Lunch Talk and Tech Lunch Talk

Beam calibration is a persistent bottleneck for next-generation 21 cm intensity mapping arrays, where instrumental beam knowledge at the percent level is required to avoid foreground contamination of the cosmological signal. I will present PEACC (Precision Emitter for 21 cm Array Coherent Calibration), a GPS-synchronized, RFSoC-based coherent digital calibration source designed for drone deployment over telescope apertures. Using anechoic chamber characterization and drone-based field tests over a 3-meter dish, we demonstrate sub-nanosecond timing precision and beam amplitude precision of 1% at −8.8 dB, with cross-correlation outperforming auto-correlation across all tested SNR regimes. To our knowledge, this represents the first free-space GPS-synchronized coherent calibration source and its first drone deployment for beam mapping. I'll discuss the measurement results and what they mean for next-generation 21-cm arrays.

In sociology, "demographic tension" refers to social and geopolitical stress caused by major imbalances or rapid shifts in population structures. Interestingly, this idea can also extend to planet populations. Recent observations suggest that the most common exoplanets—known as super-Earths—used to "live in harmony" by maintaining stable, resonant orbits. Over time, however, their orderly arrangement became unstable and broke apart, likely triggered by the ruthless intrusion of other planet populations.

A planetary growth rate, i.e., the mass accretion rate, is a fundamental parameter in planet formation, as it determines a planet's final mass. Planetary mass accretion rates have been estimated using hydrogen lines, based on the models originally developed for accreting stars, known as the accretion flow model. Recently, Aoyama et al. introduced the accretion shock model as an alternative mechanism for hydrogen line emission. However, it remains unclear which model is more appropriate for accreting planets and substellar objects. To address this, we applied both models to archival data consisting of 96 data points from 76 accreting brown dwarfs and very-low-mass stars, with masses ranging from approximately 0.02 to 0.1 Msun, to test which model best explains their accreting properties. The results showed that the emission mechanisms of 15 data points are best explained by the shock model, while 55 data points are best explained by the flow model. For the 15 data points explained by the planetary shock model, the shock model estimates up to several times higher mass accretion rates than the flow model. As this trend is more pronounced for planetary-mass objects, it is crucial to determine which emission mechanism is dominant in individual planets. We also discuss the physical parameters that determine the emission mechanisms and the variability of line ratios.

Protostellar jets and outflows play a central role in early star formation by removing angular momentum and regulating mass accretion. Recent observations with ALMA and JWST have revealed jets to be chemically rich, multi-phase, and often episodic, may be tracing accretion variability. High-resolution molecular line studies from ALMA probe cold, dense jet components and chemically evolving envelopes, while infrared spectroscopy from JWST uncovers warm and hot shocked gas with layered temperature structures. Survey results further indicate that collimated molecular jets are common and that strong jet activity can persist beyond the youngest protostellar phases. In this seminar, I will present an integrated observational perspective on protostellar jets, focusing on (i) molecular and infrared diagnostics of jet structure and kinematics, (ii) evidence for episodic accretion encoded in jet properties, and (iii) evolutionary trends inferred from multi-source and survey studies. I will highlight recent ALMA and JWST results, discuss their implications for disk–jet launching mechanisms, and outline how multiwavelength observations can constrain feedback, accretion histories.

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1- size, stellar mass, Sersic index, axis-ratio, Gini- parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass. We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1 stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers.

Red, passive galaxies that dominate galaxy clusters are thought to experience accelerated evolution compared to their counterparts in the field. Protoclusters at cosmic noon are key laboratories for investigating how these galaxies quench and transform, providing insights into the role of environment in galaxy evolution. I will summarize some recent results from recent observations related to the galaxy population in the Spiderweb protocluster at z=2.16. In particular, I will highlight the identification of quenched galaxies through grism spectroscopy in the core region of the protocluster. Half the massive galaxies are quenched—a fraction about two to three times higher than the coeval field. Leveraging the rest-frame 1μm imaging obtained by JWST, we study the galaxy population in the core of the protocluster from a morphological perspective. We found 50% of the grism-identified galaxies are bulge-dominated (Sérsic index >2.5) in the rest-frame NIR—lower than the ∼80% fraction in local clusters, and only 1σ higher from the coeval field fraction of ∼40%. Relative to the field mass–size relations, the protocluster galaxies show no statistically significant size offset. We discuss this results in the context of galaxy quenching and transformations.

Angular momentum transport by magnetic fields is important for formation and evolution of protoplanetary disks. The effects of magnetic fields are suppressed due to nonideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and Ohmic dissipation, which depend on the degree of ionization. Cosmic rays (CRs) are the primary source of ionization in star-forming clouds, and their distribution is nonuniform as it is affected by gas density and magnetic fields. Therefore, CRs, magnetic fields, and gas interact with each other. In this work, we develop a new fully implicit CR transport module in Athena++ and perform 3D simulations of disk formation from collapse of molecular cloud cores. Since CRs are strongly attenuated in the dense gas at the disk scale, distribution of magnetic fields is considerably altered compared to conventional models assuming a uniform ionization rate. While the total magnetic fluxes accreted onto the disks remain similar as the gas outside the disks remains sufficiently ionized and well coupled, the magnetic fields in the disks are less twisted due to the stronger nonideal MHD effects. As a consequence, magnetic angular momentum transport is strongly suppressed at the disk scale, resulting in more gravitationally unstable disks with more prominent spiral arms. Our simulations demonstrate the influence of nonuniform ionization resulting from CR transport and attenuation on the disk formation and evolution.

The gas distribution in galaxy clusters is highly sensitive to the strength of AGN feedback, providing key constraints on astrophysical models and on cosmological observables such as weak lensing. The kinematic Sunyaev-Zel’dovich (kSZ) effect is a velocity-induced shift on the Cosmic Microwave Background (CMB) spectrum, tracing cluster gas through their bulk peculiar motions and optical depth. Using optically selected clusters associated with DESI spectroscopic redshifts, we detect the pairwise kSZ signal for optical clusters at an unprecedented 6 sigma significance. We further measure cumulative gas profiles out to 4 arcmin and compare them with Magneticum simulations to probe feedback strength in massive halos.

The central parsec of the Milky Way Galactic Center is a dynamically extreme environment, influenced primarily by the central supermassive black hole known as Sagittarius A*. This region is also the only galactic nuclear star cluster where individual stars can be observed, which makes it a crucial location to study astrophysics around supermassive black holes. Because of the high stellar densities, adaptive optics is needed to resolve individual sources. In this talk, I will present work done by the UCLA Galactic Center Orbits Initiative collaboration, ranging from tests of fundamental physics to improved understanding of the Galactic center stellar populations. I will also discuss how developments in adaptive optics and instrumentation have been critical to scientific discoveries.

SR 12 c is a 13 Mjup gas giant orbiting its host binary at a separation of 1200 AU. As a young and actively accreting planet, it offers a rare opportunity to probe the environment of giant planet formation. Building on our previous ALMA detection of its circumplanetary disk, we present JWST/MIRI imaging and constrain the disk's physical properties using analytic modeling. In this talk, I will highlight the main results of our observations and modeling and discuss their implications.

Galactic-scale simulations rely on sub-grid models to provide prescriptions for the coupling between supernova (SN) feedback and the interstellar medium (ISM). Many of these models are computed in 1-D to allow for an efficient way to account for the variability of ISM properties. However, parsec-scale simulations revealed that the release of energy from SNe within Giant Molecular Clouds can be highly asymmetrical. This is largely due to the presence of pre-SN feedback, such as ionizing radiation, that are able to carve channels along the paths of least resistance around the progenitors. Being partially confined, the SN energy escapes to the outer ISM preferentially through these channels, departing from the spherically symmetric descriptions. In this talk, I will present our novel numerical models for semi-confined SNe in porous clouds, and demonstrate how this mode of energy release could impose a higher dynamical perturbation to its local ISM. I will then propose practical methods that could be used to incorporate partial-confinement effects into the 1-D sub-grid feedback models.

ASIAA has many members—including faculty, postdocs, and students—so it can be difficult to know everyone (especially for newcomers) and to understand who is working on what. By having a flash talk session, we hope to quickly promote mutual understanding and give everyone a chance to introduce their recent work. The talk format will be 3 minutes + 1 minute for questions, focusing on speaker's “big win” from the past year (personal or professional). We plan to hold flash talk sessions regularly. The second session will take place on May 25. We look forward to your participation.

Galaxy clusters are massive structures made of dark matter, hot gas and galaxies that grow through the accretion of smaller systems. Dense environments such as these tend to prematurely shut down star formation in member galaxies. In this presentation, I explore the link between the cluster environment and member galaxies using a statistical technique called total light stacking. I first examine the star formation activity of clusters as a functions of redshift, showing that before z~1.5, the environment does not impact star formation. I next demonstrate that total light stacking can be used to detect the splashback radius, a physical boundary between the cluster and the surrounding infalling regions. I finally present a proof of concept of the potential of total light stacking to investigate the star formation history of the cluster infalling region, showing that the fraction of the stellar mass in this region increases with increasing redshift.

Jets from young stellar objects are closely linked to the process of mass accretion and the removal of angular momentum from the star-disk system. The ejection of knot structures in the jet trace the history of variable mass accretion, while some jets show pronounced asymmetries between the kinematics, morphology and gas properties on each side of the source which may point to an underlying asymmetry in the jet launching mechanism. In this talk, I present results from high spatial resolution observations of the asymmetric Th 28 jet obtained with VLT/MUSE. These reveal new knot structures in the inner microjet and allow us to measure the jet properties within the inner 200 au of both jet lobes. The observations also point to a factor two increase in both mass accretion and outflow rates over the preceding nine years. I explore what these observations can tell us about the ongoing variability of Th 28, and the degree of intrinsic asymmetry between the two sides of the jet.

Protoplanetary disks form around young stars when dense molecular cloud cores collapse. An outer shroud of gas and dust, known as the envelope, surrounds and feeds both the young star and the forming disk. The observations of protostellar systems show a break in the radial profile of specific angular momentum (and in the rotational velocity), as evolving from the envelope to the Keplerian disk. In this talk, I will present our results based on both theoretical and observational grounds, that show the existence of a distinct transition zone, through which infalling gas motions from the envelope transforms into keplerian motions within the disk. We name this transition zone at the envelope-disk interface as ENDTRANZ (Envelope Disk Transition Zone). We first employ global MHD disk simulations of gravitational collapse starting from a starless cloud core, in order to self-consistently determine the physics of the ENDTRANZ. Our simulations reveal that the transition from the infalling-rotating envelope to the Keplerian disk gradually unfolds through a jump across a finite thickness in the radial profile of specific angular momentum. This jump serves as a tracer for the angular momentum redistribution within the ENDTRANZ. We also study a class 0/I protostar L1527 IRS using the high-resolution ALMA Large Program eDisk (Embedded Disks in Planet Formation) observations. We identify a similar jump, in the radial profile of the specific angular momentum at the envelope-disk transition of this protostellar system. Spanning a measurable radial width, this observed jump confirms the existence of an ENDTRANZ in L1527 IRS. Our results suggest that internal gravitational torques play a dominant role in shaping up disk formation, offering insights into the evolution of young stars and its rotationally supported protoplanetary disks.

Hycean planets – temperate sub-Neptunes with hydrogen-rich atmospheres and global oceans – are compelling candidates for potentially habitable planets. Future mid-infrared observatories, such as the Large Interferometer For Exoplanets (LIFE), could probe their thermal emission to reveal the atmospheric composition and potential biosignatures. In our study, we explore the detectability of key molecules of potentially habitable Hycean planets via emission spectroscopy with LIFE by applying atmospheric retrievals to simulated data.

The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research (CASTOR) is a proposed wide-field (30′×30′), high-resolution (FWHM∼0.15′′), 1-m- space telescope mission in development at the National Research Council of Canada and the Canadian Space Agency optimized for the UV/blue-optical wavelengths (0.15 to 0.55μm). Through its wide- and deep-field surveys, CASTOR will enable discoveries ranging from studies of galaxy evolution and AGNs to stellar astrophysics. CASTOR will feature 3 simultaneous imaging channels (in 5 imaging bands) for precise photometry and low- and low-medium resolution spectroscopic capabilities. The Ultraviolet Multi-Object Spectrograph (UVMOS) is a proposed instrument for CASTOR that will enable low-medium resolution (R ~ 1400) spectroscopy. The UVMOS will demonstrate a new technique for multi-object spectroscopy using digital micro mirror devices (DMD), a Texas Instrument semiconductor device commonly used in projectors. This talk will first provide a general overview of CASTOR's science missions, instrument design, and planned surveys. The second half of the talk will focus on the Ultraviolet Multi-Object Spectrograph (UVMOS) instrument and the ongoing instrumentation work conducted at the University of Calgary, NRC Herzberg, the University of Manitoba, and CASTOR's international collaborators.

State-of-the-art cosmological simulations have successfully reproduced several key galaxy properties through empirical calibration. However, the physics of feedback processes that regulate galaxy evolution remains unclear. Deciphering this feedback physics requires simulations that cover a wide dynamic range, from the ISM to the IGM, and resolve multiphase gas. The GAMER code enables us to tackle this challenge through efficient computation with GPUs and adaptive mesh refinement. We have joined the cross-code comparison project AGORA, using the GAMER code with our supernova feedback model, and have validated GAMER through these comparisons. I will present results from the AGORA runs and then discuss our study of the recombination coefficient relevant to cosmic reionization using these simulation outputs. I will also describe our code development for further accelerating GAMER via block-by-block adaptive time-stepping.

In this talk, I will examine two extreme dynamical astrophysical systems. First, triple star systems represent one of the most chaotic environments imaginable for a planet, and using a 3D N-rigid-body integrator I'll describe how we compute long-term orbital evolution in these hierarchical configurations and show where stable planetary orbits can, and cannot, survive. Second, exomoons are the next frontier in planetary science, but their orbital stability is uncertain. I'll present numerical experiments exploring the conditions under which moons survive around exoplanets and what drives their eventual loss.

PDS70 is a rare case in which the forming planets have been confirmed by direct infrared imaging observations. I have carried out the ALMA Band 7 full polarization observations on its submillimeter dust ring, which detected ~2% dust polarization with position angles (E-field) preferentially aligned with the minor axis of the dust ring. My model, coupling the 3D Monte-Carlo Radiative Transfer simulations and the Markov Chain Monte Carlo fittings, indicates that the maximum dust grain size in the PDS 70 dust ring is below 100 micrometers. This reinforces the idea that water-ice coating does not help dust growth cross over the bouncing/fragmentation barrier.

As pulsar signals propagate towards Earth, they are scattered by density fluctuations in the Interstellar Medium and produce a characteristic interference pattern known as scintillation. This effect allows us to use the pulsar as a highly effective backlight to study the ISM on the small scales or to use the ISM itself as gigantic interferometer to study the pulsar. In this talk I will introduce the basics of pulsar scintillation and discuss how it can be used in addressing a wide range of topics from extreme condensed matter physics to the gravitational wave background to cosmic ray transport and the smallest scales of the ISM and more.

Interstellar dust is a fundamentally important component of the ISM and cosmic galaxy population, both observationally and dynamically. Yet many basic questions about the origin, evolution, and properties of this dust remain unanswered, in large part because of the complexities of dust physics. I will present work I have been leading to advance our understanding of cosmic grain microphysics using the methods of modern computational chemistry, specifically by conducting a large program of molecular dynamics simulations of individual dust grains in which every atom is accounted for. This has enabled updated calculations of fundamental grain quantities and processes such as binding energies, grain collision outcomes, and gas-phase accretion rates. Some of these results significantly change our understanding of grain microphysics, and I will discuss their implications for the properties and evolution of dust grain populations in the ISM. I will also look ahead to how we can use these updated first-principles calculations to more realistically model interstellar dust throughout the universe and across cosmic time.

Relativistic jets launched from gas-accreting black holes (BHs) power a wide range of high-energy phenomena, including active galactic nuclei (AGNs), yet their formation mechanism remains elusive, largely owing to the lack of direct observation of the immediate vicinity of the jet-launching region, namely the BH magnetosphere. In this talk, I will present our recent study of the dynamical evolution of a BH magnetosphere and its observational signatures using fully kinetic particle-in-cell simulations. We show that pair creation drives the system into a quasi-steady state characterized by intermittent "spark gaps" in the polar region and an equatorial reconnection layer, which together sustain the global poloidal current. These two acceleration sites produce distinct non-thermal particle populations, and our post-processed ray-tracing calculations show that they generate substantial high-energy emission. The results suggest that both regions contribute to the high-energy emission of AGNs such as M87*, with inverse-Compton photons from the spark gap extending into the very-high-energy regime. We also find temporal correlations between the currents in the two regions, indicating a physical connection that may be relevant to the several detections of AGNs' multi-wavelength flares.

ASIAA has many members—including faculty, postdocs, and students—so it can be difficult to know everyone (especially for newcomers) and to understand who is working on what. By having a flash talk session, we hope to quickly promote mutual understanding and give everyone a chance to introduce their recent work. The talk format will be 3 minutes + 2 minutes for questions, focusing on speaker's “big win” from the past year (personal or professional). We plan to hold flash talk sessions regularly and look forward to your participation.

Cosmic rays (CR) feedback could be one of the crucial physical processes that shapes the evolution of galaxies. Yet the detailed mechanism of CR feedback remains poorly understood because of the lack of understanding of CR transport. One of the critical observational constrain is using L_IR - L_γ relation from nearby galaxies to constrain κ. However, this is often done in a simplistic manner in the literature where L_IR is converted into SFR by a simple linear relation, which could bias our interpretation. In this work, we analyzed a suite of cosmological zoom-in single-bin cosmic ray magnetohydrodynamics (CR-MHD) simulations with FIRE-2 feedback recipe to understand how would the non-trivial conversion between SFR and L_IR could impact our interpretation to the proper value of the cosmic ray diffusion coefficient (κ). We found that at the high luminosity end, heating from the old stellar population could increases L_IR by up to a factor of 2 at a given SFR comparing to the Kennicutt convention; while at the low luminosity end, a more leaky star-dust geometry, along with a low dust to gas ratio, could reduce L_IR by a factor of 10. We conclude that the non-linear relation between SFR and L_IR should be taken into consideration when trying to constrain κ using γ ray, and the significant deviation of L_γ at low L_IR when using our default κ = 3 × 10²⁹ cm² s⁻¹ hints the requirement of higher effective diffusion coefficient or higher magnetic field strength in the dwarf regime.

Parity symmetry is a fundamental principle in physics, making its violation a key indicator of new physics beyond the standard model. Recent studies have reported 3–7σ indications of parity-violating signatures in the large-scale distribution of galaxies, sparking growing interest in testing parity symmetry in the early Universe. While most existing searches rely on scalar observables, I will show how non-scalar observables in the large-scale structure (LSS) of the Universe offer a complementary, potentially more direct way to test primordial parity symmetry. In this talk, I will introduce parity-sensitive probes based on galaxy spins and galaxy shapes, discuss their observational prospects, and conclude with future opportunities from ongoing/upcoming galaxy surveys.

In the context of neutron-star asteroseismology, seismic oscillations and gravitational waves are classified into several oscillation modes according to their physical origins, such as the p-, g-, and r-modes. In particle and nuclear physics, on the other hand, relativistic fermions exhibit nontrivial transport phenomena arising from chirality. One of the typical examples is the chiral magnetic effect, in which an electric current is generated by an external magnetic field. In this talk, I will discuss collective excitations driven by chiral transport in the core of a neutron star. These excitations give rise to a new type of seismic oscillations, and the associated gravitational waves provide an observational probe of the magnetic field strength and the possible presence of quark matter in neutron stars. This talk is based on our work, https://arxiv.org/abs/2203.16133.

FU Orionis–type objects are protostars that are undergoing luminosity outbursts by several orders of magnitudes. Because the outburst events may significantly affect the mass accretion history of protostars, understanding their origin is essential. Several mechanisms have been proposed to explain FU Orionis–type outbursts, yet identifying the mechanism operating in individual systems remains observationally challenging. In this talk, I will present synthetic line observations of distinct numerical burst models based on the radiative transfer calculations. These simulations demonstrate that gas kinematics in protoplanetary disks can provide new diagnostics of the underlying burst mechanisms. As the first application of this approach, I will also present preliminary results from an analysis of ALMA molecular line data of V883 Ori.

The ALMA Central Molecular Zone Exploration Survey (ACES) is a Large Program designed to image the Central Molecular Zone(CMZ) in the Galactic center (GC). It provides homogeneous, large-scale mosaics that enable direct comparisons of physical and chemical properties across diverse GC environments. In this presentation, I will highlight the data release of spectral lines obtained from ACES's broadband spectral windows at 0.1~pc resolution. These lines reveal spatial and chemical variations that reflect the CMZ’s complex physical processes. With its high resolution and multi-line coverage, the ACES dataset is a unique resource for studying the CMZ's physical conditions, star formation, and internal structure, as well as its connection to the Circumnuclear Disk. It also enables cross-comparisons with other high-resolution ALMA datasets, offering new insights into the GC environment.

Modern cosmological data allow us to enter the era of precision cosmology. However, interpreting these measurements increasingly requires careful control of observational systematic effects. One promising approach is combining large-scale structure, particularly galaxy redshift surveys and weak lensing. In this talk, I will present the results from my PhD exploring how the overlap between galaxy surveys and weak lensing can be used to test and improve cosmological analyses. First, I will introduce the “shear ratio test”, which compares the lensing signal from background sources around the same lens. Second, I will then show how I validated the choice of “scale cuts” for a 3x2-point analysis, combining galaxy clustering, galaxy–galaxy lensing, and cosmic shear, to minimise the impact of physical effects that cannot be reliably modelled on small scales. Together, these tests provide complementary ways to assess the robustness of weak-lensing cosmological analyses.

Most stars, and therefore many planetary systems, are born in clusters inside dense molecular clumps, but how these clumps turn into clusters is still not clear. I will present a Nobeyama 45 m and JCMT survey of dense clumps and embedded clusters in nearby Milky Way star-forming regions, and show how their gas and stellar components evolve from gas-dominated clumps to gas-poor clusters. Many actively cluster-forming clumps are massive (∼10^3 Mo), very dense (∼10^5 cm^-3), and already show “infall + rotation” signatures in their position–velocity diagrams, very similar to low-mass protostellar envelopes but scaled up by three orders of magnitude in mass. A simple oblate clump model with global infall and rotation reproduces these PV structures and implies high clump-scale infall rates, suggesting global gravitational contraction in the early cluster-forming phase. I will then discuss how environment modifies this picture, including feedback from nearby H II regions, strong magnetic fields and external pressure in “gas-rich but quiet” regions, and recent star-by-star simulations that start from observed clouds. Finally, I will briefly connect these results to implications for planet formation, arguing that cluster formation sets the density, UV field, and encounter history that protoplanetary disks must experience.

ASIAA has many members—including faculty, postdocs, and students—so it can be difficult to know everyone (especially for newcomers) and to understand who is working on what. By having a flash talk session, we hope to quickly promote mutual understanding and give everyone a chance to introduce their recent work. The talk format will be 3 minutes + 2 minutes for questions, focusing on speaker's “big win” from the past year (personal or professional). We plan to hold flash talk sessions regularly and look forward to your participation.

The Nancy Grace Roman Space Telescope, NASA’s next flagship astrophysics observatory, is scheduled to launch in fall 2026 and begin its five-year primary mission. One of Roman’s central science goals is to use weak gravitational lensing to constrain cosmology. In this talk, I will trace the path from photons to weak lensing cosmological constraints, highlighting key challenges in image processing, photometric measurement, photometric-redshift estimation, and theoretical modeling. I will also introduce the infrastructure team responsible for producing cosmology-ready data products for Roman’s High-Latitude Imaging Survey and describe the expected properties and release timeline of these products. I will conclude by discussing early science opportunities enabled by Roman and synergies with the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.