We examine the counts-in-cells probability distribution functions that describe dark matter halos in the Dark Energy Universe Simulations (DEUS). We describe the measurements between redshifts $z=0$ to $z=4$ on both linear and non-linear scales. The best-fits of the gravitational quasi-equilibrium distribution (GQED), the negative binomial distribution (NBD), the Poisson-Lognormal distribution (PLN), and the Poisson-Lognormal distribution with a bias parameter (PLNB) are compared to simulations. The fits agree reasonably consistently over a range of redshifts and scales. To distinguish quintessence (RPCDM) and phantom ($w$CDM) dark energy from $Λ$ dark energy, we present a new method that compares the model parameters of the counts-in-cells probability distribution functions. We find that the mean and variance of the halo counts-in-cells on $2-25h^{-1}$Mpc scales between redshifts $0.65<z<4$ show significant percentage differences for different dark energy cosmologies. On $15-25h^{-1}$Mpc scales, the $g$ parameter in NBD, $ω$ parameter in PLN, $b$ and $C_b$ parameters in PLNB show larger percentage differences for different dark energy cosmologies than on smaller scales. On $2-6h^{-1}$Mpc scales, kurtosis and the $b$ parameter in the GQED show larger percentage differences for different dark energy cosmologies than on larger scales. For cosmologies explored in the DEUS simulations, the percentage differences between these statistics for the RPCDM and $w$CDM dark energy cosmologies relative to $Λ$CDM generally increases with redshift from a few percent to significantly larger percentages at $z=4$. Applying our method to simulations and galaxy surveys can provide a useful way to distinguish among dark energy models and cosmologies in general.
We determine the error introduced in a joint halo model analysis of galaxy-galaxy lensing and galaxy clustering observables when adopting the standard approximation of linear halo bias. Considering the Kilo-Degree Survey, we forecast that ignoring the non-linear halo bias would result in up to 5$σ$ offsets in the recovered cosmological parameters describing structure growth, $S_8$, and the matter density parameter, $Ω_{\mathrm{m}}$. We include the scales $10^{-1.3}<r_{\rm{p}} \ / h^{-1}\, \mathrm{Mpc}<10$ in the data vector, and the direction of these offsets are shown to depend on the freedom…
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos, i…
I highlight three results from cosmological hydrodynamic simulations that yield a realistic red sequence of galaxies: 1) Major galaxy mergers are not responsible for shutting off star-formation and forming the red sequence. Starvation in hot halos is. 2) Massive galaxies grow substantially (about a factor of 2 in mass) after being quenched, primarily via minor (1:5) mergers. 3) Hot halo quenching naturally explains why galaxies are red when they either (a) are massive or (b) live in dense environments.
One of the most powerful tools in the arsenal of theoretical cosmologists is the halo model of large scale structure, which provides a phenomenological description of nonlinear structure in our universe. However, it is well known that there is no simple way to impose conservation laws in the halo model. This can severely impair the predictions on large scales for observables such as weak lensing or the kinematic Sunyaev-Zel'dovich effect, which should satisfy mass and momentum conservations, respectively. For example, the standard halo model overpredicts weak lensing power spectrum by $> 8\%$ …
The standard cosmological paradigm currently lacks a detailed account of physics in the dark sector, the dark matter and energy that dominate cosmic evolution. In this paper, we consider the distinguishing factors between three alternative models - warm dark matter, quintessence and coupled dark matter-energy - and \lcdm{} through numerical simulations of cosmological structure formation. Key halo statistics - halo spin/velocity alignment between large-scale structure and neighboring haloes, halo formation time and migration - were compared across cosmologies within the redshift range 0$\leq$$…
We present and test a method for modifying the catalogue of dark matter haloes produced from a given cosmological simulation, so that it resembles the result of a simulation with an entirely different set of parameters. This extends the method of Angulo & White (2010), which rescales the full particle distribution from a simulation. Working directly with the halo catalogue offers an advantage in speed, and also allows modifications of the internal structure of the haloes to account for nonlinear differences between cosmologies. Our method can be used directly on a halo catalogue in a self cont…
Cosmological N-body simulations have been a major tool of theorists for decades, yet many of the numerical issues that these simulations face are still unexplored. This paper measures numerical biases in these large, dark matter-only simulations that affect the properties of their dark matter haloes. We compare many simulation suites in order to provide several tools for simulators and analysts which help mitigate these biases. We summarise our comparisons with practical `convergence limits' that can be applied to a wide range of halo properties, including halo properties which are traditional…
Cosmological simulations of galaxy formation often rely on prescriptions for star formation and feedback that depend on halo properties such as halo mass, central over-density, and virial temperature. In this paper we address the convergence of individual halo properties, based on their number of particles N, focusing in particular on the mass of halos near the resolution limit of a simulation. While it has been established that the halo mass function is sampled on average down to N~30 particles, we show that individual halo properties exhibit significant scatter, and some systematic biases, a…
In order to extract full cosmological information from next-generation large and high-precision weak lensing (WL) surveys (e.g. Euclid, Roman, LSST), higher-order statistics that probe the small-scale, non-linear regime of large scale structure (LSS) need to be utilized. WL peak counts, which trace overdensities in the cosmic web, are one promising and simple statistic for constraining cosmological parameters. The physical origin of WL peaks have previously been linked to dark matter halos along the line of sight and this peak-halo connection has been used to develop various semi-analytic halo…
We present a method for populating dark matter simulations with haloes of mass below the resolution limit. It is based on stochastically sampling a field derived from the density field of the halo catalogue, using constraints from the conditional halo mass function n(m|δ). We test the accuracy of the method and show its application in the context of building mock galaxy samples. We find that this technique allows precise reproduction of the two-point statistics of galaxies in mock samples constructed with this method. Our results demonstrate that the full information content of a simulation ca…
We discuss various aspects of the inner structure formation in virialized dark matter (DM) halos that form as primordial density inhomogeneities evolve in the cosmological standard model. The main focus is on the study of central cusps/cores and of the profiles of DM halo rotation curves, problems that reveal disagreements among the theory, numerical simulations, and observations. A method that was developed by the authors to describe equilibrium DM systems is presented, which allows investigating these complex nonlinear structures analytically and relating density distribution profiles within…
We present estimates of the nonlinear bias of cosmological halo formation, spanning a wide range in the halo mass from $\sim 10^{5} M_\odot$ to $\sim 10^{12} M_\odot$, based upon both a suite of high-resolution cosmological N-body simulations and theoretical predictions. The halo bias is expressed in terms of the mean bias and stochasticity as a function of local overdensity ($δ$), under different filtering scales, which is realized as the density of individual cells in uniform grids. The sampled overdensities span a range wide enough to provide the fully nonlinear bias effect on the formation…
The dark matter halo sparsity, i.e. the ratio between spherical halo masses enclosing two different overdensities, provides a non-parametric proxy of the halo mass distribution which has been shown to be a sensitive probe of the cosmological imprint encoded in the mass profile of haloes hosting galaxy clusters. Mass estimations at several overdensities would allow for multiple sparsity measurements, that can potentially retrieve the entirety of the cosmological information imprinted on the halo profile. Here, we investigate the impact of multiple sparsity measurements on the cosmological model…
Intrinsic alignments of galaxies are a significant astrophysical systematic affecting cosmological constraints from weak gravitational lensing. Obtaining numerical predictions from hydrodynamical simulations of expected survey volumes is expensive, and a cheaper alternative relies on populating large dark matter-only simulations with accurate models of alignments calibrated on smaller hydrodynamical runs. This requires connecting the shapes and orientations of galaxies to those of dark matter haloes and to the large-scale structure. In this paper, we characterise galaxy-halo alignments in the …
We study the halo bispectrum from non-Gaussian initial conditions. Based on a set of large $N$-body simulations starting from initial density fields with local type non-Gaussianity, we find that the halo bispectrum exhibits a strong dependence on the shape and scale of Fourier space triangles near squeezed configurations at large scales. The amplitude of the halo bispectrum roughly scales as $f_nl^2$. The resultant scaling on the triangular shape is consistent with that predicted by Jeong & Komatsu based on perturbation theory. We systematically investigate this dependence with varying redshif…
We introduce the Lomonosov suite of high-resolution N-body cosmological simulations covering a full box of size 32 $h^{-1}$ Mpc with low-mass resolution particles ($2\times10^7$ $h^{-1}\,M_\odot$) and three zoom-in simulations of overdense, underdense and mean density regions at much higher particle resolution ($4\times10^4$ $h^{-1}\,M_\odot$). The main purpose of this simulation suite is to extend the concentration-mass relation of dark matter halos down to masses below those typically available in large cosmological simulations. The three different density regions available at higher resolut…
Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $Λ$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes …
We present the first results from the new Bolshoi N-body cosmological LCDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was done in a volume 250Mpc on a side using 8billion particles with mass and force resolution adequate to follow subhalos down to a completeness limit of Vcirc=50km/ s circular velocity. Using excellent statistics of halos and subhalos (10M at every moment and 50M over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, a…
We study the diffuse background free-free emission induced by dark matter halos. Since dark matter halos host ionized thermal plasma, they could be an essential source of cosmological free-free emission. We evaluate the global background intensity and the anisotropy of this free-free emission. We show that the dominant contribution comes from dark matter halos with a mass close to the Jeans mass, $M_{\mathrm{halo}}\sim 10^{10} M_\odot$, around the redshift $z \sim 3$. Therefore, the intensity of the free-free emission is sensitive to the small-scale primordial curvature perturbations that form…
We systematically study the effects of varying the starting redshift z_i for cosmological simulations in the highly non-linear regime. Our primary focus lies with the (individual) properties of dark matter halos -- namely the mass, spin, triaxiality, and concentration -- where we find that even substantial variations in z_i leave only a small imprint, at least for the probed mass range M \in [10^{10}, 10^{13}] Msun/h and when investigated at redshift z=0. We further compare simulations started by using the standard Zel'dovich approximation to runs based upon initial conditions produced with se…
We present a semi-analytic, computationally inexpensive model to identify halos capable of forming a Population III star in cosmological simulations across a wide range of times and environments. This allows for a much more complete and representative set of Population III star forming halos to be constructed, which will lead to Population III star formation simulations that more accurately reflect the diversity of Population III stars, both in time and halo mass. This model shows that Population III and chemically enriched stars coexist beyond the formation of the first generation of stars in…
Dark matter models involving a very light bosonic particle, generally known as Fuzzy Dark Matter (FDM), have been recently attracting great interest in the cosmology community, as their wave-like phenomenology would simultaneously explain the longstanding mis-detection of a dark matter particle and help easing the small-scale issues related to the standard Cold Dark Matter (CDM) scenario. With the present work, we initiate a series of papers aiming at investigating the evolution of FDM structures in a cosmological framework performed with our N-body code AX-GADGET, detailing for the first time…
Using a statistical sample of dark matter haloes drawn from a suite of cosmological N-body simulations of the Cold Dark Matter (CDM) model, we quantify the impact of a simulated halo's mass accretion and merging history on two commonly used measures of its dynamical state, the virial ratio eta and the centre of mass offset Delta r. Quantifying this relationship is important because the degree to which a halo is dynamically equilibrated will influence the reliability with which we can measure characteristic equilibrium properties of the structure and kinematics of a population of haloes. We beg…
We present a halo mass function accurate over the full relevant Hu-Sawicki $f(R)$ parameter space based on spherical collapse calculations and calibrated to a suite of modified gravity $N$-body simulations that include massive neutrinos. We investigate the ability of current and forthcoming galaxy cluster observations to detect deviations from general relativity while constraining the total neutrino mass and including systematic uncertainties. Our results indicate that the degeneracy between massive neutrino and modify gravity effects is a limiting factor for the current searches for new gravi…
Associating the formation sites of haloes with the maxima of the smoothed linear density field, we present non-perturbative predictions for the Lagrangian and evolved halo correlation functions that are valid at all separations. In Lagrangian space, we find significant deviations from the perturbative bias calculation at small scales, in particular, a pronounced exclusion region where $ξ=-1$ for maxima of unequal height. Our predictions are in good agreement with the Lagrangian clustering of dark matter proto-haloes reconstructed from N-body simulations. Our predictions for the mean infall and…
In this talk we discuss intermediate mass black holes (IMBHs) by their amplilification of distant sources; MACHO searches have studied event times $2 h \lesssim t_0 \lesssim 2 y$ corresponding masses in the range $10^{-6} M_{\odot} \lesssim M \lesssim 100 M_{\odot}$. We suggest that larger masses up to $10^6 M_{\odot}$ are also of considerable interest by arguments about the entropy of the universe. One percent by mass of dark energy can provide ninety-nine percent of total entropy.
The abundance of galaxy clusters can constrain both the geometry and growth of structure in our Universe. However, this probe could be significantly complicated by recent claims of nonuniversality -- non-trivial dependences with respect to the cosmological model and redshift. In this work we analyse the dependance of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependance, we use a set of different N-body cosmological simulations (Le SBARBINE simulations), with the latest cosmological parameters from t…
A generic property of the cuspy simulated virialized halos in cold dark matter cosmogenies is that their concentration is inversely correlated with their mass. This behavior has also been confirmed in observations, although differences in the exact form and dispersion of this so-called mass-concentration relationship have been reported. Some observational studies of massive halos suggest that they are statistically over-concentrated with respect to the expectations of Lambda-CDM. Here we investigate the impact that various published mass-concentration relationships, both from simulations and d…
High-resolution cosmological N-body simulations are excellent tools for modelling the formation and clustering of dark matter haloes. These simulations suggest complex physical theories of halo formation governed by a set of effective physical parameters. Our goal is to extract these parameters and their uncertainties in a Bayesian context. We make a step towards automatising this process by directly comparing dark matter density projection maps extracted from cosmological simulations, with density projections generated from an analytical halo model. The model is based on a toy implementation …
Dark matter haloes from cosmological N-body simulations typically have triaxial shapes and anisotropic velocity distributions. Recently it has been shown that the velocity anisotropy, beta, of cosmological haloes and major merger remnants depends on direction in such a way that beta is largest along the major axis and smallest along the minor axis. In this work we use a wide range of non-cosmological N-body simulations to examine halo shapes and direction-dependence of velocity anisotropy profiles. For each of our simulated haloes we define 48 cones pointing in different directions, and from t…
The dark energy dominated warm dark matter (WDM) model is a promising alternative cosmological scenario. We explore large-scale structure formation in this paradigm. We do this in two different ways: with the halo model approach and with the help of an ensemble of high resolution N-body simulations. Combining these quasi-independent approaches, leads to a physical understanding of the important processes which shape the formation of structures. We take a detailed look at the halo mass function, the concentrations and the linear halo bias of WDM. In all cases we find interesting deviations with…
Clustering properties and peculiar velocities of halos in large-scale structure carry a wealth of cosmological information over a wide range of scales from linear to nonlinear scales. We use halo catalogs in a suite of high-resolution $N$-body simulations to construct mock catalogs of galaxies that resemble the SDSS-like luminous early-type galaxies at three redshift bins in the range $0.15\le z\le 0.7$. To do this we include 10 nuisance parameters to model variations in halo-galaxy connections for each redshift bin; the halo occupation distribution, and the spatial and velocity distributions …
We investigate 3D density and weak lensing profiles of dark matter haloes predicted by a cosmology-rescaling algorithm for $N$-body simulations. We extend the rescaling method of Angulo & White (2010) and Angulo & Hilbert (2015) to improve its performance on intra-halo scales by using models for the concentration-mass-redshift relation based on excursion set theory. The accuracy of the method is tested with numerical simulations carried out with different cosmological parameters. We find that predictions for median density profiles are more accurate than $\sim 5\,\%$ for haloes with masses of …
We investigate how different cosmological parameters, such as those delivered by the WMAP and Planck missions, affect the nature and evolution of dark matter halo substructure. We use a series of flat $Λ$ cold dark matter ($Λ$CDM) cosmological $N$-body simulations of structure formation, each with a different power spectrum but the same initial white noise field. Our fiducial simulation is based on parameters from the WMAP 7th year cosmology. We then systematically vary the spectral index, $n_s$, matter density, $Ω_M$, and normalization of the power spectrum, $σ_8$, for 7 unique simulations. A…
Redshift space distortion (RSD) observed in galaxy redshift surveys is a powerful tool to test gravity theories on cosmological scales, but the systematic uncertainties must carefully be examined for future surveys with large statistics. Here we employ various analytic models of RSD and estimate the systematic errors on measurements of the structure growth-rate parameter, $fσ_8$, induced by non-linear effects and the halo bias with respect to the dark matter distribution, by using halo catalogues from 40 realisations of $3.4 \times 10^8$ comoving $h^{-3}$Mpc$^3$ cosmological N-body simulations…
We revisit the non-sphericity of cluster-mass scale halos from cosmological N-body simulation on the basis of triaxial modelling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turn-around epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting nonsphericity of halos exhibits weak but r…
We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically motivated free parameters into the halo-model formalism and fit these to data from high-resolution $N$-body simulations. For a variety of $Λ$CDM and $w$CDM models the halo-model power is accurate to $\simeq 5$ per cent for $k\leq 10h\,\mathrm{Mpc}$ and $z\leq 2$. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spec…
The halo mass function (HMF) is a critical element in cosmological analyses of galaxy cluster catalogs. We quantify the impact of uncertainties in HMF parameters on cosmological constraints from cluster catalogs similar to those from Planck, those expected from the Euclid, Roman and Rubin surveys, and from a hypothetical larger future survey. We analyse simulated catalogs in each case, gradually loosening priors on HMF parameters to evaluate the degradation in cosmological constraints. While current uncertainties on HMF parameters do not substantially impact Planck-like surveys, we find that t…
The 21-cm power spectrum of reionization is a promising probe for cosmology and fundamental physics. Exploiting this new observable, however, requires fast predictors capable of efficiently scanning the very large parameter space of cosmological and astrophysical uncertainties. In this paper, we introduce the halo model of reionization (HMreio), a new analytical tool that combines the halo model of the cosmic dawn with the excursion-set bubble model for reionization, assuming an empirical correction factor to deal with overlapping ionization bubbles. First, HMreio is validated against results …
The bias of dark matter halos and galaxies is a crucial quantity in many cosmological analyses. In this work, using large cosmological simulations, we explore the halo mass function and halo bias within cosmic voids. For the first time to date, we show that they are scale-dependent along the void profile, and provide a predictive theoretical model of both the halo mass function and halo bias inside voids, recovering for the latter and 1% accuracy against simulated data. These findings may help shed light on the dynamics of halo formation within voids and improve the analysis of several void st…
We present a first estimate based on a cosmological gasdynamics 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 LCDM 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 uG. However, we predict significan…
We present a cosmological hydrodynamical simulation of a 10^13 Msun galaxy group and its environment (out to 10 times the virial radius) carried out using the EAGLE model of galaxy formation. Exploiting a novel technique to increase the resolution of the dark matter calculation independently of that of the gas, the simulation resolves dark matter haloes and subhaloes of mass 5x10^6 Msun . It is therefore useful for studying the abundance and properties of the haloes and subhaloes targeted in strong lensing tests of the cold dark matter model. We estimate the halo and subhalo mass functions and…
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 researches 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 to 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 convent…
It is crucial to understand and model a behavior of galaxy biasing for future ambitious galaxy redshift surveys. Using 40 large cosmological N-body simulations for a standard LambdaCDM cosmology, we study the cross-correlation coefficient between matter and the halo density field, which is an indicator of the stochasticity of bias, over a wide redshift range 0\le z \le 3. The cross-correlation coefficient is important to extract information on the matter density field, e.g., by combining galaxy clustering and galaxy-galaxy lensing measurements. We compare the simulation results with integrated…
We explore the cosmological halo-to-halo scatter of the distribution of mass within dark matter halos utilizing a well-resolved statistical sample of clusters from the cosmological Millennium simulation. We find that at any radius, the spherically-averaged dark matter density of a halo (corresponding to the "smooth-component") and its logarithmic slope are well-described by a Gaussian probability distribution. At small radii (within the scale radius), the density distribution is fully determined by the measured Gaussian distribution in halo concentrations. The variance in the radial distributi…
We present a test to quantify how well some approximate methods, designed to reproduce the mildly non-linear evolution of perturbations, are able to reproduce the clustering of DM halos once the grouping of particles into halos is defined and kept fixed. The following methods have been considered: Lagrangian Perturbation Theory (LPT) up to third order, Truncated LPT, Augmented LPT, MUSCLE and COLA. The test runs as follows: halos are defined by applying a friends-of-friends (FoF) halo finder to the output of an N-body simulation. The approximate methods are then applied to the same initial con…
Using analytical models and cosmological N-body simulations, we study the free-free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the mass function and scaling relations. Earlier works based on analytical models have shown that the average free-free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the CMB spectrum at low frequencies ($ν<$ 5 GHz). We focus on the period after the reionization time…
We describe a combined halo model to constrain the distribution of neutral hydrogen (HI) in the post-reionization universe. We combine constraints from the various probes of HI at different redshifts: the low-redshift 21-cm emission line surveys, intensity mapping experiments at intermediate redshifts, and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a Markov Chain Monte Carlo (MCMC) approach to combine the observations and place constraints on the free parameters in the model. Our best-fit model involves a relation between neutral hydrogen mass $M_{\rm HI}$ and halo m…
Models of disk galaxy formation commonly predict the existence of an extended reservoir of accreted hot gas surrounding massive spirals at low redshift. As a test of these models, we use X-ray and H-alpha data of the two massive, quiescent edge-on spirals NGC 5746 and NGC 5170 to investigate the amount and origin of any hot gas in their halos. Contrary to our earlier claim, the Chandra analysis of NGC 5746, employing more recent calibration data, does not reveal any significant evidence for diffuse X-ray emission outside the optical disk, with a 3-sigma upper limit to the halo X-ray luminosity…
