Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Galactic Archaeology from the Northern Sky

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Main Authors: Anguiano, Borja, Valls-Gabaud, David, Thomas, Guillaume F., Delgado, David Martínez, Martínez-García, Alberto M., del Pino, Andrés, Minchev, Ivan, Sanchez-Blazquez, Patricia, Gallart, Carme, Antoja, Teresa
Format: Preprint
Published: 2025
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author Anguiano, Borja
Valls-Gabaud, David
Thomas, Guillaume F.
Delgado, David Martínez
Martínez-García, Alberto M.
del Pino, Andrés
Minchev, Ivan
Sanchez-Blazquez, Patricia
Gallart, Carme
Antoja, Teresa
author_facet Anguiano, Borja
Valls-Gabaud, David
Thomas, Guillaume F.
Delgado, David Martínez
Martínez-García, Alberto M.
del Pino, Andrés
Minchev, Ivan
Sanchez-Blazquez, Patricia
Gallart, Carme
Antoja, Teresa
contents By the 2040s--50s, facilities such as \emph{Gaia}, WEAVE, 4MOST, Rubin, \emph{Euclid}, \emph{Roman}, and the ESO ELT will have transformed our global view of the Milky Way. Yet key questions will remain incompletely resolved: a detailed reconstruction of the Galaxy's assembly from its earliest building blocks, and robust tests of dark matter granularity using the fine structure of the stellar halo and outer disk -- particularly in the Galactic anticenter. Addressing these questions requires high-resolution spectroscopy of faint main-sequence stars (typically 1--2 mag below the turnoff) and turnoff stars ($r \sim 21$--23) in low-surface-brightness structures: halo streams and shells, ultra-faint dwarf galaxies, the warped and flared outer disk, and anticenter substructures. We argue that addressing this science case requires a 30\,m-class telescope in the northern hemisphere, equipped with wide-field, highly multiplexed, high-resolution spectroscopic capabilities. Such a facility would enable (i) a Northern Halo Deep Survey of $\sim 10^{5}$--$10^{6}$ faint main-sequence and turnoff stars out to $\sim 150$--200\,kpc, (ii) chemodynamical mapping of dozens of streams to measure perturbations from dark matter subhalos, and (iii) tomographic studies of the anticenter and outer disk to disentangle perturbed disk material from accreted debris. A northern 30\,m telescope would provide the essential complement to ESO's southern ELT, enabling genuinely all-sky Milky Way archaeology and delivering stringent constraints on the small-scale structure of dark matter.
format Preprint
id arxiv_https___arxiv_org_abs_2512_14789
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Galactic Archaeology from the Northern Sky
Anguiano, Borja
Valls-Gabaud, David
Thomas, Guillaume F.
Delgado, David Martínez
Martínez-García, Alberto M.
del Pino, Andrés
Minchev, Ivan
Sanchez-Blazquez, Patricia
Gallart, Carme
Antoja, Teresa
Instrumentation and Methods for Astrophysics
Astrophysics of Galaxies
By the 2040s--50s, facilities such as \emph{Gaia}, WEAVE, 4MOST, Rubin, \emph{Euclid}, \emph{Roman}, and the ESO ELT will have transformed our global view of the Milky Way. Yet key questions will remain incompletely resolved: a detailed reconstruction of the Galaxy's assembly from its earliest building blocks, and robust tests of dark matter granularity using the fine structure of the stellar halo and outer disk -- particularly in the Galactic anticenter. Addressing these questions requires high-resolution spectroscopy of faint main-sequence stars (typically 1--2 mag below the turnoff) and turnoff stars ($r \sim 21$--23) in low-surface-brightness structures: halo streams and shells, ultra-faint dwarf galaxies, the warped and flared outer disk, and anticenter substructures. We argue that addressing this science case requires a 30\,m-class telescope in the northern hemisphere, equipped with wide-field, highly multiplexed, high-resolution spectroscopic capabilities. Such a facility would enable (i) a Northern Halo Deep Survey of $\sim 10^{5}$--$10^{6}$ faint main-sequence and turnoff stars out to $\sim 150$--200\,kpc, (ii) chemodynamical mapping of dozens of streams to measure perturbations from dark matter subhalos, and (iii) tomographic studies of the anticenter and outer disk to disentangle perturbed disk material from accreted debris. A northern 30\,m telescope would provide the essential complement to ESO's southern ELT, enabling genuinely all-sky Milky Way archaeology and delivering stringent constraints on the small-scale structure of dark matter.
title Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Galactic Archaeology from the Northern Sky
topic Instrumentation and Methods for Astrophysics
Astrophysics of Galaxies
url https://arxiv.org/abs/2512.14789