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Dark Matter Density Profiles in Milky Way Dwarf Spheroidal Galaxies
Dark Matter Density Profiles in Milky Way Dwarf Spheroidal Galaxies
Dwarf spheroidal galaxies (dSphs) orbiting the Milky Way are among the most dark matter-dominated stellar systems in the Universe. By analyzing the motions of stars within these galaxies, we have revealed that their dark matter density profiles exhibit remarkable diversity, ranging from centrally dense “cuspy” profiles to flat “cored” ones. This diversity offers critical clues to understanding the nature of dark matter and the processes that shaped galaxy formation.
（Refs. Hayashi & Chiba2012, Hayashi+2020, Hayashi+2023）
Constraints on Fuzzy Dark Matter and Self-Interacting Dark Matter from Milky Way Dwarf Spheroidal Galaxies
Constraints on Fuzzy Dark Matter and Self-Interacting Dark Matter from Milky Way Dwarf Spheroidal Galaxies
Fuzzy dark matter and self-interacting dark matter (SIDM) have been proposed as alternatives to cold dark matter (CDM) to address small-scale structure challenges. Using observations of stellar dynamics and density profiles of Milky Way dSphs, we place constraints on the parameters of these models, such as the particle mass of fuzzy dark matter or the self-interaction cross section of SIDM. Our work helps narrow down the possible properties of dark matter and tests key theoretical models.
（Refs. Hayashi+2021, Hayashi+2021, Ando+2025）
Dark Matter Indirect Searches through dwarf spheroidal galaxies
Dark Matter Indirect Searches through dwarf spheroidal galaxies
If dark matter decays or annihilates, it is expected to produce high-energy cosmic rays such as gamma rays and X-rays. We aim to detect such signals indirectly from the Galactic center and Milky Way dwarf spheroidal galaxies using cosmic-ray observatories, including gamma-ray telescopes like the Cherenkov Telescope Array (CTA) and X-ray observatories like XRISM. Through this research, we place stringent constraints on dark matter decay lifetimes and annihilation cross sections, and seek potential discoveries of new physics beyond the standard model.
（Refs. Hayashi+2016, Horigome+2020）
Dark Matter Studies with Subaru PFS Observations of Dwarf Galaxies
Dark Matter Studies with Subaru PFS Observations of Dwarf Galaxies
The Prime Focus Spectrograph (PFS) on the Subaru Telescope is a powerful instrument capable of wide-field, multi-object spectroscopy. We are utilizing PFS to simultaneously measure the line-of-sight velocities of numerous stars in Milky Way dwarf galaxies. This enables unprecedentedly precise estimates of their dark matter distributions. Our goal is to uncover the internal structure of dwarf galaxies, the slope of dark matter density profiles, and the role of dark matter in galaxy formation and evolution. Future PFS observations are expected to significantly advance constraints on dark matter models.
(Refs. Takada+2014, Hayashi+2023）
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