This Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry... Show moreThis Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry leads to bistability but when coupled with the gas-grain exchange of key species, the system can show Hopf bifurcation and lead to the appearance of complex chemical oscillations. The results and discussion of the five chapters allow further understanding of the chemical evolution in a gas phase system and in a gas-grain environment, providing better predictions to compare with future observations. Show less
This thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their... Show moreThis thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their surrounding PDRs. We focus our studies on two compact HII regions: W3(A) and the Orion Nebula (Chapters 2 and 3, respsectively). Using SOFIA/FORCAST observations, we determine the properties of dust in the ionized gas, their surrounding PhotoDissociation Regions and their parent molecular clouds. One of the most important conclusions of this thesis is that the grain growth can affect the dust size distribution in regions of massive star formation. The large amount of archival data available for Orion allow us to study other important phenomena related to dust in this region, such as the photoelectric heating effect and Lyman alpha heating. The second part of this thesis presents theoretical studies of the properties of the cold neutral medium (CNM) using carbon radio recombination lines (CRRL). Chapters 4 and 5 consists on the complete theory of CRRLs from the level population equation to the radiative transfer equation. Using these models and observations of CRRLs the physical parameters of the CNM can be determined. Show less
Galaxies with all their varieties, have been home to billions of stars during their life. It is because of the presence of these shining stars that we are able to observe them through the cosmic... Show moreGalaxies with all their varieties, have been home to billions of stars during their life. It is because of the presence of these shining stars that we are able to observe them through the cosmic time. Although we observe galaxies mostly through the light emitted by their stars, we cannot resolve these stars individually unless they are very close by. Because of this, the cumulative light from billions of stars in every galaxy is analyzed using stellar population models to extract information about the evolution of galaxies. Stellar light does not reach us without passing through the interstellar medium (ISM) which contains clouds of gas and dust particles. Gas and dust can absorb and re-emit the light from stars, or scatter it towards us and make interpreting what we observe in galaxies very complicated. Despite all these difficulties, just by analyzing the total light from galaxies, we can constrain the global physical properties of galaxies such as stellar mass, star formation rate and age, based on the stellar population models. By combining stellar population models and photoionization models we can further analyze the emission line spectrum of star-forming galaxies coming from ionized gas around young stars which provide us with a wealth of information about the small-scale properties of galaxies e.g., the ISM. This thesis is an attempt in understanding the relation between these small-scale properties and global properties of star-forming galaxies over cosmic time using stellar population synthesis models and photoionization models. Show less
In this thesis we study the earliest stages of high-mass star formation. Class II methanol masers are only associated with massive star formation and are a unique probe of these environments.... Show moreIn this thesis we study the earliest stages of high-mass star formation. Class II methanol masers are only associated with massive star formation and are a unique probe of these environments. Through observations we have studied where and when the methanol maser emission occur in relation to the protostar. We have found that for a fair fraction of the sources the methanol masers appear on size scales of ca. 1000 AU, in the equatorial region of the massive protostar. It appears that infall, rather than rotation, is the dominant motion. We propose that the maser emission occur close to or in a shock interface, possibly related to the accretion flow of the more extended gas in the protostellar envelope onto an accretion disk. The morphology and kinematics of the thermal methanol gas support the hypothesis that the maser region is also the region where the methanol molecules are released from the icy mantles of the du st grains. We have also estimated the temperature and column density of the methanol gas in the outflows and find evidence for radiative excitation of the methanol gas at the location of the maser emission. Show less
Polycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by... Show morePolycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by incomplete combustion of carbon-containing fuels, hence they are found in car exhaust, cigarette smoke and (too) well-cooked meats. This makes PAHs one of the most widespread organic pollutants. In space, PAHs are an important and ubiquitous component of the Interstellar Medium, dominating the mid-infrared emission of many astronomical objects. However, very little is known about the destiny of PAHs when they are bombarded by high-velocity ions and electrons arising from interstellar shocks, hot gas and cosmic rays (CRs). The research described in this thesis shows that in shocks with velocities above 100 km/s and in a million-degree gas, PAHs are completely destroyed by collisions with electrons, and can survive only if isolated in denser clouds. Destruction by CRs is due to collisions with ions. Because of their high energy (5 MeV - 10 GeV) CRs can access these denser clouds and will set the lifetime of those protected PAHs, which can be used as a __dye__ for tracing the presence of material entrained in the hot gas. Show less
Starburst galaxies undergo a phase of vigorous star formation. In these galaxies, gas is turned into stars at such a high rate, that the reservoir of available gas is quickly emptied. Numerous... Show moreStarburst galaxies undergo a phase of vigorous star formation. In these galaxies, gas is turned into stars at such a high rate, that the reservoir of available gas is quickly emptied. Numerous massive, bright star clusters are created from the giant molecular clouds. They form an ideal laboratory for the study of rapid star formation. In this thesis, a detailed study of active star-forming regions in the starburst galaxies NGC 4038/4039 and M83 is presented. Sincethe stars are hidden from view by large quantities of dust, we observe them at infrared wavelengths. We address the properties of the newly formed star clusters and the surrounding interstellar matter. Show less
Part I: M51 is observed at a wavelength of 850 mum, where most radiation is emitted by dust. We find prominent spiral arms and an underlying exponential disk. The properties of the disk and the... Show morePart I: M51 is observed at a wavelength of 850 mum, where most radiation is emitted by dust. We find prominent spiral arms and an underlying exponential disk. The properties of the disk and the arms are studied. Part II and III: Gas in Galaxy Centers is exposed to intense radiation from a starburst region, an Active Galactic Nucleus (AGN), or both. The OB stars in starforming regions mostly radiate in the far-ultraviolet (FUV) and accreting black holes mostly in the X-ray regime. FUV and X-ray photons lead to a totally different chemical composition of gas clouds. Therefore, molecules such as H2, CO, HCN and HCO+ emit different line intensities. In the thesis, we model the line emission of the molecules in these gas clouds with Photon Dominated Regions models (FUV: PDR) and X-ray Dominated Region models (X-rays: XDR). These models are applied to nearby active galaxies such as NGC 253 and NGC 1068. Show less
