Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Northern Local Star-forming Dwarf Galaxies. Analogues of the First Galaxies and Probes of the Cosmic Metallicity Scale

Star-forming dwarf galaxies in the local Universe, especially extremely metal-poor ones, can be considered analogous to early galaxies of the Epoch of Reionization (z >= 6). Currently available telescopes cannot adequately detect and measure heavy element recombination lines and certain faint collisionally excited lines, which are essential for exploring the effects and biases that potential inhomogeneities in electron temperature and density of the ionized gas may have on determining the chemical composition of these galaxies. On the other hand, the origin of very high-ionization lines (e.g. He II, [Ne V], C IV]) measured in the spectra of an important fraction of these objects remains unknown and a challenge to current stellar models, suggesting the presence of Population III-like stars and/or the existence of non-conventional ionizing sources. Obtaining very deep spectra for a selected sample of local star-forming dwarf galaxies would provide unprecedented constraints on their nature, ionization and true chemical abundances, and could change the metallicity scale we assume to understand the chemical evolution of galaxies over cosmic time.

💡 Research Summary

The paper makes a compelling case that a 30‑ to 40‑meter class optical/near‑infrared telescope in the Northern Hemisphere is essential for advancing our understanding of local star‑forming dwarf galaxies (SFDGs), especially the extremely metal‑poor galaxies (EMPGs) that serve as analogues of the first galaxies during the Epoch of Reionization (EoR). Current 8‑10 m facilities lack the photon‑collecting power to detect the faint heavy‑element recombination lines (RLs) such as O II multiplet 1 (≈ 4650 Å) and C II λ 4267, as well as the weak collisionally excited lines (CELs) like