Activity > Colloquium

# Colloquiums and Seminars(2019)

ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend. Seminars on more specialized topics are also held on a regular basis.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

Contact: Colloquium Committee (talksasiaa.sinica.edu.tw)

No. Time/Place Speaker Topic / Abstract
12019-12-26 Thu
14:20~15:20
R1203
Hao-Yi Wu
[Ohio State University]
Seminar
Probing Cosmic Acceleration with Galaxy Clusters
Abstract

The acceleration of the Universe is one of the biggest puzzles in physics: is it due to a cosmological constant, dynamical dark energy, or modification of gravity? Galaxy clusters provide a unique opportunity to answer this question. In this talk, I will first discuss how we use cluster abundances to constrain cosmic acceleration, and how weak gravitational lensing effects play a key role in cluster surveys. I will then present my research on using simulations to understand cluster weak lensing signals and to accurately model covariance matrices. These results not only mitigate the systematic errors in current cluster surveys but also help the optimization of future ground- and space-based missions.

22019-12-20 Fri
14:20~15:20
R1203
Hui Li
[LANL]
Seminar
All Hands on Deck: What observations, theory, simulation and laboratory experiments are teaching us about the powerful AGN jets
Abstract

Powerful jets from active galactic nuclei (AGNs) are observed on scales from Mpc down to astronomical units , from essentially all observable wavebands and via multi-messengers. These enigmatic sources could hold the key to several long-standing mysteries such as ultra-high energy cosmic rays and more recently the origin of high-energy ~ PeV neutrinos. Understanding such sources has strongly influenced the development of (general) relativistic magnetohydrodynamics (MHD) and kinetic plasma astrophysics, including even laboratory experiments. We present observational and theoretical/numerical modeling results that link the large-scale global morphologies with small-scale particle energization processes. We discuss how the behavior of magnetic fields can shift the framework within which we interpret the AGN jets/lobes. These include their lobe polarization properties, lobe energy composition, Fermi flares and their corresponding optical polarization properties, as well as the efficient particle acceleration by the dissipation of jet magnetic fields, studied via comprehensive multi-dimensional plasma kinetic simulations. Future prospects of progress in simulations, experiments and observations will be discussed as well.

32019-12-19 Thu
14:20~15:20
R1203
[University of the Basque Country]
Seminar
Magnified Gravitational Waves at high-z: Revising 80% of LIGO/Virgo Black Holes
Abstract

Most of the binary black holes reported by LIGO/Virgo are centered on a chirp mass of 30M_o, with a narrow dispersion of primary to secondary black hole masses. This is far from expectations, but is readily accounted for by gravitational lensing. We demonstrate this by simply lensing the known mass distribution of Galactic black holes by the known population of lensing galaxies. We show that stellar black holes in our Galaxy cented on 8M_sun can be detected at high redshift when magnified and dominate over unlensed events by a ratio of 4:1, and the redshifted waveforms are stretched by 1+z ~3 thereby providing the high chirp mass peak observed. We claim most BBH detections to date originate at 1 < z < 3, with chirp masses typically 3 times smaller than published and repeated lensed events may also be present in the data. This is good news for LIGO/Virgo as lensing allows the evolution of binary black holes to be compared over most of cosmic history.

42019-12-18 Wed
14:20~15:20
R1203
Hui Li
[Los Alamos National Lab]
Colloquium
Dust-Gas Interactions in Protoplanetary Disks: Lessons Learned and New Puzzles
Abstract

In the recent years, high spatial resolution observations of protoplanetary disks by ALMA have revealed many details that are providing interesting constraints on the disk physics as well as dust dynamics, both of which are essential for understanding planet formation. We carry out high-resolution, 2D and 3D hydrodynamic simulations of global disks, including the effects of dust feedback. We find that a variety of instabilities can occur in PPDs which lead to both the quasi-axisymmetric rings and non-asymmetric dust traps. In particular, we find that quasi-axisymmetric dust rings can be subject to several instabilities due to dust-gas interactions and this could provide several observational signatures that can be tested. These effects are providing additional understanding of dust dynamics in PPDs. We also produce synthetic dust emission images using our simulation results and discuss the comparison between simulations and observations.

52019-12-12 Thu
14:20~15:20
R1203
Ignacio Ferreras
[IAC Spain]
Colloquium
A New Look at the Green Valley and Other Musings
Abstract

This seminar features a medley of recent results focused on two different aspects of galaxy formation and evolution, explored by two of my PhD students at UCL. The core of the talk focuses on a new definition of the green valley that circumvents potential systematics from dust attenuation. This new definition is straightforward to implement and produces substantial constraints on the subgrid physics of hydrodynamical models. The observational constraints obtained from the analysis of SDSS spectra of green valley galaxies will be contrasted with state of the art hydrodynamical simulations such as EAGLE or Illustris TNG. The second part of my talk will focus on the analysis of the effective dust attenuation law in galaxies at cosmic noon, where a remarkable correlation is found between the attenuation parameters that encode valuable information about the properties of dust in galaxies. Variations in dust attenuation impose a serious caveat on most analyses that rely on dust attenuation corrections in galaxies. The results are contrasted with detailed numerical simulations as well as with a simple phenomenological prescription motivated by the birth cloud model.

62019-12-05 Thu
14:20~15:20
R1203
Francesco Lovascio
[Queen Mary University of London]
Seminar
Vortices and planet formation: studying the stability of vortices in a dusty gas
Abstract

Forming planets is difficult, there are hurdles at every step of the way. Vortices may be able to help overcome some of the challenges by trapping dust in their cores, stopping the dust drifting away and increasing dust concentration for faster embryo growth. It is not clear however that dusty core vortices are stable long enough for significant dust growth to take place in their cores. To tackle this problem we use the terminal velocity approximation to model dusty gases in local simulations of vortices. The terminal velocity approximation is an approach to modelling tightly coupled dust and gas, which can be implemented very efficiently in a hydrodynamics solver, making it perfect for the simulation of dusty vortices. We find dusty vortices to be stable for long periods of time which could have important implications for planet formation.

72019-12-04 Wed
14:20~15:20
R1203
Nami Sakai
[RIKEN]
Colloquium
Astrochemical Approach to Star and Planet Formation
Abstract

Star and planet formation is one of the most fundamental structure-formation processes in the Universe. Physical processes of star and planet formation have widely been investigated as one of the major targets of astronomy and astrophysics by observations in the entire wavelength region during the last few decades. Although a rough outline of these processes has been presented, there still remain many unknowns and missing links. One of them is when the disk structure is formed around a protostar, and how it is evolved into a protoplanetary disk and eventually to a planetary system. At the same time, understanding the evolution of matter from interstellar clouds to stars and planets is also a goal of astronomy. So far, about 200 interstellar molecules have been identified mainly by radio-astronomical observations, and about 1/3 of them are "complex" molecules having 6 atoms or more. This indicates the high chemical complexity of interstellar clouds even in the extreme condition of low temperature (10-100 K) and low density (102-107 cm-3), which would ultimately be related to an origin of rich substances in the Solar System. Thus, approaches both from physical and chemical view points are indispensable to bridge star/planet formation studies and planetary science of the Solar System. In this talk, I am going to present importance of chemistry in astronomical studies by introducing some observational results.

82019-11-27 Wed
14:20~15:20
R1203
Toshio Matsumoto
[JAXA]
Colloquium
Origin of the optical and near-ifrared extragalactic background light
Abstract

In the optical and near-infrared background light, the excess brightness and fluctuation over the known backgrounds have been reported. To delineate its origin, fluctuation analysis of the deepest optical images was performed, and a flat fluctuation down to 0.2 arcsec was detected. The detected fluctuation is much larger than that expected for the galaxies. The sky brightness obtained from the detected fluctuation is a few times brighter than the integrated light of the galaxies. These findings require a new object. As its candidate, faint compact objects (FCOs) whose surface number density rapidly increases towards the faint end are found. FCOs are very compact and show peculiar spectra with infrared excess. If FCOs are cause of the excess brightness and fluctuation, the surface number density reaches 2.6 x10^3 arcsec^−2. g-ray observations require that the redshift of FCOs is less than 0.1 and FCOs consist of missing baryons. Very low M/L indicates FCOs are powered by the gravitational energy associated with black holes.

92019-11-21 Thu
14:20~15:20
R1203
Takahiro Nishimichi
[YITP, Kyoto University]
Seminar
Consistency relations in the large scale structure of the universe
Abstract

There are some consistency relations between multi-point correlation functions of the cosmological fluctuations known to be valid exactly or asymptotically exactly under any nonlinear effects at the non-perturbative level. These are derived based only on Gaussian initial condition and equivalence principle, and/or, the approximate universality in the equation of motion, making them a powerful avenue for the test of fundamental assumptions in cosmology. I explain how these relations can be used to provide robust theoretical predictions and to break the degeneracy between the level of cosmological perturbations and the unknown bias factor of luminous tracers.

102019-11-20 Wed
14:20~15:20
R1203
Pavel Kroupa
[Helmholtz-Instituts für Strahlen- und Kernphysik]
Colloquium
The systematically varying stellar IMF and some implications thereof
Abstract

Some ultra-compact dwarf galaxies have large dynamical mass to light (M/L) ratios and also appear to contain an overabundance of LMXB sources, and some Milky Way globular clusters have a low concentration and appear to have a deficit of low-mass stars. These observations can be explained if the stellar IMF becomes increasingly top-heavy with decreasing metallicity and increasing gas density of the forming object. The thus constrained stellar IMF then accounts for the observed trend of metallicity and M/L ratio found amongst M31 globular star clusters. Since the galaxy-wide IMF (gwIMF) is made up of the IMFs of all embedded cluster forming in a galaxy, it becomes possible to calculate the gwIMF. This calculation shows that the systematically varying IMF accounts for the overall shift of the observationally deduced gwIMF from top-light to top-heavy with increasing star formation rate amongst galaxies. This is an important self-consistency check between star formation on pc scales and galaxy-wide stellar populations. The implications of this for observations of extremely young very massive star-burst clusters observed at a high redshift which may appear quasar-like will be discussed based on our recent work (Jerabkova et al. 2017).

112019-11-19 Tue
14:20~15:20
CCMS R104
Pavel Kroupa
[Helmholtz-Instituts für Strahlen- und Kernphysik]
ASIAA/NTU Joint Colloquium
Detecting dark matter
Abstract

Neither the standard model of particle physics nor direct detection experiments have yielded any need nor any evidence for the existence of cold or warm dark matter particles. These are only hypothesised to exist if general relativity is extrapolated from the Solar-system scale to galaxies and beyond. Cases in point are the observed non-Keplerian, flat rotation curves of disk galaxies which are the by far dominant population of galaxies and the missing mass phenomenon in galaxy clusters. I will discuss the possibility of confirming the existence of such dark matter particles using Chandrasekhar dynamical friction. Explicit test cases are the satellite galaxies of the Milky Way, the M81 group of galaxies and Hickson compact groups. The observed positions and motion of the galaxies in these systems show that the action of dynamical friction on the speculative dark matter halos is not evident in the data. The systems behave dynamically as if the extended dark matter halos do not exist. Thus, the orbits of the Milky Way satellite galaxies do not seem to be decaying sufficiently with time, nor are the compact galaxy groups merging. Corroborative evidence comes from the highly symmetric distribution of all non-satellite galaxies in two 1.5Mpc extended, 50kpc-thick planes in the Local Group around the axis joining the Milky-Way and Andromeda galaxies. This symmetric arrangement of matter on Mpc scales remains entirely unexplained by current cosmological and dynamical theory, and is largely ignored by the community, despite being based on the very best extragalactic data at hand (because the involved galaxies are the nearest galaxies to the Milky Way). Further corroborative evidence comes from the five nearest major galaxies having three highly pronounced disk-of-satellite systems, which together falsify the standard dark-matter-based cosmological model with more than five sigma confidence. The evidence thus gathered consistently and unanimously shows that dark matter particles cannot be present. The observed dynamics therefore cannot be Newtonian, but must, in the classical limit, essentially be Milgromian, and cosmological theory needs a major repositioning. As a consequence, our ability to deduce the physics of galaxy evolution from observation is probably wrong as it is at present based on assuming the standard cosmological model is valid.

122019-11-19 Tue
15:30~16:30
R1203
Stephane Guilloteau
[LAB, CNRS & Univ.Bordeaux, France]
Seminar
The Mass and Ages of Young Stars
Abstract

Understanding when and how planet forms requires an appropriate clock to time the events. Age not being a direct observable, our best current clock is based on a comparison of star properties with theoretical evolutionary models. However, to provide reliable ages, these models must be validated against measurements of the star's properties, namely Luminosity, Color (effective temperature or spectral type) and Mass. I will present the result of a long term study which allowed us to determine the absolute masses of about 40 young stars in the Taurus region. The comparison between these masses and those predicted by evolutionary tracks on an HR diagram rules out many models, leaving only the most recent magnetic models as compatible with the data. Such models result in predicted ages that are typically 3 times larger than currently believed, which has significant impact on our understanding of star and planet formation.

132019-11-18 Mon
14:20~15:20
R1203
Toshifumi Futamase
[Kyoto Sangyo University]
Seminar
Cosmology with the Domain-dependent Expansion Rate as a Possible Solution to the Hubble Constant Problem
Abstract

There appears to be a discrepancy in the measured values of the Hubble constant in different scales. In fact, the Hubble constant inferred from the Planck satellite mission differs from that obtained by the magnitude-redshift relation of Type Ia supernovae by more than 3 sigma. In this talk, we show that the discrepancy can be resolved by introducing a local expansion rate generated by the domain-dependent averaged density within the framework of general relativity. It is shown that the locally averaged density which differs from the globally averaged density generates locally averaged Hubble constant, as well as the locally averaged spatial curvature irrespective of the global background curvature and the existence of the cosmological constant.

142019-11-13 Wed
14:20~15:20
R1203
Lung-Yih Chiang
[ASIAA]
Colloquium
CMB acoustic peak statistics and the excessive shift in the Planck data
Abstract

Measurement of the acoustic peaks of the cosmic microwave background (CMB) temperature anisotropies has been instrumental in deciding the geometry and content of the universe. Acoustic peak positions vary in different parts of the sky due to statistical fluctuation. I will present the statistics of the peak positions of small patches from ESA Planck data. I found the one containing the mysterious "Cold Spot", an area near the Eridanus constellation where the temperature is significantly lower than Gaussian theory predicts, displays large synchronous shift of peak positions towards smaller multipole numbers with significance lower than one in 10000. For the combined anomalies of large synchronous shifts in acoustic peaks and lower than usual temperature at the Cold Spot area, we propose there is some extra localized unknown energy to stretch out the space in the transverse direction around the Cold Spot area. And in the follow-up investigation, we calculated the total shifts of acoustic peak positions and construct a full-sky peak-shift map, from which we found strong global dipole signal compared with simulations. We discuss the possible origin of the dipole and some other features on the map.

152019-11-12 Tue
14:20~15:20
R1203
Roland Diehl
[MPE]
Seminar
Gamma-ray line spectroscopy of cosmic nuclei: Supernova explosions and ejecta flows
Abstract

Gamma ray lines from cosmic sources display the action of nuclear reactions in cosmic sites. The gamma rays at such characteristic energies result from nuclear transitions following radioactive decays or high-energy collisions with excitation of nuclei. The gamma-ray line and its associated special continuum from the annihilation of positrons at 511 keV falls into the same energy window, although of different origin. We review the status of cosmic gamma ray spectrometry, reminding of the corresponding instruments and missions and future perspectives. We then present a discussion of recent results and the challenges and open issues for the future. This includes, specifically, the diffuse radioactive afterglow of massive-star nucleosynthesis in 26Al and 60Fe gamma rays, which is now being exploited towards the cycle of matter driven by massive stars and their supernovae, and towards understanding the current Galaxy and structure and morphology of its interstellar medium. Also the complex processes making stars explode as either thermonuclear or core-collapse supernovae are subject to studies through gamma-ray lines, in this case from shortlived radioactivities from 56Ni and 44Ti decays. Herein the non-sphericities that have recently been recognised as important are reflected, probably most-directly, through gamma-ray line characteristics. We will also discuss how we should relate to the above the distribution of positron annihilation gamma ray emission with its puzzling bulge-dominated intensity distribution, which is measured through spatially-resolved spectra. These indicate that annihilation conditions may differ in different parts of our Galaxy, and helps to reveal the complex paths recycling matter from nucleosynthesis sources to next-generation stars.

162019-10-30 Wed
14:20~15:20
R1203
Eduard Vorobyov
[University of Vienna]
Colloquium
Formation of giant planets via disk gravitational fragmentation
Abstract

Giant planets play an important role in sculpturing planetary systems. They are found at a wide range of orbital distances from a fraction of au to hundreds of au, making it difficult to explain their origin in the framework of the core accretion paradigm. I will show that giant planets at orbital distances of tens of au (such as in HR 8799, PDS 70) can form through gravitational fragmentation of the outer regions of young protostellar disks followed by inward migration and tidal stripping of the fragments. An interesting by-product of this mechanism are accretion bursts, which can manifest itself as FU Orionis-type luminosity outbursts. Dust settling in the fragment interiors and likely formation of solid protoplanetary cores will also be discussed.

172019-10-29 Tue
14:20~15:20
R1203
Richard D'Souza
[University of Michigan]
Seminar
Unravelling the Andromeda Galaxy's most massive merger
Abstract

The Andromeda Galaxy (M31), our nearest large galactic neighbour, offers a unique opportunity to test how mergers affect galaxy properties. M31's stellar halo caused by the tidal disruption of satellite galaxies is the best tracer of the galaxy's accretion history. Despite a decade of effort in mapping out M31's large stellar halo, we are unable to convert M31's stellar halo into a merger history. Here we use cosmological models of galaxy formation to show that M31's massive and metal-rich stellar halo containing intermediate age stars implies that it merged with a large (M* ~ 2.5 x 10^10 M_sun) galaxy ~2 Gyr ago. The simulated properties of the merger debris help to interpret a broader set of observations of M31's stellar halo and satellites than previously considered: its compact and metal-rich satellite M32 is the tidally-stripped core of the disrupted galaxy, M31's rotating and flattened inner stellar halo contains most of the merger debris, and the giant stellar stream is likely to have been thrown out during the merger. This accreted galaxy was the third largest member of the Local Group. This merger may explain the global burst of star formation ~2 Gyr ago in the disk of M31 in which ~1/5 of its stars were formed. Moreover, M31's disk and bulge were already in place before its most important merger, suggesting that mergers of this magnitude do not dramatically affect galaxy structure.

182019-10-18 Fri
14:20~15:20
LeCosPA building 7S1
Kazunori Kohri
[KEK]
Seminar
Axion-Like Particles and Recent Observations of the Cosmic Infrared Background Radiation and the GeV-TeV Gamma-rays
Abstract

The CIBER collaboration released their first observational data of the Cosmic IR background (CIB) radiation, which has significant excesses at around the wavelength ∼ 1 μm compared to theoretically-inferred values. The amount of the CIB radiation has a significant influence on the opaqueness of the Universe for TeV gamma-rays emitted from distant sources such as AGNs. With the value of CIB radiation reported by the CIBER experiment, through the reaction of such TeV gamma-rays with the CIB photons, the TeV gamma-rays should be significantly absorbed during propagation, which would lead to energy spectra in disagreement with current observations of TeV gamma ray sources. In this talk, I discuss a possible resolution of this tension between the TeV gamma-ray observations and the CIB data in terms of axion [or Axion-Like Particles (ALPs)] that can increase the transparency of the Universe by the anomaly-induced photon-axion mixing. We find a region in the parameter space of the axion mass, m_a ∼ 7.E−10 eV -− 5.E−8 eV, and the axion-photon coupling constant, 1.2E−11 GeV^−1 < g_aγγ < 8.8E−10 GeV^−1 that solves this problem.

192019-10-17 Thu
14:20~15:20
R1203
Gilles Otten
[Laboratoire d'Astrophysique de Marseille]
Seminar
Direct imaging and characterization of extrasolar planets
Abstract

Direct imaging of exoplanets allows astronomers to directly measure the light from planets around other stars. This is in contrast to other very successful discovery methods such as transits and radial velocities, where the presence of planets is indirectly determined through the light of the star. The planet light that is captured in direct imaging allows us to characterize properties such as the molecular composition of the atmosphere, rotation speed of the surface and presence of winds around these planets. In this presentation I will talk about the different techniques (e.g., Adaptive Optics, coronagraphs and postprocessing techniques) that enabled the first direct detections and that continue to be improved to make it possible to discover fainter exoplanets closer to their stars with the eventual goal of detecting biomarkers. Lastly I will talk about my previous work on broadband coronagraphs using liquid crystal technology and my current work on vastly improving the characterization of the atmospheres of directly imaged exoplanets using a combination of a high contrast imager (SPHERE) with a high spectral resolution spectrograph (CRIRES+) through a coupling system (HiRISE) that is being developed at Laboratoire d'Astrophysique de Marseille.

202019-10-16 Wed
14:20~15:20
R1203
Che-Yu Chen
[University of Virginia]
Colloquium
From Molecular Clouds to Protostellar Systems: the Modern Picture of Star Formation
Abstract

Magnetic field, turbulence, and gas gravity are considered the key agents regulating the star forming process throughout different evolutionary stages. Despite rich observational results, it is still unclear how dynamically significant the magnetic fields are with respect to gravity and turbulence at varying physical scales, because neither the strength nor 3D structure of the magnetic field can be directly measured through observation. Our recent theoretical efforts and statistical examinations have provided new ways to characterize the 3D field structure and the relative importance of gas gravity and the magnetic field. We are also working toward a comprehensive understanding of the velocity structure within star-forming cores through both observations and simulations. Such investigation of the evolution of angular momentum during core collapse under the influence of the local magnetic field will be crucial for understanding the formation of protostellar disks, the birthplace of planets.

212019-10-09 Wed
14:20~15:20
R1203
Yueh-Ning Lee
[NTNU]
Colloquium
Protoplanetary disk assemblage and evolution revisited with effects of non-ideal magneto-hydrodynamics
Abstract

It is now commonly accepted that the formation and processing of the building blocks of our Solar System, i.e., rocky materials, water ice, and carbon complex compounds, might have occurred, earlier than what was thought before, during the initial collapse of the prestellar core and the formation of the protoplanetary disk. Very few existing works take into account the building phase of the protoplanetary disk when studying the formation and transport of refractory materials. Due to the complexity of this problem, a simplified hydrodynamic model has long been a convenient choice. We are now studying the self-consistent formation of the protoplanetary disks starting from the collapse that takes into account the environmental effects and large scale physics, including non-ideal magneto-hydrodynamic (MHD) effects that are relatively important at the disk scale, while not taken into account by many existing disk-formation models. With the help of numerical simulations that allow to follow the complex non-linear physics, we try to provide a working recipe for studies of the disk dynamics, thermal evolution of different gas and dust species, and their changes in chemical composition. In this talk I will address the properties of the disk formed in our numerical simulations, and compare the measured disk source function to the classical hydrodynamic model.

222019-10-02 Wed
14:20~15:20
R1203
Yipeng Jing
[Shanghai Jiao Tong University]
Colloquium
Next generation of galaxy redshift surveys: a few issues for clustering analysis
Abstract

I will briefly introduce the current and future galaxy redshift surveys, and discuss a couple of outstanding issues for the clustering analysis, the fiber collision effect and the bias of emission line galaxies (ELGs). I will present a new method for correcting the fiber collision effect, and our ongoing work to determine the bias for ELGs.

232019-10-01 Tue
14:20~15:20
CCMS R104
Yipeng Jing
[Shanghai Jiao Tong University]
ASIAA/NTU Joint Colloquium
Accurate unbiased measurement of the Milky Way's mass in cosmological context
Abstract

I will briefly review recent development of observational cosmology, and outline the importance of determining the mass of the Milky Way. Then I will present the current status of the Milky Way mass measurement and discuss the main uncertainties and shortcomings associated with previous methods. I will then present our new method in order to overcome most of the drawbacks. The 6D phase space distribution function of satellites is constructed from cosmological simulations based on the similarity implied by the NFW profile. Within the Bayesian statistical framework, we can not only infer the halo mass efficiently, but also handle various observational effects including the selection function, incomplete information (e.g., lack of proper motion), and measurement errors in a rigorous and straightforward manner. Through mock tests, we show that this method is accurate and unbiased, and superior to methods solely based on Jeans theorem. We also demonstrate the satellite galaxies are better tracers than stars in general. Applying our method to the recent GAIA observations has yielded the most accurate determination of the Milky Way mass. While the important application of our method is to measure the Milky Way halo mass, it can be extended to any other galaxies or clusters whose member satellites can be reliably identified.

242019-10-01 Tue
15:30~16:30
R1203
Hongsong Chou
[SETH Technologies/U. of Chicago]
Seminar
Empirical Findings on Global Market Microstructure, and the Science behind a “Close-To-Reality” Market Simulator
Abstract

Traditionally, market microstructure is a subject in finance. In recent years, with the availability of high-frequency trading and economic data, finance professionals have started to employ methodologies developed in physical sciences to conduct research in this area. I will review a few recent trends in market microstructure research using physics thinking from the point of view of a practitioner. In particular, I will discuss the needs for a “close-to-reality” market simulator, and how to build such a simulator with methodologies developed from related disciplines such as mathematics, physics and computer sciences.

252019-09-26 Thu
14:20~15:20
R1203
Thiem Hoang
[KASI]
Seminar
New physics of cosmic dust and surface astrochemistry
Abstract

Dust is ubiquitous in the Universe and plays an important role in modern astrophysics. Dust is the building blocks of stars and planets and is the home where water ice and complex organic molecules, including biogenic molecules-building blocks of life, are formed and released into the gas. Dust grains absorb starlight in optical and ultraviolet wavelengths and re-emit radiation at infrared wavelengths, which is a powerful tool for astronomers to study the Universe. The alignment of dust grains results in the polarization of starlight and infrared emission from themselves, which is a popular technique to map cosmic magnetic fields. In this talk, I will present new physics of interstellar dust and surface astrochemistry. First, I will introduce a new mechanism of dust destruction based on centrifugal stress within extremely fast rotating grains spun-up by radiative torques, which is termed Radiative Torque Disruption (RATD) mechanism. I will show that the rotational disruption of dust grains into numerous small fragments can successfully explain longstanding puzzles in dust astrophysics, from Type Ia Supernovae, Massive young star clusters, to interplanetary dust in our solar system. Second, I will introduce new surface chemistry in space by presenting two new mechanisms to desorb water ice and complex organic molecules (COMs) from the icy grain mantle in star-forming regions, including rotational desorption and ro-thermal desorption. Finally, I will discuss the implications of newly discovered effect of dust in the time-domain astronomy era using supernovae and gamma-ray bursts afterglows to probe environments of transients.

262019-09-25 Wed
14:20~15:20
R1203
Richard Ellis
[UCL]
Colloquium
The Remarkable Assembly History of Elliptical Galaxies
Abstract

Once considered the simplest morphological class with smooth surface brightness profiles and homogenous old stellar populations, elliptical galaxies continue to reveal surprises. I will present the results of several comprehensive spectroscopic campaigns of what are considered to be the precursors of present-day ellipticals seen at redshifts up to and beyond 2. Good signal to noise absorption line spectra are capable of probing the stellar kinematics and stellar populations in early examples providing valuable insight into the assembly history of passive galaxies. I will discuss several puzzles that have emerged from such data including how the compact precursors (or `red nuggets’) grew in physical size but hardly in stellar mass, and why early massive examples display rapidly rotating stellar disks in contrast with local examples.

272019-09-24 Tue
14:20~15:20
CCMS R104
Richard Ellis
[UCL]
ASIAA/NTU Joint Colloquium
Cosmic Dawn: The Observational Quest for the First Galaxies
Abstract

The birth of galaxies represents the last unexplored frontier of cosmic history and it is commonly believed such early systems led to the transformation of neutral gas in the intergalactic medium into its present fully-ionised state. Some progress has been made in charting the demographics of early galaxies into the era when reionisation is thought to occur, but little is known about the nature of their stellar populations, the possible role of active nuclei and whether galaxies are capable of generating sufficient ionising radiation. Spectroscopy holds the key to addressing these questions, targeting both individual sources at high redshift as well as carefully-chosen analogues at intermediate redshift. I will describe the recent progress and challenges as we anticipate the launch of the James Webb Space Telescope and the arrival of next-generation large telescopes.

282019-09-18 Wed
14:20~15:20
R1203
Peter Scicluna
[ASIAA]
Colloquium
Dusty mass-loss from evolved stars
Abstract

Evolved Stars play key roles, enriching galaxies with dust, gas that fuels star formation and the products of nucleosynthesis through their mass loss.For low- and intermediate-mass stars, a large part of this mass loss occurs on the Asymptotic Giant Branch through a dusty wind, while the more massive Red Supergiants undergo similar processes. In this talk, I will review some recent progress in understanding the mechanisms driving this mass loss and how it enriches the ISM. I will then present some results from the ongoing JCMT large program the Nearby Evolved Stars Survey, which is observing a statistical sample of evolved stars in the Solar Neighbourhood. NESS aims to determine the total mass return to the Solar Neighbourhood and obtain a statistical picture of the physics of mass loss. Finally, I will explore some important avenues for future work in this field.

292019-09-11 Wed
14:20~15:20
R1203
Haifeng Yang
[Tsinghua University]
Colloquium
Origins of (sub)millimeter disk polarization
Abstract

Polarized (sub)millimeter dust thermal emission has been established as an important tool to probe magnetic fields. Its application to the protoplanetary disk, however, hasn't been successful. The first resolved polarization map in a classical T Tauri system, HL Tau, yields a uniform magnetic fields, which is a rather unphysical configuration. We were then motivated to search for alternatives and find that the scattering of dust thermal emission by dust grains themselves can naturally produce the observed uniform pattern. I will first review how scattering-induced polarization works and why it has the potential to study the grain growth, as well as to probe dust settling, which is hard to do otherwise. I will then focus on the best studied system, the HL Tau system. This shows a transition from scattering to a complete different picture as we move from ALMA Band 7 (0.87 mm) to ALMA Band 3 (3 mm). The azimuthal pattern at Band 3 was initially proposed to come from a third mechanism, radiative alignment, which is different from either scattering or magnetic alignment. I will argue that this explanation fails to explain some of the important features and cannot be the whole story. At the end, I will discuss the growing tension between scattering-induced polarization and beta-index method in probing grain sizes.

302019-09-06 Fri
14:20~15:20
R1203
Tetsuya Hashimoto
[NTHU]
Seminar
Recent three discoveries from NTHU cosmology group
Abstract

I will present my recent papers on (i) a blue cluster in the local Universe, (ii) the luminosity-duration relation of fast radio bursts (FRBs), and (iii) ALMA observations of Gamma-Ray Burst (GRB) host galaxies. Brief summaries of each paper are as follows.
(i) A young galaxy cluster in the old Universe: We discovered a 'blue cluster', that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue cluster challenges the current standard understanding of galaxy formation under the Lambda CDM Universe.
(ii) Luminosity-duration relation of fast radio bursts: We discovered an empirical correlation between luminosity and duration of FRBs. We propose a new distance measure using the relation of FRBs, which can reach more distant Universe than type Ia supernovae in quantity. This method can potentially reveal the time variability of the dark energy, which is one of the central foci of observational cosmology.
(iii) SFRs of two GRB host galaxies at z~2 and a [CII] deficit observed with ALMA: We discovered a new parameter to characterize GRB host galaxies, [CII] deficit, by overcoming a serious dust-extinction problem of GRB host galaxies. Possible parameters controlling the deficit include the metallicity, initial mass function, and gas density.

312019-09-05 Thu
14:20~15:20
R1203
Yin Li
[Kavli IPMU / UC Berkeley]
Seminar
Model the Nonlinear Universe with Machine Learning
Abstract

Cosmological structure formation is a highly nonlinear process that forms the tiny fluctuations of the early universe into the cosmic web at the late time. Its accurate and efficient modeling is necessary to recover the physical information contained in the early-universe fluctuations from the late-time observables. The two conventional approaches are the numerical simulation and the perturbation theory, with the former being accurate but computationally costly, while the latter being fast but invalid below the nonlinear scale. Machine learning offers a promising third route, given its many huge successes at building nonlinear mappings. Trained with N-body simulations, our deep learning models can predict structure formation with a comparable accuracy, much higher than that of the perturbation theories, at only a moderate cost. I will also discuss other applications and ongoing works towards building a complete forward model of the observable Universe.

322019-09-04 Wed
14:20~15:20
R1203
Freeke van de Voort
[MPA]
Colloquium
Cosmic gas flows and their effect on galaxy formation
Abstract

Galaxies are intimately connected to the environments they live in. The haloes around them contain the gas reservoir from which the galaxies grow, while galactic outflows heat and enrich this circumgalactic medium (CGM). In this talk, I will use ALMA observations and cosmological, hydrodynamical simulations to show how the gas dynamics affects the growth of galaxies on all scales, from the interstellar medium (ISM) to the intergalactic medium. Our observations reveal that the star formation efficiency of early-type galaxies can be suppressed if their molecular gas disc is morphologically and kinematically disturbed. Our high-resolution simulations show that the CGM has higher overdensities than previously thought, which strongly affects predicted observables in the CGM. For example, the neutral hydrogen (HI) column density and H-alpha emission from ionised gas are dramatically enhanced, more in line with observations. I will end by showing how, at high redshift, sheets in the cosmic web can fragment and lead to high HI column density systems with no associated metals, explaining observations of metal-free Lyman Limit Systems.

332019-08-28 Wed
14:20~15:20
R1203
Gregory Herczeg
[KIAA]
Colloquium
The evolution of protostars and their planet-forming disks
Abstract

The history of star and planet formation in our local neighborhood is written in nearby clusters and ongoing bursts of newborn stars. In this talk, I will begin by discussing the ongoing revolution in planet-forming disks being driven by ALMA. High-resolution images and complete surveys reveal a diverse array of disk properties and morphologies, yet we are unable to place these disks in an evolutionary sequence because of large uncertainties in ages of pre-main sequence stars. I will then discuss the challenges in assigning accurate ages of young stars and prospects for improvements, driven especially by the Gaia mission.

342019-08-27 Tue
11:00~12:00
R1203
Hongsu Kim
[KASI]
Seminar
The Blandford- Znajek mechanism versus the Znajek process
Abstract

The Blandford- Znajek mechanism states that the bottom line environment for angular momentum & rotational kinetic energy extraction for the central engine of AGN is the presence of large scale strong poloidal magnetic field from ‘force-free plasma and the spinning supermassive black hole. The Znajek process, meanwhile states that the bottom line environment for angular momentum & rotational kinetic energy extraction for central engine of AGN is the presence of large scale strong poloidal ‘vacuum’ magnetic field. (i.e., NO ‘force-free plasma ) and the spinning, supermassive black hole. We clarify/reconcile the two conflicting claims in terms of various choices of ‘tetrad frames’ in Riemann-Cartan formalism for Einstein GR.

352019-08-27 Tue
14:20~15:20
R1203
Zeljko Ivezic
[University of Washington]
Colloquium
LSST: the greatest movie of all time is coming to you!
Abstract

The Large Synoptic Survey Telescope (LSST, www.lsst.org) will deliver the most comprehensive optical sky survey ever undertaken. Starting in 2022, LSST will take panoramic images of the entire visible sky twice each week for 10 years. The resulting hundred-petabyte imaging dataset for close to 40 billion objects will be used for scientific investigations ranging from the properties of potentially hazardous asteroids to characterizations of dark matter and dark energy. In this talk, I will start with a brief overview of the LSST science drivers, system design, and the status of its construction, and then touch on some Big Data research challenges that need to be tackled to make the best use of LSST data.

362019-08-22 Thu
14:20~15:20
R1203
Chien-Chang Feng
[Tokyo U.]
Seminar
Stellar Explosions of the Neutron Star and White Dwarf Collisions
Abstract

The merge of two neutron stars have been observed in both gravitaional wave source GW170817 electromagnetic observation, which is mainly powered by radioactivity of r-process elements(Smartt et al. 2017). In order to study the similar scenario of the merger of a neutron star and white dwarf, we simulate the direct collision of a neutron star and white dwarf and examine the explosion signature of this event. The simulations have shown this kind of impact will trigger deflagration burning of the white dwarf and expose whole star eventually. During the explosion small amount of radioactive 51Ni is synthesised and energy level is close to Type-Ia supernova explosion.

372019-08-14 Wed
14:20~15:20
R1203
Sherry Suyu
[Max Planck Institute for Astrophysics]
Colloquium
Cosmology with Gravitational Lens Time Delays
Abstract

Strong gravitational lenses with measured time delays between the multiple images can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tension in current H0 measurements. I will describe techniques for measuring H0 from lensing with a realistic account of systematic uncertainties. A program initiated to measure the Hubble constant to <3.5% in precision from strong lenses is in progress, and I will present the latest results and their implications. Search is underway to find new lenses in imaging surveys. An exciting discovery of the first strongly lensed supernova offered a rare opportunity to perform a true blind test of our modeling techniques. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.

382019-08-08 Thu
14:20~15:20
R1203
Ellis Owen
[UCL]
Seminar
Star forming galaxies at high redshift: the feedback impact of energetic cosmic rays
Abstract

High redshift star forming galaxies are complex multi-phase systems where hot interstellar gas, cold dense molecular clouds and energetic particles (i.e. cosmic rays) all coexist. These starburst galaxies are especially likely to be environments abundant in energetic cosmic rays due to the presence of massive stars and their remnants. Stellar remnants can supply seed particles and generate the shocks (via supernova explosions and other violent events) needed to accelerate the seeds to very high energies. This talk considers the interplay and interactions between the ambient partially ionized gases, dense clouds, and the energetic cosmic ray particles in these environments. I will present the energy deposition rates by cosmic rays as they propagate though their host galaxy and beyond, accounting for their high-energy hadronic interactions with interstellar matter and the influence of developing galactic magnetic fields. I will discuss the astrophysical implications on the host galaxy and its circum-galactic environment and outline possible mechanisms by which cosmic ray feedback may operate, with particular reference to the recently observed young high redshift system, MACS1149-JD1.

392019-08-07 Wed
14:20~15:20
R1203
[University of Portsmouth]
Colloquium
Forward Modelling the Universe: Application to cosmic shear
Abstract

Observational cosmology is going through a golden age. In particular, we are in the midst of an influx of data from on-going experiments, such as the Dark Energy Survey (DES). In the coming five years, the volume and quality of data will rapidly increase as Stage IV surveys, Euclid, LSST and WFIRST, come online. Processing this data will require new algorithms and methods to maximise our science reach and to control for systematic errors. In this talk, I will present a method that we have developed called Monte-Carlo-Control-Loops that relies heavily on forward modelling the observed data by simulating all the processes from cosmology theory to images. Given the complexities of the late-time Universe, these forward models need to capture the important properties of galaxy populations and key features imprinted on the data from the experiments themselves. By bringing together all these elements with advanced statistical methods and new machine learning algorithms, we can build a process for extracting maximal information from the new data, which will allow us to extensively test the physics of the dark sector.

402019-08-01 Thu
14:20~15:20
R1203
Janet Ting-Wan Chen
[MPE]
Seminar
ePESSTO+ (the advanced Public ESO Spectroscopic Survey of Transient Objects): survey and scientific output
Abstract

Gathering the ESO community working on supernovae and unusual transients into one coherent team, the Public ESO Spectroscopic Survey of Transient Objects (PESSTO) has revolutionised the exploitation of wide-field surveys, developing efficient synergies with multi-messenger experiments and making the NTT a crucial global facility. In this talk, I will present the advanced ePESSTO+ programme, building on the success of our PESSTO consortium and bridging the gap to the SOXS instrument. Some of our scientific goals include gravitational wave sources, transients that evolve on the timescale of a few days, and those with extreme energetics. I will also present the transients followed-up by the ePESSTO and GROND collaboration, which represent the extreme (e.g. the brightest or the fastest) of the luminosity-space of cosmic transients, providing a new dataset to understand their nature. Finally, I will share my experience on applying for Alexander von Humboldt and Marie Skłodowska-Curie Fellowships which might be especially helpful for junior researchers.

412019-07-31 Wed
14:20~15:20
R1203
Richard Nelson
[QMUL]
Colloquium
Planet migration in inviscid and laminar protoplanetary discs
Abstract

The discovery of more than 4000 confirmed exoplanets over the last 25 years has raised important questions about how planetary systems form and evolve. Planetary formation theories must take into account how the gravitational interaction between growing planets and the surrounding protoplanetary disk influences the orbital evolution of the planets. In recent years, there has been a significant change in our understanding of how protoplanetary disks evolve, and the traditional view of angular momentum transport occurring in disks because of turbulent viscosity has been replaced by one involving layered accretion due to magnetised winds. In this talk, I will discuss our current knowledge of exoplanet systems and how it motivates planet formation theories, and I will present recent work that explores how planetary migration changes when moving from traditional viscous/turbulent models to more modern laminar disc models.

422019-07-24 Wed
14:20~15:20
R1203
Cheng Li
[Tsinghua University, Beijing]
Colloquium
Mapping the stars, gas and dust in nearby galaxies
Abstract

The cosmic star formation rate density has been declining since z~2-3, suggesting that the cessation of star formation has been the dominating process in galaxy evolution since then. However, it is unclear how the star formation gets quenched inside the galaxies and what physical mechanisms have been driving this process. Current integral field unit (IFU) surveys such as CALIFA and MaNGA are providing resolved spectroscopy for large samples of galaxies in the local Universe, allowing the star formation histories across the whole galaxy area to be studied with high accuracy. In addition, maps of molecular gas are also being obtained by arrays of radio antenna, thus providing additional data for linking the star formation and gas accretion processes in the IFU era. I'll talk about our recent work based on the CALIFA, MaNGA and CARMA-EDGE surveys, particularly focusing on the roles of environmental effect and internal structure in driving galaxy evolution.

432019-07-19 Fri
14:20~15:20
R1203
[Clemson]
Seminar
Astronomy with Meteorites
Abstract

Meteorites are pieces of bodies that were ejected from asteroids, the Moon, or Mars and fell to Earth. Primitive meteorites (from small asteroids) contain objects older than the Solar System (presolar grains) and old Solar-System-formed objects (calcium-aluminum-rich inclusions or CAIs). I will review how CAIs contain evidence of once-live radioactivity in the early Solar System, which informs us about the circumstances of the Sun's birth, and how presolar grains tell us about minor nucleosynthesis processes and velocity mixing in core-collapse supernovae.

442019-07-17 Wed
14:20~15:20
R1203
Satoshi Ohashi
[RIKEN]
Colloquium
ALMA polarization observations toward protoplanetary disks
Abstract

Protoplanetary disks (PPDs) are beleived to be birth places of planets. Recent ALMA high resolution observations have shown prominent structures such as multiple rings and crscent. In order to understand the physical and chemical properties of PPDs, dust continuum and molecular line observations have been carried out with ALMA. Here, we introduce another observing mode, which is the polarization of dust continuum emission. The mechanisms of the polarization have been discussed with great attention since ALMA succeeded in detecting the polarized emission from the protoplanetary disk of HD 142527 (Kataoka et al. 2016). Taking into account the grain growth in PPDs to form planets, dust polarization is possibly produced by magnetic fields, radiation, gas flow, and scattering. Identifying the polarization mechanisms allow us to understand the physical conditions of PPDs such as dust grain size, dust scale height, or magnetic field structure. In this talk, I will show recent results of ALMA polarization observations. In particular, I focus on the two different morphology disks (a lopsided disk and multiple rings). For a lopsided disk, we found different polarization mechanisms of self-scattering and magnetic fields between north and south regions. These different polarizations can be understood by different grain size distributions (Ohashi et al. 2018). The magnetic fields are toroidal. For multiple rings, we found that the polarization is produced by self-scattering. The dust grains are 140 micrion in the gaps, while those are much larger (or smaller) in the rings. Furthermore, the dust scale height needs to be less than one-third of the gas scale height inside the 70 au ring, while it reaches two-thirds of the gas scale height outside of the 70 au ring. Then, we can constrain the gas turbulence to be $\alpha\lesssim1.5\times10^{-3}$ at the 50 au gap and $\alpha\sim 0.015-0.3$ at the 90 au gap, respectively. The transition of the turbulent strength at the boundary of the 70 au ring indicates the existence of the dead zone (Ohashi & Kataoka submitted to ApJ).

452019-07-10 Wed
14:20~15:20
R1203
Frank Eisenhauer
[MPE]
Colloquium
GRAVITY and VLTI - the harvest from the first two years (Galactic Center, AGN, and exoplanets), and a bright future ahead
Abstract

Optical/IR interferometry has entered a new era with GRAVITY and the VLTI. The last two years brought forward breakthrough discoveries in a wide range of astrophysics, including spectra of exo-planets, probing Einstein’s theory of general relativity and the black hole paradigm in the Galactic Center, and zooming in to supermassive black holes in the distant universe. GRAVITY outperforms earlier interferometers by factors 100-1000 in sensitivity and accuracy, now offering milli-arcsecond resolution imaging for objects as faint as 19 magnitude, and astrometry with ten micro-arcsecond accuracy. In our presentation we will introduce the technology behind GRAVITY, give an overview of the science results with focus on the Galactic Center, and sketch out the plans towards GRAVITY+ with new adaptive optics, laser guide stars and better throughput towards faint science, all sky milli arcsecond optical interferometric imaging.

462019-07-09 Tue
14:20~15:20
R1203
Chia-Yu Hu
[Center for Computational Astrophysics]
Seminar
Dust destruction by supernova shocks in hydrodynamical simulations
Abstract

Dust plays a central role in the physics of the interstellar medium (ISM) and the observational properties of galaxies. However, its evolution has been largely ignored in simulations of galaxy formation until very recently. I will give an overview of models that follow dust evolution in large-scale simulations and comment on their success and limitations. I will then present our recent effort on modeling the destruction of dust via supernova shocks in an ab initio fashion which does not rely on over-simplified sub-grid models. We follow the dust dynamics governed by direct collisions, plasma drag and betatron acceleration, which allows us to investigate both thermal and nonthermal sputtering of dust. We quantify the dust destruction efficiency per supernova as a function of grain size and ambient gas density. We apply this method to 3D hydrodynamical simulations of a multiphase ISM and quantify the destruction timescale of dust in the solar neighborhood which turns out to be around 0.4 Gyr, indicating the importance of grain growth in the ISM as well recognized in the literature.

472019-07-03 Wed
14:20~15:20
R1203
Yusuke Tsukamoto
[Kagoshima University]
Colloquium
Impact of non-ideal effects on circumstellar disk formation and their possible observational signatures
Abstract

In this talk, I will talk about recent progress of theoretical studies about circumstellar disk formation. In particular, I will focus on the impact of non-ideal MHD effect. Recent theoretical studies have shown that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for protostar and circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the first core and disk, which enables the formation of the circumstellar disk at the formation epoch of protostar. Ambipolar diffusion set an upper limit to the magnetic field strength of ~ 0.1 G in and around the newly born disk (Masson+16, Tsukamoto+17). Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum (Krasnopolsky+11, Tsukamoto+15b, Tsukamoto+17). This suggests that the bimodal evolution of the disk size may realize in the early disk evolutionary phase. Hall effect and ambipolar diffusion imprint the characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect makes a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100-1000 AU. Ambipolar diffusion causes the significant ion-neutral drift in the envelope. Our estimate show that the drift velocity of ion could become significant (~km/s ) in the Class 0/I YSOs.

482019-06-28 Fri
14:20~15:20
R1203
Denis Burgarella
[Aix-Marseille University]
Seminar
The dust emission of galaxies from the local universe to z ~ 10.
Abstract

Galaxies form stars and stars form dust. We found that the amount of dust attenuation is not constant over cosmic times but varies and presents a maximum at z ~ 1.5. This talk will focus on the related aspects of galaxies and dust: 1) can we measure the dust attenuation using stellar masses at all redshift? For this first part, we will present a novel approach that uses the evolution of the average dust attenuation in galaxies. 2) what is the amount of dust attenuation of galaxies at 4 < z < 10 and how can we model these galaxies and the physical mechanisms controlling the formation/destruction of dust grains in the early universe but also more locally, in low-metallicity galaxies. For this part, we have collected a sample of Lyman break galaxies at 4 < z < 10with ALMA detections and upper limits. Some of these galaxies are not detected and several explanations have been proposed (evolution of dust temperature, effect of molecular clouds). We will suggest another mechanism that has the advantage to also explain low-metallicity local dwarf galaxies. Finally, I will shortly present ongoing observational programmes performed with IRAM NIKA2 and NOEMA.

492019-06-26 Wed
14:20~15:20
R1203
Chao-Lin Kuo
[Stanford]
Colloquium
Search for Gravitational waves from Big Bang: Recent BICEP results and prospects
Abstract

Inflation is a compelling theory that describes the process of Big Bang. Many predictions of inflation theory have been confirmed by observations of cosmic microwave background (CMB) over the last decade. A most exciting, yet unobserved prediction of inflation is the production of a scale-invariant gravitational wave background, which would leave a distinct imprint of “B-mode” polarization in the CMB. I will describe the physics behind this prediction, our ongoing effort to search for this signal with the BICEP program at the South Pole, and the outlook for the next decade.

502019-06-24 Mon
14:20~15:20
R1203
Devendra Ojha
[TIFR]
Seminar
Evidence for cloud-cloud collision as a trigger of high-mass star formation in our Galaxy
Abstract

The formation processes of massive OB stars and young stellar clusters are still poorly understood. In recent years, the study of the triggered star formation through the cloud-cloud collision (CCC) process has become an interesting and important topic in the star formation research. It has been suggested that the CCC process can form massive OB stars and young stellar clusters at the junction of molecular clouds. The onset of the CCC process in a given star-forming region could be observationally inferred through the detection of a bridge feature connecting the two clouds in velocity space, the broad CO line wing in the intersection of the two clouds, and the complementary distribution of the two colliding clouds. However, the investigation of observational signatures of star formation (including massive stars) via the CCC mechanism is still rare and very challenging. A multi-wavelength approach has been effectively used as a promising observational tool for understanding the ongoing physical processes in Galactic star-forming regions. In this talk, new observational results of an analysis of some promising Galactic star-forming regions will be presented, where the star formation activities (including massive stars) appear to be influenced by the CCC mechanism at the junction of molecular clouds.

512019-06-13 Thu
14:20~15:20
R1203
Chien-Hao Lin
[Carnegie Mellon University]
Seminar
Weak Lensing Science in the New Era
Abstract

2020s will be exciting years for cosmology with the launch of cosmic surveys including LSST, Euclid and WFIRST. These upcoming weak lensing surveys are expected to provide high quality data that is both wider and deeper compared to current surveys and lower the statistical uncertainty of the probe. With such high statistical precision, it is crucial to improve the control of systematic biases and develop new algorithms to extract the most information from the scientific output of surveys. In this talk, I would like to present summaries of the upcoming weak lensing surveys and how they are going to help the weak lensing science. I will also cover the challenges in weak lensing and the current status of them.

522019-06-12 Wed
14:20~15:20
R1203
Abdurrouf
[ASIAA]
Colloquium
Study spatially resolved stellar population properties of galaxies with spatially resolved SED fitting
Abstract

Photometric observations of galaxies over the last decades have revealed many important clues in the understanding of galaxy evolution. Despite the current improvement in spatial resolution of the imaging surveys (by HST in particular), most of the photometric studies of galaxies have only been done by treating galaxy as a single point object. On the other hand, the advent of IFU surveys has revolutionized the way we study galaxies. Despite its powerful capabilities, wide area IFU surveys have only limited to local galaxies. In this presentation, I will introduce a spatially resolved SED fitting method that uses broad bands imaging to derive spatially resolved stellar population properties of galaxies. I will present results of our studies on the spatially resolved analysis of stellar mass buildup and quenching in massive disk galaxies from z~2 to present time. We studied the evolution of the radial profiles of SFR, stellar mass, and sSFR and construct an evolutionary empirical model. We also confirmed the existence of sub-galactic star formation main sequence which holds in local as well as high redshift. Our studies found that massive disk galaxies built their stellar masses and quenched their star formations in 'inside-out' manner. I will also talk about my efforts on upgrading the method using MCMC technique to get a better inference of stellar population parameters (Z, age, E(B-V), and SFH). Currently, we have applied our spatially resolved SED fitting method to imaging data from HST and GALEX+SDSS. Future photometric surveys (using JWST, WFIRST, LSST, and Euclid) will provide large dataset from which we can conduct spatially resolved SED fitting to a large number of galaxies across wide redshift range to study the evolution of their internal structures.

532019-06-06 Thu
14:20~15:20
R1203
Bo Reipurth
[University of Hawaii]
Seminar
The Dynamical Evolution of Newborn Triple Systems
Abstract

Observational evidence increasingly supports that most, if not all, stars are formed in small multiple systems, which through internal instabilities and external perturbations decay to produce the separation distribution function and multiplicity statistics of the field. I will summarize observations of newborn stars that document their enhanced multiplicity fraction and discuss them in terms of dynamical evolution during the earliest evolutionary stages based on extensive numerical simulations. Various poorly understood phenomena in early stellar evolution find an explanation as a result of the dynamical evolution of multiple systems, including Herbig-Haro jets and FU Orionis eruptions, as well as the formation of spectroscopic binaries and the widest binaries.

542019-06-03 Mon
14:20~15:20
R1203
Ue-Li Pen
[CITA]
Seminar
Probing cosmic initial conditions with galaxy spin vectors
Abstract

Disk galaxies exhibit prominent rotation axis. We present recent results to predict the spin vector of galaxies. Previously, the sign of the spin vector was thought random, with the direction correlated along the primordial tidal field. New numerical studies show how the initial inertia tensor can be predicted, enabling the use of the signed galaxy spin vector field to probe the early universe, including effects of neutrinos, and testing cosmic parity violation. We discuss observables and future prospects.

552019-05-30 Thu
14:20~15:20
R1203
Howard Yee
[University of Toronto]
Seminar
H-alpha Imaging Spectroscopy of Cluster Galaxies Using SITELLE
Abstract

SITELLE is an 11'x11' field-of-view imaging Fourier transform spectrograph (iFTS) on CFHT. I will briefly describe the history of iFTS and the capability of this new, unique, IFU-like instrument. We have started a program to use SITELLE to study the H-alpha emission in star-forming galaxies in a sample of z~0.25 galaxy clusters. I will describe the current data on two clusters, Abell 2390 and Abell 2465, and the pipeline we developed to generate complete samples of cluster emission-line galaxies (ELGs). I will present some initial results from the data, in particular, the alignment of the difference vectors between emission-line and continuum light with the cluster center, a signature of ram pressure in operation; and the strong emission region in the core of the Brightest Cluster Galaxy in Abell 2390. I will end with a discussion of the prospect of using SITELLE for large surveys of emission-line galaxies, such as the survey for Lyman-alpha galaxies at z ~ 3 to 6.

562019-05-29 Wed
14:20~15:20
R1203
Albert Zijlstra
[Jodrell Bank Centre for Astrophysics, University of Manchester]
Colloquium
Stars in retirement
Abstract

At the end of their evolution, low and intermediate mass stars eject much of their envelopes into space. The mass loss terminates the Asymptotic Giant Branch and forms a planetary nebula, while the star rapidly evolves towards the white dwarf stage. Planetary nebulae are important tracers of stellar populations and initial-final mass relations.The talk will discuss the mass loss process, the evolution of planetary nebulae, and the formation of hydrogen-poor central star.

572019-05-23 Thu
14:20~15:20
R1203
I-Da Chiang
[UCSD]
Seminar
Dust-to-Metals Relation in Nearby Galaxies
Abstract

Dust in the interstellar medium (ISM) participate in many important physical and chemical processes, e.g., dust is crucial to star formation by being a catalyst for formation of molecular hydrogen, and by shielding gas from the interstellar radiation field. Dust also plays an important role in the observed spectral energy distribution (SED) of galaxies: it absorbs and scatters around 30% of starlight, and re-emits at infrared (IR) wavelengths. In this talk, I will focus on our work in the life cycle of dust from the observational perspective. We observe the dust-to-metals ratio and other physical tracers in the ISM to infer dust life cycle. The dust-to-metals relation shows how much metal is locked in solid form and how the various dust forming/destruction mechanisms balance each other, especially dust growth in the ISM. This will provide keen insight into the dust life cycle. If I still have time, I will share our recent work about analyzing the empirical radiation heating law for dust grains, and its implications for high-z studies.

582019-05-22 Wed
14:20~15:20
R1203
Thavisha Dharmawardena
[ASIAA]
Colloquium
Tracing Historic Mass Loss from Evolved Stars with Thermal Emission from Cold Dust
Abstract

Evolved stars play a key role in the life cycle of dust in the universe. Through strong winds and supernovae, they inject the material reprocessed in their cores to the interstellar medium, replenishing the interstellar medium with heavy elements. As evolved stars are so numerous, they are extremely effective in this role. In this talk I will explore the role of historic mass loss. The typical treatment of evolved stars only accounts for present day mass loss or assumes they undergo constant mass loss throughout their lifetime. Historic mass loss can be effectively traced using thermal emission from the dust which cools down as it moves away from the central star. We exploit Herschel/PACS and JCMT/SCUBA-2 observations to study this historic mass loss. These two sets of observations are especially powerful, tracing the radial variation in the circumstellar envelopes of evolved stars. We establish the presence of variations in mass loss for a sample of Milky Way evolved stars by studying features observed in surface-brightness, temperature, dust mass-column density and spectral index of dust emissivity radial profiles. By comparing these results to predictions for a constant-outflow model I find significant deviations between the total dust masses determined for the two scenarios, demonstrating that the effect of mass loss variation cannot be ignored. We determine the complexities of the detached shell of U Ant with the aid of radiative transfer modelling, prompting the need for further study at higher angular resolution. The analysis of the sub-mm periodicity of IRC+10216 and o Ceti, two well-known evolved stars, shows that it may be possible to use sub-mm light curves of evolved stars to study the nature of dust formation/destruction in their inner envelope effectively. The optical and sub-mm light curves of IRC+10216 shows an offset in phase of ~ 3/4. Using model predictions and past reports I find that this is likely due to the relationship between the stellar pulse and the formation/destruction of dust. Moving on from the Milky Way to the Magellanic clouds I stack evolved stars identified in the mid-infrared but not detected in the far-IR from Herschel at 100micron allowing a statistical study of the existence or absence of a far-IR component. We successfully produce detections for the highest mass-loss rate sources, showcasing the merits of the stacking method. Here I emphasize the variations in structure and hence historic mass loss of evolved stars and by doing so highlight the importance of including these variations in studies which include dust production by evolved stars in the future.

592019-05-21 Tue
14:20~15:20
CCMS R104
Seiji Sugita
[U. of Tokyo]
ASIAA/NTU Joint Colloquium
The evolution of asteroid Ryugu and its parent body constrained by Hayabusa2 observations
Abstract

JAXA’s Hayabusa2 spacecraft arrived at asteroid 162173 Ryugu on June 27, 2018 and conducted global observa-tions (~2 m/pix) from 20 km of altitude first and subsequently conducted a number of high-resolution regional and local observations (down to ~1mm/pix) during low-altitude descents including touch-down operation for sampling on Feb. 22, 2019. In this study, we summarize optical imaging observation results obtained from these wide range of spatial resolutions, focusing on the constraints they provide on Ryugu’s parent body.

602019-05-16 Thu
14:20~15:20
R1203
Masaki Fujimoto
[JAXA]
Seminar
Hayabusa2 and JAXA's small body exploration program
612019-05-15 Wed
14:20~15:20
R1203
Di Li
[NAOC]
Colloquium
Present science/technical achievements of the Five hundred meter Aperture Spherical Telescope and future prospects
Abstract

TBA

622019-05-08 Wed
14:20~15:20
R1203
Bo Zhao
[MPE]
Colloquium
Protostellar Disk Formation & Fragmentation Enabled by Removal of Small Dust Grains
Abstract

It has been shown that a realistic level of magnetization of dense molecular cloud cores can suppress the formation of a rotationally supported disk (RSD) through catastrophic magnetic braking. We show that removing from the standard MRN distribution the large population of very small grains (VSGs: ~10 to few 100 angstrom) that dominate the coupling of the bulk neutral matter to the magnetic field increases the ambipolar diffusivity by ~1-2 orders of magnitude at densities below 10^10 cm^-3. The enhanced ambipolar diffusion in the envelope causes the infall speed of ions (and thus the magnetic field lines tied to them) to almost vanish in the 100-1000 AU scale "pseudo-disk", where the field lines are most severely pinched and most of protostellar envelope mass infall occurs. As a result, the bulk neutral envelope matter can collapse without dragging much magnetic flux into the disk forming region, which lowers the magnetic braking efficiency. We find that the initial disks enabled by VSGs removal tend to be Toomre-unstable, which leads to the formation of prominent spiral structures that function as centrifugal barriers. The piling-up of infall material near the centrifugal barrier often produces dense fragments of tens of Jupiter masses, especially in cores that are not too strongly magnetized. Some fragments accrete onto the central stellar object, producing bursts in mass accretion rate. Others are longer lived, although whether they can survive long term to produce multiple systems remains to be ascertained. Our results highlight the importance of dust grain evolution in determining the formation and properties of protostellar disks and potentially multiple systems.

632019-05-02 Thu
14:20~15:20
R1203
Sara Beck
[Tel Aviv]
Colloquium
Molecules, Dust and Ions in the Youngest Massive Clusters
Abstract

The deeply embedded star clusters of starburst galaxies are the most extreme form of star formation in the local Universe. With sizes of only a few parsec, they can hold thousands of OB stars younger than 5 Myr and stellar masses of 106M⊙. These clusters have star formation efficiency at least 10 times greater than typical Galactic sources, and can be powerful sources of local cloud heating and metal enrichment. We can now measure ions, molecules and dust in these clusters with subarcsecond resolution and 3kms−1 velocity resolution. In this talk we report ALMA , SMA , VLA and TEXES observations of massive clusters in nearby dwarf galaxies which show directly how cluster formation can be triggered by filament accretion, how clusters emerge from molecular clouds, and the details of feedback and enrichment processes.

642019-04-25 Thu
14:20~15:20
R1203
Etsuko Mieda
[NAOJ]
Seminar
High resolution? Wide science field? AO projects at TMT and Subaru
Abstract

As telescopes become larger, the improvement and development of adaptive optics (AO) techniques become crucial to fully utilize their large aperture size. In this talk, I will briefly review the basics of AO, and then focus on two AO projects, NAFIRAOS at TMT and ULTIMATE at Subaru, as two opposite extreme spectrum of AO techniques. They both use multiple laser beams, but one is optimized to achieve highest spatial resolution in a narrow field whereas the other is optimized to achieve the largest science field with a moderate resolution.

652019-04-24 Wed
14:20~15:20
R1203
Martin Bureau
[Oxford]
Colloquium
WISDOM: Probing Supermassive Black Holes and their Immediate Environments with ALMA
Abstract

I will present key results from the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM), a high resolution survey of molecular gas in galaxy nuclei. First, I will show that CO can be used to easily and accurately measure the mass of the supermassive black holes lurking at galaxy centres. I will discuss substantial ongoing efforts to do this, and present many spectacular new ALMA measurements, the latest of which rival the best black hole measurements to date. This opens the way to literally hundreds of measurements across the Hubble sequence (in both active and non-active galaxies) with a unique method. Second, I will briefly show how the same data allow to study the spatially-resolved properties of the giant molecular clouds in all the galaxies studied. This will yield cloud censuses in non-local galaxies (including early-type galaxies) for the first time, providing a new tool to understand and contrast the star formation efficiency across galaxies. Already, it appears that basic cloud properties are not universal and vary systematically along the Hubble sequence, contrary to long-held assumptions.

662019-04-23 Tue
11:00~12:00
R1203
Kevin Koay / Shoko Koyama / Masanori Nakamura
[ASIAA]
Seminar
Imaging Black Holes with the Event Horizon Telescope
Abstract

The first EHT imaging of the black hole shadow towards M87 is summarized in a series of six papers, which are published in ApJ letters. We present a brief overview of the observations, data processing, imaging, and interpretation of the observed emission. Our image of the shadow confines the 6.5 billion solar masses, consistent with the stellar dynamical mass, within its photon orbit, providing the strongest case for the existence of supermassive black holes. Future plans and development of EHT arrays are also discussed.

672019-04-16 Tue
14:20~15:20
R1203
[Indian Institute of Astrophysics]
Seminar
Building a large Optical-NIR Telescope in India
Abstract

At present the largest telescope in India is 3.6m Devasthal Optical Telescope (DOT). In the near future the TMT partnership will provide access to one of the world largest optical telescope to Indian astronomers. However, these two telescopes would not be enough to cater the need of growing Indian astronomical community. Access to 10-12m size optical-NIR telescope, equipped with state of the art back-end instruments can bridge the gap between the DOT and the TMT. Realising the need of a large optical-NIR telescope a serious effort toward building a telescope has been initiated by Indian Institute of Astrophysics. At present project is at very early stage and we have been working toward generating science cases, conceptualizing hardware, capacity building and fund raising exercise. In my presentation I will provide the current status of the project as well as plan for the near future.

682019-04-10 Wed
14:20~15:20
R1203
Alexei Pozanenko
[Institute of Space Research]
Colloquium
Observations of phenomena associated with Gamma-ray Bursts (afterglow, supernova, kilonova and follow-up of EM LIGO/Virgo)
Abstract

I will discuss optical observations of phenomena associated with Gamma-ray Bursts carrried out by IKI GRB follow-up team. I will describe facilities used for networked observations, results and future prospects. In particular I will discuss the observation of GRB 170817A associated with grawitational wave event of LIGO/Virgo GW 170817 and current follow-up search for electromagnetic counterparts of LIGO/Virgo.

692019-04-03 Wed
14:20~15:20
R1203
Yuji Matsumoto
[ASIAA]
Colloquium
The formation of close-in super-Earths through in-situ giant impacts
Abstract

Observations have found over 3000 exoplanets so far (exoplanets.org). These planets are located in close-in region of their central stars, typically within ~ 0.3 au. Most planets, especially members of multiple planet systems, are super-Earths whose main compositions are rock or ice (e.g., Batalha et al., 2013; Thompson et al. 2017). There are some scenarios of formation of close-in super-Earths systems (e.g., Raymond et al., 2014; Izidoro & Raymond 2018; Lambrechts et al. 2019). In all of these scenarios, most of the formed close-in super-Earths experience giant impacts. The planet growth via giant impacts at ~ 1 au around G dwarfs is intensively studied (e.g., Chambers & Wetherill 1998; Kokubo et al., 2006; Hansen 2009). It is expected that planet-planet scattering in close-in region becomes less effective than that at ~ 1au due to the strong central gravity. However, the dependences of the planet growth in the giant impact stage on the semimajor axis and central star mass are not well understood yet. We investigate the growth of close-in super-Earths in the giant impact stage by N-body simulations. In close-in region, planets collide soon after their orbits are crossed due to small scattering cross-section. The eccentricities and inclinations of planets are kept small, i.e., the evolution in close-in region is dynamically cold. The distributions of eccentricities and inclinations of close-in super-Earths are well reproduced when the initial inclinations are small.

702019-04-02 Tue
14:20~15:20
R1203
Xiaoying Pang
[Xi'an Jiaotong Liverpool University]
Seminar
The fundamental plane of open clusters in the Milky Way
Abstract

The fundamental plane (FP) is a scaling relation among effective radius, central velocity dispersion and average surface brightness of spherical dynamical systems, which is expected to be originated from the virial equilibrium of their members. Observations show that two kind of old and (relatively) isolated dynamical systems (age > 10 giga-year (Gyr)) both have FP: 1) elliptical galaxies (mass of ~10^12 solar masses), and 2) globular clusters (mass of 10^6 solar masses). Open clusters are the lower-mass counterparts of globular clusters, with masses are in the range of 100–104 solar masses. On the contrary to globular clusters, which are isolated in the remote halo of Milky Way without much perturbation, open clusters reside in the crowded plane of the Milky Way. They are subjected to strong tidal disturbance, such as disk shock, spiral arm passage, molecular cloud encounter, which increase the internal cluster energy, and consequently lead to their expansion and disruption. Many studies have suggested a typical survival timescale of 200 million-year (Myr) for open clusters and only 3% of the known open clusters have ages above 1 Gyr. Besides, the velocity dispersion of open clusters is at the order of 0.5-1 km/s, which requires spectroscopy of very high resolution. Therefore, their FP is not been studied or investigated in the past, due to the complexity of their dynamical evolution and the difficulty in obtaining precise velocity dispersion. We are motivated to extend the FP study to open clusters and quantify their dynamical status. We select a sample of old open clusters (aged older than 1 Gyr) from the Milky Way open cluster catalog, and make use of the data from the Apache Point Observatory Galactic Evolution Experiment-2 in the fourteenth data release of the Sloan Digital Sky Survey. For the first time, we establish a fundamental plane among cluster parameters, the line-of-sight velocity dispersion σ1D, Ks band luminosity LKs, and the half-light radius rh. The existence of this relation, which deviates significantly from the virial theorem prediction, implies that the dynamical structures of the old open clusters are quite similar, when survived from complex dynamical evolution to age older than 1 Gyr. Nbody simulation will be an approach to investigate the dynamical evolution of open clusters. In the end, most recent Nbody simulations of star clusters and discoveries of the nearby disrupted open clusters in the solar neighborhood will be mentioned briefly.

712019-03-27 Wed
14:20~15:20
R1203
Miho Ishigaki
[Tohoku]
Colloquium
Element production by supernovae across the cosmic time probed by metal-poor stars
Abstract

Supernova explosions have been a dominant contributor of metals in the Universe. Thanks to recent large spectroscopic surveys of metal-poor stars in our Milky Way Galaxy, unprecedentedly large data sets of elemental abundances in the atmosphere of metal-poor, and thus likely very old, stars are now available. Statistical properties of the measured elemental abundances have put useful constraints on nucleosynthetic yields of supernovae of different generations of stars. I would like to review what we can learn from comparison between observed elemental abundances in metal-poor stars and theoretical supernova yield models, including core-collapse supernovae of the very first generation of stars and Type Ia supernovae of various progenitor metalicities. Prospects for future large spectroscopic surveys in the outskirt of the Milky Way will also be discussed.

722019-03-21 Thu
14:20~15:20
R1203
Sara Ellison
[Univ. of Victoria]
Seminar
Galaxy mergers in the nearby Universe
Abstract

Astronomy's current model of galaxy evolution is built on a foundation of hierarchical growth, in which small galaxies merge together to form larger ones. In addition to the simple accrual of mass, this merging process is predicted to fundamentally change the galaxies’ properties, such as dramatic morphological transformations, the triggering of bursts of star formation and high rates of accretion onto the central supermassive black hole. In this talk I will explain the physical processes behind these predictions, and present the observations that we are performing in order to test the theory. Although many of the predictions are indeed borne out by experiment, there have been some surprising conflicts as well, that demand revisions to our models of how mergers shape galaxy evolution.

732019-03-20 Wed
14:20~15:20
R1203
Kathryn Volk
[University of Arizona]
Colloquium
Combining theory and observations of trans-Neptunian objects to pin down Neptune’s migration history
Abstract

The current orbital structure of the trans-Neptunian region holds the key to understanding how the giant planets migrated to their present-day orbits. In particular, the population of trans-Neptunian objects (TNOs) captured into orbital resonance with Neptune during migration are capable of recording properties of that migration. There are, however, challenges in observationally constraining the current distribution of resonant TNOs, determining which resonant TNOs were likely captured during migration, and in generalizing theoretical studies and numerical simulations of resonant capture during migration. I will discuss some of my recent and ongoing investigations into these challenges. I will discuss recent modeling of the transient resonant TNO populations and how this can inform the interpretation of observationally derived resonant TNO population models. I will also present the results of investigations into how Neptune’s migration characteristics affect the distributions of primordially captured TNOs in the 3:2 and 2:1 resonance; some of these results offer counterpoints to recent investigations in the literature, highlighting the difficulty of uniquely constraining Neptune’s migration based on numerical investigations. I will end by discussing current and future observational investigations that will help guide further theoretical work.

742019-03-18 Mon
14:20~15:20
R1203
Yi-Kuan Chiang
[JHU]
Seminar
How Dark is the Universe? Intensity Mapping in Broadband and Beyond
Abstract

Why is the night sky dark if the universe is filled with stars? As modern cosmology has linked this ancient observation to a profound implication that the age of the universe is finite, naturally the next question to ask is: How dark is the universe? To address this, we aim for measuring the extragalactic background light (EBL) budget as a function of redshift and frequency. I will discuss the state of the art in EBL constraints, focusing on the sky monopole intensities in wide-field broadband surveys across the electromagnetic spectrum. I then introduce a method to recover previously collapsed redshift information in these broadband intensity mapping datasets, and further show that one can even retrieve sub-bandpass frequency information to probe the spectrum of the universe. I will demonstrate this method by probing the continuum, Lyα, and Lyman break in the cosmic UV background up to z~2 using GALEX imaging. This allows us to perform spectral diagnostics for the entire body of the UV background and provide insights on cosmic star-formation, black hole accretion, and potential emission from the diffuse intergalactic medium. I will conclude with a discussion of prospects of intensity mapping in broadband, grism spectroscopy, time domain, and multi-messenger astronomy.

752019-03-15 Fri
14:20~15:20
R1203
Wentao Luo
[Kavli IPMU]
Seminar
Weak Gravitational Lensing and its Applications
Abstract

Based on the high quality imaging survey data, we can achieve unprecedented measurement of of weak lensing signal and further study the connection between dark matter halo and galaxies redising inside them. What's more, people also realize that weak lensing can achieve way more than only galaxy formation in LCDM frame work. For instance, there are constraints on Emergent Gravity, and cosmologies where dark matter and dark energy interacts with each other e.t.c. Here in this talk, I would like to present non-standard cosmology constraints other than LCDM from weak gravitational lensing.

762019-03-14 Thu
14:20~15:20
R1203
Annalisa Pillepich
[MPIA]
Colloquium
Universe(s) in a box
Abstract

I will describe the numerical efforts to simulate galaxies across an unprecedented range of masses, environments, evolutionary stages and cosmic times. In particular, I will focus on the IllustrisTNG project (www.tng-project.org), a series of three cosmological simulations encompassing volumes of 50, 100, and 300 Mpc a side, respectively. There gravity, magnetohydrodynamics and prescriptions for star formation, stellar evolution, the enrichment of gas with chemical elements beyond Helium, cooling and heating of the gas, galactic outflows and feedback from the supermassive black holes are all taken into account within the LCDM cosmology, i.e. the standard cosmological paradigm. In practice, in these simulations we simultaneously resolve and model the structural details of thousands of galaxies together with the large-scale cosmic web. The IllustrisTNG simulations are obtained with the moving-mesh code AREPO through field-leading computational investments of more than 100 million computing hours on thousands of computing cores and producing more than 1PB of data. In this talk, I will review our efforts to generate and effectively exploit such simulations, describe our strategies for dissemination, discuss what is explicitly and empirically solved in gravity+magnetohydrodynamics simulations for galaxy formation in a cosmological context and what is required and what it means to “successfully” reproduce populations of galaxies which resemble the real ones. Finally, I will showcase some of the insights they are allowing us to uncover and quantify. In particular, I will focus on the outcome of the final run of the series, TNG50, a cosmological volume at zoom resolution. TNG50 is allowing to reveal, for example, the quantitative details of gas outflows and their relation to galaxy properties as well as to follow the emergence of stellar and gaseous disks across cosmic times.

772019-03-07 Thu
14:20~15:20
R1203
Sean Dougherty
[ALMA]
Seminar
ALMA – current status and looking to the future
Abstract

The Atacama Large Millimeter Array (ALMA) located at 5000m altitude in northern Chile is an extraordinary achievement of innovation and construction. This talk will introduce briefly the ALMA telescope system and the remote, high-altitude site, provide a report on the current status of the telescope, and describe some of the ground-breaking results that have been produced over the first five years of operation. Looking to the future of the telescope, the development plans for the next decade set out in the Development Roadmap will also be described.

782019-03-06 Wed
11:00~12:00
R1203
Chueh-Yi Richard Chou
[ASIAA]
Seminar
Optical Developments for WIFIS and Subaru PFS Projects
Abstract

My expertise is in optical design as well as follow up developments such as performance simulation, optics fabrication details, instrument integration and testing, etc. My instrumentation experience includes the development of a Wide Integral Field Infrared Spectrograph (WIFIS), the development for the Subaru Prime Focus Spectrograph (PFS), and the development of a star tracker camera system. WIFIS is the largest Etendue (AΩ) near-infrared integral field spectrograph recently commissioned on Bok telescope at Kitt Peak in 2017. I was in charge of the optical design of WIFIS and optics fabrication details. For PFS project, my main contribution is on the fiber probes and one of the sub-system called Metrology Camera System (MCS). The fiber probe is designed to measure the fiber status (tilt, shift and focus). The fiber probe is built by myself and characterized to satisfy all system requirements. Currently the fiber probe has been installed on the instrument calibration stand and taking data. On the other hand, MCS is designed to provide accurate fiber position information by taking images of back illuminated fibers. The MCS optical design, optics fabrications and performance simulations were completed by myself. Currently MCS has been integrated and shipped to Subaru observatory in 2018. In the engineering runs in late Oct. 2018, MCS demonstrated its capability to successfully take images of objects located at the telescope prime focal plane. Besides that, I will present my work in the optical design and performance tests of a star tracker camera system that will be used on a micro-satellite. For future developments, in the near future I will coordinate with group engineers to accomplish the installation and status verification of PFS fiber modules. For MCS project, I will keep improving the MCS image quality and the goal is to deliver MCS to Subaru observatory in 2019. For longer time scale developments, I will describe my work in ULTIMATE-Subaru and present potential optical developments for Subaru telescope and TMT first light instrument MOBIE.

792019-03-06 Wed
14:20~15:20
R1203
Wen-Pin Hsieh
[ASIES]
Colloquium
A journey to the Earth and icy bodies’ interiors
Abstract

Physical properties of constituent materials in the Earth and planetary interiors are key to determine their formation history and thermo-chemical structures, etc. In particular, knowledge of the thermal conductivity of these constituent materials under relevant pressure-temperature conditions plays critical roles in understanding many geophysical phenomena within the Earth and planetary bodies, such as the temperature profile and dynamics of the mantle and core, as well as the heat flux across the core-mantle boundary. Recently we have successfully combined ultrafast optics with high pressure diamond cells to precisely measure lattice thermal conductivity of Earth’s mantle and core materials and water-volatile mixtures under extreme conditions. Modeling of our new data show significant influences of hydration, iron, aluminum, and volatiles on the thermal states and dynamics of the Earth and icy bodies. I will also discuss some future directions that are important to further understand the thermal history of the Earth and icy bodies.

802019-03-05 Tue
14:20~15:20
R1203
Liton Majumdar
[JPL]
Seminar
Multi-wavelength Astronomy and the Origin of Planetary Systems
Abstract

One of the most exciting developments in astronomy is the discovery of planets around stars other than our Sun. More than two thousand exo-planets have now been detected. But how do these planets form, and why are they so different from those in our own solar system? Which ingredients are available to build them? Thanks to powerful ground-based telescopes such as the Atacama Large Millimeter Array (ALMA) and soon the James Webb Space Telescope (JWST), we are now in a position to address these age-old questions scientifically. The formation of stars and planetary systems takes place in "molecular clouds". These dense, cold, dust enshrouded regions of the interstellar medium exhibit a high degree of molecular complexity. I will discuss how this complexity develops in protostellar envelopes, and how far it progresses before the molecules are incorporated as ices into planetesimals in protoplanetary disks and delivered to planets in the habitable zone.

812019-03-04 Mon
11:00~12:00
R1203
Jeffrey Fung
[UC Berkeley]
Seminar
Simulating Protoplanetary Disks Using GPU
Abstract

Protoplanetary disks are gas-rich disks around young stars, and cradles of planets. Observations of these disks have revealed that they are all rich in features, containing gaps and spiral arms that are potentially the results of gravitational disk-planet interaction. Using hydrodynamics simulations, we can study them and probe the early stages of planet formation. However, these simulations have stringent requirements on both resolution and duration, and their significant computational cost has been a bottleneck in research. In this talk, I will discuss how we are able to lower this cost by an order of magnitude by adapting to GPU (Graphics Processing Unit) computing. I will describe my GPU-based hydrodynamics code PEnGUIn, and explain the optimization that helps it reach a speed of about 100 million cells per second per GPU. I will present results from PEnGUIn simulations, where we not only model specific disks in detail, but also perform parameter space studies to provide quantitative links between disk features and the properties of potential planets. I will discuss how these results have informed us about planet formation, tying back to the known population of exoplanets. In the end, I will also give a few examples of other board applications of GPU computing in astronomical research.

822019-02-27 Wed
14:20~15:20
R1203
Takafumi Ootsubo
[JAXA]
Colloquium
Comets, asteroids, and interplanetary dust observed with infrared satellites: from AKARI to SPICA
Abstract

AKARI, the Japanese infrared astronomical satellite, was launched in February 2006 and made a number of pointed observations for deep imaging and spectroscopy together with the all-sky survey. The data of the AKARI observations are essential not only for the studies of the Galactic and extragalactic sciences, but also for the Solar System sciences on comets, asteroids, TNOs, and interplanetary dust. AKARI has already provided many precious survey data sets and outcomes for the Solar System sciences, including the asteroid catalog and the zodiacal emission map. AKARI has a spectroscopic capability in near- and mid-infrared wavelength region. We carried out spectroscopic observations for tens of asteroids and comets in 2.5-5 micron. AKARI detects clear absorption/emission features related to hydrated minerals in many asteroids and carbon dioxide in cometary comae. AKARI also made the spectroscopy of the zodiacal emission in the mid-infrared (5.5 to 12.5 micron) and detected the silicate feature around 10-micron region toward the various ecliptic latitude regions. These data sets provide us the information on the physicochemical environment in the early solar nebula. SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an ESA-JAXA joint mission for infrared astrophysics after AKARI, Spitzer and Herschel. SPICA covers infrared wavelength (12 to 230 micron) region spectroscopically with the scientific instruments SMI and SAFARI. In this talk, I will summarize the successful results of AKARI and introduce the SPICA science goals on the Solar System sciences.

832019-02-26 Tue
11:00~12:00
R812
Ippei Obata
[The University of Tokyo]
Seminar
Axion Dark Matter Search with Optical Cavity Experiment
Abstract

The outline of this talk is mainly based on our recent paper 10.1103/PhysRevLett.121.161301. In this talk, I will present a novel experimental approach to search for axion dark matter which does not need a conventional strong magnetic field but use an optical cavity. This new method aims to measure the difference of phase velocity between two circular-polarized photons which is caused by the coupling to axion dark matter. The experimental sensitivity is in principle only limited by quantum noise which enables us to probe tiny axion-photon coupling g_{aγ} <~ 10^{−11}GeV^{-1} with axion mass range m_a <~ 10^{-10}eV, which is competitive with other experimental proposals. If I have time, I will also discuss the possibility to test axion dark matter with ongoing and upcoming gravitational wave detectors by using a scheme similar to our proposed method.

842019-02-25 Mon
11:00~12:00
R1203
Kohei Hayashi
[University of Tokyo]
Seminar
Galactic Archaeology: a unique probe of the nature of dark matter
Abstract

Dark matter is now known to be the vital ingredient for the growth of structure in the Universe, while its nature remains a mystery. Galaxies in the Local Group are excellent laboratories to shed light on the nature of dark matter and its role in the galaxy formation. This is because these galaxies are sufficiently close to measure photometry, spectroscopy, and astrometry for their resolved stars, and this information enables us to study their chemo-dynamical structures in detail. Such studies are so-called "Galactic Archaeology". In particular, dwarf spheroidal (dSph) galaxies are ideal sites for studying the basic properties of dark matter as they are largely dark-matter dominated. Revealing dark matter distributions in dSphs is of crucial importance in testing dark matter models and constraining particle candidate of dark matter. In this talk, I will discuss dark halo structures in the dSphs through our dynamical analysis of their current available data. I will also discuss how dynamical studies for the dSphs can place constraints on the nature of dark matter. I will also present the future prospects for Galactic Archaeology science with deep and wide-field photometric and spectroscopic surveys, especially Subaru-HSC and PFS.

852019-02-22 Fri
11:00~12:00
R1203
Karen Yang
[UMD]
Seminar
The Microphysics of AGN Feedback
Abstract

Feedback from active galactic nuclei (AGN) is one of the most important processes governing the formation and evolution of galaxies and galaxy clusters. It is believed to be responsible for inhibiting the formation of massive galaxies and for solving the long-standing "cooling-flow problem" in galaxy clusters. A lot of understanding of AGN feedback has been gained using hydrodynamic simulations; however, some of the relevant physical processes are unresolvable or not captured by pure hydrodynamics, such as plasma effects and cosmic-ray (CR) physics. In this talk, I will present how we use simulations that incorporate this "microphysics" to understand how AGN jets feedback on galactic and cluster scales. Specifically, I will discuss our recent progress on the understanding of AGN heating in clusters, and how the heating processes depends on the AGN jet composition. I will also talk about how we could use multi-messenger observations of the Fermi bubbles as a nearby laboratory for studying AGN feedback. Finally, I will conclude with open questions and future prospects of applying simulations beyond hydrodynamics to various interesting astrophysical systems.

862019-02-22 Fri
14:20~15:20
R1203
Veronica Allen
[NASA/GSFC]
Seminar
Organic chemistry around young high-mass stars: Observational and theoretical
Abstract

In the study of high-mass star formation, hot cores are empirically defined stages where chemically rich emission is detected toward a high-mass protostar. It is unknown whether the physical origin of this emission is a disk, inner envelope, or outflow cavity wall and whether the hot core stage is common to all massive stars. With the advent of the highly sensitive sub-millimeter interferometer, ALMA, the ability to chemically characterize high-mass star-forming regions other than Orion has become possible. These sensitive high-resolution observations have opened up opportunities to find small scale variations in young protostellar sources. Taking a two part approach, we investigate the chemistry of the hot cores within star-forming region G35.20-0.74N (G35.20) using high spatial resolution (~1000 AU) Cycle 0 ALMA observations and rate-equation-based chemical models. The observational analysis uncovered an interesting asymmetry in the distribution of the Nitrogen-bearing species (especially those with the CN-group) within G35.20 B. This was unexpected as this source contains a candidate Keplerian disk and such a segregation in chemistry is unexpected because of the short dynamical time-scale of the system. The first part of my talk outlines the observational result and results of our follow-up chemical modelling to determine a cause for small scale chemical segregation, and therefore the usefulness of complex cyanides as chemical clocks. In the second part of my talk, I detail the results of a second study where I observe several different young stars and how the extent and movement of formamide (NH2CHO) in the gas surrounding the stars compares to its two possible parent species. This is important astrochemical work because there is debate about whether formamide is formed in ice and melts off once it becomes warm (from one parent) or in already warm gas (from the other parent). Formamide itself is important because it may lead to amino acids and other important molecules of life.

872019-02-21 Thu
14:20~15:20
R1203
Maresuke Shiraishi
[NIT, Kagawa College]
Seminar
Finding higher spinning particles through cosmic symmetry breakings
Abstract

Higher spin fields can play a key role not only in particle physics but also in cosmology. They may act as a source of e.g. large-scale magnetic fields and the gravitational wave background. Detecting their signatures therefore draws attention around the world. I would talk about the search of primordial higher spin fields through cosmic symmetry breakings (i.e. parity violation, rotational asymmetry).

882019-02-20 Wed
14:20~15:20
R1203
Tien-Hao Hsieh
[ASIAA]
Colloquium
Chronology of Episodic Accretion in Protostars - ALMA Survey of the CO and H2O snow lines
Abstract

Episodic mass accretion is one of the promising solutions to the long-standing "luminosity problem" in star formation, although its process is not full understood yet. We present our new ALMA results of 39 Class 0/I protostars in the Perseus molecular cloud, aiming at measuring the locations of the CO and H2O snow lines. The CO and H2O snow lines are determined from the measurements of the N2H+ and HCO+ line emission, respectively, combined with the time-dependent chemical model. The CO/H2O snow lines allow us to probe the past accretion burst; during the burst, the increase of accretion luminosity pushes the snow lines outwards; once the luminosity goes back to normal, the snow lines move back to their initial position after a delay of the freeze-out time scale. Since CO and H2O have different freeze-out time scales, the snow lines of these two species would further allow us to trace the event from different timescales, in the past ~1000 yr from H2O and in the past 10,000 yr from CO. As a result, we estimate the time from the last burst and the mass accretion rate during it toward individual source. Based on our survey, we try to reveal the evolution of the burst-occur frequency and the mass accretion rate at the burst-phase.

892019-02-18 Mon
11:00~12:00
R1203
[ASIAA]
Seminar
Astrochemistry in external galaxies
Abstract

Astrochemistry has been used to study physical properties of the interstellar medium (ISM) in star-forming molecular clouds. Recent development of high-capability telescopes, especially ALMA, has enabled detailed studies of astrochemistry in external galaxies. These studies have the potential to reveal the state of the interstellar medium influenced by extreme activities of starburst or active galactic nuclei (AGNs). Such ISM properties are important factors that affect future star formation / AGN activities in those galaxies. On the other hand, this field needs both observations of prototypical sources and theoretical modeling to establish the molecular composition as a quantitative measure of those activities. My research has focused on this "calibration" of molecules as diagnostic tools to study the ISM in galaxies. I will start this talk by introducing the modeling of the chemistry in the extragalactic scale. Then, I will present ALMA astrochemical observations of starburst galaxies M83 and NGC 3256 to show how galactic dynamics and star formation activity affects chemical composition. Finally, I will conclude with the future prospects of this field including the preliminary results of our ALMA Large Program ALCHEMI.

902019-02-14 Thu
11:00~12:00
R1203
Yuan-Sen Ting
[Carnegie / Princeton / IAS]
Seminar
Milky Way, machine learning, big data
Abstract

Understanding physical processes responsible for the formation and evolution of galaxies like the Milky Way is a fundamental but unsolved problem in astrophysics. Fortunately, most stars are long-lived. As such, using the stars as "fossil records" (what is known as Galactic archaeology) can offer unparalleled insight into the assembly of galaxies. In recent years, the landscape of Galactic archaeology is rapidly changing thanks to on-going large-scale surveys (astrometry, photometry, spectroscopy, asteroseismology) which provide a few orders of magnitude more stars than before. In this talk, I will discuss new "phenomenological" opportunities enabled by large surveys. I will also discuss how machine-learning tools could leverage the big data about the Milky Way by maximally harnessing information from low-resolution stellar spectra as well as the time-series photometric fluxes of stars. I will also present the new opportunities in Galactic archaeology in the era of deep photometry and spectroscopy, such as LSST, HSC, and PFS.

912019-02-13 Wed
14:20~15:20
R1203
Fang-Chun Liu
[NTNU]
Colloquium
The physical and chemical structure of continuum sources in Orion KL
Abstract

Orion Kleinmann–Low (Orion KL) hot molecular core, the nearest massive star-forming region to Earth, is one of the richest molecular reservoirs in Milky Way. With the Atacama Large Millimeter/submillimeter Array (ALMA) high-angular resolution observations, we investigate the millimeter/submillimeter continuum emission of Orion KL. In this study, twenty-four separate continuum sources are identified. Moreover, the physical and chemical properties of each individual continuum, such as the velocity, temperature and mass, and chemical abundances of nitrogen-/oxygen-bearing molecules, are also inferred based on the continuum and spectral emission observed. Marked correlations between certain physical and chemical parameters thus derived are evident and may be attributed to different evolutionary stages in these continuum sources.

922019-02-12 Tue
11:00~12:00
R1203
Chen, Chian-Chou
[ESO Fellow at Garching]
Seminar
Caught in the act - witnessing the formation of the most massive galaxies across cosmic time
Abstract

More than half of the stellar mass in the local Universe are found in galaxies that are very massive yet have long ceased to form new stars. Exactly when and how did they form remain open questions and dominant uncertainties in the state-of-the-art galaxy formation models. Detailed archaeological type of studies have suggested that these galaxies were assembled in a very dramatic fashion, with most of their stellar mass formed very early on when the Universe was about 20% of its age, within a strikingly short period of time corresponding to only around 10% of their lifetime. My main research interests have therefore been focused on uncovering these progenitors via extragalactic submillimeter surveys, and studying their evolution and physical properties using multi-wavelength data sets. In this talk, I will first give a brief summary of my past and current research achievements, followed by a plan in the next few years, in particular focusing on three novel methodologies in studying the environments and the ISM of these progenitors. Finally, I will describe my long-term research aspiration, with the expectation of it being realized in around 10 years timescale.

932019-01-30 Wed
14:20~15:20
R1203
Masato Shirasaki
[NAOJ]
Colloquium
Gravitational lensing effect of large-scale structures and its correlations to multi-wavelength extragalactic background
Abstract

Modern galaxy surveys aim at collecting billions of distant galaxies with precise measurement of their redshifts and shapes. Gravitational lensing effect causes an arc-shaped distortion in images of distant galaxies and offers a unique method to probe underlying mass density distribution in the universe. The information of cosmic mass density from gravitational lensing analyses is thought to be the basis for understanding the nature of multi-wavelength extragalactic background. I will introduce two representative examples of cross correlations of gravitational lensing with extragalactic emission at different wavelength. One is the correlation with gamma-ray background emission, and another is the correlation with thermal Sunyaev-Zel'dovich (tSZ) effect in cosmic microwave background. The former allows us to explore a possible signature of annihilating dark matter, while the latter provides meaningful information of the physics of intra-cluster medium. I will summarize the results of cross correlation analyses performed so far, and discuss some key issues remaining unsolved in the analyses. Those include accurate modeling of dark-matter substructures in cluster-sized objects and the statistical relationship among dark mater halos, blazars in gamma rays, and flat-spectrum sources in radio.

942019-01-23 Wed
14:20~15:20
R1203
Tomohisa Kawashima
[NAOJ]
Colloquium
Black hole shadow and relativistic jet image in M87
Abstract

he Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array aiming for imaging black hole (BH) shadows on event horizon scales, and exploring fundamental properties of BHs as well as physics of accretion flows/relativistic jets. M87 is one of the prime target of EHT, because the expected diameter of the black hole shadow is larger than the beam size of EHT. Theoretical studies of BH shadow and relevant disk-jet images are very important to estimate the mass and spin of black holes and to reveal the physics of accretion flow and launching mechanism of relativistic jets. We have recently developed a new general relativistic radiative transfer (GRRT) code and have carried out calculations of the black hole shadow in M87, assuming a simple model of accretion flow or disk-jet model based on GRMHD simulations (Nakamura et al. 2018 and in prep.). Based on the simple accretion flow model, we have newly found that the BH spin can be constrained by measuring the dark-crescent feature which appears in the rapidly spinng BHs. We also introduce our recent GRRT calculation results of disk-jet models based on GRMHD simulations from horizon to mili-arcsecond scale (i.e., one thousand gravitational radius scale). The resultant image shows the limb-brightened jet far from the black hole, that is consistent with the VLBI observation images.

952019-01-22 Tue
11:00~12:00
R1203
Seog-Tae Han
[KASI]
Seminar
Abstract

We have developed a compact triple-band receiver which enables simultaneous observations in the three frequency intervals K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. The quasi-optics design enables the triple-band receiver to fit into a single cryostat with some of the mirrors and dichroic filters outside the cryostat. The total receiver system is 600 mm(W) x 980 mm(L) x 370 mm(H) including the optical circuit. When compared with the present KVN optical bench of size 2600 mm x 2300 mm x 60 mm, the system is significantly more compact and is tailorable for use in telescopes with a small receiver cabin. The receiver performance and test observation results will be presented. We have shown that it is possible to design a quasi-optical circuit that has simultaneous observation capability for three or four frequency bands for millimeter and sub-millimeter receivers. Ultimately, this concept may lead to development of much more compact multi-frequency receiver systems for mm-wave and sub-mm radio telescopes.

962019-01-17 Thu
14:20~15:20
R1203
Jongho Park
[Seoul National University]
Seminar
Faraday Rotation in the Jet of M87 Inside the Bondi Radius: Indication of Winds from Hot Accretion Flows Confining the Relativistic Jet
Abstract

Active galactic nuclei (AGNs) often produce highly collimated relativistic jets, one of the most energetic phenomena in the Universe. Theoretical models predict that AGN jets can be accelerated to nearly speed-of-light by magnetic fields if they are confined by an external medium. Winds, nonrelativistic un-collimated gas outflows launched from accretion flows onto the supermassive black holes in AGNs, are primary candidates for this medium. Recent observations have indeed revealed gradual collimation and acceleration of the jet in M87, a nearby AGN that possesses a black hole with a mass of three to six billion Suns which provides a unique opportunity to investigate the region under the influence of the black hole's gravity. However, it has not been possible to either probe the external medium by observations or verify the general picture of jet collimation and acceleration. Here we report radio observations of Faraday rotation (the rotation of the plane of polarization by intervening magnetic fields) in the M87 jet, where information on the external medium (which is not directly observable) is imprinted. The Faraday rotation systematically decreases with increasing distance from the black hole from 5,000 to 200,000 Schwarzschild radii, in good agreement with the gas density being inversely proportional to the distance. This behavior matches the theoretically expected signature of moderately magnetized winds, which can naturally serve as the external confining medium. The sign of the Faraday rotation is predominantly negative, suggesting that jet and accretion axis are misaligned and the jet emission exposes only one side of the toroidal magnetic fields in the winds. Our results demonstrate that winds are indeed a key element of the black hole inflow-outflow system.

972019-01-16 Wed
14:20~15:20
R1203
Ryo Tazaki
[Tohoku]
Colloquium
Probing grain growth in protoplanetary disks via millimeter-wave polarization
Abstract

Dust coagulation in protoplanetary disks is the first step of planetesimal formation. However, a pathway from dust aggregates to planetesimals remains unclear. Both laboratory and numerical studies have so far shown that the structure of a dust aggregate plays important roles in planetesimal formation. However, the aggregate structure has been poorly constrained by disk observations. Recently, ALMA opens a new window to observe (sub-)millimeter-wave polarization of disks, which is expected to provide additional constraints on dust aggregate properties. In this study, we perform 3D radiative transfer simulations in order to study how the structure of dust aggregates affect millimeter-wave polarization from disks. As a result, it is found that relatively compact particles are favorable to explain observed millimeter-wave scattering polarization of disks, whereas highly porous and fractal particles fail to explain the observations. Furthermore, it is also shown that observed millimeter-wave scattering polarization is consistent with grain radii of a few hundreds of microns, which are an order of magnitude smaller than that previously estimated. We discuss a possibility that these relatively small grains are due to efficient fragmentation of CO2-ice coated grains in disks.

982019-01-15 Tue
14:20~15:20
R1203
Chao-Chin Yang
Seminar
Planetesimal Formation through the Streaming Instability
Abstract

The formation of kilometer-scale planetesimals is one of the most difficult stages in the course of planet formation around young stars. It is faced with several major barriers. Direct dust growth by coagulation is limited, up to mm to cm in size, due to inefficient sticking, bouncing, and fragmentation at collision. Even if the dust grains manage to grow past cm in size, they continually lose angular momentum to their surrounding gas due to constant head wind, leading to rapid orbital decay to the star. One promising mechanism for circumventing these barriers is the streaming instability, in which the solids actively participate in the dust-gas dynamics to concentrate themselves to high density, leading to direct gravitational collapse and the formation of planetesimals.
I will review our current understanding of the streaming instability and planetesimal formation. Specifically, how the instability operates, under what conditions it drives strong concentration of solid materials, the initial mass function of the resulting planetesimals, and its interaction with turbulent gas will be examined.

992019-01-09 Wed
14:20~15:20
R1203
Kenji Kurosaki
[Nagoya University]
Colloquium
Thermal Evolution and Obliquity of Solar System Ice giants
Abstract

Our solar system has two ice giants, Uranus and Neptune. The intrinsic luminosity and the obliquity are different between Uranus and Neptune, though they have similar mass and radius. In particular, Uranus has a tilted rotation axis, which is supposed to be caused by a giant impact. In general, an impact event also changes the internal compositional distribution and drives mass ejection from the planet. The present luminosity of a planet infers not only the present atmospheric composition but also the origin of the accretion energy that the planet gained during its formation and impact event. I will talk thethermal evolution history and the impact event that reproduces the present Uranus’s intrinsic luminosity and obliquity. We demonstrate that the latent heat of those species keeps the atmosphere hot and thus the emission flux high for billions of years, resulting in acceleration of the cooling of ice giants. Also, we find that young ice giants with highly enriched atmospheres are much brighter in mid-infrared than those with unenriched atmospheres. This provides important implication for future direct imaging of extrasolar ice giants. We also perform hydrodynamics simulations for the impact events of Uranus-size ice giants composed of a water core surrounded by a hydrogen envelope using two variant methods of the smoothed particle hydrodynamics. We suggest the range of possible initial conditions for the giant impact on proto-Uranus that reproduces the present rotation tilt of Uranus and sufficiently provides the total angular momentum of the satellite system that can be created from the fragments from the giant impact.

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