Star formation is a process of crucial importance in modern astrophysics to understand the evolution of galaxies and of the Universe after the Big Bang. With the advent of radio-astronomy, we have discovered that star-forming regions in the interstellar medium (ISM), are characterized by the emission of rotational transitions of molecular species and in the last decades astronomers have identified more than 200 molecules, from simple diatomic to complex organic molecules (COMs, molecules containing carbon with 6 or more atoms). Some of these molecules have also a prebiotic importance, hence understanding how these molecules are formed is essential to understand how the basic “bricks of life” can form in star-forming regions. Hot molecular cores (HMCs) in high-mass star-forming regions are the most chemically-rich sources in the Galaxy. For this reason, they represent a unique environment to study the chemistry in the early phases of star-formation. From an observational perspective, high-mass young stellar objects are challenging to study since they are rare and usually located at distances larger than 1 kpc. Moreover, the timescale of the evolution of these sources is short if compared to low-mass young stellar objects, and during the formation process the protostar is deeply embedded within the natal cloud. The main pathway for the formation of high-mass stars is still debated, nevertheless a rough classification in evolutionary stages is possible. The main goal of this thesis is to understand the degree of chemical richness that can be reached in high-mass star-forming regions and trace how the chemistry evolves with evolutionary phases. To reach this goal, observational large surveys are necessary to derive properties that can be considered as typical for such regions. The first project presented in this thesis is the TOPGot project that aims to study the evolution of chemistry by targeting a large sample of high-mass star-forming regions, covering all the evolutionary phases. This project collects observations carried out with the IRAM 30m telescope toward 86 sources. As first step, mandatory to prepare the ground for any future chemical study, I have derived the main physical properties of the sources (luminosity, mass, dust temperature, H2 column density) necessary to properly model the chemistry, and investigated how the presence and the parameters of the COM CH3CN evolve with time. The second project is the G31.41+0.31 (G31) Unbiased ALMA sPectral Observational Survey (GUAPOS). The data covers the entire band 3 of the ALMA interferometer (∼ 32 GHz) with a spatial resolution of 1.2′′and a spectral resolution of 0.4884 MHz. The full coverage of the ALMA band 3 allows us to properly identify the molecular species present in this extremely rich HMC, especially for COMs. In the first work of this project, I have analyzed the emission of the three isomers of C2H4O2: methyl formate, glycolaldehyde (the simplest sugar-related molecule), and acetic acid. The derived physical properties and abundances of the three isomers can help to constrain the predictions of chemical models and provide important input in the discussion of the main formation pathway of these molecular species. Moreover, glycolaldehyde is also of prebiotic interest, since it has been indicated as one of the precursors of ribose. Therefore, studying its possible formation route will help us to understand how prebiotic chemistry has developed in star-forming regions. In the second work presented in this, thesis I have analyzed the emission of 13 COMs containing O and N atoms, to investigate the possible presence of chemical differentiation within G31. This is a work-in-progress: here I present the preliminary results from the spectral analysis. In the future, I will conclude the study by analyzing the maps of emission of selected molecular transitions to see if the different molecular species are spatially segregated, as discovered in other sources.

Complex organic chemistry in high-mass star-forming regions / Chiara Mininni, Francesco Fontani, Guido Risaliti. - (2021).

Complex organic chemistry in high-mass star-forming regions

Chiara Mininni;Francesco Fontani;Guido Risaliti
2021

Abstract

Star formation is a process of crucial importance in modern astrophysics to understand the evolution of galaxies and of the Universe after the Big Bang. With the advent of radio-astronomy, we have discovered that star-forming regions in the interstellar medium (ISM), are characterized by the emission of rotational transitions of molecular species and in the last decades astronomers have identified more than 200 molecules, from simple diatomic to complex organic molecules (COMs, molecules containing carbon with 6 or more atoms). Some of these molecules have also a prebiotic importance, hence understanding how these molecules are formed is essential to understand how the basic “bricks of life” can form in star-forming regions. Hot molecular cores (HMCs) in high-mass star-forming regions are the most chemically-rich sources in the Galaxy. For this reason, they represent a unique environment to study the chemistry in the early phases of star-formation. From an observational perspective, high-mass young stellar objects are challenging to study since they are rare and usually located at distances larger than 1 kpc. Moreover, the timescale of the evolution of these sources is short if compared to low-mass young stellar objects, and during the formation process the protostar is deeply embedded within the natal cloud. The main pathway for the formation of high-mass stars is still debated, nevertheless a rough classification in evolutionary stages is possible. The main goal of this thesis is to understand the degree of chemical richness that can be reached in high-mass star-forming regions and trace how the chemistry evolves with evolutionary phases. To reach this goal, observational large surveys are necessary to derive properties that can be considered as typical for such regions. The first project presented in this thesis is the TOPGot project that aims to study the evolution of chemistry by targeting a large sample of high-mass star-forming regions, covering all the evolutionary phases. This project collects observations carried out with the IRAM 30m telescope toward 86 sources. As first step, mandatory to prepare the ground for any future chemical study, I have derived the main physical properties of the sources (luminosity, mass, dust temperature, H2 column density) necessary to properly model the chemistry, and investigated how the presence and the parameters of the COM CH3CN evolve with time. The second project is the G31.41+0.31 (G31) Unbiased ALMA sPectral Observational Survey (GUAPOS). The data covers the entire band 3 of the ALMA interferometer (∼ 32 GHz) with a spatial resolution of 1.2′′and a spectral resolution of 0.4884 MHz. The full coverage of the ALMA band 3 allows us to properly identify the molecular species present in this extremely rich HMC, especially for COMs. In the first work of this project, I have analyzed the emission of the three isomers of C2H4O2: methyl formate, glycolaldehyde (the simplest sugar-related molecule), and acetic acid. The derived physical properties and abundances of the three isomers can help to constrain the predictions of chemical models and provide important input in the discussion of the main formation pathway of these molecular species. Moreover, glycolaldehyde is also of prebiotic interest, since it has been indicated as one of the precursors of ribose. Therefore, studying its possible formation route will help us to understand how prebiotic chemistry has developed in star-forming regions. In the second work presented in this, thesis I have analyzed the emission of 13 COMs containing O and N atoms, to investigate the possible presence of chemical differentiation within G31. This is a work-in-progress: here I present the preliminary results from the spectral analysis. In the future, I will conclude the study by analyzing the maps of emission of selected molecular transitions to see if the different molecular species are spatially segregated, as discovered in other sources.
Francesco Fontani, Guido Risaliti
ITALIA
Chiara Mininni, Francesco Fontani, Guido Risaliti
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2158/1275292
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