Dr. Pedro Humire
Abstract: We assess the study of the central parts of spiral galaxies using two main tracers: (1) sulfur and carbon rare isotopes, mainly synthesized in massive stars and expelled to the interstellar medium by stellar winds and supernova explosions, and (2) maser lines from methanol. The study of sulfur and carbon through its most abundant molecule, carbon monosulfide (CS), is a feasible path to probe what happens inside of stars. By using carbon isotopologue ratios it is possible to prove that the nucleus of our Galaxy is “older” compared to its spiral arms, supporting the inside-out growth scenario of the Galactic Disk. The CS observation also gives us information about the metallicity of the environment in which massive stars reside. The latter is relevant for the refinement of star formation models. Masers can originate in a variety of environments, from planetary nebulae to active galactic nuclei. Methanol masers are more restricted in origin and can be used to trace the earliest stages of high-mass star formation. The study of extragalactic methanol masers is a promising new field of research and has great potential to be explored in detail in the coming years. We have found that the decreasing trend of the 32S/34S abundance ratio towards the Galactic nucleus is halted somewhere between 1 kpc and ∼130 pc from the galactic center and then reverts to values similar to those encountered in the solar neighborhood. This confirms that the metallicity in the nuclear regions of our Galaxy is similar to the solar one, and indicates a drop in the production of massive stars from the outer limits of our Galaxy until 1 kpc from its nucleus. Concerning the second topic, we have found that methanol masers pumped by shocks are the brightest and that the conditions required to produce them are weak shocks, generated where entrained material by spiral arms interacts with the nuclear bar. Complementarily, dissociating UV radiation is the most likely explanation for the lack of methanol masers at the very center of spiral galaxies. Quantitatively speaking, we have increased the number of known galaxies hosting methanol masers beyond the local group: the sample now includes Maffei 2. Furthermore, we have expanded the number of extragalactic methanol maser transitions detected so far from 5 to 11, reporting the first detections at 95, 132, 146, 198, 229, and 278 GHz around the core of NGC 253. Currently, we are looking for Galaxy sources where the missing methanol maser transition at ~181 GHz can be detected, in this talk, we will provide our latest results using radiative transfer and rotation diagrams techniques to discriminate between maser and LTE methanol emission in a sample of low-mass young stellar objects.
Mini-bio: Possui doutorado em Radio Astronomía pela Max-Planck-Institut für Radioastronomie(2022). Atualmente é Pós-Doutorado da Universidade de São Paulo. Tem experiência na área de Astronomia.
Google Meet: https://meet.google.com/pcw-gmem-jyi
Link da transmissão: https://www.youtube.com/c/AstronomiaIAGUSP/live