1,720,973 research outputs found
Zoomed high-resolution simulations of Multi-coupled Dark Energy: Cored galaxy density profiles at high redshift
Full text linkWe perform for the first time high-resolution zoom-in re-simulations of individual halos in the context of the Multi-coupled Dark Energy (McDE) scenario, which is characterised by the existence of two distinct Dark Matter particle species with opposite couplings to a Dark Energy scalar field. We compare the structural properties of the simulated halos to the standard ΛCDM results. The zoomed-in initial conditions are set up using a specifically designed code called ZInCo that we publicly release along with the present paper. Our numerical results allow to investigate in detail and with unprecedented resolution the halo segregation process that characterises McDE cosmologies from its very early stages. In particular, we find that in contrast to what could be inferred from previous numerical analysis at lower resolution, the segregation process is already in place at redshifts as high as z ∼ 7. Most remarkably, we find that the subsequent evolution of the segregation leads to the formation of cored total matter density profiles with a core size that progressively increases in time. The shape of the cored profiles can be accurately predicted as the superposition of two NFW profiles with an increasing offset, thereby confirming the interpretation of the simulations results in terms of the segregation of the two dark matter components of the halo as a consequence of their different coupling to the Dark Energy field
Dynamic zoom simulations: A fast, adaptive algorithm for simulating light-cones
Full text linkThe advent of a new generation of large-scale galaxy surveys is pushing cosmological numerical simulations in an uncharted territory. The simultaneous requirements of high resolution and very large volume pose serious technical challenges, due to their computational and data storage demand. In this paper, we present a novel approach dubbed dynamic zoom simulations – or dzs – developed to tackle these issues. Our method is tailored to the production of light-cone outputs from N-body numerical simulations, which allow for a more efficient storage and post-processing compared to standard comoving snapshots, and more directly mimic the format of survey data. In dzs, the resolution of the simulation is dynamically decreased outside the light-cone surface, reducing the computational work load, while simultaneously preserving the accuracy inside the light-cone and the large-scale gravitational field. We show that our approach can achieve virtually identical results to traditional simulations at half of the computational cost for our largest box. We also forecast this speedup to increase up to a factor of 5 for larger and/or higher resolution simulations. We assess the accuracy of the numerical integration by comparing pairs of identical simulations run with and without dzs. Deviations in the light-cone halo mass function, in the sky-projected light-cone, and in the 3D matter light-cone always remain below 0.1 per cent. In summary, our results indicate that the dzs technique may provide a highly valuable tool to address the technical challenges that will characterize the next generation of large-scale cosmological simulations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Zoomed simulations of Halo segregation in cosmological models with two species of coupled dark matter
Full text linkLa materia ordinaria copre soli pochi punti percentuali della massa-energia totale dell'Universo, che è invece largamente dominata da componenti “oscure”. Il modello standard usato per descriverle è il modello LambdaCDM. Nonostante esso sembri consistente con la maggior parte dei dati attualmente disponibili, presenta alcuni problemi fondamentali che ad oggi restano irrisolti, lasciando spazio per lo studio di modelli cosmologici alternativi.
Questa Tesi mira a studiare un modello proposto recentemente, chiamato “Multi-coupled Dark Energy” (McDE), che presenta interazioni modificate rispetto al modello LambdaCDM. In particolare, la Materia Oscura è composta da due diversi tipi di particelle con accoppiamento opposto rispetto ad un campo scalare responsabile dell'Energia Oscura. L'evoluzione del background e delle perturbazioni lineari risultano essere indistinguibili da quelle del modello LambdaCDM.
In questa Tesi viene presentata per la prima volta una serie di simulazioni numeriche “zoomed”. Esse presentano diverse regioni con risoluzione differente, centrate su un singolo ammasso di interesse, che permettono di studiare in dettaglio una singola struttura senza aumentare eccessivamente il tempo di calcolo necessario.
Un codice chiamato ZInCo, da me appositamente sviluppato per questa Tesi, viene anch'esso presentato per la prima volta. Il codice produce condizioni iniziali adatte a simulazioni cosmologiche, con differenti regioni di risoluzione, indipendenti dal modello cosmologico scelto e che preservano tutte le caratteristiche dello spettro di potenza imposto su di esse.
Il codice ZInCo è stato usato per produrre condizioni iniziali per una serie di simulazioni numeriche del modello McDE, le quali per la prima volta mostrano, grazie all'alta risoluzione raggiunta, che l'effetto di segregazione degli ammassi avviene significativamente prima di quanto stimato in precedenza. Inoltre, i profili radiale di densità ottenuti mostrano un appiattimento centrale nelle fasi iniziali della segregazione. Quest'ultimo effetto potrebbe aiutare a risolvere il problema “cusp-core” del modello LambdaCDM e porre limiti ai valori dell'accoppiamento possibili
CoReCon: an open, community-powered collection of Reionization constraints
Full text linkThe number of available constraints on the Universe during and before cosmic
reionization is rapidly growing. These are often scattered across inhomogeneous
formats, unit systems and sampling strategies. In this paper, I introduce
CoReCon, a Python package designed to provide a growing set of constraints on
key physical quantities related to the Epoch of Reionization and a platform for
the high-redshift research community to collect and store, in an open way,
current and forthcoming observational constraints.Comment: Published in the Journal of Open Source Softwar
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
From galaxies to the cosmic web and back: the interplay of different scales in galaxy formation and cosmic reionization
Full text linkThe evolution of the Universe is primarily governed by gravity, that triggers the development of a complex web-like distribution of galaxies. The latter are embedded in larger structures, called haloes, mainly composed by an exotic form of matter that does not interact with light, and is therefore called dark. Within this cosmic web, astrophysical phenomena occur on a large variety of spatial scales. Although ubiquitous, the interaction between them is often neglected because of the difficulties in their simultaneous modeling. In this Thesis we employ advanced numerical simulations of structure formation in the universe to investigate three cases where this interplay is of primary importance, namely: the assembly bias, the radial acceleration relation and the epoch of cosmic reionization.
Assembly bias denotes the fact that dark matter haloes of the same mass have clustering properties that depend on their formation time. This effect is due to the cosmic environment of such haloes, that halts the accretion of new material in regions where the tidal field exerted by nearby structures is strong. Therefore, the assembly of objects strongly clustered is more efficiently suppressed. In this Thesis, we study the properties of satellite galaxies that reside within haloes with different assembly histories, and therefore cosmic environments. We show that their content is insensitive to the large-scale geometry of the matter distribution. However, the latter has a strong impact on the satellite dynamics, producing a preferentially-radial motion in objects embedded in a knot of the cosmic web, and isotropically-distributed velocities in region within filaments. We apply this knowledge to the satellites of the Milky Way and infer that our Galaxy must reside in a prominent filamentary structure.
Recent observations of a large sample of galaxies unveiled a tight correlation between the total radial acceleration experienced by bodies orbiting around the galactic center and the same quantity inferred only from the galactic baryonic content. Theoretical models of structure formation have been tested against this radial acceleration relation (RAR) only for large structures. Here, we predict for the first time the RAR of small satellite galaxies, opening up the possibility to test our knowledge of galaxy formation mechanisms in an uncharted territory. Additionally, we study the redshift evolution of this relation and its secondary dependence on physical properties of the satellites. We then make use of these results to devise an observational test that can distinguish between the standard cosmological model and one popular alternative theory, the Modified Newtonian Dynamics.
Finally, we study the role of quasars in the reionization of the Universe on the largest scales. We do so by simulating a reionization scenario where the ionizing photons production is dominated by quasars and compare it with one where galaxies are the main source of such photons. We show that, despite the peculiar emission properties of quasars, the former leads to global properties of the inter-galactic medium that are in agreement with observations. Additionally, we produce synthetic absorption spectra and use them to show that, in a quasar-dominated scenario, the properties of helium absorption features are incompatible with available observations. However, we also find indications that a modest contribution from quasars can explain the observed distribution of patches of inter-galactic neutral hydrogen. To unravel these apparently-controversial findings, we identify and investigate two promising methods that, using future observations, will enable a determination of the quasar contribution to cosmic reionization
CoReCon: an open, community-powered collection of Reionization constraints
No full textUser-friendly collection of Reionization-related constraintsIf you use this software, please cite our article in the Journal of Open Source Software
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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