Lunch Talk and Tech Lunch Talk

Understanding how distant galaxies enriched their ISM with metals and dust is key to understanding early galaxy evolution. In this talk, I will discuss early metal and dust enrichment in the context of the REBELS-IFU program, which combines JWST and ALMA observations of 12 massive galaxies at z ~ 7. Using JWST/NIRSpec spectroscopy, I will show that these galaxies appear more metal-enriched than the typical galaxy population at this early epoch. I will then combine the metallicity measurements with ALMA observations of cold dust and gas to investigate the pathways of dust build-up in the early Universe.

In this talk, I will explore two unresolved mysteries of our Solar System and how my research at Cambridge aims to solve them. The first concerns Venus, which may have once exhibited an Earth-like climate with a temperate atmosphere and bodies of liquid water. However, a runaway greenhouse process and cataclysmic resurfacing have rendered Venus a hostile planet and obscured direct evidence of its past conditions. I will discuss how Venusian rocks were ejected during asteroid impacts and subsequently transported to the Moon's surface. I will also comment on forthcoming Moon missions and their prospects for recovering these samples to reveal Venus' ancient climate. The second mystery involves 'Oumuamua, the first confirmed interstellar object, which made a brief passage through our Solar System in 2017. Its non-gravitational acceleration and lack of coma oppose conventional classification, leaving its origin and composition uncertain. Theoretical models struggle to reconcile its properties with known processes of planetesimal and small-body formation. I will present my contributions to recent hypotheses on ‘Oumuamua’s formation and evolution, including the potential role of impact craters and X-ray observations to probe the physical characteristics of 'Oumuamua analogues.

Recent $2-4\sigma$ deviations from the Cosmological Constant $\Lambda$ suggest that dark energy may be dynamical, based on baryon acoustic oscillations and full-shape galaxy clustering analyses. This calls for even tighter dark energy constraints to narrow down its true nature. In this talk, I will show that the full-shape power spectrum of the intrinsic shape alignments of galaxies can tighten dark energy constraints obtained from the full-shape galaxy clustering. We perform Fisher forecasts on various extensions of dynamical dark energy models, including scenarios with curvature, massive neutrinos, and modified gravity. Our results show that the full-shape intrinsic alignment information improves the dark energy Figure-of-Merit by $42-57\%$, promoting the intrinsic alignment of galaxy shapes as a valuable cosmological probe complementary to galaxy clustering.

Prestellar cores set the initial conditions for star formation, yet heavy molecules like CO are heavily depleted in these cold, dense environments, limiting our ability to probe core centers. In contrast, deuterated molecular ions, particularly ortho-H₂D⁺, emerge as key tracers owing to enhanced deuterium fractionation at low temperatures. We present the first interferometric map of ortho-H₂D⁺ depletion in the prestellar core G205.46M3 based on high-sensitivity ALMA 820 µm continuum and molecular line observations. Our data reveal two distinct substructures, B1 and B2, separated by ~1200 au, with a significant ortho-H₂D⁺ depletion zone of ~600 au in diameter toward B1. Chemo-dynamical modeling reproduces the observed deuteration profiles and indicates a core age comparable to the free-fall time, implying that the substructures likely formed via turbulent-dominated fragmentation. Furthermore, the enhanced N₂D⁺/N₂H⁺ ratio, peaking at ~1.4, suggests that further deuteration converts H₂D⁺ into D₂H⁺ and D₃⁺, underscoring the advanced chemical evolution of G205.46M3. Our results demonstrate the critical role of deuterated ions in probing both the chemical evolution and dynamical state of dense cores.

Since March 2019, a large international collaboration (known as “Transients and Pulsars with MeerKAT”, or “TRAPUM”) has been using the 64-antenna MeerKAT radio telescope array in South Africa to search for pulsars in globular clusters. These surveys have been exceptionally successful, with the discovery of 105 new pulsars in globular clusters, which represent one third of the current pulsar population in globular clusters. Among these discoveries is a set of 14 new pulsars in the globular cluster NGC 1851, where only one pulsar was previously known (NGC 1851A). One of the newly discovered pulsars (NGC 1851E) is quite extraordinary: it is in an usually eccentric orbit with a very unusual companion. The latter has a mass that is intermediate between the most massive neutron stars known and the lightest known black holes. From considerations on stellar evolution, we can conclude that this system formed in a binary exchange, which is only likely to happen in the dense environment of a globular cluster. Similarly massive objects have been discovered in merging binaries with the LIGO and Virgo interferometers; but were until now undetected in our Galaxy. The discovery of a millisecond pulsar orbiting one of these objects implies that we will be able to study its properties in some detail in the near future by measuring relativistic effects in the orbit of the millisecond pulsar. In particular, by 2028 we will know the masses of the individual components with a precision of 0.02 solar masses. A particularly exciting possibility is that this massive companion is a black hole that formed in the merger of two neutron stars, in which case it will be spinning very fast. This will cause an observable relativistic precession of the orbital plane, an effect known as Lense-Thirring precession. Measuring this effect, which might be possible using the SKA, we will be able to gain some insight into the origin of the companion and possibly test the cosmic censorship hypothesis of general relativity.

Turbulence in protoplanetary disks play critical roles in the planet formation process. Previous observational studies have placed constraints on the strength of turbulence in disks around pre-main sequence stars; they generally found moderate or weak turbulence (alpha < 10^-3 or less than a few percent of isothermal sound speed) with a few exceptional sources exhibiting strong turbulence (alpha >10^-2 or more than 20% of sound speed). These weak turbulence levels are consistent with the prevailing planet formation scenario. In contrast, there have been no measurements of turbulence in embedded disks around protostars, which is a critical missing piece in understanding whether planet formation can occur in such young disks. In this talk, I will present the first direct measurement of turbulence in the embedded disk around HL Tau using archival ALMA line data. Our analysis based on a parametric model-fitting approach reveals strong turbulence of ~50% of sound speed at outer radii of r>100 au. The HL Tau disk is known to host multiple rings at inner radii of r<100 au and turbulence in these rings is estimated to be less than a few percent of sound speed. Our new measurements highlight a striking contrast in turbulence strength across the disk. I will discuss possible origins of the observed strong turbulence, including the potential contribution of infalling envelope in driving turbulence.

Star formation through the dynamical magnetized collapse remains an active area of astrophysical research. We carry out a comprehensive exploration on the magnetized gravitational collapse of a non-rotating self-gravitating initially spherically symmetric prestellar cloud core using two-dimensional nonideal magnetohydrodynamic simulations incorporating ambipolar diffusion and Ohmic dissipation. Our study encompasses a broader range of equations of state (EOSs) in the form of P(ρ)∝ρ^Γ, with the aim of constraining the choice of EOSs for allowing star formation. Our results reveal that the collapse with a Γ no stiffer than 4/3, complemented by magnetized virial theorem, allows the dynamical contraction of the prestellar core to happen continuously where a central point mass forms and steadily builds up its mass from the infalling envelope, with a mass accretion rate of a scale of the order of c_s^3/G. The choice of an isothermal EOS most naturally facilitates the collapse as a magnetic analog of the inside-out collapse. In addition to that, our study exhibits that the nonisothermal magnetized collapse models with a Γ no stiffer than 4/3 qualitatively demonstrate similar infall features to those of an isothermal EOS. Furthermore, the collapse models with a Γ stiffer than 4/3 fail to ensure the sufficient cooling to allow the direct mass growth of the central point mass, thus delaying the infall. Our work can offer deeper insights in understanding the significance of EOSs on the magnetized gravitational collapse, enabling star formation.

The Subaru Prime Focus Spectrograph (PFS) is a massively multiplexed spectroscopic survey designed to address key questions in cosmology. The PFS cosmology program will observe approximately 4 million emission-line galaxies (ELGs) over 1,200 deg², targeting redshifts from 0.8 to 2.4. Uniquely, PFS will probe ELGs in the redshift range 2.0 < z < 2.4, extending beyond the reach of ongoing surveys like DESI and offering critical complementarity. With these data, PFS will deliver high-precision measurements of baryon acoustic oscillations (BAO) and the Alcock-Paczyński (AP) effect, enabling robust constraints on the Hubble expansion history and potential redshift evolution of dark energy out to z = 2.4. Combined with low-redshift BAO data, PFS is expected to constrain the dark energy density to ~7% per redshift bin. In parallel, redshift-space distortion (RSD) measurements will allow us to reconstruct the growth rate of cosmic structure, $f\sigma_8(z)$, with ~6% accuracy, leading to a precise constraint on the sum of neutrino masses with an expected uncertainty of $\sigma(\sum m_\nu) = 0.02$ eV. In this talk, I will provide an overview of the PFS cosmology survey design, highlight its key science goals, and present the current status of the program as we move toward survey operations.

Supernova 1987A (SN 1987A) is a unique object for understanding the early evolution of a core-collapse supernova remnant thanks to its proximity and youth. Recent ALMA and JWST observations of the inner ejecta of SN 1987A, revealing a ring-like carbon monoxide gas and a broken dipole iron distributions, respectively, provided potential clues to unveil not-yet-elucidated explosion mechanisms of core-collapse supernovae. We have conducted long-term 3D hydrodynamical simulations and estimated relevant observables based on the 3D models to link the progenitor and explosion properties with those at early supernova remnant phases; the results suggested, e.g., the progenitor formation through a binary merger, an asymmetric bipolar-like explosion with a natal kick of the (undetected) neutron star, and a non-thermal emission from the neutron star. Motivated by the molecular gas distributions revealed by ALMA, the aspherical explosion's impact on the molecular formation in the ejecta was also investigated. This talk highlights several breakthrough SN 1987A observations and our ongoing attempts with open issues.

The early solar system contained a short-lived radionuclide, 26Al (its half-life time t1／2 = 0.7 Myr). The decay energy 26Al is thought to have controlled thermal evolution of planetesimals and, possibly, the water contents of planets. Mmany hypotheses have been proposed for the origin of 26Al in the solar system. One of the possible hypotheses is the ‘disk injection scenario’; when the protoplanetary disk of the solar system had already formed, a nearby (< 1 pc) supernova (SN) injected radioactive material directly into the disk. Such a 26Al injection hypothesis has been tested so far with limited setups for disk structure and SN distance. Moreover, a nearby SN could disrupt a disk, but disruption and injection conditions have been considered separately. Here we revisit this problem to investigate whether there are self-consistent conditions under which the surviving disk radius can receive enough 26Al which can account for the abundance in the early solar system. We also consider a range of disk mass and structure, 26Al yields from SN, and large dust mass fraction ηd. We find that 26Al yields of SN are required as ≳ 2.1 × 10−3M⊙(ηd/0.2)−1, which is difficult to reproduce given the possible range of ejected 26Al mass and large dust mass fractions from the supernovae. Furthermore, we find that even if the above conditions are met, the SN shock changes the disk temperature, which may not be consistent with the solar-system record. Our results place a strong constraint on the disk injection scenario. Rather, we suggest that the fresh 26Al of the early solar system must have been synthesized/injected in other ways.

We investigate the occurrence of accretion bursts, dust accumulation, and the prospects for planetesimal formation in a gravitationally unstable magnetized protoplanetary disk with globally suppressed but episodically triggered magnetorotational instability (MRI), particularly in young intermediate-mass stars (YIMSs) but with a brief comparison to low-mass counterparts. We use numerical magnetohydrodynamics simulations in the thin-disk limit (FEOSAD code) to model the formation and long-term evolution of a gravitationally unstable magnetized protoplanetary disk, including dust dynamics and growth, since the collapse of a massive slowly-rotating prestellar cloud core. Massive gas concentrations and dust rings form within the inner disk region owing to the radially varying efficiency of mass transport by gravitational instability (GI). These rings are initially susceptible to streaming instability (SI). However, gradual warming of the dust rings, thanks to high opacity and GI-induced influx of matter increases the gas temperature above a threshold for the MRI to develop via thermal ionization of alkaline metals. The ensuing MRI bursts destroy the dust rings, making planetesimal formation via SI problematic. In the later evolution phase, when the burst activity starts to diminish, SI becomes inefficient because of growing dust drift velocity and more extended inner dead zone, both acting to reduce the dust concentration below the threshold for SI to develop. Low-mass objects appear to be less affected by these adverse effects. Our results suggest that disks around young intermediate-mass stars may be challenging environments for planetesimal formation via SI. This may explain the dearth of planets around stars with M∗>3.0 M⊙.

This talk explores how unmanaged stress impacts researchers' performance and well-being. Using the Window of Tolerance model, participants will learn to recognize personal stress signs and will be introduced to evidence-based strategies, such as breathwork, to regulate their nervous systems, and to practice self-care and self-compassion amid the demands of academic research.

To build comprehensive models of planet formation, it is essential to observe younger exoplanets, which are still embedded in their native gas-rich disks, and actively accrete material through their circumplanetary disks (CPDs). Being embedded, they are difficult to observe and characterize because of lack of good tracers. Among the disks with features suggestive of embedded protoplanets, AB Aurigae system appears promising due to the existence of inner spirals, the asymmetric dust ring and the accreting features seen in HCO+, the tentative shock emission in SO in the dust cavity, and the infalling outer spirals from the envelope to the disk. In this talk, I will present the results of recent search for CPDs in AB Aur using the ALMA and SPHERE/VLT data and discuss alternative tracers of the CPDs.

I will present ALMA observations of the H13CO+, C17O, and CO line emission from the protostellar system HH 212 at ∼24 au spatial resolution and compare them with those of the HCO+, SiO, and SO lines reported in the literature. We find that the CO emission traces four distinct regions: (1) an outer outflow shell, (2) a rotating wind region between the SiO and CO shells, (3) a shocked, wide-angle inner X-wind inside the SiO shell, and (4) the jet. The origin of the outer CO outflow shell could be associated with entrained envelope material or an extended disk wind. The rotating wind, which is shocked, is launched from a radius of 9–15 au, slightly beyond that of the previously detected SO shell, which marks the boundary where the wide-angle X-wind interacts with and shocks the disk wind. Additionally, SO is found to be mixed with CO emission within the thick and extended rotating wind region. The large-scale shocked CO wind coexists with SO emission near the upper portion of the inner shocked region, converging above the inner SiO knots. The CO jet is traced by a chain of knots with roughly equal spacing, exhibiting quasiperiodicity, as reported for other jets in the literature. Meanwhile, the H13CO+ and C17O lines trace the emission from the rotating envelope surrounding the outflow.

The cosmic dawn began roughly 200–400 million years after the Big Bang, marking the end of the cosmic dark ages with the emergence of the first stars (Population III stars) and galaxies. The formation of these primordial galaxies was governed not only by the underlying dark matter structure but also by complex baryonic processes. Chemical enrichment, radiative feedback, and mechanical energy input from the first stars and their supernovae played critical roles in regulating early star formation and shaping the stellar populations of the first galaxies. In this talk, I will present results from our high-resolution radiation-hydrodynamical simulations, exploring how Population III supernova remnants (SNRs) impact the assembly and evolution of the first galaxies.

I will present the current status of the fast radio burst (FRB) search conducted by the Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) project. BURSTT is a dedicated survey targeting nearby FRBs, characterized by its exceptionally wide field of view and continuous 24/7 operation. The first phase, BURSTT-256 (comprising 256 antennas) is now fully operational, with a real-time FRB search running around the clock. Daily detections of giant pulses from the Crab pulsar demonstrate the system’s performance, and localization tests with multiple outrigger stations are currently underway. I will also highlight a few side projects, including studies of Crab giant pulses and solar radio bursts, where BURSTT is proving to be a valuable facility for broader scientific investigations.

In this talk, I will present my research on the dynamical structure of young stellar objects in the early stages of star and planet formation, through the combination of physically motivated modeling and ALMA observations, using radiative transfer and synthetic observation simulations. The advent of ALMA has enabled us to directly observe protostellar disks in the earliest phases of star formation with sufficient resolution. These disks are also crucial as the initial conditions and environment for planet formation. However, even at millimeter and submillimeter wavelengths, protostellar disks are highly optically thick, making it challenging to probe their internal structures observationally. Theoretically, they are predicted to be in a complex physical state involving strong coupling between magnetic fields, turbulence, and dust dynamics, and there is still no consensus regarding their internal structure and evolution. To address this, we have constructed physically motivated models based on ALMA data, incorporating radiative transfer and synthetic observations. Our results support the presence of layered accretion at approximately two scale heights above the disk midplane, as proposed in non-ideal MHD simulations, rather than accretion driven by simple α-viscosity. Regarding dust evolution, the findings suggest that significant grain growth occurs in the radial direction, while vertical dust settling remains inefficient. These results place strong constraints on theoretical models of protostellar disks. In the latter half of the talk, I will introduce additional works that apply this same approach to the evolution of protostars themselves, with particular focus on binary and multiple systems, which represent the primary mode of star formation.

Understanding when, how, and why the first generation of stars and galaxies formed is crucial for revealing the early chapters of cosmic history. To pursue this goal, the JWST was developed. Although definitive evidence for pristine Population III stars (composed purely of hydrogen and helium) has not yet been found, the first three years of JWST observations have brought us significantly closer to this milestone. High-ionization He II, a key spectral signature expected from Pop III stars, has already been detected in early galaxies, including distinct pockets of emission in GN-z11 at z = 10.6. The most direct route has also been taken to discover extremely metal-poor objects, reaching down to ~0.4% solar in LAP-1 at z = 6.63. Additional chemical clues, such as the carbon enhancement observed in GS-z12 at z = 12.5, may also point to enrichment from earlier first stars. Thanks to gravitational lensing, we have studied early galaxies at unprecedented resolution, including structures as small as ~1 parsec in the Cosmic Gems Arc at z ∼ 10, and even an individual star system, Earendel, z∼6. With incoming Cycle 3 and future Cycle 4 JWST programs, our understanding of these primordial objects will continue to deepen, and new discoveries are almost certainly on the horizon.

Based on arXiv: 2409.13022 and arXiv: 2504.15340 (both published 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 & DR2 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.

Understanding the origin and evolution of the universe is one of the most challenging but interesting subjects in theoretical physics. In this talk, I will outline the significance of gravitational waves, particularly those at ultra-high frequencies, as powerful probes of the primordial universe.

This talk is based on my recent work (arXiv:2507.11156). Turbulence in protoplanetary disks plays a key role in dust evolution and planetesimal formation. One possible source of turbulence is the vertical shear instability (VSI), which can develop when gas cools quickly. Interestingly, dust particles not only respond to VSI-driven turbulence but also affect the cooling and potentially regulate turbulence itself. In this talk, I present results from global two-dimensional simulations including gas and dust to investigate this interaction. We find that VSI mixing, dust settling, and the local dust cooling reach an equilibrium, forming a thick dust layer. This balance strongly depends on dust size and dust-to-gas mass ratio. Larger grains or lower mass ratios weaken the turbulence, leading to dust settling. Our results suggest that the efficiency of dust growth can depend on the VSI in protoplanetary disks. I will also discuss possible implications for disk observations and further planet formation.

The active galactic nucleus (AGN) is an accreting supermassive black hole (SMBH) located at the center of a galaxy. AGNs not only trace the growth of SMBHs via mass accretion but also impact their host galaxies through outflows. One of the primary driving mechanisms of these outflows is the radiation pressure on the dusty gas surrounding the AGN, and its strength depends on the amount of dust grains. While the dust content can be estimated from dust extinction, it has been difficult to measure large dust extinctions for large samples, which is especially important to know the radiation pressure effect. For this reason, the effect of radiation pressure has been investigated using gas column densities. However, recent studies have raised concerns about the validity of this approach. In this study, we develop a new method to measure large dust extinctions in large samples, enabling a more accurate evaluation of the radiation pressure acting on AGN gas structures.

Galaxy clusters are massive bound systems. Their virialized core extending to ~ 1-2 Mpc, accretes matter from the outer region that extends for ~ 5-10 Mpc. We use the radial velocity profile of galaxies drawn from IllustrisTNG clusters with M200>10^14 Msun and 0.01<=z<=1.04 to explore cluster growth. We locate distinct dynamical regions and estimate mass accretion rate (MAR). The MAR is correlated with cluster mass and redshift. The typical MAR ~ 10^4-10^5 Msun/yr. Dense spectroscopy of real clusters' infall region will soon be a platform for applying and testing these model results.

In recent years, observations of core-collapse supernovae have implied the possible presence of a dense circumstellar medium in the vicinity of the progenitor star. While this can be a clue to understand the mass-loss activity of massive stars in their final moments, it remains unspecified what the origin would be. One of the critical hints would be the asphericity of the circumstellar medium, as demonstrated by the detection of the polarization in the nearby supernova event SN 2023ixf. This makes us consider the scenario where the mass loss activity was executed in an aspherical way. In this talk, I will review the current understanding of how we interpret observational signatures of supernovae in the early phase, together with the inference of a circumstellar medium, and introduce my preliminary results about the examination of stellar rotation as a formation scenario of an aspherical circumstellar medium.

Planets with sizes between Earth and Neptune are the most common class of exoplanets. Due to the bulk density degeneracy, their internal structures remain an open question. Both theoretical predictions and observations suggest that a population of sub-Neptunes can be explained by either gas dwarfs with a thick hydrogen envelope or with a water-rich interior. Notably, several close-in sub-Neptunes lie within the habitable zones of M-dwarf stars. Their larger spectral features, compared to those of Earth-like atmospheres, allow atmospheric characterization with current instruments. Yet understanding their true nature is essential to assessing their habitability. In this talk, I will follow the intriguing journey of an archetypal habitable-zone sub-Neptune, K2-18 b, exploring how we can assess its habitability. I will discuss recent JWST reports of potential biosignature detections. Finally, I will present our ongoing efforts to better understand K2-18 b and other habitable-zone sub-Neptunes.

High-mass stars play a critical role in the physical and chemical evolution of their immediate surroundings, by their strong stellar wind, ultraviolet emission, and supernova explosion. Although significant progress has been made in understanding the formation of low-mass stars, the physical mechanisms behind the formation of high-mass stars is still under debate. As the molecular clouds consist of partially ionized gas and dust, the magnetic field has been found to be ubiquitous in the interstellar medium, and therefore, expected to affect the formation of low-mass as well as high-mass stars. However, the contribution of magnetic fields in the formation of high-mass stars is poorly understood. Recently, because of its very high angular resolution, ALMA has opened an opportunity to investigate the magnetic fields in the molecular clouds with minute details. We report the magnetic field geometry towards the high-mass star-forming region G333.46-0.16, which is obtained by ALMA at high-angular-resolution (~0.3") 1.2 millimeter observations. This is one of the sources observed in the survey of Magnetic fields in Massive star-forming Regions (MagMaR), that contains 30 targets in total. This region shows the formation of a binary system. The magnetic field lines threading this area are found to be deformed, acquiring an "hourglass" morphology on the plane-of-sky. We investigated the interplay among turbulence, gravity, and magnetic field in the formation of stars at the envelope scale, and to find out the dominant agent between them. In this talk I will present the results obtained from our study.

Galaxy spins are shaped by multiple physical processes operating across cosmic time. In the early universe, galaxies acquire angular momentum through tidal torques from the surrounding large-scale structures. At later times, the non-linear growth of the universe produces vorticity fields, while galaxy interactions along the cosmic web drive spin reorientations. In this talk, I present findings from the IllustrisTNG cosmological simulations on three major aspects of galaxy spin evolution. First, I examine the spin-orbit alignment in galaxy pairs, showing how galaxy-galaxy interactions lead to changes in spin directions. Second, I discuss the intrinsic spin alignment with the cosmic web, focusing on the peculiar behavior of inner stellar spins compared to dark matter halos. Third, I address the role of initial conditions by quantifying the primordial misalignment between the inertia and tidal tensors, revealing its connection to present-day galaxy properties.

The cosmic infrared background (CIB) encodes dust emission from all galaxies and carries key information on star formation and chemical enrichment. Yet its basic properties are still poorly constrained due to projection effects. We address this by cross-correlating 11 far-infrared intensity maps from Planck, Herschel, and IRAS with SDSS galaxies and quasars tomographically. This yields a 60σ detection of the evolving CIB spectrum over 0

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