Dependency of halo concentration on mass, redshift and fossilness in Magneticum hydrodynamic simulations

We study the dependency of the concentration on mass and redshift using three large N-body cosmological hydrodynamic simulations carried out by the Magneticum project. We constrain the slope of the mass-concentration relation with an unprecedented mass range for hydrodynamic simulations and find a negative trend on the mass-concentration plane and a slightly negative redshift dependency, in agreement with observations and other numerical works. We also show how the concentration correlates with the fossil parameter, defined as the stellar mass ratio between the central galaxy and the most massive satellite, in agreement with observations. We find that haloes with high fossil parameter have systematically higher concentration and investigate the cause in two different ways. First we study the evolution of haloes that lives unperturbed for a long period of time, where we find that the internal region keeps accreting satellites as the fossil parameter increases and the scale radius decreases (which increases the concentration). We also study the dependency of the concentration on the virial ratio and the energy term from the surface pressure $E_s$. We conclude that fossil objects have higher concentration because they are dynamically relaxed, with no in-fall/out-fall material and had time to accrete their satellites.Comment: 13 pages, 10 figure

Simulation view of galaxy clusters with low X-ray surface brightness

X-ray selected samples are known to miss galaxy clusters that are gas poor and have a low surface brightness. This is different for the optically selected samples such as the X-ray Unbiased Selected Sample (XUCS). We characterise the origin of galaxy clusters that are gas poor and have a low surface-brightness by studying covariances between various cluster properties at fixed mass using hydrodynamic cosmological simulations. We extracted approx. 1800 galaxy clusters from a high-resolution Magneticum hydrodynamic cosmological simulation and computed covariances at fixed mass of the following properties: core-excised X-ray luminosity, gas fraction, hot gas temperature, formation redshift, concentration, galaxy richness, fossilness parameter, and stellar mass of the bright central galaxy. We also compared the correlation between concentration and gas fractions in non-radiative simulations, and we followed the trajectories of particles inside galaxy clusters to assess the role of AGN depletion on the gas fraction. In simulations and in observational data, differences in surface brightness are related to differences in gas fraction. Simulations show that the gas fraction strongly correlates with assembly time, in the sense that older clusters are gas poor. Clusters that formed earlier have lower gas fractions because the feedback of the active galactic nucleus ejected a significant amount of gas from the halo. When the X-ray luminosity is corrected for the gas fraction, it shows little or no covariance with other quantities. Older galaxy clusters tend to be gas poor and possess a low X-ray surface brightness because the feedback mechanism removes a significant fraction of gas from these objects. Moreover, we found that most of the $L_X$ covariance with the other quantities is explained by differences in the gas fraction.Comment: 9 pages, 8 figures, accepte

From the mass-concentration relation of haloes to GPUs and into the web

Aufgrund ihrer Größe birgt die Durchführung von modernen, hydrodynamischen, kosmologischen Simulationen eine ganzen Reihe von Herausforderungen in sich, umso mehr, da hier das Ziel ist, derartige Simulationen für noch größere und besser aufgelöste Volumina durchzuführen. Dabei helfen die Analysen derartiger Simulationen die so verbesserten numerischen Modelle mit Beobachtungsdaten zu vergleichen. Zu aller erst ist es hier unbedingt notwendig in den Anwendungsprogrammen SIMT (Single Instruction Multiple Thread) und/oder SIMD (BSingle Instruction Multiple Data) Instruktionen zu nutzen, um die Rechenleistung der aktuellen und kommenden Generationen von Supercomputern so gut wie möglich auszunutzen zu können. Darüber hinaus stellt die Datenmenge, welche derartige hydrodynamischen, kosmologischen Simulationen der jüngsten Generation ($>0.5PB$) generieren, eine große Herausforderung dar, wenn es darum geht wissenschaftliche Ergebnisse und die Simulationsdaten selbst öffentlich zugänglich zu machen und mit anderen Wissenschaftlern zu teilen: Abfragen, Durchsuchen und Filtern einer so großen Datenmenge erfordern Kenntnisse aus dem Bereich des High Performance Computing (HPC). Diese gehören häufig nicht zum Ausbildungshintergrund eines auf diesem Gebiet tätigen Wissenschaftlers. Da für solche Datenmenge HPC Speichersysteme zum Einsatz kommen, wird der öffentliche Zugriff auf diese wissenschaftlichen Daten und Ergebnisse zusätzlich stark erschwert, da der Zugriff üblicherweise für Wissenschaftler nur mit einem Account für die jeweilige HPC-Einrichtungen möglich ist. In dieser Arbeit werden diese verschiedenen Aspekte miteinader verknüpft. Eine ausführliche Optimierung des zugrundeliegenden Simulationsprogramm (Gadget3) erlaubte es, die bisher größte derartige Simulation durchzuführen. Diese erlaubt durch ihren großen dynamischen Bereich die Wechselwirkung der sichtbaren und der dunklen Materie auf die zugrundeliegende Form der sich bildenden Halos sehr genau und über einen großen Bereich, von Galaxien bis zu den massivsten Galaxienhaufen, zu studieren. Des weiteren wurde ein Webinterface entwickelt, mit denen die Ergebnisse derartiger Simulationen mit anderen Wissenschaftlern einfach und umfangreich geteilt werden können. Im ersten Schritt ergab die detaillierte Performance-Analyse, dass der Prozess des Suchens von Nachbarteilchen, welche mit einem Teilchen in direkter Wechselwirkung stehen (im Folgenden Neighbour-Search genannt), die Zeit, welche für die Berechnung der eigentlichen physikalischen Prozesse zur Verfügung steht, stark limitiert. Dieser Neighbour-Search besteht darin, einem Baum-Graphen zu folgen und die in ihm angeordneten, benachbarten Teilchen entweder mithilfe eines öffnungskriteriums des Baumes (in der Regel ein geometrisches Kriterium, welches den erlaubten Fehler in der Gravitationsberechnung beschreibt) oder mit Hilfe einer vordefinierten Suchlänge (z. B. die in der Hydrodynamik verwendete Kernelgröße) zu sammeln. Wir haben das oben skizzierte Problem mit Hilfe eines Optimierungsschemas, welches wir als Neighbour-Recycling bezeichnen, auf ein akzeptables Maß vermindert. Dafür nutzen wir die raumfüllende Peano-Kurve, welche in der Gadget-Implementierung für den Lastbalance-Algorithmus verwendet wird. Diese sorgt dabei dafür, dass im simulierten Volumen benachbarte Teilchen auch im Hauptspeicher des Rechners benachbart abgelegt werden. Wir minimierten den oben genannten Engpass, indem wir die Teilchen in Blöcken gruppieren, welche fortlaufend im Hauptspeicher liegen und die normale Neighbour-Search für die einzelnen Teilchen durch einen Neighbour-Search mit entsprechend leicht größerer Suchlängen ersetzten. Dieses oben beschriebene Code-Refactoring eröffnete die Möglichkeit, die Anwendung Gadget3 auf das gesamte SuperMUC-System zu skalieren und so die bis dato größte, hydrodynamische, kosmologische Simulation (Box0/mr, Magneticum-Projekt, \footnote{\href{http://www.magneticum.org}{http://www.magneticum.org}}) durchzuführen. Wir analysieren die Ergebnisse dieser Simulation und zweier weiterer Magneticum Simulationen und vergleichen den Konzentrationsindex (Verhältnis Cluster-Radius zu Skalen-Radius) von Galaxien und Galaxienhaufen mit früheren Theorie- und Beobachtungsarbeiten zu diesem Thema in einem bis dahin für hydrodynamische Simulationen unerreichten Massenbereich. Unter Berücksichtigung von baryonischer Materie in den Magneticum-Simulationen konnten wir zeigen, dass sogenannte fossile Gruppen (d. H. Objekte, die den größten Teil ihrer Lebensdauer existiert haben ohne Störungen ausgesetzt gewesen zu sein) den höchsten Wert von Konzentrationsindex haben. Dies ist in klarer übereinstimmung mit aktuellen Beobachtungen. Um diese größten Simulationen öffentlich zugänglich zu machen, haben wir ein Webportal entwickelt und implementiert. In diesem kann ein Benutzer zunächst eine Simulation auswählen und interessante Galaxienhaufen suchen und auswählen. Dazu stehen einerseits sehr hoch aufgelöste 2D-Karten zum Navigieren zur Verfügung, andererseits erlaubt ein Interface komplexe Abfragen von Detailinformationen der Galaxie und Galaxienhaufen. Diese können sogar grafisch zusammengestellt werden und als Elemente in benutzerdefinierten Grafen dargestellt werden. Nach der Auswahl eines Objekts (z.B. Galaxienhaufen) kann der Benutzer weitere, über das Portal zur Verfügung stehende Post-Processing Jobs starten. Durch die komplexe Architektur des Portals ist dies möglich, ohne dass der Nutzer einen eigenen Nutzer-Account auf dem HPC-System besitzt. Es reicht eine simple Registrierung im Portal aus. Inzwischen hat das Portal mehr als hundert registrierte Nutzen und es werden jeden Monat tausende von Post-Processing Jobs über das Portal ausgeführt. Da in der aktuellen und kommenden Generationen von Supercomputern Beschleuniger (z. B. Grafikkarten) eine zunehmend wichtigere Rolle spielen, haben wir des weiteren daran gearbeitet, Gadget3 auch auf GPU-basierten Systemen effizient nutzen zu können. Diese Neuentwicklung in Gagdet3 ermöglicht es, rechenintensive Teile der Applikation auch auf den GPUs der entsprechenden Supercomputer auszuführen. Damit eröffnen wir erstmals die Möglichkeit, die kommende Generation von Supercomputern, welche SIMT-/SIMD freundliche Programme benötigen, hoch effizient nutzen zu können. Tests der neuen Implementierung ergaben eine Beschleunigung von $>2\textrm{x}$ bei der Verwendung der Beschleuniger für ein realistische Setup, entsprechend einer der hochauflösenden Magneticum-Simulationen.The current generation of hydrodynamic cosmological simulations is facing a number of challenges when it comes to running and analysing larger and more resolved volumes in order to compare numerical studies with observational data. First, simulation codes need to take advantage of Single Instruction Multiple Thread (SIMT) and Single Instruction Multiple Data (SIMD) paradigms in order to fully exploit the computational capabilities of current and future generations of super computers. Additionally, the amount of data generated by the most recent hydrodynamic simulations ($>0.5 PB$) poses a physical barrier when it comes to opening the access and sharing results with the scientific community: queries, look ups and filtering over such high amount of data need High Performance Computing (HPC) skills that are often not part of the background knowledge of a scientist working in such field; additionally, since only HPC storages are capable of containing this amounts of data, this prevents a public access of the scientific results, as scientists are required to apply and register to HPC facilities. In this work, these different aspects are linked together. A tailored optimisation and a refactoring of a widely used code for simulations (Gadget3) made it possible to perform the largest hydrodynamic simulation so far. As the various simulated matter contents (dark matter, gas, stars and black holes) cluster together to form haloes, by combinig three cosmological hydrodynamic simulations it was possible to study in detail the shape of simulated objects with masses from the ones of single galaxies to masses comparable to the largest galaxy clusters of our universe. Furthermore, a web interface has been developed, where the results of simulations can be easily and extensively shared with other scientists. And finally, there has been an effort in shaping and preparing the code for the new and current generation of super computers, by porting it to the GPUs. The first part of this work shows how the process of neighbour search prevents large Gadget simulations from spending most of its execution time in actual physical computations. The neighbour search consists of walking the tree and collecting neighbouring particles over a tree opening criteria or over a pre-defined searching length. To solve the issue an approach to recycle neighbours is used. This approach takes advantage of the space-filling curve ordering of Gadget particles, which itself ensures that particles that are nearby in memory are also nearby in the simulated volume. This algorithm solves the aforementioned bottleneck by grouping particles in memory-consecutive chunks and by performing less neighbour searches over larger searching length. This refactoring opens the possibility to scale the code over the whole SuperMUC machine and run one of the largest cosmological hydrodynamic simulations (Box0/mr and Box2b/hr from the Magneticum project). I analyse the results of this simulation and other two Magneticum simulations and compare the concentration parameter (ratio between cluster radius and its scale radius) of galaxy clusters with previous theoretical and observational works over an unprecedented mass range for hydrodynamic simulations. Thanks to the presence of baryons in Magneticum simulations, it is possible to show how Magneticum simulations predict that fossil groups (i.e. objects that have lived un-perturbed for most of their life) have the highest value of concentration values, in agreement with observations. In order to share and make the largest simulations accessible, a web portal \footnote{\href{http://c2papcosmosim.uc.lrz.de}{http://c2papcosmosim.uc.lrz.de}} is built to let users find interesting clusters by (i) navigating over zoomable 2D maps, (ii) by graphically composing complex queries over galaxy and galaxy cluster properties and (iii) by selecting elements in user-defined plots. Users can then select a galaxy cluster and submit some pre-defined post-processing jobs that will run in a computing cluster, without any actual registration at the computing facility. As the current and new generations of super computers may employ accelerators (e.g. graphic cards), I present a way to port Gadget3 to the GPUs. The reason of this porting is twofold: besides making it possible to run on the current GPU based super computers, to fully exploit the new generation of super computer it is anyway necessary to have SIMT and SIMD friendly code. A test of the new implementation of the code shows a total speedup greater than $2$ in one of the high-resolution Magneticum cosmological boxes

Cosmology dependency of halo masses and concentrations in hydrodynamic simulations

We employ a set of Magneticum cosmological hydrodynamic simulations that span over $15$ different cosmologies, and extract masses and concentrations of all well-resolved haloes between $z=0-1$ for critical over-densities $\Delta_\texttt{vir}, \Delta_{200c}, \Delta_{500c}, \Delta_{2500c}$ and mean overdensity $\Delta_{200m}.$ We provide the first mass-concentration (Mc) relation and sparsity relation (i.e. $M_{\Delta1} - M_{\Delta2}$ mass conversion) of hydrodynamic simulations that is modelled by mass, redshift and cosmological parameters $\Omega_m, \Omega_b, \sigma_8, h_0$ as a tool for observational studies. We also quantify the impact that the Mc relation scatter and the assumption of NFW density profiles have on the uncertainty of the sparsity relation. We find that converting masses with the aid of a Mc relation carries an additional fractional scatter ($\approx 4\%$) originated from deviations from the assumed NFW density profile. For this reason we provide a direct mass-mass conversion relation fit that depends on redshift and cosmological parameters. We release the package hydro\_mc, a python tool that perform all kind of conversions presented in this paper.Comment: 17 pages, 11 figures, accepted at MNRAS, hydro_mc URL https://github.com/aragagnin/hydro_m

Weak lensing mass bias and the alignment of center proxies

Galaxy cluster masses derived from observations of weak lensing suffer from a number of biases affecting the accuracy of mass-observable relations calibrated from such observations. In particular, the choice of the cluster center plays a prominent role in biasing inferred masses. In the past, empirical miscentring distributions have been used to address this issue. Using hydro-dynamical simulations, we aim to test the accuracy of weak lensing mass bias predictions based on such miscentring distributions by comparing the results to mass biases computed directly using intra-cluster medium (ICM)-based centers from the same simulation. We construct models for fitting masses to both centered and miscentered Navarro-Frenk-White profiles of reduced shear, and model the resulting distributions of mass bias with normal and log-normal distributions. We find that the standard approach of using miscentring distributions leads to an over-estimation of cluster masses at levels of between 2\% and 6\% when compared to the analysis in which actual simulated ICM centers are used, even when the underlying miscentring distributions match in terms of the miscentring amplitude. We find that neither log-normal nor normal distributions are generally reliable for approximating the shapes of the mass bias distributions, regardless of whether a centered or miscentered radial model is used.Comment: 15 pages, 9 figures, submitted to MNRA

Cidades invisíveis: ideais de urbanidade a partir da literatura turística, o caso de Porto Alegre (RS)

A proposta deste estudo foi compreender como espaço designado como 'Porto Alegre' é apresentado e significado enquanto turístico. Realizou-se uma análise de discurso, com exame 135 documentos de diferentes épocas e gêneros textuais. Metodologicamente, atribui-se a todos os textos pesquisados um patamar de igualdade, independente de sua autoria, data e cenografia. Como resultado apontam-se cinco balizas a partir das quais a cidade é descrita e significada: ‘evocação geográfica’; ‘enquadramento temporal’; ‘lugar e seus personagens’; 'ideais de urbanidade' e ‘ identidade do gentílico'. Em um contexto do crescimento da participação dos serviços na economia urbana e do uso frequente do turismo como subterfúgio para projetos com repercussões importantes na vida das cidades, este trabalho procura contribuir ao apontar os processos discursivos de transformação de um espaço em turístico. Também evidência o caráter situado e político do que é compreendido enquanto turismo e qual papel é atribuído à figura do turista

Invisibles : ideales de urbanidad en la literatura turística, el caso de Porto Alegre (Brasil)

A proposta deste estudo foi compreender como espaço designado como 'Porto Alegre' é apresentado e significado enquanto turístico. Realizou-se uma análise de discurso, com exame 135 documentos de diferentes épocas e gêneros textuais. Metodologicamente, atribui-se a todos os textos pesquisados um patamar de igualdade, independente de sua autoria, data e cenografia. Como resultado apontam-se cinco balizas a partir das quais a cidade é descrita e significada: ‘evocação geográfica’; ‘enquadramento temporal’; ‘lugar e seus personagens’; 'ideais de urbanidade' e ‘ identidade do gentílico'. Em um contexto do crescimento da participação dos serviços na economia urbana e do uso frequente do turismo como subterfúgio para projetos com repercussões importantes na vida das cidades, este trabalho procura contribuir ao apontar os processos discursivos de transformação de um espaço em turístico. Também evidência o caráter situado e político do que é compreendido enquanto turismo e qual papel é atribuído à figura do turista.This study aims to understand how a space named as 'Porto Alegre' is presented and signified as touristic. A discourse analysis with a 135 documents corpus from different times and textual genres was done. A methodological assumption was to attribute an equal status to all examined texts, regardless of its authorship, date or setting. The results points to five tokens from which the city is described and meant: 'geographical summon'; 'timeframing', 'place characters', 'urban ideals' and 'local identity'. The paper contributes in the description of the discursive processes that convert a space into tourist space. This is relevant in a context where there is a growth of the services share in urban economy and where tourism is often used as a pretext to carry on projects with significant impacts on cities' lives. It also stresses the situated and political character of what is understood as tourism and of the role attributed to tourists.El objetivo de este estudio era comprender cómo se presenta y se entiende como turístico el espacio designado como "Porto Alegre". Se realizó un análisis del discurso, con el examen de 135 documentos de diferentes épocas y géneros textuales. Metodológicamente, a todos los textos investigados se les atribuyó una equidad, independientemente de su autoría, fecha y escenografía. En consecuencia, señalamos cinco pautas desde las que se describe y se significa la ciudad: "evocación geográfica"; "encuadre temporal"; "lugar y sus personajes"; "ideales de urbanidad" e "identidad del gentilicio". En un contexto de creciente participación de los servicios en la economía urbana y de frecuente utilización del turismo como subterfugio de proyectos con importantes repercusiones en la vida de las ciudades, este trabajo pretende contribuir señalando los procesos discursivos de transformación de un espacio en un espacio turístico. También destaca el carácter situado y político de lo que se entiende por turismo y qué papel se atribuye a la figura del turista

Tourism and Geography: in the Pursuit of a Complex Relation

Este é um ensaio sobre as diferentes propostas de estudo do turismo que emergem desde a Geografia. Procuramos registrar os distintos matizes e entendimentos epistêmicos resultantes do encontro desses campos de estudo e suas contribuições. Nesse gênero de texto é usual o expediente da criação de (falsas) oposições entre tais entendimentos e seus autores como recurso narrativo. Isso possui um caráter disjuntivo e empobrecedor, na medida em que as diferentes abordagens são os fios de uma trama complexa cuja tessitura auxilia uma compreensão mais abrangente, embora sempre temporária. Para federar as diferentes proposições geográficas sobre o Turismo utilizamos como dispositivo a concepção proposta por Di Méo & Bulèon (2007) de uma ontologia tripartite do espaço, que é ao mesmo tempo extensão objetiva, dimensão vivida e produto social. Percebemos que o turismo, assim como o espaço, também possui uma ontologia múltipla. Nesse sentido, apontamos para três possíveis aberturas de seu estudo pela Geografia que preenchem o significante de modo distinto ao caráter de mercado que lhe é frequentemente atribuído. Um destaque do texto é o uso de bibliografia pouco frequente em trabalhos em língua portuguesa.This is an essay on tourism different study proposals since Geography. We intend to record the distinguished epistemic understandings that result from the meeting of these fields of inquire and its contributions. In this kind of text, it is common to create (false) oppositions between such understandings and its authors as a narrative underpin. With that comes a more poor and disjunctive knowledge, since the different approaches are threads of a complex fabric of which interweave helps us to form a more broad comprehension, although always a temporary one. To federate the different geographical propositions on tourism we utilized triple ontology of space from Di Méo & Buléon (2007). There, space is at the same time an objective extension, a lived dimension and a social construct. We acknowledge that tourism, as space, has a multiple ontology. In this sense, we point three possible openings of its study by Geography, all of which fill this significant in a different way than the market character that is commonly attributed to it