F608
The nature of dark matter, such as its mass and interactions, remains elusive despite the convincing evidence for its existence from the astrophysical observations. The environment around the black hole can provide us a promising playground to study the dark matter properties because of the large dark matter density from accretion. I will explore the multi-messenger probes on the dark matter in the vicinity of black holes. More concretely, I will discuss (1) the gravitational wave signals from a black hole binary whose dynamics is affected by the dark matter (2) the multi-wavelength signals covering the radio, optical and gamma rays and (3) the prospects for the neutrino signals which can arise from the dark matter annihilation.
F608
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The advent of the James Webb Space Telescope (JWST) has opened up a new window to investigate the inter-stellar medium (ISM) properties and the stellar population in detail in high-redshift galaxies (z=4 to 10) using the rest-frame optical spectroscopic signatures. In this talk, I will provide an overview of recent advancements in our understanding of ISM properties and stellar populations. Specifically, our research focuses on exploring the evolution of the mass-metallicity (MZ) and star-formation rate-mass-metallicity (SFR-MZ) relations across the redshift range of z=4-10. We have analyzed a sample of 140 galaxies identified in the JWST/NIRSpec data from the three major public spectroscopy programs: ERO, GLASS, and CEERS. Our findings reveal a modest evolution in the MZ relation from z~2-3 to z=4-10. Interestingly, the SFR-MZ relation shows no significant evolution up to z~8 but exhibits a noteworthy decline at z>8 beyond the error. This decrease in the SFR-MZ relation at z>8 may indicate a break of the metallicity equilibrium state driven by star formation, gas inflow, and outflow. While our sample reveals a mild evolution in metallicity, it is worth noting that recent studies have reported the existence of extremely metal-poor objects that resemble Pop-III star galaxies. I will review these recent progresses in our understanding of galaxies during the early phase of galaxy evolution.
F608
To understand the energy-equipartition law in the interstellar medium, in which the energy densities of cosmic-rays (CRs), thermal gas, turbulence, and magnetic field are comparable with each other, we study the long-term evolution of our galaxy over cosmic time by modeling the star formation, metallicity, CRs, outflows, and inflows of the galactic system to obtain various insights into the galactic evolution. Considering the consistencies between the observed Galactic diffuse X-ray emissions (GDXEs) and possible conditions to drive the Galactic wind by CRs, we find that the star formation rate becomes half of the mass accretion rate of the disk. The mass accretion of the disk is modeled by using the results of the dark matter N-body simulations. We find that if the gas accretion is characterized by the dark matter core radius, the rotation curve of the low-mass stars in our galaxy can be explained. These results simultaneously provide consistent amounts of metals and CRs with the current conditions of our galaxy. The most significant model predictions are that there is unidentified accretion flow with a possible number density of ∼ 0.01 /cc and the (part of) GDXEs originated from the diffuse plasma formed by consuming a roughly tenth of supernova explosion energy. The latter is the science case of future X-ray missions; XRISM, Athena, and JEDI. In this seminar, we review the interplay between the CRs and thermal gas that plays a key role in launching the Galactic wind.
F608 & Zoom (hybrid)
Newly-born stars evolve with their circumstellar disks. It is widely accepted that the evolution of both the star and its disk is tightly linked through the process of star-disk interaction. The manner in which gas accretes onto stars plays a pivotal role in shaping stellar evolution, while the influence of stellar magnetic fields and starlight extends to the evolution of disk gas across a wide range of radii. Despite the importance, the dynamics of star-disk interaction have remained elusive due to the complexity of this process and the small size of the interaction region. Our research has been dedicated to a comprehensive numerical investigation of this phenomenon at various stages of star formation. In this talk, I will provide an overview of our ongoing study on star-disk interaction, with a specific emphasis on recent code development and the future directions of our research.
F608
Details of the explosion mechanism of core-collapse supernovae (CCSNe) are not yet fully understood. There is now an increasing number of successful examples of reproducing explosions in the first-principles simulations, showing a slow increase of explosion energy. Here, radioisotope 56Ni is an important product, which drives supernova brightness. It was recently pointed out that the growth rates of the explosion energy of these simulations are insufficient to produce enough 56Ni mass to account for observations. We refer to this issue as the "nickel mass problem" (56Ni problem, hereafter; Sawada et al. 2019, Suwa et al. 2019, Sawada & Suwa 2021). In this talk, I would like to start with the basics of nucleosynthesis of the radioisotope 56Ni in supernova explosions and the mechanism of supernova explosions, then discuss the diversity of supernova explosions that has recently been revealed, and finally discuss the "56Ni problem," focusing on my own research.
F608
To understand the origin of the Solar system, the physical/chemical evolution along the star/planet formation is a key issue. With the advent of ALMA, extensive observational studies have revealed that both the physical structure and the chemical composition drastically change during the disk formation around protostars. Furthermore, it has been found that molecular distributions are sensitive to changes in the physical conditions. Some kinds of molecular lines are therefore prospected to work as 'molecular markers' to selectively highlight particular structures of disk forming regions. Specifically, sulfur-bearing species seem good tracers; for instance, the kinematic structures of its circummultiple structure and its circumstellar disk are traced by the OCS and H2CS emission, respectively, in a young low-mass protostellar source IRAS 16293-2422 Source A. The gas in its circummultiple structure was found to keep falling even beyond its centrifugal radius, which is often assumed to be the outer edge of a Keplerian disk. Angular momentum of the gas is the essential topic to understand the structure formation. The chemical diagnostics with the aid of the molecular markers can be a helpful tool to tackle with the redistribution of the angular momentum among the disk/envelope and outflow structures. Conversely, detailed physical characterization is essential to elucidating the chemical evolution occurring there.
F608
Recent galaxy formation simulations have been implemented using the N-body/SPH method, the moving mesh approach, and adaptive mesh refinement. However, achieving sufficient parallelization efficiency presents challenges. To represent each individual star in a Milky Way-sized galaxy, approximately one billion particles are required. Nevertheless, even with the Zoom-in simulation, ten million particles can be handled, and the mass resolution is limited to around 1,000 Msun (Applebaum et al. 2021). To overcome these limitations, we are developing a new code that leverages the supercomputer "Fugaku" to simulate down to individual stars within the galaxy. Such codes employ hierarchical individual time-stepping methods, which can increase computational and communication costs by several hundred times. These costs are caused by short timescale phenomena, such as supernova explosions, leading to parallelization efficiency issues. As a solution to this problem, we are developing a surrogate model using machine learning to rapidly duplicate supernova feedback. This model learns from the results of supernova explosion simulations within giant molecular clouds and predicts the physical quantities at one hundred thousand years later. I will report the fidelity of this technique in this presentation.
F608 & Zoom (hybrid)
Magnetic field transport is a theoretical model of the formation of large-scale magnetic fields which can drive outflows (e.g. jets, winds) in accretion disks. We develop a two-dimensional (2D) kinematic mean-field model for poloidal field transport which is governed by both inward advection and outward diffusion of the field (Yamamoto & Takasao submitted). This 2D model enables us to investigate the multidimensional effects on field transport that the traditional 1D model cannot consider. However, it is necessary that the treatment of transporting process is updated to obtain more realistic field distribution, such as dynamo effects and fast accretion flow near the disk surface (surface accretion flow). We also perform the 3D MHD simulation for radiatively inefficient accretion flows around black holes. We obtained the spatial distribution of dynamo coefficients by data analysis used in Dhang et al. 2020. We also investigated the radial distribution of the alpha viscous parameter and surface accretion flow. We plan to perform the 2D field transport simulation by using results from the 3DMHD simulation. In this talk, I will discuss the progress of these studies.
F608
Recently, IceCube has reported possible detection of high-energy neutrinos from several nearby unjetted Seyfert galaxies. Due to lack of strong jet activity and weak gamma-ray fluxes, it is widely believed that neutrinos are generated in the coronae in the vicinity of central supermassive black holes. However, given the uncertainty of neutrino measurements, cosmic-ray powers are highly uncertain. In this talk, I would like to overview how neutrinos are generated in corona and the related coronal magnetic activity. Then, I would like to discuss the available cosmic-ray power for coronal neutrinos based on accretion physics.
F313
A complete theory of galaxy formation requires understanding the details of how gas is converted into stars over cosmic time, which is affected by gas supply, star formation, and feedback-driven outflows. Based on the results of state-of-the-art cosmological zoom simulations, I will argue that galaxy formation is a violent process: at high redshift, stellar feedback causes all star-forming galaxies to undergo rapid fluctuations in their star formation rates on ~10-Myr timescales. Bursts of star formation are followed by strong outflows, which cause the star formation rate to drop precipitously. Fresh gas supply from galactic fountains rejuvenates star formation and restarts the cycle. At z ~ 1, simulations of massive galaxies exhibit a qualitative transition: outflows are no longer driven effectively, and the galaxies transition to steadily star-forming, well-order disk galaxies. I will present a simple analytic model that potentially explains the reasons for this transition.
F608
Studying the formation of the first-generation stars and the mass growth of their remnant black holes (BH) is crucial for understanding supermassive black hole (SMBH) formation in the early universe. I have investigated the gas accretion process in metal-free or low-metallicity environments by performing radiation hydrodynamics simulations. Throughout a series of studies, I have derived the mass distribution of the first-generation stars and revealed the conditions for super-Eddington gas accretion onto intermediate-mass BHs. Additionally, I currently conduct radiation hydrodynamics simulations of the mass transfer process in BH binaries to understand the formation process of merging binary BHs observed through gravitational waves. In this presentation, I will introduce my past research and report on the initial results of the ongoing study.
F608
IceCube has successfully detected the diffuse neutrino background, identified two neutrino sources, and measured the neutrino flux of the Galactic plane during its 15 years of operation. These are milestones in neutrino astronomy, considering how notoriously hard it is to detect these ghost particles and how rare are these ultra-high-energy neutrinos. With KM3NeT (running), Baikal-GVD (running) and P-ONE (planning) to come and reach their full potential within the next decade, neutrino astronomy is no longer a fantasy. Neutrino observation will advance our understanding of astrophysics beyond the reach of traditional photon-based observations. I will present in this seminar one of our case studies, which is the Galactic Centre (GC) neutrino emission. Gamma-ray observations of the GC have provided compelling evidence of hadronic interactions between cosmic rays (CRs) and baryonic matter in the GC. It is however difficult to disentangle the leptonic and hadronic components in the observed gamma-ray flux, and the origins of these GC CRs remain poorly understood. Unlike gamma rays, TeV neutrinos in the GC are exclusively generated through hadronic CR interactions. We propose that millisecond pulsars (MSPs) are possible accelerators of GC CRs, and a resolved GC neutrino intensity map can constrain the GC MSP population and their spatial distribution.
F620
Galactic Cosmic Rays are known to reach energies beyond the so-called Cosmic Ray “knee”, a spectral break occurring at ~3 PeV in the all particle cosmic ray spectrum. However, finding evidence for hadronic particle accelerators reaching PeV energies - PeVatrons - has proven elusive. Within the last five years, astrophysical sources of gamma-rays above 100 TeV have been identified for the first time; gamma-rays that are produced through interactions of particles with PeV energies. Many of these sources are associated with the most energetic pulsars known. Only this year, the number of known emitters at these Ultra-High-Energies has potentially tripled, from ~12-14 known in 2021, to over 40 in 2023. In this talk, I will review the current status of the research and discuss implications for our understanding of pulsar environments and PeVatrons. Open questions include: Which particle types are being accelerated and generating the gamma-ray emission? How are the particles transported through the surrounding medium? What is the maximum energy limit for particle acceleration in pulsar environments? What are the nature of the enigmatic PeVatrons? In the near future, data from current and forthcoming facilities will help us to address these questions.
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One way to form the supermassive black hole seed at high redshift involves the direct collapse model. We use high-resolution zoom-in cosmological simulations to model outflow triggered by radiation and thermal drivers around the central mass accumulation during direct collapse within the dark matter (DM) halo. Due to the high accretion rate of ~ 1 𝑀⊙ /yr determined by the DM halo, accretion is supercritical, resulting in supercritical luminosity which affects the inflow rate, with the duty cycle of ~ 0.9. We observe a fast development of hot cavities which quickly extend into polar funnels and expanding dense shells. Within the funnels, fast winds, ~ 10^3 km/s, are mass-loaded by the accreting gas. Finally the formation of funnels and powerful outflows around, e.g., SMS, can have interesting observational corollaries. We study the Lyα signature from this SMS in a wide variety of configurations. We perform Lyα radiative transfer through a Monte Carlo algorithm, and consider the effect of collisional de-excitation of the 2p state, which would transfer Lyα into two-photon emissions. We find that Lyα photons could escape when the outflow driven by the SMS radiative feedback clean the gas above the disk, otherwise Lyα would be destructed into two-photon emissions. With the help of outflow, the escaped Lyα profiles show enhanced red wing, and suppressed blue wing.
F608
Understanding the intricate distribution of matter in the Universe is a fundamental objective in contemporary cosmological studies of structure formation. In this talk, we will delve into the significance of cosmic filaments and their prominence in cosmological investigations. In the framework of the Lambda cold dark matter (CDM) paradigm, the distribution of baryons broadly follows that of dark matter, albeit with subtle biases between the two. These biases manifest in various observations in diverse ways, underscoring the crucial need to comprehend the intricacies of this bias and its relationship with galaxy formation. Specifically, we will explore the profound impact of feedback on the circumgalactic and intergalactic environments. The role of cosmic filaments in shaping the mass acquisition and spin of galaxies will also be highlighted.
F608 & Zoom (hybrid)
In this seminar, at the beginning it is planned to present , a previous effort to extend the Hartle-Hawking tidal heating formula in the presence of torsion and also the applicability of this scheme will be discussed in the context of black hole-neutron star merger scenario. Recent observation of binary neutron star merger, specifically GW170817 created a lot of enthusiasm in the astrophysic community with a hope to put a stringent constrain on the viable equation of state (EOS) of the dense matter. Matter in the core of a neutron star, i.e. in an extreme density is predicted to be in state called quark-gluon plasma. Considering this kind of core and a hadronic crust, a crossover EOS can be prepared. In this line of research, the study of binary neutron star merger simulation with a quark-hadron crossover EOS will be discussed.
F608
The James Webb Space Telescope (JWST) has successfully performed spectroscopic identification of galaxies at redshifts z > 10. However, observing the first galaxies with Mstar < 10^6 Msun remains challenging. Therefore, studying Extremely Metal-Poor Galaxies (EMPGs), which are observed in the local Universe, becomes crucial. By examining the chemical abundance, we can trace the star formation history of galaxies. The relationship between helium abundance (He/H) and metallicity allows us to determine the primordial helium abundance resulting from Big Bang nucleosynthesis (Matsumoto et al. 2023). To explain the observed chemical abundance in EMPGs, a better theoretical understanding of the correlation between the formation process and chemical evolution of low-metallicity galaxies is needed. In this study, we investigate the chemical enrichment history of low-metallicity galaxies using both one-zone model calculations and cosmological hydrodynamic simulations coupled with the chemical evolution library CELib. Our one-zone model reveals that the presence of more active star formation, with a specific star formation rate (sSFR) comparable to that of observed EMPGs, leads to a lower He/H ratio for the same metallicity. This effect is attributed to the increased abundance of helium in Asymptotic Giant Branch (AGB) stars. Additionally, we explore the formation of the first galaxies through high-resolution zoom-in simulations using the cosmological Smoothed Particle Hydrodynamics (SPH) code GADGET3-Osaka. Our simulations successfully reproduce the Fe/O ratio in EMPG candidates but fall short in reproducing the He/H ratio. At the conclusion of my presentation, I will discuss the prospects and plans for my Ph.D. thesis.
F608
Our universe is filled with relativistic particles known as Cosmic Rays (Cos). Their energy spectrum exhibits a broken power law with a notable softening at ~3 PeV, called the CR knee. Observations have confirmed that the CR component below this energy threshold originates within our Milky Way. Identifying the source of these Galactic CRs remains a prominent question in the field of astroparticle physics. Supernova remnants (SNRs) have emerged as the most plausible candidates for this source, although a firm confirmation is still missing. Gamma-ray instruments, particularly ones operating in the TeV energy range, have provided valuable insights into SNR systems and may still hold the key for resolving this longstanding debate. In this talk, I will discuss recent studies conducted on SNRs using gamma-ray instruments, with a specific focus on the MAGIC imaging Cherenkov telescopes. Additionally, I will examine the theoretical implications of these results for the SNR hypothesis.
F608 & Zoom (hybrid)
Active galactic nuclei (AGN) jets have been mostly simulated with grid-based codes. However, when it comes to cosmological simulations, SPH-based codes, such as GADGET3-Osaka, have more advantages in terms of following the structure formation as well as computational cost. Therefore, it is natural to expect AGN jets to be simulated in this codes to study their impacts on star formation and galaxy evolution. Previous study has been done by Husko & Lacey (2023) using SPH-based code SWIFT to analyze its feasibility in resolving AGN jets evolution at larger scale. Following their setup, we run similar tests using GADGET3-Osaka code. On top of that, we also do some comparison regarding artificial viscosity models that are commonly used in SPH codes, as well as resolution test to see if lower resolution can handle AGN jets evolution. In general, our jets follow closely the analytical prediction given by Kaiser & Best (2007). Moreover, we also show some preliminary results of how AGN jets impact the galaxy evolution. In the future, we are also working on how to properly implement this feedback self-consistently integrated with black hole physics and perform self-regulated BH-AGN simulation at cosmological scale.
F620
The new generation of galaxy redshift surveys is going to trace modes embedded in cubical volumes of ~10 Gpc/h side. Nowadays computational resources do not allow us to simulate such volumes with full n-body solvers. Therefore we resort to learning techniques applied to smaller volume simulations to obtain mock catalogues for all tracers of the large scale structure covering the redshift range from zero to about four. A deep understanding of the mathematical connection between the cosmic web and its tracers becomes crucial. These techniques will allow us to accurately assess the uncertainties in cosmological information inference.
F608
Galaxy evolution crucially depends on how gas is converted into stars in giant molecular clouds (GMCs) and on how ensuing stellar feedback from young massive stars (in the form of UV radiation, stellar winds, and supernovae) interacts with the surrounding interstellar medium. Observations indicate that GMCs in normal disk galaxies turn only a small fraction of gas mass into stars per free-fall time and over their lifetimes, while clouds in denser environments may form stars more efficiently. Although stellar feedback is believed to play an important role in controlling the efficiency of star formation and cloud lifecycle, details remain elusive. In this talk, I will present results from radiation (M)HD simulations of star-forming GMCs with stellar feedback. I will show how the star formation efficiency and destruction timescale depend on various integrated cloud properties such as mass, size, turbulence level, and magnetization, and discuss the relative importance of different feedback mechanisms. We explain the observed star formation rate of the Milky Way by applying our finding that the efficiency per free-fall time decreases with the virial parameter of a molecular cloud.
F608 & Zoom (hybrid)
Massive galaxies are thought to acquire most of their fuel above redshift 2 by cold filamentary accretion. Such cold stream scenario is ubiquitous in cosmological simulations but direct observational evidence remains difficult. Upon entering the hot halo of a galaxy, a cold stream can emit strong Lyman-alpha radiation which could be linked to the numerous Lyman-alpha emitters observed at high redshift. Recent high-resolution simulations of idealized cold streams aim to understand this emission mechanism. Through a comprehensive suite of two-dimensional simulations, we hereby study further the cold stream emission signature by considering anisotropic thermal conduction and initially uniform magnetic field with different angles. Notably, radiative cooling is included but not self-gravity and self-shielding. Simulations are done using the Athena++ code. Despite an initially small magnetic field (with a ratio of thermal pressure to magnetic pressure of hundred-thousand), we find that, as long as the magnetic field is not parallel to the stream, the emission signature of the stream can decrease up to one order of magnitude compared to hydrodynamical case. Such decrease is due both to a magnetic field amplification up to a few hundred times its initial value and to the diffusion of the mixing layer where the emission takes place. Also, in such conditions, the stream sustains at least 80% of its initial mass flux, still allowing a large amount of cold gas to reach the halo centre. We provide a tentative fitting and physical model for prediction.
F608
Supernova explosions play a critical role in regulating the formation and evolution of galaxies. It requires a one-parsec resolution to resolve each supernova bubble, which is four orders of magnitude smaller than the size of the entire galactic disk, and this wide dynamic range poses a challenge in directly simulating the galactic-scale impact of supernovae. Thus, a subgrid model for supernova feedback is necessary to study its effect on galaxies. As the sensitivity of the telescopes increases, it has begun to be realized that current simulations cannot explain matter distributions on circum- and inter-galactic media, and a better understanding and modeling of feedback is necessary. In the first part, I talk about our feedback model development. We studied the momentum of a superbubble formed by multiple supernovae on an idealized interstellar medium. The results indicate that a simple analytic model reasonably captures the metallicity dependence of the superbubble's terminal momentum. Using the results, We developed a subgrid model for large-scale simulations. I will demonstrate the model in an isolated-galaxy simulation to show that the inclusion of an additional model is necessary to reproduce galactic wind, which is important for the metal enrichment of the circumgalactic medium. In the second part, I will talk about current ongoing work. We employed our model in cosmological simulations and compared the results with observational data. I will discuss how the model is constrained in the comparison. At the end of my talk, I will talk about the prospects and plans for my Ph.D. thesis.
F608
Accreting black holes are powered by the conversion of the gravitational potential energy from the matter falling down on the black hole. They emit high energy emission in the UV, X-ray, γ energy range and can produce powerful relativistic jets observed in the radio. Both stellar mass black holes found in galactic X-ray Binaries (XrB) and the supermassive black holes present in Active Galactic Nuclei (AGN) show a strong correlation between the hard X-ray and the radio luminosities, suggesting a link between the accretion and ejection processes across the entire black hole mass scale. Yet the nature of this connection still eludes us. To elucidate this connection, Ferreira 2006 proposed a paradigm called the Jet Emitting Disk - Standard Accretion Disk (JED-SAD). The JED is a highly magnetized inner accretion flow that produces a jet and is modeled using semi-analytical MHD solutions (from Ferreira 1997). The JED is hot (~100-1000 keV), namely a corona, and generates the hard X-rays. Whereas, the SAD is an outer cold disk modeled on an α-disk (Shakura & Sunyaev 1973). In 2018, Marcel et al. developed a two temperature plasma code able to compute the thermal equilibrium and the resulting spectrum for any given JED-SAD configuration. I will present the JED-SAD model and how we compute spectra of the thermal accretion flow. I will discuss the first applications of the model to observations of XrB and AGN carried out during my thesis. And finally, I will discuss some of the physical interpretations of our results.
F608 & Zoom (hybrid)
The corona is the outermost layer of low-mass stellar atmospheres consisting of the high-temperature plasma with > 10^6 K. A systematic understanding of coronal heating is necessary because the energy radiation from coronae has a strong impact on its surroundings such as planetary environments and the ionization history of our universe. To this end, it is important to understand the mechanism of energy transport from the photosphere to the upper atmosphere, and the coronal properties in different stellar environments. In this study, we addressed these issues by performing 1D MHD simulations of coronal heating. We found that the coronal property is closely linked to the physical state in the underlying atmosphere (chromosphere). Based on these findings, we identified that the condition for the coronal formation is determined by the chromospheric temperature and loop length in a simple relation. Furthermore, we investigated the effect of stellar metallicity on coronal heating to enhance our understanding of stellar coronae beyond the Sun. Our simulations demonstrated that metallicity is a crucial parameter that determines the coronal properties due to differences in radiative cooling efficiency. We also derived scaling laws that link the fundamental physical quantities of a steady coronal loop corresponding to differences in elemental abundances to define the basic coronal structure with various metallicities.