Today, there are only a limited number of surveys of the sky at 1 to 20 GHz. These frequencies lie below the all-sky surveys of WMAP and Planck, but are critical in constraining the spectral slope of Galactic synchrotron emission. Knowledge of the large-scale spectral morphology of Galactic synchrotron emission is critical in the understanding of the interstellar medium and the weak signal from the polarised cosmic microwave background. Recently, ground based observations from S-PASS, C-BASS and the QUIJOTE Multifrequency Instrument (MFI) have been populating these missing frequencies. This thesis presents the first QUIJOTE MFI maps of the Northern sky in total intensity at 11, 13, 17 and 19 GHz, and the first single-dish mapping observations of Lynds dark cloud, LDN1622 at 5 and 13.7GHz. The observations from both instruments are used to probe the nature of spinning dust emission on degree and arcminute scales within the Galaxy. A full data reduction and calibration pipeline for QUIJOTE MFI time-ordered-data is described. The absolute flux density scale uncertainty of the MFI data is between 2 and 3 per cent. The pipeline characterises key properties of the MFI, such as the RFI sources, beams, bandpasses, 1/f noise and more. A key part of the pipeline was the development of an MPI ready Destriping map-maker and a maximum-likelihood map-maker. The map-making code can be applied to a range of different single-dish instruments and is used to reduce both the QUIJOTE MFI wide-survey maps of the Northern sky, and the GBT arcminute resolution raster observations of LDN 1622. A detailed discussion is given on the simulations used to test the integrity of the map-making implementation. Parametric model fitting to the SEDs of four spinning dust emission regions is performed. The MFI wide-survey maps are used in conjunction with existing multifrequency 1degree survey data. The addition of MFI maps is used to confirm the previously tentative spinning dust emission source LDN 1582/84. The mean peak frequency of spinning dust emission over the four spinning dust sources is found to be ⟨νsp⟩ = 27.2 +/- 0.7 GHz, and the mean ratio of the peak spinning dust brightness over the dust optical depth is ⟨Asp/τ250⟩ = 1.24 +/- 0.18 × 104 Jy/τ250. Spectral index maps are derived from the MFI wide-survey data in combination with 408 MHz and WMAP 23 GHz data. These maps are used to further quantify the ubiquity of spinning dust emission throughout the Galaxy. The results show that the median flux density spectral index within the inner Galactic disk for |b| < 2° is 0.24 +/- 0.07. This implies that at 23 GHz, spinning dust emission contributes 25 +/- 5 per cent of the total integrated emission within the inner disk of the Galaxy.

In this thesis I present work done on the subject of star formation through the study of infrared dark clouds. We studied the velocity fields in several IRDCs using spectral line mapping. We also performed observations of a high density tracer and its deuterated counterpart. These observations allow me to assess the kinematics of these clouds and the evolutionary state of the observed targets. The sample observed is an important starting point for the search of early and quiescent high-mass regions. We mapped several IRDCs using the 22m ATNF Mopra Telescope in high-density molecular tracers at 3 mm, HNC (1-0) and N2H+ (1-0). We present integrated intensity emission and velocity field maps of these IRDCs. The molecular emission in the maps matches well with the extinction seen in the mid-IR. For an IRDC-complex we see connecting emission in the whole filament. We calculate kinematic distances and masses of the IRDCs. The IRDCs typically display an ordered velocity field within the clouds. The mean velocity gradient of the sample was 0.4 km/s/pc. We show how this velocity gradient can mean gas flows within the cloud into the central regions in order to feed the central cores. We observed 54 cores in IRDCs using N2H+ (1-0) and (3-2) to determine the kinematics of the densest material, where stars will form. We also observed N2D+ (3-2) towards 29 of the brightest peaks to analyze the level of deuteration which is an excellent probe of the quiescent of the early stages of star formation. There were 13 detections of N2D+ (3-2). This is one of the largest samples of IRDCs yet observed in these species. The deuteration ratio in the sources with detected N2D+ (3-2) has a mean of 0.024 and reaches a maximum value of 0.14. For most of the sources the material traced by N2D+ and N2H+ (3-2) still has significant turbulent motions, however three objects show subthermal N2D+ velocity dispersion. Surprisingly the presence or absence of an embedded 70 micron source shows no correlation with the detection of N2D+ (3-2), nor does it correlate with any change in velocity dispersion or excitation temperature. Comparison with recent models of deuteration suggest evolutionary timescales of these regions of several freefall times or less.

Les études astrochimiques de la formation stellaire sont particulièrement importantes pour la compréhension de l'évolution de l'Univers, du milieu interstellaire diffus à la formation des systèmes stellaires. Les récentes avancées en matière de modélisation chimique permettent d'apporter de nouveaux résultats sur le processus de formation stellaire et les structures mises en jeu. L'objectif de ma thèse était donc d'apporter un regard neuf sur la chimie de la formation stellaire en utilisant les récentes avancées sur le modèle chimique Nautilus. J'ai pour cela étudié l'évolution de la chimie du soufre durant la formation stellaire pour tenter d'apporter de nouvelles réponses au problème de déplétion du soufre. J'ai d'abord effectué une révision du réseau chimique soufré et étudié son effet sur la modélisation du soufre dans les nuages denses. En comparant aux observations, j'ai montré que le modèle textsc{Nautilus} était capable de reproduire les abondances des espèces soufrées dans les nuages denses en utilisant comme abondance élémentaire de soufre son abondance cosmique. Ce résultat m'a permis d'apporter de nouveaux indices sur les reservoirs de soufre dans ces objets. Puis j'ai effectué une étude complète de la chimie du souffre dans les coeurs chauds en me concentrant sur les effets sur la chimie de la composition pre-effondrement. J'ai également étudié les conséquences des différentes simplifications couramment faites pour la modélisation des coeurs chauds. Mes résultats montrent que la composition pre-effondrement est un paramètre majeur de l'évolution chimique des coeurs chauds, fournissant de nouveaux indices pour expliquer la variété de compositions en espèces soufrées observée dans ces objets. De plus, ma recherche a mis en évidence la nécessité d'uniformiser les modèles de chimie utilisés pour les coeurs chauds. Enfin, j'ai développé une méthode efficace pour inverser les paramètres initiaux d'effondrement de nuages denses en me basant sur une base de données de modèles physico-chimiques d'effondrement, ainsi que sur l'observation d'enveloppes de protoétoiles de Classe 0. A partir d'un échantillon de 12 sources, j'ai pu en déduire des probabilités concernant les possibles paramètres initiaux d'effondrement de la formation d'étoiles de faible masse. / Astrochemical studies of star formation are of particular interest because they provide a better understanding of how the chemical composition of the Universe has evolved, from the diffuse interstellar medium to the formation of stellar systems and the life they can shelter. Recent advances in chemical modeling, and particularly a better understanding of grains chemistry, now allow to bring new hints on the chemistry of the star formation process, as well as the structures it involves. In that context, the objective of my thesis was to give a new look at the chemistry of star formation using the recent enhancements of the Nautilus chemical model. To that aim, I focused on the sulphur chemistry throughout star formation, from its evolution in dark clouds to hot cores and corinos, attempting to tackle the sulphur depletion problem. I first carried out a review of the sulphur chemical network before studying its effects on the modeling of sulphur in dark clouds. By comparison with observations, I showed that the textsc{Nautilus} chemical model was the first able to reproduce the abundances of S-bearing species in dark clouds using as elemental abundance of sulphur its cosmic one. This result allowed me to bring new insights on the reservoirs of sulphur in dark clouds. I then conducted an extensive study of sulphur chemistry in hot cores and corinos, focusing on the effects of their pre-collapse compositions on the evolution of their chemistries. I also studied the consequences of the use of the common simplifications made on hot core models. My results show that the pre-collapse composition is a key parameter for the evolution of hot cores which could explain the variety of sulphur composition observed in such objects. Moreover, I highlighted the importance of standardizing the chemical modeling of hot cores in astrochemical studies. For my last study, I developed an efficient method for the derivation of the initial parameters of collapse of dark clouds via the use of a physico-chemical database of collapse models, and comparison with observations of Class 0 protostars. From this method, and based on a sample of 12 sources, I was able to derive probabilities on the possible initial parameters of collapse of low-mass star formation.

The plague raged in Venice from 1348 to 1797, striking in successive deadly waves. Countless votive images produced as "spiritual remedies" brought solace to the faithful terrified of the ongoing scourge. However, in the retables directly related to the plague, we observe the frequent presence of dark clouds. This pattern, which has gone largely unnoticed, is studied here for the first time in detail and associated with contemporary medical theories regarding the aerial spread of the disease. The dark cloud is first examined as an iconographic motif and placed in the context of Venice's health and sanitary situation in the 15th and 16th centuries, as well as the ancient literature on the plague that influenced the humanist thought of the Venetian Renaissance. Furthermore, we examine the theoretical function of the dark cloud, as a "figure" (E. Auerbach and L. Marin), as a "pictorial graph" (H. Damisch) and as a "detail" (D. Arasse). The use of these different theoretical models allows us to reconsider the presence and possible meanings of the dark cloud as a metaphor for the plague. The thesis concludes with a typology test of the plague cloud. / La peste sévit à Venise de 1348 à 1797, frappant par vagues mortelles successives. D'innombrables images votives produites comme « remèdes spirituels » participaient au réconfort des fidèles terrifiés par le fléau. Or, dans les retables directement liés à la peste, on observe la présence fréquente de nuages sombres. Ce motif passé à peu près inaperçu est étudié ici pour la première fois en détail et associé aux théories médicales contemporaines concernant la propagation aérienne de la maladie. Le nuage sombre est d'abord examiné comme motif iconographique et replacé dans le contexte de la situation sanitaire de Venise au XVe et au XVIe siècle et de la littérature antique sur la peste ayant influencé la pensée humaniste de la Renaissance vénitienne. Dans un deuxième temps, nous examinons la fonction théorique du nuage sombre, comme « figure » (E. Auerbach et L. Marin), comme « graphe pictural » (H. Damisch) et comme « détail » (D. Arasse). L'usage de ces différents modèles théoriques permet de reconsidérer la présence et les significations possibles du nuage sombre comme métaphore de la peste. Le mémoire se conclut par un essai de typologie du nuage de peste.