Measurement of the top quark mass in multijet events with the CMS experiment at LHC

La massa del quark top è qui misurata per mezzo dei dati raccolti dall’esperimento CMS in collisioni protone-protone ad LHC, con energia nel centro di massa pari ad 8 TeV. Il campione di dati raccolto corrisponde ad una luminosità integrata pari a 18.2 /fb. La misura è effettuata su eventi con un numero di jet almeno pari a 6, di cui almeno due b-taggati (ovvero identificati come prodotto dell’adronizzazione di due quark bottom). Il valore di massa trovato è di (173.95 +- 0.43 (stat)) GeV/c2, in accordo con la media mondiale. The top quark mass is here measured by using the data that have been collected with the CMS experiment in proton-proton collisions at the LHC, at a center-of-mass energy of 8 TeV. The dataset which was used, corresponds to an integrated luminosiy of 18.2 /fb. The mass measurement is carried out by using events characterized by six or more jets, two of which identified as being originated by the hadronization of bottom quarks. The result of the measurement of the top quark mass performed here is: (173.95 +- 0.43 (stat)) GeV/c2, in accordance with the recently published world average.

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 (4In a few hundred Myrs, galaxies increase their stellar mass, change their morphological type and progressively become more obscured due to increased dust attenuation of the UV light. Therefore, determining physical parameters regarding dust is essential to trace the history of the star formation rate (SFR). The main purpose of this thesis is to determine the spatial extent of the dust emission in high-redshift galaxies and to provide a lower limit on dust temperature, to constrain the dust mass. This is achieved by studying 23 FIR continuum detected main-sequence galaxies of the ALMA Large Program to INvestigate (ALPINE) survey, performed at high redshift (4inally, we put these results in a broader context, by studying the dust size evolution as a function of cosmic 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⊙.

Modelling the Halo mass number counts in modified gravity cosmological scenarios

In this Thesis work we investigate some of different cosmological background scenarios using one of the main probes used in cosmology: the halo mass function. The observed abundance of galaxy clusters (or similarly DM haloes) can indeed be compared to its theoretical predictions to derive fundamental constrains on the cosmological scenario assumed. Given the importance of exploring and constraining models degenerate with the ΛCDM one, we test the applicability of some notable halo mass function models to these scenarios. To this purpose, we made use of the DUSTGRAIN-pathfinder N-body simulations, which assume cosmological scenarios that include modified gravity in the form of f(R) models and massive neutrinos. We carried on the analysis of 3 simulation snapshots at different redshifts, z = 0, 0.5, 1, building multiple samples of dark matter haloes by applying different overdensity thresholds during the procedure of halo identification. We started our analysis by considering the halo mass function model introduced by Despali et al. (2016), who proposed a parametrization that encapsulates the effect of the different halo mass definitions and the relative evolution with the redshift. We calibrated the main parameters of this relation by using the ΛCDM halo catalogues extracted from the DUSTGRAIN-pathfinder simulations, fitting the measured halo abundances at all redshifts and density thresholds. Afterwards we tested the same model parametrization with halo catalogues extracted from the simulations implementing both modified gravity and massive neutrinos. We repeated therefore the calibration procedure on these data to search for discrepancies with respect to the ΛCDM model. Finally we focused the analysis on the cosmological models implementing modified gravity only. We took our ΛCDM calibrated halo mass function and we modified it with the additional f (R) gravity form proposed by Gupta et al. (2022).

A study of the turbulence of the neutral medium in two nearby spiral galaxies

The width of the 21 cm line (HI) emitted by spiral galaxies depends on the physical processes that release energy in the Interstellar Medium (ISM). This quantity is called velocity dispersion (σ) and it is proportional first of all to the thermal kinetic energy of the gas. The accepted theoretical picture predicts that the neutral hydrogen component (HI) exists in the ISM in two stable phases: a cold one (CNM, with σ~0.8 km/s) and a warm one (WNM, with σ~8 km/s). However, this is called into question by the observation that the HI gas has usually larger velocity dispersions. This suggests the presence of turbulence in the ISM, although the energy sources remain unknown. In this thesis we want to shed new light on this topic. We have studied the HI line emission of two nearby galaxies: NGC6946 and M101. For the latter we used new deep observations obtained with the Westerbork radio interferometer. Through a gaussian fitting procedure, we produced dispersion maps of the two galaxies. For both of them, we compared the σ values measured in the spiral arms with those in the interarms. In NGC6946 we found that, in both arms and interarms, σ grows with the column density, while we obtained the opposite for M 101. Using a statistical analysis we did not find a significant difference between arm and interarm dispersion distributions. Producing star formation rate density maps (SFRD) of the galaxies, we studied their global and local relations with the HI kinetic energy, as inferred from the measured dispersions. For NGC6946 we obtained a good log-log correlation, in agreement with a simple model of supernova feedback driven turbulence. This shows that in this galaxy turbulent motions are mainly induced by the stellar activity. For M 101 we did not find an analogous correlation, since the gas kinetic energy appears constant with the SFRD. We think that this may indicate that in this galaxy turbulence is driven also by accretion of extragalactic material.

Galactic fountain flows in high-resolution hydrodynamical simulations of galaxy disks

Feedback from the most massive components of a young stellar cluster deeply affects the surrounding ISM driving an expanding over-pressured hot gas cavity in it. In spiral galaxies these structures may have sufficient energy to break the disk and eject large amount of material into the halo. The cycling of this gas, which eventually will fall back onto the disk, is known as galactic fountains. We aim at better understanding the dynamics of such fountain flow in a Galactic context, frame the problem in a more dynamic environment possibly learning about its connection and regulation to the local driving mechanism and understand its role as a metal diffusion channel. The interaction of the fountain with a hot corona is hereby analyzed, trying to understand the properties and evolution of the extraplanar material. We perform high resolution hydrodynamical simulations with the moving-mesh code AREPO to model the multi-phase ISM of a Milky Way type galaxy. A non-equilibrium chemical network is included to self consistently follow the evolution of the main coolants of the ISM. Spiral arm perturbations in the potential are considered so that large molecular gas structures are able to dynamically form here, self shielded from the interstellar radiation field. We model the effect of SN feedback from a new-born stellar cluster inside such a giant molecular cloud, as the driving force of the fountain. Passive Lagrangian tracer particles are used in conjunction to the SN energy deposition to model and study diffusion of freshly synthesized metals. We find that both interactions with hot coronal gas and local ISM properties and motions are equally important in shaping the fountain. We notice a bimodal morphology where most of the ejected gas is in a cold $10^4$ K clumpy state while the majority of the affected volume is occupied by a hot diffuse medium. While only about 20\% of the produced metals stay local, most of them quickly diffuse through this hot regime to great scales.