the de Sitter vacuum Kimberly K. Boddy, Sean M. Carroll and Jason Pollack; 12. Holographic inflation revised Tom Banks; 13. Progress and gravity: overcoming divisions between general relativity and particle physics and between physics and HPS J. Brian Pitts; Part IV. Quantum Foundations and Quantum Gravity: 14. Is time's arrow perspectival? Carlo Rovelli; 15. Relational quantum cosmology Francesca Vidotto; 16. Cosmological ontology and epistemology Don N. Page; 17. Quantum origin of cosmological structure and dynamical reduction theories Daniel Sudarsky; 18. Towards a novel approach to semi-classical gravity Ward Struyve; Part V. Methodological and Philosophical Issues: 19. Limits of time in cosmology Svend E. Rugh and Henrik Zinkernagel; 20. Self-locating priors and cosmological measures Cian Dorr and Frank Arntzenius; 21. On probability and cosmology: inference beyond data? Martin Sahlén; 22. Testing the multiverse: Bayes, fine-tuning and typicality Luke A. Barnes; 23. A new perspective on Einstein's philosophy of cosmology Cormac O
Effects of the cosmological constant on cold dark matter clusters
NASA Astrophysics Data System (ADS)
Membrado, M.; Pacheco, A. F.
2014-07-01
Context. Cold dark matter inhomogeneities are considered in a homogeneous background of matter, radiation, and the cosmological constant in a flat universe. Aims: We investigate the influence of the cosmological constant on the non-linear collapse of cold dark matter clusters. Methods: For simplicity, a spherical infall model has been used to describe the collapse of non-relativistic mass shells; besides, an average distribution of density around a cluster of galaxies has been taken. Boundary conditions are imposed by the solution of the linearized equation for the growth of matter perturbations and by the cold dark matter power spectrum. Results: For an average cluster, the radii of shells and masses enclosed by them have been obtained at their zero proper acceleration (ZA) redshifts, at their turn-around (TA) redshifts and at their virialization (VIR) redshifts. According to our results at present, the shell that reaches its turn-around point shows [rTA] 0 = 6.85 Mpc and [ℳTA] 0 = 6.76 × 1014 ℳ⊙. The virializing shell fulfills [rTA] 0 = 4.57 [rVIR] 0 and [ℳTA] 0 = 1.95 [ℳVIR] 0. These results differ appreciably from those derived from a model with cosmological constant equal to zero in a flat universe: [rTA(Λ = 0)] 0 = 6.62 [rVIR(Λ = 0)] 0 and [ℳTA(Λ = 0)] 0 = 5.26 [ℳVIR(Λ = 0)] 0; this discrepancy could be considered as a new independent proof of the existence of dark energy. The shell with zero proper acceleration presents [rZA] 0 = 1.59 [rTA] 0 and [ℳZA] 0 = 1.63 [ℳTA] 0. We have found that there is a limit to the mass of the average cluster, which is able to virialize; its value is { ℳVIR } MAX = 8.1 × 1014 M⊙. As expected, we found that shells present null proper acceleration at redshift values that are smaller than 0.755. Conclusions: We have noticed that the cosmological constant imposes an upper limit for the mass enclosed by shells, which are able to reach zero proper velocity. Hence, this mass is the maximum mass of the
Effect of Shear and Bulk Viscosities on Interacting Modified Chaplygin Gas Cosmology
NASA Astrophysics Data System (ADS)
Naji, J.; Pourhassan, B.; Amani, Ali R.
2014-12-01
In this paper, we study interacting modified Chaplygin gas (MCG) which has shear and bulk viscosities. We consider sign-changeable interaction between MCG and matter, then investigate the effects of shear and bulk viscosities on the cosmological parameters such as energy, density, Hubble expansion parameter, scale factor and deceleration parameter.
Cosmological non-linearities as an effective fluid
Baumann, Daniel; Senatore, Leonardo; Zaldarriaga, Matias; Nicolis, Alberto E-mail: nicolis@phys.columbia.edu E-mail: matiasz@ias.edu
2012-07-01
The universe is smooth on large scales but very inhomogeneous on small scales. Why is the spacetime on large scales modeled to a good approximation by the Friedmann equations? Are we sure that small-scale non-linearities do not induce a large backreaction? Related to this, what is the effective theory that describes the universe on large scales? In this paper we make progress in addressing these questions. We show that the effective theory for the long-wavelength universe behaves as a viscous fluid coupled to gravity: integrating out short-wavelength perturbations renormalizes the homogeneous background and introduces dissipative dynamics into the evolution of long-wavelength perturbations. The effective fluid has small perturbations and is characterized by a few parameters like an equation of state, a sound speed and a viscosity parameter. These parameters can be matched to numerical simulations or fitted from observations. We find that the backreaction of small-scale non-linearities is very small, being suppressed by the large hierarchy between the scale of non-linearities and the horizon scale. The effective pressure of the fluid is always positive and much too small to significantly affect the background evolution. Moreover, we prove that virialized scales decouple completely from the large-scale dynamics, at all orders in the post-Newtonian expansion. We propose that our effective theory be used to formulate a well-defined and controlled alternative to conventional perturbation theory, and we discuss possible observational applications. Finally, our way of reformulating results in second-order perturbation theory in terms of a long-wavelength effective fluid provides the opportunity to understand non-linear effects in a simple and physically intuitive way.
Eingorn, Maxim; Brilenkov, Maxim; Vlahovic, Branislav
We point out a weak side of the commonly used determination of scalar cosmological perturbations lying in the fact that their average values can be nonzero for some matter distributions. It is shown that introduction of the finite-range gravitational potential instead of the infinite-range one resolves this problem. The concrete illustrative density profile is investigated in detail in this connection.
NASA Astrophysics Data System (ADS)
Kulier, Andrea; Ostriker, Jeremiah P.; Natarajan, Priyamvada; Lackner, Claire N.; Cen, Renyue
2015-02-01
Accretion is thought to primarily contribute to the mass accumulation history of supermassive black holes (SMBHs) throughout cosmic time. While this may be true at high redshifts, at lower redshifts and for the most massive black holes (BHs) mergers themselves might add significantly to the mass budget. We explore this in two disparate environments—a massive cluster and a void region. We evolve SMBHs from 4 > z > 0 using merger trees derived from hydrodynamical cosmological simulations of these two regions, scaled to the observed value of the stellar mass fraction to account for overcooling. Mass gains from gas accretion proportional to bulge growth and BH-BH mergers are tracked, as are BHs that remain "orbiting" due to insufficient dynamical friction in a merger remnant, as well as those that are ejected due to gravitational recoil. We find that gas accretion remains the dominant source of mass accumulation in almost all SMBHs; mergers contribute 2.5% ± 0.1% for all SMBHs in the cluster and 1.0% ± 0.1% in the void since z = 4. However, mergers are significant for massive SMBHs. The fraction of mass accumulated from mergers for central BHs generally increases for larger values of the host bulge mass: in the void, the fraction is 2% at M *, bul = 1010 M ⊙, increasing to 4% at M *, bul >~ 1011 M ⊙, and in the cluster it is 4% at M *, bul = 1010 M ⊙ and 23% at 1012 M ⊙. We also find that the total mass in orbiting SMBHs is negligible in the void, but significant in the cluster, in which a potentially detectable 40% of SMBHs and ≈8% of the total SMBH mass (where the total includes central, orbiting, and ejected SMBHs) is found orbiting at z = 0. The existence of orbiting and ejected SMBHs requires modification of the Soltan argument. We estimate this correction to the integrated accreted mass density of SMBHs to be in the range 6%-21%, with a mean value of 11% ± 3%. Quantifying the growth due to mergers at these late times, we calculate the total energy
Kulier, Andrea; Ostriker, Jeremiah P.; Lackner, Claire N.; Cen, Renyue; Natarajan, Priyamvada
2015-02-01
Accretion is thought to primarily contribute to the mass accumulation history of supermassive black holes (SMBHs) throughout cosmic time. While this may be true at high redshifts, at lower redshifts and for the most massive black holes (BHs) mergers themselves might add significantly to the mass budget. We explore this in two disparate environments—a massive cluster and a void region. We evolve SMBHs from 4 > z > 0 using merger trees derived from hydrodynamical cosmological simulations of these two regions, scaled to the observed value of the stellar mass fraction to account for overcooling. Mass gains from gas accretion proportional to bulge growth and BH-BH mergers are tracked, as are BHs that remain ''orbiting'' due to insufficient dynamical friction in a merger remnant, as well as those that are ejected due to gravitational recoil. We find that gas accretion remains the dominant source of mass accumulation in almost all SMBHs; mergers contribute 2.5% ± 0.1% for all SMBHs in the cluster and 1.0% ± 0.1% in the void since z = 4. However, mergers are significant for massive SMBHs. The fraction of mass accumulated from mergers for central BHs generally increases for larger values of the host bulge mass: in the void, the fraction is 2% at M {sub *,} {sub bul} = 10{sup 10} M {sub ☉}, increasing to 4% at M {sub *,} {sub bul} ≳ 10{sup 11} M {sub ☉}, and in the cluster it is 4% at M {sub *,} {sub bul} = 10{sup 10} M {sub ☉} and 23% at 10{sup 12} M {sub ☉}. We also find that the total mass in orbiting SMBHs is negligible in the void, but significant in the cluster, in which a potentially detectable 40% of SMBHs and ≈8% of the total SMBH mass (where the total includes central, orbiting, and ejected SMBHs) is found orbiting at z = 0. The existence of orbiting and ejected SMBHs requires modification of the Soltan argument. We estimate this correction to the integrated accreted mass density of SMBHs to be in the range 6%-21%, with a mean value of 11% ± 3
Laniakea in a Cosmological Context
NASA Astrophysics Data System (ADS)
Hernandez-Charpak, S. D.; Forero-Romero, J. E.
2017-07-01
Laniakea, our local supercluster, was defined by recent observationa of the local cosmic flow. In this work we present a study on large cosmological N-body simulations aimed at establishing the significance of Laniakea in a cosmological context. We find that superclusters similar in size and structure to Laniakea are relatively uncommon on a broader cosmological context.
Concordance cosmology without dark energy
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Vavagiakis, Eve Marie; De Bernardis, Francesco; Aiola, Simone; Battaglia, Nicholas; Niemack, Michael D.; ACTPol Collaboration
2017-06-01
We have made improved measurements of the kinematic Sunyaev-Zel’dovich (kSZ) effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). We used a map of the Cosmic Microwave Background (CMB) from two seasons of observations each by ACT and the Atacama Cosmology Telescope Polarimeter (ACTPol) receiver. We evaluated the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog via 600 square degrees of overlapping sky area. The measurement of the kSZ signal arising from the large-scale motions of clusters was made by fitting data to an analytical model. The free parameter of the fit determined the optical depth to microwave photon scattering for the cluster sample. We estimated the covariance matrix of the mean pairwise momentum as a function of galaxy separation using CMB simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based uncertainties gave signal-to-noise estimates between 3.6 and 4.1 for various luminosity cuts. Additionally, we explored a novel approach to estimating cluster optical depths from the average thermal Sunyaev-Zel’dovich (tSZ) signal at the BOSS DR11 catalog positions. Our results were broadly consistent with those obtained from the kSZ signal. In the future, the tSZ signal may provide a valuable probe of cluster optical depths, enabling the extraction of velocities from the kSZ sourced mean pairwise momenta. New CMB maps from three seasons of ACTPol observations with multi-frequency coverage overlap with nearly four times as many DR11 sources and promise to improve statistics and systematics for SZ measurements. With these and other upcoming data, the pairwise kSZ signal is poised to become a powerful new cosmological tool, able to probe large physical scales to inform neutrino physics and test models of modified gravity and dark energy.
NASA Astrophysics Data System (ADS)
Viaggiu, Stefano
2016-07-01
In this paper we present a statistical description of the cosmological constant in terms of massless bosons (gravitons). To this purpose, we use our recent results implying a non vanishing temperature {T_{Λ }} for the cosmological constant. In particular, we found that a non vanishing T_{Λ } allows us to depict the cosmological constant Λ as composed of elementary oscillations of massless bosons of energy hbar ω by means of the Bose-Einstein distribution. In this context, as happens for photons in a medium, the effective phase velocity v_g of these massless excitations is not given by the speed of light c but it is suppressed by a factor depending on the number of quanta present in the universe at the apparent horizon. We found interesting formulas relating the cosmological constant, the number of quanta N and the mean value overline{λ } of the wavelength of the gravitons. In this context, we study the possibility to look to the gravitons system so obtained as being very near to be a Bose-Einstein condensate. Finally, an attempt is done to write down the Friedmann flat equations in terms of N and overline{λ }.
Testing supernova cosmology and progenitor effects with the SDSS-II supernova survey
NASA Astrophysics Data System (ADS)
D'Andrea, Christopher Brian
The study of Type Ia Supernovae, the brilliant explosions of White Dwarfs, has ushered in a new era of observational Cosmology, one in which we have learned that the Universe is not only expanding, but accelerating in its expansion. For further advances to be made in the the field of Supernova Cosmology, future planned surveys will have to understand the systematic differences in these explosions. We use the full 3-year observational data from the Sloan Digital Sky Survey - II Supernova Survey to explore this field. First, we show that the environment a Type Ia Supernova occurs in biases the distance modulus at which current algorithms place them, resulting in a systematic error in derived cosmological parameters. We then investigate the ability Type II-P Supernovae to be used as complements to their brighter cousins as cosmological distance indicators, subject to different progenitor effects and thus different sources of uncertainty. Finally we quantify the diversity in Type II-P Supernovae themselves and the relationship the environment has on their observational properties, and the propensity this might have for biasing distance measurements with these objects.
The influence of environment on the HI mass functions in cosmological simulations
NASA Astrophysics Data System (ADS)
Prada-Gonzalez, J. D.; Jones, M. G.; Forero-Romero, J. E.; Haynes, M. P.
2017-07-01
We use the Illustris simulation to study the effect of environment on gas mass functions. We find that the knee-mass parameter changes in different environment. while the low mass slope does not show any clear change. These results in agreement with previous results by Jones et al.
Precision cosmology, Accuracy cosmology and Statistical cosmology
NASA Astrophysics Data System (ADS)
Verde, Licia
2014-05-01
The avalanche of data over the past 10-20 years has propelled cosmology into the ``precision era''. The next challenge cosmology has to meet is to enter the era of accuracy. Because of the intrinsic nature of studying the Cosmos and the sheer amount of data available now and coming soon, the only way to meet this challenge is by developing suitable and specific statistical techniques. The road from precision Cosmology to accurate Cosmology goes through statistical Cosmology. I will outline some open challenges and discuss some specific examples.
Cosmology in the Bucharest Observatory
NASA Astrophysics Data System (ADS)
Suran, Marian Doru
2008-09-01
At the Bucharest Observatory cosmology started in the early'80s as a theoretical branch directly related to the computational facilities available in our Observatory. With the help of our instruments, from a small Z8080 computer (early'80s) to a superscalar supercomputer of 44 processors (now), our cosmology team has developed models, methods and techniques related to: the investigation of 2D and 3D catalogues of galaxies, clusters and superclusters; investigation of the log tails of the 2-points correlation functions; cosmological simulations (N-body+SPH) of the Large Scale Structure of the Universe (LSS) investigation of environmental effects in clusters of galaxies; application of neural methods in cosmology. The use of such models and techniques has permitted us to study problems concerning: correlated signals in the long tail of the correlation functions for galaxies, clusters and superclusters (due to baryon oscillations) HD simulations of the LSS and of the evolution of the first and secondary Web structures; studies of the epochs of the formation of DM halos in a LCDM scenario (earlier than z 15) studies of the evolution of halos and galaxies due to the parental merging phenomena; detection of the Butcher-Oemler and Oemler-Butcher effects in far or close clusters; studies of E+A galaxies; study of the synthetic spectra of galaxies and of the chemo-spectro-photometrical evolution of galaxies (for z<30) photometric redshift determination (for z<10).
NASA Astrophysics Data System (ADS)
Enea Romano, Antonio; Sanes Negrete, Sergio; Sasaki, Misao; Starobinsky, Alexei A.
2014-06-01
We study effects on the luminosity distance of a local inhomogeneity seeded by primordial curvature perturbations of the type predicted by the inflationary scenario and constrained by the cosmic microwave background radiation. We find that a local underdensity originated from a one, two or three standard deviations peaks of the primordial curvature perturbations field can induce corrections to the value of a cosmological constant of the order of 0.6{%},1{%},1.5{%} , respectively. These effects cannot be neglected in the precision cosmology era in which we are entering. Our results can be considered an upper bound for the effect of the monopole component of the local non-linear structure which can arise from primordial curvature perturbations and requires a fully non-perturbative relativistic treatment.
Wong, Yvonne Y. Y.
2008-01-24
I give an overview of the effects of neutrinos on cosmology, focussing in particular on the role played by neutrinos in the evolution of cosmological perturbations. I discuss how recent observations of the cosmic microwave background and the large-scale structure of galaxies can probe neutrino masses with greater precision than current laboratory experiments. I describe several new techniques that will be used to probe cosmology in the future.
NASA Astrophysics Data System (ADS)
Feldmann, Robert; Mayer, Lucio
2015-01-01
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, hydrodynamical zoom-in simulation that follows the evolution of a massive galaxy at z ≥ 2. This simulation adopts the same subgrid recipes of the Eris simulations, which have been shown to form realistic disc 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* ˜ 1011 M⊙) galaxies at z ˜ 2 and with abundance matching predictions. Our models do not include active galactic nuclei (AGN) feedback indicating that supermassive black holes likely play a subordinate role in determining masses and sizes of massive galaxies at high-z. The specific star formation rate (sSFR) of the simulated galaxy matches the observed M*-sSFR relation at early times. This period of smooth stellar mass growth comes to a sudden halt at z = 3.5 when the sSFR drops by almost an order of magnitude within a few hundred Myr. The suppression is initiated by a levelling off and a subsequent reduction of the cool gas accretion rate on to the galaxy, and not by feedback processes. This `cosmological starvation' occurs as the parent dark matter halo switches from a fast collapsing mode to a slow accretion mode. Additional mechanisms, such as perhaps radio mode feedback from an AGN, are needed to quench any residual star formation of the galaxy and to maintain a low sSFR until the present time.
Inhomogeneous cosmology with numerical relativity
NASA Astrophysics Data System (ADS)
Macpherson, Hayley J.; Lasky, Paul D.; Price, Daniel J.
2017-03-01
We perform three-dimensional numerical relativity simulations of homogeneous and inhomogeneous expanding spacetimes, with a view toward quantifying nonlinear effects from cosmological inhomogeneities. We demonstrate fourth-order convergence with errors less than one part in 1 06 in evolving a flat, dust Friedmann-Lemaître-Roberston-Walker spacetime using the Einstein Toolkit within the Cactus framework. We also demonstrate agreement to within one part in 1 03 between the numerical relativity solution and the linear solution for density, velocity and metric perturbations in the Hubble flow over a factor of ˜350 change in scale factor (redshift). We simulate the growth of linear perturbations into the nonlinear regime, where effects such as gravitational slip and tensor perturbations appear. We therefore show that numerical relativity is a viable tool for investigating nonlinear effects in cosmology.
Conducting Effective Simulator Training.
ERIC Educational Resources Information Center
Gerling, Kenneth D.
This paper describes the simulator phase of Commonwealth Edison's program for training and licensing operators of nuclear power stations. Topics covered include (1) preparing the students before starting the simulator phase; (2) the simulator schedule and the number of students that can be trained effectively in a class; (3) format and structure…
Non-singular bounce scenarios in loop quantum cosmology and the effective field description
Cai, Yi-Fu; Wilson-Ewing, Edward E-mail: wilson-ewing@phys.lsu.edu
2014-03-01
A non-singular bouncing cosmology is generically obtained in loop quantum cosmology due to non-perturbative quantum gravity effects. A similar picture can be achieved in standard general relativity in the presence of a scalar field with a non-standard kinetic term such that at high energy densities the field evolves into a ghost condensate and causes a non-singular bounce. During the bouncing phase, the perturbations can be stabilized by introducing a Horndeski operator. Taking the matter content to be a dust field and an ekpyrotic scalar field, we compare the dynamics in loop quantum cosmology and in a non-singular bouncing effective field model with a non-standard kinetic term at both the background and perturbative levels. We find that these two settings share many important properties, including the result that they both generate scale-invariant scalar perturbations. This shows that some quantum gravity effects of the very early universe may be mimicked by effective field models.
NASA Astrophysics Data System (ADS)
López-Corredoira, M.
2009-08-01
Certain results of observational cosmology cast critical doubt on the foundations of standard cosmology but leave most cosmologists untroubled. Alternative cosmological models that differ from the Big Bang have been published and defended by heterodox scientists; however, most cosmologists do not heed these. This may be because standard theory is correct and all other ideas and criticisms are incorrect, but it is also to a great extent due to sociological phenomena such as the ``snowball effect'' or ``groupthink''. We might wonder whether cosmology, the study of the Universe as a whole, is a science like other branches of physics or just a dominant ideology.
Cosmology and neutrino properties
Dolgov, A. D.
2008-12-15
A brief review for particle physicists on the cosmological impact of neutrinos and on restrictions on neutrino properties from cosmology is given. The paper includes a discussion of upper bounds on neutrino mass and possible ways to relax them, methods to observe the cosmic-neutrino background, bounds on the cosmological lepton asymmetry which are strongly improved by neutrino oscillations, cosmological effects of breaking of the spin-statistics theorem for neutrinos, bounds on mixing parameters of active and possible sterile neutrinos with account of active-neutrino oscillations, bounds on right-handed currents and neutrino magnetic moments, and some more.
NASA Astrophysics Data System (ADS)
Cui, Weiguang; Power, Chris; Biffi, Veronica; Borgani, Stefano; Murante, Giuseppe; Fabjan, Dunja; Knebe, Alexander; Lewis, Geraint F.; Poole, Greg B.
2016-03-01
Galaxy clusters are an established and powerful test-bed for theories of both galaxy evolution and cosmology. Accurate interpretation of cluster observations often requires robust identification of the location of the centre. Using a statistical sample of clusters drawn from a suite of cosmological simulations in which we have explored a range of galaxy formation models, we investigate how the location of this centre is affected by the choice of observable - stars, hot gas, or the full mass distribution as can be probed by the gravitational potential. We explore several measures of cluster centre: the minimum of the gravitational potential, which would expect to define the centre if the cluster is in dynamical equilibrium; the peak of the density; the centre of brightest cluster galaxy (BCG); and the peak and centroid of X-ray luminosity. We find that the centre of BCG correlates more strongly with the minimum of the gravitational potential than the X-ray defined centres, while active galactic nuclei feedback acts to significantly enhance the offset between the peak X-ray luminosity and minimum gravitational potential. These results highlight the importance of centre identification when interpreting clusters observations, in particular when comparing theoretical predictions and observational data.
NASA Astrophysics Data System (ADS)
Chon, Sunmyon; Hirano, Shingo; Hosokawa, Takashi; Yoshida, Naoki
2016-12-01
Gravitational collapse of a massive primordial gas cloud is thought to be a promising path for the formation of supermassive black holes in the early universe. We study conditions for the so-called direct collapse (DC) black hole formation in a fully cosmological context. We combine a semianalytic 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 {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 merge before the onset of cloud collapse. When the DC halo is assembled through major mergers, the gas density increases rapidly to trigger gravitational instability. Based on our cosmological simulations, we conclude that the event rate of DC is an order of magnitude smaller than reported in previous studies, although the absolute rate is still poorly constrained. It is necessary to follow the dynamical evolution of a DC cloud and its nearby halo(s) in order to determine the critical radiation flux for DC.
NASA Astrophysics Data System (ADS)
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.
Hořava Gravity in the Effective Field Theory formalism: From cosmology to observational constraints
NASA Astrophysics Data System (ADS)
Frusciante, Noemi; Raveri, Marco; Vernieri, Daniele; Hu, Bin; Silvestri, Alessandra
2016-09-01
We consider Hořava gravity within the framework of the effective field theory (EFT) of dark energy and modified gravity. We work out a complete mapping of the theory into the EFT language for an action including all the operators which are relevant for linear perturbations with up to sixth order spatial derivatives. We then employ an updated version of the EFTCAMB/EFTCosmoMC package to study the cosmology of the low-energy limit of Hořava gravity and place constraints on its parameters using several cosmological data sets. In particular we use cosmic microwave background (CMB) temperature-temperature and lensing power spectra by Planck 2013, WMAP low- ℓ polarization spectra, WiggleZ galaxy power spectrum, local Hubble measurements, Supernovae data from SNLS, SDSS and HST and the baryon acoustic oscillations measurements from BOSS, SDSS and 6dFGS. We get improved upper bounds, with respect to those from Big Bang Nucleosynthesis, on the deviation of the cosmological gravitational constant from the local Newtonian one. At the level of the background phenomenology, we find a relevant rescaling of the Hubble rate at all epoch, which has a strong impact on the cosmological observables; at the level of perturbations, we discuss in details all the relevant effects on the observables and find that in general the quasi-static approximation is not safe to describe the evolution of perturbations. Overall we find that the effects of the modifications induced by the low-energy Hořava gravity action are quite dramatic and current data place tight bounds on the theory parameters.
Cosmological study with galaxy clusters detected by the Sunyaev-Zel'dovich effect
NASA Astrophysics Data System (ADS)
Mak, Suet-Ying
In this work, we present various studies to forecast the power of the galaxy clusters detected by the Sunyaev-Zel'dovich (SZ) effect in constraining cosmological models. The SZ effect is regarded as one of the new and promising technique to identify and study cluster physics. With the latest data being released in recent years from the SZ telescopes, it is essential to explore their potentials in providing cosmological information and investigate their relative strengths with respect to galaxy cluster data from X-ray and optical, as well as other cosmological probes such as Cosmic Microwave Background (CMB). One of the topics regard resolving the debate on the existence of an anomalous large scale bulk flow as measured from the kinetic SZ signal of galaxy clusters in the WMAP CMB data. We predict that if such measurement is done with the latest CMB data from the Planck satellite, the sensitivity will be improved by a factor of >5 and thus be able to provide an independent view of its existence. As it turns out, the Planck data, when using the technique developed in this work, find that the observed bulk flow amplitude is consistent with those expected from the LambdaCDM, which is in clear contradiction to the previous claim of a significant bulk flow detection in the WMAP data. We also forecast on the capability of the ongoing and future cluster surveys identified through thermal SZ (tSZ) in constraining three extended models to the LambdaCDM model: modified gravity f( R) model, primordial non-Gaussianity of density perturbation, and the presence of massive neutrinos. We do so by employing their effects on the cluster number count and power spectrum and using Fisher Matrix analysis to estimate the errors on the model parameters. We find that SZ cluster surveys can provide vital complementary information to those expected from non-cluster probes. Our results therefore give the confidence for pursuing these extended cosmological models with SZ clusters.
The history of chemical enrichment in the intracluster medium from cosmological simulations
NASA Astrophysics Data System (ADS)
Biffi, V.; Planelles, S.; Borgani, S.; Fabjan, D.; Rasia, E.; Murante, G.; Tornatore, L.; Dolag, K.; Granato, G. L.; Gaspari, M.; Beck, A. M.
2017-06-01
The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analysing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the smoothed particle hydrodynamics (SPH) gadget-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large cluster-centric distances (˜R180). In the outskirts, namely outside of ˜0.2 R180, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z > 2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z = 2 and z = 0, across the entire radial range.
Cosmological recombination: feedback of helium photons and its effect on the recombination spectrum
NASA Astrophysics Data System (ADS)
Chluba, J.; Sunyaev, R. A.
2010-02-01
In this paper, we consider the reprocessing of high-frequency photons emitted by HeII and HeI during the epoch of cosmological recombination by HeI and HI. We demonstrate that, in comparison to computations which neglect all feedback processes, the number of cosmological recombination photons that are related to the presence of helium in the early Universe could be increased by ~40-70 per cent. Our computations imply that per helium nucleus ~3-6 additional photons could be produced. Therefore, a total of ~12-14 helium-related photons per helium atom are emitted during cosmological recombination. This is an important addition to cosmological recombination spectrum which in the future may render it slightly easier to determine the primordial abundance of helium using differential measurements of the cosmic microwave background (CMB) energy spectrum. Also, since these photons are the only witnesses of the feedback process at high redshift, observing them in principle offers a way to check our understanding of the recombination physics. Here, most interestingly, the feedback of HeII photons on HeI leads to the appearance of several additional, rather narrow spectral features in the HeI recombination spectrum at low frequencies. Consequently, the signatures of helium-related features in the CMB spectral distortion from cosmological recombination at some given frequency can exceed the average level of ~17 per cent several times. We find that in particular the bands around ν ~ 10, ~35, ~80 and ~200GHz seem to be affected strongly. In addition, we computed the changes in the cosmological ionization history, finding that only the feedback of primary HeI photons on the dynamics of HeII -> HeI recombination has an effect, producing a change of ΔNe/Ne ~ +0.17 per cent at z ~ 2300. This result seems to be ~2-3 times smaller than the one obtained in earlier computations for this process, however, the difference will not be very important for the analysis of future CMB data.
NASA Astrophysics Data System (ADS)
Huang, Qing-Guo; Wang, Ke
2017-07-01
The early reionization (ERE) is supposed to be a physical process which happens after recombination, but before the instantaneous reionization caused by the first generation of stars. We investigate the effect of the ERE on the temperature and polarization power spectra of cosmic microwave background (CMB), and adopt principal components analysis (PCA) to model-independently reconstruct the ionization history during the ERE. In addition, we also discuss how the ERE affects the cosmological parameter estimates, and find that the ERE does not impose any significant influences on the tensor-to-scalar ratio r and the neutrino mass at the sensitivities of current experiments. The better CMB polarization data can be used to give a tighter constraint on the ERE and might be important for more precisely constraining cosmological parameters in the future.
Newtonian and Relativistic Cosmologies
NASA Astrophysics Data System (ADS)
Green, Stephen; Wald, Robert
2012-03-01
Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the Friedmann equations, and also that a correspondence between Newtonian and relativistic dust cosmologies holds in linearized perturbation theory. Nevertheless, it is not obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology with significant nonlinear dynamical behavior at small scales. We investigate this issue in light of a perturbative framework that we have recently developed. We propose a straightforward dictionary---exact at the linearized level---that maps Newtonian dust cosmologies into GR dust cosmologies, and we use our ordering scheme to determine the degree to which the resulting metric and matter distribution solve Einstein's equation. We then find additional corrections needed to satisfy Einstein's equation to ``order 1'' at small scales and to ``order ɛ'' at large scales. We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations to describe GR cosmologies.
Cosmological Implications of Geometrothermodynamics
NASA Astrophysics Data System (ADS)
Luongo, O.; Quevedo, H.
2015-01-01
We use the formalism of Geometrothermodynamics to derive a series of fundamental equations for thermodynamic systems. It is shown that all these fundamental equations can be used in the context of relativistic cosmology to derive diverse scenarios which include the standard cosmological model, a unified model for dark energy and dark matter, and an effective inflationary model.
NASA Astrophysics Data System (ADS)
Hoeft, M.; Mücket, J. P.; Heide, P.
2002-05-01
We investigate the energy release due to large-scale structure formation and the subsequent transfer of energy from larger to smaller scales. We calculate the power spectra for the large-scale velocity field and show that the coupling of modes results in a transfer of power predominately from larger to smaller scales. We use the concept of cumulative energy to calculate the amount of energy deposited into small scales during the cosmological structure evolution. To estimate the contribution due to the gravitational interaction only, we perform our investigations by means of dark matter simulations. The global mean of the energy transfer increases with redshift ~(z+1)3 this can be traced back to the similar evolution of the merging rates of dark matter halos. The global mean energy transfer can be decomposed into its local contributions, which allows us to determine the energy injection per unit mass into a local volume. The obtained energy injection rates are at least comparable to other energy sources driving interstellar turbulence, e.g., supernova kinetic feedback. On that basis, we make the crude assumption that processes causing this energy transfer from large to small scales, e.g., the merging of halos, may contribute substantially to the driving of interstellar medium turbulence, which may eventually result in star formation on much smaller scales. We propose that the ratio of the local energy injection rate to the energy already stored within small-scale motions is a rough measure for the probability of local star formation, applicable within cosmological large-scale N-body simulations.
NASA Astrophysics Data System (ADS)
Avila-Reese, V.; Colín, P.; González-Samaniego, A.; Valenzuela, O.; Firmani, C.; Velázquez, H.; Ceverino, D.
2011-08-01
By means of cosmological N-body + hydrodynamics simulations of galaxies in the context of the Λ cold dark matter (ΛCDM) scenario we explore the specific star formation rates (SSFR = SFR/Ms , Ms is the stellar mass) and stellar mass fractions (Fs ≡ Ms /Mh , Mh is the halo mass) for sub-M* field galaxies at different redshifts (0 <~ z <~ 1.5). Distinct low-mass halos (2.5 <~ Mh /1010 M sun <~ 50 at z = 0) were selected for the high-resolution re-simulations. The Hydrodynamics Adaptive Refinement Tree (ART) code was used and some variations of the sub-grid parameters were explored. Most simulated galaxies, specially those with the highest resolutions, have significant disk components and their structural and dynamical properties are in reasonable agreement with observations of sub-M* field galaxies. However, the SSFRs are 5-10 times smaller than the averages of several (compiled and homogenized here) observational determinations for field blue/star-forming galaxies at z < 0.3 (at low masses, most observed field galaxies are actually blue/star forming). This inconsistency seems to remain even at z ~ 1-1.5, although it is less drastic. The Fs of simulated galaxies increases with Mh as semi-empirical inferences show. However, the values of Fs at z ≈ 0 are ~5-10 times larger in the simulations than in the inferences; these differences increases probably to larger factors at z ~ 1-1.5. The inconsistencies reported here imply that simulated low-mass galaxies (0.2 <~ Ms /109 M sun <~ 30 at z = 0) assembled their stellar masses much earlier than observations suggest. Our results confirm the predictions found by means of ΛCDM-based models of disk galaxy formation and evolution for isolated low-mass galaxies, and highlight that our understanding and implementation of astrophysics into simulations and models are still lacking vital ingredients.
The perfect cosmological principle and the Hubble effect
NASA Astrophysics Data System (ADS)
Kropotkin, P. N.
An examination of three approaches to the problem of photon 'aging' shows that, during the motion of bodies and particles at large velocities, a drag effect should arise which is connected with the asymmetric effect of the gravitational field of the universe on these bodies and particles. Astronomical data on values of the Hubble constant and the mean density of matter in the universe (rho) tend to confirm this conclusion. They also confirm Zwicky's hypothesis that the photon aging effect is fully determined by rho and is analogous to the conventional red shift.
Baryon effects on void statistics in the EAGLE simulation
NASA Astrophysics Data System (ADS)
Paillas, Enrique; Lagos, Claudia D. P.; Padilla, Nelson; Tissera, Patricia; Helly, John; Schaller, Matthieu
2017-10-01
Cosmic voids are promising tools for cosmological tests due to their sensitivity to dark energy, modified gravity and alternative cosmological scenarios. Most previous studies in the literature of void properties use cosmological N-body simulations of dark matter (DM) particles that ignore the potential effect of baryonic physics. Using a spherical underdensity finder, we analyse voids using the mass field and subhalo tracers in the Evolution and Assembly of Galaxies and their Environment (EAGLE) simulations, which follow the evolution of galaxies in a Λ cold dark matter universe with state-of-the-art subgrid models for baryonic processes in a (100 cMpc)3 volume. We study the effect of baryons on void statistics by comparing results with DM-only simulations that use the same initial conditions as EAGLE. When identifying voids in the mass field, we find that a DM-only simulation produces 24 per cent more voids than a hydrodynamical one due to the action of galaxy feedback polluting void regions with hot gas, specially for small voids with rvoid ≤ 10 Mpc. We find that the way in which galaxy tracers are selected has a strong impact on the inferred void properties. Voids identified using galaxies selected by their stellar mass are larger and have cuspier density profiles than those identified by galaxies selected by their total mass. Overall, baryons have minimal effects on void statistics, as void properties are well captured by DM-only simulations, but it is important to account for how galaxies populate DM haloes to estimate the observational effect of different cosmological models on the statistics of voids.
Testing loop quantum cosmology
NASA Astrophysics Data System (ADS)
Wilson-Ewing, Edward
2017-03-01
Loop quantum cosmology predicts that quantum gravity effects resolve the big-bang singularity and replace it by a cosmic bounce. Furthermore, loop quantum cosmology can also modify the form of primordial cosmological perturbations, for example by reducing power at large scales in inflationary models or by suppressing the tensor-to-scalar ratio in the matter bounce scenario; these two effects are potential observational tests for loop quantum cosmology. In this article, I review these predictions and others, and also briefly discuss three open problems in loop quantum cosmology: its relation to loop quantum gravity, the trans-Planckian problem, and a possible transition from a Lorentzian to a Euclidean space-time around the bounce point.
Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation
NASA Astrophysics Data System (ADS)
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
Planck CMB anomalies: astrophysical and cosmological secondary effects and the curse of masking
Rassat, A.; Starck, J.-L.; Paykari, P.; Sureau, F.; Bobin, J. E-mail: jstarck@cea.fr E-mail: florent.sureau@cea.fr
2014-08-01
Large-scale anomalies have been reported in CMB data with both WMAP and Planck data. These could be due to foreground residuals and or systematic effects, though their confirmation with Planck data suggests they are not due to a problem in the WMAP or Planck pipelines. If these anomalies are in fact primordial, then understanding their origin is fundamental to either validate the standard model of cosmology or to explore new physics. We investigate three other possible issues: 1) the trade-off between minimising systematics due to foreground contamination (with a conservative mask) and minimising systematics due to masking, 2) astrophysical secondary effects (the kinetic Doppler quadrupole and kinetic Sunyaev-Zel'dovich effect), and 3) secondary cosmological signals (the integrated Sachs-Wolfe effect). We address the masking issue by considering new procedures that use both WMAP and Planck to produce higher quality full-sky maps using the sparsity methodology (LGMCA maps). We show the impact of masking is dominant over that of residual foregrounds, and the LGMCA full-sky maps can be used without further processing to study anomalies. We consider four official Planck PR1 and two LGMCA CMB maps. Analysis of the observed CMB maps shows that only the low quadrupole and quadrupole-octopole alignment seem significant, but that the planar octopole, Axis of Evil, mirror parity and cold spot are not significant in nearly all maps considered. After subtraction of astrophysical and cosmological secondary effects, only the low quadrupole may still be considered anomalous, meaning the significance of only one anomaly is affected by secondary effect subtraction out of six anomalies considered. In the spirit of reproducible research all reconstructed maps and codes will be made available for download here http://www.cosmostat.org/anomaliesCMB.html.
Planck CMB Anomalies: Astrophysical and Cosmological Secondary Effects and the Curse of Masking
NASA Astrophysics Data System (ADS)
Rassat, Anais
2016-07-01
Large-scale anomalies have been reported in CMB data with both WMAP and Planck data. These could be due to foreground residuals and or systematic effects, though their confirmation with Planck data suggests they are not due to a problem in the WMAP or Planck pipelines. If these anomalies are in fact primordial, then understanding their origin is fundamental to either validate the standard model of cosmology or to explore new physics. We investigate three other possible issues: 1) the trade-off between minimising systematics due to foreground contamination (with a conservative mask) and minimising systematics due to masking, 2) astrophysical secondary effects (the kinetic Doppler quadrupole and kinetic Sunyaev-Zel'dovich effect), and 3) secondary cosmological signals (the integrated Sachs-Wolfe effect). We address the masking issue by considering new procedures that use both WMAP and Planck to produce higher quality full-sky maps using the sparsity methodology (LGMCA maps). We show the impact of masking is dominant over that of residual foregrounds, and the LGMCA full-sky maps can be used without further processing to study anomalies. We consider four official Planck PR1 and two LGMCA CMB maps. Analysis of the observed CMB maps shows that only the low quadrupole and quadrupole-octopole alignment seem significant, but that the planar octopole, Axis of Evil, mirror parity and cold spot are not significant in nearly all maps considered. After subtraction of astrophysical and cosmological secondary effects, only the low quadrupole may still be considered anomalous, meaning the significance of only one anomaly is affected by secondary effect subtraction out of six anomalies considered. In the spirit of reproducible research all reconstructed maps and codes are available online.
NASA Astrophysics Data System (ADS)
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.
N-body simulations, weak lensing, and photo-z's: Numerical projects in cosmology
NASA Astrophysics Data System (ADS)
Stabenau, Hans Friedrich
General Relativity is an extremely well-tested theory over 15 orders of magnitude, on laboratory to solar system scales. However, recent measurements, including evidence from Type Ia supernovae, show that the expansion of the universe is accelerating. This means that GR, cannot unproblematically be extrapolated to fit the properties of our universe on horizon scales. With recourse to either a strange form of energy density ("dark energy"), or a modification of GR, the acceleration can be explained; distinguishing which is the correct model requires detailed observations of large-scale structure formation. In this thesis, I address three issues that are important to these observations: generating predictions by N-body simulation of alternate gravity models, efficiently obtaining accurate redshifts for galaxies using photometric redshifts with surface brightness priors, and finally modeling PSF effects for a proposed weak lensing survey.
NASA Astrophysics Data System (ADS)
Wang, Mei-Yu; Peter, Annika H. G.; Strigari, Louis E.; Zentner, Andrew R.; Arant, Bryan; Garrison-Kimmel, Shea; Rocha, Miguel
2014-11-01
We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable dark matter particle and a non-interacting light particle with decay lifetime comparable to the Hubble time. We study the effects of the recoil kick velocity (Vk) received by the stable dark matter on the structures of dark matter haloes ranging from galaxy-cluster to Milky Way-mass scales. For Milky Way-mass haloes, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, haloes with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that models with lifetimes Γ-1 ˜ H_0^{-1} and recoil speeds Vk ˜ 20-40 km s-1 can significantly reduce both the abundance of Galactic subhaloes and their internal densities. We find that decaying dark matter models that do not violate current astrophysical constraints can significantly mitigate both the `missing satellites problem' and the more recent `too big to fail problem'. These decaying models predict significant time evolution of haloes, and this implies that at high redshifts decaying models exhibit the similar sequence of structure formation as cold dark matter. Thus, decaying dark matter models are significantly less constrained by high-redshift phenomena than warm dark matter models. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of small galaxies observations in the Local Group and can be tested as well as by forthcoming large-scale surveys.
Cosmological Implications of the Effects of X-Ray Clusters on the Cosmic Microwave Background
NASA Technical Reports Server (NTRS)
Forman, William R.
1996-01-01
We have been carrying forward a program to confront X-ray observations of clusters and their evolution as derived from X-ray observatories with observations of the cosmic microwave background radiation (CMBR). In addition to the material covered in our previous reports (including three published papers), most recently we have explored the effects of a cosmological constant on the predicted Sunyaev-Zel'dovich effect from the ensemble of clusters. In this report we summarize that work from which a paper will be prepared.
Cosmology of a holographic induced gravity model with curvature effects
Bouhmadi-Lopez, Mariam; Errahmani, Ahmed; Ouali, Taoufiq
2011-10-15
We present a holographic model of the Dvali-Gabadadze-Porrati scenario with a Gauss-Bonnet term in the bulk. We concentrate on the solution that generalizes the normal Dvali-Gabadadze-Porrati branch. It is well known that this branch cannot describe the late-time acceleration of the universe even with the inclusion of a Gauss-Bonnet term. Here, we show that this branch in the presence of a Gauss-Bonnet curvature effect and a holographic dark energy with the Hubble scale as the infrared cutoff can describe the late-time acceleration of the universe. It is worthwhile to stress that such an energy density component cannot do the same job on the normal Dvali-Gabadadze-Porrati branch (without Gauss-Bonnet modifications) nor in a standard four-dimensional relativistic model. The acceleration on the brane is also presented as being induced through an effective dark energy which corresponds to a balance between the holographic one and geometrical effects encoded through the Hubble parameter.
NASA Astrophysics Data System (ADS)
Orban, Chris
2013-05-01
In setting up initial conditions for ensembles of 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 real-space statistics and allowing the DC mode (i.e. overdensity) to vary from box to box as it would in the real universe. As a stringent test of both approaches, I perform ensembles of simulations using power law and a ``powerlaw times a bump'' model inspired by baryon acoustic oscillations (BAO), exploiting the self-similarity of these initial conditions to quantify the accuracy of the matter-matter two-point correlation results. The real-space method, which was originally proposed by Pen 1997 [1] and implemented by Sirko 2005 [2], performed well in producing the expected self-similar behavior and corroborated the non-linear evolution of the BAO feature observed in conventional simulations, even in the strongly-clustered regime (σ8gtrsim1). In revisiting the real-space method championed by [2], it was also noticed that this earlier study overlooked an important integral constraint correction to the correlation function in results from the conventional approach that can be important in ΛCDM simulations with Lboxlesssim1 h-1Gpc and on scales rgtrsimLbox/10. Rectifying this issue shows that the fourier space and real space methods are about equally accurate and efficient for modeling the evolution and growth of the correlation function, contrary to previous claims. An appendix provides a useful independent-of-epoch analytic formula for estimating the importance of the integral constraint bias on correlation function measurements in ΛCDM simulations.
Orban, Chris
2013-05-01
In setting up initial conditions for ensembles of 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 real-space statistics and allowing the DC mode (i.e. overdensity) to vary from box to box as it would in the real universe. As a stringent test of both approaches, I perform ensembles of simulations using power law and a ''powerlaw times a bump'' model inspired by baryon acoustic oscillations (BAO), exploiting the self-similarity of these initial conditions to quantify the accuracy of the matter-matter two-point correlation results. The real-space method, which was originally proposed by Pen 1997 [1] and implemented by Sirko 2005 [2], performed well in producing the expected self-similar behavior and corroborated the non-linear evolution of the BAO feature observed in conventional simulations, even in the strongly-clustered regime (σ{sub 8}∼>1). In revisiting the real-space method championed by [2], it was also noticed that this earlier study overlooked an important integral constraint correction to the correlation function in results from the conventional approach that can be important in ΛCDM simulations with L{sub box}∼<1 h{sup −1}Gpc and on scales r∼>L{sub box}/10. Rectifying this issue shows that the fourier space and real space methods are about equally accurate and efficient for modeling the evolution and growth of the correlation function, contrary to previous claims. An appendix provides a useful independent-of-epoch analytic formula for estimating the importance of the integral constraint bias on correlation function measurements in ΛCDM simulations.
Renormalization-group flow of the effective action of cosmological large-scale structures
NASA Astrophysics Data System (ADS)
Floerchinger, Stefan; Garny, Mathias; Tetradis, Nikolaos; Wiedemann, Urs Achim
2017-01-01
Following an approach of Matarrese and Pietroni, we derive the functional renormalization group (RG) flow of the effective action of cosmological large-scale structures. Perturbative solutions of this RG flow equation are shown to be consistent with standard cosmological perturbation theory. Non-perturbative approximate solutions can be obtained by truncating the a priori infinite set of possible effective actions to a finite subspace. Using for the truncated effective action a form dictated by dissipative fluid dynamics, we derive RG flow equations for the scale dependence of the effective viscosity and sound velocity of non-interacting dark matter, and we solve them numerically. Physically, the effective viscosity and sound velocity account for the interactions of long-wavelength fluctuations with the spectrum of smaller-scale perturbations. We find that the RG flow exhibits an attractor behaviour in the IR that significantly reduces the dependence of the effective viscosity and sound velocity on the input values at the UV scale. This allows for a self-contained computation of matter and velocity power spectra for which the sensitivity to UV modes is under control.
NASA Astrophysics Data System (ADS)
Codello, Alessandro; Jain, Rajeev Kumar
2017-02-01
Following our previous work wherein the leading order effective action was computed in the covariant effective field theory of gravity, here we specialize the effective action to the FRW spacetime and obtain the effective Friedmann equations. In particular, we focus our attention on studying the cosmological implications of the non-local terms when each of them is combined with the Einstein–Hilbert action. We obtain both analytical and iterative solutions to the effective background equations in all the cases and also briefly comment on the consistency between the iterative and numerical solutions whenever possible. We find that among all the non–local terms, the imprints induced by R\\frac{1}{{{\\square}2}}R are very significant. Interpreting these corrections as an effective dark energy component characterized by an equation of state parameter, we find that the R\\frac{1}{{{\\square}2}}R correction can indeed lead to an accelerated expansion of the universe at the present epoch even in the absence of a cosmological constant. We briefly discuss some phenomenological consequences of our results.
Voids in massive neutrino cosmologies
Massara, Elena; Villaescusa-Navarro, Francisco; Viel, Matteo; Sutter, P.M. E-mail: villaescusa@oats.inaf.it E-mail: sutter@oats.inaf.it
2015-11-01
Cosmic voids are a promising environment to characterize neutrino-induced effects on the large-scale distribution of matter in the universe. We perform a comprehensive numerical study of the statistical properties of voids, identified both in the matter and galaxy distributions, in massive and massless neutrino cosmologies. The matter density field is obtained by running several independent N-body simulations with cold dark matter and neutrino particles, while the galaxy catalogs are modeled by populating the dark matter halos in simulations via a halo occupation distribution (HOD) model to reproduce the clustering properties observed by the Sloan Digital Sky Survey (SDSS) II Data Release 7. We focus on the impact of massive neutrinos on the following void statistical properties: number density, ellipticities, two-point statistics, density and velocity profiles. Considering the matter density field, we find that voids in massive neutrino cosmologies are less evolved than those in the corresponding massless neutrinos case: there is a larger number of small voids and a smaller number of large ones, their profiles are less evacuated, and they present a lower wall at the edge. Moreover, the degeneracy between σ{sub 8} and Ω{sub ν} is broken when looking at void properties. In terms of the galaxy density field, we find that differences among cosmologies are difficult to detect because of the small number of galaxy voids in the simulations. Differences are instead present when looking at the matter density and velocity profiles around these voids.
Cosmological leverage from the matter power spectrum in the presence of baryon and nonlinear effects
Bielefeld, Jannis; Huterer, Dragan; Linder, Eric V. E-mail: huterer@umich.edu
2015-05-01
We investigate how the use of higher wavenumbers (smaller scales) in the galaxy clustering power spectrum influences cosmological constraints. We take into account uncertainties from nonlinear density fluctuations, (scale dependent) galaxy bias, and baryonic effects. Allowing for substantially model independent uncertainties through separate fit parameters in each wavenumber bin that also allow for the redshift evolution, we quantify strong gains in dark energy and neutrino mass leverage with increasing maximum wavenumber, despite marginalizing over numerous (up to 125) extra fit parameters. The leverage is due to not only an increased number of modes but, more significantly, breaking of degeneracies beyond the linear regime.
Effects of the interaction between dark energy and dark matter on cosmological parameters
He, Jian-Hua; Wang, Bin E-mail: wangb@fudan.edu.cn
2008-06-15
We examine the effects of possible phenomenological interactions between dark energy and dark matter on cosmological parameters and their efficiency in solving the coincidence problem. We work with two simple parameterizations of the dynamical dark energy equation of state and the constant dark energy equation of state. Using observational data coming from the new 182 Gold type Ia supernova samples, the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, we perform a statistical joint analysis of different forms of phenomenological interaction between dark energy and dark matter.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Sanchez, Natalie; Bellovary, Jillian M.; Holley-Bockelmann, Kelly
2016-01-01
With the use of cosmological hydrodynamic simulations of Milky Way-type galaxies, we identify the preferential source of gas that is accreted by the supermassive black holes (SMBHs) they host. We examine simulations of two Milky Way analogs, each distinguished by a differing merger history. One galaxy is characterized by several major mergers and the other has a more quiescent history. By examining and comparing these two galaxies, which have a similar structure at z=0, we asses the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which studied accretion onto SMBHs in massive, high redshift galaxies. Bellovary found that the fraction of gas accreted by the galaxy was proportional to that which was accreted by its SMBH. Contrary to Bellovary's previous results, we found that though the gas accreted by a quiescent galaxy will mirror the accretion of its central SMBH, a galaxy that is characterized by an active merger history will have a SMBH that preferentially accretes gas gained through mergers. We move forward by examining the angular momentum of the gas accreted by these Milky Way-type galaxies to better understand the mechanisms fueling their central SMBH.
NASA Astrophysics Data System (ADS)
Lee, T. S.; Nagamine, K.; Hernquist, L.; Springel, V.
2011-02-01
We calculate the cross-correlation function (CCF) between damped Lyα systems (DLAs) and Lyman break galaxies (LBGs) using cosmological hydrodynamic simulations at z= 3. We compute the CCF with two different methods. First, we assume that there is one DLA in each dark matter halo if its DLA cross-section is non-zero. In our second approach we weight the pair count by the DLA cross-section of each halo, yielding a cross-section-weighted CCF. We also compute the angular CCF for direct comparison with observations. Finally, we calculate the autocorrelation functions of LBGs and DLAs, and their bias against the dark matter distribution. For these different approaches, we consistently find that there is good agreement between our simulations and observational measurements by Cooke et al. and Adelberger et al.. Our results thus confirm that the spatial distribution of LBGs and DLAs can be well described within the framework of the concordance Λ cold dark matter model. We find that the correlation strengths of LBGs and DLAs are consistent with the actual observations, and in the case of LBGs it is higher than would be predicted by low-mass galaxy merger models.
NASA Technical Reports Server (NTRS)
Wilson, Michael J.; Sherwin, Blake D.; Hill, J. Collin; Addison, Graeme; Battaglia, Nick; Bond, J. Richard; Das, Sudeep; Devlin, Mark J.; Dunkley, Joanna; Duenner, Rolando; Fowler, Joseph W.; Gralla, Megan, B.; Hajian, Amir; Halpern, Mark; Hilton, Matt; Hincks, Adam D.; Hlozek, Renee; Huffenberger, Kevin; Hughes, John P.; Kosowsky, Arthur; Louis, Thibaut; Marriage, Tobias A.; Marsden, Danica; Menanteau, Felipe; Wollack, Ed
2012-01-01
We present a detection of the unnormalized skewness (T(sup )(sup 2)(n(circumflex)) induced by the thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope (ACT) 148 GHz cosmic microwave background temperature maps. Contamination due to infrared and radio sources is minimized by template subtraction of resolved sources and by constructing a mask using outlying values in the 218 GHz (tSZ-null) ACT maps. We measure (T(sup )(sup 3) (n(circumflex)) = -31 plus or minus 6 micro-K(sup 3) (measurement error only) or plus or minus 14 micro-K(sup 3) (including cosmic variance error) in the filtered ACT data, a 5sigma detection. We show that the skewness is a sensitive probe of sigma(sub 8), and use analytic calculations and tSZ simulations to obtain cosmological constraints from this measurement. From this signal alone we infer a value of sigma(sub 8) = 0.78 sup +0.03 sub -0.04 (68% C.L.) sup +0.05 sub -0.16. Our results demonstrate that measurements of nonGaussianity can be a useful method for characterizing the tSZ effect and extracting the underlying cosmological information.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Lin, Weikang; Ishak, Mustapha
2017-07-01
The continuous progress toward more precise cosmological surveys and experiments has galvanized recent interest into consistency tests on cosmological parameters and models. At the heart of this effort is quantifying the degree of inconsistency between two or more cosmological data sets. We introduce an intuitive moment-based measure we call the index of inconsistency (IOI) and show that it is sensitive to the separation of the means, the size of the constraint ellipsoids, and their orientations in the parameter space. We find that it tracks accurately the inconsistencies when present. Next, we show that parameter marginalization can cause a loss of information on the inconsistency between two experiments, and we quantify such a loss using the drop in IOI. In order to zoom on a given parameter, we define the relative residual IOI and the relative drop in IOI. While these two quantities can provide insights on the parameters that are most responsible for inconsistencies, we find that the full IOI applied to the whole parameter spaces is what must be used to correctly reflect the degree of inconsistency between two experiments. We discuss various properties of IOI, provide its eigenmode decomposition, and compare it to other measures of discordance. Finally, we apply IOI to current geometry data sets (i.e., an improved Supernovae Type Ia compilation, baryon acoustic oscillations from 6dF, SDSS MGS and Lyman-α forest, and high-ℓ cosmic microwave background (CMB) temperature data from Planck-2015) versus growth data sets (i.e., Redshift Space Distortions from WiggleZ and SDSS, Weak Lensing from CFHTLenS, CMB Lensing, Sunyav-Zeldovich effect, and low-ℓ CMB temperature and polarization data from Planck-2015). We find that a persistent inconsistency is present between the two data sets. This could reflect the presence of systematics in the data or inconsistencies in the underlying model.
FLY: a code for LSS cosmological simulations for a PC Linux Cluster
NASA Astrophysics Data System (ADS)
Comparato, M.; Becciani, U.; Antonuccio-Delogu, V.; Costa, A.
2006-07-01
We developed FLY with the main goal of maximizing the number of particles that can be simulated in an MPP system without data replication. FLY builds a tree that is shared among all the processes that execute a simulation, each process having the same number of bodies which evolve during each time-step. Now we present the new version of the code that runs on a PC Linux Cluster using the one side communication paradigm MPI-2 and the performance results obtained.
Kehagias, A.; Riotto, A.
2016-05-25
Symmetries play an interesting role in cosmology. They are useful in characterizing the cosmological perturbations generated during inflation and lead to consistency relations involving the soft limit of the statistical correlators of large-scale structure dark matter and galaxies overdensities. On the other hand, in observational cosmology the carriers of the information about these large-scale statistical distributions are light rays traveling on null geodesics. Motivated by this simple consideration, we study the structure of null infinity and the associated BMS symmetry in a cosmological setting. For decelerating Friedmann-Robertson-Walker backgrounds, for which future null infinity exists, we find that the BMS transformations which leaves the asymptotic metric invariant to leading order. Contrary to the asymptotic flat case, the BMS transformations in cosmology generate Goldstone modes corresponding to scalar, vector and tensor degrees of freedom which may exist at null infinity and perturb the asymptotic data. Therefore, BMS transformations generate physically inequivalent vacua as they populate the universe at null infinity with these physical degrees of freedom. We also discuss the gravitational memory effect when cosmological expansion is taken into account. In this case, there are extra contribution to the gravitational memory due to the tail of the retarded Green functions which are supported not only on the light-cone, but also in its interior. The gravitational memory effect can be understood also from an asymptotic point of view as a transition among cosmological BMS-related vacua.
NASA Astrophysics Data System (ADS)
Kehagias, A.; Riotto, A.
2016-05-01
Symmetries play an interesting role in cosmology. They are useful in characterizing the cosmological perturbations generated during inflation and lead to consistency relations involving the soft limit of the statistical correlators of large-scale structure dark matter and galaxies overdensities. On the other hand, in observational cosmology the carriers of the information about these large-scale statistical distributions are light rays traveling on null geodesics. Motivated by this simple consideration, we study the structure of null infinity and the associated BMS symmetry in a cosmological setting. For decelerating Friedmann-Robertson-Walker backgrounds, for which future null infinity exists, we find that the BMS transformations which leaves the asymptotic metric invariant to leading order. Contrary to the asymptotic flat case, the BMS transformations in cosmology generate Goldstone modes corresponding to scalar, vector and tensor degrees of freedom which may exist at null infinity and perturb the asymptotic data. Therefore, BMS transformations generate physically inequivalent vacua as they populate the universe at null infinity with these physical degrees of freedom. We also discuss the gravitational memory effect when cosmological expansion is taken into account. In this case, there are extra contribution to the gravitational memory due to the tail of the retarded Green functions which are supported not only on the light-cone, but also in its interior. The gravitational memory effect can be understood also from an asymptotic point of view as a transition among cosmological BMS-related vacua.
Constraints on Cosmological Parameters From The Sunyaev-Zel'dovich Effect and Thermal Bremsstrahlung
NASA Technical Reports Server (NTRS)
Molnar, S. M.; Mushotzky, R. F.; White, Nicholas E. (Technical Monitor)
2000-01-01
We discuss the possibility of constraining cosmological parameters using the Sunyaev-Zel'dovich (SZ) effect and thermal bremsstrahlung caused by intra-cluster gas in clusters of galaxies. The new generation of X-ray satellites and ground based interferometers dedicated to SZ observations will enable one to reduce uncertainties in these measurements, and thus make this method potentially quite promising in the near future. The importance of this method is that, unlike most other methods, it is based on physical principles, no 'standard candles' or 'rulers' needed. We estimate the accuracy achievable in the determination of the matter density, OMEGA(sub m), the cosmological constant, OMEGA(sub LAMBDA), and the Hubble constant, h, using the redshift dependence of the angular diameter distance derived from observations in the near future. We demonstrate that constraints from the angular diameter distance are orthogonal to those from Cosmic Microwave Background (CMB) fluctuations in the parameter space defined by OMEGA(sub m), OMEGA(sub LAMBDA), and h. Assuming a statistical error of five percent in the angular diameter distance for each cluster in a sample of five hundred clusters, we show that the redshift dependence of the angular diameter distance combined with constraints from CMB fluctuations can put stringent constraints on OMEGA(sub m) (+/- 0.03), OMEGA(sub LAMBDA) (+/- 0.03) and h (+/- 0.03, 3(sigma) errors). We also show that, with as few as 50 clusters between redshifts 0.01 and 1.5 with an assumed 10% statistical error in the angular diameter distance determination, one can distinguish between models with zero cosmological constant and spatially flat models with a cosmological constant with high confidence level (independently from the supernova results) and put meaningful constraints on OMEGA(sub m) (+/- 0.01), OMEGA(sub LAMBDA) (+/- 0.01) and h (+/- 0.01, 3(sigma) errors). With the expected advances in observational technology, we will be limited by
Constraints on Cosmological Parameters From The Sunyaev-Zel'dovich Effect and Thermal Bremsstrahlung
NASA Technical Reports Server (NTRS)
Molnar, S. M.; Mushotzky, R. F.; White, Nicholas E. (Technical Monitor)
2000-01-01
We discuss the possibility of constraining cosmological parameters using the Sunyaev-Zel'dovich (SZ) effect and thermal bremsstrahlung caused by intra-cluster gas in clusters of galaxies. The new generation of X-ray satellites and ground based interferometers dedicated to SZ observations will enable one to reduce uncertainties in these measurements, and thus make this method potentially quite promising in the near future. The importance of this method is that, unlike most other methods, it is based on physical principles, no 'standard candles' or 'rulers' needed. We estimate the accuracy achievable in the determination of the matter density, OMEGA(sub m), the cosmological constant, OMEGA(sub LAMBDA), and the Hubble constant, h, using the redshift dependence of the angular diameter distance derived from observations in the near future. We demonstrate that constraints from the angular diameter distance are orthogonal to those from Cosmic Microwave Background (CMB) fluctuations in the parameter space defined by OMEGA(sub m), OMEGA(sub LAMBDA), and h. Assuming a statistical error of five percent in the angular diameter distance for each cluster in a sample of five hundred clusters, we show that the redshift dependence of the angular diameter distance combined with constraints from CMB fluctuations can put stringent constraints on OMEGA(sub m) (+/- 0.03), OMEGA(sub LAMBDA) (+/- 0.03) and h (+/- 0.03, 3(sigma) errors). We also show that, with as few as 50 clusters between redshifts 0.01 and 1.5 with an assumed 10% statistical error in the angular diameter distance determination, one can distinguish between models with zero cosmological constant and spatially flat models with a cosmological constant with high confidence level (independently from the supernova results) and put meaningful constraints on OMEGA(sub m) (+/- 0.01), OMEGA(sub LAMBDA) (+/- 0.01) and h (+/- 0.01, 3(sigma) errors). With the expected advances in observational technology, we will be limited by
SHORT-LIVED STAR-FORMING GIANT CLUMPS IN COSMOLOGICAL SIMULATIONS OF z Almost-Equal-To 2 DISKS
Genel, Shy; Genzel, Reinhard; Foerster Schreiber, Natascha M.; Naab, Thorsten; Oser, Ludwig; Sternberg, Amiel; Johansson, Peter H.; Dave, Romeel; Oppenheimer, Benjamin D.; Burkert, Andreas E-mail: genzel@mpe.mpg.de E-mail: amiel@wise.tau.ac.il E-mail: oser@usm.lmu.de E-mail: phjohans@astro.helsinki.fi E-mail: oppenheimer@strw.leidenuniv.nl
2012-01-20
Many observed massive star-forming z Almost-Equal-To 2 galaxies are large disks that exhibit irregular morphologies, with Almost-Equal-To 1 kpc, Almost-Equal-To 10{sup 8}-10{sup 10}M{sub o-dot} clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M{sub *} Almost-Equal-To 10{sup 10.5}M{sub o-dot} galaxies in Almost-Equal-To 10{sup 12}M{sub o-dot} halos at z Almost-Equal-To 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f{sub g} Almost-Equal-To 50%), and high specific star formation rates ({approx}>1 Gyr{sup -1}). In accord with recent models, giant clumps (M{sub clump} Almost-Equal-To (5 Multiplication-Sign 10{sup 8}-10{sup 9})M{sub o-dot}) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.
Cosmological effects of scalar-photon couplings: dark energy and varying-α Models
Avgoustidis, A.; Martins, C.J.A.P.; Monteiro, A.M.R.V.L.; Vielzeuf, P.E.; Luzzi, G. E-mail: Carlos.Martins@astro.up.pt E-mail: up110370652@alunos.fc.up.pt
2014-06-01
We study cosmological models involving scalar fields coupled to radiation and discuss their effect on the redshift evolution of the cosmic microwave background temperature, focusing on links with varying fundamental constants and dynamical dark energy. We quantify how allowing for the coupling of scalar fields to photons, and its important effect on luminosity distances, weakens current and future constraints on cosmological parameters. In particular, for evolving dark energy models, joint constraints on the dark energy equation of state combining BAO radial distance and SN luminosity distance determinations, will be strongly dominated by BAO. Thus, to fully exploit future SN data one must also independently constrain photon number non-conservation arising from the possible coupling of SN photons to the dark energy scalar field. We discuss how observational determinations of the background temperature at different redshifts can, in combination with distance measures data, set tight constraints on interactions between scalar fields and photons, thus breaking this degeneracy. We also discuss prospects for future improvements, particularly in the context of Euclid and the E-ELT and show that Euclid can, even on its own, provide useful dark energy constraints while allowing for photon number non-conservation.
Hamann, Jan; Wong, Yvonne Y Y E-mail: ywong@mppmu.mpg.de
2008-03-15
We estimate the effect of the experimental uncertainty in the measurement of the temperature of the cosmic microwave background (CMB) on the extraction of cosmological parameters from future CMB surveys. We find that even for an ideal experiment limited only by cosmic variance up to l=2500 for both the temperature and polarization measurements, the projected cosmological parameter errors are remarkably robust against the uncertainty of 1 mK in the firas CMB temperature monopole measurement. The maximum degradation in sensitivity is 20%, for the baryon density estimate, relative to the case in which the monopole is known infinitely well. While this degradation is acceptable, we note that reducing the uncertainty in the current temperature measurement by a factor of five will bring it down to {approx}1%. We also estimate the effect of the uncertainty in the dipole temperature measurement. Assuming the overall calibration of the data to be dominated by the dipole error of 0.2% from firas, the sensitivity degradation is insignificant and does not exceed 10% in any parameter direction.
Investigations in theoretical cosmology
NASA Astrophysics Data System (ADS)
Barnard, Michael James
This report is a compilation of research I have done in the field of cosmology while at the University of California, Davis. The topics are all closely linked to the physics of scalar fields in General Relativity. This thesis contains the text of two papers, both of which deal with the goals and motivations of future projects in observational cosmology. The first is an evaluation of the effect of future observations on constraints on the parameter space of the Albrecht- Skordis model of dark energy. These future data sets were found to be able of constraining the scalar field model parameters in ways consistent with the constraints on the phenomenological equation of state parameters used by the Dark Energy Task Force. The second paper used principle component analysis of the equation of state parameter on simulated future data sets to construct parameter spaces. Distributions of dark energy quintessence models were then projected into these parameter spaces; it was found that there is structure in the separation of these models that is marginally detectable by so called "Stage 4" experiments. Also included are a review of the derivation of the scale invariant primordial power spectrum and an evaluation of a model of open inflation as the cause of the low CMB quadrupole.
Simulations and cosmological inference: A statistical model for power spectra means and covariances
Schneider, Michael D.; Knox, Lloyd; Habib, Salman; Heitmann, Katrin; Higdon, David; Nakhleh, Charles
2008-09-15
We describe an approximate statistical model for the sample variance distribution of the nonlinear matter power spectrum that can be calibrated from limited numbers of simulations. Our model retains the common assumption of a multivariate normal distribution for the power spectrum band powers but takes full account of the (parameter-dependent) power spectrum covariance. The model is calibrated using an extension of the framework in Habib et al. (2007) to train Gaussian processes for the power spectrum mean and covariance given a set of simulation runs over a hypercube in parameter space. We demonstrate the performance of this machinery by estimating the parameters of a power-law model for the power spectrum. Within this framework, our calibrated sample variance distribution is robust to errors in the estimated covariance and shows rapid convergence of the posterior parameter constraints with the number of training simulations.
NASA Astrophysics Data System (ADS)
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.
Zhuravleva, I.; Allen, S. W.; Churazov, E. M.; Gaspari, M.; Schekochihin, A. A.; Lau, E. T.; Nagai, D.; Nelson, K.; Parrish, I. J.
2014-06-10
We address the problem of evaluating the power spectrum of the velocity field of the intracluster medium 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: (δρ{sub k}/ρ){sup 2}=η{sub 1}{sup 2}(V{sub 1,k}/c{sub s}){sup 2}, where δρ {sub k}/ρ is the spectral amplitude of the density perturbations at wavenumber k, V{sub 1,k}{sup 2}=V{sub k}{sup 2}/3 is the mean square component of the velocity field, c{sub s} is the sound speed, and η{sub 1} is a dimensionless constant of the order of unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find η{sub 1} ≈ 1 ± 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 proportional because the former are a passive scalar advected by the latter. This opens an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters across a wide range of scales.
Dynamical Effects of the Cosmological Constant - the Evolution of Aspherical Structures
NASA Astrophysics Data System (ADS)
Lemson, G.
1993-08-01
I investigate the influence of a non-zero cosmological constant on the evolution of anisotropy in overdensities that grow by gravitational collapse. The claim that a positive value of Λ might produce stronger asphericities is considered by following the collapse of homogeneous spheroids imbedded in Friedman-Lemaitre backgrounds. It is shown that, although the calculations indeed show this effect, it is small for the values of Λ allowed by the classical cosmological tests. When we do not limit ourselves by constraints arising from the choice of an initial fluctuation spectrum, structures in an open universe (Ω0=0.1, λ0=0), including the peculiar velocity structure, can be reproduced in a flat Lemaitre universe (Ω0=0.1, λ0=0.9) for a large part of their evolution. From initial conditions that are not too extreme, these two world models are both able to produce strong anisotropies that easily persist for a Hubble time. This stability of flattening is the only aspect in which these two models differ significantly from the Einstein-de Sitter model. Taking into account the crudeness of the model, together with the fact that observed large-scale structures are not isolated, we conclude that use of this aspect of the dynamics of structure formation is not a promising method of placing tighter constraints on the value of Λ.
NASA Astrophysics Data System (ADS)
De Bernardis, F.; Aiola, S.; Vavagiakis, E. M.; Battaglia, N.; Niemack, M. D.; Beall, J.; Becker, D. T.; Bond, J. R.; Calabrese, E.; Cho, H.; Coughlin, K.; Datta, R.; Devlin, M.; Dunkley, J.; Dunner, R.; Ferraro, S.; Fox, A.; Gallardo, P. A.; Halpern, M.; Hand, N.; Hasselfield, M.; Henderson, S. W.; Hill, J. C.; Hilton, G. C.; Hilton, M.; Hincks, A. D.; Hlozek, R.; Hubmayr, J.; Huffenberger, K.; Hughes, J. P.; Irwin, K. D.; Koopman, B. J.; Kosowsky, A.; Li, D.; Louis, T.; Lungu, M.; Madhavacheril, M. S.; Maurin, L.; McMahon, J.; Moodley, K.; Naess, S.; Nati, F.; Newburgh, L.; Nibarger, J. P.; Page, L. A.; Partridge, B.; Schaan, E.; Schmitt, B. L.; Sehgal, N.; Sievers, J.; Simon, S. M.; Spergel, D. N.; Staggs, S. T.; Stevens, J. R.; Thornton, R. J.; van Engelen, A.; Van Lanen, J.; Wollack, E. J.
2017-03-01
We present a new measurement of the kinematic Sunyaev-Zel'dovich effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area, we evaluate the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A non-zero signal arises from the large-scale motions of halos containing the sample galaxies. The data fits an analytical signal model well, with the optical depth to microwave photon scattering as a free parameter determining the overall signal amplitude. We estimate the covariance matrix of the mean pairwise momentum as a function of galaxy separation, using microwave sky simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based errors give signal-to-noise estimates between 3.6 and 4.1 for varying galaxy luminosity cuts. We discuss how the other error determinations can lead to higher signal-to-noise values, and consider the impact of several possible systematic errors. Estimates of the optical depth from the average thermal Sunyaev-Zel'dovich signal at the sample galaxy positions are broadly consistent with those obtained from the mean pairwise momentum signal.
NASA Technical Reports Server (NTRS)
De Bernardis, F.; Aiola, S.; Vavagiakis, E. M.; Battaglia, N.; Niemack, M. D.; Beall, J.; Becker, D. T.; Bond, J. R.; Calabrese, E.; Cho, H.;
2017-01-01
We present a new measurement of the kinematic Sunyaev-Zel'dovich effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area, we evaluate the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A non-zero signal arises from the large-scale motions of halos containing the sample galaxies. The data fits an analytical signal model well, with the optical depth to microwave photon scattering as a free parameter determining the overall signal amplitude. We estimate the covariance matrix of the mean pairwise momentum as a function of galaxy separation, using microwave sky simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based errors give signal-to-noise estimates between 3.6 and 4.1 for varying galaxy luminosity cuts. We discuss how the other error determinations can lead to higher signal-to-noise values, and consider the impact of several possible systematic errors. Estimates of the optical depth from the average thermal Sunyaev-Zel'dovich signal at the sample galaxy positions are broadly consistent with those obtained from the mean pairwise momentum signal.
Detection of the pairwise kinematic Sunyaev-Zel'dovich effect with BOSS DR11 and the Atacama Cosmology Telescope
Bernardis, F. De; Aiola, S.; Vavagiakis, E. M.; ...
2017-03-07
Here, we present a new measurement of the kinematic Sunyaev-Zel'dovich effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area, we evaluate the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A non-zero signal arises from the large-scale motions of halos containing the sample galaxies. The data fits an analytical signal model well, with the optical depth to microwave photon scattering as a free parameter determining the overall signal amplitude. We estimate the covariancemore » matrix of the mean pairwise momentum as a function of galaxy separation, using microwave sky simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based errors give signal-to-noise estimates between 3.6 and 4.1 for varying galaxy luminosity cuts. We discuss how the other error determinations can lead to higher signal-to-noise values, and consider the impact of several possible systematic errors. Estimates of the optical depth from the average thermal Sunyaev-Zel'dovich signal at the sample galaxy positions are broadly consistent with those obtained from the mean pairwise momentum signal.« less
The double-soft limit in cosmological correlation functions and graviton exchange effects
NASA Astrophysics Data System (ADS)
Alinea, Allan L.; Kubota, Takahiro; Misumi, Nobuhiko
2017-01-01
The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and (1‑ns) ≈ 0.042, where ns is the scalar spectral index. It is argued that the graviton exchange effects are more dominant than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.
The effective two-dimensional phase space of cosmological scalar fields
NASA Astrophysics Data System (ADS)
Edwards, David C.
2016-08-01
It has been shown by Remmen and Carroll [1] that, for a model universe which contains only a kinetically canonical scalar field minimally coupled to gravity it is possible to choose `special coordinates' to describe a two-dimensional effective phase space. The special, non-canonical, coordinates are phi,dot phi and the ability to describe an effective phase space with these coordinates empowers the common usage of phi-dot phi as the space to define inflationary initial conditions. This paper extends the result to the full Horndeski action. The existence of a two-dimensional effective phase space is shown for the general case. Subsets of the Horndeski action, relevant to cosmology are considered as particular examples to highlight important aspects of the procedure.
THE DISTRIBUTION OF SATELLITES AROUND CENTRAL GALAXIES IN A COSMOLOGICAL HYDRODYNAMICAL SIMULATION
Dong, X. C.; Lin, W. P.; Wang, Yang Ocean; Kang, X.; Dutton, Aaron A.; Macciò, Andrea V. E-mail: kangxi@pmo.ac.cn
2014-08-20
Observations have shown that the spatial distribution of satellite galaxies is not random, but rather is aligned with the major axes of central galaxies (CGs). The strength of the alignment is dependent on the properties of both the satellites and centrals. Theoretical studies using dissipationless N-body simulations are limited by their inability to directly predict the shape of CGs. Using hydrodynamical simulations including gas cooling, star formation, and feedback, we carry out a study of galaxy alignment and its dependence on the 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 the CG better traces the dark matter distribution. The dependence of alignment on the color of CGs arises from the halo mass dependence, since the alignment between the shape of the central stellar component and the inner halo increases with halo mass. We also find that the alignment of satellites is most strongly dependent on their metallicity, suggesting that the metallicity of satellites, rather than color, is a better tracer of galaxy alignment on small scales. This could be tested in future observational studies.
ACCRETION SHOCKS IN CLUSTERS OF GALAXIES AND THEIR SZ SIGNATURE FROM COSMOLOGICAL SIMULATIONS
Molnar, Sandor M.; Hearn, Nathan; Evrard, August E.; Lake, George E-mail: nhearn@ucar.edu E-mail: evrard@umich.edu
2009-05-10
Cold dark matter (CDM) hierarchical structure formation models predict the existence of large-scale accretion shocks between the virial and turnaround radii of clusters of galaxies. Kocsis et al. suggest that the Sunyaev-Zel'dovich signal associated with such shocks might be observable with the next generation radio interferometer, ALMA (Atacama Large Millimeter Array). We study the three-dimensional distribution of accretion shocks around individual clusters of galaxies drawn from adaptive mesh refinement (AMR) and smoothed particle hydrodynamics simulations of {lambda}CDM (dark energy dominated CDM) models. In relaxed clusters, we find two distinct sets of shocks. One set ('virial shocks'), with Mach numbers of 2.5-4, is located at radii 0.9-1.3 R {sub vir}, where R {sub vir} is the spherical infall estimate of the virial radius, covering about 40%-50% of the total surface area around clusters at these radii. Another set of stronger shocks ({sup e}xternal shocks{sup )} is located farther out, at about 3 R {sub vir}, with large Mach numbers ({approx}100), covering about 40%-60% of the surface area. We simulate SZ surface brightness maps of relaxed massive galaxy clusters drawn from high-resolution AMR runs, and conclude that ALMA should be capable of detecting the virial shocks in massive clusters of galaxies. More simulations are needed to improve estimates of astrophysical noise and to determine optimal observational strategies.
NASA Astrophysics Data System (ADS)
Chluba, J.; Vasil, G. M.; Dursi, L. J.
2010-09-01
In this paper we discuss the effect of recombinations to highly excited states (n > 100) in hydrogen during the cosmological recombination epoch. For this purpose, we developed a new ordinary differential equation solver for the recombination problem, based on an implicit Gear's method. This solver allows us to include up to 350 l-resolved shells or ~61000 separate levels in the hydrogen model and to solve the recombination problem for one cosmology in ~27 h. This is a huge improvement in performance over our previous recombination code, for which a 100-shell computation (5050 separate states) already required ~150 h on a single processor. We show that for 350 shells down to redshift z ~ 200, the results for the free electron fraction have practically converged. The final modification in the free electron fraction at z ~ 200 decreases from about ΔNe/Ne ~ 2.8 per cent for 100 shells to ΔNe/Ne ~ 1.6 per cent for 350 shells. However, the associated changes in the cosmic microwave background power spectra at large multipoles l are rather small, so that for accurate computations in connection with the analysis of Planck data already ~100 shells are expected to be sufficient. Nevertheless, the total value of τ could still be affected at a significant level. We also briefly investigate the effect of collisions on the recombination dynamics. With our current estimates for the collisional rates we find a correction of ΔNe/Ne ~ -8.8 × 10-4 at z ~ 700, which is mainly caused by l-changing collisions with protons. Furthermore, we present results on the cosmological recombination spectrum, showing that at low frequencies collisional processes are important. However, the current accuracy of collisional rates is insufficient for precise computations of templates for the recombination spectrum at ν <~ 1GHz, and also the effect of collisions on the recombination dynamics suffers from the uncertainty in these rates. Improvements in collisional rates will therefore become
Villani, Mattia
2014-06-01
We consider the Goode-Wainwright representation of the Szekeres cosmological models and calculate the Taylor expansion of the luminosity distance in order to study the effects of the inhomogeneities on cosmographic parameters. Without making a particular choice for the arbitrary functions defining the metric, we Taylor expand up to the second order in redshift for Family I and up to the third order for Family II Szekeres metrics under the hypotesis, based on observation, that local structure formation is over. In a conservative fashion, we also allow for the existence of a non null cosmological constant.
Effects of quantized scalar fields in cosmological spacetimes with big rip singularities
Bates, Jason D.; Anderson, Paul R.
2010-07-15
Effects of quantized free scalar fields in cosmological spacetimes with big rip singularities are investigated. The energy densities for these fields are computed at late times when the expansion is very rapid. For the massless minimally coupled field it is shown that an attractor state exists in the sense that, for a large class of states, the energy density of the field asymptotically approaches the energy density it would have if it was in the attractor state. Results of numerical computations of the energy density for the massless minimally coupled field and for massive fields with minimal and conformal couplings to the scalar curvature are presented. For the massive fields the energy density is seen to always asymptotically approach that of the corresponding massless field. The question of whether the energy densities of quantized fields can be large enough for backreaction effects to remove the big rip singularity is addressed.
NASA Astrophysics Data System (ADS)
Crawford, David F.
Curvature Cosmology proposes a new cosmological model very different from, and more elegant than, the Big-Bang Theory. Curvature Cosmology is based on two major hypotheses that Hubble redshift is due to an interaction of photons with curved spacetime and that there is a pressure that acts to stabilise expansion and provides a static, stable universe. The main focus of this book is to describe these two hypotheses in detail and to examine all relevant cosmological data in the context of this new model of the universe. This model proposes that, though evolution of stars and galaxies is evident, the statistical properties of the universe are the same at all places and at all times. In short, the universe is ageless, has no defined beginning (unlike the Big-Bang model), and carries no evidence of expansion, despite the changeability of its components. Curvature Cosmology calls for a paradigm shift in current cosmology and requires at least basic (if not more complex) knowledge of past and current cosmological models and equations.
Testing fractional action cosmology
NASA Astrophysics Data System (ADS)
Shchigolev, V. K.
2016-08-01
The present work deals with a combined test of the so-called Fractional Action Cosmology (FAC) on the example of a specific model obtained by the author earlier. In this model, the effective cosmological term is proportional to the Hubble parameter squared through the so-called kinematic induction. The reason of studying this cosmological model could be explained by its ability to describe two periods of accelerated expansion, that is in agreement with the recent observations and the cosmological inflation paradigm. First of all, we put our model through the theoretical tests, which gives a general conception of the influence of the model parameters on its behavior. Then, we obtain some restrictions on the principal parameters of the model, including the fractional index, by means of the observational data. Finally, the cosmography parameters and the observational data compared to the theoretical predictions are presented both analytically and graphically.
Cosmology in a petri dish? Simulation of collective of colloids at fluid interfaces
NASA Astrophysics Data System (ADS)
Bleibel, J.
2014-04-01
Interfacially trapped, micrometer-sized colloidal particles interact via ranged capillary attraction which is analogous to two-dimensional screened Newtonian gravity with the capillary length λ as the tuneable screening length. Using Brownian namics simulations and density functional theory, we study the dynamics of an initially prepared distribution of colloids, either a random homogeneous distribution, or a finitely- sized patch of colloids. Whereas the limit λ → ∞ corresponds to the global collapse self-gravitating fluid, for smaller λ the dynamics crosses over to spinodal decomposition showing a coarsening of regions of enhanced density which emerge from initial fluctuations. For the finite patch of colloids and intermediate λ we predict theoretically and serve in simulations a ringlike density peak at the outer rim of the disclike patch, moving as an inbound shock wave. Experimental realizations of this crossover scenario appear be well possible for colloids trapped at water interfaces and having a radius of around micrometer. Finally, the influence of hydrodynamic interactions on this capillary collapse will be discussed briefly.
NASA Astrophysics Data System (ADS)
Devriendt, Julien
2015-08-01
In this talk I will review how numerical hydrodynamics simulations predict galaxies evolve in the redshift range 1
Simulations of solitonic core mergers in ultralight axion dark matter cosmologies
NASA Astrophysics Data System (ADS)
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.
Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations
NASA Astrophysics Data System (ADS)
Hirano, Shin'ichi; Nishi, Sakine; Kobayashi, Tsutomu
2017-07-01
We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic F(Script R) theory is plagued with the Ostrogradsky instability.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Chan, T. K.; Kereš, D.; Oñorbe, J.; Hopkins, P. F.; Muratov, A. L.; Faucher-Giguère, C.-A.; Quataert, E.
2015-12-01
We study the distribution of cold dark matter (CDM) in cosmological simulations from the FIRE (Feedback In Realistic Environments) project, for M* ˜ 104-11 M⊙ galaxies in Mh ˜ 109-12 M⊙ haloes. FIRE incorporates explicit stellar feedback in the multiphase interstellar medium, 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. This is broadly consistent with previous work using simpler feedback schemes, but we find steeper mass dependence of α, and relatively late growth of cores. Because the star formation efficiency M*/Mh is strongly halo mass dependent, a rapid change in α occurs around Mh ˜ 1010 M⊙ (M* ˜ 106-107 M⊙), as sufficient feedback energy becomes available to perturb the DM. Large cores are not established during the period of rapid growth of haloes because of ongoing DM mass accumulation. Instead, cores require several bursts of star formation after the rapid build-up 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 haloes produce DM profiles slightly shallower than the Navarro-Frenk-White profile, consistent with the normalization of the observed Tully-Fisher relation.
NASA Astrophysics Data System (ADS)
Krauss, L. M.
1999-01-01
The long-derided cosmological constant - a contrivance of Albert Einstein's that represents a bizarre form of energy inherent in space itself - is one of two contenders for explaining changes in the expansion rate of the Universe.
NASA Astrophysics Data System (ADS)
Chen, P.
2014-05-01
Recent years have witnessed tremendous progress in our understanding of the cosmos, which in turn points to even deeper questions to be further addressed. Concurrently the laser technology has undergone dramatic revolutions, providing exciting opportunity for science applications. History has shown that the symbiosis between direct observations and laboratory investigation is instrumental in the progress of astrophysics. We believe that this remains true in cosmology. Current frontier phenomena related to particle astrophysics and cosmology typically involve one or more of the following conditions: (1) extremely high energy events;(2) very high density, high temperature processes; (3) super strong field environments. Laboratory experiments using high intensity lasers can calibrate astrophysical observations, investigate underlying dynamics of astrophysical phenomena, and probe fundamental physics in extreme limits. In this article we give an overview of the exciting prospect of laser cosmology. In particular, we showcase its unique capability of investigating frontier cosmology issues such as cosmic accelerator and quantum gravity.
NASA Astrophysics Data System (ADS)
Blau, S. K.; Guth, A. H.
Contents: 1. Introduction. 2. Summary of the standard cosmological model. 3. Problems of the standard cosmological model. 4. The original inflationary universe. 5. Successes of the original inflationary model. 6. Problems of the original inflationary model. 7. The new inflationary universe. 8. Density perturbations in the new inflationary universe. 9. Quantum theory of the new inflationary universe phase transition. 10. Inflation in the minimal SU(5) grand unified theory. 11. False vacuum bubbles and child universes. 12. Conclusion.
Bag, Satadru; Sahni, Varun; Shtanov, Yuri; Unnikrishnan, Sanil E-mail: varun@iucaa.ernet.in E-mail: sanil@lnmiit.ac.in
2014-07-01
We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed past-eternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result in a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.
The impact of non-Planckian effects on cosmological radio background
NASA Astrophysics Data System (ADS)
Colafrancesco, Sergio; Shehzad Emritte, Mohammad; Marchegiani, Paolo
2015-05-01
Non-Planckian (NP) spectral modifications of the CMB radiation spectrum can be produced due to the existence of a non-zero value of the plasma frequency at the recombination epoch. We present here an analysis of NP effects on the cosmological radio background and we derive, for the first time, predictions of their amplitude on three different observables: the CMB spectrum, the Sunyaev-Zel'dovich (SZ) effect in cosmic structures, and the 21-cm background temperature brightness change. We find that NP effect can manifest in the CMB spectrum at ν lesssim 400 MHz as a drastic cut-off in the CMB intensity. Using the available CMB data in the relevant ν range (i.e., mainly at lesssim 1 GHz and in the COBE-FIRAS data frequency range), we derive upper limits on the plasma frequency νp = 206, 346 and 418 MHz at 1, 2 and 3 σ confidence level, respectively. We find that the difference between the pure Planck spectrum and the one modified by NP effects is of the order of mJy/arcmin2 at ν lesssim 0.5 GHz and it becomes smaller at higher frequencies where it is ~ 0.1 mJy/arcmin2 at ν gtrsim 150 GHz, thus indicating that the experimental route to probe NP effects in the early universe is to observe the cosmological radio background at very low frequencies. We have calculated for the first time the NP SZ effect (SZNP) using the upper limits on νp allowed by the CMB data. We found that the SZNP effect shows a unique spectral feature, i.e. a peak located exactly at the plasma frequency νp and this is independent of the cluster parameters (such as its temperature or optical depth). This offers a way, therefore, to measure directly and unambiguously the plasma frequency in the early universe at the epoch of recombination by using galaxy clusters in the local universe, thus opening a unique window for the experimental exploration of plasma effects in the early universe. We have shown that the SKA-LOW has the potential to observe such a signal integrating over the central
The impact of non-Planckian effects on cosmological radio background
Colafrancesco, Sergio; Emritte, Mohammad Shehzad; Marchegiani, Paolo E-mail: emrittes@yahoo.com
2015-05-01
Non-Planckian (NP) spectral modifications of the CMB radiation spectrum can be produced due to the existence of a non-zero value of the plasma frequency at the recombination epoch. We present here an analysis of NP effects on the cosmological radio background and we derive, for the first time, predictions of their amplitude on three different observables: the CMB spectrum, the Sunyaev-Zel'dovich (SZ) effect in cosmic structures, and the 21-cm background temperature brightness change. We find that NP effect can manifest in the CMB spectrum at ν ∼< 400 MHz as a drastic cut-off in the CMB intensity. Using the available CMB data in the relevant ν range (i.e., mainly at ∼< 1 GHz and in the COBE-FIRAS data frequency range), we derive upper limits on the plasma frequency ν{sub p} = 206, 346 and 418 MHz at 1, 2 and 3 σ confidence level, respectively. We find that the difference between the pure Planck spectrum and the one modified by NP effects is of the order of mJy/arcmin{sup 2} at ν ∼< 0.5 GHz and it becomes smaller at higher frequencies where it is ∼ 0.1 mJy/arcmin{sup 2} at ν ∼> 150 GHz, thus indicating that the experimental route to probe NP effects in the early universe is to observe the cosmological radio background at very low frequencies. We have calculated for the first time the NP SZ effect (SZ{sub NP}) using the upper limits on ν{sub p} allowed by the CMB data. We found that the SZ{sub NP} effect shows a unique spectral feature, i.e. a peak located exactly at the plasma frequency ν{sub p} and this is independent of the cluster parameters (such as its temperature or optical depth). This offers a way, therefore, to measure directly and unambiguously the plasma frequency in the early universe at the epoch of recombination by using galaxy clusters in the local universe, thus opening a unique window for the experimental exploration of plasma effects in the early universe. We have shown that the SKA-LOW has the potential to observe such a
NASA Astrophysics Data System (ADS)
Ricotti, Massimo; Ostriker, Jeremiah P.; Gnedin, Nickolay Y.
2005-02-01
We use numerical simulations of a cosmological volume to study the X-ray ionization and heating of the intergalactic medium (IGM) by an early population of accreting black holes (BHs). By considering theoretical limits on the accretion rate and observational constraints from the X-ray background and faint X-ray source counts, we find that the maximum value of the optical depth to Thompson scattering which can be produced using these models is τe~= 0.17, in agreement with previous semi-analytic results. The redshifted soft X-ray background produced by these early sources is important in producing a fully ionized atomic hydrogen in the low-density intergalactic medium before stellar reionization at redshift z~ 6-7. As a result, stellar re-ionization is characterized by an almost instantaneous `overlap phase' of HII regions. The background also produces a second HeII re-ionization at about redshift 3 and maintains the temperature of the IGM at about 10000K even at low redshifts. If the spectral energy distribution of these sources has a non-negligible high-energy power-law component, the luminosity in the soft X-ray band of the `typical' galaxies hosting intermediate-mass accreting BHs is maximum at z~ 15 and is about one or two orders of magnitude below the sensitivity limit of the Chandra Deep Field. We find that about a thousand of these sources may be present per square arcmin of the sky, producing potentially detectable fluctuations. We also estimate that a few rare objects, not present in our small simulated volume, could be luminous enough to be visible in the Chandra Deep Field. The XEUS and Constellation-X satellites will be able to detect more of these sources that, if radio loud, could be used to study the 21-cm forest in absorption. A signature of an early X-ray pre-ionization is the production of secondary cosmic microwave background (CMB) anisotropies on small angular scales (<1arcmin). We find that in these models the power spectrum of temperature
NASA Astrophysics Data System (ADS)
Governato, Fabio
The physical processes shaping the galaxies 'Hubble Sequence' are still poorly understood. Are gas outflows generated by Supernovae the main mechanism responsible for regulating star formation and the establishing the stellar mass - metallicity relation? What fraction of stars now in spheroids was originated in mergers? How does the environment of groups and clusters affect the evolution of galaxy satellites? The PI will study these problems analyzing a new set of state of the art hydro simulations of uniform cosmological volumes. This project has already been awarded a computational budget of 200 million CPU hours (but has only limited seed funding for science, hence this proposal). The best simulations will match the force and spatial resolution of the current best 'zoomed in' runs, as 'Eris' and will yield the first large statistical sample (1500+) of internally resolved galaxy systems with stellar masses ranging from from 10^7 to 10^10.5 solar masses. These simulations will allow us, for the very first time on such a large statistical set, to fully map the thermodynamical history of the baryons of internally resolved galaxies and identify the relative importance of the processes that shape their evolution as a function of stellar mass and cosmic time. As a novel, significant improvement over previous works we will introduce a new, unbiased statistical approach to the exploration of parameter space to optimize the model for star formation (SF) and feedback from supernovae and super massive back holes. This approach will also be used to evaluate the effects of resolution. The simulations will be run using ChaNGa, an improved version of Gasoline. Our flagship run will model a large volume of space (15.6k cubic Mpc) using 25 billion resolution elements. ChaNGa currently scales up to 35,000 cores and include a new version of the SPH implementation that drastically improves the description of temperature/density discontinuities and Kelvin-Helmholtz instabilities (and
The Convergence of Particle-in-Cell Schemes for Cosmological Dark Matter Simulations
NASA Astrophysics Data System (ADS)
Myers, Andrew; Colella, Phillip; Van Straalen, Brian
2016-01-01
Particle methods are a ubiquitous tool for solving the Vlasov-Poisson equation in comoving coordinates, which is used to model the gravitational evolution of dark matter (DM) in an expanding universe. However, these methods are known to produce poor results on idealized test problems, particularly at late times, after the particle trajectories have crossed. To investigate this, we have performed a series of one- and two-dimensional “Zel’dovich pancake” calculations using the popular particle-in-cell (PIC) method. We find that PIC can indeed converge on these problems provided that the following modifications are made. The first modification is to regularize the singular initial distribution function by introducing a small but finite artificial velocity dispersion. This process is analogous to artificial viscosity in compressible gas dynamics, and, as with artificial viscosity, the amount of regularization can be tailored so that its effect outside of a well-defined region—in this case, the high-density caustics—is small. The second modification is the introduction of a particle remapping procedure that periodically reexpresses the DM distribution function using a new set of particles. We describe a remapping algorithm that is third-order accurate and adaptive in phase space. This procedure prevents the accumulation of numerical errors in integrating the particle trajectories from growing large enough to significantly degrade the solution. Once both of these changes are made, PIC converges at second order on the Zel’dovich pancake problem, even at late times, after many caustics have formed. Furthermore, the resulting scheme does not suffer from the unphysical, small-scale “clumping” phenomenon known to occur on the pancake problem when the perturbation wavevector is not aligned with one of the Cartesian coordinate axes.
THE CONVERGENCE OF PARTICLE-IN-CELL SCHEMES FOR COSMOLOGICAL DARK MATTER SIMULATIONS
Myers, Andrew; Colella, Phillip; Van Straalen, Brian
2016-01-10
Particle methods are a ubiquitous tool for solving the Vlasov–Poisson equation in comoving coordinates, which is used to model the gravitational evolution of dark matter (DM) in an expanding universe. However, these methods are known to produce poor results on idealized test problems, particularly at late times, after the particle trajectories have crossed. To investigate this, we have performed a series of one- and two-dimensional “Zel’dovich pancake” calculations using the popular particle-in-cell (PIC) method. We find that PIC can indeed converge on these problems provided that the following modifications are made. The first modification is to regularize the singular initial distribution function by introducing a small but finite artificial velocity dispersion. This process is analogous to artificial viscosity in compressible gas dynamics, and, as with artificial viscosity, the amount of regularization can be tailored so that its effect outside of a well-defined region—in this case, the high-density caustics—is small. The second modification is the introduction of a particle remapping procedure that periodically reexpresses the DM distribution function using a new set of particles. We describe a remapping algorithm that is third-order accurate and adaptive in phase space. This procedure prevents the accumulation of numerical errors in integrating the particle trajectories from growing large enough to significantly degrade the solution. Once both of these changes are made, PIC converges at second order on the Zel’dovich pancake problem, even at late times, after many caustics have formed. Furthermore, the resulting scheme does not suffer from the unphysical, small-scale “clumping” phenomenon known to occur on the pancake problem when the perturbation wavevector is not aligned with one of the Cartesian coordinate axes.
Weinstein, M
2003-11-19
This paper discusses the problem of inflation in the context of Friedmann-Robertson-Walker Cosmology. We show how, after a simple change of variables, one can quantize the problem in a way which parallels the classical discussion. The result is that two of the Einstein equations arise as exact equations of motion; one of the usual Einstein equations (suitably quantized) survives as a constraint equation to be imposed on the space of physical states. However, the Friedmann equation, which is also a constraint equation and which is the basis of the Wheeler-DeWitt equation, acquires a welcome quantum correction that becomes significant for small scale factors. We then discuss the extension of this result to a full quantum mechanical derivation of the anisotropy ({delta}{rho}/{rho}) in the cosmic microwave background radiation and the possibility that the extra term in the Friedmann equation could have observable consequences. Finally, we suggest interesting ways in which these techniques can be generalized to cast light on the question of chaotic or eternal inflation. In particular, we suggest that one can put an experimental bound on how far away a universe with a scale factor very different from our own must be, by looking at its effects on our CMB radiation.
Cosmology in bimetric theory with an effective composite coupling to matter
Gümrükçüoğlu, A. Emir; Heisenberg, Lavinia; Mukohyama, Shinji; Tanahashi, Norihiro E-mail: laviniah@kth.se E-mail: N.Tanahashi@damtp.cam.ac.uk
2015-04-01
We study the cosmology of bimetric theory with a composite matter coupling. We find two possible branches of background evolution. We investigate the question of stability of cosmological perturbations. For the tensor and vector perturbations, we derive conditions on the absence of ghost and gradient instabilities. For the scalar modes, we obtain conditions for avoiding ghost degrees. In the first branch, we find that one of the scalar modes becomes a ghost at the late stages of the evolution. Conversely, this problem can be avoided in the second branch. However, we also find that the constraint for the second branch prevents the doubly coupled matter fields from being the standard ingredients of cosmology. We thus conclude that a realistic and stable cosmological model requires additional minimally coupled matter fields.
Newtonian and relativistic cosmologies
NASA Astrophysics Data System (ADS)
Green, Stephen R.; Wald, Robert M.
2012-03-01
Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is well known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the same equations as arise in relativistic Friedmann-Lemaître-Robinson-Walker cosmology, and it also is known that a correspondence between Newtonian and relativistic dust cosmologies continues to hold in linearized perturbation theory in the marginally bound/spatially flat case. Nevertheless, it is far from obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology when there is significant nonlinear dynamical behavior at small scales. We investigate this issue in the light of a perturbative framework that we have recently developed [S. R. Green and R. M. Wald, Phys. Rev. DPRVDAQ1550-7998 83, 084020 (2011).10.1103/PhysRevD.83.084020], which allows for such nonlinearity at small scales. We propose a relatively straightforward dictionary—which is exact at the linearized level—that maps Newtonian dust cosmologies into general relativistic dust cosmologies, and we use our “ordering scheme” to determine the degree to which the resulting metric and matter distribution solve Einstein’s equation. We find that, within our ordering scheme, Einstein’s equation fails to hold at “order 1” at small scales and at “order ɛ” at large scales. We then find the additional corrections to the metric and matter distribution needed to satisfy Einstein’s equation to these orders. While these corrections are of some interest in their own right, our main purpose in calculating them is that their smallness should provide a criterion for the validity of the original dictionary (as well as simplified versions of this dictionary). We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations
Local gravitational redshifts can bias cosmological measurements
Wojtak, Radosław; Davis, Tamara M.; Wiis, Jophiel E-mail: tamarad@physics.uq.edu.au
2015-07-01
Measurements of cosmological parameters via the distance-redshift relation usually rely on models that assume a homogenous universe. It is commonly presumed that the large-scale structure evident in our Universe has a negligible impact on the measurement if distances probed in observations are sufficiently large (compared to the scale of inhomogeneities) and are averaged over different directions on the sky. This presumption does not hold when considering the effect of the gravitational redshift caused by our local gravitational potential, which alters light coming from all distances and directions in the same way. Despite its small magnitude, this local gravitational redshift gives rise to noticeable effects in cosmological inference using SN Ia data. Assuming conservative prior knowledge of the local potential given by sampling a range of gravitational potentials at locations of Milky-Way-like galaxies identified in cosmological simulations, we show that ignoring the gravitational redshift effect in a standard data analysis leads to an additional systematic error of ∼1% in the determination of density parameters and the dark energy equation of state. We conclude that our local gravitational field affects our cosmological inference at a level that is important in future observations aiming to achieve percent-level accuracy.
Local gravitational redshifts can bias cosmological measurements
NASA Astrophysics Data System (ADS)
Wojtak, Radosław; Davis, Tamara M.; Wiis, Jophiel
2015-07-01
Measurements of cosmological parameters via the distance-redshift relation usually rely on models that assume a homogenous universe. It is commonly presumed that the large-scale structure evident in our Universe has a negligible impact on the measurement if distances probed in observations are sufficiently large (compared to the scale of inhomogeneities) and are averaged over different directions on the sky. This presumption does not hold when considering the effect of the gravitational redshift caused by our local gravitational potential, which alters light coming from all distances and directions in the same way. Despite its small magnitude, this local gravitational redshift gives rise to noticeable effects in cosmological inference using SN Ia data. Assuming conservative prior knowledge of the local potential given by sampling a range of gravitational potentials at locations of Milky-Way-like galaxies identified in cosmological simulations, we show that ignoring the gravitational redshift effect in a standard data analysis leads to an additional systematic error of ~1% in the determination of density parameters and the dark energy equation of state. We conclude that our local gravitational field affects our cosmological inference at a level that is important in future observations aiming to achieve percent-level accuracy.
NASA Astrophysics Data System (ADS)
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.
The effect of early radiation in N-body simulations of cosmic structure formation
NASA Astrophysics Data System (ADS)
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.
Hwang, Jai-chan; Noh, Hyerim
2007-11-15
We present general relativistic correction terms appearing in Newton's gravity to the second-order perturbations of cosmological fluids. In our previous work we have shown that to the second-order perturbations, the density and velocity perturbation equations of general relativistic zero-pressure, irrotational, single-component fluid in a spatially flat background coincide exactly with the ones known in Newton's theory without using the gravitational potential. We also have shown the effect of gravitational waves to the second order, and pure general relativistic correction terms appearing in the third-order perturbations. Here, we present results of second-order perturbations relaxing all the assumptions made in our previous works. We derive the general relativistic correction terms arising due to (i) pressure, (ii) multicomponent, (iii) background spatial curvature, and (iv) rotation. In the case of multicomponent zero-pressure, irrotational fluids under the flat background, we effectively do not have relativistic correction terms, thus the relativistic equations expressed in terms of density and velocity perturbations again coincide with the Newtonian ones. In the other three cases we generally have pure general relativistic correction terms. In the case of pressure, the relativistic corrections appear even in the level of background and linear perturbation equations. In the presence of background spatial curvature, or rotation, pure relativistic correction terms directly appear in the Newtonian equations of motion of density and velocity perturbations to the second order; to the linear order, without using the gravitational potential (or metric perturbations), we have relativistic/Newtonian correspondences for density and velocity perturbations of a single-component fluid including the rotation even in the presence of background spatial curvature. In the small-scale limit (far inside the horizon), to the second-order, relativistic equations of density and
NASA Astrophysics Data System (ADS)
Lattanzi, M. G.
The accurate measurement of the motions of stars in our Galaxy can provide access to the cosmological signatures in the disk and halo, while astrometric experiments from within our Solar System can uniquely probe possible deviations from General Relativity. This article will introduce to the fact that astrometry has the potential, thanks also to impressive technological advancements, to become a key player in the field of local cosmology. For example, accurate absolute kinematics at the scale of the Milky Way can, for the first time in situ, account for the predictions made by the cold dark matter model for the Galactic halo, and eventually map out the distribution of dark matter, or other formation mechanisms, required to explain the signatures recently identified in the old component of the thick disk. Final notes dwell on to what extent Gaia can fulfill the expectations of astrometric cosmology and on what must instead be left to future, specifically designed, astrometric experiments.
NASA Astrophysics Data System (ADS)
Harvey, Alex
1993-10-01
Two of the most common terms employed in discussing cosmological models are open and closed. They are occasionally misused either by not recognizing or by not making it clear that each term may be used to characterize, independently and simultaneously, both the dynamic behavior and spatial geometric structure of the model under discussion. In addition, the spatial geometric structure implied by the terms open and closed is itself often either misunderstood or misused. Lastly, the role played by the cosmological constant is often improperly slighted. This paper is intended to give several examples of the abuse of terminology and clarify the distinction by means of a brief, elementary overview of Friedmann-Robertson-Walker cosmological models.
Effective dynamics, big bounces, and scaling symmetry in Bianchi type I loop quantum cosmology
Chiou, D.-W.
2007-12-15
The detailed formulation for loop quantum cosmology (LQC) in the Bianchi I model with a scalar massless field has been constructed. In this paper, its effective dynamics is studied in two improved strategies for implementing the LQC discreteness corrections. Both schemes show that the big bang is replaced by the big bounces, which take place up to 3 times, once in each diagonal direction, when the area or volume scale factor approaches the critical values in the Planck regime measured by the reference of the scalar field momentum. These two strategies give different evolutions: In one scheme, the effective dynamics is independent of the choice of the finite sized cell prescribed to make Hamiltonian finite; in the other, the effective dynamics reacts to the macroscopic scales introduced by the boundary conditions. Both schemes reveal interesting symmetries of scaling, which are reminiscent of the relational interpretation of quantum mechanics and also suggest that the fundamental spatial scale (area gap) may give rise to a temporal scale.
Effective dynamics, big bounces, and scaling symmetry in Bianchi type I loop quantum cosmology
NASA Astrophysics Data System (ADS)
Chiou, Dah-Wei
2007-12-01
The detailed formulation for loop quantum cosmology (LQC) in the Bianchi I model with a scalar massless field has been constructed. In this paper, its effective dynamics is studied in two improved strategies for implementing the LQC discreteness corrections. Both schemes show that the big bang is replaced by the big bounces, which take place up to 3 times, once in each diagonal direction, when the area or volume scale factor approaches the critical values in the Planck regime measured by the reference of the scalar field momentum. These two strategies give different evolutions: In one scheme, the effective dynamics is independent of the choice of the finite sized cell prescribed to make Hamiltonian finite; in the other, the effective dynamics reacts to the macroscopic scales introduced by the boundary conditions. Both schemes reveal interesting symmetries of scaling, which are reminiscent of the relational interpretation of quantum mechanics and also suggest that the fundamental spatial scale (area gap) may give rise to a temporal scale.
Physical effects involved in the measurements of neutrino masses with future cosmological data
NASA Astrophysics Data System (ADS)
Archidiacono, Maria; Brinckmann, Thejs; Lesgourgues, Julien; Poulin, Vivian
2017-02-01
Future Cosmic Microwave Background experiments together with upcoming galaxy and 21-cm surveys will provide extremely accurate measurements of different cosmological observables located at different epochs of the cosmic history. The new data will be able to constrain the neutrino mass sum with the best precision ever. In order to exploit the complementarity of the different redshift probes, a deep understanding of the physical effects driving the impact of massive neutrinos on CMB and large scale structures is required. The goal of this work is to describe these effects, assuming a summed neutrino mass close to its minimum allowed value. We find that parameter degeneracies can be removed by appropriate combinations, leading to robust and model independent constraints. A joint forecast of the sensitivity of Euclid and DESI surveys together with a CORE-like CMB experiment leads to a 1σ uncertainty of 14 meV on the summed neutrino mass. Finally the degeneracy between Mν and the optical depth at reionization τreio, originating in the combination of CMB and low redshift galaxy probes, might be broken by future 21-cm surveys, thus further decreasing the uncertainty on Mν. For instance, an independent determination of the optical depth with an accuracy of σ(τreio)=0.001 (which might be achievable, although this is subject to astrophysical uncertainties) would decrease the uncertainty down to σ(Mν)=12 meV.
NASA Astrophysics Data System (ADS)
Ricotti, Massimo; Ostriker, Jeremiah; Mack, Katherine
2017-01-01
We investigate the effect of nonevaporating primordial black holes (PBHs) on the ionization and thermal history of the universe. X-rays emitted by gas accretion onto PBHs modify the cosmic recombination history, producing measurable effects on the spectrum and anisotropies of the cosmic microwave background (CMB). Using the third-year WMAP data and COBE FIRAS data we improve existing upper limits on the abundance of PBHs with masses > 0 . 1 M⊙ by several orders of magnitude, thus ruling out PBHs in this mass range as a significant component of the dark matter. Fitting WMAP/Planck data with cosmological models that do not allow for nonstandard recombination histories, as produced by PBHs or other early energy sources, leads to underestimating the best-fit values of the amplitude of linear density fluctuations (σ8) and the scalar spectral index (ns). We find that a fraction > 0 . 1 % - 1 % of the dark matter in 30 M⊙ PBHs produces CMB spectral distortions at a level detectable by FIRAS. Therefore, even allowing for possible modeling uncertainties, future missions measuring CMB spectral distortions will detect the imprint of dark matter if it's composed of 30 M⊙ PBHs, as suggested to interpret recent LIGO results.
Information entropy in cosmology.
Hosoya, Akio; Buchert, Thomas; Morita, Masaaki
2004-04-09
The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is identical to a fluid model of the Kullback-Leibler relative information entropy, expressing the distinguishability of the local inhomogeneous mass density field from its spatial average on arbitrary compact domains. We discuss the time evolution of "effective information" and explore some implications. We conjecture that the information content of the Universe-measured by relative information entropy of a cosmological model containing dust matter-is increasing.
Gravitation and modern cosmology - The cosmological constant problem
NASA Astrophysics Data System (ADS)
Zichichi, Antonino; de Sabbata, Venzo; Sanchez, Norma
An updated version of different approaches to the cosmological constant problem discussed at a symposium in honor of Peter Gabriel Bergmann's 75th birthday, that took place in Erice on 17-20 September 1990, is presented. Topics addressed include an effective action model for the cosmological constant revisited; torsion, quantum effects, and the problem of cosmological constant; variations of constants and exact solutions in multidimensional gravity; null surface canonical formalism; qualitative cosmology; and the gravitational field of an arbitrary axisymmetric mass with a magnetic dipole moment. Attention is also given to a simple model of the universe without singularities; string theory and quantization of gravity; and velocity of propagation of gravitational radiation, mass of the gravitation, range of the gravitational force, and the cosmological constant.
NASA Astrophysics Data System (ADS)
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.
The Lyman Alpha Forest in hierarchical cosmologies
Anninos, P; Bryan, G L; Machacek, M; Moiksin, A; Norman, M L; Zhang, Y
1999-07-02
The comparison of quasar absorption spectra with numerically simulated spectra from hierarchical cosmological models of structure formation promises to be a valuable tool to discriminate among these models. We present simulation results for the column density, Doppler b parameter, and optical depth probability distributions for five popular cosmological models.
Cosmology Solved? Quite Possibly!
NASA Astrophysics Data System (ADS)
Turner, Michael S.
1999-03-01
The discovery of the cosmic microwave background (CMB) in 1964 by Penzias and Wilson led to the establishment of the hot big bang cosmological model some 10 years later. Discoveries made in 1998 may ultimately have as profound an effect on our understanding of the origin and evolution of the universe. Taken at face value, they confirm the basic tenets of inflation + cold dark matter, a bold and expansive theory that addresses all the fundamental questions left unanswered by the hot big bang model and holds that the universe is flat, slowly moving elementary particles provide the cosmic infrastructure, and quantum fluctuations seeded all the structure seen in the universe today. Just as it took a decade to establish the hot big bang model after the discovery of the CMB, it will likely take another 10 years to establish the latest addition to the standard cosmology and make the answer to ``Cosmology solved?'' ``YES!'' Whether or not 1998 proves to be a cosmic milestone, the coming avalanche of high-quality cosmological data promises to make the next 20 years an extremely exciting period for cosmology.
NASA Astrophysics Data System (ADS)
Adler, Stephen L.
2016-06-01
A frame-dependent effective action motivated by the postulates of three-space general coordinate invariance and Weyl scaling invariance exactly mimics a cosmological constant in Robertson-Walker spacetimes. However, in a static spherically symmetric Schwarzschild-like geometry it modifies the black hole horizon structure within microscopic distances of the nominal horizon, in such a way that g00 never vanishes. This could have important implications for the black hole “information paradox”.
NASA Astrophysics Data System (ADS)
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: Multidimensional cosmology
NASA Astrophysics Data System (ADS)
Alvarez, Enrique
This paper briefly reports on some recent attempts to construct a cosmology consistent with present ideas about the fundamental theories of nature, which generally involve extra dimensions. The decoupling of the extra dimensions from the usual ones is analyzed, as well as the possiblity of phase transitions in a "superstring universe".
Higher dimensional loop quantum cosmology
NASA Astrophysics Data System (ADS)
Zhang, Xiangdong
2016-07-01
Loop quantum cosmology (LQC) is the symmetric sector of loop quantum gravity. In this paper, we generalize the structure of loop quantum cosmology to the theories with arbitrary spacetime dimensions. The isotropic and homogeneous cosmological model in n+1 dimensions is quantized by the loop quantization method. Interestingly, we find that the underlying quantum theories are divided into two qualitatively different sectors according to spacetime dimensions. The effective Hamiltonian and modified dynamical equations of n+1 dimensional LQC are obtained. Moreover, our results indicate that the classical big bang singularity is resolved in arbitrary spacetime dimensions by a quantum bounce. We also briefly discuss the similarities and differences between the n+1 dimensional model and the 3+1 dimensional one. Our model serves as a first example of higher dimensional loop quantum cosmology and offers the possibility to investigate quantum gravity effects in higher dimensional cosmology.
Revisiting the decoupling effects in the running of the Cosmological Constant
NASA Astrophysics Data System (ADS)
Antipin, Oleg; Melić, Blaženka
2017-09-01
We revisit the decoupling effects associated with heavy particles in the renormalization group running of the vacuum energy in a mass-dependent renormalization scheme. We find the running of the vacuum energy stemming from the Higgs condensate in the entire energy range and show that it behaves as expected from the simple dimensional arguments meaning that it exhibits the quadratic sensitivity to the mass of the heavy particles in the infrared regime. The consequence of such a running to the fine-tuning problem with the measured value of the Cosmological Constant is analyzed and the constraint on the mass spectrum of a given model is derived. We show that in the Standard Model (SM) this fine-tuning constraint is not satisfied while in the massless theories this constraint formally coincides with the well known Veltman condition. We also provide a remarkably simple extension of the SM where saturation of this constraint enables us to predict the radiative Higgs mass correctly. Generalization to constant curvature spaces is also given.
Cosmological variation of the MOND constant: Secular effects on galactic systems
NASA Astrophysics Data System (ADS)
Milgrom, Mordehai
2015-02-01
The proximity of the MOND acceleration constant with cosmological accelerations—for example, a0≈c H0/2 π —points to its possibly decreasing with cosmic time. I begin to consider the secular changes induced in galactic systems by such presumed variations, which are assumed to be adiabatic. It is important to understand these effects, in isolation from other evolutionary influences, in order to identify or constrain a0 variations by detection of induced effects, or lack thereof. I find that as long as the system is fully in the deep-MOND regime—as applies to many galactic systems—the adiabatic response of the system obeys simple scaling laws. For example, in a system that would be stationary for fixed a0, the system expands homologously as a0-1 /4, while internal velocities decrease uniformly as a01 /4. If a0∝c H at all relevant times, this change amounts to a factor of ˜2.5 since redshift 10. For rotating systems, the angular frequency Ω ∝a01 /2. The accelerations increase relative to a0 as a0-1 /4, pushing the system towards the Newtonian regime. All this follows from the appearance of a0 in MOND and the scale invariance of the deep-MOND limit—two basic tenets of MOND. More complicated evolution ensues when parts of the system become Newtonian, or are so from inception. For example, these parts may become unstable since they are not protected by MOND's stabilizing effects. The existence of such regions also modifies the MONDian regime since they affect the potential everywhere, and constituents might migrate between the Newtonian and MONDian regimes. Studying these last effects would require detailed numerical calculations.
Cosmological parameter estimation: impact of CMB aberration
Catena, Riccardo; Notari, Alessio E-mail: notari@ffn.ub.es
2013-04-01
The peculiar motion of an observer with respect to the CMB rest frame induces an apparent deflection of the observed CMB photons, i.e. aberration, and a shift in their frequency, i.e. Doppler effect. Both effects distort the temperature multipoles a{sub lm}'s via a mixing matrix at any l. The common lore when performing a CMB based cosmological parameter estimation is to consider that Doppler affects only the l = 1 multipole, and neglect any other corrections. In this paper we reconsider the validity of this assumption, showing that it is actually not robust when sky cuts are included to model CMB foreground contaminations. Assuming a simple fiducial cosmological model with five parameters, we simulated CMB temperature maps of the sky in a WMAP-like and in a Planck-like experiment and added aberration and Doppler effects to the maps. We then analyzed with a MCMC in a Bayesian framework the maps with and without aberration and Doppler effects in order to assess the ability of reconstructing the parameters of the fiducial model. We find that, depending on the specific realization of the simulated data, the parameters can be biased up to one standard deviation for WMAP and almost two standard deviations for Planck. Therefore we conclude that in general it is not a solid assumption to neglect aberration in a CMB based cosmological parameter estimation.
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Sarkar, Abir; Mondal, Rajesh; Das, Subinoy; Sethi, Shiv. K.; Bharadwaj, Somnath; Marsh, David J. E.
2016-04-01
The particle nature of dark matter remains a mystery. In this paper, we consider two dark matter models—Late Forming Dark Matter (LFDM) and Ultra-Light Axion (ULA) models—where the matter power spectra show novel effects on small scales. The high redshift universe offers a powerful probe of their parameters. In particular, we study two cosmological observables: the neutral hydrogen (HI) redshifted 21-cm signal from the epoch of reionization, and the evolution of the collapsed fraction of HI in the redshift range 2 < z < 5. We model the theoretical predictions of the models using CDM-like N-body simulations with modified initial conditions, and generate reionization fields using an excursion set model. The N-body approximation is valid on the length and halo mass scales studied. We show that LFDM and ULA models predict an increase in the HI power spectrum from the epoch of reionization by a factor between 2-10 for a range of scales 0.1 < k < 4 Mpc-1. Assuming a fiducial model where a neutral hydrogen fraction bar xHI = 0.5 must be achieved by z = 8, the reionization process allows us to put approximate bounds on the redshift of dark matter formation zf > 4 × 105 (for LFDM) and the axion mass ma > 2.6 × 10-23 eV (for ULA). The comparison of the collapsed mass fraction inferred from damped Lyman-α observations to the theoretical predictions of our models lead to the weaker bounds: zf > 2 × 105 and ma > 10-23 eV. These bounds are consistent with other constraints in the literature using different observables; we briefly discuss how these bounds compare with possible constraints from the observation of luminosity function of galaxies at high redshifts. In the case of ULAs, these constraints are also consistent with a solution to the cusp-core problem of CDM.
A small cosmological constant due to non-perturbative quantum effects
NASA Astrophysics Data System (ADS)
Holland, Jan; Hollands, Stefan
2014-06-01
We propose an explanation for the ‘unnatural smallness’ of the cosmological constant, arguing that the stress-energy tensor of the Standard Model should be given by
ERIC Educational Resources Information Center
Wallace, Colin S.; Prather, Edward E.; Duncan, Douglas K.
2012-01-01
This is the final paper in a five-paper series describing our national study of the teaching and learning of cosmology in general education astronomy college-level courses. A significant portion of this work was dedicated to the development of five new "Lecture-Tutorials" that focus on addressing the conceptual and reasoning difficulties that our…
ERIC Educational Resources Information Center
Wallace, Colin S.; Prather, Edward E.; Duncan, Douglas K.
2012-01-01
This is the final paper in a five-paper series describing our national study of the teaching and learning of cosmology in general education astronomy college-level courses. A significant portion of this work was dedicated to the development of five new "Lecture-Tutorials" that focus on addressing the conceptual and reasoning difficulties that our…
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
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 ...
NASA Astrophysics Data System (ADS)
Kirillov, A. A.; Savelova, E. P.
2016-05-01
We describe in details the procedure how the Lobachevsky space can be factorized to a space of the constant negative curvature filled with a gas of wormholes. We show that such wormholes have throat sections in the form of tori and are traversable and stable in the cosmological context. The relation of such wormholes to the dark matter phenomenon is briefly described. We also discuss the possibility of the existence of analogous factorizations for all types of homogeneous spaces.
Graviton fluctuations erase the cosmological constant
NASA Astrophysics Data System (ADS)
Wetterich, C.
2017-10-01
Graviton fluctuations induce strong non-perturbative infrared renormalization effects for the cosmological constant. The functional renormalization flow drives a positive cosmological constant towards zero, solving the cosmological constant problem without the need to tune parameters. We propose a simple computation of the graviton contribution to the flow of the effective potential for scalar fields. Within variable gravity, with effective Planck mass proportional to the scalar field, we find that the potential increases asymptotically at most quadratically with the scalar field. The solutions of the derived cosmological equations lead to an asymptotically vanishing cosmological ;constant; in the infinite future, providing for dynamical dark energy in the present cosmological epoch. Beyond a solution of the cosmological constant problem, our simplified computation also entails a sizeable positive graviton-induced anomalous dimension for the quartic Higgs coupling in the ultraviolet regime, substantiating the successful prediction of the Higgs boson mass within the asymptotic safety scenario for quantum gravity.
Infinity in string cosmology: A review through open problems
NASA Astrophysics Data System (ADS)
Antoniadis, Ignatios; Cotsakis, Spiros
We review recent developments in the field of string cosmology with particular emphasis on open problems having to do mainly with geometric asymptotics and singularities. We discuss outstanding issues in a variety of currently popular themes, such as tree-level string cosmology asymptotics, higher-order string correction effects, M-theory cosmology, braneworlds and finally ambient cosmology.
NASA Technical Reports Server (NTRS)
Horack, J. M.; Emslie, A. G.; Hartmann, D. H.
1995-01-01
In this work, we explore the effects of burst rate density evolution on the observed brightness distribution of cosmological gamma-ray bursts. Although the brightness distribution of gamma-ray bursts observed by the BATSE experiment has been shown to be consistent with a nonevolving source population observed to redshifts of order unity, evolution of some form is likely to be present in the gamma-ray bursts. Additionally, nonevolving models place significant constraints on the range of observed burst luminosities, which are relaxed if evolution of the burst population is present. In this paper, three analytic forms of density evolution are examined. In general, forms of evolution with densities that increase monotonically with redshift require that the BATSE data correspond to bursts at larger redshifts, or to incorporate a wider range of burst luminosities, or both. Independent estimates of the maximum observed redshift in the BATSE data and/or the range of luminosity from which a large fraction of the observed bursts are drawn therefore allow for constraints to be placed on the amount of evolution that may be present in the burst population. Specifically, if recent measurements obtained from analysis of the BATSE duration distribution of the actual limiting redshift in the BATSE data at z(sub lim) = 2 are correct, the BATSE N(P) distribution in a Lambda = 0 universe is inconsistent at a level of approximately 3 alpha with nonevolving gamma-ray bursts and some form of evolution in the population is required. The sense of this required source evolution is to provide a higher density, larger luminosities, or both with increasing redshift.
Cosmological test using strong gravitational lensing systems
NASA Astrophysics Data System (ADS)
Yuan, C. C.; Wang, F. Y.
2015-09-01
As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay Δτ of images, the velocity dispersion σ of the lensing galaxies and the combination of these two effects, Δτ/σ2. In this paper, in order to carry out one-on-one comparisons between ΛCDM universe and Rh = ct universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the Sloan Lens Advanced Camera for Surveys (SLACS) and Lens Structure and Dynamic survey (LSD) survey. Concerning the time-delay effect, 12 two-image lensing systems with Δτ are also used. In addition, Monte Carlo simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the 99.7 per cent confidence level. Comparing with constraints from Δτ and the velocity dispersion σ, we find that using Δτ/σ2 can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between Δτ/σ2 and σ, Δτ/σ2 could be considered as an improved method of σ if more data samples are available.
Sefusatti, Emiliano; Crocce, Martin; Pueblas, Sebastian; Scoccimarro, Roman; /CCPP, New York
2006-04-01
The present spatial distribution of galaxies in the Universe is non-Gaussian, with 40% skewness in 50 h{sup -1} Mpc spheres, and remarkably little is known about the information encoded in it about cosmological parameters beyond the power spectrum. In this work they present an attempt to bridge this gap by studying the bispectrum, paying particular attention to a joint analysis with the power spectrum and their combination with CMB data. They address the covariance properties of the power spectrum and bispectrum including the effects of beat coupling that lead to interesting cross-correlations, and discuss how baryon acoustic oscillations break degeneracies. They show that the bispectrum has significant information on cosmological parameters well beyond its power in constraining galaxy bias, and when combined with the power spectrum is more complementary than combining power spectra of different samples of galaxies, since non-Gaussianity provides a somewhat different direction in parameter space. In the framework of flat cosmological models they show that most of the improvement of adding bispectrum information corresponds to parameters related to the amplitude and effective spectral index of perturbations, which can be improved by almost a factor of two. Moreover, they demonstrate that the expected statistical uncertainties in {sigma}s of a few percent are robust to relaxing the dark energy beyond a cosmological constant.
NASA Astrophysics Data System (ADS)
Gill, Stuart P. D.; Knebe, Alexander; Gibson, Brad K.; Flynn, Chris; Ibata, Rodrigo A.; Lewis, Geraint F.
2003-04-01
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.
BOOK REVIEW: Observational Cosmology Observational Cosmology
NASA Astrophysics Data System (ADS)
Howell, Dale Andrew
2013-04-01
Observational Cosmology by Stephen Serjeant fills a niche that was underserved in the textbook market: an up-to-date, thorough cosmology textbook focused on observations, aimed at advanced undergraduates. Not everything about the book is perfect - some subjects get short shrift, in some cases jargon dominates, and there are too few exercises. Still, on the whole, the book is a welcome addition. For decades, the classic textbooks of cosmology have focused on theory. But for every Sunyaev-Zel'dovich effect there is a Butcher-Oemler effect; there are as many cosmological phenomena established by observations, and only explained later by theory, as there were predicted by theory and confirmed by observations. In fact, in the last decade, there has been an explosion of new cosmological findings driven by observations. Some are so new that you won't find them mentioned in books just a few years old. So it is not just refreshing to see a book that reflects the new realities of cosmology, it is vital, if students are to truly stay up on a field that has widened in scope considerably. Observational Cosmology is filled with full-color images, and graphs from the latest experiments. How exciting it is that we live in an era where satellites and large experiments have gathered so much data to reveal astounding details about the origin of the universe and its evolution. To have all the latest data gathered together and explained in one book will be a revelation to students. In fact, at times it was to me. I've picked up modern cosmological knowledge through a patchwork of reading papers, going to colloquia, and serving on grant and telescope allocation panels. To go back and see them explained from square one, and summarized succinctly, filled in quite a few gaps in my own knowledge and corrected a few misconceptions I'd acquired along the way. To make room for all these graphs and observational details, a few things had to be left out. For one, there are few derivations
Sehgal, Neelima; Hlozek, Renee; Addison, Graeme; Dunkley, Joanna; Louis, Thibaut; Battaglia, Nick; Battistelli, Elia S.; Bond, J. Richard; Hajian, Amir; Hincks, Adam D.; Das, Sudeep; Devlin, Mark J.; Duenner, Rolando; Gralla, Megan; Halpern, Mark; Hasselfield, Matthew; Hilton, Matt; Hughes, John P.; Kosowsky, Arthur; Lin, Yen-Ting; and others
2013-04-10
We present the measured Sunyaev-Zel'dovich (SZ) flux from 474 optically selected MaxBCG clusters that fall within the Atacama Cosmology Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in this analysis covers 510 deg{sup 2} and overlaps Stripe 82 of the Sloan Digital Sky Survey. We also present the measured SZ flux stacked on 52 X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an ACT Southern survey region covering 455 deg{sup 2}. We find that the measured SZ flux from the X-ray-selected clusters is consistent with expectations. However, we find that the measured SZ flux from the optically selected clusters is both significantly lower than expectations and lower than the recovered SZ flux measured by the Planck satellite. Since we find a lower recovered SZ signal than Planck, we investigate the possibility that there is a significant offset between the optically selected brightest cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due to its finer resolution. Such offsets can arise due to either an intrinsic physical separation between the BCG and the center of the gas concentration or from misidentification of the cluster BCG. We find that the entire discrepancy for both ACT and Planck can be explained by assuming that the BCGs are offset from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc. Such large offsets between gas peaks and BCGs for optically selected cluster samples seem unlikely given that we find the physical separation between BCGs and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters to have a much narrower distribution that peaks within 0.2 Mpc. It is possible that other effects are lowering the ACT and Planck signals by the same amount, with offsets between BCGs and SZ peaks explaining the remaining difference between ACT and Planck measurements. Several effects that can lower the SZ signal equally for both ACT and Planck, but not explain
A hydrodynamic approach to cosmology - Methodology
NASA Technical Reports Server (NTRS)
Cen, Renyue
1992-01-01
The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.
Towards the Future of Supernova Cosmology
NASA Astrophysics Data System (ADS)
Knights, Michelle; Bassett, Bruce A.; Varughese, Melvin; Hlozek, Renée Kunz, Martin; Smith, Mat; Newling, James
2015-01-01
For future surveys, spectroscopic follow-up for all supernovae will be extremely difficult. However, one can use light curve fitters, to obtain the probability that an object is a Type Ia. One may consider applying a probability cut to the data, but we show that the resulting non-Ia (nIa) contamination can lead to biases in the estimation of cosmological parameters. A different method, which allows the use of the full dataset and results in unbiased cosmological parameter estimation, is Bayesian Estimation Applied to Multiple Species (BEAMS). BEAMS is a Bayesian approach to the problem which includes the uncertainty in the types in the evaluation of the posterior. Here we outline the theory of BEAMS and demonstrate its effectiveness using both simulated datasets and SDSS-II data. We also show that it is possible to use BEAMS if the data are correlated, by introducing a numerical marginalisation over the types of the objects.
Cosmology with Clusters of Galaxies
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Vander Vliet, Jacob R.; Churchill, C. W.; Trujillo-Gomez, S.; Klimek, E. S.; Klypin, A. A.
2014-01-01
Dwarf galaxies are predicted to have a unique halo structure. They experience the same feedback as more massive galaxies but lack the strong gravitational potential. The structure and composition of gas around dwarfs should be different than for gas around massive galaxies. These differences would show up in quasar absorption spectra. We test this idea by examining mock quasar spectra of the circumgalactic medium of two simulated dwarf galaxies to determine the extent of their metal halos at redshift zero. The galaxies are from a cosmological zoom-in simulation using Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code. Both galaxies have the same initial conditions but are simulated with different physical conditions. One uses only supernova feedback while the other adds in radiative pressure and an increase in star formation efficiency to recreate the correct stellar properties. We measure the absorption lines of several ions including MgII, CIV, OVI, SiIV, and Ly beta and compare the covering fraction, equivalent width distribution and the velocity distribution for both simulations. These are then compared to more massive halos to explore how the galaxy's mass affects their CGM structure.
NASA Technical Reports Server (NTRS)
Sehgal, Neelima; Addison, Graeme; Battaglia, Nick; Battistelli, Elia S.; Bond, J. Richard; Das, Sudeep; Devlin, Mark J.; Dunkley, Joanna; Duenner, Rolando; Gralla, Megan; Hajian, Amir; Halpern, Mark; Hasselfield, Matthew; Hilton, Matt; Hincks, Adam D.; Hlozek, Renee; Hughes, John P.; Kosowsky, Arthur; Lin, Yen-Ting; Louis, Thibaut; Marriage, Tobias A.; Marsden, Danica; Menateau, Felipe; Moodley, Kavilan; Wollack, Ed
2012-01-01
We present the measured Sunyaev-Zel'dovich (SZ) flux from 474 optically-selected MaxBCG clusters that fall within the Atacama Cosmology Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in this analysis covers 510 square degrees and overlaps Stripe 82 of the Sloan Digital Sky Survey. We also present the measured SZ flux stacked on 52 X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an ACT Southern survey region covering 455 square degrees. We find that the measured SZ flux from the X-ray-selected clusters is consistent with expectations. However, we find that the measured SZ flux from the optically-selected clusters is both significantly lower than expectations and lower than the recovered SZ flux measured by the Planck satellite. Since we find a lower recovered SZ signal than Planck, we investigate the possibility that there is a significant offset between the optically-selected brightest cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due to its finer resolution. Such offsets can arise due to either an intrinsic physical separation between the BCG and the center of the gas concentration or from misidentification of the cluster BCG. We find that the entire discrepancy for both ACT and Planck can be explained by assuming that the BCGs are offset from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc. In contrast, the physical separation between BCGs and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters shows a much narrower distribution that peaks within 0.2 Mpc. We conclude that while offsets between BCGs and SZ peaks may be an important component in explaining the discrepancy, it is likely that a combination of factors is responsible for the ACT and Planck measurements. Several effects that can lower the SZ signal equally for both ACT and Planck, but not explain the difference in measured signals, include a larger percentage of false detections in the
The Cosmological Constant in Quantum Cosmology
Wu Zhongchao
2008-10-10
Hawking proposed that the cosmological constant is probably zero in quantum cosmology in 1984. By using the right configuration for the wave function of the universe, a complete proof is found very recently.
A dipole moment of the microwave background as a cosmological effect
NASA Technical Reports Server (NTRS)
Paczynski, Bohdan; Piran, Tsvi
1990-01-01
A spherically symmetrical Tolman-Bondi cosmological model is presented in which the curvature of space and the entropy variety with distance from the center. The dipole and quadrupole moments in the distribution of the microwave background radiation are calculated as a function of cosmic time and position of an observer, assuming that the distance to the horizon is much smaller than any characteristic scale in the model. The quadrupole moment is found to be affected mostly by the gradient in the curvature of space while the dipole moment is dominated by the gradient of entropy. The results indicate that the observed dipole in the microwave background may be cosmological in origin. Observational tests of this argument are suggested.
Nonlocal teleparallel cosmology.
Bahamonde, Sebastian; Capozziello, Salvatore; Faizal, Mir; Nunes, Rafael C
2017-01-01
Even though it is not possible to differentiate general relativity from teleparallel gravity using classical experiments, it could be possible to discriminate between them by quantum gravitational effects. These effects have motivated the introduction of nonlocal deformations of general relativity, and similar effects are also expected to occur in teleparallel gravity. Here, we study nonlocal deformations of teleparallel gravity along with its cosmological solutions. We observe that nonlocal teleparallel gravity (like nonlocal general relativity) is consistent with the present cosmological data obtained by SNe Ia + BAO + CC + [Formula: see text] observations. Along this track, future experiments probing nonlocal effects could be used to test whether general relativity or teleparallel gravity gives the most consistent picture of gravitational interaction.
Perivolaropoulos, L.
2008-05-15
We consider a universe with a compact extra dimension and a cosmological constant emerging from a suitable ultraviolet cutoff on the zero-point energy of the vacuum. We derive the Casimir force between parallel conducting plates as a function of the following scales: plate separation, radius of the extra dimension and cutoff energy scale. We find that there are critical values of these scales where the Casimir force between the plates changes sign. For the cutoff energy scale required to reproduce the observed value of the cosmological constant, we find that the Casimir force changes sign and becomes repulsive for plate separations less than a critical separation d{sub 0}=0.6 mm, assuming a zero radius of the extra dimension (no extra dimension). This prediction contradicts Casimir experiments which indicate an attractive force down to plate separations of 100 nm. For a nonzero extra dimension radius, the critical separation d{sub 0} gets even larger than 0.6 mm and remains inconsistent with Casimir force experiments. We conclude that with or without the presence of a compact extra dimension, vacuum energy with any suitable cutoff cannot play the role of the cosmological constant.
NASA Astrophysics Data System (ADS)
Li, Xiao-Dong; Park, Changbom; Sabiu, Cristiano G.; Park, Hyunbae; Weinberg, David H.; Schneider, Donald P.; Kim, Juhan; Hong, Sungwook E.
2016-12-01
We apply the methodology developed in Li et al. to BOSS DR12 galaxies and derive cosmological constraints from the redshift dependence of the Alcock-Paczynski (AP) effect. The apparent anisotropy in the distribution of observed galaxies arise from two main sources, the redshift-space distortion (RSD) effect due to the galaxy peculiar velocities, and the geometric distortion when incorrect cosmological models are assumed for transforming redshift to comoving distance, known as the AP effect. Anisotropies produced by the RSD effect are, although large, maintaining a nearly uniform magnitude over a large range of redshift, while the degree of anisotropies from the AP effect varies with redshift by a much larger magnitude. We split the DR12 galaxies into six redshift bins, measure the two-point correlation function in each bin, and assess the redshift evolution of anisotropies. We obtain constraints of {{{Ω }}}m=0.290+/- 0.053,w=-1.07+/- 0.15, which are comparable with the current constraints from other cosmological probes such as SNe Ia, cosmic microwave background, and baryon acoustic oscillation (BAO). Combining these cosmological probes with our method yield tight constraints of {{{Ω }}}m=0.301+/- 0.006,w=-1.054+/- 0.025. Our method is complementary to the other large-scale structure (LSS) probes like BAO and topology. We expect this technique will play an important role in deriving cosmological constraints from LSS surveys.
NASA Technical Reports Server (NTRS)
Lucchin, Francesco; Matarrese, Sabino; Melott, Adrian L.; Moscardini, Lauro
1994-01-01
We calculate reduced moments (xi bar)(sub q) of the matter density fluctuations, up to order q = 5, from counts in cells produced by particle-mesh numerical simulations with scale-free Gaussian initial conditions. We use power-law spectra P(k) proportional to k(exp n) with indices n = -3, -2, -1, 0, 1. Due to the supposed absence of characteristic times or scales in our models, all quantities are expected to depend on a single scaling variable. For each model, the moments at all times can be expressed in terms of the variance (xi bar)(sub 2), alone. We look for agreement with the hierarchical scaling ansatz, according to which ((xi bar)(sub q)) proportional to ((xi bar)(sub 2))(exp (q - 1)). For n less than or equal to -2 models, we find strong deviations from the hierarchy, which are mostly due to the presence of boundary problems in the simulations. A small, residual signal of deviation from the hierarchical scaling is however also found in n greater than or equal to -1 models. The wide range of spectra considered and the large dynamic range, with careful checks of scaling and shot-noise effects, allows us to reliably detect evolution away from the perturbation theory result.
NASA Technical Reports Server (NTRS)
Lucchin, Francesco; Matarrese, Sabino; Melott, Adrian L.; Moscardini, Lauro
1994-01-01
We calculate reduced moments (xi bar)(sub q) of the matter density fluctuations, up to order q = 5, from counts in cells produced by particle-mesh numerical simulations with scale-free Gaussian initial conditions. We use power-law spectra P(k) proportional to k(exp n) with indices n = -3, -2, -1, 0, 1. Due to the supposed absence of characteristic times or scales in our models, all quantities are expected to depend on a single scaling variable. For each model, the moments at all times can be expressed in terms of the variance (xi bar)(sub 2), alone. We look for agreement with the hierarchical scaling ansatz, according to which ((xi bar)(sub q)) proportional to ((xi bar)(sub 2))(exp (q - 1)). For n less than or equal to -2 models, we find strong deviations from the hierarchy, which are mostly due to the presence of boundary problems in the simulations. A small, residual signal of deviation from the hierarchical scaling is however also found in n greater than or equal to -1 models. The wide range of spectra considered and the large dynamic range, with careful checks of scaling and shot-noise effects, allows us to reliably detect evolution away from the perturbation theory result.
Noncommutativity and scalar field cosmology
Guzman, W.; Sabido, M.; Socorro, J.
2007-10-15
In this work we extend and apply a previous proposal to study noncommutative cosmology to the Friedmann-Robertson-Walker cosmological background coupled to a scalar field. This is done in classical and quantum scenarios. In both cases noncommutativity is introduced in the gravitational field as well as in the scalar field through a deformation of minisuperspace, and we are able to find exact solutions. Finally, the effects of noncommutativity on the classical evolution are analyzed.
Sarkar, Abir; Sethi, Shiv K.; Mondal, Rajesh; Bharadwaj, Somnath; Das, Subinoy; Marsh, David J.E. E-mail: rm@phy.iitkgp.ernet.in E-mail: sethi@rri.res.in E-mail: david.marsh@kcl.ac.uk
2016-04-01
The particle nature of dark matter remains a mystery. In this paper, we consider two dark matter models—Late Forming Dark Matter (LFDM) and Ultra-Light Axion (ULA) models—where the matter power spectra show novel effects on small scales. The high redshift universe offers a powerful probe of their parameters. In particular, we study two cosmological observables: the neutral hydrogen (HI) redshifted 21-cm signal from the epoch of reionization, and the evolution of the collapsed fraction of HI in the redshift range 2 < z < 5. We model the theoretical predictions of the models using CDM-like N-body simulations with modified initial conditions, and generate reionization fields using an excursion set model. The N-body approximation is valid on the length and halo mass scales studied. We show that LFDM and ULA models predict an increase in the HI power spectrum from the epoch of reionization by a factor between 2–10 for a range of scales 0.1 < k < 4 Mpc{sup −1}. Assuming a fiducial model where a neutral hydrogen fraction x-bar {sub HI} = 0.5 must be achieved by z = 8, the reionization process allows us to put approximate bounds on the redshift of dark matter formation z{sub f} > 4 × 10{sup 5} (for LFDM) and the axion mass m{sub a} > 2.6 × 10{sup −23} eV (for ULA). The comparison of the collapsed mass fraction inferred from damped Lyman-α observations to the theoretical predictions of our models lead to the weaker bounds: z{sub f} > 2 × 10{sup 5} and m{sub a} > 10{sup −23} eV. These bounds are consistent with other constraints in the literature using different observables; we briefly discuss how these bounds compare with possible constraints from the observation of luminosity function of galaxies at high redshifts. In the case of ULAs, these constraints are also consistent with a solution to the cusp-core problem of CDM.
Cosmological string solutions by dimensional reduction
Behrndt, K.; Foerste, S.
1993-12-01
We obtain cosmological four dimensional solutions of the low energy effective string theory by reducing a five dimensional black hole, and black hole-de Sitter solution of the Einstein gravity down to four dimensions. The appearance of a cosmological constant in the five dimensional Einstein-Hilbert produces a special dilaton potential in the four dimensional effective string action. Cosmological scenarios implement by our solutions are discussed.
Precision cosmology and the landscape
Bousso, Raphael; Bousso, Raphael
2006-10-01
After reviewing the cosmological constant problem -- why is Lambda not huge? -- I outline the two basic approaches that had emerged by the late 1980s, and note that each made a clear prediction. Precision cosmological experiments now indicate that the cosmological constant is nonzero. This result strongly favors the environmental approach, in which vacuum energy can vary discretely among widely separated regions in the universe. The need to explain this variation from first principles constitutes an observational constraint on fundamental theory. I review arguments that string theory satisfies this constraint, as it contains a dense discretuum of metastable vacua. The enormous landscape of vacua calls for novel, statistical methods of deriving predictions, and it prompts us to reexamine our description of spacetime on the largest scales. I discuss the effects of cosmological dynamics, and I speculate that weighting vacua by their entropy production may allow for prior-free predictions that do not resort to explicitly anthropic arguments.
Semiclassical cosmology with polymer matter
NASA Astrophysics Data System (ADS)
Moeez Hassan, Syed; Husain, Viqar
2017-04-01
In loop quantum cosmology, polymer quantization is applied to gravity and Schrödinger quantization to matter. This approach misses interesting cosmological dynamics coming from the polymer quantization of matter. We demonstrate this in semiclassical cosmology with a scalar field and pressureless dust: gravity is kept classical, dust is used to fix the time gauge, and polymer quantization effects are isolated in the scalar field. The resulting dynamics shows a period of inflation, both with and without a scalar potential, and the emergence of a classical universe at late times. Since gravity is not quantized, the cosmological singularity is not resolved, but our results suggest that polymer quantization of both gravity and matter are important for a complete picture.
Krioukov, Dmitri; Kitsak, Maksim; Sinkovits, Robert S; Rideout, David; Meyer, David; Boguñá, Marián
2012-01-01
Prediction and control of the dynamics of complex networks is a central problem in network science. Structural and dynamical similarities of different real networks suggest that some universal laws might accurately describe the dynamics of these networks, albeit the nature and common origin of such laws remain elusive. Here we show that the causal network representing the large-scale structure of spacetime in our accelerating universe is a power-law graph with strong clustering, similar to many complex networks such as the Internet, social, or biological networks. We prove that this structural similarity is a consequence of the asymptotic equivalence between the large-scale growth dynamics of complex networks and causal networks. This equivalence suggests that unexpectedly similar laws govern the dynamics of complex networks and spacetime in the universe, with implications to network science and cosmology.
Krioukov, Dmitri; Kitsak, Maksim; Sinkovits, Robert S.; Rideout, David; Meyer, David; Boguñá, Marián
2012-01-01
Prediction and control of the dynamics of complex networks is a central problem in network science. Structural and dynamical similarities of different real networks suggest that some universal laws might accurately describe the dynamics of these networks, albeit the nature and common origin of such laws remain elusive. Here we show that the causal network representing the large-scale structure of spacetime in our accelerating universe is a power-law graph with strong clustering, similar to many complex networks such as the Internet, social, or biological networks. We prove that this structural similarity is a consequence of the asymptotic equivalence between the large-scale growth dynamics of complex networks and causal networks. This equivalence suggests that unexpectedly similar laws govern the dynamics of complex networks and spacetime in the universe, with implications to network science and cosmology. PMID:23162688
NASA Astrophysics Data System (ADS)
Rubin, D.; Aldering, G.; Barbary, K.; Boone, K.; Chappell, G.; Currie, M.; Deustua, S.; Fagrelius, P.; Fruchter, A.; Hayden, B.; Lidman, C.; Nordin, J.; Perlmutter, S.; Saunders, C.; Sofiatti, C.; Supernova Cosmology Project, The
2015-11-01
While recent supernova (SN) cosmology research has benefited from improved measurements, current analysis approaches are not statistically optimal and will prove insufficient for future surveys. This paper discusses the limitations of current SN cosmological analyses in treating outliers, selection effects, shape- and color-standardization relations, unexplained dispersion, and heterogeneous observations. We present a new Bayesian framework, called UNITY (Unified Nonlinear Inference for Type-Ia cosmologY), that incorporates significant improvements in our ability to confront these effects. We apply the framework to real SN observations and demonstrate smaller statistical and systematic uncertainties. We verify earlier results that SNe Ia require nonlinear shape and color standardizations, but we now include these nonlinear relations in a statistically well-justified way. This analysis was primarily performed blinded, in that the basic framework was first validated on simulated data before transitioning to real data. We also discuss possible extensions of the method.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Forero-Romero, J. E.
2017-07-01
This talk summarizes different algorithms that can be used to trace the cosmic web both in simulations and observations. We present different applications in galaxy formation and cosmology. To finalize, we show how the Dark Energy Spectroscopic Instrument (DESI) could be a good place to apply these techniques.
Cosmology with the WFIRST High Latitude Survey
NASA Astrophysics Data System (ADS)
Dore, Olivier
Cosmic acceleration is the most surprising cosmological discovery in many decades. Testing and distinguishing among possible explanations requires cosmological measurements of extremely high precision that probe the full history of cosmic expansion and structure growth. The WFIRST-AFTA mission, as described in the Science Definition Team (SDT) reports (Spergel 2013, 2015), has the ability to improve these measurements by 1-2 orders of magnitude compared to the current state of the art, while simultaneously extending their redshift grasp, greatly improving control of systematic effects, and taking a unified approach to multiple probes that provide complementary physical information and cross-checks of cosmological results. We have assembled a team with the expertise and commitment needed to address the stringent challenges of the WFIRST dark energy program through the Project's formulation phase. After careful consideration, we have elected to address investigations A (Galaxy Redshift Survey) and C (Weak Lensing and Cluster Growth) of the WFIRST SIT NRA with a unified team, because the two investigations are tightly linked at both the technical level and the theoretical modeling level. The imaging and spectroscopic elements of the High Latitude Survey (HLS) will be realized as an integrated observing program, and they jointly impose requirements on instrument and telescope performance, operations, and data transfer. The methods for simulating and interpreting weak lensing and galaxy clustering observations largely overlap, and many members of our team have expertise in both areas. The team PI, Olivier Dore, is a cosmologist with a broad expertise in cosmic microwave background and large scale structures. Yun Wang and Chris Hirata will serve as Lead Co-Investigators for topics A and C, respectively. Many members of our team have been involved with the design and requirements of a dark energy space mission for a decade or more, including the Co-Chair and three
NASA Astrophysics Data System (ADS)
Tsamis, N. C.; Woodard, R. P.
2016-08-01
We study a class of nonlocal, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the Universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense Universe the nonlocal screening terms become constant as the Universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller antiscreening effect that could explain the current phase of acceleration.
Bojowald, Martin
2015-02-01
In quantum cosmology, one applies quantum physics to the whole universe. While no unique version and no completely well-defined theory is available yet, the framework gives rise to interesting conceptual, mathematical and physical questions. This review presents quantum cosmology in a new picture that tries to incorporate the importance of inhomogeneity. De-emphasizing the traditional minisuperspace view, the dynamics is rather formulated in terms of the interplay of many interacting 'microscopic' degrees of freedom that describe the space-time geometry. There is thus a close relationship with more-established systems in condensed-matter and particle physics even while the large set of space-time symmetries (general covariance) requires some adaptations and new developments. These extensions of standard methods are needed both at the fundamental level and at the stage of evaluating the theory by effective descriptions.
Gravitomagnetic amplification in cosmology
Tsagas, Christos G.
2010-02-15
Magnetic fields interact with gravitational waves in various ways. We consider the coupling between the Weyl and the Maxwell fields in cosmology and study the effects of the former on the latter. The approach is fully analytical and the results are gauge invariant. We show that the nature and the outcome of the gravitomagnetic interaction depends on the electric properties of the cosmic medium. When the conductivity is high, gravitational waves reduce the standard (adiabatic) decay rate of the B field, leading to its superadiabatic amplification. In poorly conductive environments, on the other hand, Weyl-curvature distortions can result into the resonant amplification of large-scale cosmological magnetic fields. Driven by the gravitational waves, these B fields oscillate with an amplitude that is found to diverge when the wavelengths of the two sources coincide. We present technical and physical aspects of the gravitomagnetic interaction and discuss its potential implications.
Tatekawa, Takayuki
2014-04-01
We study the initial conditions for cosmological N-body simulations for precision cosmology. In general, Zel'dovich approximation has been applied for the initial conditions of N-body simulations for a long time. These initial conditions provide incorrect higher-order growth. These error caused by setting up the initial conditions by perturbation theory is called transients. We investigated the impact of transient on non-Gaussianity of density field by performing cosmological N-body simulations with initial conditions based on first-, second-, and third-order Lagrangian perturbation theory in previous paper. In this paper, we evaluates the effect of the transverse mode in the third-order Lagrangian perturbation theory for several statistical quantities such as power spectrum and non-Gaussianty. Then we clarified that the effect of the transverse mode in the third-order Lagrangian perturbation theory is quite small.
Cosmological perturbations in an effective and genuinely phantom dark energy Universe
NASA Astrophysics Data System (ADS)
Albarran, Imanol; Bouhmadi-López, Mariam; Morais, João
2017-06-01
We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three set-ups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted ΛCDM model. In addition, each of the models under study induce different future singularities or abrupt events known as (i) Big Rip, (ii) Little Rip and (iii) Little Sibling of the Big Rip. Only the first one is regarded as a true singularity since it occurs at a finite cosmic time. For this reason, we refer to the others as abrupt events. With the aim to find possible footprints of this scenario in the Universe matter distribution, we not only obtain the evolution of the cosmological scalar perturbations but also calculate the matter power spectrum for each model. We have carried the perturbations in the absence of any anisotropic stress and within a phenomenological approach for the speed of sound. We constrain observationally these models using several measurements of the growth rate function, more precisely fσ8, and compare our results with the observational ones.
NASA Astrophysics Data System (ADS)
Hirschmann, Michaela; Dolag, Klaus; Bachmann, Lisa
2015-08-01
We provide new insights into the cosmic evolution of black holes (BHs) and their host galaxies by employing large-scale cosmological, hydrodynamic simulations capturing a huge volume of (500 Mpc)3. They are shown to be successful in reproducing a number of observational, statistical constraints, e.g. the evolution of the AGN luminosity function (in the soft and hard X-ray band) together with the corresponding downsizing trend. This is mainly due to the evolution of the gas density in the vicinity of a BH and due to the correction for dust obscuration on a torus-level. We further demonstrate that only luminous AGN are preferentially triggered by merger events, while for the majority of moderately luminous AGN, additional driving mechanisms seem to be necessary. Exploring the AGN-host connection, we find that host SFRs and AGN luminosities are always correlated (albeit with a large scatter) when averaging over the AGN luminosities (but not when averaging over SFR) in reasonably good agreement with recent observations. Interestingly, for the most luminous AGN, a slightly tighter and steeper correlation between AGN luminosities and SFRs emerges, which may originate from the increasing relevance of mergers in driving their nuclear activity. Overall, the new generation AGN, BH and galaxy catalogues, provided by our simulation, are expected to significantly contribute to the interpretation of current and up-coming large-scale surveys (XMM, ATHENA, eRosita, Euclid) with respect to the evolution of BHs within the emerging cosmic structure.
Loop quantum cosmology gravitational baryogenesis
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-11-01
Loop quantum cosmology is an appealing quantum completion of classical cosmology, which brings along various theoretical features which in many cases offer a remedy for or modify various classical cosmology aspects. In this paper we address the gravitational baryogenesis mechanism in the context of loop quantum cosmology. As we demonstrate, when loop quantum cosmology effects are taken into account in the resulting Friedmann equations for a flat Friedmann-Robertson-Walker Universe, then even for a radiation-dominated Universe, the predicted baryon-to-entropy ratio from the gravitational baryogenesis mechanism is non-zero, in contrast to the Einstein-Hilbert case, in which case the baryon-to-entropy ratio is zero. We also discuss various other cases apart from the radiation domination case, and we discuss how the baryon-to-entropy ratio is affected from the parameters of the quantum theory. In addition, we use illustrative exact solutions of loop quantum cosmology and we investigate under which circumstances the baryon-to-entropy ratio can be compatible with the observational constraints.
NASA Astrophysics Data System (ADS)
Ma, Xiangcheng; Kasen, Daniel; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Quataert, Eliot; Kereš, Dušan; Murray, Norman
2015-10-01
We present a series of high-resolution (20-2000 M⊙, 0.1-4 pc) cosmological zoom-in simulations at z ≳ 6 from the Feedback In Realistic Environment (FIRE) project. These simulations cover halo masses 109-1011 M⊙ 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 per cent), while the time-averaged fesc over long time-scales generally remains ≲ 5 per cent, 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 mostly come from populations between 3 and 10 Myr, whose birth clouds have been largely cleared by stellar feedback. However, these populations only contribute a small fraction of intrinsic ionizing photon budgets according to standard stellar population models. We show that fesc can be boosted to high values, if stellar populations older than 3 Myr produce more ionizing photons than standard stellar population models (as motivated by, e.g. models including binaries). By contrast, runaway stars with velocities suggested by observations can enhance fesc by only a small fraction. We show that `sub-grid' star formation models, which do not explicitly resolve star formation in dense clouds with n ≫ 1 cm-3, will dramatically overpredict fesc.
NASA Astrophysics Data System (ADS)
Dolag, Klaus; Beck, Alexander M.; Arth, Alexander
Using the MHD version of Gadget3 (Stasyszyn, Dolag & Beck 2013) and a model for the seeding of magnetic fields by supernovae (SN), we performed simulations of the evolution of the magnetic fields in galaxy clusters and study their effects on the heat transport within the intra cluster medium (ICM). This mechanism - where SN explosions during the assembly of galaxies provide magnetic seed fields - has been shown to reproduce the magnetic field in Milky Way-like galactic halos (Beck et al. 2013). The build up of the magnetic field at redshifts before z = 5 and the accordingly predicted rotation measure evolution are also in good agreement with current observations. Such magnetic fields present at high redshift are then transported out of the forming protogalaxies into the large-scale structure and pollute the ICM (in a similar fashion to metals transport). Here, complex velocity patterns, driven by the formation process of cosmic structures are further amplifying and distributing the magnetic fields. In galaxy clusters, the magnetic fields therefore get amplified to the observed μG level and produce the observed amplitude of rotation measures of several hundreds of rad/m2. We also demonstrate that heat conduction in such turbulent fields on average is equivalent to a suppression factor around 1/20th of the classical Spitzer value and in contrast to classical, isotropic heat transport leads to temperature structures within the ICM compatible with observations (Arth et al. 2014).
Topics in inflationary cosmologies
Mahajan, S.
1986-04-01
Several aspects of inflationary cosmologies are discussed. An introduction to the standard hot big bang cosmological model is reviewed, and some of the problems associated with it are presented. A short review of the proposals for solving the cosmological conundrums of the big bang model is presented. Old and the new inflationary scenarios are discussed and shown to be unacceptable. Some alternative scenarios especially those using supersymmetry are reviewed briefly. A study is given of inflationary models where the same set of fields that breaks supersymmetry is also responsible for inflation. In these models, the scale of supersymmetry breaking is related to the slope of the potential near the origin and can thus be kept low. It is found that a supersymmetry breaking scale of the order of the weak breaking scale. The cosmology obtained from the simplest of such models is discussed in detail and it is shown that there are no particular problems except a low reheating temperature and a violation of the thermal constraint. A possible solution to the thermal constraint problem is given by introducing a second field, and the role played by this second field in the scenario is discussed. An alternative mechanism for the generation of baryon number within the framework of supergravity inflationary models is studied using the gravitational couplings of the heavy fields with the hidden sector (the sector which breaks supersymmetry). This mechanism is applied to two specific models - one with and one without supersymmetry breaking. The baryon to entropy ratio is found to be dependent on parameters which are model dependent. Finally, the effect of direct coupling between the two sectors on results is related, 88 refs., 6 figs.
Ekpyrotic loop quantum cosmology
Wilson-Ewing, Edward
2013-08-01
We consider the ekpyrotic paradigm in the context of loop quantum cosmology. In loop quantum cosmology the classical big-bang singularity is resolved due to quantum gravity effects, and so the contracting ekpyrotic branch of the universe and its later expanding phase are connected by a smooth bounce. Thus, it is possible to explicitly determine the evolution of scalar perturbations, from the contracting ekpyrotic phase through the bounce and to the post-bounce expanding epoch. The possibilities of having either one or two scalar fields have been suggested for the ekpyrotic universe, and both cases will be considered here. In the case of a single scalar field, the constant mode of the curvature perturbations after the bounce is found to have a blue spectrum. On the other hand, for the two scalar field ekpyrotic model where scale-invariant entropy perturbations source additional terms in the curvature perturbations, the power spectrum in the post-bounce expanding cosmology is shown to be nearly scale-invariant and so agrees with observations.
NASA Astrophysics Data System (ADS)
Aref'eva, I. Ya.; Volovich, I. V.
2011-08-01
Classical versions of the Big Bang cosmological models of the universe contain a singularity at the start of time, hence the time variable in the field equations should run over a half-line. Nonlocal string field theory equations with infinite number of derivatives are considered and an important difference between nonlocal operators on the whole real line and on a half-line is pointed out. We use the heat equation method and show that on the half-line in addition to the usual initial data a new arbitrary function (external source) occurs that we call the daemon function. The daemon function governs the evolution of the universe similar to Maxwell's demon in thermodynamics. The universe and multiverse are open systems interacting with the daemon environment. In the simplest case the nonlocal scalar field reduces to the usual local scalar field coupled with an external source which is discussed in the stochastic approach to inflation. The daemon source can help to get the chaotic inflation scenario with a small scalar field.
NASA Astrophysics Data System (ADS)
Tipler, Frank J.
1996-09-01
I show that if Newtonian gravity is formulated in geometrical language, then Newtonian cosmology is as rigorous as relativistic cosmology. In homogeneous and isotropic universes, the geodesic deviation equation in Newtonian cosmology is proven to be exactly the same as the geodesic deviation equation in relativistic Friedmann cosmologies. This equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: by generalizing the flat-space Newtonian gravity force law to Riemannian metrics, I show that ever-expanding and recollapsing universes are allowed in any homogeneous and isotropic spatial geometry.
Landscape predictions from cosmological vacuum selection
Bousso, Raphael; Bousso, Raphael; Yang, Sheng
2007-04-23
In Bousso-Polchinski models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to staggering, an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.
Landscape predictions from cosmological vacuum selection
Bousso, Raphael; Yang, I-S.
2007-06-15
In Bousso-Polchinski models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to staggering, an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.
NASA Astrophysics Data System (ADS)
Bojowald, Martin
The universe, ultimately, is to be described by quantum theory. Quantum aspects of all there is, including space and time, may not be significant for many purposes, but are crucial for some. And so a quantum description of cosmology is required for a complete and consistent worldview. At any rate, even if we were not directly interested in regimes where quantum cosmology plays a role, a complete physical description could not stop at a stage before the whole universe is reached. Quantum theory is essential in the microphysics of particles, atoms, molecules, solids, white dwarfs and neutron stars. Why should one expect this ladder of scales to end at a certain size? If regimes are sufficiently violent and energetic, quantum effects are non-negligible even on scales of the whole cosmos; this is realized at least once in the history of the universe: at the big bang where the classical theory of general relativity would make energy densities diverge.
Constraints on cosmological parameters in power-law cosmology
NASA Astrophysics Data System (ADS)
Rani, Sarita; Altaibayeva, A.; Shahalam, M.; Singh, J. K.; Myrzakulov, R.
2015-03-01
In this paper, we examine observational constraints on the power law cosmology; essentially dependent on two parameters H0 (Hubble constant) and q (deceleration parameter). We investigate the constraints on these parameters using the latest 28 points of H(z) data and 580 points of Union2.1 compilation data and, compare the results with the results of ΛCDM . We also forecast constraints using a simulated data set for the future JDEM, supernovae survey. Our studies give better insight into power law cosmology than the earlier done analysis by Kumar [arXiv:1109.6924] indicating it tuning well with Union2.1 compilation data but not with H(z) data. However, the constraints obtained on i.e. H0 average and q average using the simulated data set for the future JDEM, supernovae survey are found to be inconsistent with the values obtained from the H(z) and Union2.1 compilation data. We also perform the statefinder analysis and find that the power-law cosmological models approach the standard ΛCDM model as q → -1. Finally, we observe that although the power law cosmology explains several prominent features of evolution of the Universe, it fails in details.
Constraints on cosmological parameters in power-law cosmology
Rani, Sarita; Singh, J.K.; Altaibayeva, A.; Myrzakulov, R.; Shahalam, M. E-mail: aziza.bibol@mail.ru E-mail: jainendrrakumar@rediffmail.com
2015-03-01
In this paper, we examine observational constraints on the power law cosmology; essentially dependent on two parameters H{sub 0} (Hubble constant) and q (deceleration parameter). We investigate the constraints on these parameters using the latest 28 points of H(z) data and 580 points of Union2.1 compilation data and, compare the results with the results of ΛCDM . We also forecast constraints using a simulated data set for the future JDEM, supernovae survey. Our studies give better insight into power law cosmology than the earlier done analysis by Kumar [arXiv:1109.6924] indicating it tuning well with Union2.1 compilation data but not with H(z) data. However, the constraints obtained on i.e. H{sub 0} average and q average using the simulated data set for the future JDEM, supernovae survey are found to be inconsistent with the values obtained from the H(z) and Union2.1 compilation data. We also perform the statefinder analysis and find that the power-law cosmological models approach the standard ΛCDM model as q → −1. Finally, we observe that although the power law cosmology explains several prominent features of evolution of the Universe, it fails in details.
Cosmological Hydrodynamics on a Moving Mesh
NASA Astrophysics Data System (ADS)
Hernquist, Lars
We propose to construct a model for the visible Universe using cosmological simulations of structure formation. Our simulations will include both dark matter and baryons, and will employ two entirely different schemes for evolving the gas: smoothed particle hydrodynamics (SPH) and a moving mesh approach as incorporated in the new code, AREPO. By performing simulations that are otherwise nearly identical, except for the hydrodynamics solver, we will isolate and understand differences in the properties of galaxies, galaxy groups and clusters, and the intergalactic medium caused by the computational approach that have plagued efforts to understand galaxy formation for nearly two decades. By performing simulations at different levels of resolution and with increasingly complex treatments of the gas physics, we will identify the results that are converged numerically and that are robust with respect to variations in unresolved physical processes, especially those related to star formation, black hole growth, and related feedback effects. In this manner, we aim to undertake a research program that will redefine the state of the art in cosmological hydrodynamics and galaxy formation. In particular, we will focus our scientific efforts on understanding: 1) the formation of galactic disks in a cosmological context; 2) the physical state of diffuse gas in galaxy clusters and groups so that they can be used as high-precision probes of cosmology; 3) the nature of gas inflows into galaxy halos and the subsequent accretion of gas by forming disks; 4) the co-evolution of galaxies and galaxy clusters with their central supermassive black holes and the implications of related feedback for galaxy evolution and the dichotomy between blue and red galaxies; 5) the physical state of the intergalactic medium (IGM) and the evolution of the metallicity of the IGM; and 6) the reaction of dark matter around galaxies to galaxy formation. Our proposed work will be of immediate significance for
Zemp, Marcel; Ramirez-Ruiz, Enrico; Diemand, Juerg E-mail: enrico@ucolick.or
2009-11-10
Merging compact binaries are the one source of gravitational radiation so far identified. Because short-period systems that will merge in less than a Hubble time have already been observed as binary pulsars, they are important both as gravitational wave sources for observatories such as LIGO, but also as progenitors for short gamma-ray bursts (SGRBs). The fact that these systems must have large systemic velocities implies that by the time they merge, they will be far from their formation site. The locations of merging sites depend sensitively on the gravitational potential of the galaxy host, which until now has been assumed to be static. Here we refine such calculations to incorporate the temporal evolution of the host's gravitational potential as well as that of its nearby neighbors using cosmological simulations of structure formation. This results in merger site distributions that are more diffusively distributed with respect to their putative hosts, with locations extending out to distances of a few Mpc for lighter halos. The degree of mixing between neighboring compact binary populations computed in this way is severely enhanced in environments with a high number density of galaxies. We find that SGRB redshift estimates based solely on the nearest galaxy in projection can be very inaccurate, if progenitor systems inhere large systematic kicks at birth.
Systematics in Connecting Cluster Surveys and Cosmology
NASA Astrophysics Data System (ADS)
Mohr, J. J.; Hoffman, M. B.; Bialek, J. J.; Evrard, A. E.
2000-10-01
Large cluster surveys which extend to intermediate and high redshift are powerful cosmological probes. Survey yields per solid angle depend on (i) the volume per solid angle as a function of redshift, (ii) the evolution of cluster number density with redshift, and (iii) the virial mass of the minimally detectable cluster as a function of redshift. The first two of these dependences are well understood theoretically for a wide range of cosmological parameters; however, the third dependence is more problematic, because it requires an understanding of the evolution of the relationship between the cluster virial mass and cluster observables like the X-ray emission weighted temperature, X-ray luminosity and Sunyaev-Zel'dovich effect (SZE) decrement. We use hydrodynamical simulations of cluster formation to examine the effects of preheating-- the entropy increase in intergalactic gas before cluster formation-- on X-ray and SZE cluster survey yields. The source of this preheating is presumably galaxy formation, and evidence supporting preheating (or perhaps some other physics) lies in the steepness of the local X-ray luminosity-temperature, intracluster medium mass-temperature and X-ray isophotal size-temperature relations. We tune the preheating level to reproduce these local cluster scaling relations. We use these simulations to estimate the impact of preheating on the accuracy of cosmological parameters inferred from X-ray and SZE cluster surveys. Finally, we discuss future observations which can further constrain preheating models, and we discuss analyses which are less sensitive to biases from unknown aspects of preheating. JJM is supported by Chandra Fellowship grant PF8-1003, awarded through the Chandra Science Center. AEE acknowledges support from NSF AST-9803199 and NASA NAG5-8458.
Cooperative Radiation Effects Simulation Program.
1980-12-16
G . Doran, W. G . Johnston, G . L . Kulcinski , I...Microstructure and Properties of Metals, ASTM STP 611, pp. 284-297, November 1976. 46 -- IM 108. L . G . Kirchner, F. A. Smidt, Jr., G . L . Kulcinski , J. A...AD-A093 743 NAVAL RESEARCH LAB WASHINGTON DC F/ G 18/6 COOPERATIVE RADIATION EFFECTS SIMULATION PROGRAM. (U) DEC 80 L A BEACH. F A SNIOT
Singularities in loop quantum cosmology.
Cailleteau, Thomas; Cardoso, Antonio; Vandersloot, Kevin; Wands, David
2008-12-19
We show that simple scalar field models can give rise to curvature singularities in the effective Friedmann dynamics of loop quantum cosmology (LQC). We find singular solutions for spatially flat Friedmann-Robertson-Walker cosmologies with a canonical scalar field and a negative exponential potential, or with a phantom scalar field and a positive potential. While LQC avoids big bang or big rip type singularities, we find sudden singularities where the Hubble rate is bounded, but the Ricci curvature scalar diverges. We conclude that the effective equations of LQC are not in themselves sufficient to avoid the occurrence of curvature singularities.
Constraining Lorentz violation with cosmology.
Zuntz, J A; Ferreira, P G; Zlosnik, T G
2008-12-31
The Einstein-aether theory provides a simple, dynamical mechanism for breaking Lorentz invariance. It does so within a generally covariant context and may emerge from quantum effects in more fundamental theories. The theory leads to a preferred frame and can have distinct experimental signatures. In this Letter, we perform a comprehensive study of the cosmological effects of the Einstein-aether theory and use observational data to constrain it. Allied to previously determined consistency and experimental constraints, we find that an Einstein-aether universe can fit experimental data over a wide range of its parameter space, but requires a specific rescaling of the other cosmological densities.
Bojowald, Martin
2005-01-01
Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical space-time inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding space-time is then modified. One particular realization is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. Main effects are introduced into effective classical equations which allow to avoid interpretational problems of quantum theory. They give rise to new kinds of early universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function which allows to extend space-time beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of space-time arising in loop quantum gravity and its application to cosmology sheds new light on more general issues such as time.
Bojowald, Martin
2008-01-01
Quantum gravity is expected to be necessary in order to understand situations in which classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular theory is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. The main effects are introduced into effective classical equations, which allow one to avoid the interpretational problems of quantum theory. They give rise to new kinds of early-universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function, which allows an extension of quantum spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds light on more general issues, such as the nature of time.
COSMOLOGICAL DENSITY FLUCTUATIONS ON 100 Mpc SCALES AND THEIR ISW EFFECT
Papai, Peter; Szapudi, Istvan
2010-12-20
We measure the matter probability distribution function (PDF) via counts in cells in a volume-limited subsample of the Sloan Digital Sky Survey Luminous Red Galaxy Catalog on scales from 30 h {sup -1} Mpc to 150 h {sup -1} Mpc and estimate the linear Integrated Sachs-Wolfe effect produced by supervoids and superclusters in the tail of the PDF. We characterize the PDF by the variance, S{sub 3}, and S{sub 4}, and study in simulations the systematic effects due to finite volume, survey shape, and redshift distortion. We compare our measurement to the prediction of {Lambda}CDM with linear bias and find a good agreement. We use the moments to approximate the tail of the PDF with analytic functions. A simple Gaussian model for the superstructures appears to be consistent with the claim by Granett et al. that density fluctuations on 100 h {sup -1} Mpc scales produce hot and cold spots with {Delta}T {approx} 10 {mu}K on the cosmic microwave background.
NASA Astrophysics Data System (ADS)
Roca-Fàbrega, Santi; Valenzuela, Octavio; Colín, Pedro; Figueras, Francesca; Krongold, Yair; Velázquez, Héctor; Avila-Reese, Vladimir; Ibarra-Medel, Hector
2016-06-01
We introduce a new set of simulations of Milky Way (MW)-sized galaxies using the AMR code ART + hydrodynamics in a Λ cold dark matter cosmogony. The simulation series is called GARROTXA and it follows the formation of a halo/galaxy from z = 60 to z = 0. The final virial mass of the system is ˜7.4 × 1011 M ⊙. Our results are as follows. (a) Contrary to many previous studies, the circular velocity curve shows no central peak and overall agrees with recent MW observations. (b) Other quantities, such as M\\_\\ast (6 × 1010 M ⊙) and R d (2.56 kpc), fall well inside the observational MW range. (c) We measure the disk-to-total ratio kinematically and find that D/T = 0.42. (d) The cold-gas fraction and star formation rate at z = 0, on the other hand, fall short of the values estimated for the MW. As a first scientific exploitation of the simulation series, we study the spatial distribution of hot X-ray luminous gas. We have found that most of this X-ray emitting gas is in a halo-like distribution accounting for an important fraction but not all of the missing baryons. An important amount of hot gas is also present in filaments. In all our models there is not a massive disk-like hot-gas distribution dominating the column density. Our analysis of hot-gas mock observations reveals that the homogeneity assumption leads to an overestimation of the total mass by factors of 3-5 or to an underestimation by factors of 0.7-0.1, depending on the used observational method. Finally, we confirm a clear correlation between the total hot-gas mass and the dark matter halo mass of galactic systems.
NASA Astrophysics Data System (ADS)
Clancy, Dominic; Feinstein, Alexander; Lidsey, James E.; Tavakol, Reza
1999-04-01
Global symmetries of the string effective action are employed to generate tilted, homogeneous Bianchi type VIh string cosmologies from a previously known stiff perfect fluid solution to Einstein gravity. The dilaton field is not constant on the surfaces of homogeneity. The future asymptotic state of the models is interpreted as a plane wave and is itself an exact solution to the string equations of motion to all orders in the inverse string tension. An inhomogeneous generalization of the Bianchi type III model is also found.
Galileons on cosmological backgrounds
Goon, Garrett; Hinterbichler, Kurt; Trodden, Mark E-mail: kurthi@physics.upenn.edu
2011-12-01
We construct four-dimensional effective field theories of a generalized DBI galileon field, the dynamics of which naturally take place on a Friedmann-Robertson-Walker spacetime. The theories are invariant under non-linear symmetry transformations, which can be thought of as being inherited from five-dimensional bulk Killing symmetries via the probe brane technique through which they are constructed. The resulting model provides a framework in which to explore the cosmological role that galileons may play as the universe evolves.
NASA Technical Reports Server (NTRS)
Gregory, Ruth
1988-01-01
The effect of an infinite cosmic string on a cosmological background is investigated. It is found that the metric is approximately a scaled version of the empty space string metric, i.e., conical in nature. Results are used to place bounds on the amount of cylindrical gravitational radiation currently emitted by such a string. The gravitational radiation equations are then analyzed explicitly and it is shown that even initially large disturbances are rapidly damped as the expansion proceeds. The implications of the gravitational radiation background and the limitations of the quadrupole formula are discussed.
Generalized second law in cosmology from causal boundary entropy
Brustein
2000-03-06
A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions, forbids certain cosmological singularities, and is compatible with entropy bounds. This second law is based on the conjecture that causal boundaries and not only event horizons have geometric entropies proportional to their area. In string cosmology the second law provides new information about nonsingular solutions.
Warm-Polytropic Cosmology with and Without Bulk Viscosity
NASA Astrophysics Data System (ADS)
Saadat, Hassan
2014-12-01
In this paper we consider warm-polytropic cosmology including bulk viscosity and study cosmological parameters. We can obtain effect of viscosity on the important cosmological parameters such as Hubble expansion, deceleration and scale factor parameters. We compare our results with observational data and fix our solution. We find that the bulk viscosity increases both energy density and Hubble expansion parameter.
Cosmological tests of coupled Galileons
Brax, Philippe; Davis, Anne-Christine; Gubitosi, Giulia E-mail: Clare.Burrage@nottingham.ac.uk E-mail: g.gubitosi@imperial.ac.uk
2015-03-01
We investigate the cosmological properties of Galileon models which admit Minkowski space as a stable solution in vacuum. This is motivated by stable, positive tension brane world constructions that give rise to Galileons. We include both conformal and disformal couplings to matter and focus on constraints on the theory that arise because of these couplings. The disformal coupling to baryonic matter is extremely constrained by astrophysical and particle physics effects. The disformal coupling to photons induces a cosmological variation of the speed of light and therefore distorsions of the Cosmic Microwave Background spectrum which are known to be very small. The conformal coupling to baryons leads to a variation of particle masses since Big Bang Nucleosynthesis which is also tightly constrained. We consider the background cosmology of Galileon models coupled to Cold Dark Matter (CDM), photons and baryons and impose that the speed of light and particle masses respect the observational bounds on cosmological time scales. We find that requiring that the equation of state for the Galileon models must be close to -1 now restricts severely their parameter space and can only be achieved with a combination of the conformal and disformal couplings. This leads to large variations of particle masses and the speed of light which are not compatible with observations. As a result, we find that cosmological Galileon models are viable dark energy theories coupled to dark matter but their couplings, both disformal and conformal, to baryons and photons must be heavily suppressed making them only sensitive to CDM.
Philosophical Roots of Cosmology
NASA Astrophysics Data System (ADS)
Ivanovic, M.
2008-10-01
We shall consider the philosophical roots of cosmology in the earlier Greek philosophy. Our goal is to answer the question: Are earlier Greek theories of pure philosophical-mythological character, as often philosophers cited it, or they have scientific character. On the bases of methodological criteria, we shall contend that the latter is the case. In order to answer the question about contemporary situation of the relation philosophy-cosmology, we shall consider the next question: Is contemporary cosmology completely independent of philosophical conjectures? The answer demands consideration of methodological character about scientific status of contemporary cosmology. We also consider some aspects of the relation contemporary philosophy-cosmology.
NASA Astrophysics Data System (ADS)
Rasanen, Syksy
The thesis consists of three research papers and an introduction which provides background and also contains some new observations not included in the papers. In the thesis I consider certain questions in the new field of brane cosmology. The basic idea of brane cosmology is that the visible universe is a four- dimensional slice in higher-dimensional spacetime. I give a self-contained introduction to the field, starting from the Randall-Sundrum model and proceeding to the general case of brane gravity and cosmology in the case of one extra dimension. I emphasise the main result of studies of brane gravity: it is possible to obtain approximately four-dimensional gravity independent of the size of the extra dimension, in contrast to set-ups where the observers are not localised in the extra dimension. I proceed to examine a new and promising brave cosmology set-up, the ekpyrotic scenario, in detail. The ekpyrotic scenario aims to be a comprehensive model of the primordial universe and has been presented as an alternative to the prominent scenarios, inflation and pre-big bang. I give an overview of these three scenarios of the primordial universe. I then present the starting point of the ekpyrotic scenario and the construction of the four-dimensional effective theory. After briefly discussing the internal problems of the four-dimensional effective theory, I proceed to the far more serious problems of the four- dimensional construction itself. I conclude that the four-dimensional effective theory does not give a correct description even at a qualitative level. I then discuss some problems faced by the five-dimensional approach, and comment on the spin-off known as the “cyclic model of the universe”. I conclude that the ekpyrotic scenario is a welcome new idea but that most work done thus far is not solid. Careful analysis in the five-dimensional setting is needed to promote the scenario from an interesting concept to a working model with testable predictions.
Troxel, M. A.; Ishak, Mustapha; Peel, Austin E-mail: mishak@utdallas.edu
2014-03-01
The study of relativistic, higher order, and nonlinear effects has become necessary in recent years in the pursuit of precision cosmology. We develop and apply here a framework to study gravitational lensing in exact models in general relativity that are not restricted to homogeneity and isotropy, and where full nonlinearity and relativistic effects are thus naturally included. We apply the framework to a specific, anisotropic galaxy cluster model which is based on a modified NFW halo density profile and described by the Szekeres metric. We examine the effects of increasing levels of anisotropy in the galaxy cluster on lensing observables like the convergence and shear for various lensing geometries, finding a strong nonlinear response in both the convergence and shear for rays passing through anisotropic regions of the cluster. Deviation from the expected values in a spherically symmetric structure are asymmetric with respect to path direction and thus will persist as a statistical effect when averaged over some ensemble of such clusters. The resulting relative difference in various geometries can be as large as approximately 2%, 8%, and 24% in the measure of convergence (1−κ) for levels of anisotropy of 5%, 10%, and 15%, respectively, as a fraction of total cluster mass. For the total magnitude of shear, the relative difference can grow near the center of the structure to be as large as 15%, 32%, and 44% for the same levels of anisotropy, averaged over the two extreme geometries. The convergence is impacted most strongly for rays which pass in directions along the axis of maximum dipole anisotropy in the structure, while the shear is most strongly impacted for rays which pass in directions orthogonal to this axis, as expected. The rich features found in the lensing signal due to anisotropic substructure are nearly entirely lost when one treats the cluster in the traditional FLRW lensing framework. These effects due to anisotropic structures are thus likely to
NASA Astrophysics Data System (ADS)
Tipler, Frank J.
1996-10-01
It is generally believed that it is not possible to rigorously analyze a homogeneous and isotropic cosmological model in Newtonian mechanics. I show on the contrary that if Newtonian gravity theory is rewritten in geometrical language in the manner outlined in 1923-1924 by Élie Cartan [Ann. Ecole Norm. Sup. 40, 325-412 (1923); 41, 1-25 (1924)], then Newtonian cosmology is as rigorous as Friedmann cosmology. In particular, I show that the equation of geodesic deviation in Newtonian cosmology is exactly the same as equation of geodesic deviation in the Friedmann universe, and that this equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: Ever-expanding and recollapsing universes are allowed in any noncompact homogeneous and isotropic spatial topology. I shall give a brief history of attempts to do cosmology in the framework of Newtonian mechanics.
Large imaging surveys for cosmology: cosmic magnification and photometric calibration
NASA Astrophysics Data System (ADS)
Boucaud, Alexandre
2013-09-01
This work focuses on the use of deep, wide field surveys to extract new cosmo- logical information. Precise photometry plays a large role in this quest, through the determination of photometric redshifts and the propagation of photometric errors into the cosmological results. This is a unifying theme which effectively ties both parts of the thesis together. After a general review of cosmology and the measurements that support the ΛCDM model, and a description of the Large Synoptic Survey Telescope (LSST), the first part of this work deals with the influence of the variation of main atmospheric con- stituents on ground-based photometry, focusing particularly on the LSST site at Cerro Pachón, Chile. We process all recent available data on ozone, water vapor and aerosols to construct a long-term atmospheric simulation and estimate quanti- tatively how the spatial and temporal gradients of these constituents would affect LSST calibration process. The second part of this work starts with a theoretical description of gravitational lensing, concentrating on the weak lensing aspect. After discussing the advantages and difficulties of cosmic shear measurements, we explore the use of cosmic magni- fication, together with the redshift tomography enabled by the LSST, to constrain cosmological models. We find that cosmic magnification covariance is beset by in- trinsic clustering but nevertheless represents a useful probe of galaxy bias and dark energy that complements cosmic shear, and which can increase the robustness of cosmological constraints from lensing surveys.
NASA Astrophysics Data System (ADS)
Patel, Ekta; Besla, Gurtina; Mandel, Kaisey
2017-07-01
In the era of high-precision astrometry, space observatories like the Hubble Space Telescope (HST) and Gaia are providing unprecedented 6D phase-space information of satellite galaxies. Such measurements can shed light on the structure and assembly history of the Local Group, but improved statistical methods are needed to use them efficiently. Here we illustrate such a method using analogues of the Local Group's two most massive satellite galaxies, the Large Magellanic Cloud (LMC) and Triangulum (M33), from the Illustris dark-matter-only cosmological simulation. We use a Bayesian inference scheme combining measurements of positions, velocities and specific orbital angular momenta (j) of the LMC/M33 with importance sampling of their simulated analogues to compute posterior estimates of the Milky Way (MW) and Andromeda's (M31) halo masses. We conclude that the resulting host halo mass is more susceptible to bias when using measurements of the current position and velocity of satellites, especially when satellites are at short-lived phases of their orbits (i.e. at pericentre). Instead, the j value of a satellite is well conserved over time and provides a more reliable constraint on host mass. The inferred virial mass of the MW (M31) using j of the LMC (M33) is {{M}}_{vir, MW} = 1.02^{+0.77}_{-0.55} × 10^{12} M⊙ ({{M}}_{vir, M31} = 1.37^{+1.39}_{-0.75} × 10^{12} M⊙). Choosing simulated analogues whose j values are consistent with the conventional picture of a previous (<3 Gyr ago), close encounter (<100 kpc) of M33 about M31 results in a very low virial mass for M31 (˜1012 M⊙). This supports the new scenario put forth in Patel, Besla & Sohn, wherein M33 is on its first passage about M31 or on a long-period orbit. We conclude that this Bayesian inference scheme, utilizing satellite j, is a promising method to reduce the current factor of 2 spread in the mass range of the MW and M31. This method is easily adaptable to include additional satellites as new 6D
The effect of AGN feedback on the X-ray morphologies of clusters: Simulations vs. observations
NASA Astrophysics Data System (ADS)
Chon, Gayoung; Puchwein, Ewald; Böhringer, Hans
2016-07-01
Clusters of galaxies probe the large-scale distribution of matter and are a useful tool to test the cosmological models by constraining cosmic structure growth and the expansion of the Universe. It is the scaling relations between mass observables and the true mass of a cluster through which we obtain the cosmological constraints by comparing to theoretical cluster mass functions. These scaling relations are, however, heavily influenced by cluster morphology. The presence of the slight tension in recent cosmological constraints on Ωm and σ8 based on the CMB and clusters has boosted the interests in looking for possible sources for the discrepancy. Therefore we study here the effect of active galactic nucleus (AGN) feedback as one of the major mechanisms modifying the cluster morphology influencing scaling relations. It is known that AGN feedback injects energies up to 1062 erg into the intracluster medium, controls the heating and cooling of a cluster, and re-distributes cold gas from the centre to outer radii. We have also learned that cluster simulations with AGN feedback can reproduce observed cluster properties, for example, the X-ray luminosity, temperature, and cooling rate at the centre better than without the AGN feedback. In this paper using cosmological hydrodynamical simulations we investigate how the AGN feedback changes the X-ray morphology of the simulated systems, and compare this to the observed Representative XMM-Newton Cluster Structure Survey (REXCESS) clusters. We apply two substructure measures, centre shifts (w) and power ratios (e.g. P3/P0), to characterise the cluster morphology, and find that our simulated clusters are more substructured than the observed clusters based on the values of w and P3/P0. We also show that the degree of this discrepancy is affected by the inclusion of AGN feedback. While the clusters simulated with the AGN feedback are in much better agreement with the REXCESS LX-T relation, they are also more substructured
Cosmological parameter estimation using Particle Swarm Optimization
NASA Astrophysics Data System (ADS)
Prasad, J.; Souradeep, T.
2014-03-01
Constraining parameters of a theoretical model from observational data is an important exercise in cosmology. There are many theoretically motivated models, which demand greater number of cosmological parameters than the standard model of cosmology uses, and make the problem of parameter estimation challenging. It is a common practice to employ Bayesian formalism for parameter estimation for which, in general, likelihood surface is probed. For the standard cosmological model with six parameters, likelihood surface is quite smooth and does not have local maxima, and sampling based methods like Markov Chain Monte Carlo (MCMC) method are quite successful. However, when there are a large number of parameters or the likelihood surface is not smooth, other methods may be more effective. In this paper, we have demonstrated application of another method inspired from artificial intelligence, called Particle Swarm Optimization (PSO) for estimating cosmological parameters from Cosmic Microwave Background (CMB) data taken from the WMAP satellite.
Weak lensing cosmology beyond ΛCDM
Das, Sudeep; Linder, Eric V.; Nakajima, Reiko; Putter, Roland de E-mail: rdeputter@icc.ub.edu E-mail: reiko@astro.uni-bonn.de
2012-11-01
Weak gravitational lensing is one of the key probes of the cosmological model, dark energy, and dark matter, providing insight into both the cosmic expansion history and large scale structure growth history. Taking into account a broad spectrum of physics affecting growth — dynamical dark energy, extended gravity, neutrino masses, and spatial curvature — we analyze the cosmological constraints. Similarly we consider the effects of a range of systematic uncertainties, in shear measurement, photometric redshifts, intrinsic alignments, and the nonlinear power spectrum, on cosmological parameter extraction. We also investigate, and provide fitting formulas for, the influence of survey parameters such as redshift depth, galaxy number densities, and sky area on the cosmological constraints in the beyond-ΛCDM parameter space. Finally, we examine the robustness of results for different fiducial cosmologies.
On under-determination in cosmology
NASA Astrophysics Data System (ADS)
Butterfield, Jeremy
2014-05-01
I discuss how modern cosmology illustrates under-determination of theoretical hypotheses by data, in ways that are different from most philosophical discussions. I emphasise cosmology's concern with what data could in principle be collected by a single observer (Section 2); and I give a broadly sceptical discussion of cosmology's appeal to the cosmological principle as a way of breaking the under-determination (Section 3). I confine most of the discussion to the history of the observable universe from about one second after the Big Bang, as described by the mainstream cosmological model: in effect, what cosmologists in the early 1970s dubbed the 'standard model', as elaborated since then. But in the closing Section 4, I broach some questions about times earlier than one second.
Particle physics and cosmology
Kolb, E.W.
1986-10-01
This series of lectures is about the role of particle physics in physical processes that occurred in the very early stages of the bug gang. Of particular interest is the role of particle physics in determining the evolution of the early Universe, and the effect of particle physics on the present structure of the Universe. The use of the big bang as a laboratory for placing limits on new particle physics theories will also be discussed. Section 1 reviews the standard cosmology, including primordial nucleosynthesis. Section 2 reviews the decoupling of weakly interacting particles in the early Universe, and discusses neutrino cosmology and the resulting limits that may be placed on the mass and lifetime of massive neutrinos. Section 3 discusses the evolution of the vacuum through phase transitions in the early Universe and the formation of topological defects in the transitions. Section 4 covers recent work on the generation of the baryon asymmetry by baryon-number violating reactions in Grand Unified Theories, and mentions some recent work on baryon number violation effects at the electroweak transition. Section 5 is devoted to theories of cosmic inflation. Finally, Section 6 is a discussion of the role of extra spatial dimensions in the evolution of the early Universe. 78 refs., 32 figs., 6 tabs.
Simulating Hydrologic Effects of Urbanization
NASA Astrophysics Data System (ADS)
Downer, C. W.; Ogden, F. L.; Pradhan, N.
2012-12-01
Urbanization of watersheds introduces multiple effects on hydrology and water quality. Roads, parking lots, roof tops and other impervious areas increase total runoff production. Soils are extensively modified through compaction and importation of fill and placement of sod. Streams are modified, moved, and replaced with lined channels, further increasing runoff and storm peaks. Subsurface drainage may supplement or supplant the function of natural streams, compounding the effects of channel modifications. Increased runoff results in increased erosion and transport of sediment and associated contaminants. Efforts to mitigate the effects of urbanization, channel improvements, levees, low impact development, detention basins, grassed swales, and other best management practices further complicate the issue. These attempts may or may not affect the overall system response as anticipated or desired. Analysis of the effects of urbanizing watersheds and design of abatement measures using simplified empirical methods and/or analyzing only the local effects may produce erroneous results. In this paper we will present and discuss simulation results from various studies related to the application of models to predicting the effects of urbanizing watersheds. We will contrast physics based hydrologic modeling efforts to simpler, empirical methods. We will also discuss the relative importance of various urbanizing features and modeling strategies to incorporate the important features. Dead Run Watershed
NASA Astrophysics Data System (ADS)
Chaicherdsakul, Kanokkuan
2006-08-01
Quantum theory of cosmological fluctuations with other matters is studied to higher order to understand the origin of the universe during the time of inflation. This study also links gravitational and all matter fluctuations with the observed cosmic microwave background (CMB) anisotropy. It is important to keep in mind that what is tested observationally is the paradigm that the primordial spectrum of inhomogeneities was nearly scale invariant and predominantly adiabatic. Therefore, if other matters such as fermion and gauge fields which do not drive inflation predict the scale invariant spectrums, their existence during inflation cannot be ruled out. We therefore extend the calculation of quantum corrections to the cosmological correlation
Noncommutative Quantum Scalar Field Cosmology
Diaz Barron, L. R.; Lopez-Dominguez, J. C.; Sabido, M.; Yee, C.
2010-07-12
In this work we study noncommutative Friedmann-Robertson-Walker (FRW) cosmology coupled to a scalar field endowed with an exponential potential. The quantum scenario is analyzed in the Bohmian formalism of quantum trajectories to investigate the effects of noncommutativity in the evolution of the universe.
NASA Astrophysics Data System (ADS)
Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne; Teyssier, Romain
2012-03-01
We develop a subgrid model for the growth of supermassive black holes (BHs) and their associated active galactic nucleus (AGN) feedback in hydrodynamical cosmological simulations. This model transposes previous attempts to describe BH accretion and AGN feedback with the smoothed particle hydrodynamics (SPH) technique to the adaptive mesh refinement framework. It also furthers their development by implementing a new jet-like outflow treatment of the AGN feedback which we combine with the heating mode traditionally used in the SPH approach. Thus, our approach allows one to test the robustness of the conclusions derived from simulating the impact of self-regulated AGN feedback on galaxy formation vis-à-vis the numerical method. Assuming that BHs are created in the early stages of galaxy formation, they grow by mergers and accretion of gas at a Eddington-limited Bondi accretion rate. However this growth is regulated by AGN feedback which we model using two different modes: a quasar-heating mode when accretion rates on to the BHs are comparable to the Eddington rate, and a radio-jet mode at lower accretion rates which not only deposits energy, but also deposits mass and momentum on the grid. In other words, our feedback model deposits energy as a succession of thermal bursts and jet outflows depending on the properties of the gas surrounding the BHs. We assess the plausibility of such a model by comparing our results to observational measurements of the co-evolution of BHs and their host galaxy properties, and check their robustness with respect to numerical resolution. We show that AGN feedback must be a crucial physical ingredient for the formation of massive galaxies as it appears to be able to efficiently prevent the accumulation of and/or expel cold gas out of haloes/galaxies and significantly suppress star formation. Our model predicts that the relationship between BHs and their host galaxy mass evolves as a function of redshift, because of the vigorous accretion
Cosmological constant, violation of cosmological isotropy and CMB
Urban, Federico R.; Zhitnitsky, Ariel R. E-mail: arz@physics.ubc.ca
2009-09-01
We suggest that the solution to the cosmological vacuum energy puzzle does not require any new field beyond the standard model, but rather can be explained as a result of the interaction of the infrared sector of the effective theory of gravity with standard model fields. The cosmological constant in this framework can be presented in terms of QCD parameters and the Hubble constant H as follows, ε{sub vac} ≅ H⋅m{sub q}( q-bar q)/m{sub η'} ≅ (4.3⋅10{sup −3}eV){sup 4}, which is amazingly close to the observed value today. In this work we explain how this proposal can be tested by analyzing CMB data. In particular, knowing the value of the observed cosmological constant fixes univocally the smallest size of the spatially flat, constant time 3d hypersurface which, for instance in the case of an effective 1-torus, is predicted to be around 74 Gpc. We also comment on another important prediction of this framework which is a violation of cosmological isotropy. Such anisotropy is indeed apparently observed by WMAP, and will be confirmed (or ruled out) by future PLANCK data.
Cosmological studies of the Sunyaev-Zel'dovich Effect with the APEX-SZ instrument
NASA Astrophysics Data System (ADS)
Mehl, Jared Joseph
We have built the APEX-SZ instrument to observe galaxy clusters with the Sunyaev-Zel'dovich Effect (SZE), in which Cosmic Microwave Background (CMB) photons are scattered off of the hot electron gas within a galaxy cluster. Galaxy clusters are the largest collapsed objects in the universe and make excellent tracers of the distribution and evolution of matter. Galaxy cluster surveys can be used to measure the matter density of the universe O m , the equation of state of dark energy w, the amplitude of matter fluctuations at 8 h -1 Mpc s 8 , and the Hubble constant H 0 . Galaxy cluster observations with the SZE also provide a unique probe of galaxy cluster physics. I will describe the design and fabrication of the 330-element Transition-Edge Sensor (TES) bolometer array used in APEX-SZ. CMB power is measured with an aluminum-titanium bilayer TES centered on a silicon-nitride spiderweb covered with a thin-film gold absorber. Frequency-domain multiplexing is used to read out the TESs. An integration cavity is formed behind a smooth-walled conical horn by the silicon wafer in direct contact with a metal backshort. This cavity couples the gold absorber to incoming millimeter-wave radiation. I will also describe finite element analysis electromagnetic simulations of the integration cavity intended to optimize the optical efficiency of the bolometer array. The full configuration APEX-SZ instrument was deployed to the 12-meter diameter APEX telescope sited in Chile in March 2007. Observations of the Bullet cluster, a massive galaxy cluster merger perpendicular to the line-of-sight, were made in August 2007. The Bullet cluster was detected in the SZE with a23s significance within the central 1' radius of the source position. We measure a temperature decrement of --880 ± 80mK CMB using an isothermal elliptical b- model fit to the temperature map. We measure a cluster gas mass fraction fg = 0.121±0.038 within a radius 1.42 Mpc, consistent with X-ray and weak lensing results
NASA Astrophysics Data System (ADS)
Mahootian, F.
2009-12-01
The rapid convergence of advancing sensor technology, computational power, and knowledge discovery techniques over the past decade has brought unprecedented volumes of astronomical data together with unprecedented capabilities of data assimilation and analysis. A key result is that a new, data-driven "observational-inductive'' framework for scientific inquiry is taking shape and proving viable. The anticipated rise in data flow and processing power will have profound effects, e.g., confirmations and disconfirmations of existing theoretical claims both for and against the big bang model. But beyond enabling new discoveries can new data-driven frameworks of scientific inquiry reshape the epistemic ideals of science? The history of physics offers a comparison. The Bohr-Einstein debate over the "completeness'' of quantum mechanics centered on a question of ideals: what counts as science? We briefly examine lessons from that episode and pose questions about their applicability to cosmology. If the history of 20th century physics is any indication, the abandonment of absolutes (e.g., space, time, simultaneity, continuity, determinacy) can produce fundamental changes in understanding. The classical ideal of science, operative in both physics and cosmology, descends from the European Enlightenment. This ideal has for over 200 years guided science to seek the ultimate order of nature, to pursue the absolute theory, the "theory of everything.'' But now that we have new models of scientific inquiry powered by new technologies and driven more by data than by theory, it is time, finally, to relinquish dreams of a "final'' theory.
Anisotropic Cosmology and Curvature Invariants.
NASA Astrophysics Data System (ADS)
Skea, James E. F.
Available from UMI in association with The British Library. In Part 1 of this thesis we study the phase-planes of two classes of Kaluza-Klein (higher-dimensional) cosmologies, namely those containing a barotropic (p = nrho ) perfect fluid in a product-space of two flat manifolds, and those with a vacuum energy-momentum tensor in a product -space of one flat and one curved manifold. For the first class, we determine some general characteristics of the phase-plane--the number of types of solution possible is almost always found to be six, seven and three for the cases where the higher-dimensional cosmological constant (|{Lambda}) is zero, positive and negative respectively; the only stable solutions correspond to generalisations of the Einstein -De-Sitter solutions and De-Sitter solutions when |{Lambda} = 0 and |{Lambda} > 0 respectively; there are no stable solutions when |{Lambda} < 0. We identify higher-dimensional generalisations of barotropic fluids of particular cosmological interest and classify the different types of solution in terms of the asymptotic behaviour of the Hubble factors of the manifolds. Having identified criteria for compatibility of the cosmologies with observation, we check whether the proposed fluids satisfy these criteria, and find that only a very restricted subset of the fluids permit feasible cosmologies. Those fluids which do not conform to the general classification scheme are identified and their phase-planes studied. In Part 2, we evaluate the effects of the production of free particles on the Bianchi type I, VIII and IX homogeneous cosmologies. The theoretical predictions in the axisymmetric Bianchi I model are calculated, and comparison made with both the theory of Lukash and Starobinskii and subsequent numerical integrations of the Field Equations. From the numerical integrations, we find that isotropisation time will be a factor 50 greater than previously expected for axisymmetric models, and can be a further factor of 10 ^3
Braneworld cosmology and noncommutative inflation
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca
2005-03-01
In this work we develop the patch formalism, an approach providing a very simple and compact description of braneworld-motivated cosmologies with nonstandard effective Friedmann equations. In particular, the Hubble parameter is assumed to depend on some power of the brane energy density, H^2 propto rho^q. The high-energy limit of Randall-Sundrum (q=2) and Gauss-Bonnet (q=2/3) braneworlds are considered, during an accelerating era triggered by a single ordinary or tachyonic scalar field. The inflationary dynamics, solutions, and spectra are provided. Using the latest results from WMAP and other experiments for estimates of cosmological observables, it is shown that future data and missions can in principle discriminate between standard four-dimensional and braneworld scenarios. The issue of non-Gaussianity is also studied within nonlinear perturbation theory. The introduction of a fundamental energy scale reinforces these results. Several classes of noncommutative inflationary models are considered and their features analyzed in a number of ways and energy regimes. Finally, we establish dual relations between inflationary, cyclic/ekpyrotic and phantom cosmologies, as well as between scalar-driven and tachyon-driven cosmologies. The exact dualities relating the four-dimensional spectra are broken in favour of their braneworld counterparts. The dual solutions display new interesting features because of the modification of the effective Friedmann equation on the brane.
Investigating inhomogeneous Szekeres models and their applications to precision cosmology
NASA Astrophysics Data System (ADS)
Peel, Austin Chandler
. Despite nontrivial evolution and density distributions of the structures, the effect of tidal shearing on the beams remains small. Finally, we study source magnification probability distributions for various redshifts, finding a limitation of the models in that the distributions do not consistently resemble those of gravitational lensing analyses in cosmological simulations.
Inherent weaknesses of cosmology
NASA Technical Reports Server (NTRS)
Chiu, H.-Y.
1986-01-01
Sources of astrophysical evidence necessary to verify a cosmological model are reviewed. Cosmological history of the universe is divided into four epochs, each unique in its physical conditions related to observability at present. The current epoch, started after recombination of hydrogen in the universe, offers the most in observability. In earlier epochs, verifiable astrophysical evidence gradually disappeared. It seems that no astrophysical evidence has been left behind from the singularity epoch of the Universe. The gradual disappearance of astrophysical evidence ascertainable at present is the result of physical conditions structured within the cosmological models, hence indicating certain inherent weaknesses of cosmology as a verifiable physical theory.
NASA Astrophysics Data System (ADS)
Davydov, E. A.
2012-06-01
Vector fields can arise in the cosmological context in different ways, and we discuss both abelian and nonabelian sector. In the abelian sector vector fields of the geometrical origin (from dimensional reduction and Einstein-Eddington modification of gravity) can provide a very non-trivial dynamics, which can be expressed in terms of the effective dilaton-scalar gravity with the specific potential. In the non-abelian sector we investigate the Yang-Mills SU(2) theory which admits isotropic and homogeneous configuration. Provided the non-linear dependence of the lagrangian on the invariant FμνF~μν, one can obtain the inflationary regime with the exponential growth of the scale factor. The effective amplitudes of the `electric' and `magnetic' components behave like slowly varying scalars at this regime, what allows the consideration of some realistic models with non-linear terms in the Yang-Mills lagrangian.
Bonaldi, A.; Battye, R. A.; Brown, M. L.
2014-05-10
The accumulation of redshifts provides a significant observational bottleneck when using galaxy cluster surveys to constrain cosmological parameters. We propose a simple method to allow the use of samples where there is a fraction of the redshifts that are not known. The simplest assumption is that the missing redshifts are randomly extracted from the catalog, but the method also allows one to take into account known selection effects in the accumulation of redshifts. We quantify the reduction in statistical precision of cosmological parameter constraints as a function of the fraction of missing redshifts for simulated surveys, and also investigate the impact of making an incorrect assumption for the distribution of missing redshifts.