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At the center of galaxy clusters, a dramatic interplay known as feedback cycle occurs between the hot intracluster medium (ICM) and the active galactic nucleus (AGN) of the central galaxy. The footprints of this interplay are evident from X-ray observations of the ICM, where X-ray cavities and shock fronts are associated with radio lobe emission tracing energetic AGN outbursts. While such jet activity reduces the efficiency of the hot gas to cool to lower temperatures, residual cooling can generate warm and cold gas clouds around the central galaxy. The condensed gas parcels can ultimately reach the core of the galaxy and be accreted by the AGN. This picture is the result of tremendous advances over the last three decades. Yet, a deeper understanding of the details of how the heating–cooling regulation is achieved and maintained is still missing. In this Thesis, we delve into key aspects of the feedback cycle. To this end, we leverage high-resolution (sub-arcsecond), multifrequency observations (mainly X-ray and radio) of several top-level facilities (e.g., Chandra, JVLA, VLBA, LOFAR). First, we investigate which conditions trigger a feedback response to gas cooling, by studying the properties of clusters where feedback is just about to start. Then, we focus on the details of how the AGN–ICM interaction progresses by examining cavity and shock heating in the cluster RBS797, an exemplary case of the jet feedback paradigm. Furthermore, we explore the importance of shock heating and the coupling of distinct jet power regimes (i.e., FRII, FRI and FR0 radio galaxies) to the environment. Ultimately, as heating models rely on the connection between the direct evidence (the jets) and the smoking gun (the X-ray cavities) of feedback, we examine the cases in which these two are dramatically misaligned.

The Intracluster medium (ICM) is the best archive to consult when we want to retrieve information about the past and recent history of galaxy clusters. All those processes that can affect the dynamical state of these systems, such as merger events, are indeed expected to leave traces in the ICM distribution, both in the form of variations of integrated quantities and local edges and discontinuities. The detailed analysis of the X-ray morphology of galaxy clusters and its link to the non-thermal components have been the main goal of this PhD Thesis. Most of the studies carried out to investigate this topic have been realised using the complete XMM-Newton observations of the 118 galaxy clusters that are part of the Cluster HEritage project with XMM-Newton Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE). These X-ray maps allowed us to inspect the ICM distribution of the CHEX-MATE systems looking for an answer to the question: How do galaxy clusters appear?

This thesis comprehensively explores Active Galactic Nuclei (AGN) since cosmic noon and down to the lowest luminosities, utilizing a multiwavelength approach spanning X-ray to radio wavelengths. A key contribution is a method leveraging narrowband data from the miniJPAS survey, enabling the characterization of AGN properties while constraining their host galaxies. Robust physical parameters for X-ray-selected AGN up to z∼2.5 are derived. The analysis includes the examination of accretion ratios, a comparison with their proxies, and a forward modeling approach for assessing coevolution scenarios relative to local relations. Another significant contribution is a novel SED fitting module tailored for Low-Luminosity AGN (LLAGN), accurately characterizing their properties. Validated with diverse AGN samples, this module proves effective even in scenarios with galaxy contamination. The derived X-ray bolometric correction and exploration of UV-X-ray relations for LLAGN are presented. We further explore the host galaxy contamination problem and the possible impact of LLAGN on their host galaxies' specific star formation rate. The thesis concludes with a case study on how an LLAGN influences the interstellar medium of its host galaxy. High-resolution observations of the spiral galaxy M58 unveil H2 emission from warm molecular gas, indicating suppressed star formation in the inner kiloparsecs. Dust molecules remain unaffected compared to more luminous AGN. Optical forbidden line ratios suggest heating by low-velocity shocks caused by a low-power radio jet, highlighting the significant impact of LLAGN feedback on their host galaxies.

The exact mechanism that drove the formation of the bulge in the Milky Way and in analogous galaxies is still largely debated. Two main formation channels are currently invoked to reproduce the observed chemo-dynamical properties of the MW inner region: a dynamical secular evolution of the disk, and the merging at high redshift of massive clumps formedfrom the fragmentation of the primordial gas-rich disk. The global picture emerging from the photometric and spectroscopic analyses presented in this Thesis is that two peculiar Bulge stellar clusters, Terzan 5 and Liller 1, at odds with their appearance, did not undergo the same formation and evolution path of globular clusters (GCs). Conversely, they experienced a prolonged, multi-episode star formation history fueled by iron-enriched gas that had been deposited in the central region of the clusters. This is more likely explainable by invoking a self-enrichment process. These evidences make them strong candidate present-day remnants of the massive clumps observed in high-redshift galaxies, opening a new line of investigation: these peculiar stellar systems could represent the first observational proof of the hierarchical assembling process predicted by the clump-origin scenario, shedding new light on the formation of our bulge and galaxies’ bulges in a more general cosmological picture.

Gamma-Ray Bursts (GRBs) are brief flashes of gamma-rays that last from a fraction of second up to a few hundreds of seconds, during which a significant amount of isotropic equivalent energy is released (ranging from 10^48 to 10^54 erg). These explosive transients are associated with the catastrophic explosion of an isolated massive star (long-duration GRBs), or with the merger of compact objects (short-duration GRBs). Both scenarios lead to the formation of a highly magnetised neutron star or a spinning, stellar-mass black hole, which are thought to accrete material and launch two relativistic jets, causing the observed gamma-ray emission via magnetic processes or internal shocks. These jets interact with the surrounding material, producing the afterglow emission that extends from gamma-rays to radio waves. To understand GRB formation and evolution, a standard model involving an ultra-relativistic outflow is commonly employed. However, even sophisticated models face degeneracy in the multi-dimensional parameter space. To alleviate or possibly break the degeneracy, broad-band observations across the electromagnetic spectrum are crucial. In particular, the Very Long Baseline Interferometry technique (VLBI) has proven to be a unique asset, providing direct evidence of apparent superluminal expansion (for on-axis GRBs), centroid displacement of the outflow (for slightly off-axis GRBs) and the first confirmation that merger events can launch successful jets. In this Thesis, we employed radio and VLBI observations to characterise and constrain the outflow, the circum-burst medium, and the properties of the progenitors of GRBs. This included studies on individual events (GRB201015A and GRB221009A), which are important to test the predictions of current models, GRB host galaxies (GRB200716C), which are fundamental to constrain the nature of the progenitor through the characterisation of the surrounding environment, and the statistical properties of GRB afterglows, in order

In this Thesis, we present the study of the clustering properties of 1000 dark matter halo catalogues from the Pinocchio simulations. In this Thesis, we also present the results published in Romanello et al. (2024).

Blazars, active galactic nuclei with relativistic jets pointed to the observer, emit radiation across the spectrum and can produce neutrinos via hadronic processes. Being neutral and nearly massless, neutrinos offer unique insights into energetic astrophysical processes. The flaring gamma-ray blazar TXS0506+056 detected in spatial coincidence with the IceCube-170922A neutrino event confirmed theoretical expectations, emphasising the need for further observational insights into the neutrino-blazar connection. A part of this thesis investigates high-resolution VLBI (parsec-scale) regions of gamma-ray blazars coinciding with IceCube Neutrino Observatory detections. Our VLBI follow-ups aim to identify neutrino-emitting blazars by examining radio properties like coincident flares and jet morphology features. While some of the examined sources show hints of elevated activity at the neutrino arrival, further VLBI and MWL observations are essential for understanding the neutrino production mechanisms in blazars. The low-energy part of blazar broadband SEDs is explained with synchrotron radiation. Regarding the high-energy part, the ongoing debate involves hypotheses on hadronic processes and Inverse Compton scatterings - sometimes with the same low-energy synchrotron photons (SSC models). VHE (E > 100 GeV) long-term monitoring, as with the MAGIC telescopes, complemented with MWL observations, contributes to the comprehensive investigations of blazar emission mechanisms. A part of this thesis analyses a three-year (2020-2022) MWL monitoring of the blazar 1ES1959+650 during a low state. The flux and spectral variability are studied and the SEDs during different low and high VHE states in these three years are interpreted with SSC models. Findings are compared with past active and non-active states. The two parts of this project aim to deepen our understanding of particle acceleration complementarily, using radio and gamma-ray (+MWL) observations, considering future crucial ad

Dynamical models, even when simplified, are of great importance, because they can be used, for example, to understand the dynamics of more complicated (i.e., realistic) models, as well as to obtain first indications about sensible choices of parameters to be subsequently refined with more time-consuming numerical methods. In this Thesis we present the construction of galaxy models simple enough to provide some insight into the main structural and dynamical properties of real galaxies. The work focuses on axisymmetric Jeans modelling for galaxies, assumed to be stationary collisionless stellar systems. In particular, we consider ellipsoidal galaxies characterized by weakly flattened shape: this allows for the application of a technique, known as homoeoidal expansion, representing the theoretical framework underlying the entire modelling procedure. We apply this technique to two families of two-component galaxy models, solving the two-integral Jeans equations also in presence of a central black hole. The expansion method is then reviewed, analyzing and applying its two different interpretations to the case of simple one-component models: here the effectiveness of the homoeoidal approximation is examined using both analytical and numerical techniques; this method is finally adopted for the phenomenological interpretation of a real globular cluster. A part of the Thesis is devoted to the study of the polytropic accretion of gas onto the black hole at the centre of spherical galaxies, modelled as the spherical limit of one of the two families of axisymmetric models previously discussed. In order to study the motion of gas flows we generalize the classical Bondi problem by taking into account the effects of the gravitational field of the host galaxy, and the radiation pressure due to electron scattering. We also elucidate some important thermodynamical properties of accretion, determining the underlying cooling/heating function leading to the phenomenological value of the

The PhD thesis is focused on characterizing the properties of the obscuring torus in active galactic nuclei (AGN) by analyzing X-ray and multi-wavelength spectral energy distributions. The torus, consisting of molecular and dusty clouds, is believed to cause nuclear obscuration. However, its exact properties remain uncertain. AGN emit diffuse X-ray radiation, contributing significantly to the cosmic X-ray background (CXB), with Compton-thick AGN (CT-AGN) being major contributors around its peak energy. Despite this, observations reveal a discrepancy with AGN population synthesis models, indicating a need for a comprehensive census of obscured AGN at various wavelengths. In the first part of my thesis, I conducted X-ray spectral analysis on seven heavily obscured AGN candidates in the local Universe. Utilizing data from Chandra, XMM-Newton, and NuSTAR, I examined torus properties using advanced X-ray torus models. Results identified three bona fide CT-AGN and three Compton-Thin AGN. Notably, one source was found to be less obscured than previously thought, underscoring the importance of reliable constraint methods. Combining this analysis with previous studies, only a small fraction of AGN are CT-AGN, contrary to model predictions. In the second part, I focused on NGC 6300, a changing-look AGN candidate, conducting comprehensive X-ray spectroscopic analysis using advanced torus models. Results revealed no variability in line-of-sight column density but showed intrinsic flux variability. Additionally, evidence of an inner CT-ring of gas was found, contributing to reflection-dominated spectra. Optical to far-infrared band fluxes were extracted for broad-band spectral energy distribution fitting, allowing investigation of torus geometry and host galaxy properties. Overall, this research provides valuable insights into the properties and behavior of heavily obscured AGN and contributes to our understanding of the nature of the obscuring torus in AGN.

The molecular phase of the interstellar medium (ISM) is crucial for star formation (SF) and galaxy evolution, undergoing significant changes due to feedback processes from SF and active galactic nuclei (AGNs). Newly formed stars and AGNs emit high-energy radiation, creating photodissociation regions (PDRs) and X-ray dominated regions (XDRs) in the ISM, influencing its heating/cooling rates and chemistry. They also induce turbulence and molecular outflows, crucial for galaxy evolution. This thesis examines the impact of AGNs on molecular gas from radiative and kinematic perspectives, using observational and theoretical approaches. Carbon monoxide (CO) emission, its spectral line energy distribution (SLED), and spatially resolved kinematics are used to trace excitation conditions. A study on the relative contribution of SF and AGN in a new sample of local active galaxies is presented, along with a physically motivated model for estimating CO excitation and line emission in active galaxies. Finally, a detailed kinematical analysis is provided for the multiphase ISM in the nearby Seyfert NGC 5506. This thesis demonstrates that AGNs influence both the excitation and kinematics of molecular gas, primarily in central regions, potentially constraining SF efficiency and contributing to its quenching., La fase molecolare del mezzo interstellare (ISM) è essenziale per la formazione stellare (SF) e l'evoluzione galattica. Subisce cambiamenti significativi a causa dei processi di feedback da SF e nuclei galattici attivi (AGN). Le stelle di nuova formazione e gli AGN emettono radiazioni ad alta energia, creando regioni di fotodissociazione (PDRs) e regioni dominate dai raggi X (XDRs) nell'ISM, influenzandone i tassi di riscaldamento/raffreddamento e la chimica. Inoltre, inducono turbolenza e flussi molecolari, fondamentali per l'evoluzione galattica. Questa tesi analizza l'impatto degli AGN sul gas molecolare da prospettive radiative e cinematiche, utilizzando osservazioni e approcci teorici. Per tracciare le condizioni di eccitazione, si utilizza l'emissione di monossido di carbonio (CO), il suo spettro di distribuzione energetica delle righe (SLED) e la sua cinematica risolta spazialmente. Si studia il contributo relativo di SF e AGN in un nuovo campione di galassie attive locali, e si presenta un modello fisicamente motivato per stimare l'eccitazione del CO e la sua emissione in riga nelle galassie attive. Infine, si fornisce un'analisi cinematica dettagliata dell'ISM multifase nella Seyfert locale NGC 5506. Questa tesi dimostra che gli AGN influenzano sia l'eccitazione che la cinematica del gas molecolare, soprattutto nelle regioni centrali, e che questo può limitare l'efficienza della SF, contribuendo al suo spegnimento.

This Thesis explores two novel and independent cosmological probes, Cosmic Chronometers (CCs) and Gravitational Waves (GWs), to measure the expansion history of the Universe. CCs provide direct and cosmology-independent measurements of the Hubble parameter H(z) up to z∼2. In parallel, GWs provide a direct measurement of the luminosity distance without requiring additional calibration, thus yielding a direct measurement of the Hubble constant H0=H(z=0). This Thesis extends the methodologies of both of these probes to maximize their scientific yield. This is achieved by accounting for the interplay of cosmological and astrophysical parameters to derive them jointly, study possible degeneracies, and eventually minimize potential systematic effects. As a legacy value, this work also provides interesting insights into galaxy evolution and compact binary population properties. The first part presents a detailed study of intermediate-redshift passive galaxies as CCs, with a focus on the selection process and the study of their stellar population properties using specific spectral features. From their differential aging, we derive a new measurement of the Hubble parameter H(z) and thoroughly assess potential systematics. In the second part, we develop a novel methodology and pipeline to obtain joint cosmological and astrophysical population constraints using GWs in combination with galaxy catalogs. This is applied to GW170817 to obtain a measurement of H0. We then perform realistic forecasts to predict joint cosmological and astrophysical constraints from black hole binary mergers for upcoming gravitational wave observatories and galaxy surveys. Using these two probes we provide an independent reconstruction of H(z) with direct measurements of H0 from GWs and H(z) up to z∼2 from CCs and demonstrate that they can be powerful independent probes to unveil the expansion history of the Universe.

In this Thesis, we present a series of works that encompass the fundamental steps of cosmological analyses based on galaxy clusters, spanning from mass calibration to deriving cosmological constraints through counts and clustering. Firstly, we focus on the 3D two-point correlation function (2PCF) of the galaxy cluster sample by Planck Collaboration XXVII (2016). The masses of these clusters are expected to be underestimated, as they are derived from a scaling relation calibrated through X-ray observations. We derived a mass bias which disagrees with simulation predictions, consistent with what derived by Planck Collaboration VI (2020). Furthermore, in this Thesis we analyse the cluster counts and 2PCF, respectively, of the photometric galaxy cluster sample developed by Maturi et al. (2019), based on the third data release of KiDS (KiDS-DR3, de Jong et al. 2017). We derived constraints on fundamental cosmological parameters which are consistent and competitive, in terms of uncertainties, with other state-of-the-art cosmological analyses. Then, we introduce a novel approach to establish galaxy colour-redshift relations for cluster weak-lensing analyses, regardless of the specific photometric bands in use. This method optimises the selection completeness of cluster background galaxies while maintaining a defined purity threshold. Based on the galaxy sample by Bisigello et al. (2020), we calibrated two colour selections, one relying on the ground-based griz bands, and the other including the griz and Euclid YJH bands. In addition, we present the preliminary work on the weak-lensing mass calibration of the clusters detected by Maturi et al. (in prep.) in the fourth data release of KiDS (KiDS-1000, Kuijken et al. 2019). This mass calibration will enable the cosmological analyses based on cluster counts and clustering, from which we expect remarkable improvements in the results compared to those derived in KiDS-DR3.

Turbulence introduced into the intra-cluster medium (ICM) through cluster merger events transfers energy to non-thermal components (relativistic particles and magnetic fields) and can trigger the formation of diffuse synchrotron radio sources. Owing to their steep synchrotron spectral index, such diffuse sources can be better studied at low radio frequencies. In this respect, the LOw Frequency ARray (LOFAR) is revolutionizing our knowledge thanks to its unprecedented resolution and sensitivity below 200 MHz. In this Thesis we focus on the study of radio halos (RHs) by using LOFAR data. In the first part of this work we analyzed the largest-ever sample of galaxy clusters observed at radio frequencies. This includes 309 Planck clusters from the Second Data Release of the LOFAR Two Metre Sky Survey (LoTSS-DR2), which span previously unexplored ranges of mass and redshift. We detected 83 RHs, half of which being new discoveries. In 140 clusters we lack a detected RH; for this sub-sample we developed new techniques to derive upper limits to their radio powers. By comparing detections and upper limits, we carried out the first statistical analysis of populations of clusters observed at low frequencies and tested theoretical formation models. In the second part of this Thesis we focused on ultra-steep spectrum radio halos. These sources are almost undetected at GHz frequencies, but are thought to be common at low frequencies. We presented LOFAR observations of two interesting clusters hosting ultra-steep spectrum radio halos. With complementary radio and X-ray observations we constrained the properties and origin of these targets.

The presence of multiple stellar populations in globular clusters (GCs) is now well accepted, however, very little is known regarding their origin. In this Thesis, I study how multiple populations formed and evolved by means of customized 3D numerical simulations, in light of the most recent data from spectroscopic and photometric observations of Local and high-redshift Universe. Numerical simulations are the perfect tool to interpret these data: hydrodynamic simulations are suited to study the early phases of GCs formation, to follow in great detail the gas behavior, while N-body codes permit tracing the stellar component. First, we study the formation of second-generation stars in a rotating massive GC. We assume that second-generation stars are formed out of asymptotic giant branch stars (AGBs) ejecta, diluted by external pristine gas. We find that, for low pristine gas density, stars mainly formed out of AGBs ejecta rotate faster than stars formed out of more diluted gas, in qualitative agreement with current observations. Then, assuming a similar setup, we explored whether Type Ia supernovae affect the second- generation star formation and their chemical composition. We show that the evolution depends on the density of the infalling gas, but, in general, an iron spread is developed, which may explain the spread observed in some massive GCs. Finally, we focused on the long-term evolution of a GC, composed of two populations and orbiting the Milky Way disk. We have derived that, for an extended first population and a low-mass second one, the cluster loses almost 98 percent of its initial first population mass and the GC mass can be as much as 20 times less after a Hubble time. Under these conditions, the derived fraction of second-population stars reproduces the observed value, which is one of the strongest constraints of GC mass loss.

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.

This Thesis presents the results of my work on how galaxy clusters form by the accretion of sub-clumps and diffuse materials, and how the accreted energy is distributed in the X-ray emitting plasma. Indeed, on scales larger than tens of millions of light years, the Universe is self-organised by gravity into a spiderweb, the Cosmic Web. Galaxy clusters are the knots of this Cosmic Web, but a strong definition of filaments (which link different knots) and their physical proprieties, is still uncertain. Even if this pattern was determined by studying the spatial distribution of galaxies in the optical band, recently, also in the X-rays probes of filamentary structures around galaxy clusters were obtained. Therefore, given these observational facilities, the galaxy clusters’ outskirts are the best candidate regions to detect filaments and study their physical characteristics. However, from X-rays observations, we have only a few detections of cosmic filaments to date. On the other hand, it is crucial to understand how the accreted energy is dissipated in the baryon content of galaxy clusters and groups. Indeed, it is well known that in the central region of galaxy clusters and groups, the baryon fraction increases with the halo mass. On the outer region, the lack of X-rays constraints influences our understanding of the evolution of baryons in the halos volume. The standard assumption of “closed-box” system, for which the baryon fraction should approach the cosmological ratio Omega_bar/Omega_m, for galaxy clusters and groups seems to be too strong, especially for less massive objects. Moreover, a complete redshift evolution of baryons in galaxy clusters and groups is still missing.

White dwarfs (WDs) are electron-degenerate structures that are commonly assumed to evolve via a pure cooling process, with no stable thermonuclear activity at work. Their cooling rate is adopted as a cosmic chronometer to constrain the age of several Galactic populations, including the disk, Globular Clusters (GCs) and open clusters. This thesis work is aimed at the study of the WD populations in globular clusters and is articulated in two branches. The first was focused on the study of the bright portion of the WD cooling sequence. By analyzing high resolution UV data acquired with the Hubble Space Telescope (HST), we compared the WD luminosity functions (LFs) in four Galactic GCs (namely M13, M3, NGC6752, and M5) finding an unexpected over-abundance of WDs in M13 and NGC6752 with respect to M3 and M5. Theoretical models suggest that, consistently with the blue-tail horizontal branch (HB) morphology of M13 and NGC6752, this overabundance is due to a population of slowly cooling WDs, i.e., WDs fading more slowly than in a pure cooling process thanks to an extra-energy source provided by stable thermonuclear burning in their residual hydrogen-rich envelope. This is the first empirical evidence of WDs fading at a slower rate than usually assumed, and has a crucial impact on the use of the cooling sequence as a cosmic chronometer. The second branch was focused on the search for the companion star to binary millisecond Pulsars (MSP) in the globular clusters M13 and NGC 6652: the identified companions turned out to be helium-core WDs, and provided a invaluable constraints on the mass of the neutron star and the epoch of the MSP formation.

Understanding how Active Galactic Nuclei (AGN) shape galaxy evolution is a key challenge of modern astronomy. In the framework where black hole (BH) and galaxy growth are linked, AGN feedback must be tackled both at its “causes” (e.g. AGN-driven winds) and its “effects” (alteration of the gas reservoir in AGN hosts). The most informative cosmic time is z~1-3, at the peak of AGN activity and galaxy buildup, the so-called cosmic noon. The aim of this thesis is to provide new insights regarding some key questions that still remain open in this research field: i) What are the properties of AGN-driven sub-pc scale winds at z>1? ii) Are AGN-driven winds effective in influencing the life of galaxies? iii) Do AGN impact directly on star formation (SF) and gas content of their hosts? I first address AGN feedback as “caught in the act” by studying ultra-fast outflows (UFOs), X-ray AGN-driven winds, in gravitationally lensed quasars. I build the first statistically robust sample of high-z AGN, not preselected based on AGN-driven winds. I derive a first estimate of the high-z UFO detection fraction and measure the UFO duty cycle of a single high-z quasar for the first time. I also address the “effects” of AGN feedback on the life of host galaxies. If AGN influence galaxy growth, then they will reasonably impact the molecular gas reservoir first, and SF as a consequence. Through a comparative study of the molecular gas content in cosmic-noon AGN hosts and matched non-active galaxies (i.e., galaxies not hosting an AGN), we find that the host galaxies of more regular AGN (not selected to be the most luminous) are generally similar to non-active galaxies. However, we report on the possibility of a luminosity effect regulating the efficiency by which AGN might impact on galaxy growth.

This thesis presents a study of globular clusters (GCs), based on analysis of Monte Carlo simulations of globular clusters (GCs) with the aim to define new empirical parameters measurable from observations and able to trace the different phases of their dynamical evolution history. During their long term dynamical evolution, due to mass segregation and and dynamical friction, massive stars transfer kinetic energy to lower-mass objects, causing them to sink toward the cluster center. This continuous transfer of kinetic energy from the core to the outskirts triggers the runaway contraction of the core, known as "core collapse" (CC), followed by episodes of expansion and contraction called gravothermal oscillations. Clearly, such an internal dynamical evolution corresponds to significant variations also of the structure of the system. Determining the dynamical age of a cluster can be challenging as it depends on various internal and external properties. The traditional classification of GCs as CC or post-CC systems relies on detecting a steep power-law cusp in the central density profile, which may not always be reliable due to post-CC oscillations or other processes. In this thesis, based on the normalized cumulative radial distribution (nCRD) within a fraction of the half-mass radius is analyzed, and three diagnostics (A5, P5, and S2.5) are defined. These diagnostics show sensitivity to dynamical evolution and can distinguish pre-CC clusters from post-CC clusters.The analysis performed using multiple simulations with different initial conditions, including varying binary fractions and the presence of dark remnants showed the time variations of the diagnostics follow distinct patterns depending on the binary fraction and the retention or ejection of black holes. This analysis is extended to a larger set of simulations matching the observed properties of Galactic GCs, and the parameters show a potential to distinguish the dynamical stages of the observed clusters as we

Radio galaxies (RGs) are extremely relevant in addressing important unknowns concerning the interaction among black hole accretion, radio jets, and the environment. In the classical scheme, their accretion rate and ejection of relativistic jets are directly linked: efficient accretion (HERG) is associated with powerful edge-brightened jets (FRIIs); inefficient accretion (LERG) is associated with weak edge-darkened jets (FRIs). The observation of RGs with an inefficient engine associated with edge-brightened radio emission (FRII-LERGs) broke this scheme. FRII-LERGs constitute a suitable population to explore how accretion and ejection are linked and evaluate the environment's role in shaping jets. To this aim, we performed a multiwavelength study of different RGs catalogs spanning from Jy to mJy flux densities. At first, we investigated the X-ray properties of a sample of 51 FRIIs belonging to the 3CR catalog at z<0.3. Two hypotheses were invoked to explain FRII-LERGs behavior: evolution from classical FRIIs; the role of the environment. Next, we explored the mJy sky by studying the optical-radio properties of hundreds of RGs at z<0.15 (Best & Heckman 2012 sample). FRII-LERGs appear more similar to the old FRI-LERGs than to the young FRII-HERGs. These results point towards an evolutive scenario, however, nuclear time scale changes, star population aging, and kpc-Mpc radio structure modification do not agree. The role of the Mpc environment was then investigated. The Wen et al. 2015 galaxy clusters sample, built exploiting the SDSS survey, allowed us to explore the habitat of 7219 RGs at z<0.3. Most RGs are found to live in outside clusters. For these sources, differences among RG classes are still present. Thus, the environment is not the key parameter, and the possibility of intrinsic differences was reconsidered: we speculated that different black hole properties (spin and magnetic field at its horizon) could determine the observed spread in jet luminosity.

Globular clusters (GCs) are traditionally described as simple quasi-relaxed non-rotating stellar systems, characterized by spherical symmetry and isotropy in velocity space. However, recent studies have shown deviations from isotropic velocity distributions and significant internal rotation in many GCs, suggesting that their internal structure and kinematics are more complex than previously thought. The aim of this thesis is to investigate the internal kinematics of Galactic Globular Clusters (GGCs) as part of the Multi-Instrument Kinematic Survey (MIKiS), which exploits the capabilities of different ESO-VLT spectrographs to obtain comprehensive velocity dispersion (VD) and rotation profiles of GGCs. Moreover, this thesis has the particular goal of unraveling the kinematics of GC cores, which are still largely unexplored, by taking advantage of the exceptional spatial resolution of the adaptive-optics assisted integral-field spectrograph MUSE/NFM. The thesis presents a thorough kinematic study of three GGCs NGC 1904, NGC 6440, and NGC 6569. By combining the data sets acquired with four different spectrographs, we obtained the radial velocity (RV) of more than 1000 individual stars in each cluster, sampling from the innermost to the outermost regions. This allowed us to obtain the entire VD profile of each cluster and exclude the presence of an intermediate-mass black hole in the core of NGC 1904, at odds with previous findings obtained from integrated-light spectra. The studies also revealed signatures of internal rotation in each of the GCs studied. These results, supported by those of N-body simulations, prove that GCs were born with a significant initial rotation that they gradually lost through internal two-body relaxation and angular momentum loss carried away by escaping stars. Furthermore, we derived the structural parameters of NGC 6440 and NGC 6569, obtaining a comprehensive overview of the internal kinematics and structure of these GCs, which is necessary

Quasars beyond redshift z ~ 6 (age of the Universe < 1 Gyr) are the most luminous sources in the Universe and are believed to be the progenitors of present-day early-type massive galaxies. The immense luminosities from their active nuclei are powered by rapid accretion of matter onto a central supermassive black hole such that quasars outshine the starlight emission of their host galaxies. The fast growth of the black hole in these quasars pairs with the rapid consumption of huge gas reservoirs through vigorous episodes of star formation. Such active galactic nuclei can regulate the star formation activity in the host by expelling gas from galaxy via large-scale outflows thus constraining both the final stellar mass and dynamical properties of the host. This and other feedback mechanisms set a closely linked evolution between growing black holes and the assembling galaxies across the cosmic time, giving place to the black hole--galaxy scaling relations observed in the local Universe. The host galaxies of z > 6 quasars are therefore ideal laboratories to characterize the physical properties of the interstellar medium in extreme conditions, and they provide an insight of the interplay between star formation and black hole accretion in massive galaxies emerging from cosmic dawn. The redshift z ~ 6 range is of particular interest because it coincides with the last phase transition of the Universe -- from neutral to mostly ionized. Hence, z > 6 quasars can be used as beacons to shed new light on the properties of intergalactic medium at the end of the Epoch of Reionization. Models and numerical simulations of massive black hole formation at early epochs predict that z>6 quasars reside at the extreme peak of the large-scale density structure such that they can be used to pinpoint the first galaxy overdensities. [abridged]

Cosmic collisionless shocks are highly energetic phenomena in which different non-thermal processes take place. Above all, particle acceleration is arguably the most important, and observations of its signatures can be a powerful tool to constrain the local plasma and magnetic properties at the acceleration site. Within large-scale structures, the presence of cosmic rays can be revealed by means of different detection approaches: relativistic electrons can emit in radio via synchrotron radiation (radio relics), while energetic protons can interact with thermal protons of the intracluster medium and emit in the gamma-ray band. Both electrons and protons should in principle be accelerated by the first order Fermi acceleration mechanism known as diffusive shock acceleration: however, only evidence of cosmic-ray electrons has been detected so far in galaxy clusters, while no signatures of cosmic-ray proton have been reported. With a comprehensive analysis from 'macroscopic' to 'microscopic' scales, I address the missing gamma-ray issue by means of advanced numerical simulations, in which extragalactic magnetic fields are evolved together with the dynamics of large-scale structures. The primary factor at play is obliquity, the angle between the shock propagation direction and the magnetic field. I first determine the distribution of obliquity in cosmological simulations as a function of the medium in which the shock takes place. Then, I detect a pattern in the arrangement of the magnetic field around filaments and perform a quantitative study of the topological properties of the magnetic field surrounding the cosmic web. Finally, shocks in filaments are more closely investigated with new particle-in-cell simulations on much smaller scales, where the actual acceleration efficiency by realistic shocks can be measured. The new insights obtained from these numerical simulations provide a tool for the correct interpretation of observations and to estimate the magnetic propert

A stately fraction of the Universe volume is dominated by almost empty space. Alongside the luminous filamentary structures that make it up, there are vast and smooth regions that have remained outside the Cosmology spotlight during the past decades: cosmic voids. Although essentially devoid of matter, voids enclose fundamental information about the cosmological framework and have gradually become an effective and competitive cosmological probe. In this Thesis work we present fundamental results about the cosmological exploitation of voids. We focused on the number density of voids as a function of their radius, known as void size function, developing an effective pipeline for its cosmological usage. We proposed a new parametrisation of the most used theoretical void size function to model voids identified in the distribution of biased tracers (i.e. dark matter haloes, galaxies and galaxy clusters), a step of fundamental importance to extend the analysis to real data surveys. We then applied our built methodology to study voids in alternative cosmological scenarios. Firstly we exploited voids with the aim of breaking the degeneracies between cosmological scenarios characterised by modified gravity and the inclusion of massive neutrinos. Secondly we analysed voids in the perspective of the Euclid survey, focusing on the void abundance constraining power on dynamical dark energy models with massive neutrinos. Moreover we explored other void statistics like void profiles and clustering (i.e. the void-galaxy and the void-void correlation), providing cosmological forecasts for the Euclid mission. We finally focused on the probe combination, highlighting the incredible potential of the joint analysis of multiple void statistics and of the combination of the void size function with different cosmological probes. Our results show the fundamental role of the void analysis in constraining the fundamental parameters of the cosmological model and pave the way for future studies

This PhD project is aimed at investigating the chemical composition of the stellar populations in the closest satellites of the Milky Way (MW), namely the Large and Small Magellanic Cloud (LMC and SMC, respectively) and the remnant of the Sagittarius (Sgr) dwarf spheroidal galaxy. Their proximity allows us to resolve their individual stars both with spectroscopy and photometry, studying in detail the characteristics of their stellar populations. All these objects are interacting galaxies: LMC and SMC are in an early stage of a minor merger event, and Sgr is being disrupted by the tidal field of the MW. There is a plenty of literature regarding the chemical composition of these systems, however, the extension of these galaxies prevents a complete and homogeneous analysis. Therefore, we homogeneously analysed stellar spectra belonging to MW and its satellites galaxies and we derived their chemical compositions. We highlighted the importance of a homogeneous analysis in the comparison among different galaxies or different samples, to avoid systematics due to different methods or physical assumptions.

Diffuse radio emission in galaxy clusters has been observed with different size and properties. Giant radio halos (RH), Mpc-size sources found in merging clusters, and mini halos (MH), 0.1-0.5 Mpc size sources located in relaxed cool-core clusters, are thought to be distinct classes of objects with different formation mechanisms. However, recent observations have revealed the unexpected presence of diffuse emission on Mpc-scales in relaxed clusters that host a central MH and show no signs of major mergers. The study of these sources is still at the beginning and it is not yet clear what could be the origin of their unusual emission. The main goal of this thesis is to test the occurrence of these peculiar sources and investigate their properties using low frequency radio observations. This thesis consists in the study of a sample of 12 cool-core galaxy clusters which present some level of dynamical disturbances on large-scale. The heterogeneity of sources in the sample allowed me to investigate under which conditions a halo-type emission is present in MH clusters; and also to study the connection between AGN bubbles and the local environment. Using high sensitivity LOFAR observations, I have detected large-scale emission in four non-merging clusters, in addition to the central MH. I have constrained for the first time the spectral properties of diffuse emission in these double radio component galaxy clusters, and I have investigated the connection between their thermal and non-thermal emission for a better comprehension of the acceleration mechanism. Furthermore, I derived upper limits to the halo power for the other clusters in the sample, which could present large-scale diffuse emission under the detection threshold. Finally, I have reconstructed the duty-cycle of one of the most powerful AGN known, located at the centre of a galaxy cluster of the sample.

In this Thesis we focus on non-standard signatures from CMB polarisation, which might hint at the existence of new phenomena beyond the standard models for Cosmology and Particle physics. With the Planck ESA mission, CMB temperature anisotropies have been observed at the cosmic variance limit, but polarisation remains to be further investigated. CMB polarisation data are important not only because they contribute to provide tighter constraints of cosmological parameters but also because they allow the investigation of physical processes that would be precluded if just the CMB temperature maps were considered. We take polarisation data into account to assess the statistical significance of the anomalies currently observed only in the CMB temperature map and to constrain the Cosmic Birefringence (CB) effect, which is expected in parity-violating extensions of the standard electromagnetism. In particular, we propose a new one-dimensional estimator for the lack of power anomaly capable of taking both temperature and polarisation into account jointly. With the aim of studying the anisotropic CB we develop and perform two different and complementary methods able to evaluate the power spectrum of the CB. Finally, by employing these estimators and methodologies on Planck data we provide new constraints beyond what already known in literature. The measure of CMB polarisation represents a technological challenge and to make accurate estimates, one has to keep an exquisite control of the systematic effects. In order to investigate the impact of spurious signal in forthcoming CMB polarisation experiments, we study the interplay between half-wave plates (HWP) non-idealities and the beams. Our analysis suggests that certain HWP configurations, depending on the complexity of Galactic foregrounds and the beam models, significantly impacts the B-mode reconstruction fidelity and could limit the capabilities of next-generation CMB experiments. We provide also a first study of the impa

The correlations between the evolution of the Super Massive Black Holes (SMBHs) and their host galaxies suggests that the SMBH accretion on sub-pc scales (active galactice nuclei, AGN) is linked to the building of the galaxy over kpc scales, through the so called AGN feedback. Most of the galaxy assembly occurs in overdense large scale structures (LSSs). AGN residing in powerful sources in LSSs, such as the proto-brightest cluster galaxies (BCGs), can affect the evolution of the surrounding intra-cluster medium (ICM) and nearby galaxies. Among distant AGN, high-redshift radio-galaxies (HzRGs) are found to be excellent BCG progenitor candidates. In this Thesis we analyze novel interferometric observations of the so-called "J1030" field centered around the z = 6.3 SDSS Quasar J1030+0524, carried out with the Atacama large (sub-)millimetre array (ALMA) and the Jansky very large array (JVLA). This field host a LSS assembling around a powerful HzRG at z = 1.7 that shows evidence of positive AGN feedback in heating the surrounding ICM and promoting star-formation in multiple galaxies at hundreds kpc distances. We report the detection of gas-rich members of the LSS, including the HzRG. We showed that the LSS is going to evolve into a local massive cluster and the HzRG is the proto-BCG. we unveiled signatures of the proto-BCG's interaction with the surrounding ICM, strengthening the positive AGN feedback scenario. From the JVLA observations of the "J1030" we extracted one of the deepest extra-galactic radio surveys to date (~12.5 uJy at 5 sigma). Exploiting the synergy with the X-ray deep survey (~500 ks) we investigated the relation of the X-ray/radio emission of a X-ray-selected sample, unveiling that the radio emission is powered by different processes (star-formation and AGN), and that AGN-driven sample is mostly composed by radio-quiet objects that display a significant X-ray/radio correlation.

Queste note sono state trascritte in LATEX dalle dispense manoscritte delle Lezioni tenute nell’A.A. 2001/2002 nella Facoltà di Scienze MM. FF. NN. dell’Università di Bologna dal Prof. Daniele Cattani, libero Docente in Astrofisica Teorica, e debitamente aggiornate con le ultime scoperte.

Cool giant and supergiant stars are among the brightest populations in any stellar system and they are easily observable out to large distances, especially at infrared wavelengths. These stars also dominate the integrated light of star clusters in a wide range of ages, making them powerful tracers of stellar populations in more distant galaxies. High-resolution near-IR spectroscopy is a key tool for quantitatively investigating their kinematic, evolutionary and chemical properties. However, the systematic exploration and calibration of the NIR spectral diagnostics to study these cool stellar populations based on high-resolution spectroscopy is still in its pioneering stage. Any effort to make progress in the field is innovative and of impact on stellar archaeology and stellar evolution. This PhD project takes the challenge of exploring that new parameter space and characterizing the physical properties, the chemical content and the kinematics of cool giants and supergiants in selected disc fields and clusters of our Galaxy, with the ultimate goal of tracing their past and recent star formation and chemical enrichment history. By using optical HARPS-N and near-infrared GIANO-B high-resolution stellar spectra in the context of the large program SPA-Stellar Population Astrophysics: the detailed, age-resolved chemistry of the Milky Way disk” (PI L. Origlia), an extensive study of Arcturus, a standard calibrator for red giant stars, has been performed. New diagnostics of stellar parameters as well as optimal linelists for chemical analysis have been provided. Then, such diagnostics have been used to determine evolutionary properties, detailed chemical abundances of almost 30 different elements and mixing processes of a homogeneous sample of red supergiant stars in the Perseus complex.

Dynamical models of stellar systems represent a powerful tool to study their internal structure and dynamics, to interpret the observed morphological and kinematical fields, and also to support numerical simulations of their evolution. We present a method especially designed to build axisymmetric Jeans models of galaxies, assumed as stationary and collisionless stellar systems. The aim is the development of a rigorous and flexible modelling procedure of multicomponent galaxies, composed of different stellar and dark matter distributions, and a central supermassive black hole. The stellar components, in particular, are intended to represent different galaxy structures, such as discs, bulges, halos, and can then have different structural (density profile, flattening, mass, scale-length), dynamical (rotation, velocity dispersion anisotropy), and population (age, metallicity, initial mass function, mass-to-light ratio) properties. The theoretical framework supporting the modelling procedure is presented, with the introduction of a suitable nomenclature, and its numerical implementation is discussed, with particular reference to the numerical code JASMINE2, developed for this purpose. We propose an approach for efficiently scaling the contributions in mass, luminosity, and rotational support, of the different matter components, allowing for fast and flexible explorations of the model parameter space. We also offer different methods of the computation of the gravitational potentials associated of the density components, especially convenient for their easier numerical tractability. A few galaxy models are studied, showing internal, and projected, structural and dynamical properties of multicomponent galaxies, with a focus on axisymmetric early-type galaxies with complex kinematical morphologies. The application of galaxy models to the study of initial conditions for hydro-dynamical and $N$-body simulations of galaxy evolution is also addressed, allowing in particular to i

Investigating the mechanisms that regulate star formation (SF) across cosmic time is a complex issue. Most of our knowledge of the cosmic SF history at z > 3 relies on UV surveys, which could miss SF obscured by dust. IR/mm-selections of galaxies are thus a crucial tool for unveiling the total amount of SF. In addition, active galactic nuclei (AGN) are considered to play a crucial role in galaxy evolution. According to models, AGN could be decisive in suppressing SF in massive galaxies. Despite this, some theories predict that AGN could also trigger SF inside outflows. These two mechanisms have been named as “negative” and “positive” AGN feedback and their study is crucial to understand what regulates SF inside galaxies. The aim of this thesis is to investigate the processes that fuel and suppress SF across cosmic time. On one side, we focused on the study of cold gas in the early Universe. We derived the first [C II] luminosity function at z~5 from a mm-selection of galaxies. By using [C II] as a SF rate indicator, we measured the cosmic SF rate density at z~5, which shows a possible excess compared to previous estimates. On the other side, we studied the impact of negative and positive AGN feedback on SF. First, we investigated negative feedback in a massive galaxy at z~2, which will possibly evolve into a passive galaxy. Then, we studied positive feedback in a sample of 70 nearby star-forming galaxies by using UV spectroscopy. We detected in several objects blueshifted stellar absorption, which could be indicative of young stars formed inside outflows. Despite the uncertainties affecting our analysis, studying cold gas and AGN feedback represents a powerful approach to constrain the processes that feed and quench SF across cosmic time.

Galaxy clusters are complex ecosystems, where galaxies with powerful active galactic nuclei, thermal plasma, magnetic fields, and cosmic rays can interact and flourish in spectacular astrophysical phenomena. Decades of studies have investigated these systems, and as the boundaries of our knowledge were pushed forward, new questions emerged awaiting to be answered. The main focus of this Thesis is the interplay between the relativistic and thermal plasma of the intra-cluster medium. The study of the intra-cluster medium (ICM) allows to understand the way energy is injected from large scale dynamics and dissipated in different channels. These channels include viscous heating and the generation of non-thermal components that, eventually, generate diffuse radio emission. Furthermore, studying the ICM provides complementary insights into the physics of cluster galaxy evolution. We mainly focus on the case of relaxed galaxy clusters, where the connection between the central, massive, radio-loud galaxies and the diffuse radio emission is still unclear. In this context, we investigate also the interactions between the ICM and the cluster galaxies. The cornerstone of our works is a multi-wavelength analysis based on radio and X-ray observations, which features brand-new Low-Frequency Array (LOFAR) observations and new approaches to the study of the spatial correlation between these emissions.

The observation of diffuse synchrotron radio emission in galaxy clusters reveals the existence of relativistic electrons and large-scale magnetic fields permeating the intra-cluster volume. Shocks developed during mergers of galaxy clusters are thought to originate the elongated, arc-shaped, and polarized sources found in cluster outskirts known as radio relics. The properties of the magnetic fields in radio relics, the possible magnetic field amplification caused by the shock passage, and its connection to the relics formation mechanism, as well as the value of large-scale magnetic fields in cluster outskirts, are the main topics addressed in this Thesis. Using polarimetric radio observations performed with the Jansky Very Large Array (JVLA) and with the Low Frequency Array (LOFAR), I have investigated the properties of magnetic fields in galaxy clusters outskirts via both statistical Faraday rotation measures and diffuse source polarimetry. The comparison of measured quantities with advanced numerical simulations of, both, radio relic emission and intra-cluster magnetic fields has proved to be a fundamental tool to constrain magnetic field physical parameters. Among the results, the Faraday rotation studies of two double relic galaxy clusters presented in this Thesis show that magnetic-fields are not significantly amplified in the shock region. Despite this, low Mach numbers shocks can stretch and align magnetic field lines, which appear well ordered on the emission scales of radio relics from polarimetric observations. The magnetic field structure inside radio relics is complex and likely filamentary. These results will be corroborated by an ongoing systematic study of clusters with double radio relics. The results achieved in this Thesis proved the extraordinary potential of low-frequency polarization observations for the study of large-scale magnetic fields in the outskirts of galaxy clusters and beyond.