Improving the cosmic distance ladder. Distance and structure of the Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is widely considered as the first step of the cosmological distance ladder, since it contains many different distance indicators. An accurate determination of the distance to the LMC allows one to calibrate these distance indicators that are then used to measure the distance to far objects. The main goal of this thesis is to study the distance and structure of the LMC, as traced by different distance indicators. For these purposes three types of distance indicators were chosen: Classical Cepheids,``hot'' eclipsing binaries and RR Lyrae stars. These objects belong to different stellar populations tracing, in turn, different sub-structures of the LMC. The RR Lyrae stars (age >10 Gyr) are distributed smoothly and likely trace the halo of the LMC. Classical Cepheids are young objects (age 50-200 Myr), mainly located in the bar and spiral arm of the galaxy, while ``hot'' eclipsing binaries mainly trace the star forming regions of the LMC. Furthermore, we have chosen these distance indicators for our study, since the calibration of their zero-points is based on fundamental geometric methods. The ESA cornerstone mission Gaia, launched on 19 December 2013, will measure trigonometric parallaxes for one billion stars with an accuracy of 20 micro-arcsec at V=15 mag, and 200 micro-arcsec at V=20 mag, thus will allow us to calibrate the zero-points of Classical Cepheids, eclipsing binaries and RR Lyrae stars with an unprecedented precision.

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.

Black Hole and Galaxy Growth over Cosmic Time: the Chandra COSMOS Legacy Survey

The study of supermassive black hole (SMBH) accretion during their phase of activity (hence becoming active galactic nuclei, AGN), and its relation to the host-galaxy growth, requires large datasets of AGN, including a significant fraction of obscured sources. X-ray data are strategic in AGN selection, because at X-ray energies the contamination from non-active galaxies is far less significant than in optical/infrared surveys, and the selection of obscured AGN, including also a fraction of heavily obscured AGN, is much more effective. In this thesis, I present the results of the Chandra COSMOS Legacy survey, a 4.6 Ms X-ray survey covering the equatorial COSMOS area. The COSMOS Legacy depth (flux limit f=2x10^(-16) erg/s/cm^(-2) in the 0.5-2 keV band) is significantly better than that of other X-ray surveys on similar area, and represents the path for surveys with future facilities, like Athena and X-ray Surveyor. The final Chandra COSMOS Legacy catalog contains 4016 point-like sources, 97% of which with redshift. 65% of the sources are optically obscured and potentially caught in the phase of main BH growth. We used the sample of 174 Chandra COSMOS Legacy at z>3 to place constraints on the BH formation scenario. We found a significant disagreement between our space density and the predictions of a physical model of AGN activation through major-merger. This suggests that in our luminosity range the BH triggering through secular accretion is likely preferred to a major-merger triggering scenario. Thanks to its large statistics, the Chandra COSMOS Legacy dataset, combined with the other multiwavelength COSMOS catalogs, will be used to answer questions related to a large number of astrophysical topics, with particular focus on the SMBH accretion in different luminosity and redshift regimes.

Towards a full cosmological exploitation of cosmic voids

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 on this topic.

Microwave and millimeter-wave spectroscopy of sulfur-containing molecules

The rotational spectroscopy of several sulfur bearing molecules and their 1:1 water complex, cysteamine, cysteamine monohydrate, 1-thioglycerol and 1-propanethiol were studied in the micro-wave and (or) millimeter-wave range. Precise laboratory spectra and conformational information were obtained. For cysteamine, the conformational space (at the B3LYP-GD3(BJ)/Def2-TZVP level) and the measurement and analysis of its rotational spectra in the 6 - 18 and 59.6 - 120 GHz are reported. The hyperfine structure of the rotational spectra was observed and analyzed for the first time. Based on the measured spectra, a search of the different conformers of cysteamine was performed toward the G+0.693-0.027 molecular cloud. We computed the upper limit of the ratio of ethanolamine to cysteamine, which is >0.8−5.3. For the cysteamine monohydrate, the conformational space was explored (at the B3LYP-GD3(BJ)/Def2-TZVP level). The rotational spectra of the cysteamine monohydrate complex have been assigned in the frequency range 6 – 18.5 GHz. The global minimum, Conf A1, was the only observed one. The 34S isotopologue of Conf A1 was observed in natural abundance, while 18O isotopologue was detected by introducing the H218O. In this conformer, the water molecule plays both proton donor and acceptor roles, forming a OHw···N interaction, a SH···Ow interaction and a CH···Ow interaction. The conformational space of 1-thioglycerol has been characterized by quantum mechanical calculation and its rotational spectrum has been recorded and analyzed in the frequency range 59.6 - 78.4 GHz. The global minimum of 1-thioglycerol is gTg’Gg’ and were detected together with gTg’Tg and gGgG’g, while the two detected conformers are g’G’gGg’ and tGgGg. The high-resolution rotational spectrum of 1-propanethiol in the frequency range 59.6 – 78.4 GHz was measured. Two conformers, Gg and Tg, were observed and their spectra were analyzed. Considering the overall conformational space calculated at the B3LYP-GD3(BJ)/Def2-TZVP level they are among the lowest energy conformers.

On the role of AGN feedback in shaping galaxies across cosmic time

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.

The cosmic ray tagger of the ICARUS detector: construction, commissioning and performances in the first physics run

The Short Baseline Neutrino Program at Fermilab aims to confirm or definitely rule out the existence of sterile neutrinos at the eV mass scale. The program will perform the most sensitive search in both the nue appearance and numu disappearance channels along the Booster Neutrino Beamline. The far detector, ICARUS-T600, is a high-granularity Liquid Argon Time Projection Chamber located at 600 m from the Booster neutrino source and at shallow depth, thus exposed to a large flux of cosmic particles. Additionally, ICARUS is located 6 degrees off axis with respect to the Neutrino beam from the Main Injector. This thesis presents the construction, installation and commissioning of the ICARUS Cosmic Ray Tagger system, providing a 4 pi coverage of the active liquid argon volume. By exploiting only the precise nanosecond scale synchronization of the cosmic tagger and the PMT optical flashes it is possible to determine if an event was likely triggered by a cosmic particle. The results show that using the Top Cosmic Ray Tagger alone a conservative rejection larger than 65% of the cosmic induced background can be achieved. Additionally, by requiring the absence of hits in the whole cosmic tagger system it is possible to perform a pre-selection of contained neutrino events ahead of the full event reconstruction.

Unveiling the expansion history of the universe with cosmic chronometers and gravitational waves

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.