Isotopic fractionation study towards massive star-forming regions across the Galaxy / / Laura Colzi.

• VerfasserIn: Colzi, Laura,
• Place / Publishing House: Firenze : : Firenze University Press,, 2021.
• Year of Publication: 2021
• Language: English
• Physical Description: 1 online resource (226 pages)

One of the most important tools to investigate the chemical history of our Galaxy and our own Solar System is to measure the isotopic fractionation of chemical elements. In the present study new astronomical observations devoted to the study of hydrogen and nitrogen fractionation (D/H and 14N/15N ratios) of molecules, towards massive star-forming regions in different evolutionary phases, have been presented. Moreover, a new detailed theoretical study of carbon fractionation, 12C/13C ratios, has been done. One of the main results was the confirmation that the 14N/15N ratio increases with the galactocentric distance, as predicted by stellar nucleosynthesis Galactic chemical evolution models. This work gives new important inputs on the understanding of local chemical processes that favor the production of molecules with different isotopes in star-forming regions.

Table of Contents

1 Introduction -- 1.1 Star formation process -- 1.1.1 The challenge of high-mass star formation -- 1.2 The importance of high-mass star-forming regions for the Solar system formation -- 1.3 Astrochemical processes in the interstellar medium 1.3.1 Gas-phase chemistry -- 1.3.2 Type of reactions -- 1.4 Isotopic fractionation in the context of star formation -- 1.4.1 The evolution of chemical complexity during star forma- tion -- 1.4.2 The heritage of the Solar system -- 1.4.3 Deuterium enrichment during star formation -- 1.4.4 Nitrogen fractionation in the ISM -- 1.5 Thesis project -- 2 Nitrogen and hydrogen fractionation in high-mass star-forming regions -- 2.1 Introduction -- 2.2 Observations and data reduction -- 2.3 Results: column densities and isotopic ratios -- 2.3.1 HNC, HN13C, HCN, and H13CN -- 2.3.2 DNC -- 2.4 Isotopic fractionation -- 2.4.1 15N-fractionation as a function of evolutionary stages -- 2.4.2 D-fractionation -- 2.4.3 Comparison between D/H and 14N/15N -- 2.5 The HCN/HNC ratio -- 2.6 Conclusions -- 3 Nitrogen fractionation across the Galaxy -- 3.1 Introduction -- 3.2 Sample and observations -- 3.2.1 Description of the sample -- 3.2.2 Observations -- 3.3 Results -- 3.3.1 Line detection -- 3.3.2 Fitting procedure and column density calculation 3.3.3 14N/N ratios -- 3.4 The Galactocentric behaviour -- 3.4.1 Linear analysis -- 3.4.2 Parabolic analysis -- 3.5 Discussion and Conclusions -- 4 Enhanced nitrogen fractionation at core scales -- 4.1 Introduction -- 4.2 Source and observations -- 4.3 Results -- 4.3.1 Continuum map -- 4.3.2 Morphology of NH and 15N-isotopologues emission 4.3.3 Fitting procedure and column density calculation 4.3.4 14N/15N ratios -- 4.4 Discussion of the results -- 4.4.1 Comparison between line and continuum emission maps 4.4.2 Is N-fractionation a core-scale effect? -- 4.4.3 15NNH vs N15NH+ -- 4.4.4 14N/15N ratios in diffuse regions -- 4.5 Conclusions -- 5 Carbon isotopic fractionation: a new detailed chemical study -- 5.1 Introduction -- 5.2 Model -- 5.2.1 Chemical model -- 5.2.2 Introduction of 13C-fractionation in the chemical model 5.2.3 Isotopic exchange reactions -- 5.3 Results and Discussion -- 5.3.1 The fiducial model -- 5.3.2 The importance of Cs isotopic-exchange reaction 5.3.3 Parameter space exploration -- 5.4 Conclusions -- 6 Summary and Main Conclusions -- A Appendix: Spectra simulation tests -- A.1 15N-isotopologues at lower spectral resolution -- A.2 NH at higher spectral resolution -- A.3 The effect of a possible N2H+ line saturation -- Bibliography -- Ringraziamenti -- Acknowledgments.