Zoom Application (online)
Classical pulsating stars such as Cepheid and RR Lyrae variables are the most sensitive probes for the precision stellar astrophysics and the extragalactic distance measurements. These stellar standard candles obey well-defined period-luminosity relations which provide an absolute calibration of the first rung of the cosmic distance ladder leading to an increasingly accurate and precise local determination of the Hubble constant. Given the ongoing Hubble tension, Cepheid-independent primary calibrations are being used to not only measure Hubble constant independently but also to better understand possible systematic uncertainties in the local measurements. I will present the recent progress in the absolute calibration of period-luminosity relations of Cepheid, RR Lyrae, and Mira variables in the Gaia era. I will also discuss our ongoing theoretical and observational efforts to quantify metallicity effects and other residual systematics in the use of classical pulsators as primary standard candles in the upcoming era of extremely large telescopes.
Zoom Application (online)
Planets form and obtain their compositions in protoplanetary disks around young stars. The chemical compositions of gas
and solid dust grains in these planet-forming disks will decide planetary compositions including water and organic
molecules. Chemical structures in protoplanetary disks are determined by a combination of in situ chemical reactions
and inheritance from molecular clouds and protostellar envelopes. In addition, positions of "snowlines" always influence
planet formation, since they determine the elemental content of solids and gas at different locations in protoplanetary disks.
Recently, in addition to updates in theoretical studies, astronomical observations with ALMA
(Atacama Large Millimeter/submillimeter Array) have investigated the spatial distributions of volatiles (C/N/O) and also detected
some organic molecules in protoplanetary disks.
In this talk, first I will briefly review recent topics about astrochemistry in star and planet forming regions, and then present
our recent modeling studies about molecular composition of water and related molecules in protostellar envelopes. We also
discuss future prospects in this field and connections with planetary systems.
Zoom Application (online)
Cosmic-ray particles occupy a large portion of the energy distribution of our galaxy. Most of the particles below 10^15 eV are considered to be accelerated by diffusive shock acceleration (DSA) at galactic supernova remnants (SNRs). However, the origin of the particles in the energy range of 10^15-10^18 eV has not been explained yet. Recently, galactic microquasar jets are focused on as a candidate accelerator in this energy range, and theoretical and observational studies get active to investigate the dominant mechanism of acceleration and the energetics.
We focus on the most famous microquasar, SS433. It is located at the center of a large radio nebula W50, and the nebula and the jets ejected from SS433 are considered to be interacting. Along the eastern jet axis, there are two candidate regions in which cosmic-ray particle acceleration may occur. One is the region at which the jet broke through W50, and a recent HAWC observation identified a TeV gamma-ray emission from the point. The other is the jet terminal region in which the terminal shock should be formed and bright at radio and X-ray. We investigated the jet terminal region using the observational data with the Australia Telescope Compact Array (ATCA) and the NSF’s Karl G. Jansky Very Large Array (VLA) at a few GHz. We revealed the features of magnetic fields and motion of this region and finally estimated the maximum energy which can be reached by the particle acceleration at the jet terminal shock. In this presentation, I will review my research, including the current results and future plans.
Zoom Application (online)
We carry out unprecedentedly high-resolution calculations for the solar convection zone and reproduce the solar-like differential rotation without manipulation.
The Sun is rotating differentially with the fast equator and the slow pole. This rotation profile was thought to be maintained by turbulence, but recent high-resolution calculation fails to reproduce the solar-like differential rotation profile. This problem is called the convective conundrum, which is one of the biggest solar physics problems. In our super-high-resolution calculation, we solve a part of the problem. Details of the analysis are shown in my talk.
Zoom Application (online)
The Sun is the most well-observed star. On the one hand, our knowledge of the Sun provides accurate input parameters for theoretical models. On the other hand, the detailed and ever-improving observations put strict constraints on how we can model it correctly, in particular, to reproduce a real-looking Sun by numerical simulations. I will briefly review the development of the cutting-edge method of radiative magnetohydrodynamic simulations, which has been successfully used in studying fine structures of sunspots, emergence of magnetic flux, heating of the solar corona, as well as in solar flares, respectively. Recently we conduction an unprecedented simulation of the formation of flare productive active regions through emergence of magnetic flux through a fully self-consistent evolution. This simulation reproduces many key observable features of real solar active regions and presents a whole picture of active regions from the interior to the corona. I will discuss how this numerical simulation helps to shed new light on "active problems" in solar physics, such the corona heating problem and origin of solar flares and coronal mass ejections.
Zoom Application (online)
Cold streams play a crucial role by supplying the gas efficiently to galaxies. At redshift z > 2, a part of the cosmological accretion remains cold (T~ 10^4 K) without being shock-heated. The cold gas accretes onto galaxies with coherent, filamentary structure, so-called "cold stream". Those streams are cooled further by radiative cooling, becoming fuel for star formation in galaxies, and enhancing the star formation rate (SFR). We run cosmological zoom-in simulations with GADGET3-Osaka to clarify the nature of the cold streams and their link to star formation. In a massive halo of M_h = 10^{11.5} M_solar at z=2, the accretion rate of cold gas and the SFR decrease from z~3. Then, I will discuss the relation between cold streams and star formation, and the dependency on the halo mass, using ID tracking analysis of cold gas SPH particles. We find that metal-rich gas forms stars efficiently, however, the effect is minor compared to the halo mass dependency.
Zoom Application (online)
Almost every galaxy is believed to host a supermassive black hole (SMBH) in their nuclei and they are called active galactic nuclei (AGN) when observed as luminous sources. Feedback released by an AGN in the form of radiation, wind, and jet is important to explain the galaxy mass function and galaxy evolution, including the baryon cycle and star formation history. To further study this impact on the cosmological scale, large-scale simulation is necessary. However, the resolution is insufficient to resolve the detailed structure of the AGN at the sub-parsec scale and subgrid models are required to accommodate it in simulations. Two modes of AGN feedback are considered here, i.e., quasar and radio mode, depending on the accretion state of the central SMBH. Their impacts on the host galaxy and halo are analyzed separately to obtain a better picture of their processes at a large scale. We find that the effect of AGN feedback is dominant in the central region of the galaxy disk and effective at a larger radius only when it is working together with supernovae feedback. Quasar mode feedback quenches star formation by heating surrounding gas and cutting off the gas supply to the galaxy disk, while the radio mode maintains this quenched state by heating the gaseous halo. We also find that the SMBHs growth rate is closely related to star formation history indicating a similar fueling process is responsible for both activities.
Zoom Application (online)
The formation process of high mass stars and accompanied cluster is the fundamental piece for understanding physical/chemical evolution of our universe. They are known to be born in dynamically compressed filaments. Such a filament is basically cold, and thus, the initial mass function is determined as a consequence of hierarchical fragmentation processes. Especially fragmentation of a massive self-gravitating disk directly determines the maximum stellar mass. Recent IR/radio monitoring studies have reported episodic outburst events of high mass protostars. Some of such outbursts are probably caused by episodic accretion events via disk fragmentation. However, there was no direct observation available, mainly because of the lack of angular resolution.
Our ALMA long-baseline observations have spatially resolved the compact accretion disk around a high mass protostar at the first time. The disk is nearly face-on and we found a clear signature of the grand design spiral arms, and also, local fragmentation. The accretion age of the host protostar is only 3000 yr, consistent with the dynamical age of outflow. Taking into the account of the current envelope mass and outflow efficiency, the stellar mass will reach 15 – 20 Msun in the future, i.e., the target source is probably in the earliest phase of a proto O-type star. Our results first shed light on the ongoing disk fragmentation process around a high mass protostar.
In this talk, I first review the basics and recent concept of high mass star-formation. Then, I report on our ALMA studies and finally I also introduce our new projects by using our own Yamaguchi interferometer.
Zoom Application (online)
There are many kinds of astronomical objects having accretion disks and they show transient events because of sudden brightening of the accretion disk. Dwarf novae, one subclass of cataclysmic variables, are composed of a white dwarf surrounded by an accretion disk and a low-mass star. They experience intermittent outbursts and are the best targets for studying accretion physics ubiquitous in many kinds of accreting objects. Dwarf novae have been studied for a long time, but there are still unsolved problems. Many anomalous outbursts which are not explained by the simple disk-instability model have been detected thanks to recent progress of transient surveys. Also, the inner accretion flow has not yet been well investigated for lack of X-ray observations. Multi-wavelength observations are required to construct a unified model for dwarf-nova outbursts and to reveal common physics among accreting objects. I will introduce a few of our multi-wavelength studies of dwarf novae and X-ray binaries that are similar to dwarf novae but have a black hole or a neutron star instead of a white dwarf.
Zoom Application (online)
Study of reionization is now experiencing a surge of new insights, but the long-standing problem ‘what reionized the universe?’ still remains unsolved. Hubble observations have placed a now-commonly-held view that the intrinsically faint galaxies are responsible for driving the reionization process, but with a fundamental assumption of large escape fractions >10%. A further puzzle comes from the recent deep spectroscopy of luminous galaxies and the spatial opacity fluctuation of the intergalactic medium (IGM) at z>5.7, which suggests a possibly important role of luminous galaxies and active galactic nuclei/quasars (QSOs). In the theoretical front, simulating early galaxies and the reionization process and is extremely challenging, requring the understanding of the physics over a huge dynamic range from the scales of molecular clouds to the intergalactic medium. To shed light on theses issues, we have recently completed a spectroscopic programme surveying 5<z<7 galaxies around the Lyman alpha forest region of multiple background QSOs to directly examine the correlation among galaxies, QSOs, and the physical state of the IGM, complemented by the detailed study of lower redshift analogues of early galaxies. This enables us to directly examine the ionizing contribution of reionisation-era galaxies/quasars to reionization and the physical processes regulating the escape of ionizing radiation to the IGM. Furthermore, with a help of radiation hydrodynamic simulations, we discuss the possible origin of the large-scale galaxy-IGM clustering as well as the physics of escape fraction in reionisation-era galaxies. Finally, we also discuss the exciting new avenue soon opened up by the JWST.
Zoom Application (online)
In AGNs, outflows powered by the accretion flows are ubiquitous. Especially, ultrafast outflows (UFOs) identified via blueshifted absorption lines in the X-ray band show the large mass-loss rate and kinetic power, possibly affecting growth of the central SMBHs. However, the acceleration mechanism of UFOs and the details of the impact on SMBH growth are still unknown. In our work, we focus on the line-driven disk wind, which is accelerated by ultraviolet radiation through line transitions of metals, as an obvious candidate for UFOs. I will present our results of radiation hydrodynamics simulations line-driven winds and synthetic X-ray spectra based on the simulations. We found the X-ray observations of UFOs can be well reproduced by the line-driven winds. I will also discuss the effect on SMBH growth by estimating the mass-loss rate of the simulated winds. Our results suggest that the line-driven winds effectively slow down the growth of BHs for the BH mass larger than 10^5 solar masses in high-metallicity environments.
Zoom Application (online)
Cold streams play crucial roles in supplying the gas efficiently to galaxies. In the high-redshift universe, gravitational instability forms dark matter halos, and the gas accretes onto the halos. According to the virial theorem, the gas is shock-heated, and hot gaseous halos form. Radiative cooling prevents gas heating, and the cold gas flows into galaxies with coherent, filamentary structures, so-called “cold streams”. While the cold streams fuel star formation at redshifts z>2, star formation quenches at the lower redshift because the streams disappear. Galaxy bimodality could occur due to the quenching of star formation, which turns blue, star-forming galaxies into red, quiescent galaxies. In this colloquium, I will review this topic and discuss our numerical research. We clarify the nature of cold streams and the relation with star formation in galaxies. Most of the accreting cold gas is low-metallicity gas (Z < 10^-2 Z_sun), and cold gas has a higher spin parameter than dark matter and hot gas. In a massive halo of M_h = 10^{11.5} M_solar at z=2, the accretion rate of cold gas starts to decrease from z~3, and the SFR also declines. Galaxy mergers also trigger strong gas accretion and enhance star formation. Finally, I will present the plans for my master thesis.
Zoom Application (online)
Since its operation, the Hyper Suprime-Cam (HSC) mounted on the Subaru telescope
has been discovering a number of distant (z > 6) quasars, owing to its powerful survey ability.
As quasars are the “beacon” of supermassive black holes (SMBHs),
they are the ideal laboratory to investigate the cosmic evolution of
the SMBH mass vs host galaxy mass relation (so called “co-evolution” relation).
In this seminar, I will summarize our series of ALMA observations toward such HSC quasars.
We have revealed: massive (>10^10 Msun) host galaxies at that early universe,
wide variety of star formation activity (from starburst to almost quiescent),
mergers of galaxies that may be related to quasar activities,
quasar-driven powerful outflow that terminates star formation,
and the early shape of the SMBH-host mass relation.
I will gauge these points from the perspective of “co-evolution”,
and also discuss our future plans including JWST and ALMA observations.
Zoom Application (online)
Molecular hydrogen (H2) is a fundamental component of galaxies, being the most abundant element in molecular clouds, where stars form, and an important source of radiative cooling at low temperature. With the advent of the ALMA telescope, we have started to collect data of the CII emission in high-redshift galaxies with unprecedented resolution, and by using scaling relations between CII and SFR, we can infer the molecular gas distribution in these systems. In particular, we are now starting to resolve the distribution of CII in high redshift galaxies and quasar hosts, and this is giving us important information about their kinematics and dynamics of these systems. However, the large majority of numerical simulations on galactic and cosmological scales still lacks the ability to directly follow the formation and dissociation of H2 and the FIR line emission, and must rely on pre-calibrated sub-grid models to compare results with observations. I will present a series of numerical studies devoted to the study of the ISM in high (and low) redshift galaxies, in which the evolution of H2 and of the main coolants of the cold ISM (C,O,Si) is followed via non-equilibrium chemistry, including gas and dust shielding, H2 self-shielding, star formation, supernova feedback, and extragalactic and local stellar radiation. I will discuss in particular how an accurate modelling of the ISM is crucial for a proper comparison with observations, and the role of metallicity in the evolution of the CII-SFR relation across cosmic epochs. Finally, I will also discuss the interplay between a central BH and the ISM in high-redshift quasar hosts, focussing on the apparent obesity of these BHs and the driving of outflows.
Zoom Application (online)
Active galactic nuclei (AGN) has important roles in galaxy evolution, especially in regulating gas throughout the galaxy environment, launching hot outflow into circumgalactic medium and preventing dense gas from overcooling, thus affecting star formation rate and self-regulating the growth of the massive black hole in massive galaxies. Although having many looks, unification of AGN has been proposed, suggesting single yet many perceptions of AGN rooted from different ways of observation view, the existence of radio jet and the states of its center massive black hole accretion rate. Regardless having many faces, impact of AGN feedback on either galactical or cosmological scale is ubiquitous. However, how this feedback being distributed and to what extent it affects the baryon cycle is still unclear. Approaches of AGN feedback effect on cosmological scale through simulation is necessary. Nevertheless, it has been a great challenge for many years given that many scale involved in its implementation. I will also point out some AGN feedback schemes on this scale, including their resulting plausibility and their feasibility on large scale simulation.
Zoom Application (online)
Dark matter (DM) is a mysterious component of our Universe that occupies ~25% of the total energy density. Its nature is investigated in kinds of strategies, such as collider, direct detection, and indirect detection experiments. One important aspect of DM is that it takes the form of halos in our Universe. The halo properties are directly related to DM nature while we have to cover wide ranges of mass and redshift to extract such information. In this talk, I introduce our analytical prescription about the subhalo properties and their impacts on indirect searches of DM.
Zoom Application (online)
Planets form in protoplanetary disks rotating around young stars. Dust evolution is a fundamental physical process in planet formation, which is a long journey from sub-micron grains to thousands kilometer-sized bodies. During the evolution, solid materials are expected to be suffered from difficulties such as violent fragmentation and rapid inward migration, which prevent them from growing into planets. One preferential site of rocky planet formation is the inner edge of the so-called dead zone, where the gas temperature reaches ~800K above which magneto-rotational instability takes place. In this talk, first, I present major difficulties in the evolution from dust to planets. And then I introduce recent simulations of planetesimal and planet formation to show that planet formation at the dead-zone inner edge can be a solution of the formation of rocky planets like our inner solar system. If I have time, I also introduce some observational insights on the dust evolution in the inner region of disks.
Zoom Application (online)
Young massive star clusters (> 1.e4Msun, YMCs) are formed in the Milky Way, but they are mainly found in starburst or merger galaxies. These massive dense star clusters can be the main formation site of massive stars, which regulate the star formation in galaxies due to stellar feedback, such as photoionization, stellar wind, and supernovae. Besides, the relics of YMCs formed in the early galaxies are the globular clusters. Therefore, understanding the formation processes of YMCs are important. However, their formation processes are still unclear, especially the physical conditions of star-forming clouds. I will present our results of radiation hydrodynamics simulations. We performed the simulations of the clouds with surface densities ranging from 80 to 3200 Msun pc^-2. We found that photoionization feedback is inefficient in the deep gravitational potential of the star cluster when the cloud surface density exceeds 350 Msun pc^-2. In this case, star formation efficiencies are enhanced, and star clusters are as dense as globular clusters. Also, I will introduce the analytical model reproducing the star formation efficiencies obtained in our simulations.
Zoom Application (online)
In a variety of astrophysical problems, we find a situation where a clump of gas is irradiated by ultraviolet and X-ray from radiation sources. An important outcome of this process is that excessive photon energy goes into the heat for the gas, which results in driving winds. This wind-driving process, termed photoevaporation, is essential to determine the fate of the irradiated objects. Protoplanetary disks are one of such objects. The stellar UV and X-ray can yield sufficiently high mass-loss rates that can disperse the disks within 10 Myr. This dispersal time is consistent with infrared observations, which have suggested protoplanetary disk lifetimes are estimated typically < 10Myr - this sets the available time for planet formation. However, recent submillimeter observations detected tens of gas-rich disks with ages of > 10Myr. These objects are called gas-rich debris disks, and the origin remains an open question. In this talk, I will present two independent topics. First, I will introduce an analytical model we recently developed to understand the fundamentals of photoevaporation. Actually, the theoretical understanding of fundamental physics is still under development. This motivates us to construct an analytical model in a first-principle approach. The model describes the basic physics in the vicinity of the wind-launching region and explicitly shows the causal link between irradiation and wind excitation. As a byproduct, we found a physically strict condition necessary for wind excitation. This is the first necessary condition ever known in the field. Second, I will present our recent numerical works regarding photoevaporation of aged protoplanetary disks hosted by intermediate-mass stars. The results give implications to the origin of gas-rich debris disks; they can be long-lived protoplanetary disks survived owing to reduced photoevaporation.
Zoom Application (online)
Studying statistical properties of high redshift galaxies with large area surveys is crucial to understand the overall picture of galaxy formation and evolution. I will present our new results from ~4,000,000 star-forming galaxies at z~2-7 identified in the Subaru/Hyper Suprime-Cam survey. Obtained rest-frame UV luminosity functions at z~4-7 cover a very wide luminosity range of ~0.002-2000 L*_UV combined with previous studies, revealing that the dropout luminosity function is a superposition of the AGN luminosity function dominant at M_UV<~-24 mag and the galaxy luminosity function dominant at M_UV>~-22 mag. Galaxy luminosity functions show the bright end excess beyond the classical Schechter function, which is possibly made by inefficient mass quenching, low dust obscuration, and/or hidden AGN activity in luminous galaxies. We find a weak redshift evolution (within 0.3 dex) of the ratio of the star formation rate (SFR) to the dark matter accretion rate, SFR/(dMh/dt), indicating the almost constant star formation efficiency at z~2-7. This SFR/(dMh/dt) ratio quantitatively reproduces the redshift evolution of the cosmic SFR density (a.k.a. the Madau plot), suggesting that the evolution is primarily driven by the steep increase of the halo number density toward z~4 due to the structure formation, and the decrease of the accretion rate from z~2 to 0 due to the cosmic expansion. Extrapolating this calculation to higher redshifts assuming the constant efficiency suggests a rapid decrease of the SFR density at z>10 as 10^(-0.5(1+z)), which is consistent with our recent finding of z~13 galaxy candidates and will be directly tested with JWST. Finally I will briefly introduce our planned JWST observations.
Zoom Application (online)
Numerical simulations of galaxy formation have enjoyed great success in reproducing diverse properties of observed galaxies in the last decade. However, this is often achieved by adopting strong stellar feedback without proper justification, calling for the detailed study on the impact of feedback processes. In this talk, I will overview the roles of supernova and radiation feedback in regulating star formation and share my humble view on the lack of strong galactic outflows in simulations. I will also discuss how much we can trust subgrid star formation recipes used in galactic-scale simulations by comparing with GMC-scale simulations. I will finish my talk by briefly introducing our on-going efforts to better understand the development of strong outflows and neutral circum-galactic medium.
Zoom Application (online)
Galactic winds are likely to play an important role in shaping the growth and evolution of galaxies, especially at the peak epoch of star formation (z~1-3) where outflows are ubiquitous. Detailed measurements are now required to better constrain feedback models and to establish how outflows influence the properties of interstellar and circumgalactic gas. In this talk, I will highlight results of two recent spatially resolved studies of outflows at z~2, focusing on the launch mechanisms of star-formation-driven outflows and the variety of ways in which outflows couple AGN accretion energy to gas on nuclear, galactic and circumgalactic scales. Finally, I will discuss ongoing efforts to make precise measurements of the abundances of metal ions in the circumgalactic medium at z>5.5, one goal of which is to place unique constraints on the properties of outflows in the early Universe.
Zoom Application (online)
The X-ray and extreme-ultra-violet (EUV) emission from the low-mass stars significantly affect the evolution of planetary atmosphere. It is, however, observationally difficult to constrain the stellar high-energy emission because of the interstellar extinction. In this work, we simulate the XUV (X-ray +EUV) emission from the Sun-like stars by extending the solar coronal heating model that self-consistently solves the surface-to-corona energy transport, turbulent energy dissipation, and coronal thermal response by conduction and radiation with sufficiently high resolution. The simulations are performed for a range of loop length and magnetic filling factor at the stellar surface. When applied to the solar corona, our model is found to reproduce the observed solar XUV spectrum below the Lyman edge, which validates the capability of our model in predicting the XUV spectra of other Sun-like stars. The nearly-linear relation between the unsigned magnetic flux and X-ray luminosity is also reproduced self-consistently. From the simulation runs with various loop lengths and filling factors, we find scaling relations that connect the X-ray luminosity and EUV luminosity/photon emission rate. This study demonstrates a refined picture of solar and stellar coronal heating and provides the above observable relations that will be useful for estimating the luminosity of the hidden stellar EUV from X-ray observation.
Zoom Application (online)
The cycling of gas into galaxies, through stars, and back into the IGM via stellar or AGN winds imbues it with kinematic and chemical information that can be used to untangle a galaxy's evolutionary history. Observations of galaxies provide only a single snapshot into each of their lives, and by comparing many at different stages of evolution we can infer which physical processes are responsible. This cannot be tested in real time, of course, and the use of simulations is necessary. In this talk I will present a selection of my recent work on the connected processes of galactic inflows, outflows, and chemical evolution from a cosmological simulation that includes detailed prescriptions for star formation & chemical evolution and AGN feedback.
Zoom Application (online)
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 and evolved in the cosmic history. Analyzing the rotation curve of rotating gas disk allows us to derive the baryonic (e.g., gas and stars) and dark-matter mass distribution, which is powerful tool to investigate the internal structures of galaxies. We have been establishing a method to derive the mass (distribution) of SMBH, bulge, disk, dark matter halo in nearby galaxies using stellar and gas kinematics. Recently, we investigated publicly available data in the ALMA archive with the motivation of applying the method to further distant galaxies. As a result, we discovered a rotating disk, a central compact structure like a bulge, and spiral structure on the disk in a galaxy at the redshift of 4.4, long before the peak of cosmic star formation. Spiral-arm formation requires disk structure which have been recently discovered by ALMA at similar redshift of z=4 to 5. Although the disk formation epoch is still highly uncertain, our result may indicate that spiral structure has formed in a very short period of time after the disk formation, giving us a new question how the spiral morphology formed in such a short period of time?
Zoom Application (online)
What is dark matter, the mysterious predominant constituent of all matter in the Universe? While particle dark matter has remained elusive thus far, as I will demonstrate, large dark matter experiments themselves form impressive neutrino telescopes. This opens a new window into astronomy, leading to possible insights into major problems such as the origin of supermassive black holes. As I will show, primordial black holes from the early Universe make an attractive non-particle dark matter candidate, with intimate connections to astronomical puzzles like the origin of heavy elements (gold) as well as ongoing boom in gravity wave and multi-messenger astronomy. In fact, primordial black holes from the general formation scenario of bubble multiverse might have already been seen by Subaru Hyper Suprime-Cam.
Zoom Application (online)
Though AGN are rare, AGN feedback is an important phenomenon in galaxy formation that controls the luminosity functions and black-hole bulge correlations of galaxies. I will describe our efforts to systematically study AGN feedback with idealized hydrodynamic simulations of jets, winds, and radiation interacting with the interstellar medium of gas-rich galaxies. These include parameter space studies as well as comparisons to observations of GPS/CSS galaxies that provide insights into the efficiency with which AGN activity disperses the gas in the interstellar medium.
Zoom Application (online)
I will start with an introduction to the nuclear equation of state, neutron stars, neutron star binary mergers, and gravitational-wave detectors. Then I will illustrate some strategies to gain information on the high-density part of the nuclear equation of state from observed gravitational waves originating from binary neutron-star mergers. I will conclude talking about what the currently available observations have told us about the nature of the merging systems and on their equation of state, including the possibility of phase transitions during and after the merger.
Zoom Application (online)
Star and planet formation is fundamentally a multi-scale physics. Molecular-cloud scale structures (~10^4 au) define the outer boundary conditions, while the inner boundary conditions will depend on the physical processes of central protostars (~10^-2 au). In addition, these two scales interact with each other during evolution. To understand the system evolution in star forming regions, we need to reveal the physical processes in the central regions, namely, the star-disk interaction and stellar magnetic activities. In this talk, I will overview our recent progress on the star-disk interaction. I will also discuss the magnetic flux transport process and the production of high energy emissions and cosmic rays from protostars, which will affect the evolution of protoplanetary disks.
Zoom Application (online)
Central supermassive black holes of active galactic nuclei (AGNs) host hot plasma with a temperature of 10^9 K, namely coronae. Like the Sun, black hole coronae are theoretically believed to be heated by their magnetic activity. However, such activity has not been observed yet. In this talk, I will report the first clear detection of coronal magnetic activity in nearby AGNs using ALMA (radio telescopes). The coronal magnetic fields are typically ~10 G on scales of ~40 Schwarzschild radii. The measured magnetic field is weaker than the theoretical expectation, requiring a new corona heating mechanism. I will also discuss particle acceleration processes in the coronae of Seyferts, which may be the production sites of the high energy neutrinos seen by IceCube.
Zoom Application (online)
In the first half of this talk, I will motivate the need for AGN feedback for young students, starting by observational evidence from galaxies and supermassive black holes. Some energetic arguments will be given, and we’ll also discuss the efficiencies of feedback. In the second part of the talk, I will argue that the recent high-redshift quasar discoveries strongly point us to the direct collapse scenario of massive black hole (MBH) seeds. We will discuss some of our recent work on the direct collapse scenario using GADGET SPH and Enzo AMR code including radiation transfer.