Hydrodynamical simulations of galaxy clusters in dark energy cosmologies

In this work we investigate the influence of dark energy on structure formation, within five different cosmological models, namely a concordance $\Lambda$CDM model, two models with dynamical dark energy, viewed as a quintessence scalar field (using a RP and a SUGRA potential form) and two extended quintessence models (EQp and EQn) where the quintessence scalar field interacts non-minimally with gravity (scalar-tensor theories). We adopted for all models the normalization of the matter power spectrum $\sigma_{8}$ to match the CMB data. For each model, we perform hydrodynamical simulations in a cosmological box of $(300 \ {\rm{Mpc}} \ h^{-1})^{3}$ including baryons and allowing for cooling and star formation. We find that, in models with dynamical dark energy, the evolving cosmological background leads to different star formation rates and different formation histories of galaxy clusters, but the baryon physics is not affected in a relevant way. We investigate several proxies for the cluster mass function based on X-ray observables like temperature, luminosity, $M_{gas}$, and $Y_{X}$. We confirm that the overall baryon fraction is almost independent of the dark energy models within few percentage points. The same is true for the gas fraction. This evidence reinforces the use of galaxy clusters as cosmological probe of the matter and energy content of the Universe. We also study the $c-M$ relation in the different cosmological scenarios, using both dark matter only and hydrodynamical simulations. We find that the normalization of the $c-M$ relation is directly linked to $\sigma_{8}$ and the evolution of the density perturbations for $\Lambda$CDM, RP and SUGRA, while for EQp and EQn it depends also on the evolution of the linear density contrast. These differences in the $c-M$ relation provide another way to use galaxy clusters to constrain the underlying cosmology.

Multiple stellar populations in globular clusters with photometry and low resolution spectroscopy

Our view of Globular Clusters has deeply changed in the last decade. Modern spectroscopic and photometric data have conclusively established that globulars are neither coeval nor monometallic, reopening the issue of the formation of such systems. Their formation is now schematized as a two-step process, during which the polluted matter from the more massive stars of a first generation gives birth, in the cluster innermost regions, to a second generation of stars with the characteristic signature of fully CNO-processed matter. To date, star-to-star variations in abundances of the light elements (C, N, O, Na) have been observed in stars of all evolutionary phases in all properly studied Galactic globular clusters. Multiple or broad evolutionary sequences have also been observed in nearly all the clusters that have been observed with good signal-to-noise in the appropriate photometric bands. The body of evidence suggests that spreads in light-element abundances can be fairly well traced by photometric indices including near ultraviolet passbands, as CNO abundance variations affect mainly wavelengths shorter than ~400 nm owing to the rise of some NH and CN molecular absorption bands. Here, we exploit this property of near ultraviolet photometry to trace internal chemical variations and combined it with low resolution spectroscopy aimed to derive carbon and nitrogen abundances in order to maximize the information on the multiple populations. This approach has been proven to be very effective in (i) detecting multiple population, (ii) characterizing their global properties (i.e., relative fraction of stars, location in the color-magnitude diagram, spatial distribution, and trends with cluster parameters) and (iii) precisely tagging their chemical properties (i.e., extension of the C-N anticorrelation, bimodalities in the N content).

Chemical and kinematical properties of Blue Straggler stars in Galactic globular clusters

Blue straggler stars (BSSs) are brighter and bluer (hotter) than the main-sequence (MS) turnoff and they are known to be more massive than MS stars.Two main scenarios for their formation have been proposed:collision-induced stellar mergers (COL-BSSs),or mass-transfer in binary systems (MT-BSSs).Depleted surface abundances of C and O are expected for MT-BSSs,whereas no chemical anomalies are predicted for COL-BSSs.Both MT- and COL-BSSs should rotate fast, but braking mechanisms may intervene with efficiencies and time-scales not well known yet,thus preventing a clear prediction of the expected rotational velocities.Within this context,an extensive survey is ongoing by using the multi-object spectrograph FLAMES@VLT,with the aim to obtain abundance patterns and rotational velocities for representative samples of BSSs in several Galactic GCs.A sub-population of CO-depleted BSSs has been identified in 47 Tuc,with only one fast rotating star detected.For this PhD Thesis work I analyzed FLAMES spectra of more than 130 BSSs in four GCs:M4,NGC 6397,M30 and ω Centauri.This is the largest sample of BSSs spectroscopically investigated so far.Hints of CO depletion have been observed in only 4-5 cases (in M30 and ω Centauri),suggesting either that the majority of BSSs have a collisional origin,or that the CO-depletion is a transient phenomenon.Unfortunately,no conclusions in terms of formation mechanism could be drawn in a large number of cases,because of the effects of radiative levitation. Remarkably,however,this is the first time that evidence of radiative levitation is found in BSSs hotter than 8200 K.Finally, we also discovered the largest fractions of fast rotating BSSs ever observed in any GCs:40% in M4 and 30% in ω Centauri.While not solving the problem of BSS formation,these results provide invaluable information about the BSS physical properties,which is crucial to build realistic models of their evolution.

Homogeneous analysis of a sample of Open Clusters in the context of the BOCCE project and the Gaia-ESO Survey

The open clusters (OC) are gravitationally bound systems of a few tens or hundreds of stars. In our Galaxy, the Milky Way, we know about 3000 open clusters, of very different ages in the range of a few millions years to about 9 Gyr. OCs are mainly located in the Galactic thin disc, with distances from the Galactic centre in the range 4-22 kpc and a height scale on the disc of about 200 pc. Their chemical properties trace those of the environment in which they formed and the metallicity is in the range -0.5<[Fe/H]<+0.5 dex. Through photometry and spectroscopy it is possible to study relatively easily the properties of the OCs and estimate their age, distance, and chemistry. For these reasons they are considered primary tracers of the chemical properties and chemical evolution of the Galactic disc. The main subject of this thesis is the comprehensive study of several OCs. The research embraces two different projects: the Bologna Open Cluster Chemical Evolution project (BOCCE) and the Gaia-ESO Survey. The first is a long-term programme, aiming at studying the chemical evolution of the Milky Way disc by means of a homogeneous sample of OCs. The latter is a large public spectroscopy survey, conducted with the high-resolution spectrograph FLAMES@VLT and targeting about 10^5 stars in different part of the Galaxy and 10^4 stars in about 100 OCs. The common ground between the two projects is the study of the properties of the OCs as tracers of the disc's characteristics. The impressive scientific outcome of the Gaia-ESO Survey and the unique framework of homogeneity of the BOCCE project can propose, especially once combined together, a much more accurate description of the properties of the OCs. In turn, this will give fundamental constraints for the interpretation of the properties of the Galactic disc.

Radio halos in a mass-selected sample of galaxy clusters

A fraction of galaxy clusters host Mpc-scale Radio Halos (RH), generated by ultrarelativistic electrons in the magnetized intra cluster medium (ICM). In the current view they trace turbulent regions in merging clusters, where relativistic particles are trapped and accelerated. This model has clear expectations about the statistical properties of RHs. To test these expectations large mass-selected samples of galaxy clusters with adequate radio and X-ray data are necessary. We used the Planck SZ cluster catalogue as suitable starting point of our investigation, selecting clusters with M500>6x10^14 Msun at 0.08clusters at z<0.2 and with the Extended GMRT RH Survey for 0.2clusters with RH with the mass of the parent cluster and show that this increase is in line with statistical calculations based on the re-acceleration scenario. We confirm earlier findings that RHs are exclusively found in merging systems.

Crystal Engineering of bright luminescent copper iodide clusters with phosphorus and nitrogen-based ligands

Copper(I) halide clusters are recently considered as good candidate for optoelectronic devices such as OLEDs . Although the copper halide clusters, in particular copper iodide, are very well known since the beginning of the 20th century, only in the late ‘70s the interest on these compounds grew dramatically due their particular photophysical behaviour. These complexes are characterized by a dual triplet emission bands, named Cluster Centred (3CC) and Halogen-to-Ligand charge transfer (3XLCT), the intensities of which are strictly related with the temperature. The CC transition, due to the presence of a metallophylic interactions, is prevalent at ambient temperature while the XLCT transition, located preferentially on the ligand part, became more prominent at low temperature. Since these pioneering works, it was easy to understand the photophysical properties of this compounds became more interesting in solid-state respect to solution with an improvement in emission efficiency. In this work we aim to characterize in SS organocopper(I)iodide compounds to valuate the correlation between the molecular crystal structure and the photophysical properties. It is also considered to hike new strategies to synthesize CuI complexes from the wet reactions to the more green solvent free methods. The advantages in using these strategies are evident but, obtain a single crystal suitable for SCXRD analysis from these batches is quite impossible. The structure solution still remains the key point in this research so we tackle this problem solving the structure by X-ray powder diffraction data. When the sample was fully characterized we moved to design and development of the associated OLED-device. Since copper iodide complexes are often insoluble in organic solvents, the high vacuum deposition technique is preferred. A new non-conventional deposition process have also been proposed to avoid the low complex stability in this practice with an in-situ complex formation in a layer-by layer deposition route.

Constraining mass and shape of galaxy clusters through large scale structures

The mass estimation of galaxy clusters is a crucial point for modern cosmology, and can be obtained by several different techniques. In this work we discuss a new method to measure the mass of galaxy clusters connecting the gravitational potential of the cluster with the kinematical properties of its surroundings. We explore the dynamics of the structures located in the region outside virialized cluster, We identify groups of galaxies, as sheets or filaments, in the cluster outer region, and model how the cluster gravitational potential perturbs the motion of these structures from the Hubble fow. This identification is done in the redshift space where we look for overdensities with a filamentary shape. Then we use a radial mean velocity profile that has been found as a quite universal trend in simulations, and we fit the radial infall velocity profile of the overdensities found. The method has been tested on several cluster-size haloes from cosmological N-body simulations giving results in very good agreement with the true values of virial masses of the haloes and orientation of the sheets. We then applied the method to the Coma cluster and even in this case we found a good correspondence with previous. It is possible to notice a mass discrepancy between sheets with different alignments respect to the center of the cluster. This difference can be used to reproduce the shape of the cluster, and to demonstrate that the spherical symmetry is not always a valid assumption. In fact, if the cluster is not spherical, sheets oriented along different axes should feel a slightly different gravitational potential, and so give different masses as result of the analysis described before. Even this estimation has been tested on cosmological simulations and then applied to Coma, showing the actual non-sphericity of this cluster.

COSMIC-LAB: Unexpected Results from High-resolution Spectra of AGB Stars in Globular Clusters

We have used high-resolution spectra, acquired with UVES@ESO-VLT, to determine the chemical abundances of different samples of AGB and RGB stars in 4 Galactic globular clusters, namely 47Tuc, NGC3201, M22 and M62. For almost all the analyzed AGB stars we found a clear discrepancy between the iron abundance measured from neutral lines and that obtained from single ionized lines, while this discrepancy is not obtained for the RGB samples observed in the same clusters and analyzed with the same procedure. Such a behavior exactly corresponds to what expected in the case of Non-Local Thermodynamical Equilibrium (NLTE) in the star atmosphere. These results have a huge impact on the proper determination of GC chemistry. In fact, one of the most intriguing consequences is that, at odds with previous claims, no iron spread is found in NGC3201 and M22 if the iron abundance is obtained from ionized lines only.

OpenMP task scheduling strategies to mitigate hardware variability in tightly-coupled shared memory clusters

In questa tesi sono stati apportati due importanti contributi nel campo degli acceleratori embedded many-core. Abbiamo implementato un runtime OpenMP ottimizzato per la gestione del tasking model per sistemi a processori strettamente accoppiati in cluster e poi interconnessi attraverso una network on chip. Ci siamo focalizzati sulla loro scalabilità e sul supporto di task di granularità fine, come è tipico nelle applicazioni embedded. Il secondo contributo di questa tesi è stata proporre una estensione del runtime di OpenMP che cerca di prevedere la manifestazione di errori dati da fenomeni di variability tramite una schedulazione efficiente del carico di lavoro.

The gas mass fraction and the dynamical state in x-ray luminous clusters of galaxies at low redshift

Gli ammassi di galassie sono le strutture gravitazionalmente legate con le più profonde buche di potenziale, pertanto è previsto che questi contengano una frazione di barioni non molto diversa da quella cosmologica. Con l’introduzione di modelli sempre più accurati di fisica barionica all’interno di simulazioni idrodinamiche è stato possibile predire la percentuale cosmica di barioni presente negli ammassi di galassie. Unendo questi modelli previsionali con misure della frazione di gas in ammassi e informazioni sulla densità di barioni dell’Universo si può ottenere una stima della densità di materia cosmica Ωm. L'obiettivo di questo lavoro di Tesi è la stima di Ωm a partire dalla frazione di gas osservata in questi sistemi. Questo lavoro era stato già fatto in precedenza, ma tenendo in considerazione solo gli ammassi più massivi e dinamicamente rilassati. Usando parametri che caratterizzano la morfologia della distribuzione di brillanza superficiale nei raggi X, abbiamo classificato i nostri oggetti come rilassati o disturbati, laddove presentassero evidenze di recenti attività di interazione. Abbiamo dunque valutato l’impatto degli oggetti disturbati sulla stima del parametro cosmologico Ωm, computando il Chi2 tra la frazione di massa barionica nell’Universo e quella da noi ricavata. Infine abbiamo investigato una relazione tra il valore della frazione di gas degli ammassi rilassati e quello dei disturbati, in modo da correggere quindi questi ultimi, riportandoli nei dintorni del valore medio per i rilassati e usarli per ampliare il campione e porre un vincolo più stringente su Ωm. Anche con il limitato campione a nostra disposizione, è stato possibile porre un vincolo più stretto su Ωm, utilizzando un maggior numero di oggetti e riducendo così l’errore statistico.

The relation between mass and concentration in x-ray galaxy clusters at high-redshift.

In this Thesis work we have studied the properties of high-redshift galaxy clusters through the X-ray emission from their intracluster gas. In particular, we have focused on the relation between concentration and mass that is related to the density of the universe at the formation time of the clusters and therefore, it is a powerful cosmological probe. Concentration is expected to be a decreasing function of mass but a complete characterization of this relation has not been reached yet. We have analysed 22 clusters observed withe the Chandra satellite at high redshift and we have investigated the concentration-mass relation.

Phosphonsäurehaltige polycyclische aromatische Kohlenwasserstoffe für Anwendungen in Brennstoffzellen

Die vorliegende Arbeit umfasst die Synthese und Charakterisierung phosphonsäurehaltiger, organischer Kristalle als ionenleitende Verbindungen in Brennstoffzellen-Anwendungen. Sie zielt dabei einerseits auf die Darstellung von protonenleitenden Polyphenylenverbindungen und deren Verwendung als Linker für den Aufbau protonenleitender Aluminium-Phosphonat-Netzwerke ab und behandelt andererseits die Einführung stark polarer Phosphonsäuregruppen in einen diskreten Nanographenkern sowie deren Einfluss auf die ionen- und elektronenleitenden Eigenschaften, um diese als gemischt-leitende Kompatibilisatoren an der isolierenden Elektrode/ Membran-Grenzfläche in einer Brennstoffzelle zu verwenden. Am Beispiel eines phosphonsäurefunktionalisierten, phenylenisch-expandierten Hexaphenylbenzols konnte ein solvothermisch stabiler Protonenleiter mit einer Selbstorganisation in kolumnare, supramolekulare Strukturen und hoher, temperaturunabhängiger Leitfähigkeit mit dominierendem Grotthuss-Anteil präsentiert werden. Durch einen Wechsel dieser 1D-radialen Phosphonsäureanordnung in der Molekülhülle hin zu 2D- und 3D-H2PO3-funktionalisierten, dendritischen Stäbchen- bzw. Kugelstrukturen konnte gezeigt werden, dass eine kolumnare Molekülanordnung jedoch kein notwendiges Kriterium für einen Grotthuss-artigen Protonentransport darstellt. Durch die mehrdimensionale Orientierung der Phosphonsäuren in der Außenhülle der Dendrimere garantieren die synthetisierten Strukturen hochaggregierte Phosphonsäurecluster, die als dichtes Säurekontinuum die eigentlichen protonenleitfähigen Kanäle darstellen und somit als entscheidendes Kriterium für das Auftreten eines Grotthuss-artigen Mechanismus definiert werden müssen. Eine signifikante Erhöhung der Leitfähigkeit konnte durch den Aufbau poröser, organisch-anorganischer Netzwerke (Al-HPB-NETs) über Komplexierung einer unterstöchiometrischen Menge an Aluminium-Kationen mit der Polyphosphonsäureverbindung Hexakis(p-phosphonatophenyl)benzol als Linkereinheit erfolgen, die anschließend mit kleinen intrinsischen Protonenleitern wie Phosphonsäure dotiert wurden. Diese dotierten Netzwerke wiesen außergewöhnliche Leitfähigkeit auf, da sie die σ-Werte des Referenzpolymers Nafion® bereits in einem Temperaturbereich oberhalb von 135°C übertrafen, aber gleichzeitig ein sehr gutes Säureretentionsverhalten von einem Gew.-% Säuredesorption über eine Immersionsdauer von 14 h gegenüber wässrigem Medium zeigten. Durch Mischen dieser Aluminiumphosphonate mit einer dotierten Polymermatrix wie PBI konnten synergistische Effekte durch zusätzliche attraktive H-Brückenbindungen zwischen molekular angebundener Phosphonsäure und mobiler H3PO4 an Hand eines signifikanten Leitfähigkeitsanstiegs für die resultierenden Membranen beobachtet werden. Die Protonenleitfähigkeit lag in diesen Materialien in dem gesamten untersuchten Temperaturbereich oberhalb von Nafion®. Durch das Einbringen der NETs in PBI konnte ebenfalls die Säureretention von PBI um etwa 9 % bei kurzen Immersionszeiten (bis 1 min) verbessert werden. Darüber hinaus wurde in der vorliegenden Arbeit die synthetische Kombination eines hydrophoben, elektronenleitenden Nanographenkerns mit einer, durch eine isolierende Peripherie getrennten, stark polaren, protonenleitenden Außenhülle realisiert. Am Beispiel von zwei phosphonsäurefunktionalisierten Triphenylenen, die sich in Länge und Planarität der gewählten Peripheriebausteine unterschieden, sollten polycyclische aromatische Kohlenwasserstoffe mit gemischt protonen- und elektronenleitenden Eigenschaften hergestellt werden, die über Impedanzspektroskopie und Vierpunktmessungen untersucht wurden. Da es sich bei der Anwendung solcher gemischtleitenden Verbindungen um grenz-flächenaktive Substanzen handelt, die das ohne verbesserte Anbindung bestehende Dielektrikum zwischen Elektrode und protonenleitender Membran überbrücken sollen, wurde die Untersuchung eines möglichen Elektronentransportes durch eine Molekülmonolage ebenfalls über kombinatorische STM- und STS-Technik durchgeführt.

Connection between x-ray and radio properties of cool-core galaxy clusters hosting radio mini-halos

Gli ammassi di galassie sono gli oggetti gravitazionalmente legati più grandi dell’Universo. Questi emettono principalmente in banda X tramite bremsstrahlung. Una frazione mostra anche emissione radio diffusa da parte di elettroni relativistici che spiraleggiano nel campo magnetico. Si possono classificare tre tipi di emissione: alon, relitti e mini-aloni radio (MH). I MH sono sorgenti radio su scale di ≥ 200 – 500 kpc, osservate al centro di ammassi caratterizzati dalla presenze di cool-core (CC). L’origine dei MH non è ancora chiara. Gli elettroni relativistici che emettono in banda radio hanno tempi di vita radiativi di molto inferiori a quelli necessari per diffondere sulle scale dell’emissione diffusa. Quindi non sono semplicemente iniettati dalle galassie presenti negli ammassi ed è necessario un meccanismo di accelerazione “in-situ” nell’ICM. I MH testimoniano la presenza di meccanismi che canalizzano parte del budget energetico disponibile nei CC nell’ICM.Quindi lo studio è importante per comprendere la fisica dell’ICM e l’interazione fra le componenti non termiche e termiche. I MH si formano attraverso la riaccelerazione delle particelle relativistiche ad opera della turbolenza del gas. L’origine di questa turbolenza tuttavia non è ancora ben compresa. Gli ammassi CC sono caratterizzati da un picco della brillanza X nelle regioni centrali e da un drop della temperatura verso il centro accompagnata da aumento della densità del gas. Si ritiene che questo sia dovuto al raffreddamento del gas che quindi fluisce nelle zone centrali. Recenti osservazioni in X risultan inconsistenti con il modello classico di CF, suggerendo la presenza di una sorgente di riscaldamento del gas su scale del core degli ammassi. Recentemente Zhuravleva (2014) hanno mostrato che il riscaldamento dovuto alla turbolenza prodotta dall'AGN centrale è in grado di bilanciare il processo di raffreddamento. Abbiamo assunto che la turbolenza responsabile del riscaldamento del gas è anche responsabile dell’accelerazione delle particelle nei MH. Nell’ambito di questo scenario ci si aspetta una correlazione tra la potenza del cooling flow, PCF, che è una misura del tasso di energia emessa dal gas che raffredda nei CC, e la luminosità radio, che è una frazione dell’energia della turbolenza che è canalizzata nell’accelerazione delle particelle. In questo lavoro di tesi abbiamo utilizzato il più grande campione disponibile di MH, allo scopo di studiare la connessione fra le proprietà dei MH e quelle del gas termico nei core degli ammassi che li ospitano. Abbiamo analizzato i dati di 21 ammassi e ricavato i parametri fisici all’interno del raggio di cooling e del MH. Abbiamo ricavato la correlazione fra luminosità radio, e PCF. Abbiamo trovato che le due quantità correlano in modo quasi-lineare confermando i risultati precedenti. Tale correlazione suggerisce uno stretto legame fra le proprietà del gas nei CC e l’origine dei MH.

Radio relics and magnetic fields in galaxy clusters

Radio relics are diffuse synchrotron sources generally located in the peripheries of galaxy clusters in merging state. According to the current leading scenario, relics trace gigantic cosmological shock waves that cross the intra-cluster medium where particle acceleration occurs. The relic/shock connection is supported by several observational facts, including the spatial coincidence between relics and shocks found in the X-rays. Under the assumptions that particles are accelerated at the shock front and are subsequently deposited and then age downstream of the shock, Markevitch et al. (2005) proposed a method to constrain the magnetic field strength in radio relics. Measuring the thickness of radio relics at different frequencies allows to derive combined constraints on the velocity of the downstream flow and on the magnetic field, which in turns determines particle aging. We elaborate this idea to infer first constraints on magnetic fields in cluster outskirts. We consider three models of particle aging and develop a geometric model to take into account the contribution to the relic transverse size due to the projection of the shock-surface on the plane of the sky. We selected three well studied radio relics in the clusters A 521, CIZA J2242.8+5301 and 1RXS J0603.3+4214. These relics have been chosen primarily because they are almost seen edge-on and because the Mach number of the shock that is associated with these relics is measured by X-ray observations, thus allowing to break the degeneracy between magnetic field and downstream velocity in the method. For the first two clusters, our method is consistent with a pure radiative aging model allowing us to derive constraints on the relics magnetic field strength. In the case of 1RXS J0603.3+4214 we find that particle life-times are consistent with a pure radiative aging model under some conditions, however we also collect evidences for downstream particle re-acceleration in the relic W-region and for a magnetic field decaying downstream in its E-region. Our estimates of the magnetic field strength in the relics in A 521 and CIZA J2242.8+5301 provide unique information on the field properties in cluster outskirts. The constraints derived for these relics, together with the lower limits to the magnetic field that we derived from the lack of inverse Compton X-ray emission from the sources, have been combined with the constraints from Faraday rotation studies of the Coma cluster. Overall results suggest that the spatial profile of the magnetic field energy density is broader than that of the thermal gas, implying that the ε_th /ε_B ratio decreases with cluster radius. Alternatively, radio relics could trace dynamically active regions where the magnetic field strength is biased high with respect to the average value in the cluster volume.