Hydrodynamical Simulations of the IGM at High Mach Numbers

We present a new approach to doing Eulerian computational fluid dynamics that is designed to work at high Mach numbers encountered in hydrodynamical simulations of the IGM. In conventional Eulerian CFD, the thermal energy is poorly tracked in supersonic bulk flows where local fluid variables cannot be accurately separated from the much larger bulk flow components. We described a method in which local fluid quantities can be directly tracked and the Eulerian fluid equations solved in a local frame moving with the flow. The new algorithm has been used to run large hydrodynamical simulations on a 1024^3 grid to study the kinetic SZ effect. The KSZ power spectrum is broadly peaked at l~10^4 with temperature fluctuations on micro Kelvin levels.Comment: 6 pages, to appear in the Proc. from the IGM/Galaxy Connection conferenc

The Impact of Non-Gaussian Errors on Weak Lensing Surveys

The weak lensing power spectrum carries cosmological information via its dependence on the growth of structure and on geometric factors. Since much of the cosmological information comes from scales affected by nonlinear clustering, measurements of the lensing power spectrum can be degraded by non-Gaussian covariances. Recently there have been conflicting studies about the level of this degradation. We use the halo model to estimate it and include new contributions related to the finite size of lensing surveys, following Rimes and Hamilton's study of 3D simulations. We find that non-Gaussian correlations between different multipoles can degrade the cumulative signal-to-noise for the power spectrum amplitude by up to a factor of 2 (or 5 for a worst-case model that exceeds current N-body simulation predictions). However, using an eight-parameter Fisher analysis we find that the marginalized errors on individual parameters are degraded by less than 10% (or 20% for the worst-case model). The smaller degradation in parameter accuracy is primarily because: individual parameters in a high-dimensional parameter space are degraded much less than the volume of the full Fisher ellipsoid; lensing involves projections along the line of sight, which reduce the non-Gaussian effect; some of the cosmological information comes from geometric factors which are not degraded at all. We contrast our findings with those of Lee & Pen (2008) who suggested a much larger degradation in information content. Finally, our results give a useful guide for exploring survey design by giving the cosmological information returns for varying survey area, depth and the level of some systematic errors.Comment: To appear in MNRAS, 22 pages, 12 figures. Minor modifications made according to the referee comment

Effects of halo substructure on the power spectrum and bispectrum

We study the effects of halo substructure and a distribution in the concentration parameter of haloes on large-scale structure statistics. The effects on the power spectrum and bispectrum are studied on the smallest scales accessible from future surveys. We compare halo-model predictions with results based on N-body simulations, but also extend our predictions to 10-kpc scales which will be probed by future simulations. We find that weak-lensing surveys proposed for the coming decade can probe the power spectrum on small enough scales to detect substructure in massive haloes. We discuss the prospects of constraining the mass fraction in substructure in view of partial degeneracies with parameters such as the tilt and running of the primordial power spectrum.Comment: 9 pages, 10 figures; replaced with version published in MNRAS; removed grey-scale versions of figures which were being included at the end by the serve

Masses of high-z galaxy hosting haloes from angular clustering and their evolution in the CDM model

We examine masses of hosting haloes of two photometrically-selected high-z galaxy samples: the old passively-evolving galaxies (OPEGs) and Lyman Break Galaxies (LBGs) both taken from the Subaru/XMM-Newton Deep Survey (SXDS). The large survey area of the SXDS (1sq deg) allows us to measure the angular two-point correlation functions to a wide separation of >10 arcmin with a good statistical quality. We utilize the halo model prescription for estimating characteristic masses of hosting haloes from the measured large-scale clustering amplitudes. It is found that the hosting halo mass positively correlates with the luminosity of galaxies. Then, adopting the extended Press-Schechter model (EPS), we compute the predictions for the mass evolution of the hosting haloes in the framework of the cold dark matter (CDM) cosmology in order to make an evolutionary link between the two galaxy samples at different redshifts and to identify their present-day descendants by letting their haloes evolve forward in time. It is found that, in the view of the mass evolution of hosting haloes in the CDM model, bright LBGs are consistent with being the progenitor of the OPEGs, whereas it is less likely that the LBG population, as a whole, have evolved into the OPEG population. It is also found that the present-day descendants of both the bright LBGs and OPEGs are likely to be located in massive systems such as groups of galaxies or clusters of galaxies. Finally, we estimate the hosting halo mass of local early-type galaxy samples from the 2dF and SDSS based on the halo model and it turns out that their expected characteristic mass of hosting haloes is in good agreement with the EPS predictions for the descendant's mass of both the bright LBGs and OPEGs.Comment: 10 pages, 10 figures, submitted to MNRAS. Fortran programs used to compute the model predictions in this paper are available at http://optik2.mtk.nao.ac.jp/~hamanatk/OPENPRO/index.htm

From Weak Lensing to non-Gaussianity via Minkowski Functionals

We present a new harmonic-domain approach for extracting morphological information, in the form of Minkowski Functionals (MFs), from weak lensing (WL) convergence maps. Using a perturbative expansion of the MFs, which is expected to be valid for the range of angular scales probed by most current weak-lensing surveys, we show that the study of three generalized skewness parameters is equivalent to the study of the three MFs defined in two dimensions. We then extend these skewness parameters to three associated skew-spectra which carry more information about the convergence bispectrum than their one-point counterparts. We discuss various issues such as noise and incomplete sky coverage in the context of estimation of these skew-spectra from realistic data. Our technique provides an alternative to the pixel-space approaches typically used in the estimation of MFs, and it can be particularly useful in the presence of masks with non-trivial topology. Analytical modeling of weak lensing statistics relies on an accurate modeling of the statistics of underlying density distribution. We apply three different formalisms to model the underlying dark-matter bispectrum: the hierarchical ansatz, halo model and a fitting function based on numerical simulations; MFs resulting from each of these formalisms are computed and compared. We investigate the extent to witch late-time gravity-induced non-Gaussianity (to which weak lensing is primarily sensitive) can be separated from primordial non-Gaussianity and how this separation depends on source redshift and angular scale.Comment: 22 Pages, 12 Figures. Submitting To MNRA

Baryon Oscillations and Dark-Energy Constraints from Imaging Surveys

Baryonic oscillations in the galaxy power spectrum have been studied as a way of probing dark-energy models. While most studies have focused on spectroscopic surveys at high redshift, large multi-color imaging surveys have already been planned for the near future. In view of this, we study the prospects for measuring baryonic oscillations from angular statistics of galaxies binned using photometric redshifts. We use the galaxy bispectrum in addition to the power spectrum; this allows us to measure and marginalize over possibly complex galaxy bias mechanisms to get robust cosmological constraints. In our parameter estimation we allow for a weakly nonlinear biasing scheme that may evolve with redshift by two bias parameters in each of ten redshift bins. We find that a multi-color imaging survey that probes redshifts beyond one can give interesting constraints on dark-energy parameters. In addition, the shape of the primordial power spectrum can be measured to better accuracy than with the CMB alone. We explore the impact of survey depth, area, and calibration errors in the photometric redshifts on dark-energy constraints.Comment: 17 pages, 12 figure

A Strategy to Measure the Dark Energy Equation of State using the HII galaxy Hubble Relation & X-ray AGN Clustering: Preliminary Results

We explore the possibility of setting stringent constraints to the Dark Energy equation of state using alternative cosmic tracers like: (a) the Hubble relation using HII galaxies, which can be observed at much higher redshifts (z~3.5) than those currently traced by SNIa samples, and (b) the large-scale structure using the clustering of X-ray selected AGN,which have a redshift distribution peaking at z~1. We use extensive Monte-Carlo simulations to define the optimal strategy for the recovery of the dark-energy equation of state using the high redshift (z~2) Hubble relation, but accounting also for the effects of gravitational lensing, which for such high redshifts can significantly affect the derived cosmological constraints. Based on a "Figure of Merit" analysis, we provide estimates for the number of 2<z<3.5 tracers needed to reduce the cosmological solution space, presently provided by the Constitution SNIa set, by a desired factor. We find that it is much more efficient to increase the number of tracers than to reduce their individual uncertainties. Finally, we propose a framework to put constraints on the dark energy equation of state by using the joint likelihood of the X-ray AGN clustering and of the Hubble relation cosmological analyses. A preliminary joint analysis using the X-ray AGN clustering of the 2XMM survey and the Hubble relation of the Constitution SNIa set provide: Omega_m= 0.31+-0.01 and w=-1.06+-0.05. We also find that the joint SNIa-2XMM analysis provides significantly more stringent cosmological constraints, increasing the Figure of Merit by a factor ~2, with respect to that of the joint SNIa-BAO analysis.Comment: MNRAS in press, 12 colour figure

Cosmological Tests of Gravity

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We review recent developments in modified gravity theories, focusing on higher dimensional approaches and chameleon/f(R) theories. We classify these models in terms of the screening mechanisms that enable such theories to approach general relativity on small scales (and thus satisfy solar system constraints). We describe general features of the modified Friedman equation in such theories. The second half of this review describes experimental tests of gravity in light of the new theoretical approaches. We summarize the high precision tests of gravity on laboratory and solar system scales. We describe in some detail tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc (large-scale structure). These tests rely on the growth and inter-relationship of perturbations in the metric potentials, density and velocity fields which can be measured using gravitational lensing, galaxy cluster abundances, galaxy clustering and the Integrated Sachs-Wolfe effect. A robust way to interpret observations is by constraining effective parameters, such as the ratio of the two metric potentials. Currently tests of gravity on astrophysical scales are in the early stages --- we summarize these tests and discuss the interesting prospects for new tests in the coming decade.Comment: Invited review for Annals of Physics; 58 pages, 8 figures

Forecasting Cosmic Doomsday from CMB/LSS Cross-Correlations

A broad class of dark energy models, which have been proposed in attempts at solving the cosmological constant problems, predict a late time variation of the equation of state with redshift. The variation occurs as a scalar field picks up speed on its way to negative values of the potential. The negative potential energy eventually turns the expansion into contraction and the local universe undergoes a big crunch. In this paper we show that cross-correlations of the CMB anisotropy and matter distribution, in combination with other cosmological data, can be used to forecast the imminence of such cosmic doomsday.Comment: 12 pages, 12 figure