Multiwavelenght study of cluster mergers and consequences for the radio emission properties of galaxy clusters

In the present thesis a thourough multiwavelength analysis of a number of galaxy clusters known to be experiencing a merger event is presented. The bulk of the thesis consists in the analysis of deep radio observations of six merging clusters, which host extended radio emission on the cluster scale. A composite optical and X–ray analysis is performed in order to obtain a detailed and comprehensive picture of the cluster dynamics and possibly derive hints about the properties of the ongoing merger, such as the involved mass ratio, geometry and time scale. The combination of the high quality radio, optical and X–ray data allows us to investigate the implications of the ongoing merger for the cluster radio properties, focusing on the phenomenon of cluster scale diffuse radio sources, known as radio halos and relics. A total number of six merging clusters was selected for the present study: A3562, A697, A209, A521, RXCJ 1314.4–2515 and RXCJ 2003.5–2323. All of them were known, or suspected, to possess extended radio emission on the cluster scale, in the form of a radio halo and/or a relic. High sensitivity radio observations were carried out for all clusters using the Giant Metrewave Radio Telescope (GMRT) at low frequency (i.e. ≤ 610 MHz), in order to test the presence of a diffuse radio source and/or analyse in detail the properties of the hosted extended radio emission. For three clusters, the GMRT information was combined with higher frequency data from Very Large Array (VLA) observations. A re–analysis of the optical and X–ray data available in the public archives was carried out for all sources. Propriety deep XMM–Newton and Chandra observations were used to investigate the merger dynamics in A3562. Thanks to our multiwavelength analysis, we were able to confirm the existence of a radio halo and/or a relic in all clusters, and to connect their properties and origin to the reconstructed merging scenario for most of the investigated cases. • The existence of a small size and low power radio halo in A3562 was successfully explained in the theoretical framework of the particle re–acceleration model for the origin of radio halos, which invokes the re–acceleration of pre–existing relativistic electrons in the intracluster medium by merger–driven turbulence. • A giant radio halo was found in the massive galaxy cluster A209, which has likely undergone a past major merger and is currently experiencing a new merging process in a direction roughly orthogonal to the old merger axis. A giant radio halo was also detected in A697, whose optical and X–ray properties may be suggestive of a strong merger event along the line of sight. Given the cluster mass and the kind of merger, the existence of a giant radio halo in both clusters is expected in the framework of the re–acceleration scenario. • A radio relic was detected at the outskirts of A521, a highly dynamically disturbed cluster which is accreting a number of small mass concentrations. A possible explanation for its origin requires the presence of a merger–driven shock front at the location of the source. The spectral properties of the relic may support such interpretation and require a Mach number M < ∼ 3 for the shock. • The galaxy cluster RXCJ 1314.4–2515 is exceptional and unique in hosting two peripheral relic sources, extending on the Mpc scale, and a central small size radio halo. The existence of these sources requires the presence of an ongoing energetic merger. Our combined optical and X–ray investigation suggests that a strong merging process between two or more massive subclumps may be ongoing in this cluster. Thanks to forthcoming optical and X–ray observations, we will reconstruct in detail the merger dynamics and derive its energetics, to be related to the energy necessary for the particle re–acceleration in this cluster. • Finally, RXCJ 2003.5–2323 was found to possess a giant radio halo. This source is among the largest, most powerful and most distant (z=0.317) halos imaged so far. Unlike other radio halos, it shows a very peculiar morphology with bright clumps and filaments of emission, whose origin might be related to the relatively high redshift of the hosting cluster. Although very little optical and X–ray information is available about the cluster dynamical stage, the results of our optical analysis suggest the presence of two massive substructures which may be interacting with the cluster. Forthcoming observations in the optical and X–ray bands will allow us to confirm the expected high merging activity in this cluster. Throughout the present thesis a cosmology with H0 = 70 km s−1 Mpc−1, m=0.3 and =0.7 is assumed.

L’emergere del periurbano: il caso di Bologna

The rationale behind this piece of research is to study the movement of people from Bologna city centre to its outskirts and to find out what type of people are subject to move and the reasons for this: are they forced into or do they choose to do so? The present study will also consider how people commute from home to the city centre and the effect this has on them. For the purpose of this work, attention will be drawn to the possibility of these outer areas to develop in such a way that people will no longer need to commute to the city in order to recreate the advantages this offers to them (e.g. shops, job opportunities, ext). The theoretical framework this doctorial work is based upon concerns historical, urbanist, sociological and demographic approaches, along with the fact that the hegemony of the city centre has been benefiting has decreased. Historical centres and the central poles of metropolitan systems have lost their functional and symbolic relevance. More specifically, the Bologna Area is undergoing two tendencies: the first one is a process of residential decentralization from the capital town, capable of involving a plurality of social groups, which caused an enrichment of the social composition of "suburban" population. The second process is a partial substitution of the population in the city centre with new groups: this not only occurred with directional groups, but it has also interested new parts of the “service worker” class and members of metropolitan underclass, causing, consequentially, a growing complexity in central areas of the metropolitan system. The need to increase knowledge of Bologna territory has become more and more relevant, since the 70’s, when a series of important environmental transformations favoured a research interest that did not exclusively stopped within the city centre boarders, but rather encouraged the exploration of Bologna outer/suburban areas. Finally, in the urban/suburban discourse, this piece of research has highlighted how the search for a better quality of life (financial reasons, larger spaces, possibility to buy/rent for a better price, environmental issues) determines the choice to leave the centre of the city in favour of outer areas. The tendency that this doctorial work has brought to surface is the need to match a more manageable standard of living to the proximity to the city, despite the fact that this results in the stress caused to commuting and the lack of those cultural and entertaining facilities offered by the city. The new suburban inhabitants do not regret leaving the city, but, at the same time, do not feel emotionally attached to the new location at a community level: what they seem to look for is a more comfortable environment where to live in.

"Narrativa di frontiera". Fenomenologia di una forma aperta.

«Fiction of frontier». Phenomenology of an open form/voice. Francesco Giustini’s PhD dissertation fits into a genre of research usually neglected by the literary criticism which nevertheless is arousing much interest in recent years: the relationship between Literature and Space. In this context, the specific issue of his work consists in the category of the Frontier including its several implications for the XX century fiction. The preliminary step, at the beginning of the first section of the dissertation, is a semantic analysis: with precision, Giustini describes the meaning of the word “frontier” here declined in a multiplicity of cultural, political and geographical contexts, starting from the American frontier of the pioneers who headed for the West, to the exotic frontiers of the world, with whose the imperialistic colonization has come into contact; from the semi-uninhabited areas like deserts, highlands and virgin forests, to the ethnic frontiers between Indian and white people in South America, since the internal frontiers of the Countries like those ones between the District and the Capital City, the Centre and the Outskirts. In the next step, Giustini wants to focus on a real “ myth of the frontier”, able to nourish cultural and literary imagination. Indeed, the literature has told and chosen the frontier as the scenery for many stories; especially in the 20th Century it made the frontier a problematic space in the light of events and changes that have transformed the perception of space and our relationship with it. Therefore, the dissertation proposes a critical category, it traces the hallmarks of a specific literary phenomenon defined “ Fiction of the frontier” ,present in many literary traditions during the 20th Century. The term “Fiction” (not “Literature” or “Poetics”) does not define a genre but rather a “procedure”, focusing on a constant issue pointed out from the texts examined in this work : the strong call to the act of narration and to its oral traditions. The “Fiction of the Frontier” is perceived as an approach to the world, a way of watching and feeling the objects, an emotion that is lived and told through the story- a story where the narrator ,through his body and his voice, takes the rule of the witness. The following parts, that have an analytic style, are constructed on the basis of this theoretical and methodological reflection. The second section gives a wide range of examples into we can find the figure and the myth of the frontier through the textual analysis which range over several literary traditions. Starting from monographic chapters (Garcia Marquez, Callado, McCarthy), to the comparative reading of couples of texts (Calvino and Verga Llosa, Buzzati and Coetzee, Arguedas and Rulfo). The selection of texts is introduced so as to underline a particular aspect or a form of the frontier at every reading. This section is articulated into thematic voices which recall some actions that can be taken into the ambiguous and liminal space of the frontier (to communicate, to wait, to “trans-culturate”, to imagine, to live in, to not-live in). In this phenomenology, the frontier comes to the light as a physical and concrete element or as a cultural, imaginary, linguistic, ethnic and existential category. In the end, the third section is centered on a more defined and elaborated analysis of two authors, considered as fundamental for the comprehension of the “Fiction of the frontier”: Joseph Conrad and João Guimarães Rosa. Even if they are very different, being part of unlike literary traditions, these two authors show many connections which are pointed by the comparative analysis. Maybe Conrad is the first author that understand the feeling of the frontier , freeing himself from the adventure romance and from the exotic nineteenthcentury tradition. João Guimarães Rosa, in his turn, is the great narrator of Brazilian and South American frontier, he is the man of sertão and of endless spaces of the Centre of Brazil. His production is strongly linked to that one belonged to the author of Heart of Darkness.

Social housing: interventions of densification in urban regeneration (1995-2010). Critical analysis of strategies adopted in Milan, London, São Paulo

The prospect of the continuous multiplication of life styles, the obsolescence of the traditional typological diagrams, the usability of spaces on different territorial scales, imposes on contemporary architecture the search for new models of living. Limited densities in urban development have produced the erosion of territory, the increase of the harmful emissions and energy consumption. High density housing cannot refuse the social emergency to ensure high quality and low cost dwellings, to a new people target: students, temporary workers, key workers, foreign, young couples without children, large families and, in general, people who carry out public services. Social housing strategies have become particularly relevant in regenerating high density urban outskirts. The choice of this research topic derives from the desire to deal with the recent accommodation emergency, according to different perspectives, with a view to give a contribution to the current literature, by proposing some tools for a correct design of the social housing, by ensuring good quality, cost-effective, and eco-sustainable solutions, from the concept phase, through management and maintenance, until the end of the building life cycle. The purpose of the thesis is defining a framework of guidelines that become effective instruments to be used in designing the social housing. They should also integrate the existing regulations and are mainly thought for those who work in this sector. They would aim at supporting students who have to cope with this particular residential theme, and also the users themselves. The scientific evidence of either the recent specialized literature or the solutions adopted in some case studies within the selected metropolitan areas of Milan, London and São Paulo, it is possible to identify the principles of this new design approach, in which the connection between typology, morphology and technology pursues the goal of a high living standard.