Galactic Archaeology with the Subaru `\=Onohi`ula Prime Focus Spectrograph Strategic Program
Abstract
The recently commissioned Subaru `\=Onohi`ula Prime Focus Spectrograph (PFS) will obtain spectra from nearly 2,400 fibers that cover 1.24 square degrees. The 360 night Subaru Strategic Program for PFS is dedicating approximately one-third of its allocation (130 nights) to study the structure and evolution of galaxies in the Local Group. This Galactic Archaeological survey has three pillars. (1) We will determine whether the mass density profiles of dwarf galaxies are consistent with cusps, as expected for cold dark matter, or cores, as expected from alternative dark matter theories or baryonic feedback. We will deduce the density profiles as a function of radius from modeling of the full line-of-sight velocity and abundance distributions for six dwarf galaxies. Our total sample will consist of 18,000 member stars to beyond the nominal tidal radius of each system. (2) From measurements of the [alpha/Fe] abundance ratio, we will learn the difference in assembly history of the two most massive galaxies in the Local Group: M31 and the Milky Way. We will observe 30,000 member stars over 45 square degrees of M31's halo and outer disk. (3) We will uncover how the most fragile (outer) part of the Milky Way responded to accretion events both in the distant past (such as Gaia-Sausage Enceladus) and in more recent history (such as the Sagittarius dwarf spheroidal galaxy). To support this study, PFS will provide velocities and metallicities--from which, in combination with photometry, we will deduce ages--for tens of thousands of main-sequence stars out to a Galactocentric distance of ~30 kpc.
Cite
@article{arxiv.2604.09875,
title = {Galactic Archaeology with the Subaru `\=Onohi`ula Prime Focus Spectrograph Strategic Program},
author = {Masashi Chiba and Rosemary F. G. Wyse and Evan N. Kirby and Judith G. Cohen and László Dobos and Roman Gerasimov and Miho N. Ishigaki and Kohei Hayashi and Carrie Filion and Magda Arnaboldi and Souradeep Bhattacharya and Yutaka Hirai and Chiaki Kobayashi and Yutaka Komiyama and Pete B. Kuzma and Itsuki Ogami and Ana L. Chies-Santos and Nicole L. Klock-Miranda and Federico Sestito and Tamás Budavári and Andrew P. Cooper and Keyi Ding and Ivanna Escala and Elisa G. M. Ferreira and Ortwin Gerhard and Lauren Henderson and Jihye Hong and Shunichi Horigome and Ryota Ikeda and Ryo Ishikawa and Takanobu Kirihara and Zhuohan Li and Nicolas Martin and Rin Miyazaki Sakurako Okamoto and Rohan Pattnaik and Kyosuke Sato and Yoshihisa Suzuki and Alexander S. Szalay and Dafa Wardana and Viska Wei and Wenbo Wu and Zhenyu Wu and Xinfeng Xu and Xianhao Ye and Yohei Miki and Xiangwei Zhang and Gang Zhao and Jingkun Zhao and Xiaosheng Zhao},
journal= {arXiv preprint arXiv:2604.09875},
year = {2026}
}
Comments
The Galactic Archaeology science case for the Subaru Strategic Program for the `\=Onohi`ula Prime Focus Spectrograph. Not yet submitted to any journal. v2: Author list and affiliations updated