M. Chiba

The Milky Way Tomography with Subaru Hyper Suprime-Cam: Implications for the past orbit of the Large Magellanic Cloud

Yoshihisa Suzuki, Masashi Chiba, Rosemary F. G. Wyse

We report the discovery of diffuse stellar substructure in the Milky Way's outer halo toward Boötes, unveiled by deep imaging data of the Subaru/Hyper Suprime-Cam. This substructur…

The Milky Way Tomography with Subaru Hyper Suprime-Cam. II. Global halo structure

Yoshihisa Suzuki, Masashi Chiba, Rosemary F. G. Wyse +1

We investigate the structure of the Milky Way's stellar halo within 70 kpc of the Sun using a wide-field photometric catalog obtained from the Hyper Suprime-Cam (HSC) Subaru Strate…

astro-ph.GA2026★ 1 cited

Galactic Archaeology with the Subaru `Ōnohi`ula Prime Focus Spectrograph Strategic Program

Masashi Chiba, Rosemary F. G. Wyse, Evan N. Kirby +48

The recently commissioned Subaru `Ōnohi`ula Prime Focus Spectrograph (PFS) will obtain spectra from nearly 2,400 fibers that cover 1.24 square degrees. The 360 night Subaru Strateg…

A Long Stellar Stream in M83: Possible Connection Between XUV Disks and Minor Mergers?

Itsuki Ogami, Sakurako Okamoto, Annette M. N. Ferguson +5

We present the confirmation and characterization of a long stream (S-stream) in the southern part of M83. This feature is revealed using deep wide-field photometric data obtained b…

Fuzzy Dark Matter and the Impact of Core--Halo Diversity on Its Particle Mass Constraints

Dafa Wardana, Kohei Hayashi, Masashi Chiba +1

We investigate how diversity in the core--halo mass relation and the inclusion of higher-order velocity moments affect constraints on the fuzzy dark matter particle mass ( $m_{ψ}$ ) in…

Subaru/HSC NB395 view of NGC 5466: metallicity, mass function, and the nature of its tidal stream

Itsuki Ogami, Miho N. Ishigaki, Pete B. Kuzma +6

We present a deep photometric study of the globular cluster NGC 5466 and its tidal stream using Subaru/Hyper Suprime-Cam (HSC) imaging with the metallicity-sensitive narrowband fil…

Estimating accretion times of halo substructures in the Milky Way

Hefan Li, Masashi Chiba, Xiang-Xiang Xue +1

To unravel the formation history of the Milky Way, we estimate the accretion times of six phase-space substructures in the stellar halo, using the orbital frequencies toward two sp…

Machine Learning Techniques to Distinguish Giant Stars from Dwarf Stars Using Only Photometry -- Pushing Redwards

Keyi Ding, Carrie Filion, Rosemary F. G. Wyse +6

We present our photometric method, which combines Subaru/HSC $N B 515$ , g, and i band filters to distinguish giant stars in Local Group galaxies from Milky Way dwarf contamination. T…

The Extended Stellar Distribution in the Outskirts of the Ursa Minor Dwarf Spheroidal Galaxy

Kyosuke S. Sato, Sakurako Okamoto, Masafumi Yagi +7

We discover an extended distribution of main-sequence (MS) stars along the minor axis of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). This study is enabled by deep, wide Su…

Estimating Fe and Mg Abundances in the Milky Way Dwarf Galaxies Using Subaru/HSC and DEIMOS

Jihye Hong, Evan N. Kirby, Tiffany M. Tang +5

We investigate the chemical abundance distributions of the Fornax, Sculptor, Ursa Minor, and Draco dwarf galaxies using Subaru/HSC photometric data. The HSC dataset, which includes…

The Star Formation and Chemical Evolution Histories of Ursa Minor Dwarf Spheroidal Galaxy

Kyosuke S. Sato, Yutaka Komiyama, Sakurako Okamoto +8

We derive the star formation history (SFH) and chemical evolution history (CEH) of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). We detect two distinct stellar populations t…

Simultaneous Formation of the Andromeda Giant Southern Stream and the Substructures in the Andromeda Halo

Misa Yamaguchi, Masao Mori, Takanobu Kirihara +4

We investigate a minor merger event in M31 that simultaneously forms the Andromeda Giant Southern Stream (AGSS), Eastern Extent (EE), North-Eastern Shelf (NES), and Western Shel (W…

The $R$ -Process Alliance: Enrichment of $r$ -process Elements in a Simulated Milky Way-like Galaxy

Yutaka Hirai, Timothy C. Beers, Young Sun Lee +11

We study the formation of stars with varying amounts of heavy elements synthesized by the rapid neutron-capture process ( $r$ -process) based on our detailed cosmological zoom-in sim…

Triangulum IV: A Possible Ultra-Diffuse Satellite of M33

Itsuki Ogami, Yutaka Komiyama, Masashi Chiba +8

We report the detection of a dwarf satellite candidate (Triangulum IV: Tri IV) of the Triangulum galaxy (M33) using the deep imaging of Subaru/Hyper Suprime-Cam (HSC). From the app…

Chemo-dynamical Evolution of Simulated Satellites for a Milky Way-like Galaxy

Yutaka Hirai, Evan N. Kirby, Masashi Chiba +5

The chemical abundances of Milky Way's satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most s…

Uncovering the Ghostly Remains of an Extremely Diffuse Satellite in the Remote Halo of NGC 253

Sakurako Okamoto, Annette M. N. Ferguson, Nobuo Arimoto +12

We present the discovery of NGC253-SNFC-dw1, a new satellite galaxy in the remote stellar halo of the Sculptor Group spiral, NGC 253. The system was revealed using deep resolved st…

Disentangling gamma-beta: the 4th-order velocity moments based on spherical Jeans analysis

Dafa Wardana, Masashi Chiba, Kohei Hayashi

Distinguishing a core and a cusp within dark matter halos is complexified by the existence of mass-anisotropy degeneracy, where various combinations of velocity anisotropy ( $β$ ) an…

Detection of a Spatially Extended Stellar Population in M33: A Shallow Stellar Halo?

Itsuki Ogami, Yutaka Komiyama, Masashi Chiba +8

We analyze the outer regions of M33, beyond 15 kpc in projected distance from its center using Subaru/HSC multi-color imaging. We identify Red Giant Branch (RGB) stars and Red Clum…

New insights on the dynamics of satellite galaxies: effects of the figure rotation of a host galaxy

Genta Sato, Masashi Chiba

We investigate a mechanism to form and keep a planar spatial distribution of satellite galaxies in the Milky Way (MW), which is called the satellite plane. It has been pointed out…