The mass and structural evolution of massive galaxies is one of the hottest topics in galaxy formation. This is because it may reveal invaluable insights into the still debated evolutionary processes ...governing the growth and assembly of spheroids. However, direct comparison between models and observations is usually prevented by the so-called progenitor bias, i.e., new galaxies entering the observational selection at later epochs, thus eluding a precise study of how pre-existing galaxies actually evolve in size. To limit this effect, we here gather data on high-redshift brightest group and cluster galaxies, evolve their (mean) host halo masses down to z = 0 along their main progenitors, and assign as their "descendants" local Sloan Digital Sky Survey central galaxies matched in host halo mass. At face value, the comparison between high redshift and local data suggests a noticeable increase in stellar mass of a factor of gap2 since z ~ 1, and of gap2.5 in mean effective radius. We then compare the inferred stellar mass and size growth with those predicted by hierarchical models for central galaxies, selected at high redshifts to closely match the halo and stellar mass bins as in the data. Only hierarchical models characterized by very limited satellite stellar stripping and parabolic orbits are capable of broadly reproducing the stellar mass and size increase of a factor of ~2-4 observed in cluster galaxies since z ~ 1. The predicted, average (major) merger rate since z ~ 1 is in good agreement with the latest observational estimates.
We present a parallel implementation of the friends-of-friends algorithm and an innovative technique for reducing complex-shaped data to a user-friendly format. This code, named pFoF, contains an ...optimized post-processing workflow that reduces the input data coming from gravitational codes, arranges them in a user-friendly format and detects groups of particles using percolation and merging methods. The pFoF code also allows for detecting structures in sub- or non-cubic volumes of the comoving box. In addition, the code offers the possibility of performing new halo-findings with a lower percolation factor, useful for more complex analysis. In this paper, we give standard test results and show performance diagnostics to stress the robustness of pFoF. This code has been extensively tested up to 32768 MPI processes and has proved to be highly scalable with an efficiency of more than 75%. It has been used for analysing the Dark Energy Universe Simulation: Full Universe Runs (DEUS-FUR) project, the first cosmological simulations of the entire observable Universe, modelled with more than half a trillion dark matter particles.
Observations of colliding galaxy clusters with high relative velocity probe the tail of the halo pairwise velocity distribution with the potential of providing a powerful test of cosmology. As an ...example it has been argued that the discovery of the Bullet Cluster challenges standard Λ cold dark matter (ΛCDM) model predictions. Halo catalogues from N-body simulations have been used to estimate the probability of Bullet-like clusters. However, due to simulation volume effects previous studies had to rely on a Gaussian extrapolation of the pairwise velocity distribution to high velocities. Here, we perform a detail analysis using the halo catalogues from the Dark Energy Universe Simulation Full Universe Runs (DEUS-FUR), which enables us to resolve the high-velocity tail of the distribution and study its dependence on the halo mass definition, redshift and cosmology. Building upon these results, we estimate the probability of Bullet-like systems in the framework of Extreme Value Statistics. We show that the tail of extreme pairwise velocities significantly deviates from that of a Gaussian, moreover it carries an imprint of the underlying cosmology. We find the Bullet Cluster probability to be two orders of magnitude larger than previous estimates, thus easing the tension with the ΛCDM model. Finally, the comparison of the inferred probabilities for the different DEUS-FUR cosmologies suggests that observations of extreme interacting clusters can provide constraints on dark energy models complementary to standard cosmological tests.
We investigate the non-linear evolution of Baryon Acoustic Oscillations (BAO) in the low-redshift matter power spectrum from the DEUS-FUR ΛCDM model simulation. This is the first cosmological N-body ...simulation encompassing the full observable cosmic volume, thus allowing cosmic-variance limited predictions at BAO scales. We control the effect of numerical systematic errors using a series of large-volume high-resolution simulations. The combined analysis allows us to measure the matter power spectrum between z = 0 and 1 to 1 per cent over the entire BAO range, 0.03 < kh Mpc−1 < 0.3, in bins of size Δk/k 1 per cent. We define the BAO with respect to a non-linearly evolved wiggle-free spectrum and determine the characteristics of the BAO without recurring to extrapolation from global fitting functions. We quantify the effects of non-linearities on the position and amplitude of the BAO extrema, and the coupling to the broad-band slope of the power spectrum. We use these estimates to test non-linear predictions from semi-analytical models. Quite remarkably from the analysis of the redshift evolution of BAO we find that the second dip and third peak remains unaltered by non-linear effects. Furthermore, we find that the square of the damping factor and the shift of the position of BAO extrema scale to good approximation as the square of the growth factor, in agreement with expectations from perturbation theory. This confirms the idea that, besides cosmic distances, an accurate measurement of BAO at different redshifts can directly probe the growth of cosmic structures.
The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence ...remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z ~ 1 for stellar masses M sub(star) > ~ 2 x 10 super(11) M sub(middot in circle). Specifically, we find significant evidence for a high-mass end slope of beta > ~ 0.35-0.70 instead of the usual beta <, ~ 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (<, ~0.15 dex) in stellar mass at fixed halo mass, in the redshift range z < 0.8 and for M sub(star) > 3 x 10 super(11) M sub(middot in circle), suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z ~ 1.
We report the realization of the first cosmological simulations on the scale of the whole observable universe. These simulations have been carried out on 4752 nodes of the Curie supercomputer as a ...part of the Dark Energy Universe Simulation: Full Universe Runs (DEUS-FUR) project which aims at establishing new probes to put constraints on the nature of dark energy by comparing the growth of large-scale structures, the characteristics of extreme statistical events and the matter distribution in redshift space. The numerical challenge of the first DEUS-FUR simulation associated with the concordance ΛCDM (Λ Cold Dark Matter) model was already presented during the 2012 supercomputing conference (Alimi et al., 2012, in The international conference for high performance computing, networking, storage and analysis). Here we first focus on the numerical aspects of the two new simulations. In practice, each one of these simulations has evolved 550 billion dark matter particles in an adaptive mesh refinement grid, and one of the new simulations has pushed back the total number of grid points from 2000 billion for the ΛCDM model to 2200 billion due to the formation of a larger number of structures. We highlight the optimizations and adjustments required to run such a set of simulations and we then summarize some important lessons learnt for future exascale computing projects.
Cette thèse est consacrée à la recherche d'empreintes spécifiques relatives à la nature de l'Énergie Noire dans les processus d'effondrements gravitationnels linéaire et non-linéaire au travers de ...développements théoriques et numériques. Ainsi, plusieurs aspects de la cosmologie ont été abordés: tout d'abord, afin d'étudier l'influence de nombreuses formes complexes d'Énergie Noire sur la structuration, le développement de la théorie des perturbations dans un formalisme covariant a permis d'étendre les équations classiques de Sasaki-Mukhanov aux cas de champs scalaires couplés et en présence de multiples fluides cosmologiques. Ces travaux permettent de décrire l'évolution des perturbations linéaires de modèles d'Énergie Noire complexes en minimisant le nombre de degrés de liberté. Ces dernières années ont vu le nombre et la qualité des observations augmenter de manière vertigineuse, tant sur la distribution de la matière dans l'Univers que sur le champ de déplacement de celle-ci. En particulier, ces observations ont permis de mettre en évidence un champ de vitesse local anormalement élevé par rapport à la prédiction du modèle standard $\Lambda$CDM. L'explication de cet excès des champs de vitesse à des échelles intermédiaires constitue l'apport principal de ces travaux de recherche: en réinterprétant les mesures anormales de champs de vitesse de Watkins et al. sur des distances intermédiaires (50 Mpc/h) en termes d'événement rare dans le cadre de la théorie linéaire, nous avons proposé une nouvelle sonde cosmologique consistant à mesurer l'échelle à laquelle le flot moyen rejoint en amplitude ce que l'on attend en théorie linéaire. Nous montrons la sensibilité de cette nouvelle sonde cosmologique dans trois modèles d'Énergie Noire concurrentiels. Ces résultats, développés par des méthodes analytiques, sont comparés à des mesures effectuées sur des simulations numériques hautes performances auxquelles nous avons pris une part importante. Dans un second temps, à partir de ces simulations numériques, nous montrons que l'origine dynamique d'un tel mouvement d'ensemble local résulte d'une asymétrie de la distribution de matière à plus grande échelle (80 Mpc/h). Cette asymétrie est mise en évidence grâce à l'introduction d'un estimateur original du champ de matière quantifiant l'écart à la symétrie d'un champ. Finalement, nous démontrons que l'arrangement spatial des environnements présentant un champ de vitesse anormal dans l'Univers est corrélé avec la distribution des pics de densité. Cette corrélation nous indique de manière locale la distribution de structures responsables du mouvement d'ensemble anormalement élevé. Une caractérisation différente de l'Énergie Noire fait appel au champ de densité dans l'Univers. En particulier, nous caractérisons ce champ de densité en terme de fonctions de corrélation et étudierons les effets des champs de vitesse sur ceux-ci au travers des distorsions dans l'espace des redshifts. Nous présentons donc plusieurs résultats prometteurs à partir des fonctions de corrélation issues des simulations Dark Energy Universe Simulation (DEUSS) pour trois modèles concurrentiels d'Énergie Noire, en distinguant espace comobile et espace des redshift d'une part et corrélation suivant la masse des halos d'autre part. Deux aspects seront particulièrement abordées dans ce travail. Tout d'abord, nous soulignons l'impact de ces mesures sur le biais en cosmologie: ils permettront donc de déduire de nombreux résultats sur la dépendance de ce dernier sur le modèle cosmologique et le redshift. Dans un second temps, ces mesures permettent de montrer que l'empreinte de l'Énergie Noire sur le régime non-linéaire de formation des structures dans l'Univers, déjà mise en évidence sur les champs continus de matière, demeure lorsque l'on mesure la fonction de corrélation à partir des traceurs du champs, à savoir les halos de matière noire. Finalement, cette thèse a vu la réalisation des simulations DEUS: Full Universe Runs, première modélisation de tout l'Univers observable, du Big Bang jusqu'à aujourd'hui. Cette série de modélisations ayant demandé de nombreuses optimisations des codes cosmologiques existants, a permis de mettre en évidence quelques résultats marquants, faisant appel à la statistique inégalée de cette nouvelle série de simulations. Les méthodes numériques permettant le suivi dynamique de l'effondrement gravitationnel et la détection de structures ainsi que les efforts d'optimisations menés durant cette thèse sont présentés dans une partie numérique en fin de thèse.
The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence ...remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z similar to 1 for stellar masses M-star greater than or similar to 2 x 10(11) M-circle dot. Specifically, we find significant evidence for a high-mass end slope of beta greater than or similar to 0.35-0.70 instead of the usual beta less than or similar to 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (less than or similar to 0.15 dex) in stellar mass at fixed halo mass, in the redshift range z \textless 0.8 and for M-star \textgreater 3 x 10(11) M-circle dot, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z similar to 1.
Observations of colliding galaxy clusters with high relative velocity probe the tail of the halo pairwise velocity distribution with the potential of providing a powerful test of cosmology. As an ...example it has been argued that the discovery of the Bullet Cluster challenges standard \(\Lambda\)CDM model predictions. Halo catalogs from N-body simulations have been used to estimate the probability of Bullet-like clusters. However, due to simulation volume effects previous studies had to rely on a Gaussian extrapolation of the pairwise velocity distribution to high velocities. Here, we perform a detail analysis using the halo catalogs from the Dark Energy Universe Simulation Full Universe Runs (DEUS-FUR), which enables us to resolve the high-velocity tail of the distribution and study its dependence on the halo mass definition, redshift and cosmology. Building upon these results we estimate the probability of Bullet-like systems in the framework of Extreme Value Statistics. We show that the tail of extreme pairwise velocities significantly deviates from that of a Gaussian, moreover it carries an imprint of the underlying cosmology. We find the Bullet Cluster probability to be two orders of magnitude larger than previous estimates, thus easing the tension with the \(\Lambda\)CDM model. Finally, the comparison of the inferred probabilities for the different DEUS-FUR cosmologies suggests that observations of extreme interacting clusters can provide constraints on dark energy models complementary to standard cosmological tests.
Mon.Not.Roy.Astron.Soc.440:1420,2014 We investigate the non-linear evolution of Baryon Acoustic Oscillations (BAO)
in the low-redshift matter power spectrum from the DEUS-FUR $\Lambda$CDM model
...simulation. This is the first cosmological N-body simulation encompassing the
full observable cosmic volume, thus allowing cosmic variance limited
predictions at BAO scales. We control the effect of numerical systematic errors
using a series of large volume high-resolution simulations. The combined
analysis allows us to measure the matter power spectrum between $z=0$ and $1$
to 1% over the entire BAO range, $0.03<k \textrm{h Mpc}^{-1}<0.3$, in bins of
size $\Delta k/k\lesssim$ 1%. We define the BAO with respect to a non-linearly
evolved wiggle-free spectrum and determine the characteristics of the BAO
without recurring to extrapolation from global fitting functions. We quantify
the effects of non-linearities on the position and amplitude of the BAO
extrema, and the coupling to the broadband slope of the power spectrum. We use
these estimates to test non-linear predictions from semi-analytical models.
Quite remarkably from the analysis of the redshift evolution of BAO we find
that the second dip and third peak remains unaltered by non-linear effects.
Furthermore, we find that the square of the damping factor and the shift of the
position of BAO extrema scale to good approximation as the square of the growth
factor, in agreement with expectations from perturbation theory. This confirms
the idea that, besides cosmic distances, an accurate measurement of BAO at
different redshifts can directly probe the growth of cosmic structures.
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