In this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions... Show moreIn this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions between ions and molecules have reached a steady state. However, this assumption may not be valid if the physical conditions of the gas are evolving rapidly. Therefore, we developed a chemical model to follow the non-equilibrium evolution of ions and molecules. We then incorporated this model into hydrodynamic simulations of galaxies. We ran simulations with different metallicities (i.e. different proportions of heavy elements) and UV radiation fields, first using our full non-equilibrium chemical model and then assuming chemical equilibrium. We found that the total star formation rate is higher at higher metallicity and for weaker radiation fields. In contrast, non-equilibrium chemistry does not strongly influence the total star formation rate or outflow properties of the galaxy. However, it does affect the abundances of individual chemical species, for example in molecular outflows. Finally, we explored the properties of molecular clouds in our simulations. At low metallicity, the molecular fraction of young clouds tends to be below equilibrium, as the molecules are still forming. This also affects the observable CO emission from young clouds. Show less
This thesis discusses the structure of gas and dust in protoplanetary disks around young stars, in which the planets are formed, using ALMA (Atacama Large Millimeter/submillimeter Array)... Show moreThis thesis discusses the structure of gas and dust in protoplanetary disks around young stars, in which the planets are formed, using ALMA (Atacama Large Millimeter/submillimeter Array) observations. Primary targets of this study are the so-called 'transition disks', with a central cavity in the dust disk. A possible explanation for the presence of this cavity is the recent formation of a young planet which has cleared its own orbit. ALMA can for the first time zoom in onto the structure of both gas and dust and answer this question. The thesis presents the first ALMA observations of cold molecular gas and dust in transition disks. These data show that millimeter-dust grains are concentrated in a 'dust trap', allowing the dust particles to grow to larger sizes, an important step in the planet formation process. Also, it turns out that gas is still present in the dust cavity of the disks in this study, its structure points indeed towards the planet clearing mechanism. These discoveries form a giant leap in our understanding of planet formation. In the coming years, ALMA will be completed and allow us to see even smaller details in these disks, possibly even the planets itself. Show less
This thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass... Show moreThis thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass young stellar objects (YSOs). The studied molecular transitions have been observed with the HIFI instrument on board of Herschel Space Observatory and within the context of the Herschel key programme __WISH__. These species and transitions constitute unambiguous tracers of specific physical conditions within the inner and warmer regions of the YSO environment. The sample of sources, composed by more than 120 YSOs, covers a large range of bolometric luminosities, several evolutionary stages within the embedded phase, and different physical scales. The aim of this work is to explore the differences and similarities between low- and high-mass star-forming regions. In particular, this study focuses on investigating the physical and dynamical structure of dense warm gas within protostellar environments by characterising the velocity-resolved H2O and CO spectra in terms of line profile and line luminosity. The ultimate goal is to contribute to the understanding of the star formation process without imposing luminosity boundaries, and to put in context these processes on Galactic and extragalactic scales. Show less
This thesis is devoted to the study of regular and deuterated water in ices and on surfaces against an interstellar background. A large network for the formation of regular water has been studied... Show moreThis thesis is devoted to the study of regular and deuterated water in ices and on surfaces against an interstellar background. A large network for the formation of regular water has been studied with the use of a Kinetic Monte Carlo model. A specific reaction has been investigated as well: H2 + O -> OH + H. Furthermore, in the light of deuterium fractionation, a thermal study on deuteron scrambling in the ice has been performed: H2O + D2O -> 2 HDO. Finally, two low-temperature routes relevant to HDO formation have been investigated: H2O + OD -> OH + HDO and D2O + OH -> OD + HDO. Show less
This thesis explores the chemistry of interstellar and circumstellar molecules during star formation and death. From the perspective of chemical physics, the most important outcome of this thesis... Show moreThis thesis explores the chemistry of interstellar and circumstellar molecules during star formation and death. From the perspective of chemical physics, the most important outcome of this thesis lies in that the rates for two important reactions are determined accurately for the first time: N2 photodissociation and reaction rates (both state-to-state and thermal) of OH with H. In particular, accurate N2 photodissociation rate and shielding functions were calculated. The results are very useful in many astrophysical fields. In addition, a new method for accurately calculating molecular shielding functions in full 3D radiation field was proposed, and was employed to give new predictions for molecule distributions in a C-rich AGB star, IRC +10216, and an O-rich AGB star, IK Tau, based on the latest progress from both observations and simulations. By far, these results are the most accurate ones, and can be directly compared to the future observations. Show less
This thesis treats the chemical behaviour of carbonaceous molecules in water-dominated interstellar ices. VUV photons are considered as the chemical trigger to induce solid state chemistry as it is... Show moreThis thesis treats the chemical behaviour of carbonaceous molecules in water-dominated interstellar ices. VUV photons are considered as the chemical trigger to induce solid state chemistry as it is omnipresent. Lyman- radiation occurs even in dense molecular clouds as a result of cosmic ray excitation of H2 and subsequently emitting its excess energy at 122 nm (Mathis et al. 1983). It comprises the addition of new tools to laboratory astrochemistry, expanding knowledge on the behaviour of PAHs in interstellar ices and research into the role of C 2H2 and polyynes in interstellar ice VUV photochemistry. It provides with spectroscopic tools for observers to enable the identification of the hydrocarbons encountered in interstellar ices, and it provides modellers with reaction dynamic information that can be used as an input for their models. Show less
