Obscured AGN in deep fields: tracing accretion and star-formation up to z ∼ 5

The discovery of scaling relations between the mass of the SMBH and some key physical properties of the host galaxy suggests that the growth of the SMBH and that of the galaxy are coupled, with the AGN activity and the star-formation (SF) processes influencing each other. Although the mechanism of this co-evolution are still a matter of debate, all scenarios agree that a key phase of the co-evolution is represented by the obscured accretion phase. This phase is of the co-evolution is the least studied, mostly due to the challenge in detecting and recognizing such obscured AGN. My thesis aims at investigating the AGN-galaxy co-evolution paradigm by identifying and studying AGN in the obscured accretion phase. The study of obscured AGN is key for our understanding of the feedback processes and of the mutual influence of the SF and the AGN activity. Moreover, these obscured and elusive AGN are needed to explain the X-ray background spectrum and to reconcile the measurements and the theoretical prediction of the BH accretion rate density. In this thesis, we firstly investigate the synergies between IR and X-ray missions in detecting and characterizing AGN, with a particular focus on the most obscured ones. We exploited UV/optical emission lines to select high-redshift obscured AGN at the cosmic noon, where the highest SFR density and BH accretion rate density are expected. We provide X-ray spectral analysis and UV-to-far-IR SED-fitting. We show that our samples host a significant fraction of very obscured sources; many of these are highly accreting. Finally, we performe a thoughtful investigation of a galaxy at z~5 with unusual and peculiar features, that lead us to identify a second extremely young population of stars and hidden AGN activity.

Pulse shape studies of neutral particles with a liquid scintillator

The hadrontherapy exploits beams of charged particles against deep cancers. These ions have a depth-dose profile in which there is a little release of energy at the beginning of their path, whereas there is a sharp maximum, the Bragg Peak, near its end path. However, if heavy ions are used, the fragmentation of the projectile can happen and the fragments can release some dose outside the treatment volume beyond the Bragg peak. The fragmentation process takes place also when the Galactic Cosmic Rays at high energy hit the spaceship during space missions. In both cases some neutrons can be produced and if they interact with the absorbing materials nuclei some secondary particles are generated which can release energy. For this reason, studies about the cross section measurements of the fragments generated during the collisions of heavy ions against the tissues nuclei are very important. In this context, the FragmentatiOn Of Target (FOOT) experiment was born, and aims at measuring the differential and double differential fragmentation cross sections for different kinetic energies relevant to hadrontherapy and space radioprotection with high accuracy. Since during fragmentation processes also neutrons are produced, tests of a neutron detection system are ongoing. In particular, recently a neutron detector made up of a liquid organic scintillator, BC-501A with neutrons/gammas discrimination capability was studied, and it represents the core of this thesis. More in details, an analysis of the data collected at the GSI laboratory, in Darmstadt, Germany, is effectuated which consists in discriminating neutral and charged particles and then to separate neutrons from gammas. From this analysis, a preliminary energy-differential reaction cross-section for the production of neutrons in the 16O + (C_2H_4)_(n) and 16O + C reactions was estimated.

Primordial black holes from multi-field inflation

In this master's thesis, the formation of Primordial Black Holes (PBHs) in the context of multi-field inflation is studied. In these models, the interaction of isocurvature and curvature perturbations can lead to a significant enhancement of the latter, and to the subsequent production of PBHs. Depending on their mass, these can account for a significant fraction (or, in some cases, the entirety) of the universe's Dark Matter content. After studying the theoretical framework of generic N-field inflationary models, the focus is restricted to the two-field case, for which a few concrete realisations are analysed. A numerical code (written in Wolfram Mathematica) is developed to make quantitative predictions for the main inflationary observables, notably the scalar power spectra. Parallelly, the production of PBHs due to the dynamics of 2-field inflation is examined: their mass, as well as the fraction of Dark Matter they represent, is calculated for the models considered previously.

Investigating the origin of radio emission from the intra-cluster bridge A399-A401

Radio bridges are a newly observed class of phenomena, they are large scale filamentary structures that span between pairs of clusters in a pre-merger phase. In my Thesis, starting from the observed synchrotron emission in the bridge A399-A401, I apply a Fermi I shock re-acceleration model under different conditions to the bridge. The purpose of my work is to check the likelihood of the above mentioned model. In particular the Inverse Compton emission that the model predicts is above the current observational constraints on Inverse Compton for the bridge A399-A401, this means that a Fermi I re-acceleration model is unlikely to describe the emission from the bridge, while a Fermi II turbulent re-acceleration model could still explain the origin of the emission in the bridge.

A next-to-leading order calculation of the impact of primordial magnetic fields into cosmological observables

In this thesis, we perform a next-to-leading order calculation of the impact of primordial magnetic fields (PMF) into the evolution of scalar cosmological perturbations and the cosmic microwave background (CMB) anisotropy. Magnetic fields are everywhere in the Universe at all scales probed so far, but their origin is still under debate. The current standard picture is that they originate from the amplification of initial seed fields, which could have been generated as PMFs in the early Universe. The most robust way to test their presence and constrain their features is to study how they impact on key cosmological observables, in particular the CMB anisotropies. The standard way to model a PMF is to consider its contribution (quadratic in the magnetic field) at the same footing of first order perturbations, under the assumptions of ideal magneto-hydrodynamics and compensated initial conditions. In the perspectives of ever increasing precision of CMB anisotropies measurements and of possible uncounted non-linear effects, in this thesis we study effects which go beyond the standard assumptions. We study the impact of PMFs on cosmological perturbations and CMB anisotropies with adiabatic initial conditions, the effect of Alfvén waves on the speed of sound of perturbations and possible non-linear behavior of baryon overdensity for PMFs with a blue spectral index, by modifying and improving the publicly available Einstein-Boltzmann code SONG, which has been written in order to take into account all second-order contributions in cosmological perturbation theory. One of the objectives of this thesis is to set the basis to verify by an independent fully numerical analysis the possibility to affect recombination and the Hubble constant.

Amplification mechanisms of inflationary spectra in induced gravity

Inflation is the primordial stage of accelerated expansion of the Universe which solves the issues of the initial conditions of a decelerating Universe (horizon, flatness and entropy problems). Moreover, it is supposed that quantum fluctuations originated during the first moments after the Big Bang gave rise to the formation of galaxies and other structures of the Universe when inflation ends. Among these structures also primordial black holes (PBHs) may have been generated. The interest in PBHs relies on their possible connection with dark matter: they could constitute a portion or even the whole dark matter content of our Universe.\\ In this work we consider inflation in the Induced Gravity (IR) context and study possible mechanisms of amplification of the curvature perturbations generated during the cosmic acceleration. In particular we consider the possibility of a period of Constant Roll (CR). Starting from the previous work of Starobinsky et al. Our final purpose is to analyse the power spectrum of the scalar perturbations and to find in which conditions there is an enhancement of the power spectrum possibly leading to PBHs formation.

Uno studio della massima energia raggiungibile da nuove classi di acceleratori cosmici

I raggi cosmici sono particelle energetiche provenienti dallo spazio esterno, alle quali è esposto qualunque corpo celeste dell’Universo. Possono essere leptoni, mesoni, barioni o loro stati aggregati, ad un energia che spazia diversi ordini di grandezza rendendo così la loro natura e la loro origine complessa da studiare. Risulta interessante la massima energia che essi possono avere, ma non risulta semplice studiare come riescono a raggiungerla. Una classe di raggi cosmici sui quali le informazioni sono ancora scarse sono gli ultra high energy cosmic rays (UHECRs), ovvero i raggi cosmici con un’energia superiore a 1e18 eV. Oltre ad essere molto raro rilevarli, non si `e nemmeno a conoscenza da cosa possano essere originati. In questo testo verrà spiegato come un raggio cosmico può accrescere la sua energia e verrà stimato se tre potenziali sorgenti possano o meno generare raggi cosmici ad altissima energia. Si osserva che i tre candidati, ovvero i filamenti cosmici, il ponte intracluster tra Abell 0399 e Abell 0401 e la radiogalassia gigante Alcioneo, non soddisfano le caratteristiche per essere la fonte di UHECRs ad altissima energia, potendo al più raggiungere energie di 3.5e19 eV, a patto che i raggi cosmici siano composti da nuclei di ferro.

Calibration of the detector flight models for the HERMES and SPIRIT nanosatellite missions

The High Energy Rapid Modular Ensemble of Satellites (HERMES) is a new mission concept involving the development of a constellation of six CubeSats in low Earth orbit with new miniaturized instruments that host a hybrid Silicon Drift Detector/GAGG:Ce based system for X-ray and γ-ray detection, aiming to monitor high-energy cosmic transients, such as Gamma Ray Bursts and the electromagnetic counterparts of gravitational wave events. The HERMES constellation will also operate together with the Australian-Italian SpIRIT mission, which will house a HERMES-like detector. The HERMES pathfinder mini-constellation, consisting of six satellites plus SpIRIT, is likely to be launched in 2023. The HERMES detectors are based on the heritage of the Italian ReDSoX collaboration, with joint design and production by INFN-Trieste and Fondazione Bruno Kessler, and the involvement of several Italian research institutes and universities. An application-specific, low-noise, low-power integrated circuit (ASIC) called LYRA was conceived and designed for the HERMES readout electronics. My thesis project focuses on the ground calibrations of the first HERMES and SpIRIT flight detectors, with a performance assessment and characterization of the detectors. The first part of this work addresses measurements and experimental tests on laboratory prototypes of the HERMES detectors and their front-end electronics, while the second part is based on the design of the experimental setup for flight detector calibrations and related functional tests for data acquisition, as well as the development of the calibration software. In more detail, the calibration parameters (such as the gain of each detector channel) are determined using measurements with radioactive sources, performed at different operating temperatures between -20°C and +20°C by placing the detector in a suitable climate chamber. The final part of the thesis involves the analysis of the calibration data and a discussion of the results.

Fermion masses, leptogenesis and gravitational waves in SO(10)

Grand Unification Theories (GUTs) predict the unification of three of the fundamental forces and are a possible extension of the Standard Model, some of them predict neutrino mass and baryon asymmetry. We consider a minimal non-supersymmetric $SO(10)$ GUT model that can reproduce the observed fermionic masses and mixing parameters of the Standard Model. We calculate the scales of spontaneous symmetry breaking from the GUT to the Standard Model gauge group using two-loop renormalisation group equations. This procedure determines the proton decay rate and the scale of $U(1)_{B-L}$ breaking, which generates cosmic strings, and the right-handed neutrino mass scales. Consequently, the regions of parameter space where thermal leptogenesis is viable are identified and correlated with the fermion masses and mixing, the neutrinoless double beta decay rate, the proton decay rate, and the gravitational wave signal resulting from the network of cosmic strings. We demonstrate that this framework, which can explain the Standard Model fermion masses and mixing and the observed baryon asymmetry, will be highly constrained by the next generation of gravitational wave detectors and neutrino oscillation experiments which will also constrain the proton lifetime

Constraining FIR size, dust temperature and dust mass in ALPINE galaxies at redshift 4

The study of galaxies at high redshift plays a crucial role to understand the mechanism of galaxy formation and evolution. At redshifts just after the epoch of re-ionization (4cosmic time. We derive dust size measurements via a Gaussian fit in the image and uv plane. Out of the 23 FIR-continuum-detected targets, 20 have been considered in this work since they are isolated systems. Of these 20, 7 are spatially resolved; for each of the remaining 13, we provide an upper limit to the dust size. We find that the gas emission is more extended than the dust spatial scale, by a factor of 1.40±0.29, while the latter appears to be larger than the stellar emission size. Moreover, we do not find any significant trend for dust size as a function of the stellar mass and the redshift. In addition, we provide a minimum dust temperature estimate for the 7 resolved sources, for which we find Tmin∼16−19K. We also derive dust masses for the resolved sources, logMdust∼7−8M⊙.