午餐會報

Fast Radio Bursts (FRBs) have been shown to have diverse properties and may come from very different host environments. To better understand the FRBs' origin, multi-wavelength detailed studies of a large sample of nearby FRB hosts will provide valuable information. To fulfill this goal, BURSTT has been designed with a large field of view and sub-arcsecond localization capabilities. In this talk, I will introduce the BURSTT project and its development status, focusing on the backend system, calibration, and VLBI timing I mainly work on.

Star formation in galaxies is governed by the amount of molecular gas and the efficiency that gas is converted into stars. However, assessing the amount of molecular gas relies on the CO-to-H2 conversion factor (α_CO), which is known to vary with molecular gas conditions like density, temperature, and dynamical state – the same conditions that also alter star formation efficiency. The variation of α_CO, particularly in galaxy centers where α_CO can drop by nearly an order of magnitude, thus causes major uncertainties in current molecular gas and star formation efficiency measurements. Using ALMA observations of multiple 12CO, 13CO, and C18O lines in several barred galaxy centers, we found that α_CO is primarily driven by CO opacity changes and therefore shows strong correlations with observables like velocity dispersion and 12CO/13CO line ratio. Motivated by these results, we have established a new α_CO prescription which accounts for CO emissivity variations and verified it across a set of nearby galaxies with independent α_CO measurements from dust. Applying our new prescription to 65 galaxies from the PHANGS-ALMA survey, we found an overall 3x higher star formation efficiency in barred than non-barred galaxy centers, which is an unprecedented trend that has been obscured by past α_CO prescriptions. Our results suggest that the high star formation rates observed in barred galaxy centers is mainly due to an enhanced star formation efficiency, rather than a substantially increased amount of molecular gas.

Protostellar jets often exhibit asymmetric properties between both lobes, ranging from their morphological and kinematic features to gas properties such as density and temperature. To determine whether these differences in the surrounding medium or the intrinsic properties of the jet, we need to characterize and trace these asymmetries close to the source. The Th 28 protostellar jet highlights these features with striking asymmetries between the jet lobes, while also showing a small-scale wiggling with a point symmetry indicating precession. I will present results from an optical/NIR study of this jet which combines integral field spectroscopy from VLT/MUSE and echelle spectroscopy from VLT/X-Shooter to obtain a 3D spatial and spectral view of both jet lobes, allowing us to investigate both the asymmetries and symmetries between them.

Ten years ago I was living in Taipei as a postdoc at ASIAA. Early the following year I left to try my luck in the field of data science, which involved studying, taking on side projects to build a portfolio, and applying for jobs. Ultimately, I took a job in the field of online education. Since then I've worked with three different companies to create courses focused on artificial intelligence and machine learning that serve thousands of learners worldwide. In this talk I will include a brief summary of my work in astronomy followed by stories and learnings from my transition into the world of silicon valley ed-tech companies.

Statistical X-ray AGN studies show that a significant fraction of active galactic nuclei (AGN) show large amounts of absorption in their X-ray emission. The fraction of absorbed AGN also shows an increase with redshift and a decrease with luminosity. However, these trends are not well established above redshift 2, especially for luminous AGN (log Lx [erg /s]>44.5). Using the uniquely deep & wide multiwavelength imaging datasets in the HSC-Deep XMM-LSS field, we investigated the absorbed fraction of luminous AGN with log Lx [erg /s]>44.5 above redshift 2. We found an absorbed fraction of 76±4% which is more than twice the fraction in the local universe (~30%). We further investigated the incidence of absorption in samples of Type 1 & 2 AGN at redshift 0.8-1.8 under AGN obscuration scenarios which describe absorption properties in the local universe. For most of the sample, the Eddington ratio of Type-2 AGN is lower than type-1 broad-line AGN. The distribution is consistent with dusty nuclear obscuration regulated by radiation pressure. However, we find evidence of non-nuclear obscuration among the sample of Type-1 AGN. These observations indicate that high redshift black hole growth occurs under heavy obscuration which is not fully explained under models of nuclear obscuration by a dusty torus. It requires additional components of obscuration from the host galaxy as well as dust-free absorption by nuclear gas.

Understanding how material accretes onto a rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how these disks are formed. Recently, many observations have confirmed the existence of so-called "streamers", which are extended filamentary-like structures feeding a reservoir of mass to these protostellar disks. We present one such case of a unique Class 0 protostar, Lupus 3-MMS, which shows multiple infalling streamers along the edge of the outflows in C18O. We isolate these streamers using dendrograms and compare to a simple model of infalling trajectories, which matches the observations very well (>96% in four out of five of the dendrogram structures). We derive several properties of the streamers, such as their mass and infall rate, and compare them in the context of other confirmed streamers in Class 0 protostars and values from MHD simulations of protostellar disk formation. Our results confirm the dynamically infalling nature of multiple streamers in Lupus 3-MMS and show that even these simple models can be good approximations when compared to observations.

Quasars (QSOs) – active super-massive black holes at the center of galaxies – are the brightest non-transient sources in the Universe and are powered by intense accretion episodes. The copious radiation emitted by a luminous QSO can, like a flashlight, illuminate the surrounding material, allowing us to directly study structures extending to circumgalactic (~100 kpc) and intergalactic (Mpc) scales. In this talk I will quickly report on some of the latest results of the QSOMUSEUM survey which comprises VLT/MUSE observations for 120 z~3 single quasar fields and 8 quasar pairs. Using a high-resolution cosmological simulation I will then showcase the importance of the QSO radiation on circumgalactic scales, and show how the observation of extended emission around quasars not only give us access to the gas properties, but also to the properties of the central engine itself (black-hole mass, accretion rate, ionization cone opening angle).

Magnetic fields (B-fields) are believed to play an essential role in the formation and evolution of interstellar clouds and protostars. A vast amount of polarization data from thermal dust emission has made significant progress in studying B-fields and dust in star-forming regions. In this talk, I will present our studies on B-fields toward several molecular clouds using SOFIA/HAWC+ and JCMT/Pol-2. Then, I will focus on probing dust physics, including grain alignment (RAT-A) and rotational disruption (RAT-D) due to radiative torques (RATs), toward several filaments. Our numerical modelings using RAT theory can successfully reproduce maps of polarization fraction from observational data. Our results can explain the decrease of the polarization fraction toward the dense regions (aka. polarization holes), provide more robust evidence for the RAT paradigm, and insights into dust grains.

Planet formation mechanisms are intimately tied to the structure of protoplanetary disks and the properties of dust grains. The first theme of the talk focuses on dust settling, which may serve as a prerequisite for triggering streaming instability by enhancing the midplane dust-to-gas ratio in the protoplanetary disks. Utilizing high angular resolution observations from ALMA, I present vertically resolved, edge-on disks around HH 212 mms and IRAS 04302+2247. The results demonstrate that the dust has not completely settled yet in these young systems. The second theme attempts to understand the grain sizes using submillimeter continuum polarization. While dust scattering from spherical/randomly aligned grains can explain much of the polarization patterns, I show that scattering of aligned grains can simultaneously explain the multiwavelength polarization pattern for HL Tau and also the polarization substructure.

Thousands of other worlds beyond the Solar System (i.e., exoplanets) have been found. In this informal talk, I shall give the audience a glimpse of my view of exoplanet populations based on hydrogen isotopes. Interestingly, my view may be undermined by recent JWST observations and updated statistical analyses of these other worlds.

The physical properties of protostellar disks, such as mass and size, are likely closely related to the planet formation process. Several mechanisms have been proposed to influence disk properties during star formation. To observationally examine these theories, we have been measuring disk properties and comparing them with magnetic fields, turbulence, gas kinematics, and stellar mass in various systems. In this presentation, I will summarize our observational results on the relationships between disk properties and physical conditions in protostellar sources, discuss key mechanisms determining disk properties, and demonstrate that theoretical predictions from the combination of hydrodynamics and non-ideal MHD can explain the observed size distributions.

Until the early 2000s, uniprocessor performance climbed along with Moore's law, doubling approximately every two years. To obtain further speedups with computer programs, one had to only purchase a new machine. However, microprocessor manufacturers hit a fundamental wall, which meant that clock frequencies could not be increased further with mass-produced processor coolers. After this turning point, sequential programs had to be parallelized to obtain further speedups. The free lunch was over. Today, graphics processing units are the flagships of massively parallel accelerators, which have been used successfully to accelerate machine learning, computational chemistry, and physics by an order of magnitude compared to general-purpose purpose processors traditionally used in high-performance computing. In this talk, we will introduce the concepts of implementing physical simulation software on graphics processing units, discuss the outlook of the high-performance computing landscape, and give an overview of the state-of-the-art methods for accelerating astrophysical simulations.

We are all asked to give science talks from time to time. But whether that talk is a good talk or mediocre talk can determine whether you get the job or not, whether you get the funding, whether you effectively communicate your results to your colleagues, or actually engage your students with the material. In short, the science talk is an essential part of our job. But far too often, the talk is approached as a nuisance, an afterthought, or simply an opportunity to prove that you've been working on something. Sometimes the speaker seems bored! and in such a case, you can be assured that the audience is also disengaged, making the whole exercise performative rather than informative. Other times, speakers will just assume that the work is so inherently interesting that merely showing some esoteric plots and barely explaining them is enough to keep the audience enthralled (spoiler alert: it isn't). In this talk, I will highlight some common pitfalls that get in the way of a successful talk, and outline a range of techniques that can help improve audience engagement. Drawing on my training as a stage actor, as well as years of experience communicating science to public audiences, my aim is to help make science talks a little less of a chore and a little more useful for speakers and audiences alike.

Despite being studied for several decades, understanding molecular clouds, their substructure, and their complex dynamics leading to star formation, remains a challenge. Different models have been proposed to explain the observations of clouds and clumps connecting star-forming regions and, if possible, young stellar clusters. Each model addresses different physical mechanisms as a key ingredient for the star formation process describing some observed features. In this talk, I will resume the work I have done in my research studying numerical simulations of molecular clouds and their substructure to analyze their energies and their Larson ratio, showing supportive evidence for the gravitational hierarchy collapse (GHC) model as the mechanism operating within real molecular clouds and promising results about an evolutionary scenario where clouds exhibit growth in mass and density together with their star-forming activity in the presence of magnetic fields.

Hyper-luminous infrared (IR) galaxies (HyLIRGs) are among the most luminous objects in the Universe. Their IR luminosity exceeds 10^13 solar luminosities, produced by significant star formation (SF), active galactic nuclei (AGN), or both. HyLIRGs are thought to probe the maximum growth phase for supermassive black holes (SMBHs) and their host galaxies during galaxy-SMBH co-evolution. Because HyLIRGs are an extremely rare population, their physical properties need to be better understood. We have conducted an intensive search for HyLIRGs in the past few years using multi-wavelength data. In this talk, I will introduce how to hunt these extremely luminous monsters in the Universe and present their revealed physical properties (e.g., Toba et al. 2018; 2020; 2022; 2024).

Planetesimals -- asteroids and comets -- are the building blocks of planets in protoplanetary discs and the source of dust and gas in debris discs. Along with planets they comprise the left-over material after star formation that constitutes a planetary system. Planetesimals are dynamically stirred, exciting their orbits and inducing collisional velocities large enough to trigger a collisional cascade. This produces fragments ranging in size down to sub-micron dust grains; large, millimetre-sized dust grains are weakly affected by non-gravitational forces and therefore trace the location of dust-producing planetesimals within a system. Planets further influence the dynamics of planetesimals (and dust), sculpting the orbits of debris belts to produce asymmetries or gaps. We can constrain the architecture of planetary systems, and infer the presence of unseen planetary companions, by high spatial resolution, multi-wavelength imaging of debris discs, detecting the emission from large dust grains at (sub)millimetre wavelengths. In this talk I will present a predominantly ALMA-based perspective of the observation and modelling of the architectures of cold debris belts and the limits on planetary companions that can be inferred from these data. I will discuss these findings in the context of the ongoing ALMA large program ARKS which is targeting the radial and vertical structure of 17 bright debris discs. Finally, I will highlight potential future avenues for detection and interpretation of debris disc systems including ongoing ALMA observations and near-future facilities such as AtLAST.

Multiband observation of deep fields provides a unique scope to study different aspects of galaxy evolution by effectively detecting fainter sources in the distant universe. We utilize the angular resolution (~1.2 arcsec), sensitivity, and field of view of the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat to image several HST deep fields in the FUV and NUV bands. Our UV flux measurements of the identified sources complement existing multiband data in deep fields and enable us to probe properties of galaxies between redshift ~ 0 and 1. We studied the galaxy UV luminosity function, UV continuum slope ($\beta$), and IRX-$\beta$ relation to understand galaxy evolution during the last 6 Gyr cosmic time. I will specifically discuss the nature of dust attenuation studied using a UV-selected galaxy sample at $z\sim$0.5 in the GOODS-north field. I will also discuss how observation of AstroSat UV deep field is unique to search for Lyman Continuum leaking galaxies beyond redshift ~ 1, which is important to understand the cosmic reionization process.

One of the main observational quantities we aim to obtain from resolved spectroscopic-line observations is related to kinematics. That is, how the gas behaves under the presence of a gravitational potential and the local conditions of the ISM. There are however challenges to overcome when trying to recover kinematics from observations. These are related to instrumental configurations and the local atmospheric conditions of the observation, i.e., the line spread function (LSF/ spectral broadening) and the point spread function (PSF/Beam). These two effects, artificially broaden the observed spectral line, preventing the proper characterization of the intrinsic kinematics. In this talk, I will briefly show how to recover the intrinsic circular (and noncircular) rotation and velocity dispersion, from 3D spectroscopic observations (2 spatial and one spectral axes) like IFS, ALMA, etc. This technique is applied to galaxy gaseous disks from HI to IR, but can be extended to any emission-line disk.

Over the last years significant advances have been made in our understanding of how and where stars and planets form and how they evolve during their earliest stages, both from a physical and chemical point of view. Deep observations of the gas and ice in the environments in which young stars form demonstrate that these regions are characterised by rich and varied chemistry with high abundances of complex organic molecules – some perhaps even of prebiotic relevance. At the same time, a picture has emerged where the first seeds for planets are planted in protoplanetary disks already during the first few 100,000 years after stars form. But, what is the link between this complex chemistry and the structure of the newly formed protoplanetary disks – and does it have any implications for the origin and composition of planets outside of our own Solar System? In the colloquium I will discuss how our understanding of the earliest stages of star and planet formation has evolved over recent years. In particular, I will focus on how ALMA has helped shedding new light on how the properties of emerging protoplanetary disks may reflect the evolution of protostars and conditions in their natal environments.

Based on arXiv: 2409.13022 (accepted in ApJ Letters). We update constraints on cosmological parameters in a 12-parameter model, which extends the standard 6-parameter ΛCDM to include dynamical dark energy and massive neutrinos, along with other new parameters. We use the latest Planck PR4 (2020) likelihoods, DESI DR1 BAO, and the latest uncalibrated type Ia Supernovae (SNe) datasets. In this talk, I will discuss the implications for dynamical dark energy in such an extended model, and at the same time, provide robust bounds on neutrino masses which will be useful for the astro- and particle physics communities. I will also discuss the current status of the weak lensing tension and the Hubble tension in this extended cosmology.

As coherent radio emission from compact sources, such as pulsars, travels through the interstellar medium (ISM), a variety of physical processes can alter the phase and amplitude information of the signal received at Earth. By leveraging geometric arguments in the eikonal limit, coherent radio emission scattered by a thin screen of material --- as evidenced by discrete parabolic structures in the two-dimensional Fourier transform of the intensity as a function of time and frequency --- yields information about the structure and scale of semi-permanent formations in the ISM that are nigh-impossible to image directly. In this work, we examine a series of observations of PSR B0834+06 taken with the Arecibo Observatory 305-m dish that show lensed emission dominated by not one but two individual thin structures along the line of sight. We compare these observations with a recently-developed model (Jow et al. 2024) positing a universal explanation for the scintillation of radio emission in the ISM using corrugated plasma sheets with A3 cusp catastrophes in their density projections. We will end by discussing the open questions in our data, and the other potential optical regimes that may give rise to the observed scattering.

One of the greatest challenges in project management is efficiently managing time. While performing the project management, you have many demands on your time. Often there are competing priorities to deal with, such as the resource, and budget. Furthermore, the needs of your team and expectations from the project stakeholders. This can feel overwhelming. In today’s talk, we will introduce strategies, processes, and tools for effective project time management.

The intergalactic medium (IGM) around quasars is shaped by both their dense environments and excess ionizing radiation, forming a "quasar proximity zone" whose size and anisotropy depend on the quasar's age and radiation geometry. Using quasar pairs from the Dark Energy Spectroscopic Instrument (DESI) Year 1 data, we investigate how the foreground quasar's proximity zone affects Lyman-alpha absorption in the background quasar. The large DESI sample enables an unprecedented precision in measuring this effect, allowing a detailed investigation of the signal's dependence on the angular separation of quasar pairs and the luminosity of the foreground quasar. Our results reveal that enhanced gas clustering near quasars dominates over their ionizing effect, leading to stronger absorption on neighboring sightlines. We also model the hydrogen gas distribution and its connection to quasar luminosity, discussing implications for constraining quasar age and radiation geometry.