Searches for supermassive stars and unusual stellar populations in nearby and distant galaxies

Diplôme Thèse Searches for supermassive stars and unusual stellar populations in nearby and distant galaxies eng 2024-11-28 2025-02-19 author Kuruvanthodi Adarsh 949460 director Schaerer Daniel Olivier 23688 Département d'astronomie (ASTRO) director Charbonnel Corinne 22674 Département d'astronomie (ASTRO) 182 10.13097/archive-ouverte/unige:185867 urn:nbn:ch:unige-1858670 Sc. 5889 Multiple Stellar Populations observed in Globular Clusters (GCs) are one of the major unsolved problems in the local Universe. Old GCs, which were previously believed to host Simple Stellar Populations, unambiguously show abundance variations and anti-correlations that are found in no other environment. Supermassive stars (SMS) with a mass of 103-4M⊙ formed within the proto-GCs at their early stages are proposed to be the source of the observed chemical enrichments in GC stars. However, such massive objects have not been observed in the Universe before. Based on the predicted spectrophotometric properties of the SMS by Martins et al. (2020), I developed observational strategies and applied them to the massive star clusters in two nearby galaxies (NGC628 and M83). The atmospheric models for bright, cool, and inflated SMS predict a Balmer break (BB) in their spectra due to non-LTE effects. I found that color-color plots using the filters across and before/after the break have the potential to identify such inflated SMS hosting clusters. The spectra of such SMS hosting clusters will have a unique nature, as they exhibit both BB and nebular emission due to the presence of gas and young massive stars within the clusters. A detailed analysis performed using HST photometry and MUSE spectroscopy revealed that, although a small fraction of clusters satisfied the criteria, the clusters in our sample were not massive enough to host such an inflated SMS. Galaxies Globular Clusters Supermassive stars Stellar Populations Balmer break galaxies High redshift Universe Extragalactic astronomy Reionization Galaxy evolution Young Massive Star Clusters Dewey 520 26 Département d'astronomie 12 false 77faf3b2-fda4-4446-9b0f-dcef3dd6d829 Thesis Public PhD_Thesis_V2_final_kuruvanthodi-op.pdf 8848419 application/pdf CC BY-4.0 475d125cfc371678dd9114565b2ce35115fc5e775b9ddf86eb3eb8b911804c30 2060bf9a-65a6-4b66-8b49-49cb7490fd10 Imprimatur Public imprimatur.pdf 430375 application/pdf 83ca77aa3bf6aab6292116b662d84b3b30baa2b3b440fd2772fef72d26091d00 openAccess Faculté des sciences / Département d'astronomie

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