談話会
Colloquium

山田 智史（東北大学）
Accretion and Multi-scale Ejection Resolved by X-ray Observations from 1999 to 2025
To make a database of multiphase (e.g., ionized/dusty/neutral/molecular) outflows, we have launched a new project, X-ray Winds In Nearby-to-distant Galaxies (X-WING). As the first study of the X-WING project, we constructed a sample of 132 AGNs in z ~ 0-4 exhibiting blueshifted absorption lines of X-ray winds reported by the end of 2023. With a thorough investigation of the previous works, we created the database of outflow properties of 583 X-ray winds, including outflow velocities (Vout), outflow radii (Rout), and mass/kinetic outflow rates (Mout/Eout). The ultrafast outflows (UFOs) and slower warm absorbers cover the Vout range of ~100 to 100,000 km/s. Interestingly, we found a clear velocity gap around Vout ~ 10,000 km/s. Although the gap can be an artifact due to the confusion of the emission/absorption lines and Fe K edge in the 6-7 keV band, there is another possibility that the UFOs and galactic-scale outflows are physically disconnected. Moreover, we introduce our unprecedented high-energy-resolution spectra with XRISM operated from 2023 and provide new insights into the origin of the Vout gap and the plausible multi-scale structure of X-ray winds (e.g., Yamada+24b, ApJS; XRISM Collaboration+). Finally, we will also report the latest results of the UV-to-radio SED fittings and studies on multiphase outflows for the X-WING AGNs and discuss the accretion and multi-scale ejection in AGNs.

Colton Hill（Chiba Univ.）
South Pole Science - Neutrino Oscillations and the IceCube Neutrino Detector Upgrade
Of all the Standard Model particles, neutrinos are the least well understood. While significant global progress has been made in characterising neutrino oscillations, several key questions remain unanswered: what are the masses of the neutrinos, and do neutrino oscillations truly follow the standard three-flavour model? The cubic-kilometre IceCube Neutrino Detector located at the geographic South Pole is capable of precision measurements of neutrino oscillation properties by observing neutrinos produced from particle interactions in the atmosphere across a broad range of energies (GeV-scale) and path lengths, often travelling through the Earth. To increase IceCube's sensitivity in the GeV-range, the IceCube Upgrade will involve deploying a dense array of high-sensitivity optical modules up to 3 km deep into the Antarctic glacier at the end of this year. One of these flagship modules, the "D-Egg", was developed and tested in Japan as part of an international effort for the Upgrade, and features a factor 2.8 per-device improvement in sensitivity over the current generation detectors. With enhanced direction reconstruction and a lower energy threshold, the Upgrade is expected to probe the neutrino mass ordering at the 3 sigma level within 5 years, and observe tau-neutrino appearance after just one year of data taking. As of January 2025, all 292 D-Eggs have arrived at the South Pole, with approx. 30% having already completed pre-deployment testing. This seminar with focus on the progress of the IceCube Upgrade, including the South Pole activities of the 2024/2025 Antarctic On-Ice Season, and share the latest sensitivities for the IceCube Upgrade ahead of data-taking later next year.

堀米 俊一（東北大学）
Dwarf spheroidal galaxies as probes of dark matter
The presence of dark matter in our universe is one of the biggest open questions in particle physics, astronomy, and cosmology. Among several detection methods, astronomical observations can explore interesting parameter regions that are not easily accessible by collider or direct detection experiments. In this talk, we focus on one of the most promising targets: dwarf spheroidal galaxies (dSphs), which are dark-matter dominated satellite galaxies of the Milky Way. We show recent results of dynamical analyses using the spherical Jeans equation, a standard tool in stellar dynamics, to constrain the dark matter density profiles of dSphs. To interpret these results in a cosmological context, we use a semi-analytical cosmological model called SASHIMI (Semi-Analytical SubHalo Inference ModelIng), which predicts subhalo properties such as mass and density structure. These predictions are used as priors in a Bayesian analysis to connect observations with theoretical dark matter models. For cold dark matter (CDM), we apply this framework to estimate the J-factors of dSphs, which are important for indirect detection studies. For self-interacting dark matter (SIDM), we extend the model to SASHIMI-SIDM, which includes the effects of self-scattering on subhalo evolution. By comparing with observed satellite galaxies, we derive quantitative constraints on the self-interaction cross section, showing how small-scale structures in dSphs can inform the fundamental properties of dark matter.

Mochammad Wardana（東北大学）
Dwarf spheroidal galaxies as probes of dark matter, too: a stellar dynamics model refinement and test on the fuzzy dark matter paradigm
The preference for cored dark matter density profiles in dwarf disk galaxies has long stirred tensions over the internal structure of dark matter halos, further complicating the Cold Dark Matter (CDM) crisis at sub-galactic scales. Kinematic measurements of stars in the even more dark matter–dominated dwarf spheroidal (dSph) satellites of the Milky Way offer a promising, less baryon-contaminated avenue to revisit these issues. As data on individual member stars improve in both precision and sample size, dynamical estimates of their underlying mass distributions are becoming increasingly accessible. However, the inferred dark matter density profiles show significant variation. Some galaxies are more consistent with cored profiles, others with cuspy ones, and some analyses report that both core and cusp profiles are equally plausible. This may be a clue that the classic core–cusp problem is just the tip of a larger “diversity” problem, and it certainly signals the need for more refined modeling to distinguish cores and cusps apart more reliably. We, therefore, attempt to extract more information contained in the non-uniform shape of the line-of-sight velocity distribution, which is assumed to be fixed in traditional Jeans modeling. This is achieved by invoking the stars’ higher-order velocity moments alongside their standard velocity dispersion. We demonstrate the model’s improved capacity for recovering dark matter density profiles and discuss its inherent limitations. In addition, we explore the implications of our model within the context of fuzzy dark matter (FDM) theory, an alternative to CDM that gained growing attention for its potential to reconcile observations and theory. We provide preliminary constraints on the FDM particle mass necessary to address the core–cusp tension observed in classical Milky Way dSphs.

Zhaoran Liu（東北大学）
Unveiling Hidden Star-formation within Galaxies at 0.9 < z < 1.7
Galaxies experience their most intense stellar growth at redshifts z = 1–3, yet a significant fraction of this activity is obscured by dust. In this talk, I will present a multi-wavelength, multi-tracer investigation that combines observations from JWST, ALMA, and Subaru to trace both the fuel for star formation and its by-products, interstellar dust, in galaxies at 0.9 < z < 1.7, immediately after the cosmic noon. Some of the key questions I aim to answer include: Where in galaxies and how much is dust involved in the starburst and secular phases? How is it related to the propagation of star formation and quenching within galaxies? And how do local and large-scale environments modulate the relation between star formation and dust properties? To address these questions, I will present our work using a combination of tracers: the 3.3 μm PAH emission observed with JWST/MIRI to map dusty star-forming regions; Paα emission obtained through JWST/NIRCam WFSS to trace total star formation including hidden dusty component at high spatial resolution; CO(2–1) measurements from ALMA to probe the molecular gas reservoir fueling star formation; and Hα/Hβ-based dust extinction mapping across a z = 0.9 supercluster using Subaru narrow-band imaging. Together, these observations provide a comprehensive view of the gas, star formation, and dust cycle and reveal how internal processes and external environments shape galaxy growth during and shortly after the peak epoch

佐藤 優理（東北大学）
Multiwavelength afterglows from two-component jets in very-high-energy gamma-ray bursts
Gamma-ray bursts (GRBs) are the most luminous and violent explosive electromagnetic events in the universe. GRBs also have broadband afterglows, from radio to very-high-energy (VHE) gamma rays, which provide us with extensive physical information about their nature. Currently, it is widely believed that prompt gamma-ray photons are emitted by a relativistic jet toward us, and that the interaction of this jet with the surrounding medium of the source generates the afterglow. However, many fundamental questions remain unanswered: how is the relativistic jet formed, what is the origin of the central engine, and how is the multiwavelength afterglow radiated? In this talk, we explore the phenomena associated with the relativistic two-component jet, which consists of two top-hat jets with angularly equi-distributed energy with different opening angles, to investigate the formation mechanism of relativistic jets. In general, the GRB jets have an angular structure, which is also shown in previous hydrodynamic simulations. Such a structured jet is most simply approximated by a two-component jet. The two-component jet model has been motivated to explain the multiwavelength afterglow emission in some GRB events. Our two-component jet model successfully explains the multiwavelength afterglows of GRBs associated with VHE gamma-ray emission. These findings suggest that a structured jet, such as the two-component jet, is essential for explaining complex multiwavelength afterglows.

喜友名 正樹（東北大学）
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Nuo Chen（東北大学）
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野田 浩司 (千葉大学)
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Chris Packham (University of Texas)
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馬場 淳一 (鹿児島大学)
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横山 哲也 (東京科学大学)
Chemical and isotopic analyses of samples returned by the Hayabusa2 mission from the asteroid Ryugu
The recent success of asteroid sample return missions has led to significant advances in Solar System science. JAXA's Hayabusa2 successfully retrieved and returned to Earth a total of 5.4 grams of samples from the C-type asteroid Ryugu. Sample return missions are critical to the scientific community, particularly in the fields of planetary science and cosmochemistry. These missions provide pristine, terrestrially unaltered extraterrestrial materials, allowing detailed laboratory analyses that are not possible with remote sensing. The only other access to extraterrestrial materials is meteorites, but meteorites may have been contaminated by terrestrial materials during impact, during residence time prior to collection (meteorite finds), and during storage in meteorite collections prior to changes in curation protocols. Thus, the analytical data obtained in laboratories for samples collected by these missions will facilitate the understanding of the formation and evolution of the Solar System without bias from potentially contaminated data. For the Hayabusa2 mission, six initial analysis teams (Chemistry, Rock, Sand, Gas, SOM, and IOM) and two Phase 2 curation analysis teams were established, each consisting of up to several dozen individual researchers. I was appointed deputy leader of the Chemistry team and was heavily involved in analyzing the chemical and isotopic compositions of the Ryugu materials. A series of analyses of these samples indicated that the mineral, chemical, and isotopic compositions of Ryugu bear a strong resemblance to those of the Ivuna-type (CI) carbonaceous chondrites. CI chondrites have been recognized as a unique group of meteorites with a chemical composition similar to that of the solar photosphere except for highly volatile elements (noble gases, H, C, N, and O) and Li, which was destroyed in the Sun by nuclear reactions. In the seminar, I will present the meaning and significance of the compositional similarity between Ryugu and CI chondrites. I will also present our recent activities in a new project called the Ryugu Reference Project (RRP), which was initiated to maximize the potential value of the returned sample, aiming to establish an international standard for elemental and isotopic abundances in the solar system using the Ryugu samples and other related extraterrestrial materials.

津久井 崇史 (東北大学)
TBA

志達 めぐみ (愛媛大学)
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