报告摘要：Elemental abundance and their ratios along the Galactocentric radius provide key information about the chemical evolution of the Milky Way. The 12C/13C ratio, in particular, is widely adopted as a proxy to infer other isotopic ratios, such as 16O/18O and 14N/15N. Traditionally, emission lines of 12CN and 13CN – with their optical depths corrected based on their hyper-fine structure lines – have traditionally been exploited to measure 12C/13C isotopic ratios. However, such a method has major pitfalls, with oversimplified (and overlooked) assumptions in both theory and observational interpretations. The optically-thin satellite-lines of 12CN and 13CN transitions present the advantages over the 'classical method', but still suffers bias from non-trivial effects from non-Local Thermal Equilibrium conditions. Our new measurements of 13C18O and C18O emission lines provide a promising new avenue for isotopic ratio determinations. With it, we further obtained the virial states of low-metallicity molecular clouds in the outer Galactic disk. Our analysis shows that the turbulent kinetic energy cannot support self-gravitational energy in these clouds, suggesting that the magnetic field likely play a dominant role in supporting clouds in such conditions.
主讲人简介：Zhiyu Zhang is a faculty member at the School of Astronomy and Space Science, Nanjing University, specializing in observational radio astronomy. His research interests include the multiphase interstellar medium, astrochemistry, the stellar initial mass function, and the chemical evolution of galaxies. He earned his Master's and PhD degrees from Purple Mountain Observatory, with part of his doctoral research conducted at the Max Planck Institute for Radio Astronomy in Germany. From 2014, he held postdoctoral positions at the University of Edinburgh and the European Southern Observatory. He has been serving as a professor at Nanjing University since 2019.
