Black hole candidates display transitions between hard and soft X-ray states. During the transition, quasi-periodic oscillations and jet ejections are observed, and the black hole accretion flow shows intense activity. Our group has investigated the process of the formation of the soft X-ray emitting region by the cooling of the...
The Epoch of Reionization (EoR) shaped the properties of the baryonic content of the Universe. Using hydrodynamical and radiative-transfer numerical simulations, we investigate in detail the processes taking place in the IGM before, during and after the EoR. Present and future observations by, e.g., PAPER, LOFAR, SKA, and E-ELT, will...
This talk will highlight some progress made based on our efforts of computing the universe, in order to understand the dynamics of gas in the universe, from intergalactic to interstellar medium. Select observables presented include the cosmic web from redshift zero to z=2-4, and the escape fraction of Lyman continuum...
Dust coagulation in protoplanetary disks is the first step of planetesimal formation. However, a pathway from dust aggregates to planetesimals remains unclear. Both laboratory and numerical studies have so far shown that the structure of a dust aggregate plays important roles in planetesimal formation. However, the aggregate structure has been...
The formation of the first stars after the big bang is one of the most important outstanding problems in modern astrophysics. While recent theoretical studies of the formation of individual first stars revealed the importance of radiative feedback and led to estimates first star the masses of first stars, studies...
電波干渉系 ALMA の登場によって、宇宙再電離時代 (宇宙年齢がおそよ2-10億年) にある銀河の研究は新時代を拓いた。サブミリ波帯に赤方偏移した遠赤外の微細構造輝線 ([OIII] 88μm, [CII] 158μm など) を ALMA で観測することで、再電離時代の星形成銀河を分光同定することが可能になったのである (e.g., Inoue et al. 2016, Science)。さらに、このような宇宙初期の時代、既に豊富なダストが存在することも明らかになってきた (e.g., Watson et al. 2015, Nature)。 本発表では、私たちのグループが推進している超遠方銀河の微細構造輝線 (主に [OIII] 88 μm) およびダスト連続光の観測結果を紹介する。まず私たちは、重力レンズ効果によって明るく見えている遠方銀河１天体を観測した。この結果、赤方偏移 z = 9.11 (宇宙年齢 5.5億年) にある [OIII] 88 μm の分光検出に成功した (Hashimoto et al. 2018a, Nature)。これは現在最も遠い輝線天体である。さらに、ハッブル宇宙望遠鏡やスピッツァー宇宙望遠鏡のデータも組み合わせた多波長データ解析から、観測時点よりも過去の星形成の歴史を遡った。この結果、この銀河が星形成を開始したのは z ~ 15 (宇宙年齢2.5億年) の頃だと推定され、宇宙最初期の星形成に知見を得た。次に、z...
Narrow Line Seyfert 1s (NLS1) are the lowest mass, highest mass accretion rate Active Galactic Nuclei (AGN) in the local Universe, with black hole masses of 1-10 million x Msun, accreting at the Eddington limit or beyond. These properties are similar to those expected for the majority of the first...
Self-gravitation can play a role in protoplanetary- and AGN-disks. If they are massive enough, gravitoturbulence sets in and acts as a strong driver for angular momentum redistribution. Thereby it moves large amounts of gas from the outer parts of the disk to the central object. However, if the disk cools...
By mass, the Galactic bulge is actually dominated by a relatively metal rich bar. This population exhibits relatively rapid rotation that reflects a pattern speed independent of Galactic latitude. We have completed a survey of 955 RR Lyrae stars in the bulge region, and find a remarkable population that does...
Young stars' infrared emission shows several puzzling features: variability uncorrelated with visible-light changes, foreground extinction that recurs erratically on weekly timescales, and excesses over the stellar photosphere too large to explain with starlight absorbed and re-emitted by a hydrostatic protostellar disk. I will discuss how each of these features can...
Galaxy collisions and merging is a ubiquitous process in the theory hierarchical galaxy formation。We investigate the effects of galaxy collisions and mergers on the formation and evolution of galaxies using N-body simulations. In this seminar we present two recent results. 1. In the case in which the two colliding systems...
The molecular composition in star-forming regions in the Milky Way is useful, for example, for determining the current stage of star-formation of a system. In starburst galaxies and active galactic nuclei (AGN), the molecular composition is thought to vary strongly. In the past few years, ALMA observations of multiple species...
Gamma-ray bursts (GRB) are the one of the most energetic phenomena in the universe, with typically 1051 erg in gamma rays emitted within of order few tens of seconds. In the case long gamma-ray burst, the radiation is emitted from relativistic jets launched as a result of the gravitational collapse...
A large-scale hydrodynamical cosmological simulation, Horizon-AGN , is used to investigate the alignment between the spin of galaxies and the large-scale cosmic filaments above redshift z = 1.2. The analysis of more than 150 000 galaxies per time step in the redshift range 1.2 &less; z &less; 1.8, resolved with...
Feedback from active galactic nuclei (AGN) is routinely included in semi-analytic and numerical simulations, which have shown that such feedback is able to quench cooling flows and decrease star formation. Radio-mode feedback models from AGN jets are, however, still in the early stages of development. The impact of the jet...
I will first briefly review the current observationnal constraints on the Epoch of Reionization, then I will describe the basic physics of reionization and emission of the 21 cm signal. I will then describe the current status and future prospects of 21cm observations and finally I will present modeling techniques...
To understand the formation of molecular cores, the eventual sites of star formation, it is not enough to know only the physical state of the star-forming high-density gas. One must also determine the velocity field and density structure of the more diffuse medium surrounding the dense gas. One can go...
The Galactic center is one of the most fascinating and extreme places in the Galaxy. Harboring a supermassive black hole with a mass of order 4 million solar masses it experiences cycles of activity and star formation, separated by periods of quiescence that last of order a million years. The...
The development of virial mass estimates for the central black hole using one quasar spectrum has allowed a dramatic improvement in our understanding of supermassive black hole evolution. I will describe several new puzzles arising from the combination of virial masses with luminosity and redshift measurements, many of which are...
The assembly and evolution of galaxies over cosmic time is a complex process. Historically, galaxy evolution was thought to be governed by mainlystochastic, potentially divergent processes such as major mergers, whichwere linked to active galactic nuclei (AGN) activity and vigorous starformation followed by a rapid "quenching" process. In the last...
The development of virial mass estimates for the central black hole using one quasar spectrum has allowed a dramatic improvement in our understanding of supermassive black hole evolution. I will describe several new puzzles arising from the combination of virial masses with luminosity and redshift measurements, many of which are...
Since about 2005 our group at the ANU, in collaboration with Alex Wagner, has been conducting fundamental research on the interaction of jets with the interstellar medium of evolving galaxies. One area of research involves the interaction of relativistic jets with an inhomogeneous interstellar medium consisting of dense clouds. This...
1. One of the goals of galactic center black hole observations is the validation of theories of gravity. In addition, recent radio observations have revealed visibility and positional information of light source, and in hte near future we will obtain interferometer observations that will show how the magnetic radiation plasma...
Strong Lyman alpha emitting galaxies have been observed in large numbers over a wide range in redshift. Such galaxies are called Lyman alpha emitters (LAEs), and they are thought to be galaxies in the early stages of evolution. However, there are still many open questions regarding their formation and evolution....
It is well known nowadays that most of the mass assembly occurs at z~1-3. However, a non-negligible fraction of the star formation across cosmic time occurred within dust-enshrouded environments. One important question is therefore whether we really know the exact amount of star formation activity, which could be strongly biased...
Studies throughout the past decade indicate that the mass of the first generation of stars was extremely large, unlike most stars in our galaxy. However, according to recent work on the mass accretion phase, the gas is likely to fragment and produce a cluster of stars, rather than accreting smoothly...
One of the final frontiers in modern cosmology is the formation of the first stars and galaxies at the end of the cosmic dark ages, when the Universe transitioned from its simple initial state to one of ever increasing complexity. I will discuss how the first bound gas clouds condensed...
Recently, intense attention has focused on the possibility that merging supermassive black hole binaries could be observed with both electromagnetic and gravitational waves. Such multi-messenger studies would (i) probe dark energy out to z~10, and (ii) allow follow-up studies of active galactic nuclei with central engines whose masses and spins...
Hierarchical structure formation hypothesis inevitably leads to the formation of binary supermassive black holes (SMBHs) on a subparsec scale in merged galactic nuclei. However, to date there has been no unambiguous detection of such systems. In this talk, I propose how binary SMBHs merge and a feasible method to detect...
In the formation process of galaxies, AGN jets are thought to have the important function of feeding energy and momentum back into the halo of the host galaxies and dispersing the gas within. The set of 14 realistic 3-D simulations that we have recently performed quantitatively demonstrate the efficiency of...
Although only small by number massive stars influence the evolution of galaxies most efficiently. Their short lifetimes in combination with enormous amounts of power by radiative and kinetic energy and furthermore the release of substantial fractions of heavy elements make them the most important drivers of the thermal and chemical...
Because of various components, different gas phases and stars, their mutual interactions, and largely varying timescales galaxies represent highly complex systems. Competing but also counteracting processes occur that depend on the physical state of a region and its location in the galaxy and which are theoretically and empirically elaborated. Evolutionary...
Black hole candidates display transitions between hard and soft X-ray states. During the transition, quasi-periodic oscillations and jet ejections are observed, and the black hole accretion flow shows intense activity. Our group has investigated the process of the formation of the soft X-ray emitting region by the cooling of the...
December 2022 13 : 30 accretion discs, AGN, and MHD
The Epoch of Reionization (EoR) shaped the properties of the baryonic content of the Universe. Using hydrodynamical and radiative-transfer numerical simulations, we investigate in detail the processes taking place in the IGM before, during and after the EoR. Present and future observations by, e.g., PAPER, LOFAR, SKA, and E-ELT, will...
July 2022 13 : 30 reionization, high-z galaxies, and IGM
This talk will highlight some progress made based on our efforts of computing the universe, in order to understand the dynamics of gas in the universe, from intergalactic to interstellar medium. Select observables presented include the cosmic web from redshift zero to z=2-4, and the escape fraction of Lyman continuum...
June 2019 13 : 30 computational fluid dynamics, galaxy evolution, and cosmological simulations
Dust coagulation in protoplanetary disks is the first step of planetesimal formation. However, a pathway from dust aggregates to planetesimals remains unclear. Both laboratory and numerical studies have so far shown that the structure of a dust aggregate plays important roles in planetesimal formation. However, the aggregate structure has been...
May 2019 13 : 30 dust and protoplanetary discs
The formation of the first stars after the big bang is one of the most important outstanding problems in modern astrophysics. While recent theoretical studies of the formation of individual first stars revealed the importance of radiative feedback and led to estimates first star the masses of first stars, studies...
February 2019 15 : 15 numerical simulations, radiative transfer, and first stars
電波干渉系 ALMA の登場によって、宇宙再電離時代 (宇宙年齢がおそよ2-10億年) にある銀河の研究は新時代を拓いた。サブミリ波帯に赤方偏移した遠赤外の微細構造輝線 ([OIII] 88μm, [CII] 158μm など) を ALMA で観測することで、再電離時代の星形成銀河を分光同定することが可能になったのである (e.g., Inoue et al. 2016, Science)。さらに、このような宇宙初期の時代、既に豊富なダストが存在することも明らかになってきた (e.g., Watson et al. 2015, Nature)。 本発表では、私たちのグループが推進している超遠方銀河の微細構造輝線 (主に [OIII] 88 μm) およびダスト連続光の観測結果を紹介する。まず私たちは、重力レンズ効果によって明るく見えている遠方銀河１天体を観測した。この結果、赤方偏移 z = 9.11 (宇宙年齢 5.5億年) にある [OIII] 88 μm の分光検出に成功した (Hashimoto et al. 2018a, Nature)。これは現在最も遠い輝線天体である。さらに、ハッブル宇宙望遠鏡やスピッツァー宇宙望遠鏡のデータも組み合わせた多波長データ解析から、観測時点よりも過去の星形成の歴史を遡った。この結果、この銀河が星形成を開始したのは z ~ 15 (宇宙年齢2.5億年) の頃だと推定され、宇宙最初期の星形成に知見を得た。次に、z...
October 2018 13 : 30 reionization, ALMA, first galaxies, and first stars
Narrow Line Seyfert 1s (NLS1) are the lowest mass, highest mass accretion rate Active Galactic Nuclei (AGN) in the local Universe, with black hole masses of 1-10 million x Msun, accreting at the Eddington limit or beyond. These properties are similar to those expected for the majority of the first...
September 2018 13 : 30 seyfert galaxies, NLS1, AGN, and black holes
Self-gravitation can play a role in protoplanetary- and AGN-disks. If they are massive enough, gravitoturbulence sets in and acts as a strong driver for angular momentum redistribution. Thereby it moves large amounts of gas from the outer parts of the disk to the central object. However, if the disk cools...
August 2018 13 : 30 accretion discs, computational fluid dynamics, and numerical simulations
By mass, the Galactic bulge is actually dominated by a relatively metal rich bar. This population exhibits relatively rapid rotation that reflects a pattern speed independent of Galactic latitude. We have completed a survey of 955 RR Lyrae stars in the bulge region, and find a remarkable population that does...
March 2016 10 : 30 galaxy formation and observations
Young stars' infrared emission shows several puzzling features: variability uncorrelated with visible-light changes, foreground extinction that recurs erratically on weekly timescales, and excesses over the stellar photosphere too large to explain with starlight absorbed and re-emitted by a hydrostatic protostellar disk. I will discuss how each of these features can...
October 2015 15 : 30 protoplanetary discs and MHD
Galaxy collisions and merging is a ubiquitous process in the theory hierarchical galaxy formation。We investigate the effects of galaxy collisions and mergers on the formation and evolution of galaxies using N-body simulations. In this seminar we present two recent results. 1. In the case in which the two colliding systems...
October 2015 13 : 30 DM Halo, N-body simulation, and structure formation
The molecular composition in star-forming regions in the Milky Way is useful, for example, for determining the current stage of star-formation of a system. In starburst galaxies and active galactic nuclei (AGN), the molecular composition is thought to vary strongly. In the past few years, ALMA observations of multiple species...
September 2015 13 : 00 ULIRG, IR, radiative transfer, and protostellar disc
Gamma-ray bursts (GRB) are the one of the most energetic phenomena in the universe, with typically 1051 erg in gamma rays emitted within of order few tens of seconds. In the case long gamma-ray burst, the radiation is emitted from relativistic jets launched as a result of the gravitational collapse...
March 2015 13 : 30 GRB
A large-scale hydrodynamical cosmological simulation, Horizon-AGN , is used to investigate the alignment between the spin of galaxies and the large-scale cosmic filaments above redshift z = 1.2. The analysis of more than 150 000 galaxies per time step in the redshift range 1.2 &less; z &less; 1.8, resolved with...
October 2014 13 : 30 SMBH and galaxy formation
Feedback from active galactic nuclei (AGN) is routinely included in semi-analytic and numerical simulations, which have shown that such feedback is able to quench cooling flows and decrease star formation. Radio-mode feedback models from AGN jets are, however, still in the early stages of development. The impact of the jet...
October 2014 14 : 30 AGN feedback and galaxy evolution I will first briefly review the current observationnal constraints on the Epoch of Reionization, then I will describe the basic physics of reionization and emission of the 21 cm signal. I will then describe the current status and future prospects of 21cm observations and finally I will present modeling techniques...
September 2014 13 : 30 reionization To understand the formation of molecular cores, the eventual sites of star formation, it is not enough to know only the physical state of the star-forming high-density gas. One must also determine the velocity field and density structure of the more diffuse medium surrounding the dense gas. One can go...
July 2014 13 : 30 GMC, turbulence, MHD, star formation, molecular cores, and observations
The Galactic center is one of the most fascinating and extreme places in the Galaxy. Harboring a supermassive black hole with a mass of order 4 million solar masses it experiences cycles of activity and star formation, separated by periods of quiescence that last of order a million years. The...
February 2014 17 : 00 hydrodynamics, G2, clouds, Galactic center, SMBH, AGN, and accretion discs
The development of virial mass estimates for the central black hole using one quasar spectrum has allowed a dramatic improvement in our understanding of supermassive black hole evolution. I will describe several new puzzles arising from the combination of virial masses with luminosity and redshift measurements, many of which are...
August 2013 15 : 00 quasars, SMBH, and AGN The assembly and evolution of galaxies over cosmic time is a complex process. Historically, galaxy evolution was thought to be governed by mainlystochastic, potentially divergent processes such as major mergers, whichwere linked to active galactic nuclei (AGN) activity and vigorous starformation followed by a rapid "quenching" process. In the last...
August 2013 16 : 20 quasars, SMBH, and AGN The development of virial mass estimates for the central black hole using one quasar spectrum has allowed a dramatic improvement in our understanding of supermassive black hole evolution. I will describe several new puzzles arising from the combination of virial masses with luminosity and redshift measurements, many of which are...
August 2013 15 : 40 quasars, SMBH, and AGN
Since about 2005 our group at the ANU, in collaboration with Alex Wagner, has been conducting fundamental research on the interaction of jets with the interstellar medium of evolving galaxies. One area of research involves the interaction of relativistic jets with an inhomogeneous interstellar medium consisting of dense clouds. This...
July 2013 14 : 00 AGN, AGN feedback, AGN jets, SMBH, M-sigma relation, MHD, accretion discs, radio galaxies, and Hydra A 1. One of the goals of galactic center black hole observations is the validation of theories of gravity. In addition, recent radio observations have revealed visibility and positional information of light source, and in hte near future we will obtain interferometer observations that will show how the magnetic radiation plasma...
March 2012 13 : 30 black holes, general relativity, and radiative transfer Strong Lyman alpha emitting galaxies have been observed in large numbers over a wide range in redshift. Such galaxies are called Lyman alpha emitters (LAEs), and they are thought to be galaxies in the early stages of evolution. However, there are still many open questions regarding their formation and evolution....
March 2012 13 : 30 LAE, cosmology, radiative transfer, and Milky Way
It is well known nowadays that most of the mass assembly occurs at z~1-3. However, a non-negligible fraction of the star formation across cosmic time occurred within dust-enshrouded environments. One important question is therefore whether we really know the exact amount of star formation activity, which could be strongly biased...
February 2012 13 : 30 AGN, starbursts, high-z galaxies, galaxy formation, IR, and submm Studies throughout the past decade indicate that the mass of the first generation of stars was extremely large, unlike most stars in our galaxy. However, according to recent work on the mass accretion phase, the gas is likely to fragment and produce a cluster of stars, rather than accreting smoothly...
December 2011 13 : 30 PopIII stars, accretion discs, radiative feedback, and star formation One of the final frontiers in modern cosmology is the formation of the first stars and galaxies at the end of the cosmic dark ages, when the Universe transitioned from its simple initial state to one of ever increasing complexity. I will discuss how the first bound gas clouds condensed...
September 2011 15 : 00 first stars and first galaxies Recently, intense attention has focused on the possibility that merging supermassive black hole binaries could be observed with both electromagnetic and gravitational waves. Such multi-messenger studies would (i) probe dark energy out to z~10, and (ii) allow follow-up studies of active galactic nuclei with central engines whose masses and spins...
August 2011 15 : 00 SMBH, SMBH mergers, and accretion discs Hierarchical structure formation hypothesis inevitably leads to the formation of binary supermassive black holes (SMBHs) on a subparsec scale in merged galactic nuclei. However, to date there has been no unambiguous detection of such systems. In this talk, I propose how binary SMBHs merge and a feasible method to detect...
August 2011 15 : 00 SMBH, SMBH mergers, accretion discs, SPH, and X-raysIn the formation process of galaxies, AGN jets are thought to have the important function of feeding energy and momentum back into the halo of the host galaxies and dispersing the gas within. The set of 14 realistic 3-D simulations that we have recently performed quantitatively demonstrate the efficiency of...
October 2010 15 : 00 AGN jets, AGN feedback, galaxy formation, m-sigma relation, and hydrodynamicsAlthough only small by number massive stars influence the evolution of galaxies most efficiently. Their short lifetimes in combination with enormous amounts of power by radiative and kinetic energy and furthermore the release of substantial fractions of heavy elements make them the most important drivers of the thermal and chemical...
September 2010 15 : 00 massive stars and supernovaeBecause of various components, different gas phases and stars, their mutual interactions, and largely varying timescales galaxies represent highly complex systems. Competing but also counteracting processes occur that depend on the physical state of a region and its location in the galaxy and which are theoretically and empirically elaborated. Evolutionary...
September 2010 15 : 00 chemodynamics, massive stars, and supernovae
和 英