748 research outputs found
EoR in alternative cosmological scenarios
The aim of this Thesis is to investigate the possibility that the observations related to the epoch
of reionization can probe not only the evolution of the IGM state, but also the cosmological background in which this process occurs. In fact, the history of the IGM ionization is indeed affected
by the evolution of the sources of ionizing photons that, under the assumption of a structure formation paradigm determined by the hierarchic growth of the matter
uctuations, results strongly
dependent on the characteristics of the background universe.
For the purpose of our investigation, we have analysed the reionization history in innovative cosmological frameworks, still in agreement with the recent observational tests related to the SNIa and the CMB probes, comparing our results with the reionization scenario predicted by the commonly used LCDM cosmology. In particular, in this Thesis we have considered two different alternative
universes. The first one is a
at universe dominated at late epochs by a dynamic dark energy component, characterized by an equation of state evolving in time. The second cosmological framework we have assumed is a LCDM characterized by a primordial overdensity field having a non-Gaussian probability distribution.
The reionization scenario have been investigated, in this Thesis, through semi-analytic approaches
based on the hierarichic growth of the matter
uctuations and on suitable assumptions concerning
the ionization and the recombination of the IGM. We make predictions for the evolution and the
distribution of the HII regions, and for the global features of reionization, that can be constrained
by future observations. Finally, we brie
y discuss the possible future prospects of this Thesis work
Modeling the QSO luminosity and spatial clustering at low redshifts
We investigate the ability of hierarchical models of QSO formation and
evolution to match the observed luminosity, number counts and spatial
clustering of quasars at redshift z<2. These models assume that the QSO
emission is triggered by galaxy mergers, that the mass of the central black
hole correlates with halo properties and that quasars shine at their Eddington
luminosity except, perhaps, during the very early stages of evolution. We find
that models based on simple analytic approximations successfully reproduce the
observed B-band QSO luminosity function at all redshifts, provided that some
mechanisms is advocated to quench mass accretion within haloes larger than
about 1e13 Msun that host bright quasars. These models also match the observed
strength of QSO clustering at z~0.8. At larger redshifts, however, they
underpredict the QSO biasing which, instead, is correctly reproduced by
semi-analytic models in which the halo merger history and associated BHs are
followed by Monte Carlo realizations of the merger hierarchy. We show that the
disagreement between the luminosity function predicted by semi-analytic models
and observations can be ascribed to the use of B-band data, which are a biased
tracer of the quasar population, due to obscuration.Comment: 13 pages, 9 figures. Accepted by MNRA
Cosmic reionization in a dynamic quintessence cosmology
In this paper we investigate the effects that a dynamic dark energy component
dominant in the universe at late epochs has on reionization. We follow the
evolution of HII regions with the analytic approach of Furlanetto and Oh (2005)
in two different universes for which we assume the Peebles and Ratra (2003) and
Brax and Martin (2000) quintessence models and we compare our results to the
LCDM scenario. We show that, for a fixed ionization efficiency, at the same
cosmological epoch the topology of bubbles is dominated by high-mass objects
and the characteristic size of the ionized regions is slightly smaller than in
the LCDM model, especially at the latest stages of reionization, due to the
higher recombination efficiency. As a consequence, the bubbles' `epoch of
overlap' happens earlier than in LCDM. Finally, we show how the different
evolution of the HII regions affects the transmission of the high-z QSO
spectra, reducing the Lyman flux absorption at small optical depths.Comment: 10 pages, minor changes to match the version accepted for publication
by MNRA
Deleuze, art and social work
© 2017 GAPS. This article outlines the value of Deleuze’s philosophy to social work in offering a different understanding of the constitution of reality and being human and the importance of the visual by way of artistic and craft activities. The key concepts derived from Deleuze’s work and outlined in the article concern the idea of the ‘virtual’ as relevant to the concept of ‘a life’ and ‘difference and repetition’ as a way of conceptualising an anti-essentialist post-modern view of identity as fragmented, but dynamic. In other words partaking of chaotic, but also creative potential. This conceptualisation of life allows to think about all lives, even ‘difficult’ ones, as potentially creatively undetermined in the future, rather than just pathologically predetermined by the past. Arts and crafts are seen as having the power to provoke and soothe, allowing a process of discovery of what the material and the person might both become in the doing. Thus, the article offers an ontological grounding validating arts and crafts, experiential learning and apprenticeship models as essential to social work practice and training at a time when these might be driven out by evidence-based paradigms and budget cuts
- …