Добірка наукової літератури з теми "Hierarchical cosmology"

AbstractWe probe the evolution of globular clusters that could form in giant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that the large and dense enough gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution.

We have adapted the Barnes-Hut hierarchical N-body method for cosmological applications. A detailed study of the resulting code yielded the following conclusions: it is SIMPLE, FLEXIBLE, ACCURATE, ROBUST, and EFFICIENT.

<p>This study aims to evaluate whether the idea of ultimate reality in world religions contributes to the characteristics of the world religion paradigm, which is hierarchical cosmology or “subject-object cosmology.” Several research on this topic claims that one of the characteristics of the world religion paradigm is its hierarchical perspective. Discussing this issue is important to distinguish the world religions as the paradigm and the world religions as the most widely embraced religion. This study argues that the hierarchical perspective of the world religion paradigm can be rooted in the idea of ultimate reality, that there is a supreme, foremost, and most principal reality in the continuity of this universe, namely the supernatural or God. The hierarchical cosmology consists of three main domains: supernatural/God, culture/human, and nature. This study uses a literature study methodology, relying on books, journals, and texts related to research questions. This study finds that the world religion paradigm or hierarchical cosmology or “subject-object cosmology” is prominent, especially in Abrahamic religions such as Islam, Christianity, and Judaism, even though the concept of ultimate reality in these three religions is different.</p><p align="left"> </p><p><em>Penelitian ini bertujuan untuk mengevaluasi apakah gagasan tentang realitas tertinggi dalam agama-agama dunia turut berkontribusi membentuk karakteristik paradigma agama dunia, yaitu kosmologi hierarkis atau “kosmologi subjek-objek”. Beberapa penelitian tentang topik ini mengklaim bahwa salah satu karakteristik paradigma agama dunia adalah perspektifnya yang hierarkis. Membahas masalah ini penting untuk membedakan agama-agama dunia sebagai paradigma dan agama-agama dunia sebagai agama yang paling banyak dianut. Kajian ini berpendapat bahwa perspektif hierarkis paradigma agama dunia dapat berakar pada gagasan tentang realitas tertinggi, bahwa ada realitas tertinggi, utama, dan paling utama dalam kelangsungan alam semesta ini, yaitu supernatural atau Tuhan. Kosmologi hierarkis terdiri dari tiga domain utama: supernatural/Tuhan, budaya/manusia, dan alam. Penelitian ini menggunakan metodologi studi kepustakaan, dengan mengandalkan buku, jurnal, dan teks-teks yang berkaitan dengan pertanyaan-pertanyaan penelitian. Kajian ini menemukan bahwa paradigma agama dunia atau kosmologi hierarkis atau “kosmologi subjek-objek” menonjol, terutama dalam agama-agama Abrahamik seperti Islam, Kristen, dan Yudaisme, meskipun konsep realitas tertinggi dalam ketiga agama tersebut berbeda. </em></p>

Though great advances have been made in the field of cosmology by using numerical n-body techniques to investigate large-scale structure formation, these have been hampered by limited dynamic range. Thus there still remains considerable motivation for finding simple methods that link either the final structure or its statistical properties (such as mass and correlation functions) to the initial conditions. This thesis investigates two such approaches - linear theory and the Voronoi foam. (i) Linear Theory This is based on the principle of smoothing the non-linear density field in order to recover the underlying linear density field. Bound objects are then identified with regions where the density exceeds some critical value. Such a prescription allows the statistical properties of the bound objects to be described as a function of the power spectrum of the initial density field and the smoothing function. This thesis checks the accuracy of such models against the adhesion model, a fully non-linear description of gravitational clustering. In order to provide an accurate test of the linear theory predictions, the simulations are carried out in one dimension, where the adhesion model is exact and there is sufficient dynamic range to allow a thorough test of the linear theory predictions. It is found that despite some of the underlying assumptions of linear theory being incorrect in detail, the linear theory mass functions provide an excellent match to those calculated from the simulations. Linear theory correlation functions are also shown to be a good match to those from the simulations, but only in the case where dynamical evolution of the density field is unimportant (i.e. where large-scale power dominates over small-scale power). (ii) Voronoi foam This is a simple model where space is divided into cells, each containing a nucleus, with galaxies populating the boundaries between cells, which are equidistant between neighbouring nuclei. The geometric structure of the cells is entirely determined by the distribution of the nuclei. This forms a continuous network of walls, filaments and nodes, qualitatively similar to that observed.

2007/2008
Il lavoro di ricerca è stato orientato allo studio delle proprietà delle strutture su grande scala dell'Universo. In particolar modo si sono studiate le proprietà ottiche e fisiche di popolazioni sintetiche di galassie in ammassi di galassie in ambito cosmologico all'interno dello scenario gerarchico. Abbiamo affrontato il problema della formazione galattica seguendo due approcci complementari. Una linea di ricerca svolta è stata indirizzata allo studio della popolazione galattica in ammassi di galassie, utilizzando simulazioni idrodinamiche cosmologiche. A tale scopo si sono analizzate simulazioni realizzate con il codice Tree+SPH GADGET2 (Springel 2005) che include processi fisici quali cooling, formazione stellare ed un trattamento dettagliato dei processi di arricchimento chimico associato ai processi di nucleosintesi stellare (Tornatore et al. 2007). Dall'analisi comparata delle osservazioni tra le proprietà ottiche e fisiche di galassie in ammasso ed i risultati di codici spettro-fotometrici applicati alle simulazioni realizzate, è possibile trarre importanti informazioni sulla formazione e sull'evoluzione della componenente barionica tutta ed in particolar modo della popolazione galattica. In particolar modo sono state confrontate le proprietà fisiche e luminosità ottiche e infrarosse delle osservazioni con quelle delle galassie predette dai modelli numerici identificate tramite l'utilizzo di software specifici per il riconoscimento di sottostrutture gravitazionalmente legate (Saro et al. 2006). Sempre nell'ambito di questa linea di ricerca abbiamo studiato i processi coinvolti nella formazione delle galassie centrali d'ammasso ad alto redshift () (Saro et al. 2009), comparando le predizioni numeriche con le più recenti osservazioni ottenute tramite telescopi spaziali (Miley et al. 2006, Hatch et al. 2007), includendo in maniera autoconsistente nel calcolo delle luminosità l'assorbimento da polvere, la quale gioca un ruolo cruciale in regioni ad alto tasso di formazione stellare. Altro aspetto dell'attività di ricerca è stato rivolto allo studio ed al confronto delle predizioni delle proprietà della popolazione galattica in ammassi di galassie attraverso due diversi metodi d’indagine: simulazioni idrodinamiche cosmologiche dirette e modelli semianalitici (SAM), nei quali la popolazione galattica è invece riprodotta tramite apposite ”ricette” a partire dall’analisi dei “merging trees” degli aloni di materia oscura (p.es. De Lucia et al. 2006). Tali metodi presentano vantaggi e svantaggi complementari. Se da un lato infatti le simulazioni dirette permettono uno studio più accurato della dinamica e di seguire in dettaglio la fisica al prezzo però di enormi costi computazionali, dall'altro i modelli semianalitici permettono uno studio dello spazio dei parametri ed una statistica irragiungibile tramite le sole simulazioni. Parte di tale ricerca è stata svolta anche presso il Max Planck Institute for Astrophysics (MPA) di Garching (Monaco) in Germania in collaborazione con Klaus Dolag e Gabriella de Lucia grazie ad una borsa europea EARA - Marie Curie della durata di tre mesi, successivamente estesa per ulteriori due mesi. Lo scopo di quest’indagine si sviluppa su due fronti: confrontare le predizioni dei modelli semianalitici basati su merger trees di simulazioni con fisica diversa e confrontare le predizioni dei modelli semianalitici con quelle che si ottengono direttamente dalle simulazioni. Da un lato, infatti, confrontando le predizioni del modello semianalitico basato su merger trees di simulazioni di sola Dark Matter con le predizioni dello stesso modello semianalitico basato però su merger trees di simulazioni di Dark Matter e Gas, possiamo quantificare e valutare quanto considerare o trascurare processi fisici quali la pressione d'ariete modifichi l'evoluzione e la dinamica della popolazione galattica (Saro et al. 2008). Dall'altro, il confronto tra la popolazione galattica predetta direttamente da simulazioni idrodinamiche cosmologiche e quella predetta dai modelli semianalitici basati sugli stessi merger trees, permette di capire meglio i limiti e le differenze tra queste due tecniche nello studio della formazione di galassie in ambito cosmologico. In particolare tale confronto è stato effettuato con una fisica “semplificata” per poter quantificare l'importanza delle singole assunzioni. Nella fattispecie abbiamo considerato solo cooling e star formation, ed abbiamo trascurato processi fisici quali l'arrichimento chimico e il feedback. In questo modo sono state messe in luce le differenti trattazioni del cooling, della formazione stellare e degli effetti mareali nella creazione di una popolazione stellare intracluster (Saro et al. 2009, in prep).
XXI Ciclo
1980

In order to understand galaxy formation models it is necessary to have a reasonably clear idea of dark matter clustering. This because, in the standard cosmological scenario, galaxies are thought to reside in larger dark matter haloes, extending beyond the galaxy observable radius. Haloes form as consequence of gravitational instability of dark matter density perturbations, and collapse at a density about two hundred times that of the surrounding environment. Clustering happens at allmasses at any time. Until now no direct observations of the existence of these darkmatter haloes have been done; however, their presence may be indirectly tested by their gravitational influence. For example, galaxies in groups have a velocity dispersion much higher than that caused only by visiblematter. Astronomers thus assumed the existence of large amounts of dark matter, an hypothesis later found consistent with other independent observations like gravitational lensing, galaxy clustering on very large scales and anisotropies in the cosmic microwave background radiation. In particle physics, supersymmetry predicts the existence of a particle named neutralino (Jungman et al., 1996; Bertone et al., 2005), today regarded as the most likely candidate for the darkmatter. This particle is heavy and slow-moving (mass ? 100 Gev), so that dark matter density fluctuations can collapse for any mass larger than 10?6M? (Hofmann et al., 2001; Green et al., 2004, 2005). This places amass cut-off on the smallest darkmatter haloes that can collapse. Neutralino can also annihilatewith its anti-particle, generating ?-ray photons (Bergström, 2000; Bertone et al., 2005), with annihilation rates growing as the square of the density. Due to this process, it is expected that future ?-ray telescopes (like GLAST, Morselli (1997)) should be able to detect some excess in the ?-ray background signal from the center of theMilky-Way halo and from its satellites. This would be the first time of an in-”direct” detection of dark matter. In this PhD dissertation we study the evolution of dark matter haloes, using two complementary approaches: numerical simulations and analytical modeling (through the extended Press & Schechter formalism). The work is organized as follows. In the first three chapters we describe and review some properties of the early universe and the theory underlying models of dark matter clustering. We discuss how density perturbations evolve and formdarkmatter haloes inside which baryons can shock and cool, eventually form stars and galaxies. We also show how the number density of haloes can be estimated at any redshift using the excursion set approach, both for the spherical and ellipsoidal collapsemodels. These model mass functions are compared with those from numerical simulations in Chapter 4. We show that the ellipsoidal collapse model (Sheth et al., 2001; Sheth and Tormen, 2002) perfectly reproduces the global mass function in N-Body simulations, while, on the other hand, the spherical collapse model (Press and Schechter, 1974; Lacey and Cole, 1993; Bond et al., 1991) overpredicts the aboundace of smallmasses and underpredicts that of large ones. Dark matter clustering is hierarchical, i.e. small systems collapse first (at higher redshift), and subsequentlymerge together forming larger haloes. In this scenario, if we define a formation time as the earliest redshift when an halo assembles half of its present-daymass, small haloes formfirst and large ones form later. The top of the hierarchical pyramid is occupied by galaxy clusters, which represent the largest virialized structures in the universe. Another important quantity describing dark matter clustering is any conditional mass function. One example is the probability that an halo observed at redshift z1, will be part of a larger halo at z0 < z1. This distribution is also called progenitor mass function; theoretical predictions and N-Body simulations are compared at the end of Chapter 4. There we show that, also in this case, the ellipsoidal collapse prediction well reproduces the distribution found in numerical simulations atmost redshifts. In Chapter 5 we will discuss how it is possible to estimate the formation time distribution from the conditional mass function, and present a new formula, based on the ellipsoidal collapse, that better fits the formation redshift distributionmeasured in N-Body simulations. The progenitors accreted along themerging history tree of a halo can survive today in their host system, and constitute the so-called substructure population (Ghigna et al., 1998; Tormen et al., 2004; Gao et al., 2004; De Lucia et al., 2004; van den Bosch et al., 2005). In Chapter 6 we discuss how it is possible to analytically estimate this population using the conditionalmass function, assuming no tidal stripping andmerging among substructures. By extrapolating the power spectrumof density perturbations down to the typical neutralino Jeansmass, we estimate the substructure population in aMilky-Way size halo, both for a spherical and ellipsoidal collapse model. Modeling the neutralino annihilation rate, we then estimate the ?-ray emission from this population and its detectability with a GLAST-like telescope. In Chapter 7 we study the growth of the main progenitor halo, and the mass it accretes along itsmerging history tree using numerical simulations. Themass function of accreted haloes, called “unevolved subhalomass function”, turns out to be independent of the final host halo mass, both before and after its formation redshift. The accreted haloes, called satellites, are then followed snapshot by snapshot in order to compute their mass loss rate. This allow us to interpret the present-day subhalo population in term of the mass loss from the accreted satellites. Since smaller hosts form earlier than larger ones, the former will accrete satellites at earlier times; these satellites will therefore spend a longer time inside the host halo and lose a larger fraction of their initialmass. This translates the (mass-independent) unevolved subhalo population in a present-day subhalo distribution that depends on the host halo mass: at fixed subhalo-to-host halo mass: msb/M0, more massive hosts contain more subhaloes than smaller hosts do. Subhaloes defined in this way may contain other subhaloes within themselves (Diemand et al., 2007b; Li and Helmi, 2007), which were accreted when they were still isolated systems. In Chapter 8 we show how subhaloes within subhaloes can be identified following all branches of themerging history tree of an host halo. We also compare our definition of substructures with that of other authors (Gao et al., 2004), finding very good agreement. In the last chapter of this dissertation, we show how the merging history tree of a halo can be followed using Monte Carlo realizations. The partition code, on which the tree is based, is very fast, time step independent, and provides results in excellent agreement with the spherical collapse conditional mass function down to any required mass resolution (Sheth and Lemson, 1999). The tree has been run following the main branch and resolving all satellites down to the typical neutralino Jeans mass, in order to study the Milky-Way subhalo population.

This chapter primarily focuses on the contrast between the ‘blue-sky’ serene world of classical Confucian ethics and the vulnerability of the Confucian scholar in a power structure rooted in a conquering warrior absolute monarchy. It further provides an exhaustive and authoritative history of Confucianism within the history of China and thoroughly reinforces criticisms of Confucianism in contrast to the Dao. The chapter portrays how the concept of the Mandate of Heaven was always used by military conquerors to provide legitimacy for their use of force. As Confucianism became the official ideology of the State during the time of Emperor Wu (141–87 BC), a very sharp contrast arose between the Confucian ideology represented by Dong Zhonshu (the time of Emperor Wu) and the Dao-oriented thinking of the King of Huainan. The former represented an authoritarian institution of centralization and hierarchy, with the Confucian scholar class claiming to interpret a moral cosmology to strengthen the authority of the emperor, and, by implication, that of his scholar advisers. Their task was to interpret the will of ‘an anthropomorphic deity from Zhou theology, attributing to it a heart, intention and love. Heaven manifests his will in omens … as Heaven’s speech’. Only the sage Confucius could understand and interpret the moral consciousness of Heaven. Their recommendation was for wholesale centralization of culture, political, military, and economic. At the same time, the Chinese Empire was in constant military expansion in all directions. It concluded with a recommendation for the conquest and execution of the Huainan kings, among others, as representatives of the anti-hierarchical Daoism. As Wang puts it, ‘the ideological unification was essential for building an authoritarian and centralized imperial order. By suppressing different cultural and philosophical traditions, it established universal rules and standards that were themselves the web of the centralized empire.

This chapter situates Schuonian Perennialism within the larger discursive tradition of essentialist, religious universalism through a comparison with Friedrich Schleiermacher. It thus argues that Frithjof Schuon, and those writing within his orbit, made a Copernican turn away from Ibn ‘Arabi’s hierarchical cosmology to one of cosmic pluralism united by a Schleiermacherian notion of a transcendent and universally valid religious a priori, or “religion as such.” To clearly demonstrate this turn, Ibn ‘Arabi’s discourse is here historicized in relation to the polemical thought of Ibn Ḥazm (d. 1064). Like Ibn Hazm, Ibn ‘Arabi claims that the Jews were guilty of textual corruption (taḥrīf al-naṣṣ) and not simply a corruption of meaning (taḥrīf al-maʿānī) as implied in Perennialist discourse. Rather than the soteriological power of their religions, Ibn ‘Arabi holds that the salvation of the People of the Book is metaphysically determined by their submission to Muhammad’s prophetic authority.

Aboriginal kinship has stimulated many mathematicians. In the 1980’s, Glowczewski showed that there is a non euclidian ‘topologic’ that is common to what Indigenous Australians call their “Law”: a non hierarchical system of classificatory ritual kinship, a projection of the mythical travels of totemic ancestors (the Dreamings) into the landscape and a system of ritual obligations taboos. In other words, the social valorisation of heterogeneity recognises irreducible singularities shared by humans, non humans and the land as a condition for a commons that in no way homogenises society into a hierarchical order. The topological figure of the hypercube was used here to illustrate some complex Aboriginal relational rules that exclude the centralisation of power both in social organisation and in the totemic cosmology. To translate Indigenous spatio-temporal concepts Glowczewski was partly inspired by science fiction, that speculates about the 4^th dimension. When shown the hypercube as a tool to account for the kinship logic of their Dreamings, the Warlpiri elders thought it was a ‘good game’! First published in 1989.

This chapter compares the Rgveda, the early Upanishads, and Plato's Timaeus for their conception of the universe, the inner self, and the relation between them. All three texts envisage the universe as a hierarchically organised system in which order (rta in the Rgveda) prevails. But only in the Timaeus is there the motivation to create a cosmos endowed with beauty and goodness. Only in the Timaeus and the Upanishads is cosmology a prerequisite for self-knowledge and ethics, and both texts lay the foundations for moral realism, the belief in the objective validity of moral values.

If the 17th century could be considered the century of the reformation of science, the present century is one of counterreformation in every sense of the word. The ideology of this century can be seen in the titanic efforts to complete the development of science which foundation was laid in the 17th and 18th centuries, in the outright failures, and in attempts at reconstructing the foundation (e.g., Hilbert's formalization program, Gödel's incompleteness theorem, Charlier's theory of a hierarchic universe, Fridman's evolutionary cosmology, Newton's mechanics, relativistic and/or quantum mechanics in physics, the logical turn of the Vienna circle and epistemological anarchism in methodology). Our task is to reveal the essence of the turning points in 20th century science and to determine at least the general outlines, if not the cause, of the new type of rationality that is replacing the old one. I will focus on the history of cosmology, or rather on its three paradigms that have succeeded each other in this century: Newtonian, Fridmanian and the inflationary paradigms. By outlining the problem, I will pose a possible solution from clarifying changes in the value orientations, ideals and norms of scientific research to their possible generalization.