談話会
Colloquium

野田 博文（東北大学）
X-ray Observations and Detector Developments to Study the AGN Central Engine
The central engine which consists of an X-ray corona and accretion disk in the vicinity of a supermassive black hole is the origin of powerful radiation from an Active Galactic Nucleus (AGN). However, even its fundamental properties, such as its accretion state, geometric structure, and how these change with varying mass accretion rates have not yet been well understood. To establish the picture of the AGN central engine, we have performed X-ray and multi-wavelength observations of highly variable sources including changing-look AGNs which change their types in short timescales and are under much debate. In parallel, we have developed X-ray detectors onboard Japanese X-ray astronomical satellites, Hitomi and XRISM, to realize unprecedented X-ray spectral resolution for AGN studies. In this presentation, I introduce our observational studies, detector development, and prospects with XRISM for understanding the AGN central engine.

石崎 渉（東北大学）
Fallback Accretion in Binary Neutron Star Mergers
The gravitational wave event GW170817 with a kilonova shows that a merger of two neutron stars ejects matter with radioactivity including r-process nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering long-lasting activities of a short gamma-ray burst (sGRB). We investigate the fallback accretion with the r-process heating by performing 1D hydrodynamic simulations and developing a semi-analytical model. We show that the fallback is halted by the heating. The characteristic halting timescale is 10^4-8 sec for the GW170817-like r-process heating, which is long enough to continue the long-lasting emission of sGRBs.
Furthermore, I will present a new interpretation of the recently reported re-brightening in the annual-scale X-ray light curve of GW170817. We model the fallback of the merger ejecta and construct a simple light curve model from the accreting ejecta. We find that the X-ray flux excess can be well explained by the fallback of the post-merger ejecta rather than the dynamical ejecta.
If time allows, I would like to introduce a study on the decay of Alfven waves in strongly magnetized plasmas. This process is relevant not only to binary neutron star mergers but also to the general problem in high-energy astrophysics in the context of the conversion of electromagnetic field energy into matter energy.

Ue-Li Pen（ASIAA）
FRBs: what are they and what are they good for?
Fast Radio Bursts are short, millisecond flashes thousands of times per day, distributed isotropically on the sky. I outline our current state of understanding for their nature and environment and their unique properties of cosmic probes. I describe the new BURSTT FRB initiative for ambitious instantaneous fish-eye coverage with VLBI localization across Asia, including Ogasawara and India.

Ronaldo LAISHRAM（東北大学）
Cosmic Evolution and Environmental Dependence of Star Forming Activities and Morphologies
The distribution of galaxies in the universe is inhomogeneous, representing large-scale structures (LSS) that consist of galaxy clusters, groups, and the filaments that connect them. Understanding how galaxy characteristics are influenced by their environments and how they evolve over cosmic time within LSS is crucial. Utilizing dual narrow-band filters for precise redshift estimation, we investigate the environmental effects on star formation within large-scale structures. We explore star-forming activity and the spatial distribution of Hα and continuum emission at z=0.4, probing the cosmic web. We found that star formation in cluster core galaxies is more centrally concentrated and reduced compared to the field sample, which may imply the influence of ram-pressure stripping. We also explore the morphological features and star formation activities of [OII] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. Furthermore, we report the discovery of large filamentary structures traced by [OII] emitters, surrounding an extremely overdense core with a galaxy number density ∼ 11× higher than the field average. Heightened star-forming activity was observed in dense regions, contrary to z=0.4, suggesting an environmental impact on early galaxy evolution. Additionally, we examine the redshift evolution of star-forming activities and morphology. Future studies will explore into the chemical abundance, gas content, and kinematics to comprehend the underlying processes.

安部 大晟（東北大学）
Formation & Evolution of Star-forming Filaments in Molecular Clouds
Observations of molecular clouds indicate that dense filaments are the sites for present-day star formation. Therefore, it is crucial to understand filament formation and evolution, as these filaments provide the initial conditions for star formation. The width of filaments is a significant factor as it determines the fragmentation scale through self-gravity and affects the stellar masses to be formed. Observations suggest that the width has a universal value of 0.1 pc, regardless of the filament’s line mass. However, theoretical predictions suggest that the width of supercritical filaments (> 17 solar masses per pc) should contract due to self-gravity. Most simulations show a much narrower width due to strong gravity for massive filaments, and why massive filaments maintain their width of 0.1 pc has remained unexplained for more than ten years. Recent studies suggest that massive filaments (~100 solar masses per pc) are bound by slow mode shocks resulting from accretion flows onto the filaments. The wavefront of the slow mode shock is known to be unstable, and the corrugation of the shock front grows. This corrugation converts the accretion flow’s ram pressure into thermal/turbulent pressure across the shock front, possibly maintaining the filament’s width. In this study, we perform non-ideal MHD simulations to investigate filament evolution via slow shock instability, considering ambipolar diffusion, which is effective in dense filaments. We discovered slow shock instability including ambipolar diffusion drives anisotropic turbulence in the massive filament, named this new mechanism the “bullet mechanism”. We also conducted a simulation considering self-gravity and found that the bullet mechanism can sustain a realistic filament width, even for a filament as massive as ~100 solar masses per pc.

Jeong-Gyu Kim（National Astronomical Observatory of Japan）
Modeling Multiphase, Star-forming ISM with UV Radiation Feedback from Massive Stars
UV radiation emitted by massive stars is the major source of heating and ionization in the interstellar medium (ISM). H II regions created by ionizing photons photoevaporate and expel giant molecular clouds, controlling their star formation efficiency and lifetime. Far-UV photons escaping into the large-scale ISM produce the interstellar radiation field, which in turn sets the thermal pressure of diffuse neutral gas via grain photoelectric heating. The efficiency with which UV radiation (and supernovae) feedback recovers the ISM pressure required to meet the vertical dynamical equilibrium determines the galactic star formation rate. Drawing from recent theoretical models and numerical simulations of multiphase, star-forming ISM with UV radiation feedback, I will overview our current understanding of how stellar UV radiation interacts with the surrounding ISM and how this affects star formation and multiphase structure on both cloud and galactic scales.

Hefan Li（東北大学）
Measuring the influence of the LMC on the Milky Way based on velocity ellipsoid
The Milky Way evolved by accreting nearby dwarf galaxies. In this process, these galaxies are tidally disrupted and leave behind stellar streams and substructures in the Milky Way halo. On the other hand, they are affecting the Milky Way in a number of ways. Here, we study the velocity zero point of the inner halo caused by the Large Magellanic Cloud (LMC), the most massive galaxy near the Milky Way. By collecting data from several large surveys, a large data set of stars is assembled. The distances, ages, initial stellar masses, and reddenings for the stars are computed using the calibrated atmospheric parameters and Gaia-DR3 photometry. We kinematically and chemically select halo stars and measure the reflection motion at different locations based on their velocity ellipsoids. In addition, we find that the reflection motion reduces the radial dominance of the anisotropic parameters, thereby affecting estimates of the Milky Way mass.

和田 知己（東北大学）
Magnetar Bursting Activities: X-ray and Radio Transients
Magnetars are neutron stars whose photospheric luminosities are higher than their spin-down luminosities. They have strong magnetic fields of ∼ 10¹⁵ G, believed to be the source of their high photospheric luminosities. Magnetars frequently exhibit bursting activities in X-rays, such as short bursts, outbursts, and giant flares. Magnetars are also strong candidates for fast radio bursts, mysterious radio transients. There are many observational results about magnetar bursting activities, but many aspects remain unclear, such as the triggers of the bursts, the emission mechanisms of fast radio bursts, and the potential for other signals.
We study the bursting activities of magnetars. First, we study a possible triggering mechanism of the bursts. We focus on the Dzhanibekov effect in magnetars, which is a kind of free precession, and suggest that this effect may trigger bursting activities. Second, we study a plasma outflow that can be formed during the bursts. Our numerical simulations demonstrate that the outflow can be accelerated to ultra-relativistic velocities through radiative acceleration in a strong magnetic field. The ultra-relativistic outflow can be the energy budget for fast radio bursts. Third, we study the neutrino emission from magnetar bursts. We evaluate the neutrino luminosity from the ultra-relativistic outflow in the magnetar bursts and discuss the possibility of detecting high-energy neutrinos from magnetar bursts. Based on these studies, we discuss the origins and consequences of the magnetar bursting activities.

Juan Pablo Alfonzo（東北大学）
Katachi (形): Decoding the Imprints of Past Star Formation on Present-Day Morphology in Galaxies with Interpretable CNNs
The physical processes responsible for shaping how galaxies form and quench over time leave imprints on both the spatial (galaxy morphology) and temporal (star formation history; SFH) tracers that we use to study galaxies. While the morphology-SFR connection is well studied, the correlation with past star formation activity is not as well understood. To quantify this we present Katachi (形), an interpretable convolutional neural network (CNN) framework that learns the connection between the factors regulating star formation in galaxies on different spatial and temporal scales. Katachi is trained on 9904 galaxies at 0.02<z<0.1 in the SDSS-IV MaNGA DR17 sample to predict stellar mass (M∗; RMSE 0.22 dex), current star formation rate (SFR; RMSE 0.31 dex) and half-mass time (t50; RMSE 0.23 dex). This information allows us to reconstruct non-parametric SFHs for each galaxy from gri imaging alone. To quantify the morphological features informing the SFH predictions we use SHAP (SHapley Additive exPlanations). We recover the expected trends of M∗ governed by the growth of galaxy bulges, and SFR correlating with spiral arms and other star-forming regions. We also find the SHAP maps of D4000 are more complex than those of M∗ and SFR, and that morphology is correlated with t50 even at fixed mass and SFR. Katachi serves as a scalable public framework to predict galaxy properties from large imaging surveys including Rubin, Roman, and Euclid, with large datasets of high SNR imaging across limited photometric bands.

Ryuji Suzuki (National Astronomical Observatory of Japan)
Personal views of astronomical instrumentation and how to build/plan new instruments
This talk picks up some aspects of instrumentation for the ground-based opt-IR astronomy with a focus on the instrumentation in the carrier path, how to build an instrument, and how to plan a new instrument. The talk aims to introduce the ground-based opt-IR instrumentation to those who are not familiar with it, including researchers in different fields, students, and young researchers who are interested in the instrumentation as a part of their career.
I will start the talk by defining the instrumentation in the field of astronomy in relation to the other fields, and emphasize the importance of instrumentation in historical perspective as well as in the career of a researcher. The project size, one of the important aspects of instrumentation, is discussed in the context of an early stage of the carrier path. Some examples are given to illustrate typical instrumentation project phases and milestones as well as the possible team structure scenarios that you may need to build an instrument.
The last part of this talk is devoted to the instrumentation in a big project, how scientists are involved in the project, and how to plan the new instrument which is one of the goals of the ongoing TMT-ACCESS workshop. I will walk the audience through a requirement flow from science cases to the instrument in case of TMT.

Evan Kirby (University of Notre Dame)
The Extremes of Resolved Stellar Spectroscopy
The study of dwarf galaxies with existing spectroscopic instruments and techniques has reached the point of diminishing returns. I will describe the measurement of radial velocities and abundances of individual stars in dwarf galaxies at the threshold of spectral resolution and signal-to-noise ratio. First, I will address measurements from Keck/DEIMOS. I will discuss the case of Andromeda XVIII, at a distance of 1.3 Mpc, which is a possible backsplash galaxy after passing through M31's halo. I will also describe chemical measures of star formation histories in classical dSphs with neutron-capture elements. Finally, I will discuss the promise of the Subaru Prime Focus Spectrograph (PFS) in using dwarf galaxies to learn the nature of dark matter and to study chemical evolution at galactic subscales.

Benedetta Vulcani (Istituto Nazionale di Astrofisica)
Not all the action is in clusters: environmental effects on field galaxies
Galaxies inhabit a wide range of environments and therefore are affected by different physical mechanisms. While environmental effects are typically deemed significant mainly within galaxy clusters, even outside clusters, galaxies can be significantly affected by external processes connected to their position within the cosmic web. First, I will discuss the role of filaments in affecting galaxy properties in the local Universe, by focusing on the filaments flowing onto Virgo, the closest cluster to us. Next, exploiting the data from the GAs Stripping Phenomena in galaxies (GASP) survey I will discuss the multitude of mechanisms that can affect galaxies in isolation, groups and filaments. Spatially resolved maps combined with the knowledge of the hosting environment are indeed very powerful for classifying galaxies by physical process. I will show how a single group can host galaxies undergoing many different processes, such as starvation, ram pressure stripping and gas accretion. I will also show how filaments can assist gas cooling and increase the star formation in the densest regions in the circumgalactic gas of the galaxies flowing through them. I will then show examples of galaxy-galaxy interactions, mergers, and cosmic web stripping. I will emphasise the successes and limitations of a visual optical selection in identifying the processes that deplete galaxies of their gas content and probes the power of IFU data in pinning down the acting mechanism. Future facilities will allow to perform similar analyses at higher redshifts.

北島 歓大（名古屋大学）
An Origin of Narrow Extended Structure in the Interstellar Medium: An Interstellar Contrail Created by a Fast-moving Massive Object
The filamentary structure is the general morphology of the interstellar medium. Their length varies from less than 1 pc to over 100 pc. The formation process of long filaments is still unknown, although the formation process of filaments has been extensively studied. We investigate the thermal condensation caused by a massive object such as a black hole that passes through the interstellar medium with high velocity, and propose a mechanism for creating a filamentary gaseous object, or interstellar contrail. Our main result shows that a long interstellar contrail can form with a certain parameter; a compact object more massive than 10⁴ solar masses can make a filament whose length is larger than 100 pc. Observation of interstellar contrails may provide information on the number, masses, and velocities of fast-moving massive objects, and can be a new method for probing invisible gravitating sources such as intermediate-mass black holes.

藤林 翔（東北大学）
Mass ejection and nucleosynthesis in binary neutron star mergers
Binary neutron star merger is a fascinating astrophysical phenomenon in many aspects: It is one of the primary targets of gravitational wave detectors, it triggers various astrophysical transients in association with its mass ejection activities, and it is one of the promising sites for heavy element synthesis in the Universe. The merger is a highly non-linear process, including general relativistic gravity, hydrodynamics, magnetism, and microphysics. Therefore, numerical simulation is a crucial way to understand the merger process quantitatively. In this talk, I will present current understandings of binary neutron star mergers based on recent numerical simulations, mainly focusing on mass ejection and nucleosynthesis.

鳥羽 儀樹（National Astronomical Observatory of Japan）
Insights into AGN activity in galaxy groups/clusters: a statistical study with Subaru HSC survey
In this talk, I will present our study on the properties of active galactic nuclei (AGNs) in approximately one million member galaxies of galaxy groups and clusters with redshift z_cl < 1.4, selected using the Subaru Hyper Suprime-Cam (HSC) survey. We defined the AGN fraction in two ways: the AGN number fraction and the AGN energy fraction and investigated their dependence on the cluster redshift and the distance from the cluster center. Our findings reveal a positive correlation between the AGN number/energy fraction, with higher values for IR-AGNs at the outskirts of the clusters. We also have tentative evidence that cluster–cluster mergers could enhance AGN activity in the outskirts of massive galaxy clusters. These findings highlight the significant role of high-redshift galaxy groups and clusters in the evolution of AGNs. The seminar will delve into the implications of these results to understand the emergence of AGNs from a multi-wavelength and cluster dynamics perspective (Hashiguchi, Toba et al. 2023, PASJ, 75, 1246; Toba et al. 2024, ApJ, 967, 65).

鈴木 昭宏（東京大学）
GRB jets colliding with massive circum-stellar materials and associated electromagnetic transients
Gamma-ray bursts (GRBs) are the most energetic stellar explosion in the universe. Long-duration GRBs are supposed to arise from collapsing massive stars with an ultra-relativistic.jet. The launched jet penetrates the star and then emit electromagnetic signals from radio to gamma-ray. But, their progenitor, jet production, and radiation mechanisms are still largely unclear. Some underluminous GRBs (low-luminosity GRBs) are supposed to be produced by GRB jets deeply embedded in massive circum-stellar materials (CSMs). The presence of such CSMs can dissipate a considerable fraction the jet kinetic energy, which is channeled to less collimated ejecta component traveling at mildly relativistic speeds. The mildly relativistic ejecta is also expected to outshine radiation across electromagnetic spectrum. Such systems with less gamma-ray brightness could also be a neutrino source and are now paid a lot of attention in the context of multi-messenger astronomy. Recently, we carried out a series of 3D hydrodynamic simulations of GRB jet with massive CSMs and investigate the dynamical property of the mildly relativistic ejecta. In this talk, I introduce our results and discuss expected electromagnetic signals from GRB jet with massive CSM.

Jose Carpio（University of Nevada, Las Vegas）
High-energy astrophysical transients as probes of neutrino physics
Neutrinos are a unique probe of high-energy astrophysical processes. Being able to escape dense environments due to their weak interactions with matter, they help us understand the microphysics and mechanisms of the sources. In particular, high-energy neutrino transients play an important role as signatures of hadronic interactions and particle acceleration. In this talk, I will discuss the particle physics processes involved in neutrino production and how we can use them to study astrophysical sources. We first cover the case of newborn magnetars, which can accelerate cosmic rays to ultrahigh energies. Hadronic interactions between cosmic rays and surrounding material can produce not only pions, but heavier mesons as well, resulting in a unique neutrino signal beyond PeV energies. We then consider the neutrino emission from the next galactic supernova. Such an event can be accompanied by GeV neutrinos from neutron-loaded outflows, which can be observed by the next-generation neutrino detectors.

藤本征史（University of Texas, Austin）
Quest for the Most Distant Universe
Finding and characterizing the earliest systems are crucial for answering fundamental cosmological questions such as the emergence of the first galaxies and black holes (BHs), as well as the cosmic reionization process. The advent of JWST has advanced our capability to detect and analyze systems from the early universe, with current candidates reaching out to z~17. Simultaneously, submm/mm observations have gained prominence, providing complementary insights into the cold dust and gas characteristics and helping to verify the authenticity of ultra-high-redshift galaxy candidates against dusty lower-redshift interlopers. In this talk, I will provide an overview of my recent quest for the most distant universe. My strategy synergizes JWST, ALMA, and Gravitational Lensing to enable the most sensitive and comprehensive investigations of the earliest epochs. My systematic JWST spectroscopic survey corroborates the high abundance of z > 9 galaxies recently claimed from photometric measurements, and I will discuss its possible origins based on their initial characterizations. I have also derived the infrared luminosity function by establishing the largest faint ALMA mm sample to date. This enables the first direct attempt to quantify the total (=unobscured + dust-obscured) cosmic star formation history up to z~8, unveiling an additional star-forming component that contributes ~60% more than previously estimated from optical-NIR surveys. The underlying physics taking place in early galaxies, which is responsible for these statistical results, will be discussed based on the initial results from a total of ~160hrs of my ongoing JWST+ALMA+MUSE programs dedicated to a single lensed galaxy at z=6. Looking ahead, I will also introduce the most efficient survey design for further exploration of the most distant universe in the future.

平松大地（Center for Astrophysics）
Tracing the Final Moments of Massive Stars through Supernovae
Supernovae are the terminal explosions of massive stars with influences on every astrophysical scale. Advanced wide-field and high-cadence transient surveys routinely discover supernovae near the moment of explosion. Coupled with prompt and continuous follow-up facilities, these observations have revealed unprecedented features of dense circumstellar medium in various spatial scales as traced by the expanding supernova ejecta. Such circumstellar medium is thought to originate from mass-loss activities in the final years to decades of stellar evolution; however, their inferred densities exceed the expectations from standard theory by many orders of magnitude. In this talk, I will first introduce standard stellar evolution and supernova explosion mechanisms, and then describe novel observational probes and modeling techniques of supernovae (interacting with circumstellar medium) to reconstruct their explosion properties and progenitor mass-loss histories. Finally, I will discuss our on-going largest sample study of interacting supernovae and emerging pictures of dramatic dying breaths of massive stars.

尾上匡房（東京大学/Kavli IPMU）
JWST初年度観測で見えてきた超巨大ブラックホール初期成長
本講演ではビッグバン後10億年未満の初期宇宙に存在する活動的な超巨大ブラックホール（クェーサー）の初期成長の様子について、すばる望遠鏡とジェイムズ・ウェッブ宇宙望遠鏡（JWST）を使った最新の観測成果を中心にご紹介する。遠方クェーサーは2000年代のSloan Digital Sky Surveyを皮切りに現在までに300を超える数が報告されているが、サーベイ観測の深さが足りないことによって最も明るい対象にバイアスされていた。2014年より開始したすばる望遠鏡Hyper Suprime-Cam (HSC)による広視野サーベイは、従来より10倍程度暗いクェーサーまで探査することができる、世界的に見ても競争力の高いプロジェクトである。我々の研究チームは本プロジェクトによって発見された低光度のクェーサーをJWSTで追観測することにより、遠方宇宙における母銀河の質量とブラックホール質量の分布を制限することを目指している。JWST / NIRCamで観測された最初のターゲットから空間的に広がった母銀河を検出し、これは遠方クェーサーとしては世界で初めての成果となった。またNIRSpecの分光観測データからは、母銀河の星形成活動が抑制されたポスト・スターバースト銀河の兆候が2天体について観測された。本講演では、まず遠方クェーサー観測の概観から始め、自身が関わるその他のJWST観測の成果についても時間が許す限りご紹介したい。

井上昭雄（早稲田大学）
Exploring the early Universe through far-infrared nebular emission lines of galaxies
To understand physical processes of the galaxy formation and cosmic reionization, observations of nebular emission lines in high redshift galaxies are essentially important. Far-infrared nebular emission lines such as [CII] 158 um and [OIII] 88 um lines are targets with ALMA. I will review ALMA observations for these emission lines in the epoch of reionization, especially emphasizing [OIII] observations conducted by an international team including myself. I will also present recent observational comparisons between ALMA and JWST. The latter observes optical nebular emission lines having complimentary information to far-infrared lines. Finally I will discuss future prospects of galaxy formation studies in the early Universe by using wide-field survey space telescopes such as Euclid, Roman, and GREX-PLUS.

大森クリストファー清顕 (愛媛大学)
Identification of galaxy mergers in the HSC-SSP and investigations on their role on galaxy evolution
In the currently accepted cosmological framework, hierarchical merging is considered to be the primary pathway for structure growth and evolution in the Universe. In the context of galaxies, this occurs through galaxy interactions and mergers, or the process where multiple galaxies merge to become one larger galaxy. Galaxy interactions and mergers also are known triggers for numerous processes pertaining to galaxy evolution, such as star formation, galaxy chemical evolution, and active galactic nuclei (AGN) activity. As such, galaxy interactions and mergers are a very key process when discussing galaxy evolution. However, the relative role of galaxy interactions and mergers on galaxy evolution-related processes is still under debate. One reason for this is the difficulty in identifying galaxy mergers in observational data. In this work, we present a machine-learning based method for merger identification within the HSC-SSP. Our merger classifier is built upon Zoobot (Walmsley et al. 2023) - a deep representation learning model trained on DeCALS images and citizen science labels. We present the fine-tuning of Zoobot using both observational and simulational based images. We present our findings on a) the relationship between galaxy mergers and environment, and b) the relationship between galaxy mergers and AGN activity, based on mergers identified using each of our models.

Ehud Nakar (Tel Aviv)
Shock breakout from supernovae, gamma-ray bursts, and binary neutron star mergers
Any stellar explosions trigger radiation-mediated shocks (RMS) that cross the star and break out when the optical depth ahead is too low to sustain the shock. The photons released during shock breakout mark the first electromagnetic signal of any cosmic explosion, and they carry unique information about the medium from which the shock emerged, including geometry, radius, composition, and density profile. In my talk, I will discuss the unique properties of radiation-mediated shocks and describe the resulting breakout signal in a variety of cosmic explosions, including various types of supernovae, gamma-ray bursts, and binary neutron star mergers. I will highlight what we have learned from shock breakout observations until now, and what we expect to learn during the next decade.

小山 佑世 (National Astronomical Observatory of Japan)
Panoramic & microscopic views of galaxy evolution in distant clusters of galaxies (and an introduction to "ULTIMATE-Subaru" project)
The formation and evolution of galaxies is strongly influenced by their surrounding environment. Galaxies in the present-day galaxy clusters are predominantly massive and quiescent with elliptical morphologies - but we do not know when and how the nature of those cluster galaxies are shaped in the course of structure formation of the universe. I present a summary of our recent efforts to track down the history of cluster galaxies across ~10 Gyrs cosmic time (out to z~2.5), based on our "panoramic" observations (with Subaru), and the subsequent "microscopic" observational approaches (with HST/JWST). If time allows, I will also present an overview and the current status of the "ULTIMATE-Subaru" project. This project aims to develop a wide-field adaptive optics system (GLAO) on Subaru, to greatly enhance the scientific capabilities of Subaru Telescope toward 2030s.

久世 陸 (東北大学)
Multi-wavelength emission from relativistic jets and magnetically arrested disks in nearby radio galaxies: Application to M87
活動銀河核の一部である電波銀河は中心部から相対論的なジェットが噴出していることが確認されている。一部の電波銀河からは電波から高エネルギーガンマ線まで多波長の光子スペクトルが観測されているもののその放射機構、放射領域はわかっていない。多波長放射機構の解明は、ジェットや降着円盤の物理や高エネルギー宇宙線の加速機構の解明につながる。電波銀河中心部の磁場が強い降着円盤(Magnetically Arrested Disks: MAD)では乱流による粒子加熱・加速が効率的に働き、MADからの放射でミリ波・サブミリ波、ガンマ線の観測データを説明できる。しかし、電波からX線の観測データは説明できず、その放射源としてジェットからの放射が考えられる。そこで我々は、ブラックホール磁気圏での磁気リコネクションによる粒子注入と周りのガスからの混入を考慮したジェット・降着円盤からの多波長放射モデルを構築し、観測されている多波長の光子スペクトルを説明できる物理状態を考察した。ジェット根元での磁化率パラメータと降着円盤からの放射は質量降着率に依存しているため、質量降着率を介してジェットからの放射と降着円盤からの放射が関係づく。このモデルをM87に適用した結果、同時多波長観測データを説明するためには周りのガスからの多量の粒子混入が必要であることが明らかになった。我々のモデルでは波長ごとに放射領域が異なるため、多波長の時間変動を観測することで我々のモデルをテストすることができる。

桑田 明日香 (東北大学)
Large-scale magnetic field model of Gamma-ray burst afterglow polarization
ガンマ線バースト(GRB)の残光は、相対論的衝撃波で加速された電子からのシンクロトロン放射だと考えられている。光度曲線とモデルの比較から、残光の衝撃波下流の磁場は、衝撃波による圧縮で予想される強さよりも100倍以上増幅されていることがわかっている。これほど強い磁場の増幅機構は残光の放射機構における主要な謎であり、この解明は、GRBのジェットの物理量や放射機構、高エネルギー宇宙線の加速機構を決定する上で重要である。
これまで、磁場の増幅機構としては、プラズマ不安定と磁気流体不安定の二つが考えられてきた。しかし、いずれの機構でも現実的な設定でシミュレーションによる検証を行うことは困難であり、未だ観測が示唆する強い磁場の起源は不明である。そのため本研究では、二つの増幅機構で増幅される乱流磁場のスケールが10桁程度も異なることに着目し、そのスケールの大小を観測的に検証できる唯一の手段であるシンクロトロン偏光を用いて、この問題に決着をつけることを試みた。偏光の理論モデルは、プラズマ不安定で増幅される小スケールの乱流磁場では精力的に研究され、観測と比較されている(Sari 1999; Shimoda & Toma 2021)が、一部の観測と非整合である。そこで、本研究では、磁気流体不安定で増幅される大スケールの乱流磁場の定量的研究を初めて行い、偏光の準解析的モデルを構築した(Kuwata et al. 2023)。さらに構築したモデルにおいて、磁場の非等方性や観測者のジェット見込み角、一様磁場の影響を網羅的に調査した(Kuwata et al. submitted)。その結果、本モデルが既存の全ての偏光観測と整合的であるという示唆を得た。本講演では、大スケール磁場モデルの観測的予言やその検証方法について議論する。

藤井 俊博 (大阪公立大学)
A next-generation astronomy using the universe's most energetic particles
Clarifying origins and acceleration mechanisms of the most energetic particles in the universe has been a decades-long endeavor, being one of the most intriguing mysteries in an interdisciplinary research among astroparticle physics, high-energy physics and nuclear physics. Since ultra-high energy cosmic rays (UHECRs) are deflected less strongly by the Galactic and extra-galactic magnetic fields due to their enormous kinetic energies, their arrival directions are ostensively correlated with their origins. A next-generation “astronomy” using UHECRs is hence a potentially viable probe to unravel mysteries of extremely energetic phenomena in the nearby universe. In this talk, I will highlight an introductory cosmic-ray physics, detection techniques and latest results of the two giant observatories in operation; Telescope Array experiment and Pierre Auger Observatory, including their on-going upgrades and then address scientific objectives, requirements and developments for future UHECR observatories.

大工原 一貴 (東北大学)
Enhanced star formation activities and HI gas association in protoclusters at z=2 revealed by Subaru and JWST
遠方の原始銀河の性質を理解することは、現在の銀河団銀河の形成史を制約する上で重要な課題である。銀河の形成と進化に対する局所環境の影響については、これまで多くの研究が行われてきた。しかし、高赤方偏移では、環境の役割はあまり理解されていない。そこで、我々はz=2にある3つの原始銀河団に対して、すばる望遠鏡とJWSTの狭帯域撮像観測を行い、原始銀河団に棲む星形成銀河の性質について調査を行った。特に、これまでにない深さの撮像観測を行った蜘蛛の巣原始銀河団とUSS1558原始銀河団では、小質量銀河で爆発的な星形成活動をした銀河が多く存在することが分かった。これは、原始銀河団内では銀河間の相互作用や衝突が頻繁に起こることやcosmic webからの冷たいガスを効率よく供給できるためだと考えられる。さらに、フィラメント状をした非常にユニークな原始銀河団HS1700についても同様に星形成銀河について調査を行った。このフィラメントの存在は、この原始銀河団がより若く、激しい集団形成段階にあることを示唆している。このユニークな原始銀河団を、Lyα 、Hα、[OIII]の3つの狭帯域フィルターを用いて調査を行った結果、事実星形成活動が活発で、かつLyαエミッターは銀河の高密度領域かつフィラメントを避けるように分布することが分かった。この傾向は、Lyα光子がHIガスによって共鳴散乱されたり、ダストに吸収されたりすることが原因であると考えられる。そして、またこのフィラメント上と銀河団中心に存在する星形成銀河は、それ以外に居るものよりも重いことが分かった。これは銀河が効率的にガスを獲得することができ、加速的な銀河進化をしてきたためであると考えられる。最後に、z=7の極端な輝線銀河（EELG）の高密度領域を発見した結果についても紹介する。この領域は、単なる銀河の過密領域ではなく、EELGの過密領域である点が特徴的である。このような星形成が活発な過密領域は、初期宇宙において高密度領域周辺に電離バブルが形成されたという考えを支持している。

田中 智永 (東北大学)
Development of Microwave Kinetic Inductance Detectors (MKIDs) for GroundBIRD experiment and their onsite calibrations
ビッグバンの約10億年後、天体の形成によって天体からの放射が生じた。これにより物質は宇宙再結合後に再度電離された。この時期を宇宙再電離と呼ぶ。物質が電離したことにより、CMBは再度散乱される。これによって、再電離バンプと呼ばれる特徴的なシグナルがCMBに刻まれる。このシグナルは20度程度の角度スケールに刻まれ、宇宙再電離期の光学的厚みτによって特徴づけられる。τの測定は大角度スケールの測定が可能なWMAP、Planck衛星によって行われた。しかし最新の測定結果でもτの値には10%の誤差があり、1%以下の高い精度で測定されている他の宇宙論パラメータに比べて精度が圧倒的に悪い。さらに、報告された測定結果は報告年毎に系統的に減少しており、系統誤差の混入が否定できない。τの測定値の不定性は、CMB偏光観測によるニュートリノ質量和の測定値に2倍程度の系統的な違いを生じるなど高精度化が進む観測的宇宙論のアキレス腱になっている。このため、WMAPやPlanckとは独立なCMB偏光観測実験によるτの再測定が必須である。しかしながら、地上からの観測では、大気揺らぎが邪魔をして再電離バンプの測定は一般に困難である。
GroundBIRDは、望遠鏡を仰角60~70度に傾けて20RPMという高速で回転させることで、大気揺らぎを克服して、地上から再電離バンプの測定が可能となる独創的なCMB偏光観測実験である。観測帯域は145GHz帯、220GHz帯で、超伝導検出器の中でも反応速度が圧倒的に速いMicrowave Kinetic Inductance Detectors(MKIDs)を搭載している。検出器数は145GHz帯では23 × 6chip=138pixels、220GHz帯では23 × 1chip=23pixelsである。私が主導してデザインし、オランダ宇宙研究所、デルフト工科大学で作成した。2023年4月に私が実験室で性能評価実験を行い、検出器が期待通りの性能を示していることを確かめた。2023年5月に、これらをGroundBIRD望遠鏡へインストールし、本観測が開始された。観測は、遠隔操作で基本的に24時間体制で実施している。CMB観測データ蓄積と並行して、月や惑星の観測を行い、検出器の応答やビームパターンの性能較正を行っている。
本講演ではMKIDの開発、実験室での性能評価実験の結果及びonsiteで行われている性能較正の現状について発表する。

土本 菜々恵 (東北大学)
Signatures of heavy elements in optical and near-infrared spectra of neutron star mergers
宇宙における重元素の起源のうち、金やプラチナなど速い中性子捕獲元素合成 (rプロセス) を必要とする元素の起源は明らかになっていない。その起源天体の有力な候補が連星中性子星の合体現象である。2つの中性子星が合体すると中性子星の一部が宇宙空間に放出され、rプロセスにより合成された元素の放射性崩壊によって電磁波放射「キロノバ」が引き起こされる。2017年に中性子星合体からの重力波 (GW10817) とそれに伴うキロノバが観測されたことで、確かに中性子星合体でrプロセスが起きていることが確認されている。一方、2017年の観測では合体後10日頃まで詳細な可視光・赤外線スペクトルが取得されたものの、元素の同定の困難から、実際に合成された元素の種類もわからない状況が続いていた。そこで、我々は元素の同定に必要な重元素の束縛-束縛遷移の原子データを構築し、輻射輸送シミュレーションを用いてキロノバのスペクトルを計算することで、キロノバのスペクトルにおける吸収特徴から元素の同定を行った。その結果、可視光域の吸収特徴をストロンチウム、赤外線の吸収特徴をランタン、セリウムで説明できることを明らかにした。さらに、これらの吸収特徴を用い、中性子星合体で合成・放出された元素の割合や、元素合成の物理的環境に制限を与えることができた。

石田 光 (東北大学)
Mapping galaxies in proto-supercluster at z=2.23 with QSO clustering
銀河の形成と進化は周囲の環境と密接な関係にあることが知られているが、その詳細なプロセスは完全には理解されていない。環境と深い繋がりを持つ現象として注目されているのが、クエーサーである。クエーサーは宇宙で最も明るく輝く天体の一つであり、その強力な放射光は母銀河や周辺の銀河の形成・進化に大きな影響を与えてきたと考えられている。また、クエーサーは一般的にガスの豊富な銀河同士の合体によって発現したと考えられているため、銀河合体が起きやすい高密度な領域において見つかると期待される。しかし、クエーサーがどのような環境で発現し、周囲にどれほど影響を及ぼすのかについては、さまざまな観測間で異なる結果が得られており、明らかになっていない。我々はクエーサーが複数群れた2QZ clusterと呼ばれる領域に着目し、Hα輝線に対応するナローバンド撮像データを用いることで周辺の星形成銀河の環境を調査した。結果、現在までに銀河団程度の質量に成長する可能性があるHα輝線銀河の高密度領域を周囲に複数発見し、それらがフィラメント状につながるような構造が見られた。また、先行研究で分光同定された同じ時代の銀河団と比較すると、星形成銀河の過密度が弱いことがわかった。また、クエーサーの放射による周囲の星形成に対する影響を見積もったところ、一般的なフィールドと有意な差が見られなかった。これらのことから、複数のクエーサーが群れている領域は大スケールでは高密度領域と関連しているが、それぞれのクエーサーは同じ時代の最も重いハローに必ずしも住んでいるわけではない可能性が示唆された。

高橋 宏典 (東北大学)
Investigating galaxy mass growth and quenching mechanisms one billion years after the Big Bang
銀河内で星形成が進むと、それを抑制するフィードバックが働き、最終的に星形成が停止(quench)すると考えられている。この要因は超新星爆発や活動銀河核(AGN)、銀河周辺環境の影響など多岐にわたる。銀河がどのように星を作って成長し、quenchするかを解明することは、銀河進化における物理過程を理解する鍵となる。私はquenchして約1億年が経過したとみられる、3600Å付近に顕著なスペクトルの段差(バルマーブレイク)を持つ銀河に注目し、その候補天体のサンプルを構築した。これまで、バルマーブレイクを持つ大質量銀河(>10^11 Msun)を探査するためにRubyRushプログラムを推進し、すばる望遠鏡/SWIMSの観測から得られた候補天体に対して分光追観測を行ったほか、他の領域での探査も行ってきた。しかし、すばる望遠鏡やKeck望遠鏡を用いた分光追観測では、赤方偏移5と推定された天体が実際には異なる赤方偏移を持つことが判明した。現在その原因について調査中であり、本発表ではその途中経過と今後の展望を紹介する。また関連研究としてJWSTの公開データを使用し、赤方偏移5-6に存在する4つのバルマーブレイク銀河のスペクトル解析も行った。その結果、銀河全体は星形成を停止したばかりであるが、ダストの多い局所的な星形成領域やAGNが存在することが示唆された。特に1つの天体について、撮像データを用いた解析により、低質量銀河(~10⁹ Msun)では、超新星爆発により外側のガスが放出され、ガスの流入がなければ銀河内部の星形成やAGNも徐々に弱まる"Outside-in quenching"が起こりうることを観測的に示した。

石川 諒 (東北大学)
Extracting mono-enriched stars based on machine learning for understanding the IMF of the first stars
To unravel the history of galaxy formation, it is important to know the properties of the first stars (PopIII) in order to seek the beginning of the galaxy. Since first stars are assumed to have a larger mass distribution than the present stars, i.e. top-heavier IMF, they are unlikely to observe directly.Although theoretical predictions of chemical enrichment are currently made on the basis of nucleosynthesis models to predict how much of various elements are produced by supernovae, there is no statistical discussion based on observations of a large number of objects. By identifying stars that have been enriched by supernovae only once (mono-enriched stars) from stars enriched by multiple supernovae (multi-enriched stars), we can determine the effects of single supernova nucleosynthesis through observation. This allows us to deduce the compositions, luminosities, and masses of the first stars that underwent supernovae. In this study, we focus on second-generation stars and attempt to extract mono-enriched stars from extremely metal-poor stars (EMPs) using machine learning. We employed the method from previous studies (Hartwig+23) and constructed a machine learning model to distinguish mono-enriched stars from multi-enriched stars using the nucleosynthesis yield model from Pop III supernovae (Ishigaki+18) as training data. We applied this model to observational data of EMP stars extracted from the SAGA database. In particular, we investigated how the results vary with assumptions about the initial mass function (IMF) in addition to those made in previous studies. From the analysis of mono-enriched stars in this study, we infer that a significant fraction of first stars are likely existed not in isolation but in systems with multiple stars, which is consistent with findings from fluid-dynamics simulation studies. In this talk, we will discuss the validity of the mothod and detailed analysis results.

一ノ瀬 将也 (東北大学)
すばる望遠鏡レーザートモグラフィー補償光学に向けた波面センサーの調整手法の確立
地上望遠鏡で天体観測を行う場合、大気揺らぎによって天体からの光の波面が乱れ、天体像かがぼやけてしまう。この波面の乱れを補正し、高い解像度を得るための技術を補償光学(AO)という。従来のAOシステムは、単一のレーザーガイド星(LGS) を用いて波面の乱れを測定・補正するが、"コーン効果"と呼ばれる、観測天体とLGSの光路の違いによる補償精度の低下が課題である。この問題の解決策の一つが、レーザートモグラフィー補償光学(LTAO)である。 現在、すばる望遠鏡ではULTIMATE-STARTというLTAOの開発プロジェクトが進行中である。一般的な装置開発の流れの中に、実験室での光学調整がある。 従来の波面センサーの調整手法では、検出器の軸とLGS光の軸の不一致によりケラレが生じ、波面測定が不完全になること、限定的な高度・離角の場合のみでしか調整ができていないことが問題だった。 そこで、本研究では、検出器の軸とLGS光の軸を一致させる新たな調整手法を提案し、実験室でその有効性を検証した。新手法では、新たに加えた２つのステップにより、検出器の軸とLGS光の軸を一致させることが可能になった。さらに、焦点調整光学系のキャリブレーションにより、あらゆる高度と離角に対する調整も可能となった。その結果、従来手法の課題を克服し、新たな調整手法を確立することに成功した。

北村 文里 (東北大学)
Linking Analytic Light Curve Models to Physical Properties of Kilonovae
連星中性子星の合体現象は、速い中性子捕獲反応（r プロセス）が起きる有力な候補天体である。中性子星合体には物質の放出が伴い、理論的には重い元素からなるdynamical ejecta と、比較的軽い元素からなるpost-merger ejectaからなる２成分放出物質の存在が予想され、放出物質は放射性崩壊をエネルギー源として電磁波放射「キロノバ」 を起こす。キロノバの光度や持続期間は放出された物質の質量・速度、元素の種類に依存するため、キロノバの光度曲線からそれらの物理量を推定することで中性子星合体における質量放出と重元素合成を検証することができる。実際、Villar et al. (2017) などの先行研究では、超新星爆発に使われる解析的モデルを用いた物理量推定がこれまで行われてきた。しかし、観測例のGW170817 に対して推定された物理量と数値相対論シミュレーションの結果が示唆する各ejecta の性質は大きく異なり、その原因は理解されていなかった。本研究では、数値相対論シミュレーションを初期条件とした輻射輸送シミュレーションの結果を観測データとして利用することで、解析的モデルで推定されるパラメータの物理的意味の理解を試みた。その結果、推定される物理量がシミュレーションの初期条件を必ずしも再現しないことことが明らかになった。さらに、この違いの原因が、解析的モデルにおいて2成分のejectaからの放射の相互作用を無視していることであると特定することができた。一方で、ejecta全体の質量の推定は比較的精度が高いことが分かった。発表では、物理量推定のモデル依存性や、実際の観測の条件に対する依存性に関しても議論する。

仲間 可南子 (東北大学)
Sub-photospheric GeV-TeV Neutrinos from Gamma Ray Burst Jets: Impacts of Central Engine Time Variabilities
The formation and acceleration of a relativistic fireball, the initial condition for gamma-ray bursts (GRBs), occur below the photosphere and cannot be directly observed through electromagnetic waves, leaving the process largely unknown. Neutrons play a key role in this process. Since the fireball forms from high-density matter near a black hole, neutrons are injected in nearly equal amounts to protons. While neutrons interact with protons via nuclear forces, protons also interact with magnetic fields, photons, and electrons via electromagnetic forces. This leads to a significant relative velocity between neutrons and protons, causing inelastic collisions that produce GeV-TeV neutrinos (Bahcall & Meszaros, 2000). These neutrinos from the sub-photosphere can be messengers, which tell when, where, and how baryons (protons and neutrons) are injected into the fireball and how it expands and accelerates.
GRB 221009A is the brightest GRB ever observed. With this GRB, for the first time, they constrained the neutron abundance in the fireball and the relative velocity between protons and neutrons during its acceleration, revising previously considered typical parameter ranges.
Currently, theoretical templates for IceCube's search for GeV-TeV neutrinos assume a constant relative velocity between protons and neutrons within the accelerating fireball. In reality, the dynamics of the fireball and the effects of magnetic fields create diverse velocity distributions, making it challenging to fully extract information about GRB fireballs. This study explores the connection between jet inhomogeneities and the GeV-TeV neutrino emission spectrum. We model jet inhomogeneities as shells, and fluctuate each shell's internal energy based on a log-normal distribution. The evolution of these fluctuations is traced from the deep acceleration phase within the photosphere, linking the jet's statistical properties and fluctuation dynamics. We find that the neutrino spectrum and fluence strongly depend on the time variability of the jet. In the case of jets with higher variabilities, the subphotospheric dissipations and the GeV-TeV neutrino production are more efficient while the dissipation at beyond the phosphere and the electromagnetic emission becomes less efficient, implying that GeV-TeV neutrino searches for less luminous GRBs are rather promising.

Chris Done (Durham Univ.)
Black holes and rockets science! Using Galactic binaries to understand the physics of accretion flows and their jets
I will show how we now use the X-rays from accreting black holes in our own galaxy to test General Relativity in the strong field limit, with observational evidence for the event horizon, last stable circular orbit and, most recently, Lense-Thirring precession as the origin of the strong, low frequency quasi-periodic oscillations seen in these systems. Not only does this solve the 25 year mystery of the nature of these signals, it also addresses more recent controversies over the nature and geometry of the accretion flow in this state.

敏蔭 星治 (東北大学)
Optical Counterpart Search for IceCube Neutrinos: Toward Constraining the Origin of High-Energy Cosmic Ray
Since the discovery of cosmic rays, they have brought many insights to astrophysics and particle physics. However, the origin of high-energy cosmic rays is still poorly understood. For understanding acceleration mechanism of the high-energy cosmic rays, observations of the high-energy cosmic neutrinos offer the potential to identify the high-energy cosmic ray sources. Recently, IceCube (IC) neutrino observatory has identified two different types of Active Galactic Nuclei (AGN) as the sources of high-energy neutrinos. However, it is not clear whether these AGNs can explain all of the high-energy neutrinos or not. Thus, it is necessary to constrain the contributions from the astrophysical transients such as interacting Supernovae (SNe) and Tidal Disruption Events (TDEs). Several teams have worked for optical follow-up observations for conventional IC detections (single neutrino detection, "singlet") and the possible associations with TDEs have been reported, while these follow-up strategy for singlet have difficulty in constraining the more abundant transients such as SNe due to the large number of unrelated objects in the localization area. From these point of view, we worked for the construction of optical counterpart search strategy for multiple neutrino detections ("multiplet"). For multiplet events whose redshifts are expected to be dominant in z ≤ 0.1, we developed the data filtering system for selecting the probable counterparts based on Zwicky Transient Facility archival data. Limiting the survey volume with the distance information from multi- plet enables us to decrease the number of unrelated objects and discuss association with transients including interacting SNe. We will talk about our data filtering system and its performance with control data based on the blind analysis and the possibility of putting constraints on interacting SNe and TDEs as high-energy neutrino sources.

松本 尚輝 (東北大学)
Unveiling z>3 heavily obscured AGN missed in X-ray surveys: The contribution to the cosmic accretion density at cosmic noon
Supermassive black holes (SMBHs) with masses ranging from several millions to billions times solar mass exist at the centers of almost all massive galaxies in the nearby universe. The large masses of SMBHs in the early universe that are being discovered suggest the need for rapid growth processes like Super-Eddington accretion in the early phase of their growth. The population of active galactic nuclei (AGN) obscured by large amounts of gas and dust in the early universe (i.e., obscured AGN) that is expected to be Super-Eddington phase is said to represent an early violent formation and growth phase of the SMBHs and the host spheroidal components (e.g., Blecha+18), and investigating such population would be a key to understand how SMBHs could gain such a large mass within a limited time scale of the early universe. We performed a MIPS 24um search for z>3 heavily obscured AGN in the XMM-LSS and COSMOS fields, focusing on their strong rest-frame NIR emission originating from AGN hot dust. As a result of the selection, approximately 90% of the selected sources were not detected by the deep X-ray surveys in these fields. SED fitting analysis of all selected candidates revealed that the AGN bolometric luminosities reach log(L_bol)~46–48, indicating that they are heavily obscured and host SMBHs in a vigorous growth phase. The estimated cosmic SMBH growth rate, including heavily obscured AGN, significantly exceeds previous X-ray study estimates. These results emphasize the critical role of obscuration in the early SMBH growth and the importance of this population.

石田 怜士 (東北大学)
種族 II 星団の形成と合体による初代銀河の形成およびその普遍的性質について
初代銀河は標準宇宙論では z~10-20 の間に形成されると考えられており、近年の James Webb Space Tele- scope(JWST) の進展によって z~8-14 の宇宙初期の銀河が観測され始めている。一方で、JWST で観測された銀 河は非常にコンパクトでクランピーな内部構造を持つこと、また標準的な理論予想よりも紫外線で明るい銀河が 多いことが報告されており、この観測を説明可能な銀河形成理論の構築が求められている。 本研究では分子雲ガスを温度 T = 5000 [K]、数密度 nH = 10⁵ [1/cc] まで分解した高解像度の宇宙論的流体シミュレーションを行い、初代銀河の形成過程におけるガスのダイナミクスと星形成の物理を調べた。その結果 Lyman-Werner 輻射によって中心にコンパクトなガスクランプ (Σ_gas ≃ 3000 [M_⊙/pc²]) が形成され、さらに金属冷却によってバースト的な星形成が起こることが確認された。形成された星団の質量は ∼ 10⁶M_⊙ であるが、高い面密度 (Σ_∗ ≃ 10000 [M_⊙/pc²]) をもち、平均金属量は −2.5 < log Z[Z_⊙] < −2 と観測されている球状星団と同程度の金属量であった。さらに ∼ 5 × 10⁷ [M_⊙] の星質量を持つ初代銀河はこのようなコンパクト星団が合体することで形成されることがわかった。 また本研究ではこのようなバースト的な星形成が起こる場合における種族 II 星の IMF の変化が初代銀河の星形成に与える影響を調べた。その結果、バースト的に形成された星団からのフィードバックエネルギーがガスクランプの束縛エネルギーを遥かに超えるため、形成される星質量は種族 II 星の IMF によらないことがわかった。 対して IMF がトップヘビーになると UV 光度は増加し、IMF のべき α < 1.75 であれば JWST の観測を説明可能であることが示唆された。

伊藤 茉那 (東北大学)
IMF transition across various environments in the early universe
恒星の初期質量関数 (initial mass function, 以下IMF) を理解することは、銀河や星の形成史を解明する上で非常に重要である。z~20-30 のゼロメタル環境ででは大質量星が多く、IMFはtop-heavy型になる。また、太陽近傍のような金属豊富な環境では小質量星の多いbottom-heavy型になることが知られている。一方で、z~20-30より高赤方偏移での初代星の質量や、金属がわずかに含まれた低金属量環境でのIMFは、これまでの研究であまり調べられていない。 本研究では、z〜100以上の極初期宇宙における初代星の質量および宇宙初期から現在に至るまでの低金属量環境でのIMFを調べた。z〜20ー30における初代星の形成では、宇宙背景放射(CMB)の影響は小さいと考えられているが、高赤方偏移ではCMBは高温であるため、その影響は無視できない。そこで本研究では、重力・輻射・化学反応に加えてCMBの効果を考慮したone-zoneの熱化学進化コードを用いて、始原ガス雲の温度進化を計算することで極初期宇宙における初代星の質量を推定した。 また、宇宙初期から現在に至るまでのIMFの遷移の先行研究としては、Sharda & Krumholz (2022) が挙げられ、ガス雲に含まれる金属量がIMFの典型的質量に大きな影響を与えることが確認されている。しかしながら、彼らの計算では化学種の存在量が金属量のみで定義され、星形成過程における時間進化が考慮されていない。そこで本研究では、はじめにone-zoneの熱化学進化コードを用いて暴走的収縮過程におけるガス雲の進化を計算することにより、化学種の存在量を時間に依存したものに変更する予定である。本講演では、初めにz=20-700のゼロメタル環境における初代星の性質について述べる。次に低金属量環境におけるIMFの計算の途中経過について報告する。

鈴木寛大 (JAXA/ISAS)
Thermal and non-thermal aspects of supernova remnants revealed with XRISM X-ray observations
Supernova remnants are cosmic factories where vast amounts of explosion energy are converted into various forms of energy including kinetic energy, gas heating (thermal energy), and particle acceleration (non-thermal energy). How this conversion is going on is of great importance both from the astronomical and physical perspectives, as supernova remnants play a key role in the Galaxy evolution while providing ideal laboratory for understanding the fundamental physics of nucleosynthesis, supernova explosion, and shock and plasma physics. X-ray observations enable us to investigate the properties of thermal and non-thermal particles.
X-Ray Imaging and Spectroscopy Mission (XRISM) is the Japan’s 7th X-ray astronomical satellite, which is equipped with the microcalorimeter Resolve and large field-of-view CCD camera Xtend in combination with X-ray mirror assemblies. XRISM was successfully launched in September 2023 and observed several bright supernova remnants such as Cassiopeia A, N132D, and W49B. With performance exceeding expectations, XRISM data provide brand new information of metal abundances, ion temperatures, and gas kinematics. I will review what we have learned from these observations and present future prospects.

和南城 伸也 (東北大学)
Production of heaviest elements in the universe
The origin of r-process elements such as gold and uranium has long been a mystery in astrophysics. The discovery of an electromagnetic counterpart (kilonova) associated with the gravitational wave event GW170817 has confirmed that neutron star mergers are sites where the r-process occurs. However, whether neutron star mergers are the dominant sources of r-process nuclei in the universe remains uncertain. In this presentation, I will share our latest results of nucleosynthesis study, which are based on magnetohydrodynamic simulations of neutron star mergers, as well as other potential sites such as black hole-neutron star mergers and collapsars (black-hole forming supernovae).

西村優里 (東京大学 天文学教育研究センター)
What Molecular Lines Reveal: Insights from Local U/LIRGs and Their Implications for Galaxies at Cosmic Noon
Local ultraluminous and luminous infrared galaxies (U/LIRGs) are experiencing intense starbursts and/or active galactic nuclei (AGNs), making them excellent analogues for galaxies at cosmic noon. Molecular lines in the submillimeter windows, less affected by dust extinction, have the potential to probe the physical conditions of their nuclear regions, which are often obscured by high columns of gas and dust. In this talk, I will present progress of our CON-quest project, which seeks to uncover the nature of Compact and Obscured Nuclei (CONs). Using ALMA, we conducted sensitive observations of the HCN and HCO+ lines in 23 local U/LIRGs. Through spatially and spectrally resolved datasets, we demonstrated that the HCN/HCO+ line ratio is enhanced in nuclear outflows. This enhancement can serve as a tool to identify outflow geometry without relying on kinematic modeling, which often requires numerous arbitrary assumptions. I will also discuss the astrochemical mechanisms driving these variations in line ratios. Finally, I will connect these findings to our ALMA observations of HCN and HCO+ lines in galaxies at cosmic noon, which reveal similar chemical signatures pointing to the presence of outflows.

Lile Wang (Peking University)
Why and How Can We Take Care of Protoplanetary Disks
Protoplanetary disks (PPDs) are drawing increasing attention as the places where planets are formed. They are also one of the most complicated types astrophysical systems, whose detailed and thorough studies should involve multi-scale multiphysics. Due to the complication, most PPD problems have to be solved numerically. The speaker will briefly overview some critical issues he met and tried to solve in computational studies on PPDs, discussing the advanced computational methods and their applications in PPDs, exoplanet atmospheres, and probably other fields of research.

Stevanus Nugroho (National Astronomical Observatory / Astrobiology Center)
The Journey of Exoplanet Atmosphere Characterisation: High-Resolution Spectroscopy Then Now and Beyond
Over the past few decades astronomers have revolutionised our understanding of planetary systems discovering over 5000 planets beyond our solar system. These discoveries have paved the way for future surveys to uncover Earth-like planets in the habitable zones of nearby bright M-dwarfs. Such planets could enable the search for atmospheric biomarkers—molecules like O2, O3, H2O and CH4—using cutting-edge facilities such as the James Webb Space Telescope the Extremely Large Telescope and others. Despite this progress the detailed characterisation of Earth-like planetary atmospheres remains a future goal as current facilities lack the required sensitivity. For now hot Jupiters—gas giant planets that orbit very close to their host stars and exhibit equilibrium temperatures exceeding 1000 K—serve as the most accessible targets. Their inflated atmospheres caused by extreme heat offer high planet-to-star flux ratios and large-scale heights making them ideal for atmospheric studies. High-resolution spectroscopy has emerged as a powerful tool for characterising these exoplanetary atmospheres. It enables the detection of individual molecular lines the study of atmospheric dynamics and the refinement of observational and data analysis techniques. In this talk I will trace the journey of exoplanet atmosphere characterisation exploring how high-resolution spectroscopy has advanced our understanding of these distant worlds recent discoveries and exciting prospects.

Nick Ekanger (東北大学)
The Death of Stars and Birth of Multimessenger Signals
Core collapse supernovae provide a wealth of high energy astrophysical signals. Many supernovae have been observed optically, but only one has been observed with neutrinos. Improved observatories will allow for the detection of more events at farther distances than before and through multiple channels. Although more rare, the subclass of magnetorotational supernovae can possess outflows that are more conducive for the synthesis of heavy nuclei, production of high energy neutrinos, and emission of gamma rays. In this talk, I will discuss models of supernovae outflows driven by highly magnetized and rapidly rotating central engines. I will show that the nuclear composition and central engine properties play important roles on the character of the resulting multimessenger signals. Finally, I will discuss possible connections of rare supernovae to cosmic rays, whose origin have not yet been revealed.

津久井 崇史 (Australian National University)
New Perspectives on Disk Galaxy Formation and Evolution Across Cosmic Time by JWST and ALMA
Present-day disk galaxies, including the Milky Way, exhibit two distinct structures: an older thick disk and a younger thin disk. However, the timing and mechanisms of their formation remain open questions as these structures have not been decomposed beyond z=0. Leveraging JWST's superb capabilities, we have, for the first time, identified and investigated thin and thick disks across cosmic time, up to 10 Gyr ago. We found that galaxies form thick disks first, followed by thin disks. Moreover, thin disk formation occurs earlier in high-mass galaxies (~8 Gyr ago) and later in low-mass galaxies (~4 Gyr ago). By linking disk structural measurements with gas kinematics, we propose that the interplay between the interstellar medium and stellar components naturally explains this delayed thin disk formation in low-mass galaxies.
Looking further back in time, ALMA observations now probe the formation epoch of the thick disk z~4-5 (~12.5 Gyr ago). I will present the detailed gas kinematics and structure of the most distant known barred spiral galaxy at z=4.4 just 1.4 Gyr after the Big Bang. The early emergence of these rich structures, including bars and spirals, challenges the classical understanding. I will present a new rapid formation mechanism for bars, spirals, and thick disks, revealed through observations and high-resolution zoom-in simulations with updated gas physics. I will conclude with exciting prospects for further explorations.

高田 昌広 (東京大学/KIPMU)
Cosmology with intrinsic alignments
Inflation, which is believed to have occurred at the beginning of the universe, provides a scenario for the origin of primordial fluctuations that seeded all structures in the universe. These primordial fluctuations predict that various structures within the observable universe are causally connected to some extent. Notable examples include large-scale correlations observed in the cosmic microwave background anisotropies and the distribution of galaxies. Intrinsic alignments (IA) between galaxy shapes also exhibit correlations (causal connections) on large scales. We developed a method to measure IA, applied it to data from the Sloan Digital Sky Survey (SDSS), and used these measurements to constrain the physics of inflation, particularly anisotropic primordial non-Gaussianity. I present these results.

梅畑 豪紀 (名古屋大学)
ADF22-WEB: ALMA and JWST joint survey of the SSA22 proto-cluster at z=3.1
I will present results from a series of ALMA-JWST observations toward the SSA22 proto-cluster at z=3.1. A large number of galaxies and AGNs are embedded within Lyman-alpha filaments over four comoving Mpc, suggesting that the growth of galaxies and supermassive black holes is being accelerated simultaneously at the core of the proto-cluster. The ADF22-WEB project, a joint ALMA and JWST survey of the SSA22 proto-cluster core, has recently revealed several new aspects of the most massive galaxies, including dusty star-forming galaxies (DSFGs) and quiescent galaxies (QGs). High-resolution ALMA and JWST imaging (down to 0.05” or 350 pc at 1.1 mm) show that DSFGs often exhibit disk-like morphologies with superimposed spheroidal components in both dust and stellar emission. Combined with [C II] mapping at comparable resolution, the brightest DSFG is identified as a giant barred spiral with a highly spun-up gas disk. These findings suggest that we are witnessing an early phase of the morphology-density relation, where massive galaxies grow rapidly as late-type systems fueled by cosmic web gas filaments. For the brightest DSFG, the estimated mass ratio of a bulge to SMBH matches the local relation, suggesting that bars are a key mechanism to shape the early co-evolution of these components. For the most massive QG, a new deep ALMA Band 3 observation has detected a molecular gas reservoir—marking the first detection of molecular gas lines in a QG at such a high redshift. Possible quenching mechanisms include the cessation of gas accretion from cosmic web filaments and morphological quenching.

Norbert Langer (Universität of Bonn)
The Eddington limit in stars
The Eddington limit is an essential stability limit for stars. We discuss what happens to stars when this limit is approached or exceeded. We consider its effect for stars in our Galaxy, and for stars in the Early Universe. We explore consequences for the upper mass limit of stars, for stellar pulsations and mass loss, and for supernova explosions.