113 citations · 725 across the 26 of their papers we have counts for
26 papers
The First Star-by-star -body/Hydrodynamics Simulation of Our Galaxy Coupling with a Surrogate Model
Keiya Hirashima, Michiko S. Fujii, Takayuki R. Saitoh +9
A major goal of computational astrophysics is to simulate the Milky Way Galaxy with sufficient resolution down to individual stars. However, the scaling fails due to some small-sca…
ASURA-FDPS-ML: Star-by-star Galaxy Simulations Accelerated by Surrogate Modeling for Supernova Feedback
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +5
We introduce new high-resolution galaxy simulations accelerated by a surrogate model that reduces the computation cost by approximately 75 percent. Massive stars with a Zero Age Ma…
Simulations predict intermediate-mass black hole formation in globular clusters
Michiko S. Fujii, Long Wang, Ataru Tanikawa +2
Intermediate-mass black holes (IMBHs) are those between 100 and 10 solar masses (); their formation process is debated. One possible origin is the growth of less mas…
Surrogate Modeling for Computationally Expensive Simulations of Supernovae in High-Resolution Galaxy Simulations
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +4
Some stars are known to explode at the end of their lives, called supernovae (SNe). The substantial amount of matter and energy that SNe release provides significant feedback to st…
Probing the Galactic Halo with RR Lyrae Stars -- V. Chemistry, Kinematics, and Dynamically Tagged Groups
Jonathan Cabrera Garcia, Timothy C. Beers, Yang Huang +9
We employ a sample of 135,873 RR Lyrae stars (RRLs) with precise photometric-metallicity and distance estimates from the newly calibrated ------[Fe/H] and …
Insights on the Sun birth environment in the context of star-cluster formation in hub-filament systems
Doris Arzoumanian, Sota Arakawa, Masato I. N. Kobayashi +7
Cylindrical molecular filaments are observed to be the main sites of Sun-like star formation, while massive stars form in dense hubs, at the junction of multiple filaments. The rol…
The Origin of the Large Magellanic Cloud Globular Cluster NGC 2005
Andrés E. Piatti, Yutaka Hirai
The ancient Large Magellanic Cloud (LMC) globular cluster NGC 2005 has recently been reported to have an ex-situ origin, thus, setting precedents that the LMC could have partially…
EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies
Yi Xu, Masami Ouchi, Yuki Isobe +49
We present demography of the dynamics and gas-mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of and low stellar masses of $10^4-…
EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs
Moka Nishigaki, Masami Ouchi, Kimihiko Nakajima +16
We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data…
3D-Spatiotemporal Forecasting the Expansion of Supernova Shells Using Deep Learning toward High-Resolution Galaxy Simulations
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +3
Supernova (SN) plays an important role in galaxy formation and evolution. In high-resolution galaxy simulations using massively parallel computing, short integration timesteps for…
Chemo-Dynamically Tagged Groups of CEMP Stars in the Halo of the Milky Way. I. Untangling the Origins of CEMP- and CEMP-no Stars
Joseph Zepeda, Timothy C. Beers, Vinicius M. Placco +7
We construct a sample of 644 carbon-enhanced metal-poor (CEMP) stars with abundance analyses based on moderate- to high-resolution spectroscopic studies. Dynamical parameters for t…
SIRIUS Project. V. Formation of off-center ionized bubbles associated with Orion Nebula Cluster
Michiko S. Fujii, Kohei Hattori, Long Wang +4
Massive stars born in star clusters terminate star cluster formation by ionizing the surrounding gas. This process is considered to be prevalent in young star clusters containing m…
EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?
Yuki Isobe, Masami Ouchi, Kimihiko Nakajima +49
We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities () and low stellar masses (). Tak…
Origin of highly -process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
Yutaka Hirai, Timothy C. Beers, Masashi Chiba +5
The -process-enhanced (RPE) stars provide fossil records of the assembly history of the Milky Way and the nucleosynthesis of the heaviest elements. Observations by the -Proce…
Dark matter halo properties of the Galactic dwarf satellites: implication for chemo-dynamical evolution of the satellites and a challenge to CDM
Kohei Hayashi, Yutaka Hirai, Masashi Chiba +1
Elucidating dark matter density profiles in the Galactic dwarf satellites is essential to understanding not only the quintessence of dark matter, but also the evolution of the sate…
EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension
Akinori Matsumoto, Masami Ouchi, Kimihiko Nakajima +42
The primordial He abundance is a powerful probe of cosmology. Currently, is best determined by observations of metal-poor galaxies, while there are on…
SIRIUS Project. IV. The formation history of the Orion Nebula Cluster driven by clump mergers
Michiko S. Fujii, Long Wang, Yutaka Hirai +3
The Orion Nebula Cluster (ONC) is an excellent example for understanding the formation of star clusters. Recent studies have shown that ONC has three distinct age populations and a…
Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
Shinya Wanajo, Yutaka Hirai, Nikos Prantzos
Recent progress of nucleosynthesis work as well as the discovery of a kilonova associated with the gravitational-wave source GW170817 indicates that neutron star mergers (NSM) can…
SIRIUS Project. III. Star-by-star simulations of star cluster formation using a direct N-body integrator with stellar feedback
Michiko S. Fujii, Takayuki R. Saitoh, Yutaka Hirai +1
One of the computational challenges of cluster formation simulations is resolving individual stars and simulating massive clusters with masses of more than without…
-process enhancements of Gaia-Enceladus in GALAH DR3
Tadafumi Matsuno, Yutaka Hirai, Yuta Tarumi +3
The dominant site of production of -process elements remains unclear despite recent observations of a neutron star merger. Observational constraints on the properties of the sit…
SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
Yutaka Hirai, Michiko S. Fujii, Takayuki R. Saitoh
Most stars are formed as star clusters in galaxies, which then disperse into galactic disks. Upcoming exascale supercomputational facilities will enable performing simulations of g…
Enrichment of Strontium in Dwarf Galaxies
Yutaka Hirai, Shinya Wanajo, Takayuki R. Saitoh
Light trans-iron elements such as Sr serve as the key to understanding the astrophysical sites of heavy elements. Spectroscopic studies of metal-poor stars have revealed large star…
Enrichment of Zinc in galactic chemodynamical evolution models
Yutaka Hirai, Takayuki R. Saitoh, Yuhri Ishimaru +1
The heaviest iron-peak element, Zn has been used as an important tracer of cosmic chemical evolution. Spectroscopic observations of the metal-poor stars in Local Group galaxies sho…
Efficiency of metal mixing in dwarf galaxies
Yutaka Hirai, Takayuki R. Saitoh
Metal mixing plays critical roles in the enrichment of metals in galaxies. The abundance of elements such as Mg, Fe, and Ba in metal-poor stars help us understand the metal mixing…