專題演講 2024

Venue: F102

The supermassive black hole (SMBH) at the center of M87, the brightest galaxy in the Virgo cluster, exhibits both low luminosity and high variability. In massive galaxy clusters, SMBHs are thought to be fueled by various mechanisms, including cold chaotic accretion (CCA). However, the complexities of the CCA process remain incompletely understood, especially given the vast dynamic range. To address these challenges, we employ general relativistic magnetohydrodynamic (GRMHD) simulations of M87, using boundary conditions that mimic the infall of cold filaments and clouds, replicating the CCA scenario. Our study investigates the dynamics of gas accretion onto SMBHs, exploring the intricate interactions between turbulent cold gas flows, angular momentum cancellation, and thermalization via ADAF accretion. By linking the small-scale physics of accretion to larger galactic dynamics, we aim to uncover the mechanisms driving variability in the mass accretion rate and their impact on galaxy evolution. In particular, the study of infalling cold gas clouds offers critical insights into the variability of the inner accretion flow, shedding light on SMBH feeding mechanisms and the resulting variability in galactic centers.

The cosmic infrared background (CIB) represents one of the Universe’s most fundamental constraints, yet its origin remained elusive for decades. In this talk, I will present our long-term efforts to resolve this puzzle, highlighting our latest measurements using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT). Our results show that galaxies, in particular those that are enriched by dust, are the dominant contributors to the entire energy budget of the CIB. I will then take a deep dive and explore the properties of these dusty galaxies, discussing their formation mechanisms and their pivotal roles within the broader framework of galaxy evolution. Finally, I will introduce AtLAST, a planned 50-meter single-dish submillimeter telescope, which promises to address key challenges in galaxy evolution and cosmology, including the pressing mystery of the Hubble tension.

The semidiurnal (12.42 h) and semimonthly (14.76 days) lunar tides have been well-known by fishermen for several centuries.  The gravitational force of the relative positions between the Sun, the Moon, and the Earth results in two symmetrical tidal bulges (double bulges) appearing at equatorial latitudes directly under and opposite the Moon.  Ionospheric GNSS (Global Navigation Satellite System) radio occultation soundings reveal the global three-dimensional structures and dynamics of the double bulges of Earth’s upper atmospheric lunar tides for the first time.  The double-bulge amplitude of ionospheric F2-peak height hmF2, lagging the sublunar or antipodal point by about 2–3 h, is about 3–5 km at the equator and 1.5–2.0 km at ± 35° magnetic latitude. The electron density further depicts global three-dimensional plasma flows in the ionosphere.  Meanwhile, the most prominent feature in the ionosphere is the equatorial ionization anomaly (EIA), which is characterized by two enhanced plasma crests at low latitudes straddling the magnetic equator. Global ionosphere maps of total electron content are analyzed to see how the ionospheric EIA crests respond to changes in lunar phases.  The results show that the EIA crests exhibit prominent semimonthly lunar tides with 14.77‐day period.  Appearance times of the EIA crests on new/full moon (first/third quarter) lead (lag) those on the associated average by about 20–40 min, while the EIA crests move the furthest poleward during new/full moon and equatorward during first/third quarter with the delays of about 2–5 days.  These indicate that the lunar phase can significantly modulate the ionospheric EIA.

共同作者：Tsung‑Yu Wu (吳宗祐), Chi‐Yen Lin (林其彥)

Recent observations of high-redshift luminous QSOs and faint AGN candidates, as well as the need to predict the outcome of future space-based gravitational wave experiments, fostered the development of detailed theoretical models which focus on the formation and evolution of massive black holes (MBHs). In this talk, I will present recent results about the formation, evolution and dynamical interaction obtained with the L-GalaxiesBH (LGBH) semi-analytic model. In particular, I will showcase the capabilities of LGBH, presenting the predictions for ongoing and upcoming gravitational wave experiments (such as the PTA collaboration and the LISA mission). I particularly will focus on showing how LGBH can be used to study the cosmological evolution of heavy and intermediate-mass MBH-seeds, providing insights about the occurrence of these BH-seeding scenarios over cosmological scales. Finally, I will show how LGBH can be used to contextualize and interpret the population of Little-Red-Dots recently unveiled by the James Webb Space Telescope (JWST). LGBH is a modified version of the public L-Galaxies2015 semi-analytic model (Henriques et al. 2015), and it was recently developed in order to include a comprehensive set of physical models which describe the formation and evolution of MBHs. In particular, LGBH is able to track MBHs by employing physically-motivated recipes for their seeding, mass-growth and dynamical evolution down to z=0.

Recently, changes in the space environment have aroused people’s interest with the rise of the global space industry and the gradual increase of solar activity. The term “space weather” is frequently shown in news which refers to all variable physical parameters and conditions on the Sun and in the space environment, such as solar wind and radiation, plasma density, high-energy particles, and magnetic fields. In 1991, the National Space Program Preparatory Office was established for the purpose of implementing the national satellite program and establishing space infrastructure. In the past few decades, the payloads onboarded the Taiwan’s FORMOSAT satellites are not only providing the remote sensing images, but also probing the space environment to explore and monitoring its morphology and variations, respectively. Those instruments are included the FORMOSAT-1/IPEI, FORMOSAT-2/ISUAL, FORMOSAT-3/GOX, TIP and TBB, FORMOSAT-5/AIP, and FORMOSAT-7/TGRS, IVM, and RFB. They can measure the ion and electron parameters, radio signal influence, as well as record transient luminous events. These in-situ and remote observations are used to investigate the plasma structure and dynamics in the mid-latitude, low-latitude, and equatorial ionosphere, such as the middle latitude electron density enhancements, plasma depletion bays, non-migrating tides, and scintillations.

On January 1, 2023, the National Space Organization of the National Applied Research Laboratories was officially restructured into the Taiwan Space Agency (TASA) to enhancing the space technology research and development capabilities, implementing the national space policies and plans, as well as furthermore promoting Taiwan space activities and the development of the space industry. In this presentation will give an overview of the past and current Taiwan’s FORMOSAT missions and further show the benefits of them to the space environment study and additional application of monitoring and forecasting.

Mercury’s magnetosphere is more dynamic than Earth’s due to its proximity to the Sun, and it is subject to a lower Mach number solar wind. Regarding the solar wind interaction with Mercury, we are interested in the configurations of Mercury’s magnetosphere and the energy transport under various solar wind conditions. First, this study examines the potential impact of low Mach number solar wind on Mercury’s bow shock and the resulting effects on the magnetosphere. To analyze the variability of Mercury’s bow shock in response to solar wind properties, this study combines observations by the Helios data with theoretical solutions and MHD simulations. The results show that when Mercury encounters solar wind with an extremely low Mach number, its bow shock is expected to become more flattened, further from the planet, and may even disappear completely. Our results also suggest the need for further research on the interactions between the solar wind and Mercury’s magnetosphere, which are expected to be anomalies when Mercury’s bow shock disappears. However, there is a lack of plasma density measurements inside Mercury’s magnetosphere, which could significantly change the solar wind-magnetosphere coupling. Therefore, our findings could provide research directions worthy of digging deeply with the new data from the missions MESSENGER and BepiColombo.

Our origins — how the Solar System has formed and evolved to its observed state — is one of the main focuses of modern astronomy. The orbits of Solar System planets (which are approximately circular and coplanar) are well known signatures of the processes at work during the early stages of the Solar System evolution. Other key signatures are the inclinations of the planets’ spin axes, or “obliquities”. In this colloquium, I will review the evolution mechanisms of planetary obliquities. I will show how recent discoveries modify our understanding of the history of giant planets and their moons, in the Solar System and beyond.

Binary star systems can accrete material originating from a circumbinary disc. Since it is common for the circumbinary disc to be tilted with respect to the binary orbital plane, we test whether the accretion dynamics can be a diagnostic for binary-disc misalignment. We present hydrodynamical simulations to model the accretion flow from a circumbinary disc around an eccentric binary with initial tilts ranging from 0 deg to 180 deg in increments of 15 deg. Based on the initial tilt, the circumbinary disc will align towards three different configurations: prograde coplanar, polar, or retrograde coplanar. For discs with initial tilts evolving towards prograde coplanar alignment, the accretion rates onto the primary and secondary stars exhibit alternating preferential accretion. Circumbinary discs evolving towards polar alignment exhibit no alternating preferential accretion onto the binary unless the initial tilt is close to the critical tilt that sets the boundary between coplanar or polar alignment. Such cases cause strong disc warping, leading to disc breaking. The inner disc becomes eccentric, leading to alternating preferential accretion onto the binary. As the break propagates outward, the disc tilt damps towards a polar state, and the disc eccentricity decreases. As the disc re-circularizes, the accretion rate transitions back from alternating preferential accretion to non-alternating accretion. Lastly, no alternating preferential accretion exists for discs undergoing retrograde coplanar alignment. From the summary of the accretion rates from our suite of SPH simulations, it is evident that the accretion rate evolution can be affected by the initial tilt and subsequent evolution of the circumbinary disc.

Protostellar disks are the reservoirs of mass responsible for transferring material from the infalling envelope to protostars and forming future planetary systems. These disks are now commonly found in the earliest stages of protostellar evolution, and recent observations have even revealed the presence of infalling molecular gas structures, commonly referred to as “accretion streamers”, feeding mass directly from the surrounding protostellar envelope to these young disks. However, external factors, such as, magnetic fields and turbulence could have a significant impact on these environments in which protostellar disks are formed as shown by numerical simulations. In this talk, I will bring these ideas together to discuss how protostellar disks accrete mass through several observational studies performed during my PhD, as well as, other recent findings from observations and numerical simulations. 

https://www.asiaa.sinica.edu.tw/people/cv_c.php?i=tjthieme

(Monday)12:20-13:20(special time) Venue: NTNU Gongguan campus S801-2

Whistler-mode waves were first detected on the ground during WWI as the so-called lightning-generated whistlers, a type of electromagnetic wave in audio frequencies. The whistlers can travel through the ionosphere and magnetosphere, bringing back plasma distribution information. Satellites later also observed whistler-mode waves exhibiting various frequency-time patterns in spectrograms, including chorus and hiss. Satellite missions have also detected them on the Moon, other planets, and solar wind. These waves can exchange energies with electrons and cause electrons to precipitate into Earth’s upper atmosphere, playing a crucial role in space weather. This presentation will provide observational and audio examples, along with fundamental theory. We will also discuss our ongoing research on these waves observed by the ARTEMIS mission in lunar orbit.

This study encompasses three interrelated projects, each designed to enhance our comprehension of ionospheric profile variations and structures. The initial project leverages ground-based observations of 630.0 nm airglow emission intensities to assess atomic oxygen ion ([O⁺]) densities between 150 to 450 km altitude using photochemical models. This approach is corroborated by electron density measurements from the digisonde DPS-4 in Irkutsk, Russia, suggesting a method for employing airglow as global ionospheric indicators. Expanding on this fundamental understanding of ionospheric airglow emissions, the second project confronts the intricacies of adapting the inversion model for global satellite observations. Moreover, the application of deep learning to fine-tune Abel inversion significantly reduces the margin of error in reconstructing the previously unobservable upper segment (>300 km) of airglow intensity profiles, as captured by FORMOSAT-2. This advancement promises a marked improvement in the completeness and reliability of airglow data, opening new avenues for ionospheric study and operational forecasting. The final project delves into ionospheric scintillation during geomagnetic disturbances, particularly through an analysis of FORMOSAT-7/COSMIC-2 data in the context of a moderate geomagnetic event that led to the loss of 38 out of 49 SpaceX Starlink satellites in 2022. Our analyses identify a link between the S4 index behavior and the disturbance in the electron density profiles, underscoring the effects of prompt penetration electric (PPE) fields and disturbance dynamo (DD) on ionospheric irregularities. In conclusion, the collective endeavor of these projects offers a detailed and intricate perspective on the ionospheric profile’s variability and composition, encompassing both disruptive influences and functional mechanisms.

Keywords: Ionosphere, Airglow, Plasma irregularity, Geomagnetic storm, Deep learning.

Venue: NTNU Gongguan campus Conference Center 2F Meeting Room (師大公館校區 綜合館二樓交誼廳)

Stars are formed within molecular clouds, and the star formation processes in galaxies are greatly impacted by the environments at the galactic and large scales. Recent surveys that combine Integral Field Spectroscopy with millimeter observations offer excellent chances to examine the relationship between gas and star formation in galaxies at scales of (sub)kpc, effectively connecting the physics across different scales. During this presentation, I will introduce the ALMaQUEST survey, which I have been leading to investigate the role of molecular gas in star formation. Furthermore, I will also discuss the current understanding of the process of star formation suppression in galaxies.

https://www.asiaa.sinica.edu.tw/people/cv_c.php?i=lihwailin

(Tuesday)14:20(special time) Venue: NTNU Gongguan campus S102

As far as we know, our Earth and Solar System are unique. It could, in principle, be the only planetary system in the Universe to harbour intelligent life or even life at all. As such, attempting to reconstruct its history is one of the most fundamental pursuits in the natural sciences. Whereas astronomical observations and space missions provide a general framework for understanding the planet surfaces, more comprehensive information about the deep planets and deep time comes from the analyses of meteorites and space mission (e.g., Apollo, Hayabusa, and Chang’E missions) returning samples. These precious rocks come directly from solar system bodies such as the Moon, Mars and other asteroids, and carry important information about their formation and accretion histories. This talk focuses on using high-precision chromium isotope measurements to understand the 1 Earth differentiation time (very early), 2 the oldest volcanism in the solar system (predating the formation of Earth), and 3 the origin of water on early Mars (a blue Mars).

In recent years, the realm of space exploration has expanded significantly, garnering increased attention and utilization. The advent of companies like SpaceX, led by visionary Elon Musk, has propelled the popularity of applications such as low earth orbit (LEO) satellites. Taiwan, too, has embraced the Space Era, embarking on a journey of space science and industry development since 1991. Beginning from the ground up, Taiwan has progressed through two phases of indigenous space technology programs, laying the foundation for its current endeavors. As the Taiwan Space Agency (TASA) advances into its third phase, exciting developments are underway. Having joined TASA in 2023, I aim to provide a concise overview of TASA’s achievements and its aspirations to keep pace with global counterparts in the Space Era. Additionally, I will introduce fundamental concepts utilized by scientific payloads, such as GNSS-RO and GNSS-R, which measure atmospheric and sea level properties. Moreover, numerous universities possess the capabilities to plan, manufacture, and operate cubic satellites, further enriching Taiwan’s space endeavors. Through this presentation, we will delve into Taiwan’s historical and contemporary space missions, inviting you to embark on an engaging journey into space exploration.

[PHY colloquium]

Fast radio bursts (FRBs) are energetic millisecond transients of extragalactic origin, whose nature and emission mechanism remain mysteries. Despite >1000 FRBs having been detected, only a few dozens of them have host galaxies localized. Therefore, a radio telescope with wide field of view (FoV) and high angular resolution are required for accumulating the statistics and pinpoint host galaxies of FRBs. The BURSTT telescope are phased antenna arrays designed for the purpose, with multiple stations observing in the 300-800 MHz band, under construction in Taiwan, outlying islands and partner sites. After completion in 2024, BURSTT will have ~10,000 deg^2 instantaneous FoV with an event rate of ~1 FRB per day, and 1″ angular resolution. The wide FoV maximizes the chance of multi-wavelength/muti-messenger counterpart. BURSTT will help to understand the physics of FRBs, and clarify their application as cosmological probe.

[ES colloquium]

The Outer Planet Atmospheres Legacy (OPAL) program with Hubble was started in 2014 with the goal of studying time-domain phenomena in Jupiter, Uranus, and Neptune, with Saturn added in 2018 once the Cassini spacecraft was de-orbited. Once a year, the OPAL program images each of our four outer planets, producing pairs of global maps in multiple filters, which are made available at the MAST archive. The OPAL team (Simon, Wong, and Orton) have used the data to discover new dark spots on Neptune, discover a UV-dark oval in Jupiter’s southern polar haze cap, measure changes in Jupiter’s Great Red Spot over time, detect fine-scale waves, chronicle shifts in haze and cloud layers on all four planets, measure jet streams, and study the structure and evolution of convective storms. The data have also provided a valuable resource enhancing the science return from the Juno and New Horizons spacecraft missions, also supplementing observations from a growing list of observatories including JWST, Kepler, Spitzer, VLA, Keck, ALMA, IRTF, VLT, and Gemini.

Wong et al. (2022) https://doi.org/10.1016/j.icarus.2022.115123
Simon et al. (2022) https://doi.org/10.3390/rs14061518
Wong et al. (2021) https://doi.org/10.1029/2021GL093982

[ES colloquium]