Sailing to the next safe harbour in our trip to the early Universe: The massive star population of metal-poor galaxies
N. Castro, M. Garcia, A. Herrero, A. A. C. Sander, A. F. McLeod, M. M. Roth, I. Negueruela, J. S. Vink
TL;DR
The paper addresses how to study massive star evolution at metallicities well below those of the Magellanic Clouds, a prerequisite for understanding early-universe star formation and reionization. It argues that current surveys are biased and spatially incomplete due to instrument limitations, and that a next-generation suite of panoramic integral-field spectrographs and high-multiplex spectrographs on large telescopes is needed. The proposed approach enables a homogeneous census of massive-star populations in very metal-poor Local Group galaxies (e.g., Sextans A at $Z \approx 0.1 Z⊙$), permitting measurements of metallicity dependencies on evolution, multiplicity, chemically homogeneous evolution, and the upper stellar mass limit, plus ISM feedback. This facility-driven leap links local low-$Z$ constraints to early-Universe conditions and offers strong synergies with LSST and the Roman Space Telescope.
Abstract
Very metal-poor massive stars in the Local Group are our best proxies for the Universe's first stars, making them essential for modeling reionization and early galactic chemical evolution. Studying such stars in our Local Universe is key to extrapolating our knowledge to more distant regions, where individual massive stars cannot be resolved but are dynamically and chemically shaping their environments. The MUSE integral field spectrograph has transformed massive star studies in the Milky Way and Magellanic Clouds, but resolving star-forming galaxies containing very metal-poor stars is at the limit of the current field of view and sensitivity. Therefore, only small dedicated efforts of selected regions are studied, providing us with snapshots of low-metallicity massive stars rather than a comprehensive picture. This scarcity is a major bottleneck for understanding and sufficiently modelling the evolution and feedback of massive stars across cosmic time. We therefore envision a new generation of panoramic integral-field spectrographs and high multiplex multi-object spectrographs mounted on dedicated large optical telescopes. Such facilities will not only allow to resolve very-metal-pool galaxies, but further enable the systematic exploration of the massive stellar content across the entire Local Group, thereby reaching a new era in massive star studies and understanding.