Most of the matter in the universe is dominated by dark matter. However, its nature remains a mystery and is one of the biggest problems in modern physics. Various approaches have been taken in a wide range of fields from particle physics to astronomy to elucidate the nature of this...
In discussing the formation and evolution of galaxies, it is essential to know how the material circulation (inflow and outflow of gas) to and from intergalactic space occurs. Observing absorption lines in the spectra of distant sources as background sources is a classical method to study the intergalactic material (IGM),...
First stars or Population III stars are the first generation of stars born in primordial gas clouds in the early universe, and are considered to have formed and evolved differently from later generations of stars (Population II/I stars) whose gas clouds contain heavy elements. Recently, with the advent of the...
X-rays are emitted from many astrophysical objects, including black holes, neutron stars, galaxies, and galaxy clusters. The Imaging X-ray Polarimeter Explorer (IXPE) satellite was launched by NASA in December 2021 to observe polarization with high sensitivity, which is the only field of X-ray astrophysics that has not yet been tackled....
Active Galactic Nuclei (AGN) shine brightly due to the gravitational energy released by mass accretion onto a supermassive black hole (SMBH). AGN are smoking guns of black hole growth. Recently, the Atacama Large Millimeter/submillimeter Array (ALMA), the world's most powerful submillimeter interferometer, has made it possible to study various properties...
A gravitational collapse supernova is an explosion of a massive star at the end of its evolution. The explosion mechanism of supernovae is an unsolved problem in astrophysics. Large-scale numerical simulation studies of supernovae overcame the "failure to reproduce the explosion" problem in the 2000s and the "failure to reproduce...
The realization of direct imaging of supermassive black holes has opened a new horizon for understanding the mysterious driving mechanism of active galactic nuclear jets. We have taken this opportunity to investigate the structure of accretion disks and jets in the vicinity of black holes through the prediction of polarization...
Star formation activity in disk galaxies is known to depend on the structure of the galaxy (e.g., center, arms, bars, etc.). The dependence is particularly pronounced in barred spiral galaxies, where active star formation is observed in the arms, while star formation is weak (low star formation rate) in the...
Stars form in high-density regions in molecular clouds, which are known to be filamentary. The formation and evolution of filaments are important because they determine the initial conditions for star formation. In this presentation, I will report our results on simulations of filament formation and evolution. It is known that...
The Cosmic Microwave Background Radiation (CMB), the afterglow of the Big Bang that has expanded with the evolution of the universe, contains 13.8 billion years of history. Currently, studies on the detailed observation of the CMB polarization fluctuation patterns are attracting a great deal of attention. Many research groups are...
Since its discovery in the 1970s, the microquasar SS433 has attracted much attention as one of the most active jet objects in our Galaxy and has been the subject of numerous studies. However, there are still many unresolved questions, such as the identity of the main star and companion star...
The James Webb Space Telescope (JWST) is opening a new window of the most distant universe and will unveil the early growth of supermassive black holes (BHs) in the first galaxies. The existence of supermassive massive BHs observed when the universe was younger than one billion years strongly constrains their...
Observations of the cosmic background radiation have established the $\Lambda$ cold dark matter (CDM) model as the standard cosmological model, and on large scales the $\Lambda$CDM model has been very successful, providing the backbone of the cosmic large-scale structure. However, on small scales below 1 Mpc, there are still many...
On May 12, 2022, the Event Horizon Telescope (EHT) Collaboration released the world's first images of the close vicinity (several gravitational radii scale) of Sgr A*, the supermassive black hole at the center of our Milky Way Galaxy. The EHT is an international collaborative research project that links telescopes from...
Kiloparsec-scale outflows of gas and dust are thought to be an important mechanism in regulating star formation in galaxies and increasing the metallicity of circumgalactic and intergalactic media. In the past two decades, outflows have been discovered in numerous galaxies with vigorous star formation (starburst) and active galactic nuclei (AGN)...
Diffuse Lyα emission around galaxies, or Lyα halo (LAH), is a valuable probe of their circumgalactic medium which regulate galaxy evolution. We present UV & Lyα radial surface brightness (SB) profiles of Lyα emitters (LAEs) at z = 2.84 detected with the HSC on the Subaru Telescope. UV and Lyα...
The first stars play a particularly important role in the history of the universe because they are the first luminous objects in our universe and the first to produce heavy elements. However, no direct observational traces of them have yet been obtained. Now, the operation of a new generation of...
Massive stars are very important for the physical and chemical evolution of the interstellar medium and the galaxy as a whole. The key to their formation is the accretion of mass onto their parent molecular cloud cores. In recent years, the rapid compression caused by supersonic collisions between molecular clouds...
Recently, observations reported that the ultra diffuse galaxy NGC1052-DF2 (DF2), believed to be a member of the NGC1052 group, is dark matter (DM) deficient. Its inferred DM mass is smaller, by a factor of a few hundred, than what is expected based on its stellar mass and empirical models for...
With the success of the Event Horizon Telescope in directly imaging a supermassive black hole, the study of black holes has entered a new era in which the properties of black holes are explored through imaging observations. In particular, the polarized images reveal the magnetic field structure near the black...
Spiral galaxies observed today (redshift z=0) have distinct internal structures: supper massive black hole (SMBH), dense stellar cluster known as bulge; a flat rotating disk; and extended dark matter halo. The cosmic averaged star formation is suggested to peak at z~2. It remains unclear when and how these structures formed...
Observations confirm that the universe is accelerating and expanding. Dark energy and modified gravity theories have been proposed but a conclusive theory remains elusive. The difference between these theoretical models is reflected in the magnitude of density fluctuations and the temporal evolution of large-scale structure. Therefore, it is possible to...
The link between the intergalactic medium (IGM) and galaxies is key to understand the evolution of baryonic matter and galaxies. In fact, several observational studies have confirmed the connection between the IGM HI and galaxies up to several tens comoving Mpc. However, understanding the variations on the IGM-galaxy connection over...
Supermassive black holes in the universe that exceed one million times the mass of the sun are ubiquitous in the universe. A small proportion of supermassive black holes shine brightly and show intense activity, using accreted matter as an energy source, but most black holes hybernate quietly in the center...
Recent three-dimensional cosmological simulations of protogalaxy formation have suggested that supermassive stars (SMSs) can form in warm gas clouds in which H2–cooling is overwhelmed by dynamical heating (Wise et al. 2019), but they stopped short of following the growth of a central protostar. Here we we examine whether accretion on...
Observations of large-scale structure in the universe can place constraints on the theories of cosmology, galaxy formation, and reionization. A relatively new observation method called emission-line intensity mapping can reveal the three-dimensional distribution of galaxies and intergalactic gas over a wide area by analyzing the spatial fluctuations in emission line...
Molecular gas is a major component of the interstellar medium of the Milky Way Galaxy. Molecular cloud are the main environment in which stars form, so elucidating their spatial distribution and formation mechanism in the Galaxy is an important research field. Recent advances in interferometer observations have identified numerous macromolecular...
Recent distant quasar surveys covering z > 6 have revealed a number of supermassive black holes (SMBH). One of the models for the formation of these SMBHs is the formation of supermassive stars (SMSs) in the early universe, leaving behind a seed BH after a "direct collaps". In gas clouds,...
The observationally identifiable total mass of baryons in the present day universe is known to be significantly smaller than the mass derived from the cosmic microwave background radiation and neutral hydrogen absorption line studies of the distant universe. The unobserved baryons in the current universe are sometimes called dark baryons...
Observations of distant galaxies are important for (i) elucidating the evolution of galaxy formation, and (ii) understanding the contribution of galaxies to the reionization of the universe. In recent years, a number of candidate distant galaxies have been discovered by large ground-based telescopes and space telescopes, some of which have...
The results from Nobeyama 45 m radio telescope observations of nearby galaxies NGC 1068, NGC 253, and IC 342 on the composition of the molecular gas will presented. NGC 1068 contains an active galactic nucleus (AGN), and the 45 m observations provide good spatial resolution to investigate the composition of...
Recent observations have revealed that giant black holes with masses of several hundred million times larger than the Sun already exist in the early universe at redshift z ~ 7. One of the leading theories for the formation of supermassive black holes in such an early universe is supercritical accretion...
Most of the matter in the universe is dominated by dark matter. However, its nature remains a mystery and is one of the biggest problems in modern physics. Various approaches have been taken in a wide range of fields from particle physics to astronomy to elucidate the nature of this...
November 2023 15 : 30 dark matter, dwarf galaxies, and Subaru
In discussing the formation and evolution of galaxies, it is essential to know how the material circulation (inflow and outflow of gas) to and from intergalactic space occurs. Observing absorption lines in the spectra of distant sources as background sources is a classical method to study the intergalactic material (IGM),...
October 2023 15 : 30 IGM, protocluster, and absorption system
First stars or Population III stars are the first generation of stars born in primordial gas clouds in the early universe, and are considered to have formed and evolved differently from later generations of stars (Population II/I stars) whose gas clouds contain heavy elements. Recently, with the advent of the...
September 2023 15 : 30 first stars, early universe, and star formation
X-rays are emitted from many astrophysical objects, including black holes, neutron stars, galaxies, and galaxy clusters. The Imaging X-ray Polarimeter Explorer (IXPE) satellite was launched by NASA in December 2021 to observe polarization with high sensitivity, which is the only field of X-ray astrophysics that has not yet been tackled....
July 2023 15 : 30 AGN, ALMA, and SMBH
Active Galactic Nuclei (AGN) shine brightly due to the gravitational energy released by mass accretion onto a supermassive black hole (SMBH). AGN are smoking guns of black hole growth. Recently, the Atacama Large Millimeter/submillimeter Array (ALMA), the world's most powerful submillimeter interferometer, has made it possible to study various properties...
June 2023 15 : 30 AGN, ALMA, and SMBH
A gravitational collapse supernova is an explosion of a massive star at the end of its evolution. The explosion mechanism of supernovae is an unsolved problem in astrophysics. Large-scale numerical simulation studies of supernovae overcame the "failure to reproduce the explosion" problem in the 2000s and the "failure to reproduce...
May 2023 15 : 30 supernovae
The realization of direct imaging of supermassive black holes has opened a new horizon for understanding the mysterious driving mechanism of active galactic nuclear jets. We have taken this opportunity to investigate the structure of accretion disks and jets in the vicinity of black holes through the prediction of polarization...
April 2023 15 : 30 AGN jets, polarization, and radiative transfer
Star formation activity in disk galaxies is known to depend on the structure of the galaxy (e.g., center, arms, bars, etc.). The dependence is particularly pronounced in barred spiral galaxies, where active star formation is observed in the arms, while star formation is weak (low star formation rate) in the...
February 2023 15 : 30 molecular clouds, star formation, and galaxy evolution
Stars form in high-density regions in molecular clouds, which are known to be filamentary. The formation and evolution of filaments are important because they determine the initial conditions for star formation. In this presentation, I will report our results on simulations of filament formation and evolution. It is known that...
January 2023 15 : 30 star formation, molecular clouds, and MHD
The Cosmic Microwave Background Radiation (CMB), the afterglow of the Big Bang that has expanded with the evolution of the universe, contains 13.8 billion years of history. Currently, studies on the detailed observation of the CMB polarization fluctuation patterns are attracting a great deal of attention. Many research groups are...
December 2022 15 : 00 CMB, cosmology, and B-mode polarization
Since its discovery in the 1970s, the microquasar SS433 has attracted much attention as one of the most active jet objects in our Galaxy and has been the subject of numerous studies. However, there are still many unresolved questions, such as the identity of the main star and companion star...
November 2022 15 : 30 cosmic rays and observations
The James Webb Space Telescope (JWST) is opening a new window of the most distant universe and will unveil the early growth of supermassive black holes (BHs) in the first galaxies. The existence of supermassive massive BHs observed when the universe was younger than one billion years strongly constrains their...
October 2022 15 : 30 early universe, SMBH, and radiation hydrodynamics
Observations of the cosmic background radiation have established the $\Lambda$ cold dark matter (CDM) model as the standard cosmological model, and on large scales the $\Lambda$CDM model has been very successful, providing the backbone of the cosmic large-scale structure. However, on small scales below 1 Mpc, there are still many...
September 2022 15 : 00 cosmological simulations, CGM, and IGM
On May 12, 2022, the Event Horizon Telescope (EHT) Collaboration released the world's first images of the close vicinity (several gravitational radii scale) of Sgr A*, the supermassive black hole at the center of our Milky Way Galaxy. The EHT is an international collaborative research project that links telescopes from...
July 2022 15 : 30 SgrA*, black holes, and general relativity
Kiloparsec-scale outflows of gas and dust are thought to be an important mechanism in regulating star formation in galaxies and increasing the metallicity of circumgalactic and intergalactic media. In the past two decades, outflows have been discovered in numerous galaxies with vigorous star formation (starburst) and active galactic nuclei (AGN)...
June 2022 15 : 30 ALMA, starbursts, and AGN feedback
Diffuse Lyα emission around galaxies, or Lyα halo (LAH), is a valuable probe of their circumgalactic medium which regulate galaxy evolution. We present UV & Lyα radial surface brightness (SB) profiles of Lyα emitters (LAEs) at z = 2.84 detected with the HSC on the Subaru Telescope. UV and Lyα...
May 2022 15 : 30 early universe and high-z galaxies
The first stars play a particularly important role in the history of the universe because they are the first luminous objects in our universe and the first to produce heavy elements. However, no direct observational traces of them have yet been obtained. Now, the operation of a new generation of...
April 2022 15 : 30 first stars, gravitational waves, and first galaxies
Massive stars are very important for the physical and chemical evolution of the interstellar medium and the galaxy as a whole. The key to their formation is the accretion of mass onto their parent molecular cloud cores. In recent years, the rapid compression caused by supersonic collisions between molecular clouds...
December 2021 13 : 30 molecular clouds, Milky Way, star formation, and machine learning
Recently, observations reported that the ultra diffuse galaxy NGC1052-DF2 (DF2), believed to be a member of the NGC1052 group, is dark matter (DM) deficient. Its inferred DM mass is smaller, by a factor of a few hundred, than what is expected based on its stellar mass and empirical models for...
November 2021 12 : 30 dark matter, galaxy formation, N-body simulations, and globular clusters
With the success of the Event Horizon Telescope in directly imaging a supermassive black hole, the study of black holes has entered a new era in which the properties of black holes are explored through imaging observations. In particular, the polarized images reveal the magnetic field structure near the black...
October 2021 13 : 30 black holes, AGN jets, Sgr*, radiative transfer, and general relativity
Spiral galaxies observed today (redshift z=0) have distinct internal structures: supper massive black hole (SMBH), dense stellar cluster known as bulge; a flat rotating disk; and extended dark matter halo. The cosmic averaged star formation is suggested to peak at z~2. It remains unclear when and how these structures formed...
September 2021 13 : 30 galaxy fromation, galactic disk, ALMA, and galactic halos
Observations confirm that the universe is accelerating and expanding. Dark energy and modified gravity theories have been proposed but a conclusive theory remains elusive. The difference between these theoretical models is reflected in the magnitude of density fluctuations and the temporal evolution of large-scale structure. Therefore, it is possible to...
July 2021 13 : 30 large scale structure, 21cm line, and N-body simulations
The link between the intergalactic medium (IGM) and galaxies is key to understand the evolution of baryonic matter and galaxies. In fact, several observational studies have confirmed the connection between the IGM HI and galaxies up to several tens comoving Mpc. However, understanding the variations on the IGM-galaxy connection over...
June 2021 13 : 30 high-z galaxies, IGM, Lyman Alpha Forest, galaxy formation, and galaxy evolution
Supermassive black holes in the universe that exceed one million times the mass of the sun are ubiquitous in the universe. A small proportion of supermassive black holes shine brightly and show intense activity, using accreted matter as an energy source, but most black holes hybernate quietly in the center...
May 2021 13 : 30 hydrodynamics, dusty torus, black holes, AGN, and galaxy mergers
Recent three-dimensional cosmological simulations of protogalaxy formation have suggested that supermassive stars (SMSs) can form in warm gas clouds in which H2–cooling is overwhelmed by dynamical heating (Wise et al. 2019), but they stopped short of following the growth of a central protostar. Here we we examine whether accretion on...
April 2021 13 : 30 first stars, large scale structure, and machine learning
Observations of large-scale structure in the universe can place constraints on the theories of cosmology, galaxy formation, and reionization. A relatively new observation method called emission-line intensity mapping can reveal the three-dimensional distribution of galaxies and intergalactic gas over a wide area by analyzing the spatial fluctuations in emission line...
December 2020 13 : 30 cosmology, large scale structure, and machine learning
Molecular gas is a major component of the interstellar medium of the Milky Way Galaxy. Molecular cloud are the main environment in which stars form, so elucidating their spatial distribution and formation mechanism in the Galaxy is an important research field. Recent advances in interferometer observations have identified numerous macromolecular...
October 2020 13 : 30 molecular clouds and Milky Way
Recent distant quasar surveys covering z > 6 have revealed a number of supermassive black holes (SMBH). One of the models for the formation of these SMBHs is the formation of supermassive stars (SMSs) in the early universe, leaving behind a seed BH after a "direct collaps". In gas clouds,...
July 2020 13 : 30 cosmological simulations and black holes
The observationally identifiable total mass of baryons in the present day universe is known to be significantly smaller than the mass derived from the cosmic microwave background radiation and neutral hydrogen absorption line studies of the distant universe. The unobserved baryons in the current universe are sometimes called dark baryons...
June 2020 13 : 30 WHIM, galactic halos, cosmology, and galaxy clusters
Observations of distant galaxies are important for (i) elucidating the evolution of galaxy formation, and (ii) understanding the contribution of galaxies to the reionization of the universe. In recent years, a number of candidate distant galaxies have been discovered by large ground-based telescopes and space telescopes, some of which have...
May 2020 13 : 30 ALMA, molecular gas, and high-z galaxies
The results from Nobeyama 45 m radio telescope observations of nearby galaxies NGC 1068, NGC 253, and IC 342 on the composition of the molecular gas will presented. NGC 1068 contains an active galactic nucleus (AGN), and the 45 m observations provide good spatial resolution to investigate the composition of...
February 2020 13 : 30 Nobeyama 45m radio telescope, ALMA, molecular gas, starbursts, and AGN
Recent observations have revealed that giant black holes with masses of several hundred million times larger than the Sun already exist in the early universe at redshift z ~ 7. One of the leading theories for the formation of supermassive black holes in such an early universe is supercritical accretion...
January 2020 13 : 30 black holes, first galaxies, accretion, and radiation hydrodynamics
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